The role of 5-hydroxytryptamine on expulsion of Trichinella spiralis during the intestinal stage.

During the intestinal stage of Trichinella spiralis (T. spiralis) infection, it can stimulate host's intestinal peristalsis to expulse worms. 5-hydroxytryptamine (5-HT) is a neurotransmitter which can regulate the contraction of intestinal smooth muscle. IL-33 specifically binds to ST2 receptor to promote the secretion of 5-HT by intestinal enterochromaffin cells. However, it remains unclear whether the host is able to modulate the secretion of 5-HT to expulse worms through the IL-33-ST2 signaling pathway during the intestinal stage of T. spiralis infection. Therefore, ST2 inhibitor iST2 was used in a T. spiralis infected mouse model and MODE-K cells to analyze the role of IL-33-ST2 signaling pathway in the secretion of 5-HT during the intestinal phase of T. spiralis infection. The results indicated that the expression of ST2, IL-33, and TPH1(tryptophan hydroxylase 1, the rate-limiting enzyme in the biosynthesis of 5-HT) in the small intestine were increased during the intestinal phase of T. spiralis infection. Meanwhile the levels of secretory 5-HT and IL-33 in the small intestine were significantly increased. After iST2 treatment, the level of 5-HT was significantly decreased, resulting in diminished worms expulsion capability. The decrease of 5-HT was observed in MODE-K cells treated with excretory-secretory products of T. spiralis post iST2 treatment. The above results demonstrated that IL-33-ST2 signaling pathway might play a crucial role in promoting the secretion of 5-HT which enhancing the ability of the intestine to expulse worms during the intestinal stage of T. spiralis.