Upon influenza infection, Csf2ra–/– mice containing CSF1-cBMM–derived alveolar macrophages showed strikingly increased morbidity (i.e., loss of body weight and temperature; O2 saturation) and mortality compared with mice containing CSF2-cFLiMo–derived alveolar macrophages (Figure 5, J–M). Here, CSF1 is linked to influenza.