Immunology Notes PDF

Clinical Immunology Summary Don Davis Credit for Conception of this Document Goes To: TeachMePhysiology Bitesized Immunology Seminars & Lectures & Other Summaries Made By Seniors ...

Clinical Immunology Summary Don Davis Credit for Conception of this Document Goes To: TeachMePhysiology Bitesized Immunology Seminars & Lectures & Other Summaries Made By Seniors  Don Davis 1. Immune System – Basis of the Immune response. Anatomy & Structure: Organs of the Immune System (Central & Peripheral) Basis of the Immune Response: o The immune system is the body’s natural defence mechanism against pathogens, infections, and harmful substances. o It is composed of various organs, cells, proteins and tissues working together to defend the body o Types of Immunity: ▪ Active Immunity - body’s own immune system mounts an adaptive immune response following direct exposure to an antigen Natural Active Immunity – occurs after infection with actual disease, exposure + subsequent immune response produces memory cells that rapidly recognise + respond to pathogenic agent on re-exposure Artificial Active Immunity – vaccinations expose individual to a dead/weakened form of pathogen, eliciting the adaptive immune response and memory cell formation ▪ Passive Immunity – relies on antibodies rather than memory cells, involves introduction of ready-made antibodies to a non-immune individual. Short-lived. Natural Passive Immunity – IgG from mother to foetus, IgA antibodies present in breast milk can also transfer passive immunity Artificial Passive Immunity – IgG antibody transferred to provide passive immunity via: o Human or Animal Blood Products – serum or plasma o Pooled Human Immunoglobulin – IV, IM or subcutaneous immunoglobulin from immunised donors or those recovering from disease o Monoclonal Antibodies  Don Davis Organs of the Immune System: o Central Immune Organs: ▪ Bone Marrow: where white blood cells (WBC) are produced to fight infection, red blood cells (RBC) to carry oxygen and platelets to stop bleeding ▪ Thymus: where T-cells mature and differentiate, playing an important role in the adaptive immune response o Peripheral Immune Organs/Tissues: ▪ Lymph Nodes: filter lymph fluid which carries immune cells + assist in detecting + fighting infections. Distributed throughout the body ▪ Spleen: filters blood, removes old/damaged blood cells + stores white blood cells, also has a role in initiating an immune response by detecting + responding to foreign substances ▪ Tonsils & Adenoids: act as body’s first line defence against ingested or inhaled pathogens, trapping germs + producing antibodies to fight infections ▪ Mucosa-Associated Lymphoid Tissue (MALT): contains immune cells that protect against pathogens entering the mucous membranes found throughout the body e.g., in GI tract Structure & Function: o Leukocytes (WBCs) – immune cells that circulate in blood + lymphatic system. ▪ 5 Main Types: Neutrophils – main action against bacterial + fungal infections Eosinophils – main action against parasitic infections Basophils – responsible for responses to allergens Monocytes – main action against bacterial infections Lymphocytes – main action against viral infections ▪ Neutrophils, eosinophils, and basophils are granulocytes since they have cytoplasmic granules which can digest microorganisms ▪ Lymphocytes and monocytes are agranulocytes o Antibodies: proteins produced by B-cells that recognise + neutralise specific pathogens or foreign substances, tagging invaders for destruction by other immune cells or substances o Lymphatic System: network of vessels, lymph nodes, and organs that transport lymph throughout the body, helps in the circulation of immune cells and the removal of waste products and toxins o Antigens: foreign substances that trigger an immune response  Don Davis 2. Cells of the Immune System – Populations, Markers, Functions Function of Immune Cells: o Pathogen Recognition - through specific receptors o Response to Infections – engulfment + destruction of pathogens, antibody production, cytokine release to coordinate immune response o Memory & Regulation – formation of memory cells for rapid response to recurring infections + regulatory mechanisms to prevent immune system overactivity Lymphocytes: o Agranular leukocytes of lymphoid lineage – respond to viral infections o Diameter: 6-15µm (smallest) o Types of Lymphocytes: ▪ Natural Killer (NK) Cells ▪ B-Cells ▪ T-Cells o Natural Killer (NK) Cells: ▪ Markers: CD56, CD16, CD57 ▪ Function: Provide non-specific immunity against cells displaying foreign proteins such as cancer cells and virally-infected cells Independently detect + kill pathogens as part of the innate immune system Release perforins - cytolytic proteins which embed into the plasma membrane, create channels, allow extracellular fluid into the cells → lysis Produce cytokines to regulate immune responses o T-Cells: ▪ Populations: CD4+ T-Cells (THelper Cells) CD8+ T-Cells (TCytotoxic Cells) Regulatory T-Cells (TRegs Cells) Memory T-Cells ▪ Functions: CD4+: activate other immune cells, coordinate immune responses + assists B- cells in antibody production CD8+: directly attack + kill infected or abnormal cells Tregs: regulate immune responses, preventing excessive activation and maintaining immune tolerance o B-Cells: ▪ Markers: B-Cell Receptors (BCRs) Surface Proteins: CD19, CD20, CD21 ▪ Functions: Produce antibodies that bind to specific antigens, marking them for destruction or neutralisation Act as antigen-presenting cells (APCs), presenting antigens to T-cells  Don Davis Monocytes: o Agranular circulating leukocytes of myeloid lineage – respond to bacterial infection o Remain in blood for 8 hours before migrating into tissues where they differentiate into macrophages o In certain situations, monocytes also differentiate into dendritic cells o Macrophages: ▪ Markers: CD14, CD68, CD163 ▪ Functions: Engulf + digest pathogens and debris Present antigens to T-cells Release cytokine to regulate immune responses o Dendritic Cells: ▪ Markers: CD11c, CD1c, CD141 ▪ Functions: Initiate adaptive immune responses by activating T-cells Captures + process antigens, presenting them to T-cells Neutrophils: o Granular leukocytes of myeloid lineage o Most abundant - making up 40-70% of those found in peripheral blood o Primarily involved in immune response against bacterial infections + their presence in tissue is associated with acute inflammation o Lifespan: 2-3 days o Markers: CD15, CD16, CD177 o Functions: ▪ Migrate to infection sites + phagocytose pathogens ▪ Release degradative enzymes to kill pathogens during phagocytosis Eosinophils: o Granular leukocytes from the myeloid cell line within the bone marrow o Markers: CD9, CD11b, CCR3 o Functions: ▪ Granules contain major basic protein (MBP), cationic protein and peroxidase, which are toxic to parasites ▪ Phagocytose antigen-antibody complexes Basophils: o Granular leukocytes of myeloid lineage o Markers: CD123, CD203c, FcεRI o Functions: ▪ Contain histamine granules – cause local inflammatory responses through interaction with IgE ▪ Mediate type I hypersensitivity alongside mast cells  Don Davis 3. Molecules of the Immune System – For Intercellular Communica on, An bodies, The Complement System Molecules of the Immune System  Cytokines – group of small proteins used in cell-signalling o Produced by macrophages, lymphocytes, mast cells, endothelial cells and fibroblasts o Func ons:  Coordinate immune responses by signalling between immune cells  Regulate inflamma on, cell growth and differen a on  Modulate intensity and dura on of immune reac on o Classes of Cytokines:  Chemokines  Interferons  Interleukins (IL)  Tumour Necrosis Factor (TNF)  Chemokines: o Induce chemotaxis (chemical-induced migra on) in local cells o Produced by macrophages during infec on o Chemokine Receptors:  G Protein-Coupled Receptors – ac vate phospholipase C  intracellular Ca2+ release  This leads to cytoskeletal changes, pseudopod forma on, enhanced cell adhesion through integrins o Ac ons:  Pro-inflammatory – recrui ng immune cells to site of infec on/injury  Homeostatic – a rac ng cells required for angiogenesis + allowing for growth of new blood vessels  Immune Surveillance - allow T cells and dendri c cells to migrate and circulate through secondary lymphoid organs in search of poten al pathogens  Chemokines are also key to development of lymph organs and posi oning of cells within lymphoid ssues  Interferons: o Type of cytokine released by host cell in response to pathogens and tumour cells o Grouped according to their complementary receptor:  Type I - interferon-α and interferon-β  Type II - interferon-γ  Type III - Interferon λ  Note: Type III has similar ac ons to Type I & II o Ac ons:  Type I:  Produced by any body cell  Interfere with viral replication + helps fight viral infection  A er secre on by infected cell  bind to interferon receptors on the same cell + neighbouring cells (autocrine + paracrine signalling)  This causes changes in gene expression  destruc on of viral mRNA  prevents host + viral protein transla on  Upregulation of NK cell ligands + MHC I on cell