The role of receptor molecules for IgA in the pathogenic mechanism of IgA nephropathy

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The purpose of this study was to elucidate the mechanism of mesangial IgA deposition in IgA nephropathy, especially through investigating the dynamics of receptors for IgA molecules and their metabolisms. Three molecules, pIgR (polymeric immuno-globulin receptor), FcαR, and ASGPR (asyaloglycoprotein receptor), have been known as receptor molecules for IgA. In addition, fourth molecules, TfR (Transferrin receptor), has recently been identified as receptor of IgA. It has been shown that the expression of TfR is upregulated in glomeruli of patients with IgAN, suggesting that TfR plays a role in formation of pathological immune complex in this disease.In this study, we investigated the possible associations of genetic polymorphisms in these receptor molecules and IgAN. However, we did not find any significant association of FcαR, ASGPR, and TfR polymorphisms and IgAN.During the last decade, several lines of evidence have been reported indicating that incompleteness of O-glycosylation in the IgAl hinge region may be a plausible cause of the IgAl deposition. O-Glycans are found in many glycoproteins, particularly in secretory glycoproteins. The common core 1 O-glycan structure, Galb-1-3GalNAc-R, is a precursor for many extended mucin-type O-glycan structures on animal cell surfaces and secreted glycoproteins including IgAl. We also have published a review paper about this notion in Kidney International (Narita I, et al. 2007).