Protective immunization of hamsters against Opisthorchis viverrini infection is associated with the reduction of TGF-β expression

Opisthorchis viverrini infection is a significant health problem in Thailand and other countries in Southeast Asia. There is little known about the mechanisms of the immune response to O. viverrini in immunoprotection. However, it has been reported that this parasite can suppress both cell and antibody mediated immune responses. The TGF-β and IL-10 are immunosuppressive cytokines that play an important role in inhibition of host immune response leading to worm survival. In this study, we immunized hamsters to protect against O. viverrini infection and the IL-4, IL-10, TGF-β and IFN-γ expression in spleen was investigated by real time PCR analysis. An O. viverrini-crude somatic antigen preparation (CSAg) administered with complete Freundʹs adjuvant (CFA) or with alum was used to stimulate immune responses in O. viverrini-primed hamsters. The greatest percent protection (48.4%) was seen following immunization with CSAg plus alum. The mean number ± SD of worms recovered in the PBS control, CFA alone, CSAg plus CFA, alum alone and CSAg plus alum was 17.4 ± 2.3, 17.1 ± 3.3, 14.5 ± 3.8, 14.5 ± 2.3 and 9 ± 2.7, respectively. Significant protection correlated with the reduction of TGF-β and IL-10, but not IL-4, IFN-γ expressions. Since TGF-β expression is significantly increased in the spleens of hamsters with opisthorchiasis, stimulation of this cytokine by parasite antigens was confirmed by using CSAg and primary hamster spleen cells. Antigen fractions with molecular masses of 81–92, 64–72 and 19–21.4 kDa were found to significantly induce TGF-β production. Our results suggested that TGF-β induction by O. viverrini may have an important role in parasite survival.