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Chapter 43 THE IMMUNE SYSTEM Types of Immunity Innate Immunity • Non-specific • All plants & animals Adaptive Immunity • Pathogen-specific • Only in vertebrates • Involves B and T cells Figure 43.2 Pathogens (such as bacteria, fungi, and viruses) INNATE IMMUNITY (all animals) • Recognition of traits shared by broad ranges of pathogens, using a small set of receptors • Rapid response ADAPTIVE IMMUNITY (vertebrates only) • Recognition of traits specific to particular pathogens, using a vast array of receptors • Slower response Barrier defenses: Skin Mucous membranes Secretions Internal defenses: Phagocytic cells Natural killer cells Antimicrobial proteins Inflammatory response Humoral response: Antibodies defend against infection in body fluids. Cell-mediated response: Cytotoxic cells defend against infection in body cells. Antimicrobial Proteins: Barrier Defenses: • Interferons (inhibit viral reproduction) • Complement system (~30 proteins, membrane attack complex) •Skin •Mucous membranes •Lysozyme (tears, saliva, mucus) Innate Immunity (non-specific) Natural Killer Cells: •Virus-infected and cancer cells Inflammatory Response: • Mast cells release histamine • Blood vessels dilate, increase permeability (redness, swelling) • Deliver clotting agents, phagocytic cells • Fever Phagocytic WBCs: •Neutrophils •Macrophage (“big eaters”) •Eosinophils (parasite destroyers) •Dendritic Phagocytosis Inflammatory Response Lymphatic System: involved in adaptive immunity Adaptive Immunity Lymphocytes (WBCs): produced by stem cells in bone marrow • T cells: mature in thymus – helper T, cytotoxic T • B cells: mature in bone marrow – plasma cells make antibodies Adaptive Immunity • 1. humoral immune response: antibodies help neutralize or eliminate pathogens in the blood and lymph • 2. cell-mediated immune response specialized T cells destroy affected host cells by apoptosis • *BOTH are triggered by the helper T cells • *BOTH make memory cells • Antigen: substance that elicits lymphocyte response • Antibody (immunoglobulin – Ig): protein made by B cell that binds to antigens Figure 43.14 B cells that differ in antigen specificity Antigen Antigen receptor Antibody Memory cells Plasma cells Major Histocompatibility Complex (MHC) • Proteins displayed on cell surface • Responsible for tissue/organ rejection (“self” vs. “non-self”) • B and T cells bind to MHC molecule of antigen presenting cell in adaptive response Cytokines are chemical signals that attract B and T cells Antigenpresenting cell Antigen fragment Pathogen Class II MHC molecule Accessory protein Antigen receptor 1 Helper T cell Cytokines Humoral immunity B cell 3 2 Cytotoxic T cell Cellmediated immunity Antigenpresenting cell Cell-Mediated Immune Response (T Cells) Humoral Immune Response (antibodies) Helper T cell B cell Cytotoxic T cell Plasma cell tag for destruction Antibodies Infected cell Identify and destroy Proliferation of B and T cells • Once activated: B or T cell divides to produce clones • 1. effector cells that act immediately against the antigen • 2. memory cells make effector cells if the same antigen is encountered again Figure 43.18-3 Antigen-presenting cell Class II MHC molecule Antigen receptor Pathogen Antigen fragment B cell Accessory protein Cytokines Activated helper T cell Helper T cell 1 Memory B cells 2 Plasma cells 3 Secreted antibodies Cytotoxic T cells destroy infected cells with Perforin (creates pores) Cytotoxic T cell Accessory protein Class I MHC molecule Infected cell 1 Released cytotoxic T cell Antigen receptor Perforin Pore Antigen fragment 2 Dying infected cell Granzymes 3 Immunological Memory • Primary immune response: 1st exposure to antigen • Memory cells: – Secondary immune response: repeat exposure faster, greater response Figure 43.22 Histamine IgE Allergen Granule Mast cell • Immunizations/vaccines: induce immune memory to nonpathogenic microbe or toxin • Passive immunity: via antibodies in breast milk • Allergies: hypersensitive responses to harmless antigens • Autoimmune Diseases: – Lupus, rheumatoid arthritis, Type I diabetes, multiple sclerosis • HIV: infect Helper T cells – AIDS = severely weakened immune system Helper T cell concentration (in blood (cells/mm3) Figure 43.25 Latency AIDS Relative anti-HIV antibody concentration 800 Relative HIV concentration 600 Helper T cell concentration 400 200 0 0 1 3 7 8 2 4 5 6 Years after untreated infection 9 10