Serum secretory IgA and IgM and free secretory component in IgA nephropathy.

IgA nephropathy (IgAN) is characterized by the presence of IgA and C3 deposits in the mesangium. Mesangial IgA is mostly dimeric IgA1 with a J chain, lacking a secretory component. In view of the recent demonstration of elevated serum levels of secretory component and secretory IgA in liver disease and HIV infection associated with hyper-IgA, we measured the serum secretory component in 50 IgAN patients and 45 controls. Free secretory component and secretory IgA and IgM levels were determined by enzyme-linked immunosorbent assay. Normal or low levels were found patients. These data support previous work suggesting that in IgAN circulating and probably mesangial IgA do not originate from the epithelial compartment of the mucosal immunoglobulins as it is the case in other hyper-IgA diseases.