The immunosuppressive compound FK506 does not affect expulsion of Echinostoma trivolvis in C3H mice

C3H/HeN mice were infected with Echinostoma trivolvis metacercariae on day 0, given intramuscular injections of the immunosuppressive agent FK506 daily for 5 or 7 days, and necropsied on days 5, 8, 12, 15, 20, and 30 postinfection (p.i.). Control mice were infected with the echinostomes but were not treated with FK506. A significant reduction in mastocytosis was seen from day 12 to day 15 p.i. in the treated group. No reduction was observed in numbers of goblet cells and eosinophils in the treated group. The number of white blood cells was lower in the treated mice than in the controls. No significant difference in the optical density values of immunoglobulins appeared in control versus treated mice. Treatment with FK506 did not delay worm expulsion markedly, probably because the drug did not suppress goblet-cell hyperplasia. Increased mucus production associated with goblet-cell hyperplasia is primarily involved in the expulsion of E. trivolvis in murine hosts.