Immunology I: Innate & Adaptive Immunity PDF Fall 2024

Immunology I: Innate & Adaptive Immunity Tiffany Cooke, MSHS, PA-C, RD PHA 520 – Foundations of Clinical Practice I Fall 2024 Adapted from a previous prese...

Immunology I: Innate & Adaptive Immunity Tiffany Cooke, MSHS, PA-C, RD PHA 520 – Foundations of Clinical Practice I Fall 2024 Adapted from a previous presentation by Ian McLeod, PA-C, ATC Objectives: Identify the major types of leukocytes. List primary and secondary lymphoid organs & their functions. Describe hematopoiesis. Explain the key features and general phases of the innate immune response. Explain the key features and general phases of the adaptive immune response. Compare primary and secondary immune responses. Compare and contrast antigen recognition in both the innate and adaptive immune responses. Identify cytokines, chemokines, and adhesion molecules and describe the basic functions of these groups of molecules. Identify the phagocytic leukocytes. Define NK cells and describe the way in which NK cells destroy target cells. Objectives: Describe the steps in macrophage activation and the function of activated macrophages. Identify the major cytokines/chemokines produced by activated macrophages. Describe B cell activation and the function of B cells. Identify the ways in which B cells present antigen to T cells. Describe the function of plasma cells. Define antigen, and identify the common properties of B cell and T cell antigen receptors. Describe the basic structure of an antibody. Describe the process by which lymphocytes encounter antigens. Identify the most abundant isotype of antibody in the serum. Describe the general difference between monoclonal and polyclonal antibodies. Define CD4 and CD8 T cells. Objectives: Explain the consequences of compliment deficiency. Describe the assembly and function of the membrane attack complex (MAC). Define MHCs and HLAs. Identify the locations of both immature and mature T cells and B cells. Describe the major immunodeficiencies associated with B cell and T cell development. Define acute phase reaction, and identify the cytokine(s) involved in the production of acute phase proteins. Describe the interferon response and the consequences of Type I interferon induction. Describe the role of compliment in immunity and the process of complement activation. First things first… A (very) brief review of the immune system: Purpose First line Second line (innate) Third line (adaptive) Definitions Antigens are anything that causes an immune response Ex. bacteria, viruses, fungi, parasites, or smaller proteins that they express (aka “pathogens”). Antigens are like a name tag for each pathogen that announce the pathogens’ presence to your immune system. Some antigens are general, whereas others are very specific. A general antigen signals “danger!” A specific antigen signals “I’m a bacteria that will cause an infection in your lungs!” or “I am a virus that you have encountered before” Antibody (immunoglobulin or Ig) Protein molecule created by our immune system to target an antigen for destruction. Bind to the foreign antigen Disable the antigen “Tag it” for destruction by other immune defenses Definitions CYTOKINES are cell-to-cell communication proteins that control cell development, differentiation, and movement to a specific part of the body. Produced by a variety of immune cells. -Chemokines are a type of cytokine released by infected/injured cells. They initiate an immune response (signal circulating neutrophils and macrophages), and warn neighboring cells of the threat. -Interleukins (ILs) are 13 cytokines that regulate portions of immune responses, inflammatory reactions, and hematopoiesis IL-1 is responsible for fever IL-1 & IL-6 stimulate synthesis of “acute-phase response” -Tumor Necrosis Factor (TNF) activates neutrophils and macrophages, mediates septic shock, causes tumor necrosis. TNF is also responsible for fever -Interferons (IFN) interfere with virus replication. Alpha, beta and gamma subtypes (IFN-α, IFN-β, IFN-γ) IFN-γ* is the strongest IFN, is produced by T cells, and activates macrophages, natural killer cells, and neutrophils Interferons A note on IFNs: (α) alpha, beta (β), and gamma (γ) have been classified into two types: Type I includes the (α) & (β) forms Function is to induce viral resistance in cells Type I IFNs can be produced by almost any cell type in the body Type II is the (γ) form Type II interferon is secreted only by natural killer cells and T lymphocytes; Its main purpose is to signal the immune system to respond to infectious agents or cancerous growth. Type I IFNs – friend or foe? Have been shown under some circumstances to