Infection of influenza virus can also alter the cellular level and metabolism of purines and pyrimidines [8, 98, 100], and is associated with both increased activities of nucleotide catabolism core enzymes including adenosine deaminase (ADA) and xanthine oxidase (XO) and elevated levels of inosine, hypoxanthine, xanthine, and uric acid in serum and bronchoalveolar lavage fluid. This evidence concerns the gene ADA and infection.