What is the typical immunofluorescence finding in Goodpasture syndrome?

• A. Granular IgG deposits along basement membranes
• B. C3 deposition without immunoglobulins
• C. Linear IgG deposits along glomerular and alveolar basement membranes
• D. IgA deposition in the mesangium

Answer: (C)

Goodpasture syndrome is caused by autoantibodies against basement membrane type IV collagen, so the deposition pattern on immunofluorescence is a continuous, linear line of IgG along the glomerular basement membrane and the alveolar basement membrane. This linear staining reflects antibodies bound directly to the basement membranes, rather than immune complexes forming discrete clumps. C3 can be present as well, but the hallmark is the smooth, linear IgG along the membranes. This differs from granular, clumped IgG deposits seen in immune complex diseases like membranous nephropathy or post-infectious GN, and from IgA deposition in the mesangium seen in IgA nephropathy. The linear IgG pattern helps distinguish Goodpasture and guides therapy such as plasmapheresis to remove the offending antibodies.