Infected macrophages engage alveolar epithelium to metabolically reprogram myeloid cells and promote antibacterial inflammation

Alveolar macrophages are the primary immune cells that first detect lung infection. However, only one macrophage patrols every three alveoli. How this limited number of macrophages provides protection is unclear, as numerous pathogens block cell-intrinsic immune responses. The intracellular pathogen Legionella pneumophila inhibits host translation, thereby impairing the ability of infected macrophages to produce critical cytokines. Nevertheless, infected macrophages induce an IL-1-dependent inflammatory response by recruited myeloid cells that controls infection. Here, we show that collaboration with the alveolar epithelium is critical, in that IL-1 instructs the alveolar epithelium to produce GM-CSF. Intriguingly, GM-CSF drives maximal cytokine production in bystander myeloid cells by enhancing PRR-induced glycolysis. Our findings reveal that alveolar macrophages engage alveolar epithelial signals to metabolically reprogram myeloid cells and amplify antibacterial inflammation. One Sentence SummaryThe alveolar epithelium is a central signal relay between infected and bystander myeloid cells that orchestrates antibacterial defense.