Light chain ratios of serum immunoglobulins in disease.

We have determined the individual kappa (kappa)/lambda (lambda) ratios of serum IgG, IgA, and IgM in normal subjects and patients with rheumatoid arthritis, systemic lupus erythematosus, hepatic cirrhosis and IgA nephropathy--40 in each group. Serum samples were first screened by agarose electrophoresis to exclude paraproteinaemia. Concentrations of IgG, IgA, and IgM were determined by enzyme-linked immunosorbent assay (ELISA). The kappa and lambda chain concentrations of each immunoglobulin class were assayed by an ELISA method first developed by us for the determination of kappa/lambda ratios. Our results showed that kappa/lambda ratios of serum IgA and IgM were significantly different from that of IgG in normal subjects and the 4 groups of patients studied (p less than 0.01). The kappa/lambda ratios of individual immunoglobulins in patients with rheumatoid arthritis, systemic lupus erythematosus and liver cirrhosis were similar to those of normal subjects. However, patients with IgA nephropathy displayed a distinctly lower IgA kappa/lambda ratio, suggesting a unique antibody response in the immunopathogenesis of this disease.