TNF and chronic obstructive pulmonary disease: Importantly, the concentrations of a number of analytes were above the lower limit of quantification in only a small percentage of subjects: TNF-α (10% COPD subjects, 10% combined controls), interferon-γ (6% COPD subjects, 6% combined controls), IL-10 (14% COPD subjects, 12% combined controls), IL-15 (17% COPD subjects, 15% combined controls), IL-17 (< 1% COPD subjects, 0% combined controls) and IL-1β (21% COPD subjects, 22% combined controls).