Influenza A viruses are highly contagious respiratory pathogens that are responsible for significant morbidity and mortality worldwide on an annual basis. We have shown previously that
influenza infection of mice leads to increased
ATP and
adenosine accumulation in the airway lumen. Moreover, we demonstrated that A1-adenosine receptor activation contributes significantly to
influenza-induced
acute respiratory distress syndrome (ARDS). However, we found that development of ARDS in
influenza-infected mice does not require catabolism of
ATP to
adenosine by
ecto-5'-nucleotidase (CD73). Hence, we hypothesized that increased
adenosine generation in response to
infection is mediated by tissue nonspecific
alkaline phosphatase (TNAP), which is a low-affinity, high-capacity
enzyme that catabolizes
nucleotides in a nonspecific manner. In the current study, we found that whole lung and BALF TNAP expression and
alkaline phosphatase enzymatic activity increased as early
as 2 days postinfection (dpi) of C57BL/6 mice with 10,000 pfu/mouse of
influenza A/WSN/33 (H1N1). Treatment at 2 and 4 dpi with a highly specific quinolinyl-
benzenesulfonamide TNAP inhibitor (TNAPi) significantly reduced whole lung
alkaline phosphatase activity at 6 dpi but did not alter TNAP gene or
protein expression. TNAPi treatment attenuated
hypoxemia, lung dysfunction, histopathology, and
pulmonary edema at 6 dpi without impacting viral replication or BALF
adenosine. Treatment also improved epithelial barrier function and attenuated cellular and humoral immune responses to
influenza infection. These data indicate that TNAP inhibition can attenuate
influenza-induced ARDS by reducing
inflammation and fluid accumulation within the lung. They also further emphasize the importance of
adenosine generation for development of ARDS in
influenza-infected mice.