Vaccination of sheep against Schistosoma japonicum with either glutathione S-transferase, keyhole limpet haemocyanin or the freeze/thaw schistosomula/BCG vaccine

Abstract

The protective potential of glutathione S-transferase (GST), keyhole limpet haemocyanin (KLH) and the freeze/thaw (F/T) schistosomula/BCG vaccine was evaluated against Schistosoma japonicum in the natural sheep host. Groups of ten sheep each were vaccinated as follows: • Group I: 2 × F/T 30 000 schistosomula + BCG 3 × 10 8 organisms, with a 2 week interval between vaccinations (F/T ‘Low’). • Group II: 3 × F/T 20 000 schistosomula + BCG 3 × 10 8, with 4 week interval (F/T ‘High’). • Group III: 2 × GST 0.24 mg + FCA (Freund's complete adjuvant) with 2 week interval (GST ‘Low’). • Group IV: 3 × GST 0.24 mg + FCA, with 4 week interval (GST ‘SHigh’). • Group V: 2 × KLH 1.0 mg in phosphate-buffered saline (PBS), with 2 week interval (KLH ‘Low’). • Group VI: 3 × KLH 1.0 mg in PBS, with 4 week interval (KLH ‘High’). • Group VII: control (not vaccinated). Specific antibody, detected by GST-enzyme-linked immunosorbent assay (ELISA) and KLH-ELISA on the day after the last vaccination and 1, 2 and 3 weeks post-challenge, was found in all GST- or KLH-vaccinated groups. The same was found in F/T schistosomula-vaccinated groups against crude adult worm antigen (AWA). In Western blotting all GST-vaccinated sera recognized 26 kDa and 28 kDa bands on the challenge day and at 3 and 11 weeks post-challenge. Mean faecal egg counts between Weeks 6 and 10 post-challenge were reduced in a statistically significant way at five time points in the four groups, i.e. 83.38% ( P<0.005) in Group 11, 49.29% ( P<0.025) in Group III, 47.9% ( P<0.05) and 71.15% ( P<0.01) in Group IV, 52.0% ( P<0.025) and 66.38% ( P<0.025 S) in Group VI. On autopsy and perfusion 1 week after the last faecal count, adult worm reductions were obtained of 40.36% ( P<0.05) in Group I, 37.26% ( P<0.025) in Group II, 24.73% (not significant) in Group III, 35.93% ( P<0.025) in Group IV, 27.46% ( P<0.05 in Group V and 33.81% ( P<0.01) in Group VI. Mean tissue egg densities were also reduced significantly in Groups III, IV, and VI, especially in Group IV vaccinated animals. Mean liver egg granulation diameters of the vaccinated groups were found to be less than those of the controls but there was no statistical significance. These experimental data are analysed for each antigen in the light of the main effector pathway or the main target of immune attack, and the prospects of using them as potential prophylactic vaccines are discussed.