Synergistic increase of CCL-18 and IL-23 in COPD patients was positively correlated with COPD patients' higher GOLD grade (P < 0.001), higher mMRC score (P < 0.001) and longer medical history (P < 0.001), but negatively correlated with the forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) (P < 0.001) and FEV1% predicted (P < 0.001). Here, CCL18 is linked to chronic obstructive pulmonary disease.