Mucosal mast cells and the allergic response against nematode parasites.

IgE-mediated Type-I allergic reactions at nematode-infected mucosal surfaces are considered to have a direct protective function. The contribution of mucosal mast cells (MMC) to these mucosal allergic responses is reviewed. In addition to the T helper 2 cell-mediated regulation of MMC hyperplasia during nematode infection the kit ligand, stem cell factor (SCF), plays a key role in the early development of the MMC response. Studies in the mouse suggest that MMC protect against certain nematodes which enter the mucosa but not against lumen dwelling nematodes. The protective roles of MMC in other species, including sheep, are less certain and there is some evidence that MMC might enhance parasite fecundity. The measurement of MMC-specific granule chymases released systemically, and into the gut lumen, permits precise monitoring of mast cell activation and suggests that the secreted chymases may target epithelial junctional complex proteins, thereby causing increased mucosal permeability. The abundant intraepithelial MMC found in parasitised mucosa may, therefore, serve as epithelial gatekeepers permitting the translocation of plasma proteins onto the mucosal surface.