CD8A and infection: CD8+ T cells were isolated from the lymph nodes of pups and adults at day 10 of infection and stimulated with BMDCs loaded with NP (366–374), PA (224–233), PB1 subunit of the viral polymerase, PB1 (703–711), or PB1-F2 protein encoded by the +1 alternative open reading frame in the PB1 gene, PB1-F2 (62–70).