An unexpected counter-regulatory role of IL-10 in B-lymphocyte-mediated transplantation tolerance.

Monoclonal antibody against the CD45RB protein induces stable transplantation tolerance to multiple types of allograft. We have previously established that this tolerance protocol relies on the regulatory function of B lymphocytes for its effect. B lymphocytes have also been reported to participate in immune regulation in several other settings. In most of these systems, the regulatory function of B lymphocytes depends on the production of IL-10. Therefore, we investigated the role of IL-10 in the anti-CD45RB model of B-cell-mediated transplantation tolerance. Surprisingly, using antibody-mediated neutralization of IL-10, IL-10-deficient recipients and adoptive transfer of IL-10-deficient B lymphocytes, we found that IL-10 actually counter-regulates tolerance induced by anti-CD45RB. Furthermore, neutralization of IL-10 reduced the development of chronic allograft vasculopathy compared to anti-CD45RB alone and reduced the production of graft reactive alloantibodies. These data suggest that the participation of regulatory B lymphocytes in transplantation tolerance may be distinct from how they operate in other systems. Identifying the specific B lymphocytes that mediate transplantation tolerance and defining their mechanism of action may yield new insights into the complex cellular network through which antigen-specific tolerance is established and maintained.

Regulatory T-cell counter-regulation by innate immunity is a barrier to transplantation tolerance.

Innate immune signals foster adaptive immunity through activation of antigen-presenting cells. Recent in vitro evidence suggests that innate signaling may also contribute to immunity by countering the effects of regulatory T cells (T-regs), counter-regulation. We present in vivo evidence using a transgenic skin allograft model that the function of T-regs is lost in the setting of acute skin transplantation but remains intact when grafts were transplanted 1 month prior to allow surgery-induced inflammation to abate. Our findings identify T-reg counter-regulation as a naturally occurring process that accompanies transplantation and an important barrier to T-reg-mediated tolerance. Our finding further highlights the central role of regulatory cell deactivation in the initiation of the immune response.