Activation of A
1
-Adenosine Receptors Promotes Leukocyte Recruitment to the Lung and Attenuates Acute Lung Injury in Mice Infected with Influenza A/WSN/33 (H1N1) Virus
Authors: Aeffner Famke , Woods Parker S. , Davis Ian C. 
Published: June 2014

We have shown that bronchoalveolar epithelial A
1
-adenosine receptors (A
1
-AdoR) are activated in influenza A virus-infected mice. Alveolar macrophages and neutrophils also express A
1
-AdoRs, and we hypothesized that activation of A
1
-AdoRs on these cells will promote macrophage and neutrophil chemotaxis and activation and thereby play a role in the pathogenesis of influenza virus-induced acute lung injury. Wild-type (WT) C57BL/6 mice, congenic A
1
-AdoR knockout (A
1
-KO) mice, and mice that had undergone reciprocal bone marrow transfer were inoculated intranasally with 10,000 PFU/mouse influenza A/WSN/33 (H1N1) virus. Alternatively, WT mice underwent daily treatment with the A
1
-AdoR antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) from 1 day prior to inoculation. Infection increased bronchoalveolar lining fluid (BALF) adenosine comparably in WT and A
1
-KO mice. Infection of WT mice resulted in reduced carotid arterial O
2
saturation (hypoxemia), lung pathology, pulmonary edema, reduced lung compliance, increased basal airway resistance, and hyperresponsiveness to methacholine. These effects were absent or significantly attenuated in A
1
-KO mice. Levels of BALF leukocytes, gamma interferon (IFN-γ), and interleukin 10 (IL-10) were significantly reduced in infected A
1
-KO mice, but levels of KC, IP-10, and MCP-1 were increased. Reciprocal bone marrow transfer resulted in WT-like lung injury severity, but BALF leukocyte levels increased only in WT and A
1
-KO mice with WT bone barrow. Hypoxemia, pulmonary edema, and levels of BALF alveolar macrophages, neutrophils, IFN-γ, and IL-10 were reduced in DPCPX-treated WT mice. Levels of viral replication did not differ between mouse strains or treatment groups. These findings indicate that adenosine activation of leukocyte A
1
-AdoRs plays a significant role in their recruitment to the infected lung and contributes to influenza pathogenesis. A
1
-AdoR inhibitor therapy may therefore be beneficial in patients with influenza virus-induced lung injury.

IMPORTANCE
Because antiviral drugs are of limited efficacy in patients hospitalized for influenza virus-induced respiratory failure, there is an urgent need for new therapeutics that can limit the progression of lung injury and reduce influenza death rates. We show that influenza A virus infection results in increased production of the nucleoside adenosine in the mouse lung and that activation of A
1
-subtype adenosine receptors by adenosine contributes significantly to both recruitment of innate immune cells to the lung and development of acute lung injury following influenza virus infection. We also show that treatment with an A
1
-adenosine receptor antagonist reduces the severity of lung injury in influenza virus-infected mice. Our findings indicate that adenosine plays an important and previously unrecognized role in the innate immune response to influenza virus infection and suggest that drugs which can inhibit either generation of adenosine or activation of A
1
-adenosine receptors may be beneficial in treating influenza patients hospitalized for respiratory failure.