SEROLOGIC STUDY OF IMMUNOGLOBULIN A-FIBRONECTIN AGGREGATES IN IMMUNOGLOBULIN-A NEPHROPATHY

The immunoglobulin A (IgA)-fibronectin aggregates, detected by enzyme- linked immunosorbent assay using either antifibronectin or collagen I as binding protein, were previously found to be raised in the circulat ion of patients with IgA nephropathy (IgAN), It has been suggested tha t IgA-fibronectin aggregates are involved in the pathogenesis and that the plasma IgA-fibronectin level may even be of diagnostic value in I gAN, Nevertheless, a recent report has questioned the specificity of t hese assays as plasma IgA may interact with immobilized IgG and these assays detect not only IgA-fibronectin, but also total plasma IgA, The se doubts render the interpretation of raised IgA-fibronectin aggregat es in IgAN impossible, We isolated total IgA, in plasma by jacalin-aga rose, Monomeric and polymeric IgA, were distinctly separated by fast p rotein liquid chromatography, When the fast protein liquid chromatogra phy fractions were analyzed for Iga-fibronectin using the antifibronec tin capture assay, increased optical density values were predominantly observed in polymeric IgA but not in monomeric IgA. Similar findings were found when the fast protein liquid chromatography fractions were studied using a novel gelatin-anti-IgA assay that avoided nonspecific interaction between plasma IgA and immobilized IgG used as the capture antibody in antifibronectin capture assay, Using our gelatin-anti-IgA assay, we failed to demonstrate a diagnostic increase in IgA-fibronec tin aggregates in polymeric IgA from patients with IgAN compared with controls, Our finding of circulating IgA-fibronectin aggregates in pat ients with IgAN comparable to those of healthy controls did not suppor t the notion that these aggregates may have a pathogenetic role or dia gnostic value in IgAN. (C) 1996 by the National Kidney Foundation, Inc .