Immunoglobins and memory Immune system Notes ***

Overview of Antibodies

  • The topic covers different classes of antibodies and their respective roles and characteristics.

IgG Antibodies

  • Prevalence: Makes up 75-85% of all antibodies in the body.
  • Versatility: Most versatile antibody class with various effects.
  • Actions:
    • Includes functionalities such as agglutination, complement fixation, opsonization, and precipitation.
    • Each action is crucial for immune response efficiency.

IgM Antibodies

  • Structure: IgM is a pentamer, consisting of five units (pentamer).
  • Functionality: Highly effective in agglutination, which is the process of clumping together antigens linked via antibodies.
    • Each IgM antibody has two antigen-binding sites, allowing for increased connectivity in antigen interaction.

IgA Antibodies

  • Location: Found in mucosal areas exposed to the environment (e.g., tonsils, mucous membranes of the GI and respiratory tracts).
  • Role in Neutralization:
    • IgA neutralizes pathogens by binding to biologically active sites on viruses or bacteria, preventing their entry into the body.
    • It is essential in initial immune responses to inhaled or ingested pathogens.

IgE Antibodies

  • Chemotactic Role: IgE is crucial in recruiting eosinophils during parasitic infections and allergy responses.
  • Action Mechanism:
    • IgE binds to antigens associated with allergens, causing degranulation of mast cells and basophils.
    • This results in the release of inflammatory mediators, such as histamine and bradykinin, leading to allergic symptoms.

T Cells and Adaptive Immunity

  • Types of T Cells: Distinction between helper T lymphocytes and cytotoxic T lymphocytes.
  • Immune Response: T cells travel to sites of infection and release cytokines that promote activity in other immune components.
  • Antibody Mechanisms:
    • Antigen binding sites of antibodies facilitate neutralization, agglutination, and precipitation.
    • Constant regions (Fc) of antibodies influence opsonization, complement fixation, and activation of natural killer cells.

Immunologic Memory

  • Memory Cells Formation:
    • During the first exposure to an antigen, lymphocytes proliferate and differentiate into memory cells, which persist for extended periods (months to years).
    • Memory cells are primed for rapid response upon subsequent exposures.
  • Primary vs. Secondary Response:
    • Primary Response: Characterized by a lag phase (approximately 2-3 days) before antibody production begins.
    • Secondary Response: Significantly quicker and more robust due to presence of memory cells, leading to accelerated antibody titer.

Vaccination and Immunity

  • Active Immunity: Involves the individual's immune system responding to the antigen, leading to the formation of memory cells.
    • Natural Active Immunity: Acquired from direct exposure to pathogens.
    • Artificial Active Immunity: Developed through vaccination with antigens.
  • Passive Immunity: Involves receiving preformed antibodies, offering temporary protection without the formation of memory cells.
    • Natural Passive Immunity: Antibodies transferred from mother to fetus or infant during breastfeeding.
    • Artificial Passive Immunity: Involves administering antibodies directly after exposure (e.g., antivenom).

Immune System Disorders

  • Hypersensitivity:
    • Exhibits overreaction of the immune system to harmless antigens, leading to allergic reactions.
    • Responses include acute hypersensitivity (immediate response) and chronic hypersensitivity (delayed response).
  • Autoimmune Disorders:
    • Situations where the immune system mistakenly attacks the body's own cells due to failure to recognize self-antigens.
  • Mechanisms of Autoimmunity:
    1. Cross-Reactivity: The immune system mistakenly responds to self-antigens resembling foreign pathogens.
    2. Altered Self-Antigens: Changes in cell antigens due to infection or toxins lead to misrecognition by the immune system.
    3. Exposure in Privileged Sites: Immune reactions occur when immune cells access areas typically protected from immune responses.

Examples of Autoimmune Disorders

  • Include Type 1 Diabetes (destruction of insulin-producing beta cells), Multiple Sclerosis (immune damage to myelin), and various autoimmune skin conditions.
  • Immunodeficiency:
    • HIV/AIDS specifically targets helper T cells, leading to severe immunosuppression and increased vulnerability to infections and opportunistic diseases.