Rationale: Pulmonary infections can impair alveolar fluid clearance (AFC), contributing to formation of lung edema. Effects of influenza A virus (IAV) on AFC are unknown.

Objectives: To determine effects of IAV infection on AFC, and to identify intercellular signaling mechanisms underlying influenza-mediated inhibition of AFC.

Methods: BALB/c mice were infected intranasally with influenza A/WSN/33 (10,000 or 2,500 focus-forming units per mouse). AFC was measured in anesthetized, ventilated mice by instilling 5% bovine serum albumin into the dependent lung.

Measurements and Main Results: Infection with high-dose IAV resulted in a steady decline in arterial oxygen saturation and increased lung water content. AFC was significantly inhibited starting 1 hour after infection, and remained suppressed through Day 6. AFC inhibition at early time points (1–4 h after infection) did not require viral replication, whereas AFC inhibition later in infection was replication-dependent. Low-dose IAV infection impaired AFC for 10 days, but induced only mild hypoxemia. High-dose IAV infection increased bronchoalveolar lavage fluid ATP and UTP levels. Impaired AFC at Day 2 resulted primarily from reduced amiloride-sensitive AFC, mediated by increased activation of the pyrimidine-P2Y purinergic receptor axis. However, an additional component of AFC impairment was due to activation of A₁ adenosine receptors and stimulation of increased cystic fibrosis transmembrane regulator–mediated anion secretion. Finally, IAV-mediated inhibition of AFC at Day 2 could be reversed by addition of β-adrenergic agonists to the AFC instillate.

Conclusions: AFC inhibition may be an important feature of early IAV infection. Its blockade may reduce the severity of pulmonary edema and hypoxemia associated with influenza pneumonia.