What are the typical histopathologic features of immune complex-mediated glomerulonephritis?

• A. Linear immunofluorescence with IgG, IgM, and C3 deposits; subepithelial 'humps' on EM in some cases.
• B. No immune deposits
• C. Granular immunofluorescence with IgA deposits
• D. Granular immunofluorescence with IgG alone and no C3 deposits

Answer: (A)

Immune complex–mediated glomerulonephritis is defined by granular, or “lumpy-bumpy,” immune deposits in the glomeruli. On immunofluorescence you typically see a mix of immunoglobulins (commonly IgG and IgM) with complement component C3 distributing in a granular pattern along the capillary walls and mesangium, rather than a smooth, linear line. Electron microscopy often shows electron-dense immune complex deposits, and in conditions like post-infectious GN you may see subepithelial humps. Linear deposition along the glomerular basement membrane, by contrast, indicates anti-GBM disease rather than immune complex–mediated GN. Deposits dominated by IgA or IgG without C3 don’t fit the classic immune complex pattern.