The Arthus reaction is a localized Type III hypersensitivity reaction. The key pathological sequence is:

• A IgE on mast cells → allergen cross-linking → histamine release → immediate wheal-and-flare
• B Sensitized T cells → cytokine release → macrophage activation → granuloma formation (48-72 hours)
• C Intradermal antigen → local immune complex formation with IgG → complement activation → neutrophil influx → vessel wall damage ✓
• D IgM complement-fixing antibody → C3b opsonization → phagocytic destruction of RBCs

Explanation

The Arthus reaction is a localized immune complex (Type III) hypersensitivity; injected antigen meets preformed IgG antibodies, forming complexes in vessel walls that activate complement (C3a, C5a as anaphylatoxins) and recruit neutrophils. Neutrophil degranulation causes fibrinoid necrosis of vessel walls. Type I uses IgE; Type IV uses sensitized T cells; Type II involves cell-bound antigens with IgM/IgG.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.