Furthermore, we analyzed the levels of IL-10 production in the lung tissue resident Treg cells during effector stage of the secondary influenza infection, and found that blocking PD-1 signaling resulted in a modest but statistically significant increase in the frequency of IL-10 producing lung tissue resident Treg cells, while blocking ICOS signaling did not affect this parameter, as compared to the isotype antibody-treated group (Figure 8D). This evidence concerns the gene ICOS and influenza.