Increased serum levels of IgA1-IgG immune complexes and anti-F(ab')2 antibodies in patients with primary IgA nephropathy

A solid-phase ELISA was used to detect IgA1 immune complexes (IgA1 ICs) containing IgG and IgM in 38 serum samples from 30 patients with primary IgA nephropathy (IgAN) and 14 subjects with non-IgA chronic glomerulonephritis. A jackfruit lectin, jacalin, was used as the substrate for the selective binding of human IgA1 ICs in serum PEG precipitate (7%). The presence of IgG, A and M antibodies against the F(ab')2 region of IgG was also investigated by the solid-phase ELISA. Six patients were studied during remission and relapse (fever, upper respiratory tract infection and macroheamaturia). The results showed significant increases in serum levels of IgA1 ICs (P less than 0.001) in 39.4% of the IgAN patients, IgA1-IgG ICs (P less than 0.001) in 68.4%, and IgA1-IgM ICs (P less than 0.002) in 10.5% of the patients. A significant increase in IgA1-IgG ICs was observed during relapse (P less than 0.02). Significantly high values of IgG (P less than 0.003) and IgA (P less than 0.001) antibodies directed at the F(ab')2 region of IgG were found. A significant increase in anti F(ab')2 antibodies (class IgA and IgM) was seen in the acute phase of the disease. The data suggest that an increased production of IgA1 ICs occurs in IgAN patients; ICs are mainly IgA1-IgG ICs during relapse. The presence of high serum levels of IgG and IgA antibodies against the F(ab')2 region of IgG indicates that in addition to the multiple anomalies of IgA regulation described in IgAN patients there may be further aberrances.