J. Bain

Immunological control of hepatotoxicity and parasite egg excretion in Schistosoma mansoni infections: stage specificity of the reactivity of immune serum in T-cell deprived mice

Within seven weeks of infection with 200 Schistosoma mansoni cercariae, T-cell deprived mice have been shown to suffer from extensive microvesicular damage to hepatocytes, and an inability to excrete parasite eggs at the same rate as comparably infected, immunologically intact controls. Administration of serum (CIS) from chronically infected, immunologically intact donors prevented the development of microvesicular cell damage and partially restored egg excretion rates in infected deprived mice. Serum pools obtained from mice injected either with intact S. mansoni eggs or with a homogenate of eggs emulsified in Freunds complete adjuvant (FCA) were as effective as CIS in preventing hepatotoxicity and restoring the rate of egg excretion in infected deprived recipients. The degree of protection of liver tissue afforded by immune sera could be monitored either by histopathological examination of liver sections or by estimation of serum transaminase concentrations, the results from both assays being generally in agreement. Sera from donor mice injected with cercarial or worm antigens in FCA were relatively inactive either in protecting against S. mansoni-induced liver damage or in reconstituting egg excretion rates in infected deprived mice. Serum from donor mice infected with 25 cercariae became hepato-protective between 49 and 53 days after infection of the donors, and the degree of hepatoprotective activity and egg excretion reconstituting capacity in the serum of 25 cercariae-infected donors was shown to increase between 8 and 16 weeks after infection. Increasing the size of infection of the serum donors to 100 cercariae gave only a marginal increase of hepatoprotective activity at 7 weeks when compared with serum donors infected with 25 cercariae for 7 weeks. Liver parenchymal cells of very heavily infected, immunologically intact mice were found to show microvesicular damage similar to that in livers of infected deprived mice, and administration of CIS to these normal mice was histopathologically protective. However, the elevated serum transaminase concentrations obtaining in the infected normal mice were not reduced to any extent by CIS. The results obtained from serum-reconstituted deprived mice are discussed in terms of the contribution they may make to a better understanding of the host-parasite relationship in immunologically intact mice.

Identification and partial purification of an antigen (ω1) from Schistosoma mansoni eggs which is putatively hepatotoxic in T-cell deprived mice.

T-cell deprived mice heavily infected with Schistosoma mansoni suffer from severe microvesicular damage to hepatocytes within seven weeks of infection. The damage can be prevented by administration of serum (CIS) obtained from mice chronically infected with S. mansoni or from mice immunized with intact or homogenized S. mansoni eggs. Reaction of serum samples from individual chronically infected mice in immunoelectrophoresis with S. mansoni egg homogenate has enabled the identification of at least 12 distinct immuno precipitation reactions. Precipitating antibody against one S. mansoni egg antigen, omega 1, has been detected in all mice with patent chronic infections, and anti-omega 1 antibody is the most concentrated of the precipitating anti-egg antibody species in pooled CIS. Pooled serum obtained from infected intact mice reacting predominantly against omega 1 was found partially to prevent the hepatotoxicity reaction on transfer to infected deprived mice. Serum samples from mice injected with egg homogenate fractionated either by preparative electrophoresis or by cation exchange chromatography, and containing antibodies reactive with antigen omega 1 in immunoprecipitation, were fully protective against liver cell damage induced by S. mansoni in deprived mice. Sera from mice immunized with other S. mansoni egg fractions, and which did not contain antibodies reactive with omega 1, were not hepatoprotective. Antigen omega 1 is compared and contrasted with other S. mansoni egg antigens that have been described.

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse. I. Demonstration of resistance to reinfection using a model system that involves perfusion of mice within three weeks of challenge

The degree of resistance acquired by Schistosoma mansoni-infected mice against homologous challenge has been determined by perfusion of the animals within three weeks of the challenge, at which time the challenge-derived organisms were morphologically distinguishable from the primary infection which induced the resistance. The method has been compared with assays based on determination of the number of organisms migrating through the lung, and with perfusions at a later time when the challenge has matured. The results obtained with the three week perfusion method, showing that resistance was acquired by eight weeks after a primary infection, were confirmed by the longer survival of, and reduced egg excretion rates and tissue egg burdens in the experimental animals relative to respective challenge control animals. However, some discrepancy in challenge-derived worm numbers was found between animals perfused three weeks after challenge and those autopsied at later times. The possible reasons for this difference are discussed. The degree of resistance that was acquired was to some extent dependent on the size of the challenge infection.

