What pattern is seen on immunofluorescence in immune complex–mediated glomerulonephritis?

• A. Linear deposition of IgG along the GBM
• B. Granular deposition of IgG, IgM, and C3
• C. No immune complex deposition
• D. Granular deposition of IgA and C3 only

Answer: (B)

In this pattern, immune complexes deposit along the glomerular basement membrane and in the mesangium in a granular, patchy way, producing a “lumpy-bumpy” appearance on immunofluorescence. The immunofluorescence stains show multiple discrete spots of IgG and often IgM together with C3, reflecting the presence of antigen–antibody complexes and activated complement. This granular deposition is characteristic of immune complex–mediated glomerulonephritis, such as post-infectious or membranous types. It contrasts with a smooth, linear deposition seen in anti-GBM disease, and with pauci-immune patterns where little or no immunoglobulin or complement is detected.