Immune System

  • Viruses: Targeted by interferons, cytotoxic T cells, and NK cells.

  • Respiratory Burst: Phagocytes release reactive oxygen species to destroy pathogens.

  • Membrane Attack Complex (MAC): Formed by complement proteins to lyse bacterial cells.

Immunity Types

  • Innate Immunity: Non-specific, immediate response (e.g., barriers, phagocytes).

  • Adaptive Immunity: Specific, memory-based response (T and B cells).

    • Humoral Immunity (B cells): Produces antibodies to neutralize extracellular pathogens.

    • Cellular Immunity (T cells): Directly attacks infected or abnormal cells.

Key Immune Cells & Functions

  • B Cells:

    • Develop in bone marrow.

    • Have membrane-bound antibodies (B cell receptors).

    • Differentiate into plasma cells and memory cells.

  • Plasma Cells:

    • Effector B cells that produce large amounts of antibodies.

  • T Cells:

    • Express T cell receptors and either CD4 or CD8 proteins.

    • Helper T Cells (CD4⁺): Activate B cells, cytotoxic T cells, and macrophages via cytokines.

    • Cytotoxic T Cells (CD8⁺): Kill infected or cancerous cells using perforins and granzymes.

    • Regulatory T Cells (CD4⁺): Suppress immune responses and prevent autoimmunity.

    • Memory T Cells: Provide a faster response to future infections.

  • Natural Killer (NK) Cells: Kill infected or abnormal cells without antigen specificity.

  • Antigen-Presenting Cells (APCs): Includes dendritic cells, macrophages, and B cells, which present antigens via MHC proteins to activate T cells.

Self-Tolerance (T Cell Maturation)

  • Positive Selection: Ensures T cells recognize MHC; non-recognizing cells undergo apoptosis.

  • Negative Selection: Eliminates overly self-reactive T cells; those that fail undergo apoptosis or become regulatory T cells.

Major Histocompatibility Complex (MHC)

  • MHC I: Present on all nucleated cells; recognized by cytotoxic T cells.

  • MHC II: Present on APCs; recognized by helper T cells.

Key Immune Molecules

  • Antigens: Substances that provoke an immune response.

  • Haptens: Small molecules that become antigenic when attached to a protein.

  • Antibodies (Immunoglobulins): Y-shaped proteins produced by plasma cells; functions include:

    • Neutralization: Blocks pathogen activity.

    • Agglutination & Precipitation: Clumps pathogens for easier removal.

    • Complement Activation: Triggers MAC formation.

    • Opsonization: Marks pathogens for phagocytosis.

  • Complement System: Enhances immune responses by promoting inflammation, opsonization, and cell lysis.

  • Cytokines: Regulate immune responses and inflammation.

  • Interferons: Help protect against viral infections.

  • Perforins & Granzymes: Released by cytotoxic T cells to induce apoptosis in target cells.

Immune Response Mechanisms

  • Chemotaxis & Diapedesis: Guide immune cells to infection sites.

  • White Blood Cell Migration: Facilitates immune response at infection sites.

  • Allergies & Fever:

    • Allergies: Hypersensitivity reactions.

    • Fever: Helps inhibit pathogen growth