EDN1 and chronic obstructive pulmonary disease: On the other hand, the severity of COPD (according to FEV1) significantly correlated with CRP levels (r = −0.68, P < .0001), but not with TNF-α (r = −0.03, P = .84), IL-6 (r = −0.08, P = .64), or ET1 (r = −0.18, P = .27) (Fig. 3).