In-vitro and in-vivo immunomodulatory effects of syringin

Syringin was found to possess immunomodulatory activity by which it inhibit ed the in-vitro immunohaemolysis of antibody-coated sheep erythrocytes by g uinea-pig serum through suppression of C3-convertase of the classical compl ement. In this study, we examined its in-vitro and in-vivo activity on tumo ur necrosis factor (TNF)-alpha and nitric oxide (NO) production, CD4+ T cel l and CD8+ cytotoxic T cell (CTLL-2) proliferation, and croton oil-, arachi donic acid- and fluorescein-isothiocynate (FITC)-induced mouse ear oedema m odel. Syringin significantly inhibited both TNF-alpha production from lipop olysaccharide (LPS)-stimulated RAW264.7 cells and CD8+ T cell (CTLL-2) prol iferation in a dose-dependent manner, whereas neither NO production nor CD4 + T cell proliferation were blocked even by high concentrations of syringin . In the in vivo experiments, syringin also significantly suppressed FITC-i nduced ear oedema in mice but not the ear oedema induced by croton or arach idonic acid. These results suggest that syringin may be implicated as an im munomodulator having an anti-allergic effect rather than an antiinflammator y effect. The anti-allergic effect of syringin seems to be due, in part, to inhibition of TNF-alpha production and cytotoxic T cell proliferation.