Expression and immune response analysis of Schistosoma japonicum VAL-1, a homologue of vespid venom allergens

Many parasites such as trematodes and nematodes have been found to express members of a gene family variously termed as venom allergen-like protein (VAL) or sperm-coating protein (SCP)-like protein. The molecular functions of these proteins remain unclear. We isolated the corresponding gene from Schistosoma japonicum, which we designated as Sj-VAL-1. The cDNA of Sj-VAL-1 contains an open reading frame encoding 221 amino acids, the first 25 residues being a putative secretion signal. RT-PCR analysis confirmed that Sj-VAL-1 was transcribed mainly in cercariae and eggs stages. Western blot analysis indicated that Sj-VAL-1 protein was an egg excretory-secretory products (ES products). Immunofluorescence showed it was secreted by eggs, head gland, and penetration glands of cercariae. In S. japonicum-infected mice, Sj-VAL-1-specific antibody significantly increased 6 weeks after infection and a higher level of IgG1 antibody contrast to IgG2a antibody indicated that a polarized Th2 immune response could be induced by Sj-VAL-1. These findings suggest that Sj-VAL-1 must play a role in the interaction between parasite and host. Its role as a potential modulator of immune function or as a pathogenic factor of granuloma formation in schistosomiasis needs further study.