Human regulatory B cells control the TFH cell response

Background Follicular helper T (TFH) cells support terminal B-cell differentiation. Human regulatory B (Breg) cells modulate cellular responses, but their control of TFH cell–dependent humoral immune responses is unknown. Objective We sought to assess the role of Breg cells on TFH cell development and function. Methods Human T cells were polyclonally stimulated in the presence of IL-12 and IL-21 to generate TFH cells. They were cocultured with B cells to induce their terminal differentiation. Breg cells were included in these cultures, and their effects were evaluated by using flow cytometry and ELISA. Results B-cell lymphoma 6, IL-21, inducible costimulator, CXCR5, and programmed cell death protein 1 (PD-1) expressions increased on stimulated human T cells, characterizing TFH cell maturation. In cocultures they differentiated B cells into CD138+ plasma and IgD−CD27+ memory cells and triggered immunoglobulin secretions. Breg cells obtained by Toll-like receptor 9 and CD40 activation of B cells prevented TFH cell development. Added to TFH cell and B-cell cocultures, they inhibited B-cell differentiation, impeded immunoglobulin secretions, and expanded Foxp3+CXCR5+PD-1+ follicular regulatory T cells. Breg cells modulated IL-21 receptor expressions on TFH cells and B cells, and their suppressive activities involved CD40, CD80, CD86, and intercellular adhesion molecule interactions and required production of IL-10 and TGF-β. Conclusion Human Breg cells control TFH cell maturation, expand follicular regulatory T cells, and inhibit the TFH cell–mediated antibody secretion. These novel observations demonstrate a role for the Breg cell in germinal center reactions and suggest that deficient activities might impair the TFH cell–dependent control of humoral immunity and might lead to the development of aberrant autoimmune responses.