suppress T-cell responses and memory T-cells; this is important, especially in HIV In influenza, it limits viral replication but creates pathologic inflammation in the lung The Immune System Immunity conveyed by a Divided into two branches: complex system of: Barriers Innate Recognition aka ‘natural’, ‘non-specific’ Foreign or ‘not self’ FAST Mutated cells Destruction Adaptive Phagocytosis, lysis, etc. aka ‘specific’, ‘humoral’ or ‘cell- mediated’ SLOW HOWEVER, there is some crossover between the functions of the two branches!! Innate and Adaptive Immunity http://people.eku.edu/ritchisong/301notes4b.html  Where it all begins.. Hematopoiesis The formation and development of the cells that make up “blood” Embryo and fetus: occurs primarily in liver, spleen and thymus Birth to adult: occurs primarily in bone marrow small amount in lymphatic tissues  Video Monoblasts http://www.textbookofbacteriology.net/innate.html Innate Immunity INNATE IMMUNITY  Components:  Physical barriers  Granulocytes (aka PMNs)  Monocytes  Macrophages  Dendritic Cells  Natural Killer Cells  Complement Cascade  Characteristics  IMMEDIATE  Non-Specific Response…no memory  Response does NOT increase with repeat exposure Components of the Innate Immune System First level of protection: Commensal bacteria- “normal PHYSICAL BARRIERS bacterial flora” Microbial antagonism Both external and internal  Skin Compete with potential  Protects against invasion pathogens  Acidic pH of sweat Upset by antibiotic use  Fatty acids and enzymes from Example: vaginal candidiasis pores/follicles resulting from change in lactobacillus and/or G. vaginalis  Mucous Membranes concentrations; or c. difficile  Tears colitis All contain lysozyme….which  Saliva  Mucus protects against bacteria  Gastric secretions…external? Yes!  Acidic pH Inflammation When the barrier isn’t sufficient protection → inflammatory response → goal is to recruit leukocytes to the area and limit spread of the infection Damaged tissue and/or cell mediated histamine, prostaglandin and leukotriene release → vasodilation and leaky capillaries Cell mediated heparin release → decreased clotting RESULT: Increased blood flow to area, immunologic factors leak out of capillaries into interstitial space to do their jobs…… Hallmark inflammatory symptoms Pain Redness Warmth Swelling Inflammatory Response Vasodilation and vascular leak Prostaglandins [pain] and leukotrienes Histamine Heparin Nitric oxide (NO) → contributes to hypotension in septic shock Cytokines Activated complement Recruit and activate leukocytes (neutrophils) Cytokines and chemokines Inflammatory Response Adhesion molecules: Membrane proteins that connect cells to other cells or the extracellular matrix (ECM) Play a major role in the recruitment of neutrophils to the site of inflammation…. neutrophils “roll” along the luminal surface of blood vessel towards the site of injury, then squeeze out between cells of capillary wall. Leukocyte extravasation Selectins → sticky endothelial cells Chemokines → stimulate leukocytes to express higher levels of integrins Integrins → stops the leukocytes Mutations in genes encoding cell adhesion molecules cause (we think) a variety of disorders Vascular system (atherosclerosis?), skin, kidney and muscle, and the immune and nervous systems (Alzheimer’s disease? Autism?) Leukocyte Extravasation Innate and Adaptive Immunity http://people.eku.edu/ritchisong/301notes4b.html Innate Immune System – GRANULOCYTES Basophils Least common Mature in bone marrow Circulate in bloodstream Allergic & helminth (parasitic) responses Release histamine & heparin Reduction of clotting & increased blood flow resulting from vasodilation Release prostaglandins & leukotrienes Cause inflammation → large amounts lead to hypersensitivity reactions (urticaria to systemic anaphylaxis) Innate Immune System – GRANULOCYTES Mast Cells Leave the bone marrow as immature cells, mature in tissues Present in tissues that are boundaries b/t “inside” and “outside” (esp. mucosa) Allergic & helminth (parasitic) responses Release histamine, heparin, prostaglandins and leukotrienes causing inflammatory cascade Will degranulate if: Injured Encounters antigen or allergen Exposed to complement proteins Innate Immune System: The GRANULOCYTES Mast Cells Massive release of histamine results in anaphylaxis Body-wide vasodilation leads to edema, decreased BP etc. Innate Immune System – GRANULOCYTES Eosinophils Derived from the bone marrow Both circulating in bloodstream & present within organs… particularly the GI tract and respiratory tract Release H2O2 and other oxygen radicals to kill microbes: Viruses (double edged sword), parasites (esp. helminths) Release leukotrienes → lipid signaling molecules that causes airway smooth mm contraction Active in allergic reactions and helminth (parasitic) infections Innate Immune System – GRANULOCYTES More on Eosinophils…. Weakly phagocytic Act as “antigen presenting cells” (APCs) → allergic reactions and helminth (parasitic) infections Stimulate T-lymphocytes  Innate Immune System – GRANULOCYTES Neutrophils Most abundant of the granulocytes Circulate in the bloodstream One L of blood contains about five billion neutrophils! “First Responders” Particularly active against bacteria & fungi Arrive within minutes of injury Drawn by chemokines (chemotaxis) In turn release other cytokines to recruit monocytes & macrophages Strongly Phagocytic Neutrophil Extracellular Traps (NETs) ‘Throw out’ extracellular fibers that bind bacteria Innate Immune System: Monocytes: “Agranular” Differentiate into dendritic cells & macrophages Develop in bone marrow; half are stored in the spleen, half migrate to tissues and differentiate into dendritic cells and macrophages Macros and dendros have 3 primary functions: Phagocytosis Antigen presentation (APCs) Cytokine production  Innate Immune System: Dendritic Cells The ‘strongest’ of the APCs → best at activating helper-T lymphocytes Antigens are captured by dendritic cells The dendritic cell then migrates to the nearest lymph node & presents the antigen to T Cells and B Cells Specialized dendritic cells in skin Langerhans cells Innate Immune System: Macrophages Large phagocytes release TNF and Interleukins (ILs) Also act as APCs Present within the skin, lungs, GI tract and most other tissues Macrophages have 3 stages of readiness a) resting = cleaning up cellular debris (scavengers) b) primed = more active engulfing of bacteria, display fragments of bacteria for T cells (act as APCs) c) hyper-activated = inflammatory cytokines cause macrophages to enlarge and start rapidly destroying pathogens and/or cancerous cells After digesting a pathogen, a macrophage will present the antigen to a helper T cell. Antigen is integrated it into the cell membrane and displayed attached to an MHC class II molecule (MHCII) MHCII indicates to other white blood cells that the macrophage is not a pathogen, despite having antigens on its surface As phagocytes, macrophages may become hosts for pathogens! E.g. TB (bacterium), Leishmanisasis (parasite), Cikingunya (virus) Other immune system players Major Histocompatibility Complex (MHC) Proteins The human MHC is aka the Human Leukocyte Antigen (HLA) Cell surface molecules which help the immune system to determine if a protein is “self” or “not-self” Bind antigen to cell surface and display for recognition by T cells 3 sub-groups: MHC I,II & III Key points: Determines organ donation compatibility Certain autoimmune diseases are due to a malfunction in this recognition system (ex. ankylosing spondylitis is HLA-B27 positive) Participates in T* & B cell activation Displayed in combo with a piece of antigen by APCs Innate Immune System: Specialized Macrophages: Kupffer cells Specialized macrophages within the liver Destroy bacteria & old RBCs Chronic activation of Kupffer cells (toxins, EtOH) leads to overproduction of inflammatory cytokines & chronic inflammation Result: liver cell damage, CA  Innate Immune System: Natural Killer Cells Mature in the bone marrow, lymph nodes, spleen, tonsils, and thymus NK cells are cytotoxic lymphocytes, but don’t need to “recognize” or remember a pathogen to kill it! Killing is nonspecific → not dependent upon foreign antigen presentation Particularly active against viruses and cancerous cells NK cells also have granules that contain destructive enzymes Killing activity is enhanced by cytokines secreted by macrophages and dendritic cells → produce IFN-γ which activates macrophages (domino effect) NK cells kill their target by releasing perforins and proteases that cause cell membrane lysis or trigger apoptosis (cell death) in the target cell Can do this without antibody but antibody (IgG) enhances their effectiveness Innate Immune System: Natural Killer Cells cont. “on-call” Hang out in the bloodstream, liver and spleen Operate on a “kill” or “don’t kill” system Will kill cells that have unusual surface receptors NK cells can “kill” even during their resting phase, but are better killers when activated (by cytokines) Serve to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells that can clear the infection. Other immune system players Acute phase proteins Produced by LIVER in response to inflammation induced release (by macrophages & T cells) of IL-1,IL-6 & TNF (remember, ILs are cytokines that help regulate immune responses, inflammatory reactions, and