HMGB1 and chronic obstructive pulmonary disease: Serum levels of HMGB1 were significantly elevated in both IPAH and COPD+PH samples as compared to controls (2.6 ± 0.45 ng/ml, n = 14; 4.2 ± 0.78 ng/ml, n = 14; versus 1.05 ± 0.2 ng/ml, n = 14, respectively; Fig.3).