Medbac Lecture 3 - Study Guide PDF

Lecture Notes: Innate and Adaptive Immunity Introduction to Immunity Innate Immunity ○ Present from birth. ○ Quick response. Adaptive Immunity ○ Develops later. ○ Learned and slower response. Components of the Immune Systems Innate Immune System...

Lecture Notes: Innate and Adaptive Immunity Introduction to Immunity Innate Immunity ○ Present from birth. ○ Quick response. Adaptive Immunity ○ Develops later. ○ Learned and slower response. Components of the Immune Systems Innate Immune System ○ Physical Barriers: Skin, gastrointestinal tract, respiratory tract, nasopharynx, cilia, eyelashes, body hair. ○ Chemical Barriers: Secretions like mucus, bile, gastric acid, saliva, tears, sweat. ○ Cellular Components: Phagocytic leukocytes, dendritic cells, natural killer cells. ○ Proteins: Plasma proteins, complement, cytokines (e.g., tumor necrotic factor, granzymes). Adaptive Immune System ○ Cells: Beta cells (B lymphocytes), T cells. ○ Responses: Cell-mediated Immunity: T cells. Humoral Immunity: B cells (producing antibodies). Key Differences Innate Immunity: ○ Triggered by broad molecular patterns. ○ Involves immediate responses. ○ Protein-dependent: cytokines, complement, interferon, interleukin-1. ○ Small epigenetic changes can trigger responses. Adaptive Immunity: ○ Triggered by specific events, typically second exposure. ○ Relies on thymus-derived T-cells and B-cells. ○ Small gene rearrangements trigger responses. ○ Involves immunological memory and tolerance. Immune System Players Dendritic Cells ○ Function as sentinels, initiating adaptive responses. ○ Most potent antigen-presenting cells. Natural Killer Cells ○ Recognize and kill virus-infected and tumor cells. ○ Use granzyme and perforin. ○ Involved in antibody-dependent cellular cytotoxicity (ADCC). ○ Primary sources of gamma interferon. Phagocytic Cells ○ Include monocytes, macrophages, polymorphonuclear leukocytes (PMNs), and dendritic cells. ○ Key functions: phagocytosis, digestion, and processing of foreign proteins. Cytokines and Inflammatory Response Cytokines: ○ Small proteins important in cell signaling. ○ Function via interaction with specific cytokine receptors on target cells. Types: ○ Signalers: Tumor necrotic factor, interleukins (e.g., IL-1, IL-6). ○ Chemokines: Direct chemotaxis, attract white blood cells. Inflammatory Response: ○ Mediated by cytokines, prostaglandins, leukotrienes. ○ Results in microvessel dilation, edema, fibrin formation. ○ Enhances recruitment of monocytes and neutrophils. Complement System Function: ○ Enhances antibody and phagocytic cell functions. ○ Promotes inflammation, pathogen lysis, and opsonization. Components: ○ Over 30 proteins in serum or on cell membranes. Pathways: ○ Classical Pathway: Activated by antibody-antigen complexes. ○ Alternative Pathway: Activated by foreign material, pathogens. ○ Lectin Pathway: Activated by mannose-binding lectin on bacterial surfaces. Antigen Presentation  Antigen-Presenting Cells (APCs): ○ Include dendritic cells, macrophages, B lymphocytes. ○ Present antigens via Major Histocompatibility Complex (MHC) proteins. ○ Crucial for T-cell activation and adaptive immune responses. Opsins and Phagocytosis Opsins: ○ Extracellular proteins that tag cells or substances for phagocytosis. ○ Examples: Immunoglobulin G, mannose-binding lectin, complement C3. Opsinization: ○ Antibodies or complement proteins coat pathogens to enhance phagocytosis. Microbial Sensing Proteins Toll-like Receptors (TLRs): ○ Pattern recognition receptors (PRRs) for early immune recognition. ○ Recognize pathogen-associated molecular patterns (PAMPs). Nod-like Receptors (NLRs): ○ Intracellular sensors for PAMPs and damage-associated molecular patterns (DAMPs). RIG-1-like Receptors (RLRs): ○ Detect viral RNA, initiate antiviral responses. ○ Induce type 1 interferons and other antiviral proteins. MDA5: ○ Detects double-stranded RNA in viruses. ○ Involved in antiviral responses. Conclusion The immune system is a complex network involving multiple components and processes. Understanding both innate and adaptive immunity is crucial for comprehending how the body defends itself against pathogens and maintains homeostasis. Study Notes on Immune System and Interferons Interferons and Cytokines Function of Interferons: ○ Release: Produced by virus-infected cells. ○ Action: Induce nearby cells to heighten antiviral defenses.  ○ Class: Belong to cytokines—a broad class of proteins used for cell communication. ○ Purpose: Trigger protective defenses of the immune system to help eradicate viruses. Types of Interferons: ○ Alpha, Beta, Gamma: All inhibit viral growth. ○ Activation: Increase natural killer cell production when CD4-type lymphocytes approach MHC2. Effects of Interferons: ○ Immune Activation: Stimulate immune cells and increase host defenses. ○ Symptoms: Fever, muscle pain, flu-like symptoms are related to interferons and cytokines production. Complement, Interferon, and Inflammatory Responses Complement Response: ○ Neutrophilia, Fever, Somnolence, Anorexia, Chills, Wasting, Drop in Serum Iron Levels: Key symptoms and signs. Adaptive Immune System Overview: ○ Definition: Also known as acquired or specific immune system. ○ Function: Specialized cells and processes to eliminate or prevent pathogen growth. ○ Memory: Creates immunological memory, enhancing future responses to specific pathogens. Antibodies: ○ Role: Provide long-lasting protection. ○ Types: Include beta cells (produce antibodies) and T-cells (mediate immune responses). Beta Cells and Antibodies Humoral Response: ○ Beta Cell Activation: Mature in bone marrow, gain receptors for antigen detection. ○ Plasma Cell Proliferation: Process: Encounter antigen, activate, process, and present via MHC-2. Memory Cells: Remain inactive until re-exposure to the antigen.  Antibody Production: Plasma cells produce and release antibodies. Antibody Functions: ○ Neutralization: Block virus binding sites. ○ Opsonization: Facilitate phagocytosis. ○ Agglutination: Cross-link bacterial cells. ○ Complement Fixation: Lyse bacteria. ○ Precipitation: Aggregate antigen molecules. T-Cells Types: ○ CD4 Helper T-Cells: Activate other immune cells. ○ CD8 Cytotoxic T-Cells: Directly kill infected or cancer cells. CD4 T-Cell Subtypes: ○ Th1: Produce cytokines like IL-2 and IFN-alpha. ○ Th2: Activate MASH cells and eosinophils, switch beta cells to IgE. ○ Th17: Produce IL-17, recruit neutrophils and macrophages. ○ T-Regulatory Cells: Produce TGF-beta and IL-10 to suppress overactive responses. Antigen Recognition and MHC Molecules Epitope: Part of an antigen recognized by the immune system. MHC Class I: ○ Structure: Alpha subunits and beta macroglobulin. ○ Binding: Deep groove, peptides of 8-10 amino acids. MHC Class II: ○ Structure: Heterodimer of alpha and beta chains. ○ Binding: Shallow groove, peptides of 13-17 amino acids. Antigen Presentation: Essential for T-cell recognition; occurs via MHC molecules. Antibody Structure and Response Structure: ○ Y-Shaped Protein: Contains variable (antigen-binding) and constant regions. ○ Fab Region: Binds to antigen. ○ Fc Region: Modulates immune cell activity. Types of Antibodies: ○ IgA, IgD, IgE, IgG, IgM: Differ in number of binding sites and functions. Antibody Production:  ○ Beta Cells: Stimulated by antigens to form plasma and memory cells. ○ Response: Primary (first exposure) vs. Secondary (subsequent exposure). Hypersensitivity Reactions Type 1: ○ Mechanism: IgE binds to mast cells/eosinophils; causes degranulation and histamine release. Type 2: ○ Mechanism: Antibody-mediated cell surface antigen destruction; involves complement-mediated lysis. Type 3: ○ Mechanism: Immune complex deposition in tissues; causes inflammation and tissue damage. Type 4: ○ Mechanism: Delayed hypersensitivity; T lymphocytes release cytokines upon second exposure. AIDS and Immune Deficiency HIV Infection: ○ Target: CD4 T-helper cells. ○ Effect: Progressive loss of CD4 cells, leading to immune system impairment. ○ AIDS: Diagnosed at advanced stages with significant opportunistic infections or low CD4 count.