Immunity Types & Cells

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Immunity Overview Body's defense against harmful microorganisms (bacteria, viruses, fungi, parasites), abnormal cells, toxins, foreign substances. Complex system involving cells, molecules, and organs. Types of Immunity 1. Innate Immunity (First Line of Defense) Present at birth, immediate, non-specific protection. No prior exposure required. Components: Physical barriers, chemical defenses, innate immune cells. Examples: Physical Barriers: Skin (tightly packed epithelial cells, antimicrobial peptides). Chemical Defenses: Enzymes in tears, saliva, mucus break down bacterial cell walls. Innate Immune Cells: Macrophages: Engulf and destroy pathogens. Neutrophils: Release toxic substances to kill pathogens. Natural Killer (NK) cells: Kill infected and tumor cells. 2. Adaptive Immunity (Specific Protection) Develops after exposure to specific pathogens/antigens. Highly specific, provides long-term protection. Involves B cells and T cells. Examples: Antibody Production: B cells produce antibodies that recognize and bind to specific pathogens, marking them for destruction. Cell-mediated Immunity: T cells play a central role. Helper T cells: Activate other immune cells. Cytotoxic T cells: Directly kill infected cells. Regulatory T cells: Maintain immune homeostasis. Memory Response: Memory B and T cells "remember" pathogens for faster, more effective response upon re-exposure. 3. Active Immunity (Acquired) Acquired through pathogen exposure or vaccination. Immune system produces its own antibodies and memory cells. Provides long-term protection. Examples: Natural Infection: Immune response to actual infection leads to lasting immunity. Vaccination: Introduces weakened/inactivated pathogens or antigens to stimulate immune response without causing disease. 4. Passive Immunity (Transferred Antibodies) Acquired through transfer of pre-formed antibodies. Provides immediate, temporary protection. Does NOT generate long-term immune memory. Examples: Maternal Antibodies: Newborns receive antibodies via placenta or breast milk. Antibody Therapies: Administering purified antibodies (e.g., anti-venom) for immediate protection. Other Immunity Types Mucosal Immunity: Protects mucous membranes (respiratory, GI, genitourinary tracts). Involves specialized immune cells and antibodies. Examples: IgA Antibodies: Predominant antibody in mucosal secretions, neutralizes pathogens (e.g., in saliva). Mucosal Immune Cells: Dendritic cells, T cells survey mucosal tissues. Autoimmunity: Immune system mistakenly targets and attacks body's own cells/tissues. Results in chronic inflammatory conditions. Examples: Rheumatoid Arthritis: Immune system attacks joints. Multiple Sclerosis: Immune system attacks nerve fiber coverings in CNS. Innate Immune Cells First line of defense, present from birth, non-specific responses. Neutrophils: Most abundant WBC, highly mobile phagocytes, engulf and destroy pathogens. Macrophages: Phagocytose pathogens, cellular debris, dead cells; serve as antigen-presenting cells. Dendritic Cells: Antigen-presenting cells that initiate adaptive immune responses. Natural Killer (NK) Cells: Kill virus-infected cells and tumor cells. Mast Cells: Release histamine and other mediators in allergic reactions and immune responses. Eosinophils: Involved in allergic reactions and defense against parasites. B Cells (B Lymphocytes) Crucial component of adaptive immune system. Derived from hematopoietic stem cells in bone marrow. Primary function: Produce antibodies (immunoglobulins - Igs). Subsets: Plasma Cells: Antibody-producing factories, secrete large amounts of antibodies. Memory B Cells: Long-lived cells, provide immunological memory for rapid response upon re-exposure. T Cells (T Lymphocytes) Central role in adaptive immune system. Derived from hematopoietic stem cells, mature in thymus. Characterized by T cell receptor (TCR) on surface, recognizes antigens presented by MHC molecules. Types of T Cells: Helper T Cells (CD4+): Coordinate immune responses, recognize MHC class II, secrete cytokines to activate other immune cells (B cells, cytotoxic T cells). Differentiate into Th1, Th2, Th17, regulatory T cells (Tregs). Cytotoxic T Cells (CD8+): Directly kill infected or abnormal cells, recognize MHC class I, release perforin and granzymes to induce apoptosis. Memory T Cells: Long-lived cells, provide immunological memory for rapid response, crucial for vaccine effectiveness.