RNASE2 and chronic obstructive pulmonary disease: Studies have also shown that the eosinophils, as a source of cytokines IL-3, -4, -5, -6, and -8, eosinophil-derived neurotoxin, eosinophil peroxidase, matrix metalloproteinase, and reactive oxygen species have an important role in the pathogenesis of COPD [48].