Recruited Monocytes and Type 2 Immunity Promote Lung Regeneration following Pneumonectomy

Abstract

Summary To investigate the role of immune cells in lung regeneration, we used a unilateral pneumonectomy model that promotes the formation of new alveoli in the remaining lobes. Immunofluorescence and single cell RNA- sequencing found CD115+ and CCR2+ monocytes and M2-like macrophages accumulating in the lung during the peak of type 2 alveolar epithelial stem cell (AEC2) proliferation. Genetic loss of function in mice and adoptive transfer studies revealed that bone marrow-derived macrophages traffic to the lung through a CCL2-CCR2 chemokine axis and are required for optimal lung regeneration, along with Il4ra-expressing leukocytes. Our data suggest that these cells modulate AEC2 proliferation and differentiation. Finally, we provide evidence that group 2 innate lymphoid cells are a source of IL13 that promotes lung regeneration. Together, our data highlight the potential for immunomodulatory therapies to stimulate alveologenesis in adults.

Alveolar injury and regeneration following deletion of ABCA3

“…Cytometric analysis demonstrated increased numbers of CD11b + macrophages and expression of RNAs associated with M2 macrophage activation during regeneration. Studies of lung regeneration after partial pneumonectomy support the concept that interactions among activated macrophages and lung parenchymal cells create a proliferative microenvironment (22). In the present study, regeneration was associated with marked increase in inflammatory cell expression of ARG1 and other markers of atypical macrophage activation (M2-like), including RETNLA and CD206, proposed to contribute to repair processes (22,41,42).…”

“…During repair, BrdU incorporation was present in inflammatory, endothelial, epithelial, and stromal cells, and it was consistently observed in cell clusters containing diverse cell types. Interactions between alveolar macrophages and AT2 cells were previously suggested to enhance cell survival, via mitochondrial transfer or suppression of inflammation (22,(38)(39)(40). In the present study, CD45 + macrophages were frequently found in close proximity to proliferating AT2 cells.…”

“…Studies of lung regeneration after partial pneumonectomy support the concept that interactions among activated macrophages and lung parenchymal cells create a proliferative microenvironment (22). In the present study, regeneration was associated with marked increase in inflammatory cell expression of ARG1 and other markers of atypical macrophage activation (M2-like), including RETNLA and CD206, proposed to contribute to repair processes (22,41,42). Alveolar macrophages expressing CD206 and ARG1 were identified by immunofluorescence confocal microscopy in both Abca3-cKO mouse lung during regeneration and in lung tissue from patients with severe lung disease caused by ABCA3 mutations.…”

“…Cytometric measurements of M2 macrophages were conducted on single cell suspensions of whole lungs as previously described (22). Following perfusion, lungs were inflated with 2 ml protease solution containing collagenase type II (Worthington Biochemical Corporation, at 450 U/ml), elastase (Worthington Biochemical Corporation, at 4U/ml), and dispase (Corning, 50 U/ml).…”

Integrative Physiology of Pneumonia

“…RSV infection promotes accumulation of IL-13-expressing ILC2s in the lung, which associates with increased type 2 inflammatory responses (470), suggesting at least one connection of ILC2s to lower respiratory infection. ILC2s help repair and regenerate injured lung tissue (44,279,333), but ILC2-mediated repair after pneumonia specifically is presently speculative. ILC3s are perhaps the most relevant to pneumonia biology and acute pulmonary inflammation, particularly with regards to their influence on IL-17-mediated defense.…”