CD8A and influenza: In IL-15 blocked animals, differences in viral load were apparent as early as d2 p.i. where viral titers were about 3× higher through day 3 p.i. (Figure 2E); however, these animals seemed to regain control of viral replication by day 4 p.i., which perhaps corresponds with the early entry of cells of the adaptive immune response as anti-influenza specific CD8 T cells are first detectable in the lung airways by d6 post infection by flow cytometry ([34] and data not shown).