Since the macrophage compartment has been shown to influence TRM number (40, 48), we examined two populations of lung macrophages including fetal-derived alveolar (CD64+ CD11bint Siglec Fhi) and adult monocyte-derived macrophages (CD64+ CD11bhi Siglec FLo) prior to and after influenza infection by flow cytometry in whole lung and airway lumen (Figures 2A–C). The gene discussed is FCGR1A; the disease is influenza.