BK papovavirus immune complexes in glomerulonephritis.

Kidney biopsies from 98 patients were studied for BK virus (BKV) antigens by indirect immunofluorescence. Intense fluorescent staining was observed in 11/12 cases of lupus nephritis, 11/12 cases of membranous nephropathy, 21/23 cases of IgA mesangial glomerulonephritis, 3/4 cases of membrano-proliferative Glomerulonephritis and 5/12 cases of exudative glomerulonephritis. Antisera of different viruses did not react with any kidney sample. Deposition of BKV was strictly related to the presence of immunoglobulins in renal glomeruli. The specificity of reaction for antigens related to BKV was demonstrated by absorption of sera with different substances and BKV. Absorption of rabbit anti-BKV serum with human immunoglobulins completely abolished glomerular fluorescence. We conclude that the fluorescence obtained in kidney biopsies by staining with anti-BKV serum was a false positive reaction dependent on common antigenic determinants present in BKV capsid proteins and human immunoglobulins.