Suppression of Th1 and Th2 immune responses in mice by Sinomenine, an alkaloid extracted from the chinese medicinal plant Sinomenium acutum

Abstract

The present study was designed to investigate the effect of sinomenine (SIN), an alkaloid extracted from Sinomenium acutum, on Th1 and Th2 immune responses in mice. For this investigation, mice were S. C. immunized with ovalbumin (OVA) emulsified with complete Freund's adjuvant (day 0). Varying doses of SIN were orally administered daily over a period of 21 days, commencing on day 0. On day 21, anti-OVA IgG and proliferative responses of spleen cells to the antigen were measured. Anti-OVA IgG2a and IFN-gamma were measured as indicators of Th1 immune responses and anti-OVA IgG1, IgE, and IL-5 as those of Th2 responses. TGF-beta was measured as an indicator of Th3 immune responses. The results showed that treatment with SIN was followed by decreases in anti-OVA IgG and the antigen-specific splenocyte proliferation. Production of all isotypes of antibodies including anti-OVA IgG2a, IgG1 and IgE as well as secretion of cytokines such as IFN-gamma and IL-5 was suppressed by SIN, although the suppression of anti-OVA IgG2a and IFN-gamma by the alkaloid appeared to be greater than that of anti-OVA IgG1, IgE, and IL-5. In addition, SIN enhanced the secretion of TGF-beta. These results suggest that SIN appears to have suppressive effects on both Th1 and Th2 immune responses. The results also suggest that Th1 responses may be more preferentially suppressed by the Sinomenium acutum-derived alkaloid compared to Th2 responses. TGF-beta may at least in part contribute to the suppression of Th1 as well as Th2 immune responses.