Microbiology: The Immune System (PDF)

MICROBIOLOGY MODULE 1. TRANS 3 THE IMMUNE SYSTEM...

MICROBIOLOGY MODULE 1. TRANS 3 THE IMMUNE SYSTEM LE 1 09/01/23 RIZAL MICHAEL R. ABELLO, RPm, MD OUTLINE Adaptive Immunity: I. Introduction VI. Hypersensitivity o Specifically recognize and destroy the pathogen a. Immune System a. Type I Hypersensitivity o Antibody and antigen b. Innate vs. Adaptive b. Type II Hypersensitivity Antibody is a protein produced in a response to a particular Immunity Overview c. Type III Hypersensitivity II. Innate Immunity d. Type IV Hypersensitivity pathogen a. Physiologic Barriers VII. Clinical Correlates Antigens are the substances that induce the production of b. Mechanisms of Innate a. Complement Disorders antibodies Immunity b. B-cell Disorders Although the innate immunity is effective as a critical role in III. Adaptive Immunity c. T-cell Disorders eliminating most pathogen, sometimes it is not enough to destroy all IV. Cell-Mediated Immunity d. B and T-cell Disorders pathogenic activity that is going on in the body. That’s why our a. Antigens e. Phagocyte Dysfunction b. Major Histocompatibility VIII. References adaptive immunity would come into play. Complex Both systems (innate and adaptive) interact and collaborate to c. Superantigens achieve the final goal – destroy the pathogen! V. Humoral Immunity a. Antibody b. Immunoglobulin B. INNATE VS. ADAPTIVE IMMUNITY OVERVIEW c. Forms of Immunity Table 1. Innate vs. Adaptive Overview LEGEND INNATE ADAPTIVE Lymphocytes Neutrophils Must Lecture Book T Cells: CELLULAR Macrophages Know [lec] [bk] (either CD4 or CD8; directly Monocytes kills the pathogen) Dendritic cells Components Natural Killer Cells I. INTRODUCTION Complement B Cells: HUMORAL (produces antibodies) Immunology Physical Epithelial Barriers o The study of the immune system with regard to the gene Secreted enzymes Circulating antibodies and all the proteins that would mediate immunity. Lysozyme Immunoglobulins Complement Cytokines Secreted C-reactive protein (CRP) A. IMMUNE SYSTEM proteins Defensins Protection Cytokines o The immune system is basically our body’s way to protect NO YES (EXTREMELY) ourselves. o The immune system is composed of cells, tissues, and soluble Specificity (There is equal response to (extremely specific to certain cellular products that recognize attack and eventually destroy all pathogens and no organism and has memory the organisms that could endanger an individual’s health improvement in its strength) cells) o They also distinguish self from nonself. Structures shared by group Trigger Antigens of microbes Serves as a host defense system against infectious diseases and Memory NO YES (MEMORY CELLS)a foreign (nonself) antigens No improvement on Improves after each To be an effective immune system, it has to be: Adaptation subsequent exposure exposure o equipped with a rapid response mechanism YES, MINUTES NO, DAYS o exquisite specificity o adaptability (if a pathogen or a threat (to give time for the Effectivity o intricate regulatory network enters and attacks our body, development and production the innate immunity will act of antibodies specific to the o memory at once) target pathogen) Less IMMUNE SYSTEM ORGANS Potency (not sufficient enough to More Primary Organs destroy all of the bacteria o Bone marrow inside our body) ▪ B cell maturation site Defense line First line After exposure o Thymus Response Faster Slower ▪ T cell maturation site speed o Both your B cell and T cell originated from the bone marrow. Sufficiency NO YES Secondary Organs Lymph nodes Skin Barriers Spleen o Spleen Mucous membranes MALT o Lymph nodes a Memory cells are long-lived immune cells capable of recognizing o Tonsils foreign particles they were previously exposed to. When exposed to a o Peyer’s patches certain pathogen, the next time you get exposed to the same pathogen, ▪ Found in the ileum you already have your ready-made antibodies inside your body that will o These secondary organs allow immune cells to interact with protect you against the said pathogen, improving the immune strength their antigens or any antigen in the body. every after exposure. IMMUNE RESPONSE Response generated against a potential pathogen Innate Immunity: o Nonspecific to the invading pathogen o Rapidly mobilized at the initial site of infection o Lacks immunologic memory [MICRO] Luna, Olvido, Pacayra, Tangonan, Vinar TH Camarador Page 1 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 Bacterial interference o Most mucous membranes has a normal resident microbiota that helps and opposes establishment of pathogenic microorganisms and has important physiologic functions. o Example: In an adult vagina, an acidic pH is maintained by a normal lactobacilli, which is a normal resident microbiota in the adult vagina. ▪ The acidic pH provided by the lactobacilli inhibits the establishment of yeast infection, anaerobic infection and gram-negative bacterial infection. RESIDENT VS TRANSIENT MICROBIOTA Figure 1. Innate vs Adaptive Immunity (Source: Dr. Abello’s PPT) Resident microbiota o are microbes regularly found in a given area of the body at a given time. II. INNATE IMMUNITY Transient microbiota First line of defense o are non-pathogenic or potentially pathogenic microbes that Nonspecific inhabit the skin or the mucous for hours, days, or weeks. Does not rely on specific pathogen recognition Lacks immunologic