First, in a comprehensive survey of the immunodominance in CD4 T cell responses to influenza using the HLA-DR1 mouse strain, we found that the abundance of total influenza reactive CD4 T cells in the periphery at memory time points (e.g., day 30–60 postinfection) diminished to 5% of the levels detected at the peak of the response (day 8–10 postinfection). This evidence concerns the gene DR1 and influenza.