ICOS agonist treatment reduces the frequency of CD8⁺ T cells but does not affect the polyclonal CD4⁺ T cell compartment.

<p>IAV infected BALB/c mice were treated with ICOS agonist or hamster IgG isotype (control antibodies) as depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100970#pone-0100970-g001" target="_blank">Figure 1A</a>. On day 7–9 post infection the percentage of CD8⁺ in BAL (day 7, pooled data from two independent experiments) and lung (day 8) as well as CD4⁺ T cells in lung (day 9) was determined by flow cytometry. The dots in all experiments represent data from individual mice (A). <i>In vitro</i> apoptosis assays were performed, as described in materials and methods, followed by annexin-V staining on live T cells and subsequent flow cytometric analysis. Dot plot graphs indicate percentages of apoptotic CD8⁺ and CD4⁺ T cells (mean of triplicate wells) plotted against increasing concentration of ICOS agonist antibody added to the culture. CD3 alone (mean of triplicate wells) represents that cells were stimulated by anti-CD3 treatment, in the absence of ICOS agonist; untreated (mean of duplicate wells) represents that cells were neither anti-CD3 stimulated nor treated with ICOS agonist. Column statistics were performed for the apoptosis assay (the data is expressed by mean/SEM) (B and C).