A majority of aged C57BL/6 mice show reduced CD8 T cell responses to influenza NP, but not to PA or PB1. BAL and lung tissue were harvested from individual young (closed symbols) and aged (open symbols) C57BL/6 mice 10 d after influenza virus infection. Young and aged mice presented with comparable frequencies (A) and absolute numbers (B) of CD8 T cells within the BAL and lung tissue. The frequencies (C) and total numbers (D) of CD8 T cells positive for NP (NP_366-374/D^b), PA (PA_224-233/D^b), or PB1 (PB1_703-711/K^b), assessed by tetramer staining of the BAL cells from infected mice, are shown. Bars indicate the medians calculated from data compiled from four independent experiments (11 young and 19 aged mice for NP and PA, and 10 young and 14 aged mice for PB1). Significance was assessed using the Mann-Whitney rank test (two-tailed, 95% confidence).