Adaptive Immunity - Part 3 of Chapter 17

Overview of the Immune System

• Immune System Composition: Protects from infectious diseases and cancer.
  • Innate Immune System: Non-specific, acts against all microbes through:
    • First Line of Defense: Prevents infection.
    • Second Line of Defense: Fights microbes in tissues.
  • Adaptive Immune System: Specific response following infection, involves T-cells, B-cells, and antibodies.
    • Third Line of Defense: Adaptive immune response.

Adaptive Immune Response

• Components:
  • Humoral Immune Response: Involves B cells and antibodies.
    • Protects against viruses, bacteria, and toxins.
  • Cell-Mediated Immune Response: Involves T cells.
    • Eliminates eukaryotic microbes, cancer, virally infected cells, and transplants.

T-Cells in Cell-Mediated Immunity

• Types of T-Cells:
  • T Helper Cells (CD4): Communicators that secrete cytokines.
  • Cytotoxic T Lymphocytes (CD8): Also known as T killer cells, destroy target cells using perforin.
  • T Regulatory Cells (CD25): Stop T killer cells, turn off cell-mediated response.
  • Natural Killer Cells: Involved in antibody-dependent cell-mediated cytotoxicity, non-specific.

T-Cell Development

• Origination and Maturation:
  • Origin: Stem cells in red bone marrow.
  • Maturation: In the thymus, involves T cell education/selection to ensure correct recognition of self and non-self molecules.
  • Outcome: T cells that pass the education process migrate to lymphoid tissues.

T-Cell Education/Selection

• Testing: T cells are tested for recognition of self antigens and MHC molecules.
  • Failing: No recognition or overreaction leads to apoptosis.
  • Passing: Appropriate recognition allows survival and maturation.

Activation of B and T Cells

• B-Cells and T-Cells Activation:
  • T-Independent Activation: Only the antigen is needed, specific to B cells, results in low antibody production (IgM only).
  • T-Dependent Activation: Requires T helper cell and antigen, applicable to both B and T cells, results in stronger response (IgM and IgG production).

Process of T-Dependent Activation

• Steps Involved:
  • Antigen Processing Cell (e.g., macrophage) phagocytoses microbe, presents antigen on MHC molecule.
  • T Helper Cell: Recognizes antigen, requires IL-1 for full activation.
  • Activated T Helper Cell: Secretes IL-2 to activate other T cells and B cells.
  • B Cell Activation: Through IL-2, leads to clonal expansion and antibody production.

Summary of Adaptive Immune Response

• Humoral Immune Response: Antibody production by B cells, can be T independently activated.
• Cell-Mediated Immune Response: Requires T-dependent activation via antigen presenting cells and T helper cells.
• Memory Cells: Both pathways generate memory B and T cells, lasting for about 10 years.