surface  NK cells and cytotoxic T cells are more likely to detect and a ack virus-infected cells  Don Davis  Type II:  Produced by NK cells, cytotoxic T cells and Th1 cells in response to IL-12 & IL- 18  Activates macrophages + increases their ability to kill pathogens by enhancing pinocytosis and lysosome function  Upregulates MHC II expression, promo ng an gen presenta on + phagocytosis  Interleukins (IL): o Type of cytokines produced by T-lymphocytes, monocytes & macrophages o Currently there are >40 interleukins in the human body o Func ons:  Promotes production + differentiation of B & T-lymphocytes – IL- 1α/β, IL-4, IL-7 and IL-21  Activates neutrophils + NK cells - IL-2, IL-8 & IL-12  IL-6 causes fever, inhibiting microbial growth as well as increasing acute phase proteins such as CRP which is associated with inflammation  Promotes vascular permeability  swelling and allows faster recruitment of cells involved in immunity  Tumour Necrosis Factor (TNF): o Cytokines produced by macrophages when encountering an endotoxins o Also produced by mast cells, B-cells & T-cells o 2 Types: TNF-α & TNF-β  TNF-α:  Triggers activation of endothelial cells  increased vascular permeability  recruitment of immune cells to site of injury/infec on  Activates macrophages, neutrophils and lymphocytes  Induces apoptosis especially in tumour cells or infected cells to limit spread  Overproduc on of TNF-α  chronic inflammatory disease + autoimmune condi ons  TNF-β:  Involved in development of secondary lymphoid organs + in immune cell matura on and migra on  Similar func ons to TNF-α o High concentra ons can induce shock through the increase in vascular permeability and resul ng drop in blood pressure o Chronic exposure to low levels leads to cachexia  Growth Factors: o Regulate cellular growth, proliferation, differentiation and survival o Types:  Colony-Stimulating Factors  Interleukins  Transforming Growth Factor- β o Colony-S mula ng Factors (CSFs):  Granulocyte-CSF (G-CSF): s mulates the produc on + matura on of neutrophils, cri cal in comba ng bacterial infec ons  Macrophage-CSF (M-CSF): supports the differen a on + survival of monocytes and macrophages, crucial for innate immunity and ssue repair  Granulocyte-Macrophage-CSF (GM-CSF): s mulates the produc on + func on of granulocytes and macrophages, contribu ng to both innate and adap ve immunity  Don Davis o Transforming Growth Factor-β (TGF- β):  Inhibits activation and proliferation of T and B cells  Induces differentiation of Tregs - suppressing excessive immune responses + preven ng autoimmunity o Interleukins:  IL-2: essen al for T-cell prolifera on + ac va on  IL-4: promotes differen a on of T-Cells into Th2 tells  IL-7: supports survival + prolifera on of lymphocytes  IL-15: s mulates prolifera on + ac va on of NK cells and CD8+ T-cells Antibodies (aka Immunoglobulins)  Y-shaped glycoproteins produced by plasma cells  Present in bodily fluids, secre on and on surface of B-cells  Recognise + bind to unique epitopes – molecular structures on surface of their cognate an gens  Structure: o 2 Heavy Chains + 2 Light Chains = 2 Antigen-Binding Sites o Disulphide bonds bind heavy chains to each other and to the light chains o The chains consist of several amino-acid sequences, each corresponding to a protein domain  Protein Domain - functional units of the antibody o Each Light Chain has 1 Variable + 1 Constant domains o Each Heavy Chain has 1 Variable + 3 Constant domains o 5 Heavy Chain Types:  IgM  IgA  IgD  IgG  IgE o 2 Light Chain Types:  κ (kappa)  λ (lambda)  Each an body can have either two κ or two λ chains but not one of each  The ra o of κ and λ is 2:1 – there are func onal differences between the types o Fragment Antigen Binding (Fab) Regions:  Contain variable domains of the light & heavy chains  Variable domains make up the variable regions – gives an bodies its specificity  Also contains two constant domains – one from heavy chain and one from light chain o Fragment Crystallisable (Fc) Region:  Interacts with different immune cells + mediates various func ons e.g., opsonisa on  Consists of the remaining constant domains from the 2 heavy chains o Note: IgA & IgG antibodies have hinge regions – flexible amino-acid chains in central part of heavy chains  Don Davis  Classifica on: o Classified according to heavy chain type encoded by a gene in chromosome 14 o Different classes (in descending order of abundance in serum - GAMDE):  IgG  IgM  IgE  IgA  IgD o IgG:  Localisa on: surface of mature B-cells + serum  Only antibody to cross the placenta – transfers passive immunity from mother to foetus  Subclasses: IgG1, IgG2, IgG3 & IgG4 (in order of serum concentra on) o IgA:  Most prevalent an body in secre ons e.g., saliva and mucus  4 an gen-binding sites - forms a dimer, where a joining chain connects 2 Y-shaped molecules  Resistant to enzyma c diges on + act as neutralising an bodies  Breast milk and colostrum have high levels of IgA which coat the aerodiges ve tracts; protec ng against infec ons in breast-fed babies  In adults:  Forms a barrier layer at mucosal surfaces to prevent pathogenic invasion – hinders a achment to epithelial receptors by binding to their ligands on pathogens or toxins  Cross-link polyvalent an gens or pathogens, forming an gen-an body complexes which are then trapped in the mucus layer and cleared through peristalsis o IgM:  Localisa on: surface of B-cells  Expressed as monomers but secreted as pentameter  Pentameter – 5 antibodies connected by a joining chain = 10 antigen-binding sites  First Ig produced during foetal development + first to be produced by B-cells against new infec on  Has high avidity (strong an body-an gen complex) but low affinity – weak single epitope-an body interac on o IgD:  Localisa on: surface of B-cells  All naïve B cells express IgD & IgM  Func on: role in B-cell & an body produc on o IgE:  Localisa on: Mast Cells & (in low levels) Blood + ECF  Triggers histamine release from mast cells + basophils  Associated with Type I Hypersensi vity Reac ons  Part of body’s response to parasi c infec ons  Don Davis  Func on: o Opsonisation:  An bodies (mainly IgG1 & IgG3) act as opsonin by binding to pathogens  be er recogni on by phagocytes  phagocytes bind to an bodies via Fc receptors  phagocytosis o Neutralisation:  Blocks different parts of bacterial or viral cell surface  neutralises toxins  IgG & IgA an bodies have the greatest effect o Complement Activation:  IgM or IgG ac vates complement pathway when binding to microbial surfaces  This releases C3b which acts as an opsonin + other complement components  make up the membrane a ack complex (MAC)  MAC perforates the pathogen plasma membrane  cell lysis + death o Immune Complexes:  Binding of mul ple an gens or an bodies together (“clumping”)  immune complexes  Clumping makes it easier for phagocytes to find + ingest pathogens through phagocytosis o Antibody-Dependent Cell-Mediated Cytotoxicity:  An bodies bind + opsonise target cells  NK Cells recognise Fc por on of an body  release perforin + granzymes into target cells  apoptosis  NK cells also release interferons, a rac ng phagocytes  Monoclonal Antibodies – man-made molecules designed to act as antibodies  Don Davis The Complement System  Group of proteins that work together to enhance the body’s ability to fight infec ons, clear out damaged cells and assist in immune response  Ac va on of the Complement System: o Classical Pathway o Mannose-Binding Lectin Pathway o Alternative Pathway o All 3 pathways produce C3 convertase which triggers further effects downstream  Classical Pathway: o C1q Complement Protein binds directly to pathogen or onto an gen-an body complex o This triggers cleavage of complement proteins in cascade  C3 convertase produc on + effects o Involvement in an gen-an body complexes means it has a role in adap ve immune response as well as innate  Mannose-Binding Lec n (MBL) Pathway: o MBL protein is produced in liver o MBL role is to detect carbohydrates containing mannose on surface of pathogens  MASP ac va on (MASP is a protease) o MSAP cleaves complement components ac va ng similar cascade  C3 convertase  Alterna ve Pathway: o Activated by bacterial endotoxin  spontaneous hydrolysis of C3  C3b o C3b combines with other factors to produce C3 convertase  Immune Effects of Complement System: o Opsonisation:  C3 convertase converts C3  C3a + C3b  C3b binds to an gens on pathogen  s mulates opsonisa on o Lysis of Pathogens:  C3  C3a + C3b  C3b + Other Factors  C5 Convertase  C5  C5a + C5b  C5b + Factors  MAC  MAC ruptures bacterial cell membrane  lysis of pathogen o Chemotaxis:  C5a produc on by C5 convertase a racts neutrophils and macrophages to the site of infec on  extravasa on of leucocytes from capillaries to ssues  C3a also another complement component that acts as a chemotaxin o Inflammation:  C3a, C4a and C5a bind to mast cells + basophils  degranula on  Histamine + serotonin released increased vascular permeability  C3a, C4a and C5a also promote synthesis of pro-inflammatory cytokines  Don Davis 4. HLA System: Genes & Products, Nomenclature Major Histocompatibility Complexes (MHC)  A er