Light-chain ratio of serum IgA1 in IgA nephropathy.

Patients with primary IgA nephropathy have deposits of IgA1 in their kidneys and increased IgA1 in circulation. We had previously shown that IgA nephritic patients displayed a unique immunological response characterized by a predominance of IgA with lambda chain in glomerular deposits and in circulation. We have now studied the kappa/lambda (kappa/lambda) ratio of serum IgA1 in 21 IgA nephritic patients at quiescence, with 11 patients investigated during exacerbation as well. A novel enzyme-linked immunosorbent assay was used with monoclonal mouse anti-human IgA1 as the solid-phase capture antibody and peroxidase-labeled anti-human kappa and lambda antibodies as tracers. The ratio of serum IgA1 to total IgA (mean +/- SD) was significantly higher in patients (90.1 +/- 8.2% at quiescence, P less than 0.01; 88.7 +/- 8.1% during exacerbation, P less than 0.02) than in 20 healthy age- and sex-matched controls (80.0 +/- 9.8%). Furthermore, serum IgA1 kappa/lambda ratios were significantly lower in patients (1.02 +/- 0.27 at quiescence, P less than 0.01; 0.93 +/- 0.16 during exacerbation, P less than 0.01) than in controls (1.31 +/- 0.30). These findings indicate a predominance of lambda light-chain IgA1 in the serum of IgA nephritic patients. However, no difference in IgA1 kappa/lambda ratio was observed in these patients at quiescence and during exacerbation.