Chapter 19: Disorders of the Immune System (Part 2)

Overview

• Disorders of the immune system are divided into:
  • Hypersensitivity (Overreaction)
  • Loss of Immunity (Underreaction)
• Focus on Autoimmunity - immune response against self-antigens.

Hypersensitivity Recap

• Allergy: Immune response to non-pathogenic foreign molecules.
  • Types of Allergy:
    • Type 1: Anaphylaxis
    • Type 2: Cytotoxic
    • Type 3: Immune Complex
    • Type 4: Cell Mediated
  • Types 1-3 involve antibodies; Type 4 involves T-cells.

Autoimmunity

• Autoimmunity: Immune response to self-antigens, causing loss of self-tolerance.
• Possible Cause: Molecular Mimicry
  • Infection with a microbe leads to immune response (antibodies/CTLs).
  • Microbe antigen resembles self-molecule, leading to cross-reaction post-infection.
• Predisposing Factors:
  • More common in females.
  • Genetic component; familial occurrence.

Types of Autoimmune Diseases

1. Cytotoxic Autoimmune Diseases

• Myasthenia Gravis
  • Antibodies block muscle cell stimulation by binding to acetylcholine receptors.
  • Results in muscle paralysis.
• Graves’ Disease
  • Antibodies overstimulate thyroid cells to produce excess thyroid hormones.
  • Symptoms: Bulging eyes, goiter.

2. Immune Complex Autoimmune Diseases

• Lupus
  • Antibodies against nuclear proteins form complexes causing rashes, inflammation, and organ damage.
  • Hallmark: Butterfly rash.
• Rheumatoid Arthritis
  • Immune complexes in joints cause chronic inflammation and damage.
  • Juvenile rheumatoid arthritis also exists.

3. Cell-mediated Autoimmune Diseases

• Type 1 Diabetes
  • CTLs destroy pancreatic beta cells, reducing insulin production.
  • Known as insulin-dependent diabetes.
• Multiple Sclerosis
  • Antibodies and CTLs attack myelin sheath in neurons.
  • Leads to impaired nerve impulse transmission and muscle control loss.

Key Points

• Autoimmunity involves the immune system mistakenly attacking the body's own cells.
• Different autoimmune diseases affect different parts of the body and involve either antibodies, CTLs, or both.
• The exact causes of autoimmune diseases are not fully understood, but factors like molecular mimicry and genetics play a role.