Immune System Chapter - Part 2

Overview

• Focus on adaptive defenses of the immune system.
• Difference between innate and adaptive defenses:
  • Innate: Non-specific, quick response (e.g., skin, mucous membranes, phagocytes).
  • Adaptive: Specific, slower response, involves lymphocytes (B cells and T cells).

Key Characteristics of Adaptive Defenses

1. Specificity: Targets specific pathogens (e.g., specific strains of flu).
2. Systemic: Responses are systemic, unlike localized innate responses.
3. Memory: Adaptive immune responses improve over time due to memory cell formation.

Arms of Adaptive Immunity

1. Humoral Immunity:
   • Mediated by B-cells and their clones (plasma cells).
   • Focuses on pathogens in bodily fluids (e.g., bacteria outside cells).
   • Uses antibodies to target pathogens.
2. Cellular Immunity:
   • Mediated by T-cells.
   • Targets infected or cancerous cells within body cells.
   • Employs strategies like apoptosis to eliminate infected cells.

Antigens and Immune Response

• Antigens: Molecules on pathogens recognized by immune system.
• Complete Antigens: Large and complex, induce strong immune response.
• Incomplete Antigens (Haptens): Small, need to attach to carrier molecules to elicit a response.
• Antigenic Determinants: Specific parts of an antigen recognized by immune cells.

Self and Non-Self Recognition

• Self-Antigens: Molecules found on our cells that should be ignored by the immune system.
• Major Histocompatibility Complexes (MHC):
  • Class I: Found on all nucleated cells, indicates cell health.
  • Class II: Found on immune cells, helps mobilize immune responses.

Development and Education of Lymphocytes

• Origin: Both B and T lymphocytes originate from red bone marrow.
• Education:
  • B-cells: Educated in the bone marrow.
  • T-cells: Educated in the thymus.
• Naive Cells: Post-education, migrate to secondary lymphoid tissues.
• Activation: Occurs upon first antigen encounter (antigen challenge).

Diversity of Immunity

• Somatic Recombination: Random DNA shuffling generates diverse receptor shapes.
• Immunocompetence: Ability to bind to antigens and MHC molecules.
• Self-Tolerance: Avoids autoimmunity by not reacting to self-antigens.

Antigen Presenting Cells (APCs)

• Role: Bridge innate and adaptive immunity by presenting antigens to T-cells.
• Examples: Macrophages and dendritic cells.

Summary

• Adaptive defenses are specific, systemic, and improve with exposure due to memory cells.
• Key cells involved are lymphocytes (B and T cells).
• Two subdivisions: humoral (antibody-mediated) and cellular (cell-mediated).
• In the following lectures, details of humoral and cellular immunity will be explored further.