Background: CD8+ T cells play a predominant role in COPD inflammation. Circulating fibrocytes, also produced by the bone marrow, are increased in the blood during an exacerbation and infiltrate bronchi of COPD patients. Since blood and bronchial fibrocytes are associated with mortality and bronchial obstruction respectively, we test whether tissue fibrocytes can interact with CD8+ T cells.

Objective: To analyze the relative distribution of bronchial fibrocytes and CD8+ T cells in control and COPD patients.

Methods: We obtained bronchial specimen from surgery in 17 COPD patients and 25 control subjects. We identified tissue fibrocytes and CD8+ T cells, as CD45+ FSP1+ cells and CD8+ T cells, respectively. We developed specific image analysis methods to quantify the density of fibrocyte in contact with CD8+ T cells, as well as the minimal distance between these two cell types.

Results: The density of fibrocytes in contact with CD8+ T cells was higher in distal tissue specimens from COPD patients compared with that of control subjects. The minimal distance between both cell types was lower in COPD than in control tissues. The density of interacting cells was negatively associated with lung function parameters, such as FEV1 and Transfer Lung capacity of Carbon monoxide, and positively associated with residual volume.

Conclusion: Fibrocytes and CD8+ T cells were found within close proximity in COPD lungs. This suggests that direct fibrocyte-CD8+ T cell interaction could occur in vivo and could play a role in COPD development.