Ultrastructural immunohistochemistry of glomerulonephritis in needle biopsy

In two patients with glomerulonephritis (GN) IgG and C 3 were visualized in ultrastructure by means of HRP-conjugated antisera. The first patient had an acute postinfectious extra-intracapillary GN lasting for about two months with granular fluorescence of anti-IgG, -C 3, and -C 1q. Electron microscopy revealed widespread endothelial defects, a well-pronounced polymorphonuclear stasis, and typical perimembranous "humps". These deposits reacted with HRP-anti-C 3 but the ultrastructural proof of IgG was negative. A weak and sporadic reaction of both these conjugates was seen in the swollen mesangial matrix while intraluminal plugs of coagulated plasma and extracapillary exudates yielded a dense coarse reaction product. In the second patient (allograft, three years after transplantation) the membranous and proliferative probably recurrent GN with nephrotic syndrome showed massive perimembranous deposits in the late involution stage. Granular fluorescence of the main Ig classes and of C 3 was sporadic or absent. In the ultrastructural immunoenzyme assay, too, the residues of deposits failed to react with HRP-anti-IgG or -C 3 and the mesangial matrix harboured only sporadic foci of faint positivity; however, dense product was again seen in capillary plasmatic "microthrombi". The discrepancy between immunofluorescence microscopy and immunoenzyme histochemistry, noted also by others in experimental glomerulopathies, may reflect the instability and dynamic properties of immune deposits with an early loss of antibody reactivity and a more protracted though not persistent local activation of complement. In light microscopy, fluorescent granules may correspond not only to the sites of immune deposition but also to accidental intracapillary plasma precipitates.