MUCOSAL MAST-CELLS AND THE ALLERGIC RESPONSE AGAINST NEMATODE PARASITES

IgE-mediated Type-I allergic reactions at nematode-infected mucosal su rfaces are considered to have a direct protective function. The contri bution of mucosal mast cells (MMC) to these mucosal allergic responses is reviewed. In addition to the T helper 2 cell-mediated regulation o f MMC hyperplasia during nematode infection the kit ligand, stem cell factor (SCF), plays a key role in the early development of the MMC res ponse. Studies in the mouse suggest that MMC protect against certain n ematodes which enter the mucosa but not against lumen dwelling nematod es. The protective roles of MMC in other species, including sheep, are less certain and there is some evidence that MMC might enhance parasi te fecundity, The measurement of MMC-specific granule chymases release d systemically, and into the gut lumen, permits precise monitoring of mast cell activation and suggests that the secreted chymases may targe t epithelial junctional complex proteins, thereby causing increased mu cosal permeability. The abundant intraepithelial MMC found in parasiti sed mucosa may, therefore, serve as epithelial gatekeepers permitting the translocation of plasma proteins onto the mucosal surface.