BACKGROUND: The role of fibrocytes in chronic obstructive pulmonary disease 
(COPD) is unknown. We sought to enumerate blood and tissue fibrocytes in COPD 
and determine the association of blood fibrocytes with clinical features of 
disease.
METHODS: Utilizing flow cytometry to identify circulating, collagen type 1+ 
cells, we found two populations: (i) CD45+ CD34+ (fibrocytes) and (ii) CD45+ 
CD34- [myeloid-derived suppressor cell (MDSC)-like fibrocytes] cells in stable 
COPD (n = 41) and control (n = 29) subjects. Lung resection material from a 
separate group of subjects with (n = 11) or without (n = 11) COPD was collected 
for tissue fibrocyte detection. We examined circulating fibrocyte populations 
for correlations with clinical parameters including quantitative computed 
tomography (qCT) and determined pathways of association between correlated 
variables using a path analysis model.
RESULTS: Blood and tissue fibrocytes were not increased compared to control 
subjects nor were blood fibrocytes associated with lung function or qCT, but 
were increased in eosinophilic COPD. Myeloid-derived suppressor cell-like 
fibrocytes were increased in COPD compared to controls [2.3 (1.1-4.9), P = 
0.038]. Our path analysis model showed that collagen type 1 intensity for 
MDSC-like fibrocytes was positively associated with lung function through 
associations with air trapping, predominately in the upper lobes.
CONCLUSION: We have demonstrated that two circulating populations of fibrocyte 
exist in COPD, with distinct clinical associations, but are not prevalent in 
proximal or small airway tissue. Blood MDSC-like fibrocytes, however, are 
increased and associated with preserved lung function through a small 
airway-dependent mechanism in COPD.