phagocytosis of a pathogen, macrophages or dendri c cells digest pathogen then present the an gen on its surface  The an gen is presented as part of a receptor located on the surface of the an gen-presen ng cells (APCs)  Receptor = MHC  MHC forms an important role in s mula ng the adap ve, pathogen-specific immune system  In humans, MHC are called Human Leukocyte Antigens (HLAs) Human Leukocyte Antigen (HLA) System  Group of proteins encoded by genes of MHC  Helps body dis nguish between self and non-self  Located on chromosome 6 in humans  Encodes for major histocompa bility complex (MHC) proteins  Clinical Significance: o HLA polymorphisms influence suscep bility to autoimmune diseases, transplant compa bility, and response to pathogens. o Matching HLA markers between donor and recipient is crucial for successful organ transplanta on to minimize rejec on  2 Classes of HLA Genes – Class I & Class II  Class I HLA Genes: o Found on nearly all nucleated cells o Encodes α chains that pair with β2-microglobulin o Present endogenous antigens to CD8+ T cells for elimination o Involved in recogni on of self from non-self cells o Genes: HLA-A, HLA-B, HLA-C  Class II HLAs Genes: o Expressed primarily on APCs like dendri c cells, B cells, and macrophages. o Encode α and β chains. o Present exogenous antigens to CD4+ T cells o Essen al for ini a ng immune responses by presen ng an gens to helper T cells o Genes: HLA-DP, HLA-DQ, HLA-DR  Nomenclature: o Genes are named based on an gens they encode o Alleles are designated with a combina on of le ers and numbers o Allelic varia on is vast within popula on, allowing diverse an gen presenta on o Example: HLA-A*02:01 - HLA-A gene, allele 02:01  Don Davis 5. Innate Immunity - Characteris cs & Comparison with Acquired Immunity. Factors of Innate Immunity – Mechanical Barriers, Cellular & Humoral Clinical Significance of the Mechanisms of Innate Immunity. Inflamma on as Protec ve & Pathological Manifesta on Innate vs Acquired Immunity Innate Immunity Acquired Immunity Present at birth, providing immediate defence Developed over me a er exposure to specific against pathogens pathogens or an gens Non-specific Highly specifc No long term memory Long term memory for future encounters Includes physical barriers, cellular components and Involves B and T lymphocytes, an bodies, and complement proteins immunological memory Factors of Innate Immunity  Physical Barriers: o Skin – large surface area + covers most of body’s external surfaces. Superficially, skin has mul ple layers of dead, kera nised epithelium which is con nuously sloughed off, facilita ng the removal of any adherent microbes o Mucous Membranes of Respiratory, GI & Urinary Tract - outermost, epithelial layer is held together by ght junc ons, making it robust enough to impede deeper pathogen access o Bronchial Cilia – form the mucociliary escalator, allows the gradual removal of pathogens from the respiratory system o Secretions e.g., tears, urine, saliva, bile etc. - help protect the surfaces they flow over from infec on by reducing pathogenic a achment and dura on of contact with bodily surfaces  Physiological Barriers: o Diarrhoea o Coughing o Vomiting o Sneezing  Chemical Barriers: o Low pH - prevents pathogen growth o An microbial Molecules:  IgA – present in tears, saliva, mucous membranes  Lysozyme – bactericidal proper es, present in sebum, perspira on & urine  Mucus – an sep c proper es, passively prevents bacterial adhesion, traps bacteria for clearance  Enzymes – e.g., pepsin can help kill bacteria through proteolysis  Defensins:  Alpha defensins – found in macrophages, neutrophils, and intes nal paneth cells  Beta-defensins - help epithelial surfaces to resist microbial colonisa on by crea ng channels and disrup ng the microbial cell membrane  Biological Barriers: o Normal flora:  Consists of non-invasive commensal microorganisms that outcompete pathogens for a achment sites and resources and may even produce an microbial chemicals  Many also produce essen al vitamins, such as Vitamin K and B12  Don Davis  Cellular Barriers: o Phagocytes (e.g., macrophages, neutrophils) – engulf + destroy pathogens through phagocytosis, release cytokines to recruit other immune cells  Humoral Factors: o Complement Proteins - group of proteins that enhance phagocytosis, cause pathogen lysis, and promote inflamma on Clinical Significance of Innate Immunity  Protection Against Infections: o Rapid response to a wide range of pathogens o Crucial in preven ng ini al infec on and controlling early stages of disease  Autoimmune Diseases: o Dysregula on of innate immune mechanisms can contribute to autoimmune disorders. o Inappropriate immune response against self-an gens Inflammation as Protective & Pathological Manifestation  Protec ve Role: o Exudation of fluid helps deliver plasma proteins to injury sites. It, furthermore, dilutes toxins and increases lympha c drainage o Infiltra on of neutrophils leads to the removal of pathogens and cellular debris o Vasodilation helps to increase the delivery of necessary proteins and cells and to increase ssue temperature o Pain and loss of func on help to enforce rest and lower the risk of further ssue damage  Pathological Manifesta ons: o Prolonged or chronic inflamma on can lead to tissue damage - associated with various diseases like arthri s, cardiovascular diseases, and certain cancers. o Dysregula on of inflammatory responses can have severe health implica ons  Don Davis 6. Development of the Immune Response - Stages, Types & Forms of the Immune Response Depending on An gen (Development of the Immune Response Against Extracellular & Intracellular an gens) Development of Immune Response  Stages: o Recognition Phase:  Lymph nodes and lymphocytes survey body through blood stream  Macrophages either remove or imprint structure in memory  Body recognises foreign markers, which triggers prolifera on stage (T cell encounters an gen presented by MHC molecules) o Proliferation Phase:  T cell returns to lymph node with the an genic message  S mulates T and B lymphocytes to enlarge, divide and proliferate  T lymphocyte (cytotoxic T killer) and B lymphocytes s mulate produc on and release of an bodies o Response Phase - changed lymphocytes func on either in humoral or cellular fashion o Effector Phase:  An body or T killer cells reach the an gen on the surface of foreign invader  Coupling ini ates a series of events which lead to destruc on of invading microbe or neutralisa on of toxin (this series of events involves an bodies, complement, ac on by T killer cells)  Types & Forms: o Extracellular Antigens:  Humoral Response:  B cells differen ate into plasma cells that produce an bodies  An bodies neutralize toxins, tag pathogens for destruc on, and ac vate complement  Effec ve against extracellular bacteria, viruses, and toxins o Intracellular Antigens:  Cell-Mediated Response:  Ac vated cytotoxic T cells (CD8+) directly kill infected cells  Helper T cells (CD4+) assist in ac va ng other immune cells  Effec ve against intracellular pathogens like viruses, some bacteria, and parasites residing within host cells Development of the Immune Response against Extracellular & Intracellular Antigens  Extracellular Antigens: o B Cell Activation:  An gens bind to B cell receptors, ac va ng B cells  B cells differen ate into plasma cells, producing an bodies specific to the an gen  An bodies neutralize or eliminate extracellular pathogens  Intracellular Antigens: o T Cell Activation:  An gens from infected cells are presented by MHC I molecules to cytotoxic T cells  Cytotoxic T cells become ac vated and kill infected host cells  Helper T cells ac vate other immune cells, aiding in the immune response  Don Davis 7. Timing of Immune Response – Primary & Secondary. Immunological Memory, Regula on of Immune Response Primary Immune Response  Process: o Naïve B-cells are ac vated by T-cells and move to secondary lymph organs like spleen + lymph nodes o In the secondary lymphoid organs, they enter B-cell follicles or germinal centres within the cortex o Inside germinal centre, B-cells proliferate and undergo soma c hypermuta on which changes the affinity of their receptor o B-cells differen ate into plasma cells & memory B-cells. Plasma cells are short-lived and die quickly following the primary immune response Secondary Immune Response  Process: o Memory cells rapidly proliferate + differen ate into plasma cells when they come into contact with their specific an gen again o Subset of these memory cells can also go into the germinal centres for further class switching and affinity matura on o Memory B-cells can also ac vate effector T-cells by presen ng an gen on MHC-II molecules  Process of differen a on from memory B-cell to plasma cell is quicker than if they have differen ated from naïve B cells  Memory cells can survive for decades and so can respond to mul ple exposures over me  They also do not require con nual interac on with an gen or T-cells to survive  As they have already undergone class switching and affinity matura on, they can divide faster and produce higher affinity an bodies such as IgG in response to an gen  Don