Introduction Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory condition characterised by increased numbers of neutrophils, macrophages and CD8⁺ T cells. However, recent evidence suggests that both CD4⁺ and CD8⁺ T cells can influence the pathogenesis of the disease. We aim to characterise the T cell subsets from both airway and parenchyma.

Method Macroscopically normal lung parenchyma and bronchial airway tissue was obtained from 10 patients (average age=65.3±4.5 years, FEV1/FVC=0.57±0.04) undergoing lung resection for carcinoma and dissected into explants. Tissue explants were acetone fixed, embedded in GMA and sections immunostained for CD3, CD4, CD8 and for mast cells (AA1) as a positive control. Positive cells were counted and numbers corrected for tissue area. To examine T cell migration, explants from the same patients were incubated for 24 h at 37°C. Cells that moved out of the explants into the supernatant were recovered, stained for T cell markers (CD3-FITC, CD8-APC) and analysed via flow cytometry.

Results We found very few T cells in lung parenchyma (CD3⁺ cells=1.1±0.3/mm²) though there were substantial numbers of mast cells (65.6±13.9/mm²). There were twice as many CD4⁺ cells compared to CD8⁺ cells. In contrast, the airway had more T cells present (CD3⁺=2.8±1.1/mm²) and again CD4⁺ T cells predominated. We also used flow cytometry to characterise the CD4:CD8 ratio in T cells that migrated out of the explants. Parenchymal supernatants contained substantial numbers of T cells with significantly more CD4⁺ T cells than CD8⁺ (CD4=28.5±4.1%, CD8=20.4±2.3%, p<0.05). However in the airway, the ratio of CD4:CD8 cells was closer to 1:1 (CD4⁺=26.5±7.4%, CD8⁺=23.2±6.7%). Preliminary evidence suggests that the presence of mild/moderate airways obstruction does not affect the total number of T cells in either the parenchyma or the airway or the CD4:CD8 ratio in either compartment. There is also no evidence that the patient's smoking status affects T cell number or distribution.

Conclusion More CD3⁺ cells are seen in the bronchial tissue than in the parenchyma and the majority of these are CD4⁺. CD3⁺ cells also migrate spontaneously out of the explants in both compartments and account for the majority of cells recovered in the supernatant.