Th2 cytokines and specific donor alloantigen activated CD4+CD25+T cells reverse chronic rejection: role of IL-4 and IL-5 in promoting antigen-specific Treg

Abstract

Abstract Naïve CD4+CD25+Foxp3+T regulatory cells (tTreg) activated by specific alloantigen (Ag) and IL-4 express IL-5Ralpha. We examined if IL-5 treatment activated alloAg specific Treg to prevent chronic rejection in F344 rats grafted with Lewis hearts. 5000units rIL-5 (rIL-5Rx) was given daily from 7d after grafting when rejection had started. Changes in CD4+CD25+T cells were assessed by FACS, RT-PCR of Il5ra and response to alloAg in MLC. Sham Rx rats fully rejected their grafts by 28d while IL-5Rx for 10d reversed rejection and grafts survived 60d (p<0.01). There were rejection episodes after stopping IL-5 but continued IL-5Rx reduced this. Pre-treatment with anti-CD25 or anti-IL-4 mAb abolished the benefit of rIL-5Rx, all grafts rejected by 28d. IL-5 treated hosts had increased CD4+CD25+T cells, 6–8% vs 3–4% in controls. After 10d of rIL-5Rx, host CD4+CD25+T cells responded to Lewis but not to F344 or third-party PVG alloAg in MLC, showing activation of alloAg-specific Treg. CD4+CD25+T cells from rats treated for 50d with rIL-5 had more il5ra, remained FOXP3+ and in MLC rIL-5 enhanced responses to Lewis but not other alloAg. These findings are consistent with IL-4 and alloAg activating tTreg to induce Ag-specific Treg that suppress rejection. To demonstrate rIL-4 and specific alloantigen activated naïve tTreg to suppress rejection, these cells were prepared ex vivo. 5×106 of these IL-4 alloAg activated tTreg, given after rejection commenced, reversed rejection. 5×106 fresh naïve tTreg or 5×106 tTreg activated by third-party PVG alloAg had no effect on rejection. IL-5 prevented heart graft rejection through hosts’ CD25+Treg that had been activated by alloAg and IL-4. IL-5 therapy may have potential to prevent chronic allograft rejection.