Differential lymphocyte infiltration in small airways and lung parenchyma in COPD patients

In COPD, although histological lesions at both the small airways (wall thickening and tissue remodeling) and lung parenchyma (emphysematous destruction) are definitely different, the inflammatory cells involved in both processes are the same. Our study aims to determine if these histopathological phenotypes are related to two different lymphocyte profiles.

Distribution and cell density of CD3(+), CD4(+), CD8(+) and B lymphocytes were compared in small airways and parenchymal interstitium of 9 non-smokers, 18 smokers without COPD, 16 smokers with moderate COPD and 16 patients with very severe COPD undergoing lung transplantation. Spatial distribution of lymphocytes in periemphysematous parenchyma was also assessed.

CD3(+) and B cell densities were significantly higher in small airways than parenchyma interstitium of very severe COPD patients. Furthermore, CD8(+) cells were increased in the epithelium of airways of moderate COPD patients compared to non-smokers. Although CD8(+) cell density was increased in parenchyma of COPD patients, CD8(+) and B cell densities were similar when comparing periemphysematous and non-emphysematous alveolar interstitium.

In COPD, it is true that the small airways' wall shows a clear inflammatory pattern, with a high mononuclear infiltration and tissue remodeling. However, parenchymal interstitium shows a milder CD8(+) infiltration which, moreover, is not spatially related to emphysematous destroyed areas.