5C). Taken together, these results indicate that RAR-α mediates the regulation of cytokine production by RA. Next, to determine if RA directly affects NKT cells, the CD1d-expressing NKT-cell line DN32.D3 was stimulated with Con A or α-GalCer in the presence of RA (Supporting Information Fig. 5A). As shown in Fig. 5D and E, the secretion of IFN-γ and IL-4 but not TNF-α was reduced by RA. The mRNA expression was consistent with the quantitation data of the secreted cytokines (Supporting Information Fig. 5B). Because TNF-α production, which is regulated by NFAT, was not reduced by RA, we examined the changes in other signaling

molecules that are activated upon TCR stimulation. PKC412 research buy As a result,

the phosphorylation of MAPK, especially JNK, was reduced by RA (Fig. 5F). We measured the amount of IκB, as an indicator of NFκB signaling, by western blot, and it was not influenced by RA. Therefore, these data suggest that RA regulates cytokine production in NKT cells directly, the mechanism of which might include a modification of MAPK signaling pathway. In the current study, we demonstrated, for the first Lapatinib mw time, how RA regulates NKT cell-mediated diseases and NKT-cell responses in vivo. We showed that RA ameliorated Con A-induced hepatitis but not α-GalCer-induced hepatitis. This distinct role of RA can be explained by the finding that RA differentially regulated the secretion of various pathogenic cytokines from NKT cells, with unaltered NKT-cell activation. Mechanistically, our observations indicate that RA affects NKT cells directly by modulating signaling molecules Docetaxel chemical structure such as RAR-α and MAPK. We first attempted to examine the influence of endogenous RA using vitamin A-deficient mice; however, the results did not correlate with the data obtained from RA-pretreated

animals (unpublished observation). We found that RA deficiency affected the activation status of cells in naïve mice by an unknown mechanism. RA signaling is biphasic and has the potential to display opposite effects in various models [20-25]. These controversial findings have not been explained completely, and our observations and future studies may explain this discordance. In this study, to minimize the effect of vitamin A-deficiency on NKT cells, disulfiram was used to pretreat the animals for 3 days to reduce the amount of endogenous RA. Aggravated liver injury was observed in disulfiram-treated mice, demonstrating the regulatory role of endogenous RA in Con A-induced hepatitis (Fig. 1D and E). Disulfiram can induce liver injury by hitherto unknown mechanisms when it is administered to treat alcohol abuse [31, 32]. Our observations suggest that a defect in RA synthesis via disulfiram treatment might cause the liver to become susceptible to inflammation and increase liver injury in patients.