AT2-Derived GM-CSF Promotes CD301b? cDC2 Generation and Type 2 Inflammation in the Lung

Pulmonary conventional dendritic cells (cDCs) are functionally and phenotypically heterogeneous antigen-presenting cells essential for orchestrating adaptive immune responses in the lung. Here, we define a critical role for granulocyte-macrophage colony-stimulating factor (GM-CSF) in generating a CD301b+ subset of terminally differentiated cDC2s. GM-CSF signaling is intrinsically required for their development, independent of GM-CSF-dependent alveolar macrophages. Absence of GM-CSF results in a defect similar to that seen in CD103+XCR1+ cDC1s. Unbiased single-cell transcriptomic profiling of CD11c+ cells identified both immature and differentiated cDC populations. GM-CSF deficiency disrupted anti-apoptotic Bcl2a1 upregulation and impaired progression to the CD301b+ transcriptional state. Despite their positioning in lymphoid cell-rich adventitial cuff areas, hematopoietic GM-CSF was dispensable. Instead, genetic GM-CSF gain- and loss-of-function studies showed that alveolar epithelial type 2 cell-derived GM-CSF is required for CD301b+ cDC2 formation and pulmonary type 2 immune responses, highlighting the central role of GM-CSF signaling in shaping the pulmonary myeloid landscape. Overall design: The aim of this study was to delineate the role of GM-CSF in the differentiation and maturation of pulmonary conventional dendritic cells. We used genetic mouse models to verify the source of GM-CSF and single-cell transcriptomics to gain insight into immature and differentiated lung dendritic cell states. Using a neonatal alveolar macrophage transfer model into GM-CSF receptor deficient mice, we confirm the independence of DC development from alveolar macrophages and low-grade lung inflammation. Using bone marrow chimera and inducible GM-CSF overexpression in mice, we show that GM-CSF direct signaling is necessary for DC development and maturation and their function in type 2 immune responses in the airways, while also detailing the role of alveolar macrophages and GM-CSF signaling for eosinophil granulocytes.