PRKAA1 and pneumonia: Staining with MitoTracker Deep Red (MitoTracker DR, a dye used to measure mitochondrial mass that is sensitive to mitochondrial membrane potential) revealed lower mitochondrial mass/membrane potential in AMPKα1/α2–deficient Treg cells relative to controls at homeostasis (Figure 5D) and in the lung during influenza pneumonia (Figure 5E), consistent with their impaired maximal OCR at homeostasis.