Biological Systems II: Humoral Immunity I (Antibodies and Complements) - Prof. Yong (Tiger) Zhang

Supplemental Materials

  • Textbook: Basic Immunology: Functions and Disorders of the Immune System, 7th Edition
    • Authors: Abul K. Abbas, Andrew H. Lichtman, Shiv Pillai
    • Chapters:
    • Chapter 1: Introduction to the Immune System
    • Chapter 4: Antigen Recognition in the Adaptive Immune System
    • Chapter 7: Humoral Immune Responses
    • Chapter 8: Effector Mechanisms of Humoral Immunity

Objectives

  • Understand the distinction between cellular and humoral immunity.
  • Define immunoglobulins, antigens, and antibodies.
  • Identify the number of immunoglobulin classes in humans and their respective functions.
  • Outline the development and maturation process of B-lymphocytes.
  • Explore the mechanisms leading to immunoglobulin diversity.
  • Discuss the mechanisms of antibody-dependent cell-mediated cytotoxicity (ADCC).
  • Examine the factors influencing the diversification of the antibody repertoire.

Immune System Overview

Importance
  • The immune system is crucial for maintaining health and combating disease.
Organs and Tissues
  • Major primary organs: Bone Marrow and Thymus
    • Site of development for immune cells.
  • Immune cells involved in infection responses are concentrated in tissues like:
    • Blood
    • Spleen
    • Lymphatic tissues

Classification of Immunity

Types
  • Mucosal vs. Serosal Immunity: Locations where immunity functions.
  • Innate vs. Adaptive Immunity:
    • Innate: Immediate, general response (e.g., epithelial barriers, phagocytes).
    • Adaptive: Specific response, develops over time (e.g., antibodies, T lymphocytes).

Adaptive Immunity

Cell Types
  • B Lymphocytes: Central to humoral immunity; produce antibodies.
  • T Lymphocytes: Central to cellular immunity; activate phagocytes to eliminate pathogens.
Properties of Adaptive Immune Responses
  • Functional Significance:
    • Ensures specific responses to distinct antigens.
    • Diversity allows response to a broad range of antigens.
    • Memory enhances responses upon re-exposure.
    • Clonal expansion increases specific lymphocyte numbers.
    • Specialization enables optimal defense mechanisms.
    • Contraction maintains homeostasis within the immune system.
    • Nonreactivity to self prevents autoimmunity.

Cells of the Immune System

Lymphocytes
  • T-lymphocytes: Key players in cellular immunity.
  • B-lymphocytes: Key players in humoral immunity.
  • Antigen-Presenting Cells:
    • Include macrophages, dendritic cells, and B cells.

Antigens and Antibodies

Definitions
  • Antigen:
    • Classical: Molecule inducing and binding to an antibody.
    • Modern: Molecule initiating a specific immune response targeted by the immune system from T and B cells.
  • Antibodies:
    • Glycoproteins classified as immunoglobulins, present in serum and physiological fluids.
    • Five classes: IgA, IgD, IgE, IgG, IgM.
Immunoglobulin Structure
  • Composed of light and heavy chains with constant and variable regions.
  • Complementarity-Determining Regions (CDRs): Hypervariable regions responsible for antigen binding.

Antibody Functions

Mechanisms of Action
  • Neutralization: Antibodies neutralize toxins and block viral infections by preventing binding to host cells.
  • Opsonization: Antibodies coat pathogens, making them recognizable for phagocytosis.
  • Complement Activation: Antibodies initiate complement system to destroy pathogens directly.

B Cell Development

Stages
  1. Phase 1: B-cell precursors rearrange immunoglobulin genes in the bone marrow (heavy and light chains).
  2. Phase 2: Immature B cells undergo negative selection against self-reactivity.
  3. Phase 3: Mature B cells encounter antigens; germinal centers form, leading to differentiation into plasma and memory cells.
  4. Phase 4: Activation facilitated by helper T cells through cytokine signaling.
Primary vs. Secondary Response
  • Primary Response: Initial interaction results in IgM production.
  • Secondary Response: More robust IgG production due to memory B cells.

Monoclonal Antibodies

  • Produced by fusion of immunized spleen cells with myeloma cells to create hybridomas, which are then cloned for specific antibody production.