• Reactions tend to be systemic, as immune complexes are distributed via circulation throughout the body.

Pathophysiology

1. Antigen (e.g., the molecules of a drug in circulation) binds to IgG to form an immune complex (antigen-antibody complex)
2. Immune complexes are deposited in tissue, especially blood vessels → initiation of complement cascade → release of lysosomal enzymes from neutrophils → cell death → inflammation → vasculitis

Examples

• Vasculitis
  • Polyarteritis nodosa
  • Drug-induced hypersensitivity vasculitis
• Nephropathy
  • Poststreptococcal glomerulonephritis
• Hypersensitivity pneumonitis
• Systemic lupus erythematosus (e.g., lupus nephritis, hypertension, thrombosis)