memory Table 2. Resident Normal Microbiota Rapidly mobilized at initial site of infection Skin Staphylococcus epidermidis Does not confer long-lasting protective immunity Nose Staphylococcus aureus Includes the skin, mucus membrane, phagocytic cells, NK cells, Toll- Mouth Viridians Streptococci like receptors (TLRs), cytokine and complement Dental Streptococcus mutans plaque A. PHYSIOLOGIC BARRIERS Colon Bacteroides, Escherichia coli SKIN Vagina Lactobacillus vaginalis, Escherichia coli, Streptococcus agalactiae Skin actually provides a physiologic barrier to the entry of a pathogen and has certain antimicrobial agents to stop the pathogen at its first attempt to invade. B. MECHANISMS OF INNATE IMMUNITY Few microorganisms are capable of penetrating an intact skin Innate immunity provides a powerful line of defense despite it not but many can enter sweat or sebaceous glands and hair follicles, generating an antigen specific protective immunity and does not rely and establish themselves there. on specific recognition of the pathogen. Sweat and sebaceous secretions: o acidic pH and fatty acids MICROBIAL SENSORS ▪ (+) antimicrobial properties, eliminate pathogenic organism When a pathogen enters skin, it is actually confronted with Epithelial cell layer: macrophages and other phagocytic cells possessing microbial o Lysozyme sensors. ▪ Dissolves bacterial cell walls, protection against some Three major groups of microbial sensors: microorganisms o TLRs (Toll Like Receptors) ▪ Also in tears, respiratory, and cervical secretions o Psoriasin o NLRs (Nucleotide-binding Oligomerization Domain-like ▪ Protein with antibacterial properties receptor) o RIG-1 and MDA-5 (Retinoic Acid-Inducible Gene-Like Helicases MDA-5/Melanoma Differentiation-associated gene 5) MUCOSA Respiratory tract ⭐ TLRs (TOLL LIKE RECEPTORS) o (+) film of mucus “Pattern recognition receptors (PRRs)” ▪ Covers the surface o recognize pathogen-associated molecular patterns (PAMPs) If there is a pathogen, this will be trap in the mucus first line of defense against a variety of pathogens film critical role in initiating the innate immune response ▪ Bacteria tend to stick to this film ▪ Constantly being driven upward by ciliated cells initiate cascade → rapid and robust inflammatory response marked by cellular activation and cytokine release For this microorganisms to be expectorated o TLR2: gram positive bacteria o (+) Phagocytes act as barriers o TLR3: dsRNA virus ▪ Helps the mucociliary apparatus for removal o TLR4: gram negative bacteria o (+) special protective mechanisms o TLR7 and TLR8: ssRNA virus ▪ Hairs at the nares ▪ The cough reflex Prevents aspiration of any anaerobe NLRS (NUCLEOTIDE-BINDING OLIGOMERIZATION GIT DOMAIN-LIKE RECEPTOR) o Hydrolytic enzymes ▪ Saliva Cytoplasmic sensors of microbial products o Acidity o Activate nuclear factor-KB pathway ▪ Stomach o an example of signaling pathway ▪ Kills many ingested bacteria o inflammation and cell differentiation Example: Vibrio cholerae which is one the bacteria that causes diarrhea (rice watery stool) RIG-1 AND MDA-5 (RETINOIC ACID-INDUCIBLE GENE-LIKE Proteolytic enzymes and active macrophages HELICASES MDA-5/MELANOMA DIFFERENTIATION- o Small intestine ASSOCIATED GENE 5) o Both factors can destroy microorganisms Cytoplasmic sensors of viral ssRNA o Receptor-ligand complex go to the nucleus [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 2 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 ▪ acts as transcription factors ▪ stimulates genes MACROPHAGES ▪ triggers IFNs (inhibitors of viral replication) alpha-defensins, beta-defensins, cathelicidin, Macro = large; phage = eater lactoferricin Differentiated Monocytes, found in tissues Phagocytose bacteria, cellular debris, senescent RBCs Activated by γ-interferon PHAGOCYTOSIS Functions antigen-presenting cell (APC) via MHC II During infections the number of circulating phagocytic cells often Important cellular component of granulomas = giant cells increases. In granuloma this can be found in certain diseases like Phagocytic cells: tuberculosis or sarcoidosis where these macrophages will form giant o Monocytes and Macrophages cells o Granulocytes If there is granuloma formation in the lungs, this is to prevent the ▪ PMNs (polymorphonuclear leukocytes, pertaining to spread of the agent or pathogen that may cause infections to other neutrophils), eosinophils, and basophils sites of the body. Hence, giving this circular appearance of the o Dendritic Cells granuloma, housing the pathogen inside the circle Main functions of phagocytic cells: o Chemotaxis o Migration o Ingestion o Microbial killing Microorganisms and other exogenous antigens that enter the lymphatics, the lungs or bloodstreams will be engulfed by phagocytic cells. In lymphoid lineage, Figure 4. Macrophages o B cell will become plasma cell that will release the (Source: Dr. Abello’s PPT) immunoglobulins o T cell that will differentiate either to your helper T cells or cytotoxic T cells MONOCYTES vs MACROPHAGE o NK cells In myeloid lineage, Table 2. Monocytes - Macrophage o Red blood cells under erythropoiesis, LOCATION NOMENCLATURE o Platelets under thrombopoiesis, Blood Monocyte o Eosinophil, basophil, neutrophil under granulocytopoiesis Lungs Dust cells o Monocyte and macrophage under monocytopoiesis. Adipose tissue Adipose tissue macrophage Liver Kuppfer cells CNS Microglia Bone