CCL18 and chronic obstructive pulmonary disease: The CCL-18 concentrations in patients with acute exacerbation of COPD (AECOPD) (277.20 ± 35.76 ng/mL) showed a significant increase compared with stable COPD patients (194.49 ± 57.12 ng/mL) (t = − 8.438, p < 0.001) (Supp.