As to systemic inflammatory cytokines, we found that IL-6, 8-isoprostane, and CRP concentrations were significantly higher in the COPD groups compared to the control group (all p < 0.05, Fig. 2), which shows that systemic inflammatory cytokines were related to higher Hp2-1 and Hp2-2 levels in the COPD groups than in the healthy control group, but the Hp1-1 phenotype did not significantly differ. Here, IL6 is linked to chronic obstructive pulmonary disease.