Effector CD8+ T cells are generated in response to an immunodominant epitope in type III effector YopE during primary Yersinia pseudotuberculosis infection.

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 naïve 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 YopE69-77-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).