Osteoclasts Spleen Sinusoidal lining cell Connective tissue Histiocyte Connective tissue (Granuloma) Giant cells Peritoneal cavity Peritoneal macrophage Serosa and Lymphoid organs Macrophage Placenta Hofbauer cells Skin Langerhans cells Langerhans cell is different from Langhans giant cell o Langerhans cell is the macrophage in the skin o Langhans giant cell is the cell present when you have certain diseases such as tuberculosis DENDRITIC CELLS Figure 2. Lineages Highly phagocytic antigen-presenting cells (APCs) (Source: Dr. Abello’s ppt) Link between innate and adaptive immune systems Activate T-cells in the adaptive immune response MONOCYTES o Express MHC class II and Fc receptors on surface o Can present exogenous antigens on MHC class I (cross- Mono = one (nucleus); cyte = cell presentation) Found in blood Differentiate into macrophages in tissues Large, kidney-shaped nucleus “Frosted glass” cytoplasm Small leukocytes that circulate in the blood and mature into macrophages that can be found in almost all tissue Figure 5. Dendritic cells (Source: Dr. Abello’s PPT) NEUTROPHILS Acute inflammatory response cells Phagocytic, multilobed nucleus Figure 3. Monocyte (+) specific granules: leukocyte alkaline phosphatase (LAP), (Source: Dr. Abello’s PPT) collagenase, lysozyme, and lactoferrin [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 3 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 (+) azurophilic granules (lysosomes): proteinases, acid MAST CELLS phosphatase, myeloperoxidase, and β-glucuronidase Mediate local tissue allergic reactions Neutrophil chemotactic agents Contain basophilic granules o C5a, IL-8, LTB4, 5-HETE (leukotriene precursor) Originate from same precursor as basophils but are NOT THE o Kallikrein, platelet-activating factor, N-formylmethionine SAME CELL TYPE (bacterial proteins) Activated by: tissue trauma, C3a and C5a, surface IgE cross- o If we have an ongoing acute inflammatory response, these linking by antigen (IgE receptor aggregation) chemotactic agents will be increased that will act as chemotactic Degranulation factors to call neutrophils to go to the site of inflammation or o Release of histamine, heparin, tryptase, and eosinophil infection chemotactic factors A left shift is an increase in neutrophilic precursors in the o Tryptase – marker of Mast cell activation (type I peripheral blood which occurs in inflammation and in hypersensitivity myeloproliferative diseases like Chronic Myelogenous Leukemia or CML Figure 9. Basophils vs Mast cells (Source: Dr. Abello’s PPT) Figure 6. Neutrophils (Source: Dr. Abello’s PPT) PROCESS OF PHAGOCYTOSIS EOSINOPHILS (1) Phagocyte Activation by inflammatory mediators Defend against helminthic infections via the major basic protein – o Bacterial products helminthotoxin ▪ Bacterial proteins, capsules, LPS, peptidoglycan, teichoic acids, etc. Bilobate nucleus Packed with large eosinophilic granules of uniform size Teichoic acid – gram (+) bacteria o Produce histaminase, MBP, eosinophil peroxidase, eosinophil LPS – gram (-) bacteria cationic protein, and eosinophil-derived neurotoxin o Complement proteins Causes of Eosinophilia (MNEMONIC: PACMAN Eats) o Inflammatory cytokines o Parasites o Prostaglandins o Asthma (2) Phagocyte Chemotaxis o Chronic adrenal insufficiency o Phagocyte movement (migration; diapedesis) toward an o Myeloproliferative disorders increasing concentration on attractant o Allergic processes ▪ IL-8 and IL-17 are quite effective chemoattractants o Neoplasia (e.g.Hodgkin lymphoma) ▪ Fibrin split products, kinins, phospholipids o Eosinophilic granulomatosis with polyangiitis (Churg-Strauss) o Neutrophils attach to endothelial surface via adhesion molecules (e.g., P-selectin) (3) Phagocyte attachment to pathogen o Unenhanced ▪ PRR (endocytic) > PAMPs (peptidoglycan, teichoic acids, LPS, mannans, glucans) o Enhanced (more efficient phagocytosis) ▪ IgG; Ab-Ag complex > C3b and C4b; MBL; CRP ▪ Opsonization Figure 7. Eosinophil (4) Ingestion of pathogen (Source: Dr. Abello’s PPT) o Engulf and internalizes the pathogen into an endocytic vesicle, Phagosome BASOPHILS (5) Destruction of pathogen o Neutrophil undergoes apoptosis and die Mediate allergic reaction Densely basophilic granules Contain heparin (anticoagulant) and histamine (vasodilator) PHAGOCYTOSIS: EXTRAVASATION Leukotrienes synthesized and released on demand Basophilia is uncommon but can be a sign of chronic myelogenous leukemia (CML) o Sometimes you see this, and the patient presents with weakness and weight loss, think of possible myeloproliferative disorder specifically CML Figure 10. Extravasation (Source: First Aid for the USMLE, 32nd Ed.) In the leukocyte extravasation process, there’s margination and Figure 8. Basophil rolling, tight binding, diapedesis, and migration (Source: Dr. Abello’s PPT) o Margination and rolling [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 4 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 ▪ The sialyl-Lewis found in PMN will bind to E-selectin and o C5 convertase will cleave C5, release C5a. C5b will combine P-selectin. This binding will form a wheel causing the PMN with C6 to C9, to form the Membrane Attack Complex (MAC) to roll along the selectins. MAC is composed of C5b, C6, C7, C8, and C9 o Tight binding o This MAC will cause the lysis of the cell or toxicity ▪ The LFA-1 found in the PMN, which is an antigen, will bind to