HLA-A and influenza: To test this possibility, peptide vaccinated and naive mice were challenged i.n. with titrated numbers of the Puerto Rico/8/34 influenza strain A. We determined influenza matrix gene expression of virus infected lungs using Q-PCR, and observed a decline in lung virus titres of influenza challenged mice vaccinated with the known HLA-A*02:01 binding immunogenic M(58–66) peptide [21], but no effect in mice immunized with a mixture of the four HLA double binding peptides.