The stage-, strain- and species-specificity of a Schistosoma mansoni egg antigen fraction (CEF6) with serodiagnostic potential

The immunological properties of CEF6, a cationic fraction of Schistosoma mansoni egg homogenate (SEA) containing two antigens, omega 1 and alpha 1, have been further investigated in two assays, immunoelectrophoresis (IEP) and enzyme immunoassay (ELISA). Although precipitating antibodies to antigen omega 1 were amongst the first to appear in mice with patient infections, IgG reactivity against CEF6 in ELISA trailed somewhat behind that of IgG activity against unfractionated SEA. Specificity of the two antigens in CEF6 to the egg stage of the parasite life-cycle was demonstrated by the failure of immunizations with cercarial or worm antigens to induce antibodies which reacted against either alpha 1 or omega 1 in IEP, or against CEF6 in ELISA. Mice infected with S. mansoni strains derived from geographically distinct areas, including the Caribbean, South America and Africa, produced antibodies which were reactive against CEF6 prepared from eggs of a Puerto Rican S. mansoni strain that had been maintained in the laboratory for many years. Of the different precipitating anti-SEA antibody species induced by the various S. mansoni strains in mice, those reactive against antigen omega 1 appeared to be present in highest titre. Sera from mice chronically infected with S. japonicum and S. haematobium failed to precipitate CEF6 in IEP and were less reactive with CEF6 than with S. mansoni SEA in ELISA. However, similar degrees of ELISA reactivity against S. mansoni CEF6 and SEA were given by sera from mice infected with S. bovis. The results support the notion that the antigens in CEF6 may be useful in the serodiagnosis of schistosomiasis mansoni infections.

The pathological effects of immunosuppression of Schistosoma mansoni-infected mice, with particular reference to survival and hepatotoxicity after thymectomy and treatment with antithymocyte serum, and treatment with hydrocortisone acetate.

The effects of various immunosuppressive regimes on the survival and liver pathology of mice infected with Schistosoma mansoni were investigated. T-cell deprivation before infection (by adult thymectomy and subsequent anti-thymocyte serum administration), or treatment with hydrocortisone or cyclophosphamide or azathioprine after infection, all reduced survival of infected mice when compared with immunologically intact, infected mice. T-cell deprivation or steroids produced severe liver damage in infected mice despite a reduction in the size of the peri-oval granulomatous inflammatory reaction. Administration of chronic infection serum reduced liver damage in both T-cell-deprived and steroid-treated animals, but improved survival only in the deprived animals and not to the level seen in normal infected mice. The liver damage in immunosuppressed mice was not due to opportunistic bacterial infection. Thus, although immunosuppression reduced the granulomatous response to schistosome eggs in the livers of infected mice (as it does to eggs injected intravenously into the lungs), survival time was decreased. The relevance of these findings to human S. mansoni infections is discussed.

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse. 2. The time at which resistance to reinfection develops

Mice developed a partial resistance against homologous challenge with Schistosoma mansoni as early as two weeks after primary infections of 35 to 75 cercariae, and the degree of protection increased to an apparent maximum by 6 weeks. Animals given a primary infection of only 25 cercariae required a longer period to acquire maximum resistance.

Parasitological evaluation of curative and subcurative doses of 9-acridanone-hydrazone drugs against Schistosoma mansoni in baboons, and observations on changes in serum levels of anti-egg antibodies detected by ELISA

Derivatives in the class of 9-acridanone-hydrazones were found to be highly active against Schistosoma mansoni in baboons. Single doses of 25 mg/kg were fully effective. Data are presented showing changes detected by ELISA in antibody levels against schistosome eggs which correlated positively with the effect of chemotherapy. This approach may help to evaluate the effects of treatment of human schistosomiasis where the detection of low egg counts is problematic.