| Objective: IgA nephropathy (IgAN) is the most common form ofglomerulonephritis in the world, and in China it has became the main cause ofglomerular disease in chronic renal failure, approximately20%~50%patientsprogressed to end-stage renal disease(ESRD) within25years. The infection rateof Helicobacter pylori (Hp) is very high in China and the Asia Pacific region.Recent studies have suggested that Hp infection is associated with IgAN, butthe underlying molecular mechanism remains unclear. This study was toinvestigate the effects of cytotoxin associated gene A protein (CagA), a majorvirulence factor of Hp, on the production and underglycosylation of IgA1in a Bcell line. Methods: The surface IgA1-positive human B lymphoma cell line,DAKIKI, was cultured and stimulated by recombinant CagA protein. Fordose-dependent test, cell was cultured for48h with different dose (0.2μg/ml,0.4μ g/ml,0.8μ g/ml,1.6μ g/ml,3.2μ g/ml) of CagA. Fortime-dependent test, cell was cultured for24,48and72h. Then cellproliferation was examined by cell counting. The production and glycosylationof IgA1in supernatants were determined by ELISA and helix aspersa (HAA)lectin binding assay, respectively. For the mechanism of O-glycosylation study，cell was stimulated with1.6μg/ml CagA,12.5μg/ml lipopolysaccharide (LPS) for48h,and the expression level of C1GALT1and Cosmc were measured byreal time RT-PCR and Western blot. Results: For dose-dependent test, lowconcentration of CagA stimulated cell proliferation with CCK8and Cellcounting. However,3.2μg/ml of CagA inhibited cell proliferation. Moreover,while the dose within the range of0.2~3.2μg/ml, CagA stimulated theproduction of IgA1,1.6μg/ml of CagA significantly increased the productionof IgA1.1.6μg/ml and3.2μg/ml of CagA promoted the underglycosylation ofIgA1. For time-dependent test,1.6μg/ml of CagA stimulated the productionand underglycosylation of IgA1in a time-dependent manner. The expressionlevel of C1GALT1and Cosmc is significantly lower in cell stimulated by CagAor positive control(LPS) than control, but the effect of CagA was little weakerthan that ofμg/ml of LPS. Conclusions: CagA protein from Hp infectionpromoted the B cell proliferation and accompanied by increased IgA1production in vitro. CagA protein also induced underglycosylation of IgA1. Themolecular mechanisms for the underglycosylation of IgA1, at least partly,attributed to the downregulation of C1GALT1, an important enzyme in theglycosylation process of IgA1, and its chaperone Cosmc. These resultssuggested that Hp infection may play an important role in the pathogenesis ofIgAN，and anti-Hp or anti-CagA regime may be helpful for the treatment ofIgAN with Hp infection in the future. |
