OAS1 and infection: The antiviral responses of the infected alveolar barrier model were then examined by monitoring the production of type I interferon (IFN) and the expression of IFN‐stimulated gene 15 (ISG15) and the 2′–5′‐oligoadenylate synthetase 1 (OAS1) which are among the most important components of the immune system induced by IFN, at 6, 12, and 24 h after infection.