Effector CD8+ T Cells Are Generated in Response to an Immunodominant Epitope in Type III Effector YopE during Primary Yersinia pseudotuberculosis Infection

ABSTRACT YopE is a virulence factor that is secreted into host cells infected by Yersinia species. The YopE C-terminal domain has GTPase-activating protein (GAP) activity. The YopE N-terminal domain contains an epitope that is an immunodominant CD8 + T cell antigen during primary infection of C57BL/6 mice with Yersinia pseudotuberculosis. The characteristics of the CD8 + T cells generated in response to the epitope, which comprises YopE amino acid residues 69 to 77 (YopE 69–77 ), and the features of YopE that are important for antigenicity during primary infection, are unknown. Following intravenous infection of naive C57BL/6 mice with a yopE GAP mutant (the R144A mutant), flow cytometry analysis of splenocytes by tetramer and intracellular cytokine staining over a time course showed that YopE 69–77 -specific CD8 + T cells producing gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) were generated by day 7, with a peak at day 14. In addition, ∼80% of YopE 69–77 -specific CD8 + T cells were positive for KLRG1, a memory phenotype marker, at day 21. To determine if residues that regulate YopE activity by ubiquitination or membrane localization affect the antigenicity of YopE 69–77 , mice were infected with a yopE ubiquitination or membrane localization mutant (the R62K or L55N I59N L63N mutant, respectively). These mutants elicited YopE 69–77 -specific CD8 + T cells producing IFN-γ and TNF-α with kinetics and magnitudes similar to those of the parental R144A strain, indicating that primary infection primes effector CD8 + T cells independently of the ubiquitination or membrane localization of YopE. Additionally, at day 7, there was an unexpected positive correlation between the numbers of YopE 69–77 -specific CD8 + T cells and CD11b + cells, but not between the numbers of YopE 69–77 -specific CD8 + T cells and bacterial cells, in spleens, suggesting that the innate immune response contributes to the immunodominance of YopE 69–77 .