Worm expulsion and mucosal mast cell response induced by repetitive IL-3 administration in Strongyloides ratti-infected nude mice.

After a primary infection of congenitally athymic nu/nu mice with Strongyloides ratti, worms were not expelled and the number of intestinal mucosal mast cells (MMC) remained at a low level. When S. ratti-infected nu/nu mice were treated by repetitive injections of semi-purified IL-3 from Day 5 to Day 10 post-infection (total 1.4 X 10(5) U), significant reduction of larval excretion in faeces (LPG) was observed on Day 13. The number of adult worms in the small intestine of IL-3-treated mice was significantly lower than that of untreated, infected nude mice. The higher dose of IL-3 treatment from Day 4 to Day 13 (total 5.8 X 10(5) U) caused more profound reduction of LPG as early as Day 9, although complete cessation of LPG was not observed until Day 13, the end of this series of experiments. By this higher dose of IL-3 treatment, adult worms were completely expelled from the small intestine, although a small number of residual worms, which could explain the persistent low level of LPG detected from Day 9 to Day 13, was found in the caecum. Histological examination revealed that the number of MMC, especially in the epithelium, of the small intestine of IL-3-treated mice was significantly higher than that of untreated mice.