CD8^dim exhibit decreased expression of costimulatory molecules and increased expression of adhesion molecules.

<p>A) Histograms from flow-cytometry based-phenotyping at 6 weeks after infection (or age-matched, non-infected controls) compare the relative expression of the costimulatory molecules CD28, ICOS, and 4-1BB between CD8 T cells from non-infected animals (gray filled area), CD8^bright (solid black line) from MHV68-infected animals, and CD8^dim (solid red line) from MHV68-infected animals. Each cell population represents the combined results from 5 individual mice. Similar results (not shown) were observed 3 weeks after infection. B) Flow-cytometric phenotyping from mice 6 weeks after infection (or age-matched, non-infected controls) compare the relative expression of the adhesion molecules LFA-1 and VLA-4 between CD8 T cells from non-infected animals (gray filled area), CD8^bright (solid black line) from MHV68-infected animals, and CD8^dim (solid red line) from MHV68-infected animals. Each cell population represents the combined results from 5 individual mice. Similar results (not shown) were observed 3 weeks after infection. C) Comparison of gene expression profiles between CD8+ T cells from non-infected animals, CD8^bright from infected animals, and CD8^dim from infected animals (additional data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071221#pone.0071221.s002" target="_blank">Table S2</a>). Data shown from 3 independent experiments, with 1–3 biologic replicates and 1–4 technical replicates each. D) Flow cytometric analysis of CD8+ T cells from MHV68-infected animals at 6 weeks after infection identifies MHV68-specific CD8 T cells by the use of both MHC tetramers and peptide-stimulated IFN-γ release. The plots show MHV68-specificity versus CD8 surface expression. Each plot represents combined results from 5 mice. E) Flow cytometric analysis of CD8+ T cells from MHV68-infected mice at 6 weeks after infection demonstrating TCR Vβ4 staining versus CD8 staining. Each plot represents combined results from 5 mice. F) Longitudinal analysis of total CD8^dim cells (dotted red line), CD8^dim Vβ4- (solid green line), and CD8^dim Vβ4+ (dashed gray line) from MHV68-infected mice 6 weeks after infection (n = 10, except for week 1; n = 5). Error bars represent 1 standard deviation.