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Background Follicular helper T (T FH ) cells support terminal B-cell differentiation. Human regulatory B (Breg) cells modulate cellular responses, but their control of T FH cell–dependent humoral immune responses is unknown. Objective We sought to assess the role of Breg cells on T FH cell development and function. Methods Human T cells were polyclonally stimulated in the presence of IL-12 and IL-21 to generate T FH 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 T FH 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 T FH cell development. Added to T FH 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 T FH 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 T FH cell maturation, expand follicular regulatory T cells, and inhibit the T FH 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 T FH cell–dependent control of humoral immunity and might lead to the development of aberrant autoimmune responses.

International audience; BACKGROUND AND OBJECTIVES: Follicular helper T (Tfh) cells are instrumental in the development of humoral responses. They support the terminal differentiation of B cells into memory and antibody-producing cells within germinal centers. Regulatory B (Breg) cells can modulate inflammatory reactions through the control of dendritic cell maturation and function, and through the control of T cell proliferation and Th1 polarization. Our aimed was to evaluate the control of humoral responses by Breg cells. MATERIALS AND METHODS: We developed in vitro models of human Tfh cell polarisation and function. They were obtained by stimulation of purified T cells with anti-CD3 and anti-CD28 Abs in the presence of IL-12 and IL-21. Expression of Bcl-6, IL-21, ICOS, CXCR5 and PD-1, all characteristics of Tfh cells were determined by flow cytometry. Tfh functions were studied by co-cultures with non-stimulated purified B cells. Their differentiation into memory and plasma cells was appraised by flow cytometry and by ELISA to measure the production of immunolgobulins. Breg cells were obtained by stimulation of purified B cells with CpG-ODN on CD40L-transfected fibroblasts. Their effect on Tfh cell maturation and function were studied in co-culture experiments. RESULTS: in vitro Tfh cells were obtained. Thus, Bcl-6 was up-regulated, IL-21 induced and ICOS, CXCR5 and PD-1 expression increased after stimulation. Furthermore, differentiated Tfh cells fostered the maturation of IgD-CD27 + memory B cells and CD138 + plasma cells, and triggered the secretion of IgM, IgG and IgA. Added to the T cells, Breg cells restrained the expression of Tfh markers. In the co-cultures of Tfh with B cells, Breg cells inhibited the induction of IgD-CD27 + and CD138 + B cells. They also impeded the secretion of immunoglobulins. Using blocking antibodies, suppressive activities of Bregs were found to be dependent on IL-10 and TGFbeta and based on direct contact with Tfh cells involving CD40, CD80, CD86 and CD54 molecules. CONCLUSIONS: Human Breg cells can modulate the development of humoral responses through the control of Tfh cell polarization and of Tfh-dependent terminal differentiation of B cells. Whether these properties are impaired and responsible for abnormal humoral responses in autoimmune diseases needs now to be established.

International audience; Mechanims of peripheral tolerance include molecular controls and the presence of regulatory lymphocytes. Regulatory T lymphocytes (Tregs) correspond to different sub-populations of T cells that control immune responses due to the production of cytokines, such as IL-10 and with direct cell-to-cell contacts. Tregs targets are antigen presenting cells, such as dendritic cells, effector CD4(+) and CD8(+) lymphocytes but also effector antibody-producing B lymphocytes. Regulatory B lymphocytes (Bregs) have been more recently described and likely represent different sub-populations of B cells that control the development of autoimmune and inflammatory diseases due to the production of IL-10 and using intercellular contacts. Bregs targets encompass all the cells involved in the immune responses which are thus under a dual control by regulatory lymphocytes. Development and efficient activity of Tregs appear dependent of Bregs for a better regulation of autoimmune reactions, of anti-infectious reactions, but also of anti-tumor reactions.

Backgroundand objectives Mature dendritic cells (DCs) are stimulators of T cell immune response, whereas immature DCs support T cell tolerance. Murine B cells can inhibit the production of interleukin 12 (IL-12) by DCs, and thereby, hinder the inflammatory response. Notwithstanding the importance of this modulation, only a few studies are available in humans. The current study was aimed at determining the regulatory capacity of human B cells on DC maturation and function, and at evaluating their efficiency in autoimmune disorder. Materials and methods Peripheral blood B cells from six healthy donors (HDs) and six systemic lupus erythematosus (SLE) patients were stimulated by CD40 and TLR9. Peripheral blood monocytes were differentiated into immature DCs and then into mature DCs. Activated B cells were co-cultured with DCs and HLA-DR, CD80, CD86 expressions and IL-12 production by the DCs evaluated by flow cytometry. Variations of expressions were used to determine the B cell regulatory effects on maturation. CFSE-labelled T cells were cultured with mature DCs and the DC-dependent proliferative response evaluated in the presence of activated B cells to determine their influence on the function of DCs. Results Activated B cells restrained the development of monocytes into immature DCs and their differentiation into mature DCs. They decreased the density of HLA-DR from mature DCs, the expression of CD80 and CD86 co-activation molecules, the production of IL-12p70 required for antigen presentation and Th1 differentiation. They also inhibited the DC-induced T cell proliferation. These modulations were mediated by CD19+IgDlowCD38+CD24lowCD27- B cells and needed CD62L interaction for the control of CD80 and CD86 expression, and a soluble factor for the control of IL-12 production. Finally, mature DCs from SLE patients displayed insensitivity to the regulation of IL-12 by both normal and SLE B cells. Conclusions Human B cells can regulate DC maturation and function. However, they are inefficient in SLE due to refractory DCs. This may influence an improper balance between an effector inflammatory response triggered by mature DCs, and tolerance induction favoured by immature DCs, and thereby, may contribute to the pathogenesis of SLE.