Davis Immune Responses – Overview Primary Immune Response Secondary Immune Response Responding Cells Naïve B and T cells Memory B & T Cells Activation Threshold High Low Onset of Response Slow Quick Rate of Antibody Production Low High Lag Phase 4-7 Days 1-3 Days Time to Peak Antibody Response 7-10 Days 3-5 Days Antibody Types IgM >>> IgG IgG >>> IgM IgA & IgE may also be present Antibody Affinity Low affinity an bodies High affinity an bodies Response Magnitude An gen dependent but an body 100-1000x higher than primary levels are rela vely low + decline response rapidly Immunity Slow control of infec on Rapid control of infec on T-Cell Activation Delay before effector T-cell Effector T-cells act immediately ac va on Innate Immune System Innate Immunity works alone Adap ve and innate immune un l adap ve response is system work together from the ini ated start Immunological Memory  T-memory Cells serve to ‘remember’ specific an gen for future should the body come in contact with it again  T-memory cells enable for faster ac va on of B-cells  more an gen-specific an bodies produced  They also s mulate faster expansion of cytotoxic T-cells to hasten pathogen clearance from the body  Don Davis Regulation of Immune Response  Tolerance Mechanisms o Central Tolerance: elimina on of self-reac ve lymphocytes during development in the thymus (T cells) and bone marrow (B cells). o Peripheral Tolerance: suppression of poten ally harmful immune responses in the periphery to avoid autoimmune reac ons.  Immune Regulatory Cells: o T Regulatory (Treg) Cells: suppress excessive immune responses, maintaining tolerance and preven ng autoimmunity. o Cytokines: signalling molecules that regulate immune cell behaviour, promo ng or inhibi ng immune responses as needed.  Balancing Act: o Inflammation Regulation: maintaining a balance between responding adequately to pathogens and preven ng excessive inflamma on. o Homeostasis: ensuring a stable internal environment by regula ng immune responses to avoid damage to healthy ssues  Don Davis 8. Infec ous Immunology - Immune Reac ons Against Bacterial, Myco c & Viral Infec ons Bacterial Infections  There are several immune responses to bacteria: o Complement-Mediated Lysis o Phagocytosis o Cell-Mediated Immunity  Complement-Mediated Lysis: o Bacteria are a acked by complement proteins. They assist in bacterial killing via three pathways:  Classical Complement Pathway  Alterna ve Complement Pathway  Lec n Pathway o Classical Complement Pathway:  Requires binding of an bodies to surface of target bacterium – becoming a target for C1 protein complex  C1 binds to Fc region of an body  ini ates cascade of cleavage + reforming of complement complexes to bacterium cell surface in form of membrane attack complex (MAC) (Figure 1)  Alterna vely, can generate opsonin – label bacterium for destruc on  MAC inserts onto membranes of Gram -ve bacteria  perforates membrane enabling entry of lysozyme  osmotic lysis of bacteria o Alternative Complement Pathway:  C3 directly bind to bacteria  ac va on of downstream components in complement cascade  MAC forma on  lysis of bacterium o Lectin Pathway:  Mannan-Binding Lectin (MBL) binds to proteins containing mannose residues found in some types of bacteria e.g., Salmonella spp.  MBL forms complex with MBL-activated serine protease (MASP)  MASP ac vates C3 convertase  MAC forma on  Don Davis  Phagocytosis: o Opsonisation - acute phase proteins (like complement) and antibodies bind to surface of bacteria  This coats the bacteria with molecules phagocy c cells can recognise + respond to  Opsonisa on allows killing of Gram +ve bacteria that are resistant to killing by MAC o Phagocytosis - ac vated phagocytes engulf and destroy opsonised bacteria o A er inges on, bacteria are killed by various processes + broken into small fragments by enzymes o Phagocytes present the fragments on their surface via MHC class II molecules o T-Helper cells recognise the fragments and produce cytokines  Th1 cells produce interferon-g (IFN-g) – promotes cell-mediated immune mechanisms  Th2 cells produce IL-4 – promotes humoral immunity by ac va ng B cells  B cells make an bodies that s ck to extracellular bacteria and prevent their growth and survival  Cell Mediated Immunity: o Used for intracellular bacteria that live inside cell compartments and are able to avoid killing mechanisms of phagocytes e.g., Salmonella spp. o Antigen Presentation - infected macrophages present bacterial pep des on their cell surface using MHC class II molecules o T-helper cell surveys MHC class molecules with its T-cell receptor (TCR) to observe the pep des they hold o If TCR detects bacterial pep des Th1 cells release IFN-g which does two things:  S mulates killing mechanisms inside infected macrophage to digest + destroy invading bacterium  Increases an gen presenta on by cells – making bacterium more visible to immune system + prone to a ack  Don Davis Mycotic & Fungal Infections  Immune response against myco c and fungal pathogens mainly consists of innate recogni on of fungi by the immune system  Innate Recogni on of Fungi by Immune System: o Fungi are recognised by cells of the innate immune system e.g., dendritic cells + macrophages o The cells bind components of fungal cell walls using pattern-recognition receptors (PRRs) on their surface  C-type lectin receptors (CLRs) are par cularly important although several other PRRs are also involved including the Toll-like receptors (TLRs, e.g., TLR2) o When PRRs bind fungi, they signal using their intracellular tails or associated molecules (FcRγ) resul ng in phagocytosis, ini a on of killing mechanisms (e.g., produc on of reac ve oxygen species) and also help drive the development of adaptive immunity o CD4+ T-cells that make IFNγ (Th1) or IL-17 (Th17) provide the best protec on during fungal infec ons - s mulate effec ve killing by innate effector cells such as neutrophils & macrophages o CLRs use CARD9 (signalling molecule) to ac vate the an fungal immune response  CARD9 deficiency  high suscep bility to fungal infec ons Viral Infections  There are several immune responses to viruses: o Cytotoxic cells o Interferons o An bodies  Cytotoxic Cells: o MHC class I displays pieces of protein from inside cell upon the cell surface. If infected with virus, these pieces of pep de will include fragments of proteins made by the virus o Cytotoxic T-cells have TCRs which detects pep de from a virus  T-cell releases cytotoxic factors to kill infected cell + prevent survival of virus o Natural Killer Cells (NK Cells) - specialises in killing cells that have a reduced number of MHC class I molecules on their surface by releasing toxic substances o Cytotoxic cells are armed with preformed mediators:  Perforins – perforates cell membranes, enabling entry of other factors into target cell to facilitate cell destruc on o Cytotoxic factors are stored inside granules in cytotoxic T-cells and NK cells un l triggered for release  Granzymes (stored in + released from granules) enter target cells through perfora ons made by perforins and ini ate apoptosis  Don Davis  Granulysin - directly a acks the outer membrane of the target cell, destroying it by lysis o A er making contact with infected cells cytokines are also released:  Interferon-g and tumour necrosis factor-a - transfer a signal from the T cell to the infected, or other neighbouring cells, to enhance the killing mechanisms  Interferons: o Prevent replica on of viruses, by directly interfering with their ability to replicate within an infected cell o Act as signalling molecules that allow infected cells to warn nearby cells of a viral presence  This signal makes neighbouring cells increase the numbers of MHC class I molecules upon their surfaces, so that T cells surveying the area can iden fy and eliminate the viral infec on  Antibodies: o Proteins that specifically recognise invading pathogens and bind to them o This binding serves many purposes:  Neutralises virus – no longer capable of infec ng cell  Agglutination - agglu nated viruses make an easier target for immune cells than single viral par cles  Phagocyte activation – virus-bound an body binds to Fc receptors, triggering phagocytosis  Complement System activation – an bodies ac vate the complement system  opsonisa on + phagocytosis. Complement can also damage envelope present on some types of viruses  Don Davis 9. Immunodeficiency States - Defini on, Causes. Immunological Characteris cs of Inborn & Acquired Immunodeficiencies. Syndromes & Diseases. Monoclonal Gammopathies – Causes & Examples Immunodeficiency States  Immunodeficiency (ID): state of condi ons where the immune system is compromised, leading to an increased suscep bility to infec ons and some mes an inability to properly regulate immune responses  Primary Immunodeficiencies (PIDs): a heterogeneous group of monogenic diseases that result from a gene c defect in one of the components of the innate and/or acquired immune system  Secondary Immunodeficiencies: acquired immunodeficiencies with diverse ae ology and occurring in different mechanisms, acquired from an environmental factors or other medical condi ons