ANALYSIS OF CIRCULATING IGA AND DETECTION OF IMMUNE-COMPLEXES IN PRIMARY IGA NEPHROPATHY

Abstract

The sera of 31 patients with primary IgA nephropathy were investigated for IgA containing immune complexes by human lymphoblastoid Raji cell-binding IgA radioimmunoassay and conglutinin-binding IgA radioimmunoassay. Positive results, without correlation with IgA serum levels, were found in 68% of the patients using the 1st assay and in 39% of the patients with the 2nd assay. Positive sera were analyzed by gel chromatography. Conglutinin-binding IgA eluted in 2 peaks, a minor 1 of 400,000-800,000 daltons MW and a major 1 corresponding to monomeric IgA. No increase of secretory IgA and of polymeric IgA was detectable. IgA immune complexes were found in the sera of patients with systemic lupus (5 of 12), rheumatoid arthritis (4 of 12), subacute bacterial endocarditis (4 of 12) and hepatitis B virus hepatitis (4 of 16). The high prevalence in these sera of IgG and IgM immune complexes detected by polyethylene glycol precipitation, solid phase complement component C1q binding assay and conglutinin-binding assay contrasted strongly with their absence in IgA nephropathy. The presence of abnormal amounts of conglutinin-reactive IgA correlated with the recurrence of IgA deposits after renal transplantation (20 patients studied). Conglutinin-reactive IgA could contribute to the glomerular deposition of IgA and subsequently play a significant role in the pathogenesis of IgA nephropathy.