INTESTINAL PROTECTION AGAINST STRONGYLOIDES-RATTI AND MASTOCYTOSIS INDUCED BY ADMINISTRATION OF INTERLEUKIN-3 IN MICE

Information about interleukin-3 (IL-3) effects in vivo is limited comp ared with the in vitro effects. We found that a repetitive injection o f a low dose of recombinant IL-3 induced protection against intestinal worms of Strongyloides ratti in C57BL/6 mice. When mice were injected i.p. with different doses of recombinant IL-3 twice a day from day -5 to day -1 and infected orally with larvae recovered from the head of infected rats on day 0, worm recovery from the small intestine was mar kedly reduced by a total of 10(4) U IL-3 or more on day 2 post-infecti on. The number of intestinal mucosal mast cells (MMC) was increased by the protective dose of IL-3. The IL-3 treatment, however, was ineffec tive in protecting mice against tissue migrating larvae, as assessed b y recovery from the head. The protective effect of IL-3 on intestinal worms was observed within 6 hr post oral infection, suggesting little concern with antigen-specific immune responses. The effective dose of IL-3 treatment increased the number of MMC progenitors five times in t he spleen and the mesenteric lymph nodes. An MMC-specific protease, MM CP-1, was secreted 200 times more than in controls in the intestinal l umen by the IL-3 treatment. The IL-3 treatment induced no protection o r mastocytosis in mast cell-deficient W/W(v) mice. These results sugge st that the IL-3-induced intestinal protection against S. ratti is med iated by MMC.