FIG. 4.

Antigen-specific CD8 T-cell responses are diminished in the absence of ICOS. ICOS^−/− and (C57BL/6 × Sv129) F1 mice were infected as described in the legend to Fig. 1 and were sacrificed on days 7, 14, 21, and 36 postinfection. (A) Cells were isolated from the spleen, counted, stained with mAb to CD8, CD62L, and H-2K^b/OVA _257-264 tetramers (Tet), and analyzed by flow cytometry. Each symbol represents a single mouse, and the averages are indicated by lines. (B) Numbers of tetramer-positive CD8 T cells, calculated from the data in panel A. The data in panels A and B are data from a single experiment and are representative of two experiments (with additional experiments on day 21) performed with an average of three mice per group. (C) Examples of flow cytometry plots for days 7, 14, 21, and 36 following Salmonella-OVA infection. The events were gated on live CD8⁺ T cells. The numbers in the upper left quadrants indicate the percentages of CD8 T cells that stained with a tetramer. An asterisk indicates that the P value is <0.05.