IL-25 facilitated Th2 cell differentiation induced by eosinophils
To further investigate the effect of IL-25 on eosinophils in initiating Th cell responses, BmEOS from WT mice and naïve CD4+ T cells from spleens were co-cultured in the absence or presence of HDM and IL-25 (Figure 7A~B). The results showed that the percentage of CD4+ IL-4+ Th2 cells was significantly increased in BmEOS-T co-culture system with HDM plus IL-25 treatment, as compared with HDM treatment alone. When culturing naïve CD4+T cells alone in the presence of HDM and IL-25, there were no detectable differences in the percentage of CD4+ IL-4+ Th2 cells among vehicle-treated, HDM-treated and HDM plus IL-25-treated T cells, suggesting that HDM plus IL-25 treatment did not lead to CD4+ Th2 cells-intrinsic differentiation (Figure 7C). In addition, HDM-treated co-cultures developed an increase in the percentages of CD4+IFN-γ+Th1 cells and CD4+IL-9+Th9 cells than vehicle-treatment group. However, there were no significantly differences in the proportions of Th1, Th9 and Th17 cells between HDM treatment and HDM plus IL-25 treatment group, no matter in BmEOS-T co-culture or cultures of T cells alone (Figure 7D). These led to the conclusion that IL-25 could promote eosinophil-induced Th2 cell polarization.