Mechanisms of Hypersensitivity Reactions

Type III Hypersensitivity: Immune Complex-Mediated Responses

Type III hypersensitivity is characterized by the formation and deposition of immune complexes, leading to inflammation and tissue damage. These reactions involve antigen-antibody complexes that precipitate in various tissues, triggering complement activation and inflammatory responses.

Pathogenesis

• Immune complexes form when antigens bind to antibodies.
• These complexes deposit in blood vessel walls, joints, and glomeruli.
• Complement activation results in recruitment of inflammatory cells.
• Tissue damage occurs due to neutrophil infiltration and enzymatic release.

Clinical Manifestations

Type III hypersensitivity can result in several clinical conditions, including:

• Serum sickness
• Systemic lupus erythematosus (SLE)
• Post-streptococcal glomerulonephritis
• Arthus reaction

Diagnosis and Treatment

Diagnosis involves detecting circulating immune complexes and complement activation markers. Treatment typically includes immunosuppressive therapy, corticosteroids, and plasmapheresis to remove pathogenic immune complexes.