Fig. 2 Pf4+-macrophages are the major resource to generate second wave of pro-inflammatory factors at late stage of IAV-driven pneumonia. a Heat-maps showing the normalized expression (Z-score) of the pro-inflammatory genes in the various cells of clusters with high ratios at day 7 p.i.. b The normalized expression (UMI counts) of some significant genes with high expression in different clusters at day 7 p.i.. c Pf4+ cells in the lung after IAV infection.