B lymphocytes have long been recognized for their critical contributions to adaptive immunity, providing defense against pathogens through cognate antigen presentation to T cells and Ab production. More recently appreciated is that B cells are also integral in securing self-tolerance; this has led to interest in their therapeutic application to downregulate unwanted immune responses, such as transplant rejection. In this study, we found that PMA- and ionomycin-activated mouse B cells acquire regulatory properties following stimulation through TLR4/TLR9 receptors (Bregs-TLR). Bregs-TLR efficiently inhibited T cell proliferation in vitro and prevented allograft rejection. Unlike most reported Breg activities, the inhibition of alloimmune responses by Bregs-TLR relied on the expression of TGF-β and not IL-10. In vivo, Bregs-TLR interrupted donor-specific T cell expansion and induced Tregs in a TGF-β–dependent manner. RNA-Seq analyses corroborated the involvement of TGF-β pathways in Breg-TLR function, identified potential gene pathways implicated in preventing graft rejection, and suggested targets to foster Breg regulation.
Kang Mi Lee, Qiang Fu, Guoli Huai, Kevin Deng, Ji Lei, Lisa Kojima, Divyansh Agarwal, Peter van Galen, Shoko Kimura, Naoki Tanimine, Laura Washburn, Heidi Yeh, Ali Naji, Charles G. Rickert, Christian LeGuern, James F. Markmann