Intestinal protection against <em>Strongyloides ratti</em> and mastocytosis induced by administration of interleuki-3 in mice.

Information about interleukin-3 (IL-3) effects in vivo is limited compared with the in vitro effects. We found that a repetitive injection of a Iow 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 markedly reduced by a total of 10⁴ U IL-3 or more on day 2 post-infection. The number of intestinal mucosal mast cells (MMC) was increased by the protective dose of IL-3. The IL-3 treatment, however, was ineffective in protecting mice against tissue migrating larvae, as assessed by 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 the spleen and the mesenteric lymph nodes. An MMC-specific protease, MMCP-1, was secreted 200 times more than in controls in the intestinal lumen by the IL-3 treatment. The IL-3 treatment induced no protection or mastocytosis in mast cell-deficient W/W^v mice. These results suggest that the IL-3-induced intestinal protection against S. ratti is mediated by MMC. [ABSTRACT FROM AUTHOR]