Features of Schistosoma mansoni infection in SCID mice.

Features of Schistosoma mansoni infection in SCID mice, which lack functional T- and B-lymphocytes, were investigated. The retarded development of parasites as well as reduction of liver egg recovery in SCID mice was significantly lower than those in congenic counterpart C.B-17 mice. Furthermore, the rate of parasite recovery from SCID mice with primary infection was always lower than that from C.B-17 mice by 20%, showing the innate resistance to S. mansoni infection. SCID mice vaccinated with UV-attenuated S. mansoni cercariae did not show protective immunity against a homologous challenge infection. The present innate resistance exhibited in SCID mice is discussed in relation to cell mediated immunity of macrophage activation by IFN-gamma which would not involve T-lymphocytes but is initiated by IL-12 and TNF-alpha cytokines. SCID mice may provide novel information on the host-parasite relationship in schistosome infections.

Schistosoma mansoni: relocation of parasites to lungs from hepatic portal system in rodents.

The prevalence and development of adult worms in the lungs of mice and gerbils infected with Schistosoma mansoni was investigated. All infected BALB/c mice harbored the schistosomes in their lungs at 10-12 weeks post-infection, showing the distinct relocation of adult worms to the lungs, from the hepatic portal system. The male and female flukes from lungs of BALB/c mice were significantly smaller than those from livers. The percentage of gravid females in lungs was considerably lower than that in the livers. The number of eggs recovered from lungs of BALB/c mice and gerbils having lung female worms, however, was higher than that from animals without lung females, indicating egg deposition of lung females. The number of eggs detected in the brains correlated well with the number of eggs from the lungs in BALB/c and ICR mice. Out of 119 infected gerbils at 8 weeks post-infection, only two animals had egg-emboli in the brain vessels, although many eggs embolized in the lungs of those animals. These data suggest that transfer of worms to the lungs from livers involves reduction of worm recovery from the portal circulation, and also pulmonary pathology of the disease.