Earlier studies of influenza-specific CD8+ T cell immunodominance hierarchies indicated that expression of the H2Kk MHC class I allele greatly diminishes responses to the H2Db-restriced DbPA224 epitope (acid polymerase, residues 224-233 complexed with H2Db). The results suggested that the presence of H2Kk during thymic differentiation led to the deletion of a prominent Vβ7+ subset of DbPA224-specific TCRs. The more recent definition of DbPA224-specific TCR CDR3β repertoires in H2b mice provides a new baseline for looking again at this possible H2Kk effect on DbPA224-specific TCR selection. We found that immune responses to several H2Db- and H2Kb-restricted influenza epitopes were indeed diminished in H2 bxk F1 versus homozygous mice. In the case of D bPA224, lower numbers of naive precursors were part of the explanation, though a similar decrease in those specific for the Db NP366 epitope did not affect response magnitude. Changes in precursor frequency were not associated with any major loss of TCR diversity and could not fully account for the diminished DbPA224-specific response. Further functional and phenotypic characterization of influenza-specific CD8+ T cells suggested that the expansion and differentiation of the DbPA224-specific set is impaired in the H2bxk F1 environment. Thus, the DbPA 224 response in H2bxk F1 mice is modulated by factors that affect the generation of naive epitope-specific precursors and the expansion and differentiation of these T cells during infection, rather than clonal deletion of a prominent Vβ7+ subset. Such findings illustrate the difficulties of predicting and defining the effects of MHC class I diversification on epitope-specific responses.