M2 macrophages promote pulmonary endothelial cells regeneration in sepsis-induced acute lung injury.

Background: Macrophages can polarize to M2 phenotype to decrease inflammation and encourage tissue repair. Nonetheless, its role in sepsis-induced acute lung injury and its effect on endothelial cells (ECs) regeneration remains unknown. The aim of the current study was to explore the impact of M2 macrophages on pulmonary ECs proliferation in sepsis-induced acute lung injury.

Methods: We co-cultured mouse lung microvascular endothelial cells (MLMVECs) with M2 macrophages following LPS challenge. M2 macrophages were intratracheally transplanted into mice subjected to cecal ligation and puncture (CLP). We further performed cytokine array for the supernatant from M2 macrophages and serum from mice subjected with CLP.

Results: We found both co-culture with M2 macrophages and treating with supernatant from M2 macrophages increased ECs viability following LPS challenge. Intratracheal transplantation of M2 macrophages markedly promoted pulmonary ECs proliferation, manifesting as attenuation of lung microvascular permeability and lung tissue edema, as well as improvement of survival rate. We further found that CXCL12, IL-1ra, TIMP-1, IL-4, and CXCL1 were increased in the supernatant of M2 macrophages . G-CSF and Complement Component 5a (C5/C5a) were increased in the serum of the M2-transplanted mice.

Conclusions: The present study suggested M2 macrophages could promote ECs proliferation in sepsis-induced ALI through secretion of anti-inflammatory cytokines and growth factors.