Background: Severe persistent asthma (SPA) and chronic obstructive pulmonary disease (COPD) are both associated with non-reversible airflow limitation and airway neutrophilia.
Objective: To compare inflammatory cell profiles and T lymphocyte subsets between SPA and COPD patients with similar severity of airflow limitation.
Methods: Sputum induction and lung function tests were performed in 15 COPD patients aged (mean+/-SD) 68+/-8 years, ex-smokers, mean forced expiratory volume in 1 s (FEV1) 45% of predicted (% pred) and 13 SPA aged 55+/-10 years, non-smokers, mean FEV(1) 49% pred. All patients were on inhaled steroid treatment. Eight asthmatics exhibited irreversible airflow limitation. Differential cell count, metachromatic cell count and double immunocytochemistry for the analysis of T lymphocyte subsets were performed on sputum slides.
Results: COPD patients had increased sputum neutrophils in comparison with SPA (P<0.03), but similar to SPA with fixed obstruction. In COPD sputum neutrophils negatively correlated with the lung transfer factor for carbon monoxide (KCO) (r=-0.462, P=0.04). SPA showed significantly increased eosinophils and metachromatic cells vs. COPD patients (P<0.04, P<0.007, respectively). Increased CD4/CD8 and decreased CD4-IFN-gamma/CD4-IL4+ cell ratio (P<0.001) were found in SPA vs. COPD. In SPA, CD4/CD8+ cell ratio correlated with sputum eosinophils (r=0.567, P=0.04).
Conclusion: In spite of treatment with inhaled steroids, SPA and COPD exhibit distinct sputum inflammatory cell patterns, although SPA with fixed airflow limitation and COPD patients have similar numbers of neutrophils.