The outcome of cross-priming during virus infection is not directly linked to the ability of the antigen to be cross-presented

The initiation of CD8(+) T cell (CTL) immune responses can occur via cross-priming. Recent data suggested a relationship between cross-presentation and immunodominance of epitope-specific T cells. To test this association, we evaluated the efficacy of cross-presentation for several virus epitopes in vitro and examined if this can be extrapolated in vivo. Employing lymphocytic choriomeningitis virus (LCMV), we demonstrate that the cross-presentation and cross-priming of LCMV antigens were dominated by NP396, but not NP205 when analyzing the LCMV-NP. Although with LCMV-GP, cross-presentation was dominated by GP276, and cross-priming was dominated by GP33. Importantly, although NP396 was significantly more efficient than GP33 in cross-presentation, cross-priming of their specific CTL was comparable. In a subsequent virus challenge after cross-priming, GP33-specific CTL dominated the response. Accordingly, based on our data, the ability of viral epitopes to be cross-presented in vitro does not entirely reflect what would occur in cross-priming. Thus, weak cross-presenting antigens may still cross-prime an efficient CTL response depending on other in vivo elements such as the nave T-cell precursor frequencies.