Schistosoma mansoni elastase: an immune target regulated during the parasite life-cycle

Recombinant Schistosoma mansoni elastase was expressed in Escherichia coli and an antiserum raised against the recombinant protein was used to investigate stage-specific control of elastase in the parasite, and to determine whether the enzyme could form the basis of a strategy to prevent larval invasion of the host. Results showed that the expression of elastase is developmentally regulated, even if the basal promoter activity does not seem to be stage specific. The analysis of mRNA expression showed the presence of elastase transcript in adult worms although we could not detect the protein at this stage, suggesting that S. mansoni employs a form of translational control. The measurement of elastase levels in supernatants of culture schistosomula combined with the localization of elastase in cercarieae invading mouse skin showed that the enzyme is heavily released during penetration. Finally, we studied the cytotoxic activity of rat anti-elastase sera, and the analysis of the isotypic profile suggested that IgG2a anti-elastase may be responsible for the cytotoxic effect.