hematopoiesis; IL 1 & TNF are also responsible for fever) C-reactive protein (CRP) Mannose-binding lectin (MBL) Lipopolysaccharide-binding protein All acute phase proteins identify or “mark” pathogens or injured cells for destruction in some way Ex. MBL binds to mannose-rich glycans on microbial cell walls, then activates complement Ex. CRP binds to bacterial and fungal cell walls and damaged or dead human cells, then activates complement  The Complement System Complement system (aka the complement cascade): enhances the ability of phagocytic cells to destroy pathogens, system itself can also attack foreign cells Composed of ~ 30 different proteins that work together to signal the other immune cells that the attack is ON! 3 possible complement activation pathways Classical (requires triggering) Lectin pathway (requires very specific type of triggering) Alternative (continuously activated at low level) Complement is activated by antigens Complement proteins are made by the liver C3 is the most abundant complement protein in humans  Functions of complement Opsonization - enhancing phagocytosis of antigens by ‘marking’ them for destruction Chemotaxis - attracting and activating macrophages, dendritic cells, and neutrophils; inducing mast cells & basophils to degranulate Lysis - rupturing pathogen cell-membranes by forming the Membrane Attack Complex (MAC) Complement Functions (video FYI only) Membrane Attack Complex C5b forms a complex with C6, C7, C8, and C9 to form the MAC This causes lysis of the cell by disrupting osmotic balance Microbe will swell and burst  Functions of complement Complement “Fixation”: Antigen combines with an antibody and its complement, causing the complement factor to become inactive or fixed. Complement-fixation reaction can be tested in the laboratory by exposing the patient's serum to antigen, complement, and specially sensitized red blood cells. Complement-fixation tests can be used to detect antibodies for infectious diseases, especially syphilis and viral illnesses. Note that complement fixation testing has been largely superseded by newer methods of pathogen detection. Innate Immunity: Key Points Response is IMMEDIATE Response is NON-SPECIFIC; it is the same each time, regardless of the pathogen Response DOES NOT INCREASE with repeat exposure to pathogen Innate and Adaptive Immunity http://people.eku.edu/ritchisong/301notes4b.html The Adaptive Immune System Components Characteristics T-cells Requires initial exposure to an agent “cell-mediated” B-cells Action requires days to develop Antibodies “humoral” Response is specific to an antigen Complement Response is enhanced through APCs repeated exposure to antigen Develops “memory”….subsequent exposures result in a more rapid and intense immune response The Adaptive Immune System Primary Lymphoid Organs: Secondary Lymphoid Organs: Where immature lymphocytes Where antigens are presented (Bs & Ts) grow up and to mature (but naïve) B & T proliferate lymphocytes to initiate the Thymus (T-cells) adaptive immune response Bone marrow (B-cells) Spleen Lymph nodes Tonsils & adenoids Appendix The Adaptive Immune System B and T lymphocytes shared features Diversity → collectively they can respond to millions of different antigens Memory → can respond many years after the initial exposure because memory T cells and memory B cells are produced Specificity → actions are directed against the antigen that initiated the response The Adaptive Immune System B-Cells (B-lymphocytes) Eliminate EXTRACELLULAR PATHOGENS Are APCs! Presents a piece of the antigen in combination w/ a MHC molecule on its surface Produce ANTIBODIES (immunoglobulins, Ig) Have membrane-bound antibodies (functions as the B-cell receptor) Recognition of antigen by the B-cell receptor (which is an antibody), coupled with a signal from “Helper” T-cells (CD-4), prompts the B-cell to divide into “clones” These “clones” or effector cells (plasma cells) produce antibodies Effector cells are relatively short-lived activated cells that defend the body during an immune response Memory B cells The Adaptive Immune System T-Cells (T-lymphocytes) Destroy INTRACELLULAR pathogens Viruses and intracellular bacteria Subtypes: ”Helper” T-Cells (CD-4*) Does not directly kill pathogens → raises the “alarm” via cytokines Assists in the activation of “killer” T-cells Signal B cells to begin secreting antibodies (Ig) Activated cell differentiates into effector cells & memory cells “Killer” T-cells (CD-8): cytotoxic → specialize in identifying and killing cells infected w/ viruses Attack cells that have been infected The Adaptive Immune System Adaptive Immunity: Antibodies Each recognizes only ONE antigen Bind to a