Induction of indoleamine 2,3-dioxygenase in small intestine of mouse infected with parasitic helminth, Hymenolepis nana

.One hundred and fifty crushed eggs of Hymenolepis nana were administrated to 5–6 week old ddY mice, and the animals were killed at 0, 7, 14, 21 or 28 days post-infection (dpi). The small intestines were recovered, and both halves, proximal and distal, were examined, observed for immunohistochemistry, and assayed on enzyme activity of IDO. Enzyme activity of IDO was increased by H. nana infection, and was parallel to a decrease of recovered worms. The expression pattern of IDO-positive cells in the proximal intestine was also the same as those of IDO activity with a little change earlier. Furthermore, IDO-positive cells coincided with goblet cells, but not all goblet cells were IDO-positive. Present findings apparently suggest that IDO might be involved in the mucous excretion process in the expulsion of worms.