Protective immunity to Schistosoma japonicum infection depends on the balance of T helper cytokine responses in mice vaccinated with gamma-irradiated cercariae

Although the strain difference in protection of mice to Schistosoma mansoni infection has been described, limited information is available in the case of Schistosoma japonicum. In the present study, we compared the protective immunity to S. japonicum infection and cytokine production in various strains of mice vaccinated with gamma-irradiated cercariae. A significant reduction in worm recovery was observed in male and female mice of DBA/2 at a 6-week interval between vaccination and a challenge infection, whereas vaccinated mice of C57BL/6, C57BL/10, (C57BL/6 x DBA/2) F1 (B6D2F1) and (C57BL/10 x DBA/2) F1 (B10D2F1) showed no detectable level of protection. No sex-linked difference in development of resistance was observed in any of the strains so far examined. Vaccination with gamma-irradiated cercariae twice with a 3-week interval also induced significant protection against a challenge infection in DBA/2 but not in BALB/c or C57BL/6 strains. Further studies demonstrated that spleen cells of vaccinated C57BL/6 mice produced lower levels of IFN-gamma compared to the cells of vaccinated BALB/c and DBA/2. On the other hand, production of IL-10 by spleen cells was relatively higher in BALB/c mice than in the other two strains. Macrophages that had been stimulated with spleen cell culture supernatants derived from vaccinated DBA/2 damaged schistosomula more effectively than cells stimulated with supernatants derived from the other strains. These results suggest that different levels of protection observed among strains of mice depend on the balance of cytokine responses which consequently activate or suppress macrophage-mediated damage to schistosomula.

Demonstration of the target molecule of a protective IgE antibody in secretory glands of Schistosoma japonicum larvae

We have demonstrated that a mouse monoclonal IgE antibody, SJ18 epsilon.1, recognizes a 97 kDa surface molecule (Sj97) of Schistosoma japonicum larvae and that the antibody induces partial but significant protection against the skin to lung-stage of S. japonicum infection. The antibody stimulates eosinophil- and macrophage-mediated killing of schistosomula in vitro. In the present study, we isolated the putative full-length cDNA of Sj97 by screening a lambda gt11 cDNA library from S. japonicum adult worms with SJ18 epsilon.1. The predicted amino acid sequence of the cDNA showed highly significant homology to that of S. mansoni paramyosin, a potential vaccine candidate for schistosomiasis. The deletion mutants of S. japonicum paramyosin were expressed in Escherichia coli and the translation product of 443 amino acid residues of paramyosin was found to be recognized by the antibody. Moreover, we observed by immunoelectron microscopy the presence of paramyosin in the post-acetabular gland as well as in the tegument and muscle layers of the larvae. These results suggest that paramyosin is a secretory protein which may be incorporated into the tegument during the development of schistosomula, thus becoming a target for protective immunity during the migratory phase of the parasite.

Comparison of the protective efficacy on mekongi schistosomiasis in mice induced by antigens derived from cercariae, schistosomulae and adult worms

Protective efficacy of the extracts of cercariae, schistosomulae and adult worms of S. mekongi was studied in mice receiving immunizations with these extracts emulsified with Freund's complete adjuvant initially and incomplete adjuvant subsequently, and compared with mice receiving physiological saline with or without adjuvants as controls. After challenge with cercariae, the animals were sacrificed and the larvae or adult worms harvested by lung recovery and perfusion techniques on day 5 and weeks 6-8, respectively. Worm reduction rates were significantly higher in mice receiving extracts of schistosomula (59%) and adult worms (51%) than in those receiving the cercarial extracts (31%). Similar findings were obtained with the perfusion technique showing worm reduction rates of 57%, 53% and 30% in mice receiving extracts of schistosomulae, adult worms and cercariae, respectively. ELISA antibody titers were correspondingly increased in mice receiving extracts of schistosomulae and adult worms, but not in those receiving cercariae. This apparent association may be inadequate to suggest that the increase in ELISA titer be used as an indicator for resistance in mekongi schistosomiasis.

Acquired resistance to Schistosoma japonicum in IgE-deficient SJA/9 mice immunized with irradiated cercariae

Participation of IgE in protective immunity against Schistosoma japonicum was examined by comparing congenital IgE-deficient SJA/9 and IgE-producing SJL/J mice. Mice immunized with 100 irradiated cercariae 7 weeks previously were infected with 50 live cercariae. In SJL/J mice at 40 days after infection, a 3-to 4-fold increase of total IgE levels and anti-S, japonicum egg IgE antibody production were observed with no significant difference between immunized and nonimmunized mice. IgE was not detected in SJA/9 mice throughout the experiments. Protective immunity evaluated by recovery of adult worms was found in SJA/9 mice and was comparable to that of SJL/J mice. These results suggest that acquired immunity in mice with irradiated cercariae of S. japonicum was not dependent on IgE in these strains of mice.

