Purpose.  Aberrant O‐glycosylation of serum IgA₁ is presumed to be one of the main pathogenesis of immunoglobulin A nephropathy (IgAN). β1,3‐galactosyltransferase (β1,3GT), whose activity requires coexistence of a specific chaperone, is the main enzyme which participate in the glycosylation process. The current study was carried out to elucidate the expression level of β1,3GT (C1GALT1) and its chaperone (Cosmc) in IgAN, and their relationships with clinical features as well as IgA glycosylation level.

Design, setting and subjects.  Forty‐one patients with IgAN, 21 patients with non‐IgAN glomerulonephritis and 26 normal controls were included in the present study. Peripheral B lymphocytes were isolated, and then expression level of C1GALT1 and Cosmc were quantitatively measured by real‐time reverse transcriptase polymerase chain reaction (RT‐PCR). Serum IgA level and glycosylation level were determined by enzyme‐linked immunosorbent assay (ELISA) and VV lectin‐binding method. Correlation analysis was performed between C1GALT1/Cosmc expression levels and clinical manifestations (severe proteinuria, renal dysfunction, gross haematuria).

Results.  B‐lymphocyte Cosmc gene expression level was significantly lower in IgAN patients than that of normal control and non‐IgAN patients (P < 0.05), whilst no apparent disparity was observed in C1GALT1 expression level. Cosmc expression showed a negative correlation with IgA O‐glycosylation level indicated by VV lectin‐binding assay. Statistical analysis also indicated that the level of Cosmc expression was negatively correlated with severe proteinuria (P < 0.05) instead of gross haematuria (P > 0.05).

Conclusion.  These data suggested that the aberrant IgA O‐glycosylation in IgAN was resulted from a downregulation of β1,3GT chaperone (Cosmc) expression in B lymphocyte, which is closely associated with clinical characteristics of the disease. This downregulation might be one of the fundamental pathogenic abnormalities in IgAN.