Predominant synthesis of IgA with lambda light chain in IgA nephropathy

The nature of the light chains in mesangial IgA deposits and serum IgA was studied in patients with IgA nephropathy. Immunofluorescence (IF) studies using murine monoclonal antibodies, rabbit and goat anti-human monospecific antisera were performed in kidney sections from 15 IgA nephritic patients with only IgA isotype detected in the renal biopsy. Lambda light chain IF was demonstrated in all biopsy specimens and kappa light chain IF in 11 renal biopsy specimens. The majority of renal biopsies showed a predominance of lambda light chain IF staining in the mesangial deposits. The concentration of individual immunoglobulins and their light chain fractions, and the kappa/lambda ratio were determined in the serum and the supernate from peripheral blood mononuclear cells culture of 30 IgA nephritic patients and 30 age-matched healthy controls. The IgA nephritic patients had a higher serum concentration of total IgA (P less than 0.001) and a significantly lower IgA kappa/lambda ratio (P less than 0.001) compared with the controls. The kappa/lambda ratio of supernatant IgA from IgA nephritic patients (N = 20) was also significantly lower than that of the normal subjects (N = 14), both in the unstimulated (P less than 0.01) and pokeweed mitogen stimulated, peripheral blood mononuclear-cell culture (P less than 0.05). Our results showed that patients with primary IgA nephropathy displayed a unique immunologic response characterized by a predominance of IgA with lambda light chain in circulation.