Comparison of airway and peripheral blood T cell characteristics in severe asthma and COPD*1

Rationale T cells have been implicated in the immunopathology of asthma and COPD. The Dutch Hypothesis proposes that COPD and asthma share common mechanisms. We compared airway and peripheral blood T cell profiles in subjects with COPD and severe asthma. Methods Absolute numbers and percentages of broncholalveolar lavage fluid (BALF) and peripheral blood cells expressing the T cell markers CD3, 4, 8, 27 and 45RA were measured in subjects (age 40-75 yrs, FEV 1 /FVC Results The mean percentages and absolute numbers of BALF cells expressing CD3 were significantly lower in COPD current smokers compared with COPD ex-smokers (0.015% vs 0.296%, p=0.09 and 0.0015 × 10 6 cells/ml BALF vs 0.1615 × 10 6 , p=0.003) and asthmatics (0.148%, p=0.02 and 0.1145 × 10 6 , p=0.002). The smokers also had significantly lower percentages of BALF cells expressing CD4 compared with the asthmatics (33.3% vs 61.7%, p=0.01). Proportions of CD8 T cells, and percentages of CD4 and CD8 cells expressing CD27 and CD45RA did not differ between the groups. However, blood and BALF (in both severe asthma and COPD) were characterized by their differential CD27, CD45RA expression. There were no significant differences in peripheral blood. Conclusions Similar numbers of CD4 and CD8 T cells expressing CD27 and CD45RA are found in BALF of subjects with COPD and severe asthma. Current smoking in COPD subjects appears to suppress the lymphocyte presence in BALF, particularly of the CD4 population.