In‐vitro and in‐vivo immunomodulatory effects of syringin

Syringin was found to possess immunomodulatory activity by which it inhibited the in‐vitro immunohaemolysis of antibody‐coated sheep erythrocytes by guinea‐pig serum through suppression of C3‐convertase of the classical complement. In this study, we examined its in‐vitro and in‐vivo activity on tumour necrosis factor (TNF)‐α and nitric oxide (NO) production, CD4 + T cell and CD8+ cytotoxic T cell (CTLL‐2) proliferation, and croton oil‐, arachidonic acid‐ and fluorescein‐isothiocynate (FITC)‐induced mouse ear oedema model. Syringin significantly inhibited both TNF‐α production from lipopolysaccharide (LPS)‐stimulated RAW264.7 cells and CD8+ T cell (CTLL‐2) proliferation 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‐induced ear oedema in mice but not the ear oedema induced by croton or arachidonic acid. These results suggest that syringin may be implicated as an immunomodulator having an anti‐allergic effect rather than an antiinflammatory effect. The anti‐allergic effect of syringin seems to be due, in part, to inhibition of TNF‐α production and cytotoxic T cell proliferation.