Studies on effects of IL-3 in protection against intestinal parasites in vivo

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Mucosal mast cells (MMC) are important in protection against intestinal Strongyloides ratti. A repetitively IL-3 injection induces marked intestinal mastocytosis and protection against S.ratti in mice. Effects of exogenous IL-3 is clear on the mastocytosis and protection. However, how endogenous IL-3 participates in the protection is unclear. We extracted total RNA from the mesenteric lymph node, the spleen and the small intestine of mice infected with S.ratti, and detected mRNA of cytokines by RT-PCR.IL-3 mRNA was detected in the mesenteric lymph node of mice on Day 7 post infection and decreased markedly on Day 11. No IL-3 mRNA was detected in the normal tissues, and the spleen or the small intestine from infected mice by the condition used. IL-4 mRNA was detectable in the normal mesenteric lymph node. Its expression peaked on Day 7 with 7 times of normal in the mesenteric lymph node, on Day 11 in the spleen and on Day 7 in the small intestine. SCF mRNA was well detected in the normal tissues. Expression of SCF mRNA was increased by infection in the mesenteric lymph node, but decreased by infection in the spleen and the small intestine. Not only IL-E but also the other cytokines like IL-4 or SCF,which participate in the differentiation and proliferation of MMC in vitro, may be important cytokines in S.ratti-infection. By the way, intestinal MMC in mice infected with S.ratti showed characteristic paracrystalline ultrastructure of granules at the time of the worm expulsion. However, the anaphylactic degranulation which is observed in human connective tissue mast cells was not detected in this study. A similar characteristic granule change to that observed in S.ratti-infection was detected in IL-3 injected mice. Therefore, IL-3 injection can induce the same level of MMC activation as induced by S.ratti-infection.