lecture recording Immune system part 2

Adaptive Defenses Overview

  • Distinguishes between innate (non-specific) and adaptive (specific) immune defenses.

  • Antibody-mediated (humoral) and cell-mediated immunity.

Humoral Immunity

  • Definition: Involves body fluids (humors).

  • Function: Protects against a wide variety of infectious agents.

    • If the adaptive immune system fails, disorders such as cancers can arise.

    • Examples include HIV disabling the immune response leading to AIDS.

  • Activation: Involves amplifying the inflammatory response and complement system.

  • Important Aspect: Adaptive immunity has a memory component crucial for rapid response upon re-exposure to pathogens.

Cellular Immunity

  • Definition: Mediated primarily by T cells.

  • Main Player: T cells target specific infected or cancerous cells.

  • Types of T cells: Each type plays a distinct role in the immune response.

Activation and Memory Mechanisms

  • Activation of Adaptive Defenses: Takes longer to respond but ramps up during an infection.

  • Memory Formation: Once an antigen is encountered, memory T and B cells are formed, enhancing the response on subsequent exposures.

  • Vaccines leverage this memory component for protection against diseases.

Antigens and Their Types

  • General Role: Antigens are molecules that provoke an immune response.

  • Types of Antigens:

    • Complete Antigens: Must have two properties: Immunogenicity (stimulates lymphocyte proliferation) and reactivity (reacts with lymphocytes and antibodies).

      • Example: Proteins, some polysaccharides.

    • Incomplete Antigens (Haptens): Only have reactivity, not immunogenicity, requiring a carrier to elicit a response.

    • Examples include penicillin and poison ivy.

Antigenic Determinants

  • Definition: Specific parts of an antigen recognized by antibodies or lymphocyte receptors.

  • Antigens with multiple determinants can evoke a response from various antibodies, enhancing immune response.

B Cells vs. T Cells

  • B Cells:

    • Maturation occurs in bone marrow.

    • Responsible for producing antibodies (plasma cells).

    • Key players in humoral immunity.

  • T Cells:

    • Maturation occurs in the thymus.

    • Engaged in cell-mediated immunity, recognizing and eliminating infected cells.

Antigen Presenting Cells (APCs)

  • Functions: Present processed antigens to T cells to activate them and signal the immune response.

  • Examples:

    • Dendritic Cells: Most effective APC, linking innate and adaptive immunity.

    • Macrophages: Can also serve as APCs while performing other immune functions.

Positive and Negative Selection of T Cells

  • Positive Selection: Ensures T cells can recognize self MHC proteins. Cells that cannot are eliminated.

  • Negative Selection: Eliminates T cells that react too strongly to self-antigens, preventing autoimmune responses.

Clonal Selection and Proliferation

  • Process:

    • When a T or B cell encounters its specific antigen, it undergoes activation, proliferation (making clones), and differentiation into effector and memory cells.

  • T and B Lymphocytes Act Differently: T cells directly attack infected cells, while B cells produce antibodies to neutralize pathogens.

Primary vs. Secondary Immune Response

  • Primary Response:

    • Occurs after first exposure to an antigen.

    • Antibody production takes about 3–6 days, peaks around 10 days.

  • Secondary Response:

    • Rapid response upon re-encountering the same antigen.

    • Antibodies peak within 2–3 days and are produced at a higher level than in primary response.

Vaccines and Their Mechanism

  • Purpose: Educate the immune system to recognize pathogens without causing disease.

  • Types of Immunity:

    • Active Immunity: Antibodies are produced by the individual (via infection or vaccination).

    • Passive Immunity: Antibodies are received from another source (like maternal breastfeeding or administered antibodies).

  • Vaccine Types: May use whole pathogens (weakened/killed) or components thereof to elicit an immune response without causing disease.

Antibody Structure and Classes

  • Structure: Comprised of heavy and light polypeptide chains.

  • Classes of Antibodies (MADGE): Includes IgM, IgA, IgD, IgG, IgE.

    • IgM: First antibody produced in response, effective in activating complement.

    • IgG: Most abundant in circulation, primarily involved in secondary responses.

    • IgE: Involved in allergic responses.

Functions of Antibodies

  • Neutralization of toxins and pathogens, precipitation of antigens, lysis through complement activation, facilitating phagocytosis through opsonization.

  • Monoclonal Antibodies: Man-made, target specific antigens used in diagnostics and therapy for various diseases.

Importance of Understanding Vaccines and Immunology

  • Public Health: Knowledge helps respond to vaccine skepticism, guiding informed discussions about immunization.

    • Understand common misconceptions about vaccines (e.g., vaccines causing autism).