ICAM-1 or VCAM-1 Take note: All cleaved “a” complements are released while o Diapedesis or transmigration cleaved “b” complements are used to combine with other ▪ PMNs traverse the endothelium via the PECAM-1 complements to form complex ▪ The most important in this process is the PECAM-1 which is found in both PMN and endothelium. o Migration vs Transmigration ▪ Transmigration or diapedesis is the crossing of the PMN to the endothelium ▪ Migration is the process after diapedesis where there is movement of PMNs from the tissue to the infection site. This is mediated by chemotactic factors NATURAL KILLER CELLS Related to T cells ( same lineage) Figure 12. Classical pathway Important in innate immunity, especially against intracellular (Source: Dr. Abello’s PPT) pathogens Larger than B and T cells With distinctive cytoplasmic lytic granules LECTIN PATHWAY o Containing perforin and granzymes Triggered by mannose or other sugars on microbe surface ▪ Induce apoptosis Almost the same as classic pathway but utilizes C1-like complex Distinguish between healthy and infected cells instead of C1 complex o Identifying cell surface proteins (induced by stress, malignant Only cleaves C4 unlike classic pathway that cleaves C4 and C2 transformation, or microbial infections) Once C4 is cleaved to C4a and C4b, C4b will combine to C2b to Source of IFN-γ become C4b2b which acts as your C3 convertase Two surface receptor types: C3 will then be cleaved into C3a and C3b, C3b will combine to your o Lectin-like receptors – recognize proteins C3 convertase and will form C4b2b3b which acts as your C5 o Killer Ig-like receptors (KIRs) - recognize MHC class I convertase Ab-dependent cellular toxicity (ADCC) C5 will then be cleaved into C5a and C5b, C5b will combine to C6- o Ab binds to target cell surface – Fc receptors on NK bind these C9 to form C5b6789 or also known as your Membrane Attack Ab - kills cell Complex (MAC) Figure 13. Lectin pathway (Source: Dr. Abello’s PPT) ALTERNATIVE PATHWAY Starts with C3 unlike Classic pathway that starts with C1 Figure 11. Natural killer cells Triggered by microbial surface molecules (Source: Dr. Abello’s PPT) Can occur spontaneously o C3 will be converted to C3b and will combine to Bb to form COMPLEMENT SYSTEM C3bBb which will act as your C3 convertase System of hepatically synthesized plasma protein that play a role in o C3 will again be cleaved to C3a and C3b, C3b will then combine innate immunity and inflammation to your C3 convertase (C3bBb) to form C3bBb3b which acts as Synthesized in the liver your C5 convertase o C5 will be cleaved in to C5a and C5b, C5 will combine to C6-C9 Consists of at least 30 distinct complement proteins to form C5b6789 also known as your Membrane Attack Complex See Appendix A for the Complement Reaction Sequence CLASSICAL PATHWAY Stimulus: Antigen-Antibody complex, either IgM or IgG mediated o C1 will cleave C4 and C2. Once cleaved, C4 and C2 will release C4a and C2a, respectively. C4b and C2b will combine, forming C4b2b (C3 convertase) o C3 convertase will cleave C3, release C3a. C3b will combine with C4b2b, to form C4b2b3b (C5 convertase) [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 5 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 CD4 T-Cell Differentiation Figure 14. Alternative pathway (Source: Dr. Abello’s PPT) Table 3. Summary of Complement System C3b Opsonization Figure 15. CD4 T-cell differentiation (Source: Dr. Abello’s PPT) Makes your particle readily ingestible Isipin mo yung bacteria yung tinapay, si T-cells starts in the bone marrow from its precursor C3b yung Nutella, tapos ikaw yung Will then migrate to the thymus for maturation and will then be phagocytic cell. Chenen! differentiated to CD4 T-cells and CD8 T-cells CD4 and CD8 T-cells will migrate to the lymph nodes as helper and C3a, C4a, C5a Anaphylaxis and inflammation (Activation of T cytotoxic cells respectively. cells and APCs) Cytotoxic T-cells will then be CD8’s last form for it kills the pathogens C5a Neutrophil chemotactic factor directly. C5b-9 or C5b6789 Membrane Attack Complex (MAC) = Helper T-cells on the other hand will differentiate further depending CYTOLYSIS on the stimulus. C4b2b C3 convertase of Classical and Lectin o Th1 Pathway ▪ Stimulated by IFN-gamma and IL-12- important in the C3bBb C3 convertase of Alternative Pathway granuloma formation during tuberculosis, sarcoidosis and C4b2b3b C5 convertase of Classical and Lectin other diseases involving granuloma formation Pathway ▪ Secretes IFN-gamma and IL-2 C3bBb3b C5 convertase of Alternative Pathway ▪ Activates macrophages and cytotoxic t-cells o Th2 CYTOKINES ▪ Stimulated by IL-2 and IL-4 Small secreted proteins important in cell signaling ▪ Releases : Tissue injury → inflammatory response → release of cytokines Pro-inflammatory: IL-4, IL-5, IL-6 o Pro-inflammatory cytokines: IL-1, IL-6, TNF-a, IFNs Anti-inflammatory: IL-10, IL-13 o Anti-inflammatory cytokines: TGF-B, IL-10, IL-11, IFN-B ▪ Activates eosinophils o Both Pro and Anti-inflammatory cytokines are released in tissue o Th17 injury because if only Pro-inflammatory cytokines are released, ▪ Releases IL-17, IL-21, IL-22 it may lead to an overdrive of the immune system, this ▪ Induces Neutrophilic inflammation phenomenon is called cytokine storm. o Treg o Cytokine storm- Causes deleterious effect to the body and ▪ Releases TGF-Beta, IL-10, IL-35 homeostasis. Anti-inflammatory