Renal function, protein excretion, and pathology of Balkan endemic nephropathy. IV. Immunohistology.

Few controversial observations on the deposition of immunoglobulins (Igs) and complement components in kidney biopsies of Balkan endemic nephropathy (BEN) patients have been reported. In the present study, direct or indirect immunofluorescence testing of the deposition of IgA, IgG, IgM, C3, C1q, C4 fibrin/fibrinogen, albumin, B2-microglobulin (beta 2m) and Tamm-Horsfall glycoprotein (THG) on frozen renal tissue sections was performed in 52 BEN patients. Glomerular findings were negative or mostly insignificant, with mild or moderate mesangial deposition of IgM in 16, IgA in 11, IgG in three, C3 in 15, C1q in two, C4 in one and fibrin/fibrinogen in two cases, respectively. The predominance of mesangial IgA deposits in five cases suggested IgA glomerulonephritis (GN) concomitant with BEN. Homogeneous lumpy or granular deposits in small extraglomerular vessels contained IgM in nine, C3 in 45, C1q in three, and C4 in one case. Focal linear or granular C3 was noted along the tubular basement membrane in eight cases. Resorptive droplets in tubular epithelial cells contained Igs and albumin, while complement, fibrin/fibrinogen and THG were found in tubular casts. There was no positive reaction with anti-beta 2m and anti-THG antibodies. According to these results, humoral immune mechanisms would not appear to play a pathogenetic role in BEN. However, immunohistologic examinations are important in recognition of possible concomitant immune complex-mediated GN.