Helper T cells induced by a purified 28-kilodalton antigen of Schistosoma mansoni protect rats against infection.

Schistosoma mansoni adult worm 28-kilodalton (kDa) proteins were separated on polyacrylamide slab gels, recovered by electrophoretic elution, and used to immunize Fischer rats. After the second or third injection, inguinal lymph node T lymphocytes were propagated in vitro for 4 weeks in the presence of syngeneic antigen-presenting cells and adult worm antigens in medium containing interleukin-2. After this period of culture, 99% of the cells expressed the W3/13+ surface phenotype and 93% of the cells expressed the W3/25+ surface phenotype. These cells were then tested for their in vivo functional activity after transfer to Fischer rats that had been either infected with S. mansoni cercariae or immunized with the 28-kDa purified protein. In each case, an increase of S. mansoni-specific antibodies was observed. Whereas anti-28-kDa antibodies were only detectable at day 40 postinfection in controls injected with normal T lymphocytes, they appeared as early as day 13 postinfection when the animals received 28-kDa protein-specific T lymphocytes. This led to an effective protection of infected rats (45 to 85%) which correlated with the increase in S. mansoni-specific antibodies. These results therefore demonstrate that the 28-kDa protein possesses epitopes capable of activating helper T cells, which confer a strong protective immunity by enhancing the production of cytotoxic antibodies. The stimulation of the 28-kDa-specific T cells with recombinant proteins suggests that the major epitopes are located toward the carboxylic end of the molecule.