Adaptive Immune Response Notes

Overview of Adaptive Immune Response

  • Adaptive immunity is the body's specific response to pathogens, characterized by the creation of memory and stronger responses upon re-exposure.

Humoral Immunity vs. Cell-Mediated Immunity

  • Humoral Immunity:

    • Primarily involves B lymphocytes (B cells).
    • Functions to eliminate pathogens present in bodily fluids (e.g., bacteria, toxins, viruses).
    • B cells produce antibodies that bind to antigens.

  • Cell-Mediated Immunity:

    • Involves T lymphocytes (T cells), particularly cytotoxic T cells (TC) and helper T cells (TH).
    • Aims to eliminate cells infected by pathogens.
    • TC cells provide a direct response by delivering 'death packages' to infected host cells.

Mechanisms of Tolerance

  • Central Tolerance:
    • Occurs during lymphocyte development, ensuring that immune cells do not attack self-antigens.
  • Peripheral Tolerance:
    • Mechanisms in place to regulate mature lymphocytes that might react to self-antigens outside of the bone marrow and thymus.

Primary vs. Secondary Immune Response

  • Primary Response:
    • Initial response when an antigen is encountered.
    • Characterized by a slower response and lower antibody production.
  • Secondary Response:
    • Follows subsequent exposure to the same antigen.
    • Faster and more robust due to the presence of memory B cells, leading to a higher level of antibodies.

Antibody-Antigen Interaction

  • Protective Outcomes:
    • Neutralization of pathogens.
    • Opsonization, enhancing phagocytosis.
    • Complement activation for lysis of pathogens.
    • Agglutination, leading to immune complexes.
    • Antibody-dependent cellular cytotoxicity (ADCC).

Lymphoid Organs and Vessels

  • Primary Lymphoid Organs:
    • Bone marrow (B cell maturation)
    • Thymus (T cell maturation)
  • Secondary Lymphoid Organs:
    • Lymph nodes, spleen, and mucosal-associated lymphoid tissue (MALT/SALT) facilitate the interaction between B and T cells with antigens.

Clonal Selection and Expansion

  • Clonal Selection:
    • Process where specific lymphocytes are activated by their specific antigens.
    • Leads to the selection of B and T cells capable of responding to that specific antigen.
  • Clonal Expansion:
    • Proliferation of selected B and T cells into effector and memory cells.

Role of T Cells

  • T-Cell Activation:
    • Dendritic cells present antigens to naïve T cells, activating them.
    • TH cells assist in B cell activation and TC cell activity.
  • CD Markers:
    • CD8 designates cytotoxic T cells.
    • CD4 designates helper T cells.

Immunoglobulin Classes

  • Types of Antibodies:
    • IgM: First responder, pentameric structure.
    • IgG: Most abundant, involved in secondary response.
    • IgA: Found in mucosal areas, protects mucous membranes.
    • IgD: Role in B cell activation.
    • IgE: Involved in allergic reactions and responses to parasites.

Importance of T-Independent Antigens

  • T-Independent Antigens:
    • Can activate B cells without T cell help, important for rapid responses, especially in cases like infections.

Natural Killer (NK) Cells

  • Function:
    • Provide a rapid immune response against virally infected or cancerous cells.
    • Kill target cells lacking MHC class I molecules by inducing apoptosis.

Conclusion of Adaptive Immunity Response

  • Summary involves the activation of B and T cells, the role of memory cells, and overall coordination of a robust immune response against pathogens.
  • Emphasizes the importance of immune tolerance to prevent autoimmunity and the strategic involvement of different immune components to ensure efficiency against infections.