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Percentage (mean ± s.e.m.) of circulating CD4+ (a) and CD8+ T lymphocytes (b) with positive intracellular staining for the different cytokines studied in patients with chronic obstructive pulmonary disease (COPD) (dark columns), smokers with normal lung function (grey columns) and never smokers (white columns). ††P < 0·01 non-smokers versus smokers with normal lung function; *P < 0·05 COPD versus smokers with normal lung function.
