ENTPD1 and chronic obstructive pulmonary disease: Although expression of CD39 (ectonucleotidase-1) was demonstrated in human leukocytes from sputum and BALF, and its activity was shown to be modulated by smoking and increased in chronic obstructive pulmonary disease (COPD) (120), no clear attribution of CD39 protein to human eosinophil cells has been done so far.