New insight into the immunomodulatory mechanisms of Tretinoin in NMRI mice

OBJECTIVES Recent evidence have proposed that Tretinoin produced in the gut preferentially promote differentiation of FoxP3+Treg cells but inhibits Th17 lymphocytes, and this may be the main immunomdulatory mechanism of Tretinoin in vivo. This study was done to investigate the effects of Tretinoin in outbred white mice after challenge with sheep red blood cells (SRBC). MATERIALS AND METHODS Twenty male NMRI-mice randomly allocated in two equal groups. Mice were treated with 1×10(9) SRBCs emulsified in CFA intraperitoneally twice with one weak interval. Animals were bled 5 days after last injection. Moreover, 48 hr before bleeding time, 1×10(9) SRBCs were injected into the left hind foot pad of mice. Tretinoin (25 mg/kg-every other day) were intraperitoneally injected into the treatment group from the beginning of the study and continued throughout the study. The levels of anti-SRBC antibody and the specific cellular immune responses were measured by microhemagglutination test and footpad thickness, respectively. Moreover, splenocytes were checked for proliferation rate, respiratory burst, cytokine production and FoxP3+Treg cells frequency. RESULTS Tretinoin markedly alleviated cellular immunity and concurrently potentiated humoral immunity after mice challenge with SRBCs. Furthermore, aside from reducing NBT reduction and lymphocyte proliferation, Tretinoin markedly suppressed the secretion of interleukin-17 and conversely, increased the production of interleukin-10. However, the level of IFN-γ and the frequency of FoxP3+Treg cells did not alter significantly. CONCLUSION The in vivo immunomudlatoty effects of Tretinoin may be partly due to immune deviation from pro-inflammatory cytokine interleukin-17 to anti-inflammatory cytokine interleukin-10, but not absolutely depend on the expansion of FoxP3(+)Treg cells.