Based on the recently established role for the master coregulator MTA1 and MTA1-containing nuclear remodeling complexes in oncogenesis and inflammation, we explored the links between parasitism by the carcinogenic liver fluke Opisthorchis viverrini and this coregulator using both an Mta1−/− mouse model of infection and a tissue microarray of liver fluke–induced human cholangiocarcinomas (CCAs). Intense foci of inflammation and periductal fibrosis in the liver and kidneys of wild-type Mta1+/+ mice were evident at 23 days postinfection with O. viverrini. In contrast, little inflammatory response was observed in the same organs of infected Mta1−/− mice. Livers of infected Mta1+/+ mice revealed strong up-regulation of fibrosis-associated markers such as cytokeratins 18 and 19 and annexin 2, as determined both by immunostaining and by reverse-transcription polymerase chain reaction compared with infected Mta1−/− mice. CD4 expression was up-regulated by infection in the livers of both experimental groups; however, its levels were several-fold higher in the Mta1+/+ mice than in infected Mta1−/− mice. Mta1−/− infected mice also exhibited significantly higher systemic and hepatic levels of host cytokines such as interleukin (IL)-12p70, IL-10, and interferon-γ compared with the levels of these cytokines in the Mta1+/+ mice, suggesting an essential role of MTA1 in the cross-regulation of the Th1 and Th2 responses, presumably due to chromatin remodeling of the target chromatin genes. Immunohistochemical analysis of ≈300 liver tissue cores from confirmed cases of O. viverrini–induced CCA showed that MTA1 expression was elevated in >80% of the specimens. Conclusion: These findings suggest that MTA1 status plays an important role in conferring an optimal cytokine response in mice following infection with O. viverrini and is a major player in parasite-induced CCA in humans. (HEPATOLOGY 2011;)