Schistosoma japonicum myosin: cloning, expression and vaccination studies with the homologue of the S-mansoni myosin fragment IrV-5

The Schistosoma japonicum homologue of the 62 kDa fragment of S. mansoni my osin (SmIrV-5), which has proved highly protective against S. mansoni infec tion in mice and mts, has been cloned and expressed as the full length 62 k Da equivalent, Sj62, and a truncated 44 kDa version, Sj44. DNA sequencing s howed the Sj62 sequence to be 88.4% identical nt the nucleic acid level and 96% identical in deduced amino acid sequence to that of SmIrV-5. The recom binant proteins (rSj44 and rSj62) were strongly recognized in Western blott ing by sera from mice multiply vaccinated with IV-irradiated S. japonicum c ercariae and weakly recognized by S. japonicum chronic infection mouse sera . Unlike SmIrV-5, mouse antisera against the recombinant S. japonicum prote ins did nor give positive recognition in immunofluorescence assay with the surface of newly transformed schistosomula of the homologous species, S. ja ponicum, nor did they react with S. mansoni schistosomula. However, the ant i-rSj62 sera clearly localized the native antigen to the subtegumental musc le layers in male adult worm sections by immunoelectron microscopy. Vaccina tion of several groups of mice and/or rats with rSj44 and rSj62 incorporate d into different adjuvants induced high titres of specific IgG but in only one experimental group was there a significant reduction in worm burden (27 %, P < 0.05). The possible reasons for the disparity between the vaccinatio n results presented here and those demonstrated in experiments using rSm62 (IrV-5) are discussed.