Cd28flox/flox Ox40cre/+ mice and heterozygous controls were infected I.N. with 104 plaque-forming units of influenza A virus. The percentage of IFNγ+CD44highCD4+ Th1 cells that lose CD28 expression was quantified at days 5, 9, 12, and 14 post infection in the lung (A and B). The proportion of IFNγ+CD44highCD4+ Th1 cells (C, D), apoptotic Pan Active Caspase+CD44highCD4+ cells (E), proliferating Ki-67+CD44highCD4+ cells (F), IL-2+CD44highCD4+ cells (G), expression of CXCR3 on CD44highCD4+ cells (H), the proportion of CXCR3+CD62LlowCD4+ (I) cells were assessed in the medLN 7 days post infection. The percentage of lung IFNγ+CD44highCD4+ Th1 cells (J) was also assessed at the same time point. In D, paired samples from the same mouse are connected with a line and heights of the bars in bar graphs represent the median value. Data are representative of three independent experiments with 5–10 mice per group. Ns = not significant, *p < 0.05, **p < 0.005, ***p < 0.005.