Osmosis Prime and Hypersensitivity Lecture

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Hypersensitivity

Definition

• Hypersensitivity: Immune system reacts harmfully instead of protectively

Types of Hypersensitivities

• Four Types
  • Type I
  • Type II
  • Type III
    • Focus of lecture
  • Type IV

Type III Hypersensitivity

Mechanism

• Mediated by Immune Complexes
  • Antigen-antibody complexes deposit in blood vessel walls
  • Causes inflammation and tissue damage

Process

1. Formation of Immune Complexes

   • Antibodies (IgG) bind to soluble antigens
   • Immune complexes are formed
   • Distinct from Type II hypersensitivity (antigens on cell surfaces)

2. Autoimmune Example: Systemic Lupus Erythematosus (SLE)

   • IgG antibodies target DNA/nucleoproteins
   • Self-reactive B and T cells escape tolerance
   • Immune complex formation lead to vasculitis

3. Complex Deposition and Activation

   • Deposited in basement membrane of blood vessels
   • Activates complement system (proteins C1-C9)
   • C3a, C4a, C5a increase vascular permeability, cause edema
   • Act as chemokines, recruit neutrophils
   • Neutrophils release enzymes causing inflammation, tissue necrosis

Clinical Implications

• Affected Areas
  • Kidneys: Glomerulonephritis
  • Joints: Arthritis

Distinctions from Type II Hypersensitivity

• Type III involves immune complexes with soluble antigens
• Clinical symptoms in Type III correspond to deposition sites, not formation sites

Serum Sickness

Description

• Occurs when receiving foreign serum
  • Example: Snake bite treated with anti-venom antibodies
  • Body produces antibodies against foreign serum

Mechanism

• Subsequent exposure leads to immune complex formation
• Causes vasculitis and tissue necrosis

Summary

• Understanding Type III Hypersensitivity is crucial for identifying conditions like lupus and serum sickness.
• Differentiating hypersensitivity types helps in accurate diagnosis and treatment.