HBsAg glomerular deposits in glomerulonephritis: fact or artifact?

To evaluate the role of the hepatitis B virus infection in the pathogenesis of glomerulonephritis, we screened 136 consecutive patients with various types of glomerular lesions for the presence of HBsAg either in serum or in kidney biopsy specimens by means of radioimmunoassay and direct immunofluorescence technique, respectively. In selected patients, we carried out the search for antiglobulin activity (AA) factor(s) within the renal tissue with a fluoresceinated aggregated human IgG preparation (FITC-IgGagg). Eleven HbsAg seropositive patients were found, none of whom showed HBsAg deposits within their kidney biopsy specimen. Five of the remaining 125 seronegative patients, 3 with mixed cryoglobulinemia and 2 with lupus nephritis, showed glomerular-positive staining with a rabbit fluoresceinated anti-HBs serum and deposits of IgM endowed with AA, along with IgG and complement factors. The presence of HBsAg within the glomeruli was not confirmed, however, when a fluoresceinated anti-HBs Fab' preparation was used instead of the fluoresceinated anti-HBs serum. The pretreatment of the tissue sections with unconjugated anti-IgM serum blocked the direct staining for HBsAg and FITC-IgGagg, but not that of the other immunoreactants. Conclusion. The IgM AA deposits may interfere with the direct immunofluorescence testing for HBsAg, leading to erroneous interpretation.