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Transformation-related protein 63-expressing (p63(+)) basal cells are confined to the trachea in the mouse lung. However, after influenza virus infection or bleomycin treatment, patches of p63(+) cells were observed in the damaged lung parenchyma. To address whether the newly induced p63(+) cells are derived from the p63(+) basal cells, we performed lineage tracing. In a keratin 5 promoter-driven CreER system, although preexisting p63(+) basal cells were labeled by enhanced green fluorescent protein (EGFP) after tamoxifen treatment, none or only a small fraction (∼ 15%) of the p63(+) patches was labeled by EGFP after bleomycin treatment or influenza virus infection, respectively. In contrast, > 60% of p63(+) patches contained EGFP(+) cells in Scgb1a1-CreER transgenic system where club cells are labeled. Many p63(+) cells were found in bronchiole-like lumen structures with columnar cells at the lumen side. The columnar cells were positive for club cell marker Cyp2f2 and could be traced to the newly induced p63(+) cells. These results suggest that most of the newly induced p63(+) cells in the damaged parenchyma are likely derived from club cells rather than from p63(+) basal cells and that newly induced p63(+) cells may be involved in the regeneration of bronchioles.

Rationale: Patients who developed acute respiratory distress syndrome (ARDS) after infection with severe respiratory viruses (e.g., severe acute respiratory syndrome-coronavirus, H5N1 avian influenza virus), exhibited unusually high levels of CXCL10, which belongs to the non-ELR (glutamic-leucine-arginine) CXC chemokine superfamily. CXCL10 may not be a bystander to the severe virus infection but may directly contribute to the pathogenesis of neutrophil-mediated, excessive pulmonary inflammation., Objectives: We investigated the contribution of CXCL10 and its receptor CXCR3 axis to the pathogenesis of ARDS with nonviral and viral origins., Methods: We induced nonviral ARDS by acid aspiration and viral ARDS by intratracheal influenza virus infection in wild-type mice and mice deficient in CXCL10, CXCR3, IFNAR1 (IFN-α/β receptor 1), or TIR domain-containing adaptor inducing IFN-β (TRIF)., Measurements and Main Results: We found that the mice lacking CXCL10 or CXCR3 demonstrated improved severity and survival of nonviral and viral ARDS, whereas mice that lack IFNAR1 did not control the severity of ARDS in vivo. The increased levels of CXCL10 in lungs with ARDS originate to a large extent from infiltrated pulmonary neutrophils, which express a unique CXCR3 receptor via TRIF. CXCL10-CXCR3 acts in an autocrine fashion on the oxidative burst and chemotaxis in the inflamed neutrophils, leading to fulminant pulmonary inflammation., Conclusions: CXCL10-CXCR3 signaling appears to be a critical factor for the exacerbation of the pathology of ARDS. Thus, the CXCL10-CXCR3 axis could represent a prime therapeutic target in the treatment of the acute phase of ARDS of nonviral and viral origins.

Influenza accounts for 5-10% of community-acquired pneumonia cases, and is a major cause of mortality. Sterile and bacterial lung injury are associated with procoagulant and inflammatory derangements in the lungs and down-regulation of the protein C (PC) pathway has been correlated with disease severity and mortality in severe bacterial pneumonia and sepsis. In addition, during lethal influenza pneumonia, pulmonary and systemic coagulation are activated, which can be attenuated by the administration of recombinant activated (A) PC. We here determined the role of endogenous PC in lethal H1N1 influenza A infection. Male C57BL/6 mice pretreated with an inhibitory monoclonal antibody directed against murine PC or a control antibody were intranasally infected with a lethal dose of a mouse-adapted H1N1 influenza A strain. Mice were killed at 48 or 96 hours after infection, after which lungs and bronchoalveolar lavage fluid were harvested, or observed for up to 9 days. Anti-PC antibody treatment aggravated pulmonary activation of coagulation as compared with control antibody treatment, as reflected by increased lung concentrations of thrombin-antithrombin complexes and fibrin degradation products, as well as intravascular thrombus formation. Anti-PC antibody treatment aggravated lung histopathology, but lowered bronchoalveolar neutrophil influx and total protein levels, and delayed mortality. In conclusion, endogenous PC has strong effects on the host response to lethal influenza A infection, inhibiting pulmonary coagulopathy and inflammation on the one hand, but facilitating neutrophil influx and protein leak and accelerating mortality on the other hand.