Heterogeneity of carbohydrate moieties of IgA1 molecules from IgA nephropathy patients and normal individuals

IgA nephropathy (IgAN) is characterized by the deposition of IgA1 in kidney mesangia and the presence of IgA1-containing immune complexes in the circulation. Structural studies of IgA1 isolated from sera of IgAN patients indicated a statistically significant decrease in the content of galactose (Gal). Using a combination of lectins specific for glycans in O- or N-linked glycan side chains, this Gal deficiency was restricted to O-linked glycans present in the hinge region of IgA1 molecules. Gal-deficient IgA1 displayed a significantly higher binding to mesangial cells through a putative non-internalizing receptor specific for N-acetyl galactosamine (GalNAc) in O-linked glycans. These data suggest that Gal deficiency results in diversion of IgA1 molecules from the usual degradative pathway and deposition of altered IgA1 in the mesangium.