Considering that the PPAR-γ was highly expressed in C8-Pf4+-macrophages, and the depletion of Pf4+-macrophages led to a significant reduction in AMs formation in the lung at late stage IAV-mediated pneumonia, we hypothesized that C8 Pf4+-macrophages may be the precursors of AMs when lung recovered from IAV infection. Here, PF4 is linked to pneumonia.