Disorders of the Immune Response

Chapter 16 Overview

Definition: Excessive or inappropriate activation of the immune response.
Key Concept: Inflammation and its five cardinal signs (redness, heat, pain, swelling, loss of function).

Common Associations: Allergies, systemic reactions (e.g., anaphylaxis), local reactions (e.g., hives, rhinitis, atopic dermatitis, bronchial asthma).
Mechanism:
- T helper cells are primed against a specific antigen.
- Activation of T helper cells releases inflammatory cytokines (Interleukin 4, 5).
- B cells turn into plasma cells that secrete IgE antibodies.
- IgE antibodies are picked up by mast cells.
- Mast cells degranulate, releasing histamine and other inflammatory mediators (e.g., cytokines, prostaglandins).
Symptoms: Vasodilation, increased vascular permeability, smooth muscle spasm, mucosal edema, increased mucus secretion.
Example: Anaphylaxis leading to massive vasodilation, decreased blood pressure, and shock.

Associations: Autoantibodies bind to antigens on cell surfaces (e.g., red/white blood cells).
Mechanism:
- Antibodies (IgG, IgM) recognize antigens, leading to phagocytosis and cell damage.
- Involvement of the complement system.
- Examples include autoimmune diseases like Graves' disease and Myasthenia Gravis.

Delayed Hypersensitivity: Antigen-antibody complexes deposit on vessel walls.
Associations: Autoimmune vasculitis, glomerulonephritis, serum sickness.
Mechanism: Complement activation, inflammation, and tissue damage.
Example: Kidney damage due to glomerulonephritis leading to renal failure.

Cell-Mediated: T-cells are hypersensitive and cause cell damage.
Delayed Hypersensitivity: Involvement of macrophages, cytotoxic T-cells, and T helper cells.
Associations: Tuberculin test, contact dermatitis, graft-versus-host disease.

Definitions: Underactive immune response (B cells, T cells, or both).
Primary Immunodeficiency Examples:
- Severe Combined Immunodeficiency (SCID)
- Thymic Hypoplasia (DiGeorge Syndrome)
- Wiskott-Aldrich Syndrome
Acquired Immunodeficiency Examples: Malnutrition, immunosuppressant drugs, radiation, HIV/AIDS.

Transmission: Direct contact (blood, sexual contact, breast milk).
Infects: CD4+ cells (T helper cells, dendritic cells, neurons).
HIV Mechanism:
- HIV is an RNA virus using reverse transcriptase to convert RNA to DNA.
- Integrates into host genome, leading to lifelong infection.
- High mutation rate complicates treatment.
Clinical Progression:
- Primary phase: fever, systemic symptoms.
- Latent phase: low viral count, gradual T helper cell decline.
- AIDS: less than 200 T-helper cells/mL, increased risk of opportunistic infections and malignancies.
Treatment Targets: Reverse transcriptase inhibitors, protease inhibitors, fusion inhibitors, integrase inhibitors.

Definition: Breakdown of self-tolerance, leading to immune system attacking self-antigens and body tissues.
Cause: Hyperactive immune system responding to self-antigens.
Examples and Mechanisms: Can span a wide variety of body tissues and functions.

Universal Donor: Type O blood (lack of A or B antigens).
Rh Factor: Rh incompatibility in pregnancy can lead to erythroblastosis fetalis; managed using Rhogam.

Types: Hyperacute, acute, chronic.
Mechanism: Preformed antibodies, T cell response against graft antigens, and gradual blood vessel damage.