A 24-year-old woman with systemic lupus erythematosus has elevated serum levels of anti-dsDNA antibodies. The renal biopsy shows granular deposits along the glomerular basement membrane on immunofluorescence. The tissue damage in this scenario is primarily mediated by which mechanism of hypersensitivity?

• A Type I — mast cell degranulation via IgE cross-linking
• B Type II — complement-mediated cytotoxicity via IgG
• C Type III — immune-complex deposition and complement activation ✓
• D Type IV — CD8+ T-cell direct cytotoxicity

Explanation

SLE nephritis is the classical example of Type III (immune-complex) hypersensitivity. Circulating anti-dsDNA/complement complexes deposit in glomeruli, activate complement (especially C3 and C5), and recruit neutrophils causing an Arthus-type reaction. Granular (lumpy-bumpy) IF pattern distinguishes it from anti-GBM disease (linear IF, Type II).

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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