FIG. 5.

ICOS is required for normal CD8 T-cell function in response to Salmonella-OVA. ICOS^−/− and (C57BL/6 × Sv129) F1 mice were infected i.p. as described in the legend to Fig. 1 and were sacrificed on day 21. (A) Cells were restimulated with the SIINFEKL peptide for 6 h in the presence of GolgiStop and then stained with mAb to CD8 and CD62L before intracellular staining for IFN-γ. The events were gated on live CD8⁺ T cells. The values are the median values from a representative experiment, and the numbers in the upper left quadrants indicate the percentages of CD8 T cells that were stained with anti-IFN-γ. The means (%) ± standard errors of the means for the groups are as follows: for WT mice, 4.43 ± 0.86; for ICOS^−/− mice, 2.28 ± 0.93; and for naïve mice, 0.40 ± 0.13. The data are representative of four experiments performed with an average of three mice per group. An asterisk indicates that the P value is <0.05. (B) Ex vivo CTL assay. Cells were incubated with ⁵¹Cr-labeled EL4 lymphoma cells pulsed with the SIINFEKL peptide, and specific lysis was measured at four ratios of effectors to target cells (E:T ratio). The data are means ± standard errors of the means for five individual mice and are representative of two separate experiments.