CD19+CD1d+CD5+ B cell frequencies are increased in patients with tuberculosis and suppress Th17 responses

Although the importance of B cells in the host immune response upon Mycobacterium tuberculosis infection has been recognized, a conclusive role for B cells has yet to be determined. In the present study, we found that primary CD19+ B cells isolated from patients with tuberculosis significantly inhibited Th17, but not Th1, cell activation. Moreover, the suppressive activity was mediated by a CD19+CD1d+CD5+ B cell population. Notably, patients with tuberculosis were found to have significantly higher frequencies of CD19+CD1d+CD5+ B cells with stronger suppressive activity than such cells from healthy donors. Furthermore, the frequency of CD19+CD1d+CD5+ B cells in peripheral blood was inversely correlated with that of Th17 cells in patients with tuberculosis. This finding that B cells negatively regulate Th17 responses provides a novel mechanism in the regulation of CD4+ T cell responses—aside from regulatory T cells—during M. tuberculosis infection, which may impact the clinical outcome of tuberculosis.