Serum CCL-18 concentrations were higher in COPD patients of GOLD 3–4 (221.36 ± 40.51 ng/mL), mMRC score of 4 (242.11 ± 40.85 ng/mL) and longer clinical medical history (241.91 ± 40.63 ng/mL) than that in those of GOLD 1–2 (161.05 ± 57.48 ng/mL) (t = − 5.896, p < 0.001) (Supp. The gene discussed is CCL18; the disease is chronic obstructive pulmonary disease.