IL6 and chronic obstructive pulmonary disease: In patients with COPD, the WBC count and the serum levels of CRP, IL-6 and fibrinogen, but not those of IL-8 and TNFα, tended to increase with the severity of airflow limitation (Table S2).In absolute terms, differences in the levels of systemic biomarkers between GOLD stages were small and often not consistent between stages (Table S2).