Immunological Characteristics of ID  Primary Immunodeficiencies: o Rare + inherited o Present early in life with severe, frequent or opportunistic infec ons o Ae ology:  Mode of Inheritance:  Autosomal Recessive  Autosomal Dominant  X-linked  Gene Dele ons, Rearrangements  Arrest in Embryogenesis:  Asplenia  DiGeorge Syndrome  Biochemical & Metabolic, Affecting Leukocyte Function:  Adenosine Deaminase (ADA) Deficiency  Purine Nucleoside Phosphorylase (PNP) Deficiency  Bio n-Dependent Mul ple Carboxylase Deficiency  Deficient Membrane Glycoproteins  Primary Immunodeficiencies - Classification: o Combined ID o Combined ID with associated or syndromic features o An body Deficiencies o Diseases of Immune Dysregula on o Congenital Phagocy c Defects o Defects in Intrinsic & Innate Immunity o Autoinflammatory Disorders o Complement Deficiencies o Bone Marrow Failure o Phenocopies of PIDs  Don Davis  B-Cell Primary Immunodeficiencies: o Ae ology:  Failure in B cell produc on  Failure to produce spectrum of an bodies =  Failure to produce high affinity memory cells in germinal centres o Rarely cause illness un l levels of maternal IgG fall at 4-6 months o Typically presents with recurrent respiratory tract infections, par cularly with encapsulated pyogenic bacteria such as Streptococcus pneumoniae & Haemophilus influenza B o Examples:  X-linked Agammaglobulinemia:  Defect in the B-cell tyrosine kinase (BTK) gene  inability for B cells to differentiate and mature  Selective IgA Deficiency:  Most common PID  Often asymptomatic but can cause respiratory infec ons and chronic diarrhoea  Some individuals may have severe anaphylactic reac ons to IgA when receiving a blood transfusion  Hyper-IgM Syndrome:  Caused by a defect in the CD40 ligand  prevents class switching  Causes recurrent respiratory, gastrointes nal, and sinus infec ons, due to normal or elevated levels of IgM but decreased levels of IgG and IgA  Common Variable Immunodeficiency  Umbrella term for antibody deficiency with unknown genetic cause  B cells are of a normal phenotype, but unable to differen ate into plasma cells  low concentra ons of all classes of immunoglobulin, but par cularly IgG, IgA and IgM  Later onset - typically presen ng in adulthood around the age of 20-35 with recurrent, severe sinopulmonary infec ons  T-Cell Primary Immunodeficienies: o Ae ology:  Reduced T-cell counts  Impaired Ac vity o T-cell deficiency predisposes the sufferer to severe infec ons by intracellular parasites, bacteria and viruses  Associated with mucosal infec on by yeasts such as candida o Can present with failure to thrive and/or diarrhoea in early life  Age of Occurrence: o Before 6 months: implies T- cell deficiency o Between 6-12 months: implies combined T & B-cell deficiency or B-cell deficiency o After 12 months: implies B- cell deficiency  Don Davis  Neutrophils Primary Immunodeficiencies: o Ae ology: reduced count or impairment of func on o Affected individuals present with severe extracellular and gram-negative bacterial infec ons that can be fatal o These pa ents are especially prone to skin infec ons and sepsis o Example:  Chronic Granulomatous Disease (CGD):  Defec ve produc on of reac ve oxygen species due to a defec ve NADPH oxidase enzyme  This decreases the oxida ve burst in neutrophils, which is normally used to destroy phagocytosed pathogens  Presents in childhood with recurrent infec ons and granuloma forma on  Congenital Neutropenia:  Characterised by decreased neutrophil count  Causes recurrent life-threatening bacterial infec ons e.g., gingivi s, o s media and respiratory infec ons  Leukocyte Adhesion Deficiency Type 1:  Disorder causing an impairment of neutrophil func on due to absence of CD18 protein  Affects the margina on of neutrophils, causing them to accumulate in the blood without being able to leave the bloodstream to fight infec on  Presents with recurrent bacterial infec ons, especially of skin and mucosa, and delayed separa on of the umbilical cord  Complement System Primary Immunodeficiencies: o Deficiency in the classical pathway causes a build-up of immune complexes in ssues and an associated inflammatory response  Causes diseases such as systemic lupus erythematosus and an increase in infec on by encapsulated bacteria o Deficiency in the alterna ve pathway can cause severe bacterial infec ons and renal disease o Hereditary Angioedema:  C1 Esterase Inhibitor Deficiency  Leads to sudden uncontrolled ac va on of complement & bradykinin pathways  recurrent spontaneous a acks of non-itchy angioedema, which can be life- threatening if affec ng the airway o Terminal Complement Deficiency:  Affects the production of C5-C9 complexes  Causes an inability to produce an gen-an body complexes  defec ve opsonisa on and phagocytosis  increased risk of infec on, par cularly by Neisseria meningi dis and Neisseria gonorrhoeae o C3 Deficiency:  Reduced levels of opsonin C3b  Causes impaired opsonisa on  recurrent severe childhood infec ons, par cularly by encapsulated bacteria  C3 deficiency is also associated with autoimmune diseases and type III hypersensitivity reactions  Don Davis  Secondary Immunodeficiencies: o These arise later in life due to external factors or diseases that weaken the immune system. o Causes include:  HIV/AIDS: The human immunodeficiency virus a acks and destroys CD4+ T cells, weakening the immune system's ability to fight infec ons.  Malnutrition: Deficiencies in essen al nutrients can compromise immune func on.  Chemotherapy or Radiation Therapy: These treatments for cancer can suppress the immune system Monoclonal Gammopathies  Conditions in which there is abnormal proliferation of a single clone of plasma cells, leading to antibody overproduction  Causes & Examples: o Multiple Myeloma: cancer of plasma cells in the bone marrow, leading to the overproduc on of a monoclonal immunoglobulin o Monoclonal Gammopathy of Undetermined Significance (MGUS): presence of an abnormal protein (monoclonal protein) in the blood but without the presence of mul ple myeloma or other related complica ons. o Waldenström Macroglobulinemia: rare, indolent lymphoma characterized by the presence of a monoclonal IgM protein.  Don Davis 10. Allergic Diseases – Defini on. Types of allergic reac ons – Characteris cs, Mechanisms of Damage. Examples of Allergic Diseases & Syndromes. Allergic Diseases: Exaggerated Immune Response to Foreign Agent Resul ng in Injury Definition  Allergy is a harmful, misguided and over-zealous immune response to antigens that causes ssue damage and disease  Form of hypersensitivity, which can be classified into four types, based on the immune reactant, the an gen type and the effector mechanism  Allergens - an gens that can induce an allergic response, o en derived from non-infec ous or non- microbial sources  Allergenic proteins are small, soluble, stable and can have pep dase ac vity Types of Allergic Reactions  Type 1: o Mast-cell activation induced by secretion of IgE antibodies o Process:  Ini al exposure to an gen  priming of Th2 cells  release of IL-4  IL-4 release  B-cells switch from IgM to IgE produc on  IgE an bodies bind to mast cells and basophils, sensi sing them to the an gen  If an gen enters body again, it cross links the IgE bound to the sensi sed cells  This causes release of preformed mediators including histamine, leukotrienes and prostaglandins  vasodila on, bronchoconstric on + increased permeability of vascular endothelium o Stages:  Immediate: release of pre-formed mediators causes the immune response  Late-Phase: 8-12 hours later, cytokines released in the immediate stage ac vate basophils, eosinophils, and neutrophils even though the an gen is no longer present o Example: Anaphylaxis  Type 2: o Antibodies targeting antigens on cell surfaces instead of the allergen  cell destruction o IgG/IgM mediated cytotoxic reaction o Process:  Cell surface an gens presented to T-cells  immune response targe ng the cells to which the an gens are a ached  An bodies binding to cells ac vates complement system  degranula on of neutrophils, release of oxygen radicals & forma on of MAC  cell destruc on  Destruc on of host cells  ssue specific damage o Type 2 is distinguished from Type 3 by the location of the antigens – in Type 2, the antigens are cell bound, whereas in Type 3 the antigens are soluble o Examples:  Acute Blood Transfusion Reac ons  Haemoly c Disease of New-born  Autoimmune Haemoly c Anaemia  Goodpasture’s Syndrome  Don Davis  Type 3: o Immune complexes formed by antigens and antibodies that deposit in tissues, causing inflammation and damage o An bodies: IgG/IgM o Process:  An gen-an body complexes in the circula on deposited in ssues  Complexes become lodged in the basement membranes of ssues which have par cularly high rates of blood filtra on  Immune complexes rapidly and significantly ac vate the complement chain  local inflamma on + a rac on of leucocytes  Complement ac va on  increased vasopermeability, a rac on + degranula on of neutrophils, release of oxygen free radicals, damaging surrounding cells o Examples:  Serum Sickness  Rheumatoid Arthri s  Systemic Lupus Erythematosus (SLE)  