Alveolar macrophage-derived NRP2 curtails lung injury while boosting host defense in bacterial pneumonia.

Clearance of airway intruders by immune cells is required to resolve infectious pneumonia. However, the molecular mechanisms underlying this process remain elusive. Here, we demonstrated that alveolar macrophage (AM)-derived neuropilin 2 (NRP2) plays an essential role in controlling severe pneumonia by enhancing microbial clearance. Mice with conditional deletion of the NRP2 gene in AM had persistent bacteria, uncontrolled neutrophil influx, and decreased survival during Escherichia coli-induced pneumonia. In vitro assays demonstrated that NRP2 could bind to CD11b+ Ly6Glo/+ neutrophils and promote their capacities in phagocytosis and killing of bacteria, which is partially contributed to the increased expression of TLR4 and TNF-a. These findings collectively revealed that AM-derived NRP2 protects the lungs from unwanted injury by promoting the clearance of invading pathogens. This study might provide a promising diagnostic biomarker and therapeutic target for severe pneumonia.