Characterisation of T cell populations in proximal and distal airways

Introduction: CD8+ T cells are known to be involved in the pathogenesis of COPD but less is known about CD4+ T cells. We have characterised T cell populations from the distal and proximal airways of patients with and without airways obstruction. Method: Macroscopically normal matched proximal and distal airway tissue was obtained from 23 patients (mean age 66±2.7 years, FEV1/FVC=0.66±0.02) undergoing lung resection. Samples were dissected into explants, fixed and processed for GMA immunohistochemistry. Sections were stained for CD3, CD4 and CD8. To examine a larger population of T cells, explants from the same patients were incubated for 24 hours to encourage T cell migration into supernatant. Recovered cells were stained for T cell markers (CD3-FITC, CD8-APC) and analyzed via FACS. Results: Immunohistochemical analysis revealed relatively few T cells in either proximal or distal airways (median CD3+ cells distal airways =1.6/mm2 compared to 1.4/mm2) in the proximal airways. We found more CD4+ than CD8+ cells in both compartments but numbers of cells counted were low. In order to characterise a larger number of T cells FACS was performed on cells that migrated out of the explants. This confirmed that there were more CD4+ cells than CD8+ cells in the distal airways though this was not seen in the proximal airways. The distribution was not significantly affected by the presence of airways obstruction. Conclusions: Similar numbers of CD3+ cells were found in the proximal and distal airways. CD4+ cells were predominant in the distal airways while the distribution of CD4 and CD8+ cells was equivalent in the proximal airways. The presence of mild/moderate COPD did not affect T cell number or distribution.