Cytokines help to prevent ▪ Prevents autoimmunity cytokine storm. Chemokines: phagocyte attractants Interleukins Adhesion molecules: selectins, integrins o Selectins- involved in margination and ruling Secreted by macrophages o Integrins- involved in attachments IL-1 Causes fever, acute inflammation. Also o PECAM1- involved in diapedesis called osteoclast-activating factor Growth factors IL-6 Causes fever. Prostaglandins and leukotrienes are also formed stimulates production of acute-phase o Receptors contain tyrosine kinase activity proteins o Vasodilation → capillary leak → plasma escapes and TNF-a Activates endothelium accumulates → fibrin forms Causes WBC recruitment, vascular leak Pyrogenic: IL-1 (fever), IL-6, TNF-alpha, IFNs Causes cachexia in malignancy Naïve CD4 T-cells: differentiate into different lineages MAINTAINS granulomas in TB o depending on the exogenous cytokine environment (Th1, Th2, IL-1, IL-6, TNF-α: mediate fever and sepsis Th17, Treg) IL-8 Major chemotactic for Neutrophils IL-12 Induces differentiation of T cells into Th1 cells Activates NK cells FACILITATES granuloma formation in TB Secreted by T-cells IL-2 Stimulates growth of helper, cytotoxic, and regulatory T cells, and NK cells. IL-3 Supports growth and differentiation of bone marrow stem cells. Functions like GM-CSF Secreted by TH1 cells INTERFERON- Secreted by NK cells and T cells in response GAMMA to antigen or IL-12 from macrophages Stimulates macrophages to kill phagocytosed pathogens [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 6 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 Inhibits differentiation of Th2 cells B. ADAPTIVE IMMUNITY: T-CELLS Induces IgG isotype switching in B cells Cell-mediated Immunity Activates macrophages to INDUCE granuloma o CD4+ T cells (helper T cells) formation ▪ Help B cells make antibodies and produce cytokines to SECRETED BY TH2 CELLS recruit phagocytes and activate other leukocytes IL-4 Induces differentiation of T cells into Th o CD8+ T cells (cytotoxic T cells) (helper) 2 cells ▪ Directly kill virus-infected and tumor cells via perforin and Promotes growth of B cells granzymes Enhances class switching to IgE and IgG CD-8 cytotoxic T-cells are similar to the natural killer IL-5 Promotes growth and differentiation of B cells cells Enhances class switching to IgA Both utilizes perforins and granzymes Stimulates growth and differentiation of ▪ Kills tumor cells Eosinophils o Delayed cell-mediated hypersensitivity (type IV) IL-10 Attenuates inflammatory response o Acute and chronic cellular organ rejection IL-13 Promotes IgE production by B cells Induces alternative macrophage activation Table 4. Arms of Adaptive Immunity Humoral Cell-Mediated Interferons Main cell B lymphocytes T lymphocytes Origin site Bone marrow Bone marrow Part of innate host defense (INF-a, INF-B-INF-y) Maturation site Bone marrow Thymus Critical immunoregulating proteins Function Extracellular Intracellular o capable of altering various cellular processes: cell growth, microbes microbes differentiation, gene transcription, translation o Receptor uses JAK-STAT pathway Viruses Toxin-induced Parasites Also play a major role in activating antitumor immunity diseases Bacteria Interfere with both RNA and DNA viruses o Cells infected with a virus synthesize these glycoproteins which (Mycobacterium) Against act on local cells, priming them for viral defense by polysaccharide Kills tumor cells downregulating protein synthesis capsules o Resists viral replication and upregulation of MHC expression for Hypersensitivity I, II, III IV recognition of infected cells Onset Rapid Delayed (type IV) End-result Differentiation to Increases cytokines III. ADAPTIVE IMMUNITY plasma cells – release of immunoglobulins Antibody formation YES NONE Evaluation Plasma levels of Skin test (i.e., TST) antibodies IV. CELL-MEDIATED IMMUNITY A. ANTIGENS Substance that reacts with an antibody Immunogenicity: o Recognition of foreignness o Size o Chemical and Structural complexity o Genes of the host o Dosage, route, and timing of antigen administration Any substance that may be specifically bound by an antibody Simple intermediary metabolites, sugars, lipids and hormones Figure 16. Adaptive Immunity (Source: Jawetz, Melnick & Adelberg’s Medical Microbiology, 28th Ed.) Macromolecules: complex carbohydrates, phospholipids, nucleic acids and proteins Recall: Adaptive Immunity o Only macromolecules are capable of stimulating B cells to o Uses T-cells and B-cells initiate Humoral Response o Both antibody mediated and cell-mediated immune response Small chemicals (e.g. dinitrophenol) may bind to an antibody but o Highly specific cannot activate B cells on their own (i.e. not immunogenic) o Confers immunologic memory Hapten o More potent and sufficient enough o Need to be attached to a macromolecule (carrier) o Improves after each exposure o Hapten-carrier complex can act as an immunogen ▪ Immunogens are molecules that stimulate the immune response. A. ADAPTIVE IMMUNITY: B-CELLS Humoral Immunity o Recognize and present antigen B. MAJOR HISTOCOMPATIBILITY COMPLEX ▪ The antigen undergoes somatic hypermutation to optimize Group of genes involved in the immunological recognition of self antigen specificity and non-self o Produce antibody Found in virtually all vertebrates ▪ B cells differentiate into plasma cells to secrete specific Found chromosome 6 in