HEPATIC RECRUITMENT OF MAST-CELLS OCCURS IN RATS BUT NOT MICE INFECTED WITH SCHISTOSOMA-MANSONI

The pathogenesis of infection with Schistosoma mansoni in rats is distinct from that in mice. Rats are non-permissive hosts and infection is terminated in the liver before egg laying commences whereas the parasite completes its life cycle in mice. Comparison of the mast cell responses in the two species reveals that a pronounced hepatic mastocytosis occurs in the rat and this is concomitant with the demise of the parasite. The majority of recruited hepatic mast cells contain the highly soluble granule chymase, rat mast cell prolease-II, which is released systemically into blood during the period of parasite elimination. In contrast, very few mast cells are found in livers of parasitized mice and none contain the soluble granule chymase mouse mast cell protease-1. However, during egg deposition in the gut, an intraepithelial mastocytosis occurs in parasitized mice. These intraepithelial cells are typical mucosal mast cells as determined by their content of mouse mast cell protease-1. Recruitment of mucosal mast cells occurs in the intestinal lamina propria of infected rats soon after the parasites migrate to the liver. These findings suggest that mast cells of the mucosal phenotype are involved in the pathogenesis of the hepatic response to infection in the rat but that, in the mouse, mucosal mastocytosis is associated with intestinal sensitization by egg antigens.