T lymphocytes and especially the subpopulations of CD8+ cells are believed to have a key role in COPD pathophysiology, but there are only few data regarding the role of these cells in COPD exacerbation.
We aimed to study prospectively changes of CD8+ T-lymphocyte subpopulations in the sputum of COPD patients at the onset of mild exacerbations and at a stable condition in order to provide further insight in the pathophysiology of the disease.
Induced-sputum samples were collected from 24 COPD patients with median age of 52 years (interquartile range [IQR], 44 to 58 years) and FEV1 percentage of predicted of 78.05% (IQR, 75.8 to 80.1%) at the onset of mild exacerbations not requiring hospitalization and when stable. Inflammatory cells and T-lymphocyte subpopulations (CD4+, CD8+, and cells producing interferon [IFN]-γ or interleukin [IL]-4) were measured using flow cytometry and immunocytochemical methods.
A significant increase in sputum CD8+ T lymphocytes (p < 0.0001) and significant decreases in CD4+ T lymphocytes as well as in CD4+/CD8+ (p = 0.0001) and CD8+IFN-γ+/CD8+IL-4+ (p = 0.001), CD4+IFN-γ+/CD4+IL-4+ (p = 0.0003) sputum cells ratios were found decreased at the onset of exacerbations compared to stable condition. The changes in T-lymphocyte subpopulations were not associated with smoking history, demographic characteristics, or disease severity.
The findings of the present study suggest that CD8+ lymphocytes are increased and potentially polarized toward a Tc2 profile in the airways of COPD patients at the onset of COPD exacerbations with respect to stable condition. The clinical impact of the observed phenomenon requires further investigation.