humans immunoglobulins MHC encoded by HLA genes o Maintain immunologic memory Present antigen fragments to T cells and bind T-cell receptors ▪ Persists and accelerates future response to antigen (TCRs) o Hypersensitivity I-III o If you hear the word “B-cells” think of adaptive immunity [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 7 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 Table 5. Major Histocompatibility Complex o Peptide antigens are inside the peptide binding cleft (as in MHC I MHC II Figure 19A) Loci HLA-A, HLA-B, HLA-C HLA-DR, HLA-DQ, Some bacterial and viral antigens can activate a large number of T- HLA-DP cells through this pathway Binding TCR and CD8 TCR and CD4 o Staphylococcal enterotoxin Structure 1 long chain, 2 equal length chains o Toxic Shock Syndrome toxin 1 short chain (which is (2a, 2b) o Group A Streptococcal Pyrogenic Exotoxin A B2-microglobulin) ▪ cytokine storm → shock and multiple organ failure Expression All nucleated cells APCs If the superantigens are ACTIVATED, there will be a cytokine (except retina and storm brain) Recall: We do not want a cytokine storm because it will APCs override/overstimulate the immune system. The patient might lead Platelets to shock and multi-organ failure Function Present ENDOgenous Present EXOgenous antigens (e.g., viral or antigens (eg, bacterial V. HUMORAL IMMUNITY cytosolic proteins) to proteins) to CD4+ CD8+ cytotoxic T cell helper T cell A. ANTIBODY FORMATION Antigen loading Antigen peptides Antigen loaded loaded onto MHC I in following release of RER after delivery via invariant chain in an TAP (transporter acidified endosome associated with antigen processing) Associated B2-microglobulin Invariant chain proteins Figure 19. Humoral immunity (Source: Dr. Abello’s ppt) (1) The initial step in antibody formation begins with the binding of antigen to the surface immunoglobulin via the B-cell receptor. (2) The BCR with its bound antigen is internalized by the B cell (3) The internalized antigen is degraded to yield peptides that are then returned to the cell surface bound to MHC class II molecules. Figure 17. Major Histocompatibility Complex Structures o Once the internalized antigen is degraded, it will release MHC 1 (left), MHC 2 (right) cytokines or any other peptide (Source: Dr. Abello’s PPT) o The antigen will also go back to the surface to MHC 2 (4) This MHC Class II-peptide complex on B cells is recognized by Table 6. Clinical Correlates with HLA subtypes antigen-specific helper (CD4) T cells. HLA subtype Disease (5) These T cells have already interacted with antigen-presenting B27 Psoriatic arthritis, Ankylosing spondylitis, IBD- dendritic cells and have differentiated in response to the same associated arthritis, Reactive arthritis pathogen. Mnemonic: PAIR (6) Chemokines, such as CXCL13 & its receptor, CXCR5, play an B57 Abacavir Hypersensitivity important role in this migration process. DQ2 / DQ8 Celiac Disease (7) The CD40 ligand on T cells bind to CD40 on B cells, & the T cell produces IL-4, IL-5, and IL-6, which induce B cell proliferation. Mnemonic: DQ na patients present with diarrhea, fatigue, weight (8) Finally, the activated B cells migrate into follicles and proliferate ice cream loss, bloating, flatulence, and abdominal pain to form germinal centers; here somatic hypermutation and especially after consumption of gluten-rich immunoglobulin class switching occur substances o Recall which interleukins are responsible for class switching DR3 DM type 1, SLE, Graves’ disease, Hashimoto (9) Germinal center B cells that survive this process now thyroiditis, Addison disease differentiate into either antibody- producing plasma cells or DR4 Rheumatoid arthritis, DM type 1, Addison’s memory B cells disease B. ANTIBODY FUNCTION C. SUPERANTIGENS TWO FORMS OF ANTIBODY: o Membrane-bound antibodies: ▪ On the surface of B lymphocytes ▪ Functions as antigen receptors and initiates humoral immune response. o Secreted antibodies: ▪ Found on circulation, tissues and mucosal sites bind antigens. ▪ Neutralize toxins ▪ Prevent entry and spread of pathogens Figure 18. Antigen processing by APC. A: Normal antigen presentation by Protective function of antibodies: APC; B: By superantigen o Enhanced phagocytosis via opsonization (Source: Jawetz, Melnick & Adelberg’s Medical Microbiology, 28th Ed.) o Virus neutralization o Toxin neutralization Do not require processing o Complement-mediated lysis Able to bind to MHC molecules outside the peptide binding cleft (as o Antibody-dependent cell cytotoxicity (ADCC) (recall which cell in Figure 19B) has this property) [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 8 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 C. ANTIBODY STRUCTURE Where most of sequence difference among different antibody are confined Each about 5-10 aa residues long Primary function: binding antibody molecules (cooperate in space to form the Ag-binding site) Forms the area of Ig complementary to the epitope (antigenic determinant) Figure 20. Antibody structure (Source: Dr. Abello’s ppt) FAB REGION (Fragment, Antigen Binding) Composed of 1 light chain, 1 heavy chain, both variable and Figure 21. Antibody with visible hypervariable regions constant region (Source: First Aid for the USMLE, 32nd Ed.) Determines idiotype: o Unique antigen-binding pocket CONSTANT REGION o Only 1 antigenic specificity expressed per B cell Do not