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1996;157:3577C3586. RA-DCs derived from iNOS?/? mice exhibited near total RETRA hydrochloride loss of tolerogenic function, despite sustained Arg-1 activity. The manifestation of iNOS and the suppressive function of RA-DCs were dependent on both IFN- and ATRA. Furthermore, the in vivo behavior of RA-DCs proved to be consistent with their in vitro behavior. Therefore, we conclude that ATRA enhances both Arg-1 and iNOS manifestation in IFN- treated DCs, resulting in a tolerogenic phenotype. These findings elucidate mechanisms through which ATRA may contribute to liver immune tolerance. Intro Hepatic stellate cells (HSCs) have been shown to contribute to the immunoregulatory properties of the liver (1, 2). One of the important mechanisms entails the induction of myeloid cells with suppressive functions, generated primarily through the production of soluble factors. The activities of these HSC induced myeloid cells promotes T cell unresponsiveness (3). 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