Objective: To identify the immunologic property of a synthetic peptide Sj97-P22 from paramyosin of Schistosoma japonicum (Sj97).
Methods: Twenty-seven female C57BL/6 mice were divided into 3 groups each with 9 mice, Sj97-P22, control peptide and PBS groups, and each mouse was respectively immunized twice (seven days interval) with 100 microg of Sj97-P22, control peptide or PBS, emulsified with equal value of complete Freund's adjuvant. Seven to ten days after the second immunization, the mouse spleen mononuclear cells were isolated for three-color flow cytometry to detect intracellular cytokines IFN-gamma and IL-4. Then the spleen mononuclear cells were co-cultured with Sj97-P22, control peptide or PBS respectively, and the incorporation rate of 3H-thymidine, as well as the levels of IL-2, IFN-gamma and IL-4 in the cultured cell supernatant, were measured.
Results: In CD4+ T cells, the percentage of IFN-gamma-producing cells in Sj97-P22 group [(8.05 +/- 0.54)%] was significantly higher than that of the control peptide group [(4.74 +/- 1.04)%] or PBS group [(6.51 +/- 0.49)%] (P<0.05), while the proportion of IL-4-producing cells was significantly lower in Sj97-P22 group [(0.60 +/- 0.11)%] than that in PBS group [(1.31 +/- 0.27)%] (P<0.05). Also, compared with control peptide or PBS stimulation, Sj97-P22 was able to effectively stimulate the proliferation with the stimulation index (3.12 +/- 1.59) and a higher secretion of IL-2 [(9.13 +/- 1.54) pg/ml] and IFN-gamma [(39.75 +/- 9.69) pg/ml] of spleen mononuclear cells in Sj97-P22-immunized mice (P<0.05). Both Sj97-P22 and control peptide were not effective stimulators to the spleen mononuclear cells from mice of PBS group.
Conclusion: It is highly possible that Sj97-P22 is a Th1-type epitope specific for C57BL/6 mice.