Protein A-gold immunoelectron microscopic study of amyloid fibrils, granular deposits, and fibrillar luminal aggregates in renal amyloidosis.

Glomeruli of archival renal biopsies, stored frozen at -70 degrees C, from three patients with amyloid were examined by protein A-gold immunoelectron microscopy. In one with both fibrillar and granular deposits from a 'skin popper' drug abuser, the granular deposits were labeled with anti-IgG, while the fibrillar deposits were labeled with anti-amyloid-A (AA) protein and amyloid P component (AP), suggesting coexisting immune complex disease and AA due to different, but possibly related, pathogenesis. In studies using double-label immunostaining of primary amyloidosis-lambda light chain type (AL) and AA associated with Crohn's disease, AP occurred as widely separated single units along the amyloid fibrils and represented 1.5% and 6.5% of the total gold label in AL and AA, respectively, while the major fibril protein was labeled in single rows, similar to beads on a string. Fibrillar aggregates in the capillary lumens were labeled similarly by antisera to the major protein and AP and appeared to be contiguous with the fibrillar deposits at the glomerular basement membrane (GBM)-luminal interface, suggesting intravascular fibrillogenesis.