Schistosoma mansoni phosphoenolpyruvate carboxykinase, a novel egg antigen: Immunological properties of the recombinant protein and identification ofa T-cell epitope

In schistosomiasis mansoni, hepatic granulomatous inflammation surrounding parasite eggs is mediated by CD4(+) T helper (Th) cells sensitized to schis tosomal egg antigens (SEA). We previously showed that a prominent lymphopro liferative response of CD4(+) Th cells from schistosome-infected C57BL/6 (B L/6) mice was directed against a 62-kDa component of SEA. A partial amino a cid sequence of the 62-kDa component was found to be identical with one pre sent in the enzyme phosphoenolpyruvate carboxykinase (PEPCK). Based on this sequence, a cDNA clone containing the entire coding region of PEPCK was id entified, and the full recombinant Schistosoma mansoni PEPCK (rSm-PEPCK) of 626 amino acids was purified from a prokaryotic expression system, rSm-PEP CK strongly stimulated a specific T-cell hybridoma, 4E6, as well as CD4(+) Th cells from SEA-immunized BL/6 mice and from infected BL/6, CBA, and BALB /c mice. In the infected mice, rSm-PEPCK elicited significant gamma interfe ron production as well as, to a lesser extent, production of interleukin-2 and -5, In BL/6 and BALB/c mice, the CD4(+) Th cell response to rSm-PEPCK w as greater than that directed against the egg antigen Sm-p40; conversely, C BA mice responded better to Sm-p40 than to Sm-PEPCK. A 12-amino-acid region (residues 398 to 409: DKSKDPKAHPNS) was demonstrated to contain a T-cell e pitope; synthetic peptides containing this epitope significantly stimulated specific hybridoma 4E6 and polyclonal CD4(+) Th cells. The identification and characterization of immunogenic egg components will contribute to the u nderstanding and possible control of T-cell-mediated schistosomal disease.