ABCG2 and chronic obstructive pulmonary disease: The results showed that the majority of viral functions were down-regulated in patients with COPD compared with healthy subjects (101 vs 39, Table S5; Fig. 4), especially glutamine amidotransferase class-I, glutamine synthetase catalytic domain, integrase core domain, glycosyl hydrolases family 25, replication initiation and membrane attachment, phage integrase protein, and ATP-binding cassette (ABC) transporter.