Alveolar Macrophages Prevent Lethal Influenza Pneumonia By Inhibiting Infection Of Type-1 Alveolar Epithelial Cells

The Influenza A virus (IAV) is a major human pathogen that produces significant morbidity and mortality. To explore the contribution of alveolar macrophages (AlvM Phi s) in regulating the severity of IAV infection we employed a murine model in which the Core Binding Factor Beta gene is conditionally disrupted in myeloid cells. These mice exhibit a selective deficiency in AlvM Phi s. Following IAV infection these AlvM Phi deficient mice developed severe diffuse alveolar damage, lethal respiratory compromise, and consequent lethality. Lethal injury in these mice resulted from increased infection of their Type-1 Alveolar Epithelial Cells (T1AECs) and the subsequent elimination of the infected T1AECs by the adaptive immune T cell response. Further analysis indicated AlvMF-mediated suppression of the cysteinyl leukotriene (cysLT) pathway genes in T1AECs in vivo and in vitro. Inhibition of the cysLT pathway enzymes in a T1AECs cell line reduced the susceptibility of T1AECs to IAV infection, suggesting that AlvM Phi-mediated suppression of this pathway contributes to the resistance of T1AECs to IAV infection. Furthermore, inhibition of the cysLT pathway enzymes, as well as blockade of the cysteinyl leukotriene receptors in the AlvM Phi deficient mice reduced the susceptibility of their T1AECs to IAV infection and protected these mice from lethal infection. These results suggest that AlvM Phi s may utilize a previously unappreciated mechanism to protect T1AECs against IAV infection, and thereby reduce the severity of infection. The findings further suggest that the cysLT pathway and the receptors for cysLT metabolites represent potential therapeutic targets in severe IAV infection.