No evidence for a specific role of IgM in mesangial proliferation of idiopathic nephrotic syndrome.

To define the relationship of mesangial IgM to various morphologic categories of idiopathic nephrotic syndrome (INS), an analysis of 100 patients was carried out in which five morphologic subgroups were evaluated: group 1, minimal glomerular change (38 patients); group 2, minimal change with focal global sclerosis (18 patients); group 3, focal segmental glomerulosclerosis ( FSG ) (23 patients); group 4, mesangial proliferation (12 patients); group 5, focal segmental glomerulosclerosis with mesangial proliferation (9 patients). Immunohistochemical studies failed to demonstrate any differences between these five groups. The intensities of immunofluorescence and the percentage of tissue samples demonstrating IgM and/or C3 in the glomerular mesangium and subendothelial regions were similar. In addition, the presence or intensity of mesangial IgM did not predict the patients' current status or responsiveness to steroid therapy. Morphologic transitions were observed in patients who had more than one biopsy: one of five in group 2 and two of eight in group 3 developed mesangial proliferation; and nine of ten patients with mesangial proliferation in the first biopsy continued to show this finding in the second. In general, a complete response to steroid therapy and a favorable outcome is less likely in patients with this morphologic abnormality. In nine of the 27 repeat biopsies, there was lack of agreement between the first and second tissue samples with respect to the presence or absence of mesangial IgM. Although mesangial proliferation is a consistent feature of the morphology of certain patients with INS, these studies do not support a unique association with mesangial IgM.