Figure 5. Increased frequency of T_regs and elevated IL-10 levels in mice treated with ICOS agonist during acute IAV infection.

(A) Mice were treated as described in Figure 1A. On day 7, 8 and 9 post infection, mice were sacrificed and CD4⁺ T cells isolated from the lung (left panel: day 8 p.i.; right panel: day 9 p.i.), BLN (left panel: day 7 p.i.; right panel: day 9 p.i.) (pooled data from two independent experiments) and spleen (left panel: day 8 p.i.; right panel day 9 p.i.) (pooled data from two independent experiments) were analyzed for the intracellular expression of the T_reg-specific transcription factor Foxp3. (B) Bronchoalveolar lavage fluid of mice infected with IAV and treated with ICOS agonist or control antibody was collected on day 8 post infection and IL-10 concentration was determined by ELISA. The data obtained were pooled from two independent experiments (C) In addition, tryptophan (trp) and kynurenine (kyn) concentrations were determined in serum samples (pooled data from two independent experiments) and bronchoalveolar lavage fluid by reversed-phase HPLC technology. IDO enzymatic activity is estimated as kyn/trp ratio. Dots represent data obtained for individual mice. Statistical analysis was done by non-parametric Mann-Whitney test.