ACE and radiation pneumonitis: As ACE expression in the myeloid compartment has previously been shown to regulate myelopoiesis, macrophage differentiation, and systemic immune function in both human and rodent models (Okwan-Duodu et al., 2010; Lin et al., 2011; Okwan-Duodu et al., 2019; Bueno et al., 2023), we surmised radiation-induced ACE activation in the bone marrow myeloid compartment may promote a systemic pro-inflammatory response that exacerbates radiation pneumonitis.