Do natural T regulatory cells become activated to antigen specific T regulatory cells in transplantation and in autoimmunity?

Antigen specific T regulatory cells (T-reg) are often CD4(+)CD25(+)FoxP3(+) T cells, with a phenotype similar to natural T-reg (nT(reg)). It is assumed that nT(reg) cannot develop into an antigen specific T-reg as repeated culture with IL-2 and a specific antigen does not increase the capacity or potency of nT(reg) to promote immune tolerance or suppress in vitro. This has led to an assumption that antigen specific T-reg mainly develop from CD4(+)CD25(-)FoxP3(-) T cells, by activation with antigen and TGF-beta in the absence of inflammatory cytokines such as IL-6 and IL-1 beta. Our studies on antigen specific CD4(+)CD25(+) T cells from animals with tolerance to an allograft, identified that the antigen specific and T-reg are dividing, and need continuous stimulation with specific antigen T cell derived cytokines. We identified that a variety of cytokines, especially IL-5 and IFN-gamma but not IL-2 or IL-4 promoted survival of antigen specific CD4(+)CD25(+)FoxP3(+) T-reg. To examine if nT(reg) could be activated to antigen specific T-reg, we activated nT(reg) in culture with either IL-2 or IL-4. Within 3 days, antigen specific T-reg are activated and there is induction of new cytokine receptors on these cells. Specifically nT(reg) activated by IL-2 and antigen express the interferon-gamma receptor (IFNGR) and IL-12p70 (IL-12R beta 2) receptor but not the IL-5 receptor (IL-5R alpha). These cells were responsive to IFN-gamma or IL-12p70. nT(reg) activated by IL-4 and alloantigen express IL-5R alpha not IFNGR or IL-12p70R beta 2 and become responsive to IL-5. These early activated antigen specific T-reg, were respectively named Ts1 and Ts2 cells, as they depend on Th1 or Th2 responses. Further culture of Ts1 cells with IL-12p70 induced Th1-like T-reg, expressing IFN-gamma, and T-bet as well as FoxP3. Our studies suggest that activation of nT(reg) with Th1 or Th2 responses induced separate lineages of antigen specific T-reg, that are dependent on late Th1 and Th2 cytokines, not the early cytokines IL-2 and IL-4.