Echinostoma caproni (Trematoda): differential in vivo cytokine responses in high and low compatible hosts.

In order to investigate the factors determining the expulsion of intestinal trematodes, we have analyzed the in vivo cytokine responses at several levels and the local responses against Echinostoma caproni (Trematoda) in two host species displaying different compatibility with the parasite. The response of the high compatible host (mice) is characterized by a mixed Th1/Th2 phenotype in the spleen, Peyer's patches and mesenteric lymph nodes. At the intestine, a marked Th1 response with a marked increase of IFN-γ together with elevated number of mucosal neutrophils and expression of induced nitric oxide synthase were observed. The responses in the host of low compatibility (rats) with the parasite at the spleen, Peyer's patches and mesenteric lymph node did not show clear differences with regard to the mice. However, the response in the intestine was markedly different. In rats, a Th2 response with increase in the levels of IL-5, IL-6 and IL-13 expression was detected. According to these results, the local production of IFN-γ and the local inflammatory responses with neutrophilic infiltration are associated with the development of chronic infections, whereas the worm expulsion is related with the development of Th2 responses and appears to be based on effects on non-bone narrow-derived cells.