Glycosylation profile of differently charged IgA1 and their binding characteristics to cultured mesangial cells in IgA nephropathy

Abstract

Background: IgA nephropathy (IgAN) is characterized by mesangial deposition of polymeric IgA1 (pIgA1), yet the pathogeneic mechanism remains unresolved. In the present study, we examined the glycosylation profile of differently charged IgA1 from IgAN patients. The binding characteristics of these IgA1 fractions to cultured human mesangial cells (HMC) and hepatoma cell lines (HepG2) were studied.

Methods: Differently charged IgA1 were isolated by ion exchange chromatography. The glycosylation profile in the carbohydrate moieties of these differently charged IgA1 was analyzed by galactose (Gal)-, galactose-acetylgalactosamine (Gal-GalNAc)-, or sialic acid-specific enzyme-linked lectin binding assays (ELLA). The binding characteristic of these IgA1 to HMC was examined by flow cytometry and competitive binding assay.

Results: Anionic pIgA from IgAN patients showed less reactivity in (Gal)- and (Gal-GalNAc)-specific ELLA (p < 0.01). There was higher reactivity for anionic pIgA1 in alpha(2,6)-linked sialic acid-specific ELLA (p < 0.01). Anionic pIgA1 from IgAN patients exhibited increased binding to cultured HMC and the binding was significantly reduced after neuraminidase treatment (p < 0.05). In contrast, anionic pIgA1 from IgAN patients bound less to cultured HepG2 cells and the binding was enhanced following neuraminidase treatment (p < 0.05).

Conclusions: We demonstrated an unusual glycosylation and sialylation pattern of anionic pIgA1 in IgAN which may have an important effect on its pathogenesis.