Mice were infected percutaneously with cercariae of Schistosoma japonicum or S. mansoni and parasites recovered by tissue-mincing from the skin or lungs or by perfusion of the mesenteric veins. S. japonicum had a narrow peak of recovery (up to 30%) from the lungs 3 days after infection, whereas lung recovery of S. mansoni peaked only on day 6 and levelled off during the following week. Infection with S. japonicum induced lung petechiae, but only after most of the parasites had left the lungs. The axillary lymph nodes draining the infection site increased in weight after infection and this effect was much greater and longer with S. mansoni than with S. japonicum. S. japonicum was perfusable from the mesenteric veins earlier (from day 3 onwards) and in higher number (40-60% from days 6 to 10) than S. mansoni (20% on day 20). The percentage of cercariae developing to adult worms was 57% for S. japonicum and 33% for S. mansoni. The data demonstrate that S. japonicum might escape from local tissue reactions in the skin and lungs and, due to its rapid migration, might induce only poor lymphocyte proliferation. As a possible consequence, S. japonicum may establish more efficiently in mice than S. mansoni.

Since pigs are important in the zoonotic transmission of schistosomiasis japonica in China, a veterinary vaccine might contribute to the control of the disease in humans. Pigs were immunized with three doses each of 10,000 cercariae of Schistosoma japonicum attenuated with ultraviolet light (400 microWatt.min/cm2). The experiment was performed with portable irradiation equipment in a rural area of the Hubei Province (P.R. China). A challenge infection of 1,000 untreated cercariae was given 2.5 or 6 months after the last immunization, and age-matched naive pigs were challenged as a control. Immunized pigs developed about 90% resistance against the challenge. The liver egg load of these animals was reduced by over 90%. Less than 0.01% of the immunizing cercariae developed to adult parasites and the vaccination had no apparent adverse influence on the pigs' health.

Various stages of Schistosoma mansoni were treated with a cytotoxin from Pseudomonas aeruginosa and their response to the damaging effect was studied in detail. Marker release and membrane potential measurements showed that the cytotoxin formed stable pores in all developmental stages. However, in juvenile 27-day-old worms, which are refractory to the killing effect of the cytotoxin, the pores had a smaller functional diameter as compared to other stages including 31-day-old worms. Furthermore, these resistant 27-day-old worms, but not susceptible older juvenile worms were able to repair the membrane lesions as shown by restoration of the resting membrane potential. In contrast, older juvenile and adult parasites were unable to cope with the breakdown of the resting potential induced by the cytotoxin. The results demonstrate the existence in 27-day-old schistosomes of effective repair mechanisms dealing with damage to the surface membrane.

When cercariae of Schistosoma mansoni and of S. japonicum were irradiated with various levels of u.v. light at 254 nm, their development to perfusable worms was reduced to below 1% at about 200 microW min cm-2. Cercariae attenuated with about 300 microW min cm-2 induced partial resistance against an homologous challenge infection in mice. No differences were observed between the two schistosome species when the same treatment was given to the cercariae. Thus the same u.v. dose can confer immunizing ability to cercariae of both S. mansoni and S. japonicum.

ABSTRACTAntibodies directed against diagnostic Mr31 000 polypeptide(s) of adultSchistosoma mansoniwere already formed in mice during prepatency. In contrast, repeated immunization of mice with homogenates of adult schistosomes failed to elicit antibodies detectable in immunoblots in the Mr31 000 region. Therefore, spleen cells of infected mice were used to produce hybridoma lines. The “miniblot technique” was developed in order to detect in hybridoma supernatants antibodies against schistosome Mr31 000 components. Electrophoretically separated totalS. mansoniproteins were transferred onto nitrocellulose, and the position of the Mr31 000 components was determined with polyclonal antisera and immunoblotting. Pieces of about 3 square mm of nitrocellulose bearing the diagnostic proteins were incubated with about 100 μ1 of hybridoma supernatant in microtitre plates and subsequently probed with peroxidase-conjugated antibody to mouse IgG. This screening technique identified hybridomas secreting antibody to the relevantS. mansoniantigens. It is applicable to other defined parasit antigens, which are, however, not available in biochemically purified form. The monoclonal antibodies produced against the proteins with diagnostic potential reacted with antigens localized in the schistosome gut.

We have examined the interaction between Schistosoma mansoni and a cytotoxin from Pseudomonas aeruginosa known to affect a variety of cell types through the formation of membrane pores. The killing effect of the cytotoxin on S. mansoni in vitro was strongly dependent on the parasite developmental stage. Skin schistosomula were most sensitive, while 4-week-old or older parasites were less so. In contrast, lung schistosomula were relatively resistant and juvenile mesenteric forms younger than 28 days were almost completely refractory to the action of the toxin. A sharp increase in sensitivity to the toxin was observed between 27 and 28 days of parasite age with a parasite length of about 1.80 mm appearing as the threshold. Thus, the schistosome sensitivity to the cytotoxin changed during parasite development in a way similar to the known sensitivity of the worms to in vitro immune attack. Killing of the parasites by the cytotoxin was preceded by the formation of vesicles which, in the case of adult worms, detached easily from the parasites. Evidence obtained by electron microscopy and by immunofluorescent assays with living worms demonstrated that the outer parasite membrane participated in the formation of the vesicle membrane. Thus, the cytotoxin may be a useful tracer for changes in the properties of the schistosome surface membrane during parasite development.

SUMMARY Living Schistosoma mansoni of various developmental stages were studied with respect to their ability to activate the complement system in sera of humans, mice and rats. Immunofluorescence assays demonstrated that binding of human C3 occurred on fresh schistosomula as well as on schistosomula prepared from mouse lymph-nodes or lungs and on adult schistosomes. However, rodent C3 was deposited only on fresh schistosomula. Deposition of human C3 on the worms' surface required activation of the complement system. The alternative pathway was shown to be involved in deposition of human C3 on schistosomes of all ages, whereas activation of the classical pathway was demonstrable only with fresh schistosomula. Immunoelectrophoretic studies demonstrated a dose-dependent cleavage of human C3 and conversion of factor B by living adult schistosomes. The results demonstrate that the ability of living schistosomes to activate complement in vitro is dependent not only on their developmental stage but also on the species of the serum.