Updated publication reference for PubMed record(s): 31253788. The magnitude of CD8+ T lymphocyte (CTL) responses to infection is a function of the available naïve T cell repertoire, combined with the context and duration of antigen presentation. Whilst T cell repertoires are relatively easily studied, the context and abundance of epitopes presented on infected cells and dendritic cells (DCs) and their subsequent impact on CTL responses are generally poorly understood. Using quantitative mass spectrometry, we identified and quantified the abundance of 21 class 1 Major Histocompatibility Complex molecule (MHCI)-restricted influenza A virus (IAV)-derived peptides following either direct presentation or cross-presentation. All identified peptides, including seven novel epitopes, elicited T cell responses in infected C57BL/6 mice. Quantitation of IAV epitopes displayed via direct presentation showed a maintenance of relative epitope abundance across distinct cell types, reflecting common antigen processing mechanisms. Comparison of epitope levels displayed via direct presentation and cross-presentation revealed a broad range of directly presented epitope abundances, which was normalised during cross-presentation. Further, we observed a clear disparity in the abundance of the two key immunodominant IAV antigens, wherein direct infection drove optimal nucleoprotein (NP)366-374 presentation, while cross-presentation was optimal for acid polymerase (PA)224-233 presentation. This study provides a detailed dissection of viral pMHCI abundance after infection and reveals the importance of both direct and cross-presentation in driving dominant CTL responses. The study also demonstrates how empirical assessment of epitope abundance in both modes of antigen presentation is necessary to fully understand the immunogenicity and response magnitude to T cell epitopes.