Barbosa, R. R.Silva, S. P.Silva, S. L.Melo, A. C.Pedro, E.Barbosa, M. P.Pereira-Santos, M. C.Victorino, R. M.Sousa, A. E.2015-06-172015-06-172011PLoS ONE August 2011 | Volume 6 | Issue 8 | e228481932-6203http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022848http://dx.doi.org/10.1371/journal.pone.0022848http://hdl.handle.net/10451/18307© 2011 Barbosa et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.IL-17 is a pro-inflammatory cytokine implicated in autoimmune and inflammatory conditions. The development/survival of IL-17-producing CD4 T cells (Th17) share critical cues with B-cell differentiation and the circulating follicular T helper subset was recently shown to be enriched in Th17 cells able to help B-cell differentiation. We investigated a putative link between Th17-cell homeostasis and B cells by studying the Th17-cell compartment in primary B-cell immunodeficiencies. Common Variable Immunodeficiency Disorders (CVID), defined by defects in B-cell differentiation into plasma and memory B cells, are frequently associated with autoimmune and inflammatory manifestations but we found no relationship between these and Th17-cell frequency. In fact, CVID patients showed a decrease in Th17-cell frequency in parallel with the expansion of activated non-differentiated B cells (CD21(low)CD38(low)). Moreover, Congenital Agammaglobulinemia patients, lacking B cells due to impaired early B-cell development, had a severe reduction of circulating Th17 cells. Finally, we found a direct correlation in healthy individuals between circulating Th17-cell frequency and both switched-memory B cells and serum BAFF levels, a crucial cytokine for B-cell survival. Overall, our data support a relationship between Th17-cell homeostasis and B-cell maturation, with implications for the understanding of the pathogenesis of inflammatory/autoimmune diseases and the physiology of B-cell depleting therapies.engjournal article