Effects of All-Trans Retinoic Acid on Th1- and Th2-Related Chemokines Production in Monocytes

Low vitamin C and reduced alpha-carotene intake are associated with increased asthma risk in children. In addition, mean serum vitamin A concentrations are significantly lower in asthmatic children than in controls. All-trans retinoic acid (ATRA) is a derivative of vitamin A. Macrophage-derived chemokine (MDC) is a T helper cell-type 2 (Th2)-related chemokine involved in the recruitment of Th2 cells toward inflammatory sites. On the other hand, Th1-related chemokine, interferon-inducible protein 10 (IP-10)/CXCL10 is also important in allergic inflammation. Both Th1- and Th2-related chemokines play an important role in allergic asthma. To survey whether ATRA and ascorbic acid effect Th1- and Th2-related chemokine expression in monocytes. To test this, THP-1 cells were pre-treated with ATRA or ascorbic acid and stimulated by lipopolysaccharide (LPS) or poly I:C. Supernatants were measured for Th2-related (MDC) and Th1-related (IP-10) chemokine concentrations by ELISA. The effects of ATRA on mitogen-activated protein kinase (MAPK) and NFkb were evaluated with Western blotting. After stimulation, ATRA significantly down-regulated MDC and IP-10 in a dose-dependent manner. Similarly, ascorbic acid reduced the LPS-induced changes in MDC but only with a high dose. However, asorbic acid had no effect on IP-10 changes either induced by LPS or poly I:C. RT-PCR showed ATRA inhibited IP-10 expression through decreasing the level of transcription. Furthermore, ATRA suppressed the expression of LPS-stimulated c-Raf, MKK1/2 and ERK expression of THP-1 cells. In conclusion, ATRA suppressed Th2- and Th1-related chemokines expression in THP-1 cells, at least in part via the c-Raf-MKK1/2-ERK/MAPK pathway.