Schistosoma mansoni: immunoreactivity of human sera with the surface antigen Sm23

Sm23, a surface antigen of Schistosoma mansoni, elicits an immune response in patients infected with the parasite, although to a lesser degree than Sj23, the homologue of Sm23 in Schistosoma japonicum. To characterize the host immune response to Sm23, we have expressed full-length Sm23 using the baculovirus expression system and have also expressed the N-terminal 133 amino acids and the 85 C-terminal amino acids by means of the prokaryotic vector pGEX. A total of 70 sera from patients from Sudan and Egypt were examined for alpha-Sm23 antibodies in an ELISA and in Western blot analysis using both the C-terminal polypeptide and the full-length protein. A subset of these sera was also tested for reactivity with the N-terminal polypeptide. The alpha-Sm23 antibody titers in infected patients varied widely and were not correlated with egg counts or age of the individuals. Most of the seroreactivity was directed against the C-terminal polypeptide.