CD4 and influenza: Using the Foxp3RFP/IL-10GFP dual reporter mouse model, we tracked the levels of IL-10 production in Treg cells during acute influenza infection and found that the lung tissue resident Foxp3+ Treg cells, along with the conventional CD4+ and CD8+ tissue resident T cells are the major producers of IL-10 during acute flu in mice (Figure 3A).