BIOL 252 Lesson 18 Notes

Adaptive Immune System

  • The adaptive immune system is a critical part of our defense against pathogens and diseases, involving specific responses mediated by various immune cells.

Immunity Types

  • Passive Immunity:

    • Definition: The acquisition of antibodies from another source rather than producing them.
    • Examples:
    • Naturally acquired from mother to fetus during pregnancy, or through breast milk.
    • Artificially acquired via injection of antibodies (e.g., RhoGAM).

  • Active Immunity:

    • Definition: The body produces its own antibodies in response to an antigen.
    • Examples:
    • Naturally acquired through infection.
    • Artificially acquired through vaccination.

Types of Immunity Responses

  • Cell-Mediated Immunity:

    • Mediators: Primarily involves CD8+ T cells (cytotoxic T cell).
    • Function: Kills infected or cancerous cells.
    • Activation: Requires antigen presentation by MHC class I molecules.

  • Humoral Immunity:

    • Mediators: B cells and antibodies.
    • Function: Produces antibodies against extracellular pathogens.
    • Activation: Requires interaction between CD4+ T helper cells and B cells, presented by MHC class II molecules.

  • Memory Immune Response:

    • Definition: A quicker and more robust response to a previously encountered pathogen due to the formation of memory cells (B and T cells).

Key Cellular Components in Adaptive Immunity

  • CD4+ T Cells: Helper T cells that activate B cells and other immune responses, recognizing antigens presented by MHC class II.
  • CD8+ T Cells: Cytotoxic T cells that destroy infected cells, recognizing antigens presented by MHC class I.
  • B Cells: Produce antibodies and can develop into memory cells for faster responses on subsequent exposures.
  • Major Histocompatibility Complex (MHC):
    • MHC class I: Found on all nucleated cells, presents antigenic peptides to CD8+ T cells.
    • MHC class II: Found on antigen-presenting cells (APCs) like dendritic cells, presents to CD4+ T cells.

Vaccine Effectiveness

  • Vaccines stimulate the adaptive immune system to develop immunity against pathogens without causing disease upon exposure.
  • Data interpretation from vaccine trials includes:
    • Antibody production levels over time post-vaccination (IgG response).
    • Activation of specific T cell populations (CD4+ and CD8+) and their cytokine profiles (IFNgamma, IL-4).

RhoGAM Example: Passive Immunity Case Study

  • Situation: For Rh-negative mothers with Rh-positive fetuses.
  • Mechanism: RhoGAM contains antibodies against Rh antigens, preventing maternal immune response in the first pregnancy and protecting future pregnancies.

Immune Response Timeline Post-Vaccination

  • 1st Phase: Humoral immunity develops within days post-vaccination.
  • 2nd Phase: Memory immune response forms over a prolonged period, leading to sustained immunity.

Antibody Structure and Function

  • Immunoglobulin (Ig) Types:
    • IgG: Major circulating antibody, capable of neutralization and opsonization.
    • IgM: First antibody produced, pentameric structure capable of binding multiple epitopes.
    • IgA: Present in mucosal areas, protecting entry points of pathogens.
    • IgE: Involved in allergic responses.

Conclusion

  • The adaptive immune system's complexity enables a targeted response to a wide range of pathogens through collaboration between various immune cells and the production of antibodies. Understanding these mechanisms is critical for the development of effective vaccines and treatments for diseases.