To investigate the effects of IL-5 on the expression of TGF-beta1 in eosinophils in vitro, eosinophils were incubated in the presence of the same concentrations of 1L-4, IL-5 and IFNgamma, different concentrations of IL-5 in vitro and changes of eosinophil viability were assessed by trypan blue exclusion. Non-cytokine was employed as a negative control. 16 h after the cultivation, supernatants and cells were assayed by using TGF-beta1 specific ELISA and RT-PCR. The mRNA expression and protein expresssion of TGF-beta1 in eosinophils stimulated with different cytokines was observed. The expression of TGF-beta1 protein in eosinophils was increased significantly by IL-4 (433.67 +/- 9.86 vs 228.9 +/- 2.87) and IL-5 (403.72 +/- 7.60 vs 228.9 +/- 2.87, P < 0.05), while decreased by IFNgamma (178.47 +/- 2.60 vs 228.9 +/- 2.87). At the same time, the results demonstrated that the basal level of TGF expression was enhanced by IL-5 in all samples (P < 0.05). The expression of TGF-beta1 mRNA was 1.42, 1.70, 1.76-folds higher than that of the non-stimulated controls. It is concluded that IL-5 can up-regulate the expression of TGF-beta1 in eosinophils in vitro, which might have effect in eosinophil-associated chronic rejection.