In addition, serum IL-33 levels were found to be significantly higher in the subgroup of COPD patients with sputum eosinophilia (43.98±4.76 pg/ml) compared to those with a sputum eosinophil level ≤3% (29.15±2.01 pg/ml; p < 0.001) (Fig. 2c). Here, IL33 is linked to chronic obstructive pulmonary disease.