Existence of a weak cytotoxic CD4+ T cell population in mice infected with ectromelia virus

This study set to delineate MHC class II immunogenic peptides encoded in proteins expressed by A33R, 14 kDa fusion protein and p42 genes of ectromelia virus (ECTV) Moscow strain (ECTV-Mos), a virus related to variola virus (Variola vera virus) responsible for smallpox in humans. A search for a safe and efficacious vaccine against poxviruses is still required mostly because of the emerging nature of certain viruses among poxviruses. In silico prediction of peptides from the 3 protein sequences revealed 6 potential candidates. Investigations included assessment of the peptide's ability to bind to MHC class II molecules on antigen-presenting cells and to induce the proliferation, cytokine synthesis and cytotoxicity of CD4(+) T cells originating from mice previously infected with ECTV-Mos. The results show that peptide ENHAETLRAAMISLA (Pep3) predicted from the protein sequence 14 kDa fusion protein induced significant proliferation, cytokine synthesis and cytotoxicity. Also Pep3 was able to bind strongly to MHC class II molecules on A20 cells. These results suggest that a small population of CD4(+) T cells play a protective role dependent on cytotoxicity and possibly complement the CD8(+) T cells population in this regard.