Detection of polymeric IgA in glomeruli from patients with IgA nephropathy

A study on the detection of polymeric IgA in glomeruli from renal biopsy specimens in patients with IgA nephropathy is described. Renal biopsy specimens were obtained from patients with IgA nephropathy. These specimens were stained with FITC-labelled anti-human J chain antisera and then examined with a fluorescent microscope. The J chain was observed in the glomerular mesangium by immunofluorescent staining. In parallel studies, renal biopsy specimens were treated with citrate buffer (pH 3.2) and the 'eluate' was neutralized by sodium hydroxide. The eluate was labelled with iodine-125, and the radiolabelled 'eluate' was fractionated by sucrose density-gradient ultracentrifugation. Polymerized IgA in the 'eluate' obtained from patients with IgA nephropathy was found to sediment predominantly as 9S to 11S using a sucrose density gradient analysis. Polymeric IgA in the fractions of the density gradient analysis was determined by anti-human IgA and anti-human J chain antisera. It was demonstrated that IgA and J chain were eluted from the glomeruli in some patients with IgA nephropathy. It is concluded that IgA deposited in the glomeruli is composed of dimers and/or larger polymers of circulating IgA in some patients with IgA nephropathy.