specific site on the invader Function in several ways Directly block binding of the invader to cells Inactivate viruses and neutralize toxins “Mark” the pathogen for destruction by phagocytes = opsonization Adaptive Immunity: Antibodies Structure 2 light chains 2 heavy chains Antigen binding sites Fab (variable) region Antigen-specific Fc region (constant) Class effect Adaptive Immunity: Antibodies Classes IgM IgG IgA IgE IgD “GAMED” IgM BIG….pentamer of 5 units First class produced Half-life of about 7-10 days Increased IgM = RECENT exposure to antigen Large molecule – usually confined to intravascular space, however Inflammation → increased capillary permeability → allows various plasma proteins, like IgM, to enter the interstitial space Primary Immune Response IgM → Formed early in the primary immune response IgG  4 subclasses…IgG 1-4  Predominantly found in  Blood  Lymph  CSF  Peritoneal fluid  Evenly distributed in intra/extravascular space  Longest half-life of the Ig’s ~ 23 days  Functions: Only class that crosses the placenta Good: confers mom’s immunity Bad: mom may form IgG against fetal RBC antigens (ie. the Rh antigen) → destruction of fetal RBCs ……more on this later Bad: difficult to use IgG as indicator of infection in baby (ex. HIV) IgG Functions cont. Helps Natural Killer cells find their targets- opsonization Immobilizes bacteria by binding to their cilia or flagella Activates complement Binding neutralizes toxins and some viruses Used for passive immunization against rabies and hepatitis IgG cont. IgG is formed late in the primary immune response Secondary Immune Response Memory B cells are capable of being activated rapidly upon reexposure to an antigen Most memory B cells have surface IgG but some have IgM More rapid response Higher levels of antibody production IgA Primarily found in external secretions Mucus Tears Saliva Gastric fluids Colostrum Sweat Function Protection of infant- present in breast milk Prevents viruses from entering cells Prevents pathogens from attaching to and penetrating epithelial surfaces Respiratory and GI tracts IgE Present in LOW amounts in serum Short half-life….2 days Binds to mast cells and basophils When it encounters its antigen, triggers degranulation Releasing histamine, leukotrienes & heparin Increased in atopic individuals Increased in presence of parasites IgD Present on surface of naïve B-cells Present in low amts in serum Function is unknown Side note: Medical applications of Antibodies Polyclonal & Monoclonal antibodies (Ab) Polyclonal Ab: Made by using many different clones of immune cells Prepared from immunized animals Each Ab can interact/bind with multiple sites on an antigen Quicker to produce but less specific Generally used for research applications Monoclonal Ab: Made by using a single clone of immune cells Produced in the lab Bind only to one site on an antigen Slower to produce but more specific Used for therapeutic drug development / treatment of disease Clear as mud?! Khan Academy Video When things go wrong… Immunodeficiencies Acquired (Secondary): medications (steroids, chemotherapy), malnutrition, splenectomy (or functional asplenia), some cancers, AIDS Congenital (Primary): autosomal recessive or X-linked, impaired or absent granulocyte, complement or lymphocyte production. May be an immunoproliferative disorder (hypergammaglobulinemia) Autoimmune disease Abnormal immune response to “self” Eg. Type I diabetes, systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Grave’s disease (autoimmune thyroiditis) Questions? References ▪ Levinson, W. (2022). Review of Medical Microbiology and Immunology. 17th edition. McGraw Hill. New York, NY. ▪ Shi, H.Z. (2004). Eosinophils function as antigen presenting cells. Journal of Leukocyte Biology. 76(3): 520-527. ▪ Volker Brinkmann, et al.(2004). Neutrophil Extracellular Traps Kill Bacteria. Science 303. 1532-1535. ▪ University of South Carolina School of Medicine. Immunology & Microbiology Online. http://pathmicro.med.sc.edu/ghaffar/innate.htm ▪ Strohl, W., Rouse, H., Fisher, B. Lippincott’s Illustrated Reviews: Microbiology. Lippincott, Williams & Wilkins: Baltimore, MD. 2001. ▪ Utay NS, Douek DC. Interferons and HIV Infection: The Good, the Bad, and the Ugly. Pathogens & immunity. 2016;1(1):107-116. doi:10.20411/pai.v1i1.125. ▪ Goldberg, S. Clinical Physiology Made Ridiculously Simple. Medmaster, Inc.: Miami, FL. 1995. ▪ Coico R, Sunchine G. Immunology: A short course (7th Ed). Wiley-Blackwell: New York. 2015. ▪ Khan Academy: Immune System Overview. https://www.youtube.com/playlist?list=PL14EB6C745989FC22 ▪ Amber Brooks-Gumbert, MMS, PA-C and Danielle Kempton DHSc, PA-C Immunology I PowerPoint Presentation