participate in antigen recognition Heavy chain C regions interact with other effector molecules Fc therefore mediate most of the biologic functions of antibodies Only heavy chain and constant region Classes and subclasses based on differences in CH structure: IgA, Constant IgD, IgE, IgG, IgM Carboxy terminal Where complement binding and macrophage binding take place. Complement binding Carbohydrate side chains D. IMMUNOGLOBULIN maCrophage binding Determines isotype: IgM, IgD, IgA, IgE TWO IDENTICAL LIGHT CHAINS Either k (kappa) or l (lambda) Classification is based on the amino acid differences in their constant regions Both light chain types occur in all classes of Ig Any one Ig molecule contains only one type of L (light) chain Amino terminal contains the Ag-binding site (end terminal) Contains 1 variable domain and 1 constant domain Antibody structures can be cleaved into certain fragments by: o ☤ Papain (Pa-pa-in, 3) Figure 22. Structures of Different Antibodies ▪ into 3 fragments: 2 Fab, 1 Fc (Source: First Aid for the USMLE, 32nd Ed.) o ☤ Pepsin (Pep-sin, 2) ▪ Into 2 fragments: 1 Fab, 1 Fc Different classes of antibodies perform different functions All isotypes can exist as monomers TWO IDENTICAL HEAVY CHAINS Mature, naive B cells, prior to activation, express IgM and IgD on Distinct for each of the 5 Ig classes: γ, μ, α, δ and ε surfaces o Differentiate in germinal centers of lymph nodes by isotype Amino terminal heavy chain participates in the Ag-binding site switching Carboxyl terminal forms the Fc fragment for complement ☤ binding ▪ Gene rearrangement and activation ▪ induced by cytokines and CD40L Contains 1 variable domain and 3 or more constant domains ☤ IL4 for IgE BOTH Light and Heavy chains participate in antigen binding ☤ IL5 for IgA ☤ IFN-y for IgG VARIABLE REGION Affinity: individual antibody-antigen interaction Composed of one Ig domain Avidity: cumulative binding strength of all antibody-antigen Contains regions of variability/changes in amino acid sequence interactions in a multivalent molecule (distinguish the antibodies, participates in antigen recognition) Variable region of 1 heavy chain (VH) is juxtaposed with the Variable IgG region of 1 light chain (VL) = antigen-binding site Participate in antigen recognition Monomer Amino Terminal = Antigen, Carboxy Terminal = Complement Most abundant isotype in serum Only isotype that crosses the placenta ☤ This provides infants with passive immunity that starts to wane HYPERVARIABLE REGION after birth, where they have the maternal IgG for the first 6 months. 3 for each VH, 3 for each VL Associated with warm autoimmune hemolytic anemia [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 9 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 Function: o Main antibody in 2° (or anamnestic) response to an antigen Application: Rabies o Fixes complement o opsonizes bacteria There are two immunoglobulins for rabies: o neutralizes bacterial toxins and viruses o Human (HRIg) ▪ More preferred o Equine (ERIg) IgA ▪ Requires skin test first before administration, since this may Monomer (in circulation), Dimer (w/ J chain when secreted) induce hypersensitivity reaction. Does not fix complement Crosses epithelial cells by transcytosis Table 7. Categories of Rabies Produced in GI tract (e.g., by Peyer patches) Category Description Management Most produced antibody overall but has lower serum I Touching or feeding Washing of exposed skin concentrations. animals, animal licks on surfaces, no PEP Function: INTACT SKIN (no o Prevents attachment of bacteria and viruses to mucous exposure) membranes II Nibbling of uncovered Wound washing and o Protects against gut infections (e.g., Giardia) skin, minor scratches or immediate VACCINATION o Released into secretions (tears, saliva, mucus) and breast milk abrasions WITHOUT for protection BLEEDING (exposure) III Single or multiple Wound washing, IgM transdermal bites or immediate VACCINATION scratches, and administration of Monomer (on B cells), Pentamer (w/ J chain when secreted CONTAMINATION OF rabies Fixes complement MUCOUS MEMBRANE IMMUNOGLOBULINa Found on the surface of naive B cell OR BROKEN SKIN with Antigen receptor on the surface of B cells saliva from animal licks, Associated with cold autoimmune hemolytic anemia exposures due to direct Function: contact with bats (severe o Produced in the 1° (Immediate) response to an antigen exposure) a It takes 4 weeks to complete the rabies vaccine course. The active IgE immunity response against the vaccine takes 7-10 days. Although this Monomer provides longer lasting immunity, its effect is not immediate. Since Binds mast cells and basophils there is the need for immediate immune response in category III, rabies Cross-links when exposed to allergen immunoglobulins are preferred instead. Associated with allergies Function: Application: Vaccines o Mediating immediate (type I) hypersensitivity Live Attenuated Vaccine o Contributes to immunity to parasites by activating eosinophils o Rendered nonpathogenic but retains capacity for transient growth IgD ▪ May revert to virulent form Monomer ▪ Contraindicated in pregnant and immunodeficient patients o Induces BOTH cell-mediated and humoral immunity Unclear function ▪ induces strong, often lifelong immunity Found on the surface of naive B cell Mnemonics for Live Vaccines E. FORMS OF IMMUNITY MR. JOVIT Sings LIVE ACTIVE IMMUNITY