CD8A and infection: In this study, at 2 and 3 weeks post intravenous infection of mice, we also found that all bacteria could induce the activation of CD4+ and CD8+ T lymphocytes, but X4550(pYA3334-P-SspH2-EscI) induced significantly lower level of CD8+T cells activation than X4550(pYA3334-P-SspH2) or X4550(pYA3334).