Plexin B1 expression on human Treg cells is required for regulation of their phenotypic stability by semaphorin 4A

Abstract

Abstract We previously reported that neuroimmune semaphorin (Sema) 4A regulates the severity of experimental allergic asthma and increases regulatory T-cell (Treg) numbers in vivo, however the mechanisms of Sema4A action remain unknown. It was also reported that Sema4A controls murine Treg cell function and survival acting through Neuropilin 1 (NRP-1) receptor. To clarify Sema4A action on human T cells, we employed T-cell lines, HuT78 and HuT102, as well as human PBMCs and CD4+ T cells in phenotypic and functional assays. We found that HuT78 demonstrated a T-effector-like phenotype (CD4+CD25lowFoxp3-), while HuT102 expressed a Treg-like phenotype (CD4+CD25hi Foxp3+). Neither cell line expressed NRP-1. However, HuT102 cells expressed high levels of the Sema4A-counter receptor, Plexin B1 whereas HuT78 cells demonstrated high cell-surface expression of Sema4A. All human peripheral blood CD4+ T cells, including Treg cells, expressed PlexinB1 and lacked both, NRP-1 and −2. Culture of HuT cells with soluble Sema4A led to an upregulation of CD25 and Foxp3 markers on HuT102 cells. Addition of soluble Sema4A increased the relative numbers of CD4+CD25+Foxp3+ cells in PBMC and CD4+ T cells which did not express NRP-1 but were PlexinB1+, suggesting the role of this receptor in Treg cell stability. The inclusion of anti-PlexinB1 blocking Ab in cultures before rSema4A addition significantly decreased Treg cell numbers as compared to cultures with rSema4A alone. Sema4A was as effective as TGF-b in iTreg induction from CD4+CD25depleted cells but did not affect Treg cell suppressive activity in vitro. These results suggest strategies for the development of new Sema4A-based therapeutic measures to combat allergic inflammatory diseases.