CXCR6 and chronic obstructive pulmonary disease: CXCR6-expressing monocytes and lymphocytes were also greater in number in COPD patients than in age-matched controls (Figures 5C–F); while the number was greater when platelets were aggregated to both leukocyte subpopulations, no significant differences between active or not active smokers COPD patients were observed, but a tendency for enhanced CXCR6 expression was noted in the former group (Figures 5C–F).