Effects of recombinant tumour necrosis factor on antibody-dependent eosinophil-mediated damage to Schistosoma japonicum larvae

Human recombinant tumour necrosis factor (rTNF) enhanced monoclonal IgE-dependent eosinophil-mediated cytotoxicity to schistosomula of Schistosoma japonicum in a dose-dependent manner. The enhancing effect of rTNF was also observed for the antibody-dependent cytotoxicity of a human eosinophilic leukemia cell line, EoL-3, but not of another cell line, EoL-1. Observation by a slow-motion movie camera demonstrated that activated EoL-3 cells adhered to the surface of schistosomula by 6 h after incubation, which triggered intracellular movement of eosinophil granules. The granules were concentrated toward the surface of the larvae and then degranulation started. The cell membrane was left as a balloon-like remnant. Cell sorting analysis by FACStar indicated that the expression of receptors for C3bi (CR3) and low affinity FcR for IgE (Fc epsilon RII) increased on the surface of EoL-3 cells after stimulation with rTNF, while this was not observed for EoL-1 cells.

Effects of heterologous helminth infections on passive transfer of immunity using a mouse monoclonal IgE antibody against Schistosoma japonicum

Passive transfer of immunity using a mouse monoclonal IgE antibody against Schistosoma japonicum was found to be enhanced by heterologous helminth infections. BALB/c mice were infected with Toxocara canis or Nippostrongylus brasiliensis so as to induce eosinophilia prior to a challenge infection with S. japonicum. Recovery of adult schistosomes decreased in a group of mice that had been infected with T. canis and challenged with cercariae at the cutaneous site of sensitization with the IgE antibody as compared with that in mice that had been similarly treated with normal serum in the absence of T. canis infection. Histological examinations revealed a close association of polymorphonuclear cells, including eosinophils, with damaged schistosomula in the skin of T. canis-infected mice that had received the IgE antibody. An enhancement in worm reduction was also observed in mice harboring either of both nematodes when the monoclonal antibody had been injected intraperitoneally during the phase of migration of schistosomula from the skin to the lungs. In vitro studies on macrophage-mediated damage to schistosomula suggested that the enhancement in worm reduction was at least partly due to the activation of macrophages induced by the heterologous infections.

Investigation on immunity induced by Schistosoma spindale against S. mekongi in experimental mice

An investigation on immunity induced by Schistosoma spindale cercariae (cattle and swamp buffalo schistosome) against S. mekongi (human schistosome) was conducted in Swiss albino mice. The studies comprised the development patterns of homologous immunity of S. spindale and heterologous immunity induced by S. spindale against S. mekongi. The development pattern of homologous immunity was studied in mice with an immunization of 100 S. spindale cercariae. At one week intervals, between 2 to 16 weeks after immunization, they were each challenged with 500 S. spindale cercariae. Significant homologous immunity, as judged by lung recovery assay five days after challenge, occurred from week 5 to week 16 with week 8 giving the highest homologous immunity (68.1% of schistosomular reduction). Using the above information mice, with an eight-week immunization period of 100 S. spindale cercariae, were tested for resistance to heterologous S. mekongi infection. The criteria used to evaluate their immune status was schistosomular lung recovery, daily egg output, worm recovery and tissue egg count. The results showed that mice immunized with S. spindale cercariae could develop heterologous immunity against S. mekongi infection. Manifestation of immunity was demonstrated by significant reduction in mean schistosomular recovery (31.4%), in mean daily egg output per female worm (16.7%), in mean worm recovery (64.2%) and in mean egg deposition in the liver tissue and intestines per female worm (37.05%).

Lung-migration patterns of Schistosoma mekongi and S. spindale in mouse

Two groups of laboratory-bred Swiss albino mice were used to study the lung-migration patterns of Schistosoma mekongi and S. spindale. The first group was individually infected with 100 S. mekongi cercariae by hair-looping application on shaved abdomen. The latter group was individually exposed to 500 S. spindale cercariae by tail immersion. Each group of these infected mice was then divided into subgroups. The number of schistosomulae was determined using a lung recovery assay starting from the second day after infection and continuing for 15 consecutive days. The results revealed a sharp peak of both S. mekongi and S. spindale on the fifth day post cercarial infection.

Role of a mouse monoclonal IgE antibody in passive transfer of immunity to Schistosoma japonicum infection

We have been able to produce a mouse monoclonal IgE antibody specific to an adult worm antigen extracted from Schistosoma japonicum (Sj). The antibody was able to elicit passive cutaneous anaphylaxis in the rat skin against Sj with the highest titer of 1:256,000 but did not cross-react with S. mansoni antigen. The antibody recognized a 97-kDa molecule expressed on the surface of mechanically transformed schistosoma of S. japonicum. Passive transfer of the antibody into mice in the early stage of challenge infection resulted in a partial but significant reduction of recovery of adult worms. Induction of eosinophilia by an oral administration of embryonated eggs of Toxocara canis prior to challenge infection enhanced the reduction.