Spectratype profiles for selected Vβ gene families of NP- and PA-specific CD8 T cells from young and aged influenza virus–infected mice. Representative spectratype analysis of CD8 T cells from young, naive mice (top row) or purified NP- (middle rows) and PA-specific (bottom rows) T cells isolated by FACS-sorting from representative individual young and aged mice 10 d after influenza virus infection. Relative intensity is plotted along the y axis and nucleotide size is plotted along the x axis. The numbers refer to the size, in base pairs, of the individual expanded peaks. Young mouse 5, aged mouse 5, and aged mouse 4 had 28, 8, and 1% NP-specific cells among total CD8 T cells. Young mouse 4, aged mouse 2, and aged mouse 4 had 9, 19, and 4% PA-specific cells among total CD8 T cells, respectively. The complete spectratype analysis for all mice examined is presented in Tables I and II. The y axis is the same for all spectratype profiles, with the maximal height at 6,400 arbitrary units.