Defining mechanisms of semaphorin 4A stimulatory action on human Treg cells

Abstract

Abstract We had shown previously that semaphorin 4A (Sema4A) suppresses allergic inflammation in mice (Mucosal Immunol., 2012, 5:409-19), regulates human Treg cell stability, and induces the generation of Treg cells in PBMC cultures acting through its Plexin B1 receptor (Immunohorizons, 2019, 3:78–87). Plexin B1 forms functional homodimers or heterodimers with other Plexin B molecules and co-precipitates with Neuropilins (NRPs) in transfected 293T cells. Furthermore, NRPs were shown to stabilize Sema/Plexin interactions. In this study, we sought to identify potential partner(s) for Plexin B1 in mediating Sema4A action. We examined surface expression of Plexin B2, B3, and NRPs 1, 2 in human Treg cells by flow cytometry, and observed that they express NRP-2 but not NRP-1, Plexin B2, or B3. Moreover, culture of PBMC with recombinant human Sema4A-Fc (rhSema4A) in vitro resulted in the downregulation of NRP-2 expression on human Treg cells suggesting a specific ligand-receptor interaction. We propose that Sema4A action on human Treg cells may be mediated by a Plexin B1-NRP-2 complex. Our ongoing research is focused on cryoEM studies of ligand-receptor and receptor-receptor interactions in conjunction with sequence/structure statistical analyses using the DARC (Deep Analysis of Residue Constraints) program (Scientific Reports, in press) with the goal of developing Sema4A-based therapies for allergic disease.