CD4＋CXCR5＋ T cells activate CD27＋IgG＋ B cells via IL-21 in patients with hepatitis C virus infection

BACKGROUND： Chronic hepatitis C virus （HCV） infection causes the skewing and activation of B cell subsets, but the characteristics of IgG＋ B cells in patients with chronic hepa- titis C （CHC） infection have not been thoroughly elucidated. CD4＋CXCR5＋ follicular helper T （Tfh） cells, via interleukin （IL）-21 secretion, activate B cells. However, the role of CD4＋CXCR5＋ T cells in the activation ofIgG＋ B cells in CHC patients is not clear. METHODS： The frequency of IgG＋ B cells, including CD27-IgG＋ B and CD27＋IgG＋ B cells, the expression of the activation markers （CD86 and CD95） in IgG＋ B cells, and the percentage of circu- lating CD4＋CXCR5＋ T cells were detected by flow cytometry in CHC patients （n=70） and healthy controls （n=25）. The con- centrations of serum IL-21 were analyzed using ELISA. The role of CD4＋CXCR5＋ T cells in the activation of IgG＋ B cells was investigated using a co-culture system. RESULTS： A significantly lower proportion of CD27＋IgG＋ B cells with increased expression of CD86 and CD95 was observed in CHC patients. The expression of CD95 was negatively correlated with the percentage of CD27＋IgG＋ B cells, and it contributed to CD27＋IgG＋ B cell apoptosis. Circulating CD4＋CXCR5＋ T cells and serum IL-21 were significantly increased in CHC patients. Moreover, circulating CD4＋CXCR5＋ T cells from CHC patients induced higher expressions of CD86 and CD95 in CD27＋IgG＋ B cells in a co-culture system; the blockade of the IL-21 decreased the expression levels of CD86 and CD95 in CD27＋IgG＋ B cells.CONCLUSIONS： HCV infection increased the frequency of CD4＋CXCR5＋ T cells and decreased the frequency of CD27＋IgG＋ B cells. CD4＋CXCR5＋ T cells activated CD27＋IgG＋ B cells via the secretion of IL-21.