Module 1 PDF

# Functions of Immune System - Defense against infections and tumors - Control of tissue regeneration and scarring - Can injure cells and induce pathological inflammation - Recognizes and responds to tissue grafts and newly introduced proteins # Innate Immune System - Provides immediate protection...

# Functions of Immune System - Defense against infections and tumors - Control of tissue regeneration and scarring - Can injure cells and induce pathological inflammation - Recognizes and responds to tissue grafts and newly introduced proteins # Innate Immune System - Provides immediate protection (kinetics: days) - Components recognize antigens that are shared among microbe classes - Initial defense: epithelial barriers, phagocytes, mast cells, dendritic cells, NK cells/ILCs, complement # Adaptive Immune System - Not immediate (kinetics: days) but specific as it develops memory - Cells have diverse/variable receptors and recognize unique antigenic structures - B cells and antibodies work extracellularly, bind to pathogens, and block infection - T cells are effector lymphocytes and kill intracellular pathogens - Two types: humoral and cell-mediated immunity # Humoral Immunity - Refers to the part of the adaptive immune system that involves soluble mediators 1. B cells develop into plasma cells 2. Plasma cells secrete antibodies into circulation 3. Antibodies bind to extracellular microbes 4. Eliminate microbes and block infections # Cell-Mediated Immunity - Part of adaptive immune system that involves direct or indirect action by cells (lymphocytes) in response against intracellular microbes - T helper cells release signaling mediators to activate cells - Cytotoxic T cells release chemicals that cause cell lysis (death) # Active Immunity - Natural: antibody made after recovering from infection - Artificial: antibody made after receiving vaccination # Passive Immunity - Natural: AB transmitted from mother to baby - Artificial: AB received as a medical treatment # Adaptive Immune Response Properties 1. **Specificity** - Ensure antigens (AG) elicit specific responses 2. **Diversity** - Enables immune system (IS) to respond to a large variety of antigens 3. **Memory** - Leads to enhanced responses to subsequent AG exposure 4. **Clonal Expansion** - Increases number of AG-specific lymphocytes from a small amount of naive lymphocytes 5. **Specialization** - Generates responses that are optimal for defense against microbes 6. **Contraction and Homeostasis** - Allows IS to respond to new AGS 7. **Immunological Tolerance** - Unresponsiveness to self-antigens while reactive to foreign antigens. # Clonal Selection Theory - AG specific clones are pre-existing (before AG enters body) - Identifies specific lymphocytes based on their receptor specificity - Antigen-specific clones are activated/"selected" by antigens, which can activate multiple clones - Clonal expansion multiplies those selected cells - T cell clones give rise to effector cells, B cell clones give rise to memory and plasma cells # Primary/Secondary Immune Responses - Memory B and T cells formed during primary response are responsible for the reaction to secondary AG exposure - Secondary response characterized by faster response times, higher AB titers, more clones activated # Lymphocytes Classes 1. **B cells** - Differentiate into plasma cells which secrete antibodies, these AB's are effectors of humoral immunity (extracellular response) 2. **Helper T cells** - CD4+ cells that act through cytokines to effect cellular immunity 3. **Cytotoxic T cells** - CD8+ cells are the effectors, directly killing target 4. **Regulatory T cells** - "T regs," a subset of CD4+ cells involved in immune regulation # Differentiation of Lymphocytes - CD markers are molecules on the surface of cells that help identify and characterize different types of cells. # Naive Lymphocytes - Mature lymphs that have not encountered an antigen. - Differentiate into effector or memory cells through antigen recognition for specific response. # Effector Lymphocytes - Produce molecules that function to eliminate antigens - Ex: plasma cells from B cells; cytokines from CD4+ T cells # Memory Cells - Generated from antigen-stimulated lymphocytes; when they encounter the same AG, they become effector cells that initiate secondary immune response. - Stay in system even in absence of antigens for a faster immune response. # B cell Maturation - Originate in bone marrow and mature in the bone marrow. - Primary/generative tissues of IS # T cell Maturation - Originate in bone marrow and mature in the thymus # Antigen Presenting Cells - Cells in epithelium capture Abs and transport them to lymphocytes in the peripheral lymphoid tissues. - Macrophages and dendritic cells are most common and have following functions: 1. Phagocytose microbes, process Ag, display peptides for recognition 2. Express co-stimulatory proteins and release stimulatory cytokines 3. Process and present antigens to T cells to activate adaptive immunity # APC requires to undergo to display its antigens: 1. APC engulfs pathogen 2. APC processes pathogen and displays its antigens on the cell surface 3. APC migrates to lymph node to interact w/ lymphocytes 4. T cells recognize antigen and become activated. # Lymphocytic Development 1. Immature lymphocyte develops and matures in primary lymphoid organ. 2. Mature lymphocytes exit BU/thymus and enters bloodstream. 3. Lymphocyte encounters AG presented by APC in secondary lymphoid organ. 4. Activated lymphocyte proliferates/differentiates into effector and memory cells. 5. Effector lymphocytes migrate to infection site to perform immune functions. 6. When AG remover. Is contracts; most effector cells apoptosis or become memory cells # Chemokines - Signaling molecules that create concentration gradient to direct lymphocytes to specific tissues, such as lymph nodes or inflamed tissues. - Achieved by binding their specific receptors on lymphocytes. # Lymph Nodes 1. **Afferent lymphatic vessel** - Bring lymph fluid + APCs into the lymph node 2. **Efferent lymphatic vessel** - Exit point for lymphocytes and lymph 3. **High endothelial valve (HEV)** - Entry point for naive lymphocytes from bloodstream 4. **Follicle** - Space in outer cortex where B cells reside. 5. **Parafollicular cortex** - Area between outer cortex and medulla where T cells localize. 6. **Germinal centers** - Site of rapid cell proliferation and involved in high- affinity antibody production. # Spleen 1. **Periarteriolar lymphoid sheath (PALS)** - Surrounds central arterioles in white pulp, where T cells reside 2. **Follicles** - Adjacent to PALS, where B cells reside 3. **Marginal zone** - Where they capture and process blood-borne Ags 4. **White pulp** - Present Ags to B and T cells 5. **Germinal centers** # Mucosal Associated Lymphoid Tissues (MALT) - Structures include tonsils, adnoids, small bowels - Ags are trapped in the mucus - M cells are epithelial cells - Lymph/ APCs present in underlying tissues. - Has collection of follicles called Peyer's patches. - IgA highly expressed, binds and neutralizes microbes. # Cutaneous Immune System - Outer keratinized layer of the skin - Ags captured in epidermis - APCs and lymphs present - Lack organized follicular regions - Fluid drains to regional lymph node