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Hypersensitivity Reactions

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Type 2 Hypersensitivity Reactions

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Summary

Type II Hypersensitivity Reactions (T2HSR) are a type of unwanted immune reaction caused by antibodies. Specifically, antibodies recognize and bind to antigens expressed by our own cells. The result of antibody binding causes 3 things: direct cell death and lysis, inflammation, or impaired function if the antibody targets a cell-surface receptor.

Antibodies can directly cause cell death in many ways, including complement activation or NK-cell-mediated damage. This can manifest as hemolysis in diseases like autoimmune hemolytic anemia or acute hemolytic transfusion reactions.

Antibodies can also bind to cell surfaces and induce local inflammation. This inflammation is the result of complement activation or cell death releasing inflammatory mediators. This is the pathophysiology of Goodpasture Syndrome or Rheumatic Fever.

Finally, antibodies can bind to receptors, and impair function by activating or blocking their signalling. This is the pathogenesis behind myasthenia gravis and Grave’s disease.

Key Points

  • Type II Hypersensitivity Reactions (T2HSR)
    • Type of unwanted immune response
    • Mediated by antibodies binding to cell-surface antigens
    • Outcomes
      • Cell Destruction
        • Binding by antibodies leads to phagocytosis, Classical Complement Activation, or NK Cell-mediated killing
          • Examples
            • Hemolysis in autoimmune hemolytic anemia, hemolytic disease of the newborn, or AHTR
            • Immune thrombocytopenia (ITP)
      • Inflammation
        • Binding by antibodies activates complement system and Fc receptor-mediated inflammation
        • Examples
          • Goodpasture syndrome
          • Rheumatic fever
          • Hyperacute transplant rejection
      • Binding to Receptors
        • Antibodies bind to cell surface receptors and act as agonists or antagonists
        • Examples
          • Myasthenia gravis
          • Graves disease
          • Pemphigus vulgaris