Background.

In Th (T helper) 1/Th2 balance in response to signals given during donor antigen presentation, induction of allograft prolongation is more often related to Th2-type than with Th1-type immunity. Here, we examined the effect of interleukin (IL)-33, a novel member of the IL-1 family, on cardiac allograft survival in mice.

Methods.

Mice heterotopic cardiac transplants were performed with sequential recipient sacrifice at anticipated time points to examine the immunoregulatory action of IL-33 in recipient mice.

Results.

In vitro Th1-polarized CD4+ T cells did not express ST2L; however, most CD4+ T cells became ST2L+ on repeated stimulation under Th2-polarizing conditions. Similarly, we found that IL-33 was able to enhance the expression of Th2-associated cytokines (IL-5 and IL-13) but not interferon (IFN)-γ. Treatment of recipient mice with IL-33 results in the improvement of allograft survival (more than 20 days) when compared with phosphate-buffered saline-or glutathione S-transferase-treated groups (all less than 9 days). Intracellular cytokine staining in CD4+ splenocytes confirmed an increase in the percentage of IL-4+ cells and a decrease in the percentage of IFN-γ+ cells in IL-33 treated mice. In addition, IL-33 significantly enhanced the gene expression of Th2-type cytokines IL-4 and IL-5 but suppressed the Th1-type cytokine IFN-γ mRNA levels in both allograft and recipient spleen.

Conclusion.

These data demonstrate that IL-33 serves as a potent inducer of Th2 immune response and can markedly contribute to the prolongation of cardiac allograft survival.