Cercariae, but not schistosomules, of Schistosoma mansoni are capable of activating the release of histamine from rat peritoneal mast cells in vitro. This activation occurs in the absence of serum and does not require adherence to mast cells. The amount of histamine released is proportional to the number of cercariae present. This mast-cell triggering factor from cercariae remains to be characterized biochemically, but may well play a causal role in the “swimmer's itch” associated with primary schistosome exposure.
Present address: Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106.