Post-Streptococcal Glomerulonephri s  Type 4: o Delayed Type Hypersensitivity: T-cell-mediated responses occurring hours to days after allergen exposure o Immune Reactant: T-cells (CD4+ & CD8+ cells) o Process:  Antigen Presentation: APCs encounter allergen, process + present it to T-cells by displaying pep des of allergen on their surface using MHC molecules  T-Cell Activation: presented an gen is recognised by TCRs on CD4+ or CD8+ cells  ac va on  CD4+ cells differen ate into Th1 cells  release of interferon gamma + IL-17  recruitment + ac va on of macrophages + neutrophils  Cellular Damage: CD8+ cells release toxic molecules e.g., perforin  cell destruc on  damage + inflamma on  symptoms o Examples:  Contact Derma s  Mantoux Test  Poison Ivy-induced rashes  Examples of Allergic Diseases & Syndromes: o Allergic Rhini s o Food Allergies o Asthma o Anaphylaxis o Atopic Derma s (Eczema) o Contact Derma s o Allergic Conjunc vi s  Don Davis 11. Autoimmune Reac ons & Diseases – Defini on Definitions  Autoimmune Reactions: body's immune system mistakenly a acks its ssues and organs as if they were harmful pathogens  Autoimmune Diseases: immune system fails to recognize "self" from "non-self," leading to an immune response against the body's own cells, ssues, or organs Autoimmune Diseases – Examples  Rheumatoid Arthritis: immune system targets the synovium (lining of joints), causing inflamma on, joint damage, and pain.  Systemic Lupus Erythematosus (SLE): autoan bodies a ack mul ple organs, leading to inflamma on and damage in the skin, joints, kidneys, heart, and other organs.  Type 1 Diabetes: immune system a acks insulin-producing cells in the pancreas, leading to a lack of insulin and high blood sugar levels.  Multiple Sclerosis: immune cells a ack the protec ve covering (myelin) of nerve fibres in the brain and spinal cord, leading to communica on issues between the brain and the rest of the body.  Hashimoto's Thyroiditis: an bodies a ack the thyroid gland, causing inflamma on and reduced thyroid func on  Celiac Disease: immune system reacts to gluten, causing damage to the small intes ne is suscep ble individual 12. Immunological Tolerance – Defini on, Immune Processes to Develop & Sustain Immune Tolerance Immunological Tolerance  Immune Tolerance: unresponsiveness of the immune system to self-antigens  Innate Immune System – provides non-specific protection against anything it iden fies as foreign by recognising common pathogenic features  Adaptive Immune System – highly specific with each B & T lymphocyte receptor recognising a unique foreign an gen. o Diversity of these cells enables the immune system to recognise a wide range of pathogens but it inevitably results in the generation of self-reactive lymphocytes  Central Tolerance o First checkpoint to prevent self-reac ve lymphocytes causing damage o Self-reac ve B and T lymphocytes are destroyed in the bone marrow & thymus o Negative selection eliminates or inac vates self-reac ve lymphocytes  Peripheral Tolerance: o Next checkpoint in a empt to prevent autoimmunity o It includes:  Deletion of self-reac ve lymphocytes by apoptosis  Suppression of self-reac ve lymphocytes by regulatory T cells (Tregs)  Induction of anergy – rendering lymphocytes unresponsive to self-an gens o Tregs also plays role in protec ng the foetus, which has foreign paternal an gens, from immune a ack by maintaining maternal immune tolerance during pregnancy  Don Davis 13. Causes for Development & Mechanisms of Damage. Types of Autoimmune Diseases – Organ Specific & Systemic. Immunologic Characteris cs Immunologic Characteristics of Autoimmune Diseases  Loss of self-tolerance: immune system fails to recognize self-an gens, leading to an a ack on the body's own ssues  Autoantibody Production: an bodies that target and a ack the body's own proteins, cells, or ssues  Tissue Damage & Inflammation: immune cells create an inflammatory response in affected ssues, causing further damage and dysfunc on  Chronic Conditions: most autoimmune diseases are chronic and can have periods of exacerba on and remission, o en requiring ongoing management and treatment to control symptoms and prevent further damage Causes for Development & Mechanism of Damage  Development of autoimmunity is due to a combina on of genetic & environmental factors  Some main risk factors include: o Genetic Predisposition - autoimmunity o en run in families, with HLA gene family contribu ng to half of gene c predisposi ons o Female Sex - many autoimmune diseases are much more common in females of childbearing age, sugges ng that oestrogen may affect immune response o Impaired Treg Response - in certain autoimmune diseases, Treg numbers may be low or have impaired func on o Infection - autoimmune condi ons may be triggered by infec on e.g., via molecular memory as seen in Rheuma c Fever & Guillan-Barré Syndrome o Certain medications, hormonal changes, and exposure to toxins may trigger the onset of autoimmune reac ons in gene cally suscep ble individuals  Mechanism of Damage: o Autoantibodies Production: immune system generates autoan bodies that target specific proteins or ssues within the body  inflamma on and ssue damage. o Inflammatory Response: immune cells, such as T cells and macrophages, contribute to inflamma on in affected ssues  destruc on & dysfunc on Types of Autoimmune Diseases  3 Types of Autoimmune Diseases: o Organ-Specific o Systemic o IgG4 Related  Organ-Specific Autoimmune Diseases: o Target specific organs or tissues o Usually effects endocrine glands o Examples:  Type 1 Diabetes – targets insulin-producing cells in the pancreas  Hashimoto’s Thyroiditis – a acks thyroid gland  Multiple Sclerosis – affects myelin sheath of nerve fibres  Myasthenia Gravis – affects neuromuscular junc on  Don Davis  Systemic Autoimmune Diseases: o Affect multiple organs or systems in the body o Mainly associated with intracellular molecules involved in transcrip on & transla on for gene c code o Examples:  Rheumatoid Arthritis  Systemic Lupus Erythematosus (SLE): target structures found in nearly all cell types such as double strand DNA (dsDNA)  Sjögren’s Syndrome: affects glands that produce moisture in the mouth and eyes but can involve other organs  IgG4 Related Diseases: o Characterized by inflammatory lesions that can affect various organs and tissues in the body o Classified as an immune-mediated fibro-inflammatory condition o Characteris cs:  Elevated IgG4 levels  Fibrosis  Inflammatory lesions  Mul -organ involvement o Immunological Basis:  Cause of IgG4 related diseases remains unclear - believed to involve an abnormal immune response, possibly an autoimmune reac on  In affected ssues, there's an accumula on of immune cells, par cularly IgG4- producing plasma cells and T cells, contribu ng to the inflammatory response and fibrosis  Don Davis 14. Tumour immunology. Types of tumour an gens. Immunological Mechanisms Against Tumours. Mechanisms of Tumour Immune Escape. Tumour Prophylac cs & Immunotherapy – Basic Approaches Tumour Immunology  Tumour immunology is focused on the interaction between the immune system and tumours: o Tumour an gens o Immune response to tumours o Tumour’s effect on host’s immune status o Use of immune system for tumour eradica on  Imbalance between cell proliferation and cell death encourages development of cancerous state  Development of cancer cells is typically: o Mul step process of clonal evolu on at cellular level o Driven by series of somatic mutations and disruption of growth-regulating genes:  Proto-oncogenes  Tumour-suppressor genes  Genes involved in apoptosis  Hallmarks of Cancer: o Sustaining prolifera ve signalling o Ac va ng invasion and metastasis o Evading growth suppressors o Reprogramming of energy o Resis ng cell death metabolism o Enabling replica ve immortality o Evading immune destruc on o Inducing angiogenesis  Tumour Immunity – Overview: o 3 proposed mechanisms by which the immune system is thought to control cancer:  Destroying viruses known to transform cells  Eliminating pathogens + reducing pro-tumour inflammation  Immunosurveillance – actively identifying + eliminating cancerous cells Types of Tumour Antigens  Neoantigens: o Tumour-Specific Antigens (TSAs):  Antigens encoded by mutated genes  Somatic mutations may change a self-protein that the pa ent is tolerant to a:  ‘Passenger’ muta on - doesn't contribute to the growth advantage of cancer and is carried along but doesn't drive tumour development  ‘Driver’ muta on - directly contributes to the ini a on or progression of cancer by providing a selec ve growth advantage to the affected cell  ‘Trunk’ muta on - found in the early stages of tumour forma on, present in most/all tumour cells, and considered a fundamental + early event in cancer development  ‘Leaf’ (or ‘Branch’) muta on – occurs later in tumour evolu on, found in a subset of tumour cells, o en providing addi onal characteris cs or features but not present in all cells of the tumour  Don Davis o Antigens of Oncogenic Viruses:  Endogenously synthesized viral proteins can be processed and presented by MHC molecules on the tumour cell surface  Tumour-Associated Antigens: o Antigens are also found on normal cells but are overexpressed or aberrantly expressed on cancer cells o Examples:  HER2/neu – highly expressed in breast cancers  CEA (Carcinoembryonic An gen) – elevated in colorectal cancer as well as in cancers of pancreas, lung, breast, and some GI cancers.  