CTLA-4-mediated suppressor effect by human T follicular regulatory cells (IRC11P.432)

Abstract

Abstract T follicular helper (Tfh) cells, a subset of CD4 T cells, help B cells produce high affinity class switched antibodies and are essential for generation of germinal centers (GC). T follicular regulatory cells (Tfr) are a newly defined regulatory CD4 T cell subset that suppresses GC formation and B cell function through CTLA-4 dependent mechanisms in murine models. We will test the hypothesis in human systems that Tfr have significant regulatory effects on antibody production in a CTLA-4 dependent manner. Tfh and Tfr cells from human mesenteric lymph nodes were analyzed using flow cytometry. Tfr were defined as CXCR5+, PD-1bright, FoxP3+ cells that were also found to be Bcl6+, CD25+, CD127dim, ICOS+. Flow sorted Tfr and Tfh cells were used to determine the effect of Tfr on Tfh-mediated B cell production of IgG. Tfh cells with mitogen helped B cells produce high amounts of IgG whereas addition of Tfr to this co-culture decreased the IgG levels >90%. Tfh/Tfh ratio directly impacts levels of suppression. The mechanism of the suppressive effect of Tfr cells was investigated by neutralizing IL-10, TGF-β RII and CTLA-4 in the co-culture functional assay. Only anti-CTLA-4 affected IgG production. The present study in the human system suggests that Tfr cells suppressed Tfh-induced antibody production by B cells with CTLA-4 playing an important role in this suppression. These regulatory interactions may play a role in autoimmune diseases and humoral response to vaccines and pathogens.