Deposition of polymeric IgA1 in idiopathic mesangial IgA-glomerulonephritis

IgA deposits in kidney and skin biopsies from patients with idiopathic mesangial IgA-glomerulonephritis were characterized with immunofluorescence microscopy using monoclonal antibodies against the IgA subclasses IgA1 and IgA2. IgA1 was the major constituent in all biopsy specimens. Double immunofluorescence microscopy showed that IgA deposits were constantly associated with J-chain. Secretory component was never found in the deposited material. In vitro fixation of free secretory component, however, was observed in some biopsies. These findings indicate that most if not all of the deposited IgA in patients with idiopathic IgA-glomerulonephritis is polymeric in nature.