Exposure time determines the protective effect of Trichinella spiralis on experimental colitis.

Several studies demonstrate the protective effect of Trichinella spiralis (T. spiralis) on autoimmune diseases, however the optimal exposure time remains unexplored. This study aimed to determine whether pre-exposure of mice to T. spiralis conferred greater protection than introduction of the parasite in the acute phase of experimental colitis. We compared the effect of T. spiralis on dextran sodium sulfate (DSS)-induced colitis using two exposure paradigms: introduction three weeks prior to, or immediately after the induction period. Inflammation scores, morphological changes and cytokine profiles in serum and colonic tissue were assessed. At a parasite dose of 300 cysts, post exposure had a more pronounced effect on cytokine profiles, improved gross appearance of colon tissue, and reduced inflammatory symptoms. In addition, we demonstrate that regardless of cyst number, pre-exposure to T. spiralis did not confer protective benefits when compared to parasite introduction in the acute phase of DSS-induced colitis. Moreover, our data indicates that the underlying mechanisms of action involve an IL-17/TNF-alpha synergistic reaction, suppression of Th1 and Th2 responses, and an upregulation of the regulatory cytokines IL-10 and TGF-beta 1. Our results demonstrate that moderate exposure to T. spiralis in the acute phase of DSS-induced colitis improves disease associated inflammation and tissue disruption.