Introduction to Hypersensitivity Reactions

This lecture introduces the types of hypersensitivity reactions, following a previous discussion on the complement system.

Types of Hypersensitivity Reactions

• Type 1: Immediate Hypersensitivity

  • Fastest reaction type.
  • Involves IgE antibodies and mast cells.
  • Triggers include allergies, anaphylaxis, and asthma.
  • Mechanism: IgE binds to allergens, mast cells degranulate, releasing histamine.

• Type 2: Cytotoxic Hypersensitivity ("Cy2 toxic")

  • Involves antibodies bound to antigens on cell surfaces.
  • Can cause cell inflammation, dysfunction, or destruction.
  • Examples include:
    • Goodpasture syndrome
    • Rheumatic fever
    • Hyperacute transplant rejection
    • Myasthenia gravis (cell dysfunction)
    • Graves' disease (antibodies stimulate target)

• Type 3: Immune Complex-Mediated Hypersensitivity

  • Antigen-antibody complexes are free-floating in plasma.
  • Can cause vasculitis, nephritis, arthritis when deposited in tissues.
  • Examples include lupus, rheumatoid arthritis.
  • Known reactions:
    • Serum sickness (generalized, acute)
    • Arthas reaction (localized, subacute)

• Type 4: Delayed-Type Hypersensitivity

  • Most delayed reaction, takes 72 hours.
  • Cell-mediated immunity involving T lymphocytes, not antibodies.
  • Forms granulomas if invaders are not destroyed.
  • Examples include:
    • Tuberculosis
    • Sarcoidosis (non-caseating granulomas)

Overview

• Type 1: Immediate, humoral immunity (IgE)
• Type 2: Cytotoxic, cell surface antigen-antibody complexes
• Type 3: Free antigen-antibody complexes causing systemic effects
• Type 4: Delayed, cell-mediated immunity, granuloma formation

Upcoming Topics

• Detailed discussion of Type 1 hypersensitivity:
  • Asthma
  • Allergies
  • Bee sting responses
  • First exposure vs. second exposure

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Additional Resources

• Renal Physiology Course: Available with 10 videos, cases, and notes.
• Endocrine Pharmacology Course: Covers insulin and dosage calculations.

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