Cytokines affecting CD4+ T regulatory cells in transplant tolerance. Interleukin-4 does not maintain alloantigen specific CD4+CD25+ Treg

IL-4 is thought to promote induction of transplantation tolerance and alloantigen-specific CD4+CD25+ T regulatory cells (Treg). This study examined the effect of IL-4 on the induction and maintenance of the CD4+ T regulatory cells (Treg) that mediate transplantation tolerance. Tolerance was induced in DA rats with PVG heterotopic cardiac allografts by a short course of cyclosporine. Naïve and tolerant lymphocytes, including the CD4+ and CD4+CD25+ T cell subsets, were assayed in mixed lymphocyte cultures with or without recombinant (r)IL-4 or other cytokines. The proliferation, cell surface and cytokine phenotype of these cells was examined, as was their capacity to adoptively transfer tolerance. rIL-4 enhanced the proliferation of naïve and tolerant lymphoid cells, including CD4+ and CD4+CD25+ T cells, but this was not alloantigen specific. Naïve or tolerant CD4+ T cells cultured with rIL-4 and donor PVG antigen effected rapid graft rejection, even though before culture tolerant CD4+ T cells transferred antigen-specific tolerance. These rIL-4 cultured CD4+ T cells had a phenotype consistent with activated CD4+CD25+FoxP3− Th2 cells. While naïve natural CD4+CD25+ T cells (nTreg) cultured with alloantigen and rIL-4 had enhanced proliferation and capacity to suppress rejection in vivo, the culture of tolerant CD4+CD25+ T cells with alloantigen and rIL-4 could not sustain their proliferation against specific donor, nor their capacity to transfer tolerance to specific donor allograft. Thus, IL-4 promotes both regulatory and effector T cells early in the immune response, but once alloimmune tolerance is established, IL-4 promoted the activation of effector cells to mediate rejection and did not support alloantigen-specific Treg that could transfer specific tolerance.