Hydration and pharmacologic manipulation of the skin may have immunomodulatory effects. In vivo RA upregulates HLA-DR as well as CD11c on epidermal LCs(LC). Because the potent immunoregulatory and reciprocally acting cytokines, IL-12 and IL-10 can be induced in LC and keratinocytes, we asked if these are modulated by in vivo manipulation of the skin. For occlusion, a gas permeable, water impermeable membrane was used (Opsite). For pharmacologic stimulation, 0.1 % RA (dissolved into 70% ethanol and 30% propylene glycol); and vehicle solvent only(V) as a control were applied on the skin of normal volunteers for 0, 6, 20, and 48 hrs. Only 1 of the 12 receiving this formulation of RA displayed visible redness. Keratomes were performed immediately treated by dispase then trypsin, followed by anti-CD1a selection of LC and depletion of keratinocytes (KC) by immunobeads. Freshly selected and depleted epidermal cells (EC) were subjected to RNA extraction, RT-PCR amplication (32 cycles) of IL-12p40, IL-10 and β-actin (as a gene control) were performed followed by Southern blot and analyzed by PhosphorImager. Occlusion alone and open vehicle alone did not induce LC immunoregulatory cytokines. However, when the propylene glycol/ethanol vehicle was occluded for 48 hrs, LC demonstrated significant induction of IL-12p40 mRNA relative to normal skin LC(n=7, p<0.001) at the 48 hr time point, and, to a much lesser extent, IL-10 as well (p=0.036), IL-12 p40 mRNA could be further induced by RA but peak induction was at the 20 hr time point in RA-treated CD1a + LC (n=6) relative to V (p=0.037) and Ohr(p=0.001). In relative to the brisk induction and fall off of IL-12, IL-10 mRNA exhibited a more delayed induction by RA, with the significant induction relative to V occurring at the 48 hr time point (n=4) (p=0.036). Neither occlusion nor RA induced IL-12 p40 or IL-10 mRNA in CD1a KC at any time points tested. In summary, both vehicle occlusion and RA occlusion can induce LC IL-12 and IL-10 mRNA; LC exhibit a rapid but transient induction of IL-12 and a more delayed induction of IL-10, perhaps reflecting the regulatory or anti-inflammatory action of IL-10 on IL-12.