CEA is an oncofoetal antigen - typically present only during foetal development but can be seen in adults with aforemen oned condi ons  PSA (Prostate-Specific An gen) – elevated levels indicate benign prosta c hyperplasia (BPH) and prostate cancer Immunological Mechanisms Against Tumours  Cell-Mediated Immune Response: o CD8+ cytotoxic T-lymphocytes (CTLs) - recognise tumour an gens presented on MHC molecules and kill tumour cells o CD4+ helper T-cells (Th1 cells) - enhances CD8+ responses by ac va ng macrophages via secre on of IFN-γ – this also increase tumour cell class I MHC expression + sensi vity to lysis by CTLs  Antibody-Mediated Immune Response: o An bodies can bind to tumour cells, tagging them for destruc on by immune cells or by interfering with their growth and signalling  Natural Killer (NK) Cells: o Many tumours express ligands for ac va ng receptor on NK cells o Ac va on of those receptors on NK cells  IFN-γ secre on – a potent an cancer cytokine that encourages dendri c cells to s mulate strong CTL responses Mechanisms of Tumour Escape  Creation of Immunosuppressive Microenvironment: o Tumours create an environment that suppresses immune responses, o en through the secre on of factors that inhibit immune cell func on  Downregulation of Antigen Presentation: o Tumours can downregulate expression of Class I MHC molecules, making it harder for immune cells to recognize them  Inhibition of Immune Responses: o Secreted products of tumour cells may suppress an tumor immune responses:  TGF-β - inhibits the prolifera on + effector func ons of lymphocytes & macrophages  Increased number of Tregs may suppress T-cell responses to tumours – they can be found in cellular infiltrates in certain tumours  Secre on of immunosuppressive cytokines, such as IL-10 and TGF-β; promote Treg differen a on  Myeloid-Derived Suppressor Cells (MDSCs) – immature myeloid precursors that accumulate in bone marrow, lymphoid ssue and blood, they suppress innate + T- cell mediated immune responses  Don Davis  Immune Checkpoint – Inhibition of Immune Responses: o Engagement of Inhibitory Molecules:  Tumours use molecules like CTLA-4 and PD-1 to dampen the response of T cells against them  Normally these molecules are involved in regula ng immune responses to prevent excessive immune reac ons or autoimmunity o Dysfunctional T Cell Phenotype:  Tumour-infiltra ng T cells o en exhibit a dysfunc onal state, where their ability to func on effec vely against the tumour is impaired  These T-cells tend to express higher levels of inhibitory molecules like CTLA-4 & PD-1 o Low Costimulation Levels:  Tumour an gens are presented by APCs in the absence of strong innate immunity and thus with low levels of B7 cos mulators  These low levels may be enough to engage the high-affinity receptor CTLA-4 o Expression of PD-L1 on Tumours:  The PD-1 pathway may be engaged in tumour-specific T cells because PD-L1, a ligand for PD-1, is expressed on many human tumours Tumour Prophylactics & Immunotherapy – Basic Approaches  Immunotherapies - designed to help eliminate a tumour by reviving, ini a ng, or supplemen ng the in vivo an -tumour immune response or by neutralizing inhibitory pathways  Basic Approaches: o Cancer Vaccines: s mulate the immune system to recognize and a ack cancer cells by presen ng tumour an gens to the immune system o Checkpoint Inhibitors: block inhibitory signals (e.g., PD-1, CTLA-4) that tumours use to evade the immune response, enhancing the immune system's ability to a ack cancer cells o Adoptive Cell Therapy (ACT): involves isola ng and expanding immune cells, such as T cells or NK cells, outside the body and reintroducing them to target and destroy cancer cells o Cytokine Therapy: using cytokines (e.g., interleukins, interferons) to boost the immune response against cancer cells  Don Davis 15. Transplanta on Immunology - Role of the MHC for Transplant Tolerance or Rejec on 16. Immune Response a er Transplanta on – Reac ons & Mechanisms of Transplant Rejec on, Gra vs Host Reac on Transplantation Immunology  Study of immune responses triggered by transplanted tissues or organs  Aims to understand how the recipient's immune system recognizes and responds to the transplanted material  In transplanta on tissue compatibility is required which is determined by genetic variation between the donor and the recipient  MHC is the largest immunologic barrier to successful allogenic transplanta on  Incomplete ssue compa bility may cause: o Rejection of transplanted organ o Graft vs Host Disease in the transplanta on of immunocompetent hemopoie c cells Major Histocompatibility Complex  The classical (transplant) HLA an gens are also known as major histocompatibility antigens  HLA proteins are encoded by linked genes on chromosome 6 in MHC + inherited as halotypes from paternal chromosomes o Offspring receive 1 maternal + 1 paternal HLA halotype  HLA proteins are heterodimeric transmembrane molecules  2 Classes: o Class I – HLA-A, B & C  Expressed on cell surface with beta-2-microglobulin  Codominantly expressed on all nucleated cells o Class II – HLA-DR, DQ & DP  Codominantly expressed mainly on antigen-presenting cells  Func on: present an gens to T cells, helping the immune system dis nguish between self and non- self Allorecognition  Transplanta on of cells or ssues between two individuals is classified by the gene c relatedness of the donor and the recipient. o Autograft - transfer of ssue from one area of the body to another of the same individual o Syngeneic Graft - transfer of cells or ssues between iden cal twins o Allograft - transfer of cells or ssue between two individuals of the same species  Most transplants are allogra s o Xenograft - transfer of ssue between two individuals of a different species  HLA disparity - between donor & recipient will result in a vigorous cellular & humoral immune response to the foreign MHC an gens and is the primary s mulus of gra rejec on  Direct Allorecognition - recipient T-cells bind + respond directly to foreign(allo)HLA proteins on gra APCs  Indirect Allorecognition - recogni on of donor an gens presented by recipient an gen-presen ng cells to recipient T cells, triggering an immune response against transplanted ssues or organs o Plays a predominant role in acute + chronic rejec on  Don Davis Role of MHC for Transplant Tolerance or Rejection  Rejection - recogni on of foreign MHC molecules on the transplanted ssue triggers an immune response, leading to rejec on o Types of Rejec on:  Hyperacute  Chronic  Acute Cellular  Tolerance - strategies aimed at inducing tolerance involve suppressing the immune response against donor MHC an gens  Hyperacute Rejection: o Minutes-hours a er transplanta on o Caused by reformed donor-specific (allo)antibodies in the recipient due to immunisa on a er pregnancy, blood transfusions, prior transplanta ons o Process:  Endothelial damage in vessels of transplanted organ  ac va on of complement + an body-mediated cellular cytotoxicity  thrombosis  Acute Cellular Rejection: o Days-weeks a er transplanta on o Characterised by parenchymal + vascular injury and infiltra on of immune cells into the gra primarily led by T-cells  Chronic Rejection: o Weeks-Months a er transplanta on - characterized by a slow and continuous immune response o Most significant cause of gra loss a er the first-year post-transplant o Process:  Exposure to triggers e.g., prolonged cold ischemia, reperfusion, acute rejec on episodes, toxicity from immunosuppressive drug  T-cells persistently recognize the transplanted organ or ssue as foreign  chronic inflamma on  Chronic inflammation  vascular damage, impairs blood flow, reducing oxygen and nutrient supply to the ssues  Over me this leads to fibrosis, scarring and eventual progressive dysfunc on  failure o Factors Contribu ng to Chronic Rejec on:  Immunological Memory - residual memory immune cells retain recogni on of the donor an gens, perpetua ng the immune response  Persistent Low-Level Rejection - even with immunosuppressive drugs, immune response against transplanted organ can persist  chronic rejec on  Non-immunological factors – such as ischemia + other factors that can damage the transplanted ssue independently of immune responses  Graft vs Host Disease (GVHD): o Seen in stem cell transplants o Process:  Donor bone marrow or peripheral blood stem cells infused  Infused produces may contain mature T-cell  massive release of cytokines due to ac va on of the donor cells and by infiltra on and destruc on of ssues  Don Davis o Acute GVHD – occurs during the first 100 days post infusion + targets the skin, GI tract & liver o Chronic GVHD – occurs beyond 100 days post-transplant, resembles autoimmune disease, with fibrosis affec ng the skin, eyes, mouth, and other mucosal surfaces Immunosuppressive Agents  Suppress antigraft immune responses in solid-organ and stem cell transplanta on  Used in several ways, including induction & maintenance of immune suppression and treatment of rejection  Combinations of different agents are frequently used to prevent gra rejec on  Disadvantage: increased susceptibility to infection, malignancies, and other associated toxic side effects  Examples: o Corticosteroids: such as prednisone, methylprednisolone - reduce inflamma on and suppressing the immune response. o Calcineurin Inhibitors: such as tacrolimus and cyclosporine - block the ac vity of calcineurin, a protein necessary for T-cell ac va on. o Antiproliferative Agents: such as azathioprine, mycophenolate mofe l, and mycophenolic acid - inhibit the prolifera on of T and B cells, thus suppressing the immune response. o mTOR Inhibitors: such as sirolimus & everolimus - interfere with T-cell prolifera on and signal transduc on. o Monoclonal Antibodies: target specific immune cells or molecules. Examples include:  Anti-Thymocyte Globulin (ATG): Targets T cells and is used in acute rejec on.  