The growth factor granulocyte/macrophage-colony stimulating factor (GM-CSF) has an important role in pulmonary surfactant metabolism and the regulation of antibacterial activities of lung sentinel cells. However, the potential of intra-alveolar GM-CSF to augment lung protective immunity against inhaled bacterial pathogens has not been defined in preclinical infection models. We hypothesized that transient overexpression of GM-CSF in the lungs of mice by adenoviral gene transfer (Ad-GM-CSF) would protect mice from subsequent lethal pneumococcal pneumonia. Our data show that intra-alveolar delivery of Ad-GM-CSF led to sustained increased pSTAT5 expression and PU.1 protein expression in alveolar macrophages during a 28 day observation period. Pulmonary Ad-GM-CSF delivery two or four weeks prior to infection of mice with S. pneumoniae significantly reduced mortality rates relative to control vector treated mice. This increased survival was accompanied by increased iNOS expression, antibacterial activity and a significant reduction in caspase 3 dependent apoptosis and secondary necrosis of lung sentinel cells. Importantly, therapeutic treatment of mice with recombinant GM-CSF improved lung protective immunity and accelerated bacterial clearance after pneumococcal challenge. We conclude that prophylactic delivery of GM-CSF triggers long-lasting immunostimulatory effects in the lung in vivo and rescues mice from lethal pneumococcal pneumonia by improving antibacterial immunity. These data support use of novel antibiotic-independent immunostimulatory therapies to protect patients against bacterial pneumonias.

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Fibrocytes are bone marrow-derived, circulating mesenchymal progenitor cells that play a role in several fibrotic disorders, including lung fibrosis. They are attracted to injured tissue by various chemokines. It is likely that fibrocytes play a detrimental role in tissue homeostasis and promote fibrosis, although this paradigm needs further confirmation. This would make fibrocytes a possible novel treatment target for fibrotic disorders. Fibrocytes also have some potential as a biomarker for idiopathic pulmonary fibrosis (IPF) and other diseases, but the promising preliminary data from single centre studies still require independent validation. Despite several, as yet, unresolved issues, it has become clear that fibrocytes are more than an incidental finding in lung injury and repair, and may hold great promise for the future of IPF management

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BACKGROUND:Current protocols for detection of circulating fibrocytes (CFs) in peripheral blood described in various pulmonary and nonpulmonary disorders involve complex and time consuming, non standardized techniques.OBJECTIVE:Testing a method to rapidly detect and quantify CFs using whole blood lysis flow cytometry-based assay in patients with idiopathic pulmonary fibrosis (IPF) and healthy controls.METHODS:One milliliter of venous blood sample in ethylenediaminetetraacetic acid (EDTA) from 33 IPF patients and 35 healthy control subjects was collected. Using whole blood lysis method peripheral blood leukocytes were labeled with monoclonal antibodies for cell surface (CD34 and CD45) and intracellular markers (collagen-1) for flow cytometric analysis. CFs were defined as CD45+ cells coexpressing collagen-I and CD34 molecules.RESULTS:In 29 (87.8%) IPF patients and 10 (28.5%) control subjects, a well-defined highly granular CD45+ cell population was detected in dot plots generated by side scatter properties of CD45+ cells. These CD45+ cells were identified as CFs on the basis of coexpression of collagen-I and CD34; none of the other cell types in the peripheral blood were labeled with these monoclonal antibodies. In IPF patients the percentage of CFs was significantly higher compared to healthy controls (median (range): 1.37% (0.52-5.65) and 1.04% (0.1-1.84), respectively; P = 0.03).CONCLUSIONS:Whole blood lysis method combined with fluorescence-activated cell sorting (FACS) allows detecting a well-defined homogeneous population of CFs. This method is simple, reproducible, and provides an accurate and rapid estimation of CFs.

ObjectiveCirculating fibrocytes are elevated in idiopathic pulmonary fibrosis, but the relationship between fibrocyte level with lung function decline and outcomes is lacking replication in prospective clinical study. We aim to validate the utility of circulating fibrocyte levels as a prognostic biomarker in idiopathic pulmonary fibrosis.MethodsWe tested associations between circulating fibrocyte levels, mortality, disease progression and longitudinal lung function in a well-defined prospective observational study of pulmonary fibrosis (PROFILE; NCT01134822). A subset of recruited participants had blood samples processed for fibrocyte measurement, with flow cytometry based on CD45 and collagen-I gating. Associations were tested using univariable and multivariable generalised linear models. Mortality data were subsequently combined with an independent cohort in a mixed-effect multilevel analysis.ResultsIn 102 participants with idiopathic pulmonary fibrosis, a previously defined mortality risk threshold of 5% circulating fibrocytes was not reproducible. An empirically defined cutpoint of 2.22% was associated with a greater risk of overall mortality in adjusted analysis (Hazard Ratio 2.24 95% CI 1.06-4.72). A 2.5 fold greater risk of mortality was supported in a pooled analysis with a historic cohort for a larger sample of 162 participants with idiopathic pulmonary fibrosis (Hazard Ratio 2.49 95% CI 2.41-2.56). We found no association of fibrocytes with lung function or disease progression.ConclusionsIn a large sample of circulating fibrocytes from people with idiopathic pulmonary fibrosis, levels of 2.22% or above were associated with greater mortality, but not with disease related decline in lung function.

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