Identification and characterization of H-2d restricted CD4+ T cell epitopes on Lpp20 of Helicobacter pylori

Background: Previous investigation has demonstrated that CD4(+) T cells play a crucial role in effective immunity against Helicobacter pylori (H. pylori) infection. It has been well proved that Lpp20 is one of major protective antigens that induce immune responses after H. pylori invades host. Therefore it is valuable to identify CD4(+) T cell epitopes on Lpp20, which is uncharacterized. Methods: Putative epitopes of H-2(d) restricted CD4(+) T cell on Lpp20 of H. pylori were predicted by the SYFPEITHI algorithm and then eight hypothetical epitope peptides were synthesized. After BALB/c mice were primed with recombinant Lpp20, splenic CD4(+) T cells were isolated and stimulated with synthesized peptides to measure T cell proliferation and MHC restriction. Cytokine profile was determined by ELISA and real-time PCR. Two identified epitopes were used to immunize mice to investigate CD4(+) T cell response by flow cytometry. Results: Two of eight peptides were able to stimulate CD4(+) T cell proliferation and were mapped to residues 83-97aa and 58-72aa on Lpp20 respectively. These two peptides additively stimulated Th1 cells to secrete IFN-gamma. The percentage of CD4(+) T cell from mice immunized with two identified epitopes respectively was higher than the control group. Conclusion: The identification and characterization of two CD4(+) T cell epitopes of Lpp20 helps understand the protective immunity of Lpp20 in H. pylori infection and design effective epitope vaccines against H. pylori.