Using a newly-developed solid-phase radioimmunoassay for DNA-binding immunoglobulins, immunoglobulin M (IgM), immunoglobulin G (IgG) and immunoglobulin A (IgA) anti-DNA were measured in serums from 11 patients with active untreated systemic lupus erythematosus (SLE) with nephritis. All patients underwent renal biopsy and were classified according to standard criteria as having diffuse or focal proliferative glomerulonephritis. Although both groups had almost identical total anti-DNA (13.1 versus 13.9 μg/ml, respectively), the IgM to IgG ratio was significantly higher (p < 0.01) in the group with DPGN (7.51) than in the group with FPGN (1.10). We suggest that the switchover mechanism from IgM to IgG antibody production is more profoundly impaired in SLE with severe renal disease than in SLE with mild renal disease.
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