Immunohistochemical distinction between amyloidosis and fibrillar glomerulopathy.

Six patients with glomerulonephritis and glomerular proteinaceous deposits constituted by fibrillar ultrastructures similar to those of amyloid but lacking the Congo red tinctorial affinity characterizing amyloid were studied. Clinically, these patients had proteinuria and hematuria; in addition, three patients had hypertension and one renal failure. Protein deposits in their kidney biopsy sections were evaluated by immunofluorescence, immunoperoxidase, and immunoelectron microscopic (protein A-gold) techniques, using antibodies against IgG, IgA, IgM, C3, C1q, fibrinogen, immunoglobulin kappa and lambda light chains, and against amyloid fibril proteins of different types, including AA, A lambda, A kappa, and AF. By immunofluorescence and immunoperoxidase, in all cases the deposits stained intensely with antibodies against IgG, C3, and kappa and lambda light chains; one case also showed C1q immunoreactivity. By contrast, none stained with antibodies against various amyloid fibril proteins. Immunoelectron microscopic findings corroborated this data, indicating that the nonamyloid fibrillar deposits studied are antigenically distinct from known amyloid deposits and that they contain IgG-derived material.