Anti-mesangial and anti-endothelial cell antibodies in IgA mesangial nephropathy.

In the present study we verified by solid phase ELISA the presence of antibodies against mesangial and endothelial cell constituents in patients with IgA-GN and Schoenlein-Henoch syndrome (SH). An antigen extract was prepared by sonication of human mesangial cell (MC) monolayers between third and fifth subculture and coated at 20 micrograms/ml on microtiter plates where sera were tested by incubation for 2 h at 37 degrees C and addition of peroxidase-conjugated anti-human IgG or IgA. In comparison to 86 normal controls, increased levels of IgG anti-MC antibodies were found in 15/84 patients with IgA-GN and 4/11 with SH. IgA antibodies were always negative. Furthermore anti-endothelial cell antibodies (AECA) were sought in the same patients and controls by ELISA as previously described. Increased levels of IgG and IgA AECA were found in 25/62 and 24/46 patients respectively. A cross-inhibition test showed that preadsorbment of positive sera for both IgG anti-MC and IgG AECA on endothelial cells in culture resulted in an inhibited binding of IgG to MC. HPLC-ELISA and Western blot analysis of the MC extract showed a significant binding of IgG from ELISA-positive sera to a protein band of 25-50 kD. Similar results were obtained by Western blot analysis of an endothelial cell extract. These results suggest the identity of the antigens recognized by IgG antibodies on endothelial cells and MC in patients with IgA-GN.