MMR, RUBELLA, JAPANESE ENCEPH, ORAL POLIO, VARICELLA, INTRANASAL INFLUENZA, TYPHOID, SMALL POX Conferred when an individual encounter a foreign antigen: o In the setting of a clinical or subclinical infection Killed or inactivated vaccines o Exposure to microbial products (e.g. toxins, toxoids) o Pathogen is inactivated o Immunization with live or killed organism ▪ Safer than live vaccines. o Transplantation of foreign tissue o Induces humoral response only Advantages: ▪ weaker immune response; booster shots required o Individual actively produces antibodies ▪ The Ab produced is long lasting ▪ Protection is delayed until Ab production reaches an VI. HYPERSENSITIVITY effective level A condition in which an immune response our body’s immune Harmful effect: Formation of circulating immune complexes response would result in an exaggerated or inappropriate reaction that is actually harmful to humans. PASSIVE IMMUNITY Administration of preformed antibodies Antibody-mediated protective effects It does not confer long-term protection Advantages: o Recipient receives a large concentration of antibody immediately o Patient has no time to produce Ab response o ☤ Example: needle-stick injury in unvaccinated patients, immunodeficient patients Figure 23. Hypersensitivity Harmful effect: initiate hypersensitivity (Source: Dr. Abello’s PPT) o ☤ This is why some are done with skin tests first before administration, especially if derived from different species. See Appendix B for a clearer image [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 10 of 14  MODULE 1. TRANS 3 LE 1 THE IMMUNE SYSTEM 09/01/23 A. TYPE I HYPERSENSITIVITY B. TYPE II HYPERSENSITIVITY ANAPHYLAXIS AND ATOPY ANTIBODY-MEDIATED An initial exposure to allergens will stimulate CD4 cells.TH2 will Antibodies bind to cell-surface antigens → (1) cellular destruction, increase the release of the pro-inflammatory cytokines (i.e., IL-4, IL- (2) inflammation, and (3) cellular dysfunction 5 and IL-6) and anti-inflammatory (i.e., IL-10 and IL-13) o IL-4 induces isotype switching from IgM to IgE. The IgE Cellular Destruction produced in response to the initial challenge will bind to Fc receptors on the mast cells and basophils. Eventually, upon Cell is opsonized (coated) by antibodies, leading to either: exposure to second antigen, cross-linking between mast cell o Phagocytosis and/or activation of complement system and antigen happens. This will promote degranulation and the o NK cell killing (antibody-dependent cellular cytotoxicity) release of histamine and prostaglandins leading to the following ▪ Releases perforin and granzymes effects to the tissues. Examples: Example: Anaphylaxis (food, drug or bee sting allergies) and o Autoimmune hemolytic anemia (including drug-induced form), Asthma o Immune thrombocytopenia, o Transfusion reactions, o Hemolytic disease of the newborn ▪ Usual example is when mother’s blood type is O positive and has a baby either A or B antigen, it means mother’s antibody will adapt the baby’s blood cells. Inflammation Binding of antibodies to cell surfaces → activation of complement system and Fc receptor-mediated inflammation Examples o Goodpasture syndrome ▪ Patients with Goodpasture syndrome have antibodies against basement membrane of both lungs and kidneys. Usual manifestations are edema, hematuria, hemoptysis. o Rheumatic fever ▪ Usually preceded by group A streptococcal infection first then eventually develop manifestations like arthritis, carditis and Sydenham’s chorea o Hyperacute transplant rejection Cellular Dysfunction Antibodies bind to cell surface receptors → abnormal blockade or activation of downstream process Examples o Myasthenia gravis Figure 24. Type I Hypersensitivity: IgE-mediated atopic and anaphylactic reactions ▪ The antibodies to nicotinic acetylcholine receptors leads (Source: Dr. Abello’s PPT) to fatigability and fluctuating weakness of patients. o Graves’ disease ▪ This is usually hyperthyroidism with ophthalmopathy like Two Phases of Type I Hypersensitivity bulging eyes and dermopathy. The thyroid stimulating Immediate (minutes) antibodies or thyroid stimulating immunoglobulin (TSI) will o Antigen crosslinks preformed IgE on pre sensitized mast cells attach to thyroid cells and act as TSH, thus releasing ▪ Immediate degranulation thyroid hormones. Release of histamine (a vasoactive amine), tryptase o Pemphigus vulgaris (marker of mast cell activation), and leukotrienes. Late (hours) o chemokines (attract inflammatory cells, e.g., eosinophils) and C. TYPE III HYPERSENSITIVITY other mediators from mast cells IMMUNE COMPLEX ▪ Inflammation and tissue damage antigen-antibody (mostly IgG) complexes activate complement o attracts neutrophils ▪ neutrophils release lysosomal enzymes ▪ can be associated with vasculitis and systemic manifestations Examples o SLE ▪ This is an autoimmune disease causing inflammation and widespread tissue damage to joints, skin, brain, lungs, kidney and blood vessels o Rheumatoid arthritis o Reactive arthritis o Polyarteritis nodosa o Poststreptococcal glomerulonephritis (PSGN) ▪ Patients usually manifest with hematuria one week or more after a strep throat infection or after a respiratory tract infection. Figure 25. Immediate and Late Phase of Type I Hypersensitivity o serum sickness (Source: Dr. Abello’s PPT) [MICRO] Luna, Olvido, Pacayra, Tangonan, Viñar TH Camarador Page 11 of 14  MODULE 1. TRANS 3