Syringaldehyde (SD), a kind of
flavonoid polyphenolic small molecule compound, has the
antioxidant and anti-inflammatory properties. But it is unknown whether SD has properties on the treatment of
rheumatoid arthritis (RA) by modulating dendritic cells (DCs). We explored the effect of SD on the maturation of DCs in vitro and in vivo. The results showed that SD significantly down-regulated the expression of CD86, CD40 and MHC II, decreased the secretion of TNF-α,
IL-6,
IL-12p40 and
IL-23, and increased
IL-10 secretion and
antigen phagocytosis in vitro induced by
lipopolysaccharides in a dose-dependent manner through reducing the activation of MAPK/NF-κB signaling pathways. SD also significantly inhibited the expression of CD86, CD40 and MHC II on DCs in vivo. Moreover, SD suppressed the expression of CCR7 and the in vivo migration of DCs. In
arthritis mouse models induced by λ-
carrageenan and complete
Freund's adjuvant, SD significantly alleviated paw and joint oedema, reduced the levels of pro-inflammatory
cytokines TNF-α and
IL-6 and increased the level of
IL-10 in serum. Interestingly, SD significantly decreased the numbers of type I helper T cells (Th1), Th2, Th17 and Th17/Th1-like (CD4+IFN-γ+IL-17A+), but increased the numbers of regulatory T cells (Tregs) in spleens of mice. Importantly, the numbers of CD11c+IL-23+ and CD11c+IL-6+ cells were negatively correlated with the numbers of Th17 and Th17/Th1-like. These results suggested that SD ameliorated mouse
arthritis through inhibiting the differentiation of Th1, Th17 and Th17/Th1-like and promoting the generation of Tregs via regulation of DC maturation.