Identification of the immunodominant T cell epitope of p38, a major egg antigen, and characterization of the epitope-specific Th responsiveness during murine schistosomiasis mansoni.

A recently cloned major Schistosoma mansoni egg Ag p38 induced and elicited strong Th1-type responsiveness in mice of H-2k haplotype. Now, we have identified the immunodominant T cell epitope of p38 and analyzed the dynamics of epitope-specific Th responsiveness during murine schistosomiasis mansoni. Overlapping recombinant and synthetic peptides that encompassed the full-length 354 amino acid of p38 were tested for proliferation and cytokine production in peptide- or p38-sensitized mice. The immunodominant T cell epitope of p38 that elicited pulmonary granuloma formation was localized within peptide P4 (amino acids 235-249). The P4-specific cytokine response of splenocytes that had been sensitized s.c. with p38, P4 or soluble egg Ags in IFA, or i.p. with 3000 eggs was predominantly as the Th1 type, with strong IL-2 and IFN-gamma, but trace amounts of IL-4 and IL-5 secretion. At 6.5 wk of infection, splenocytes and mesenteric lymph node cells responded to p38/P4 peptides with predominantly Th1-type responsiveness. This response did not switch to a Th2-type pattern from 8 wk onwards; rather, it underwent down-modulation. Moreover, the hepatic granuloma lymphocytes at 6.5 wk responded to p38/P4 predominantly with Th1-type cytokine production, indicating that they participate in early granuloma formation. From 8 wk onwards an immune deviation to the p38-specific response was observed that was manifested by rising IgG1, IgE, and IgG2a Ab production as opposed to declining Th1- and Th2-type cytokine secretion.