Role of macrophage activation and interferon in the resistance of alveolar macrophages from infected mice to influenza virus.

Lung macrophages from uninfected CD1 mice support the replication of influenza viruses (H1N1 and H0N1), but the cells from influenza-infected mice do not. The possible mechanisms of this resistance were investigated. Murine macrophages were "activated" in vitro with lipopolysaccharide and lymphokines, and in both cases activation was associated with resistance of cells to infection with influenza virus. Exposure of alveolar macrophages in vitro to 500 U of purified type I interferon per ml enhanced cell spreading and Fc receptor-mediated phagocytosis, suggesting macrophage activation, and protected the cells against infection with influenza virus. Alveolar macrophages were also protected by a soluble factor in the bronchoalveolar washings from influenza-infected mice. This effect was not virus specific and was abolished by anti-interferon serum.