Rituximab: Targets B cells and is used in condi ons like certain autoimmune diseases and rejec on in organ transplanta on.  Basiliximab & Daclizumab: target the IL-2 receptor on T cells + used to prevent acute rejec on in organ transplanta on  Don Davis 17. Pre- & Post-transplant Immune Monitoring Pre-transplant Immune Monitoring  3 mains to conduct pre-transplant immune monitoring: o HLA Typing o An body Screening o Cross-Match Reac on Test  HLA Typing - determina on of HLA genes and an gens: o HLA-Phenotyping:  Done to determine the specific alleles + antigens present in an individual's HLA system  Determined by Complement-Dependent Cytotoxicity (CDC) Test  Serum collec on + isola on of lymphocytes  Sensi sa on of donor lymphocytes  Addi on of complement  Cell lysis observa on o HLA-Genotyping:  Done to iden fy specific HLA allele or groups of alleles  PCR-based amplification is used in order for iden fica on of the specific alleles or allele groups  Antibody Screening: o Antibodies to HLA antigens can be detected in candidates + recipients of solid-organ transplants o An bodies develop in response to:  Mul ple blood transfusions  Prior HLA-mismatched transplants  Mul ple pregnancies in women o Pa ents awai ng solid-organ transplanta on are screened periodically for their presence o If detected, specificity of antibodies is determined so that donors possessing those HLA an gens can be eliminated from considera on for dona on to that pa ent o Methods for An body Detec on & Iden fica on:  CDC Method  Flowcytometry  ELISA (Enzyme-Linked Immunosorbent Assay)  Cross-Match Reaction Test: o Purpose:  Determine whether a patient has antibodies that reacts with antigens expressed by donor  Assess immunological risk for patient/donor combination o Process:  Donor lymphocytes intubated with recipient serum in CDC assay to verify lack of binding as detected by microscopic analysis a er addi on of a vital dye  Alterna vely, binding of an body can be detected by flowcytometry using an FITC- labelled an -IgG reagent  Flowcytometric crossmatch is the most sensitive method for detecting donor specific antibody  Virtual Crossmatch - based on the determina on of donor-specific alloan bodies in the pa ent serum towards HLA specific alleles of the donor  Don Davis Post-Transplant Immune Monitoring  Rejection Surveillance: o Biopsies: assessing ssue samples from the transplanted organ to detect signs of rejec on o Laboratory Tests: monitoring blood levels of crea nine, liver enzymes, and other markers to detect organ dysfunc on  Immunosuppressive Drug Monitoring: o Therapeutic Drug Monitoring (TDM): regularly measuring drug levels to ensure adequate immunosuppression while avoiding toxicity o Adjustment of Dosages: based on TDM results and individual pa ent responses  Infection Monitoring: o Serological Tests: periodic assessment for viral infec ons due to increased suscep bility in immunocompromised transplant recipients o Prophylactic Measures: administering vaccines or medica ons to prevent opportunis c infec ons  Assessment of Immune Function: o Lymphocyte Subset Analysis: monitoring T-cell, B-cell, and natural killer (NK) cell popula ons to evaluate immune recons tu on o Functional Assays: assessing immune cell func on to ensure the pa ent's immune system is recovering adequately  Complication Detection: o Iden fying and managing complica ons related to immunosuppression, such as malignancies or metabolic abnormali es o Monitoring for adverse effects of immunosuppressive drugs and adjus ng treatment as needed  Long-Term Follow-Up: o Ongoing surveillance and periodic assessments to monitor gra func on, immune status, and overall health post-transplant  Don Davis 18. Blood Transfusion Reac ons – Immunological Bases, Types, Causes & Examples ABO Grouping System  Erythrocytes have ABO antigens a ached to their cell surface – this determines a person’s blood group  An individual inherits one ABO allele from each parent, with A and B alleles being codominant and producing the A and B an gens respec vely  Each person also has ABO an bodies in their plasma which will recognise and a ack RBCs expressing foreign antigens o These an bodies develop over the first months and years of life o The A and B an bodies are predominantly IgM  This means: o Group A – has A antigens + B-antibodies o Group B – has B antigens + A-antibodies o Group AB – have both antigens + no antibodies o Group O – have no antigens + A&B antibodies Rhesus Grouping System  There are 5 clinically significant Rhesus (Rh) antigens – D, C, c, E & e  RhD is most immunogenic (i.e., likely to produce an immune response) therefore most likely to precipitate a transfusion reaction  Rh-Positive – means RhD is present on erythrocyte cell surface o Have the Rh D an gen and can receive both Rh+ and Rh- blood  Rh-Negative – means RhD is absent on erythrocyte cell surface o Lack the Rh D an gen and should only receive Rh- blood  Anti-D antibody is usually absent in Rh- patients unless they have been exposed to Rh+ erythrocytes such as fetomaternal transfusion Blood Transfusion Reactions - Immunological Basis  ABO Incompatibility: o Recipient receives blood with ABO an gens different from their own blood type o An bodies in the recipient's plasma react against the donor's RBCs  haemolysis o Most common cause of severe immunological reac ons in blood transfusions  Rh Incompatibility: o Rh-nega ve recipients receiving Rh-posi ve blood o Can lead to Rh sensi za on in Rh-nega ve individuals, causing future immune responses if exposed to Rh-posi ve blood  Other Antigen Incompatibilities: o Other blood group an gens (besides ABO and Rh) can also cause immunological reac ons if mismatched between donor and recipient  Don Davis Types of Blood Transfusion Reactions  Acute Haemolytic Reaction: o Results from ABO or other blood group incompa bili es  haemolysis of transfused blood o Severe + poten ally life-threatening o Symptoms: fever, chills, chest or back pain, haemoglobinuria & acute kidney injury  Delayed Haemolytic Reaction: o Occurs days a er transfusion o Characterized by a gradual decline in haemoglobin levels + signs of haemolysis  Febrile Non-Haemolytic Reaction: o Characterized by fever typically occurring within 1-6 hours post-transfusion o Caused by recipient an bodies reac ng against donor leukocytes or cytokines in stored blood components o Symptoms include fever, chills, and mild to moderate discomfort  Allergic Reaction: o Results from the recipient's sensi vity or allergy to components in the transfused blood, such as plasma proteins or preserva ves. o Symptoms range from mild itching or hives to severe anaphylaxis  Transfusion-Related Acute Lung Injury (TRALI): o Caused by donor an bodies in transfused blood that react with recipient leukocytes, triggering a severe inflammatory response in the lungs o Rare but severe reac on characterized by acute respiratory distress Examples & Causes  Haemolytic Disease of Newborn (HDN): o Incompa bility between the blood types of the mother and foetus, related to Rh factor or other blood group an gens o Anti-D antibodies cause the most severe type of HDN o Maternal anti-D antibodies recognise and destroy foetal Rh+ RBCs o Mechanism:  Sensitisation: upon first exposure, the an bodies are IgM, which cannot cross the placenta and will not cause issues in the first pregnancy  Antibody Production: future Rh+ pregnancies increased IgG an -D produc on which crosses placenta  haemolysis  Foetal Anaemia: RBC destruc on in foetus  anaemia  increased produc on of erythroblasts in foetal bone marrow o Effects:  Foetal Complica ons:  Severe Foetal Anaemia  Jaundice  Hepatosplenomegaly  Neonatal Jaundice  Foetal Hydrops (Severe) o Preven on + Treatment:  Administration of Rh immunoglobulin to Rh nega ve mothers  Monitoring  Intrauterine Transfusions  Don Davis Coombs’ Test (Antiglobulin Testing)  Direct (Antiglobulin) Coombs’ Test: o Detects whether a patient’s RBCs have antibodies directly attached to them o Process:  Coombs’ reagent binds to specific immunoglobulins on the RBCs  It is added into pa ent’s blood  Posi ve result - r