Recovery of schistosomula of Schistosoma mansoni from mouse skin: involvement of mast cells and vasoactive amines.

Normal and S. mansoni-infected mice were exposed to the penetration of 250-350 cercariae through one ear. Two days later, when the ear was removed and chopped, 30 to 50% more schistosomula were recovered from the ears of normal mice than from the ears of infected (immune) mice. Administration of cyproheptadine, a histamine-serotonin antagonist (2 mg/kg), 30 min before challenge infection rendered immune mice indistinguishable from normal mice. Partial depletion of histamine by pretreatment with compound 48-80, a histamine releaser (1 mg/kg) 2 days before challenge infection increased the numbers of schistosomula recovered from the ears of both normal and immune mice. These results are interpreted to mean that vasoactive amines released by skin mast cells play an important role in hindering the viable passage of schistosomula through the skin of normal and immune mice.