Rhinovirus infection induces expression of type 2 nitric oxide synthase in human respiratory epithelial cells in vitro and in vivo

Background: Human rhinovirus (HRV) infections are the predominant cause of the common cold and are associated with exacerbations of asthma, Nitric oxide (NO) may play an important role in host defense by means of its potent antiviral properties. Objective: We sought to determine whether epithelial expression of type 2 nitric oxide synthase (NOS 2), which produces NO, is induced on rhinovirus infection in vitro and in vivo. Methods: Primary cultures of human airway epithelial cells were infected with HRV-16, and NOS 2 mRNA expression was assessed by conventional and real-time RT-PCR and NOS 2 protein by using Western blot analysis. Human subjects were also infected with HRV-16 in vivo, and mRNA for NOS 2 was assessed in nasal epithelial scrapings obtained before and after infection. Results: NOS 2 mRNA levels increased within 8 hours after HRV-16 infection of cultured cells and remained elevated up to 48 hours after infection. NOS 2 protein was elevated at 24 hours. Induction of NOS 2 did not occur with UV-inactivated HRV-16 but could be reproduced by using double-stranded RNA, indicating that induction was dependent on viral replication. Increased NOS 2 expression was also observed in nasal epithelial scrapings during symptomatic colds. Conclusion: Increased epithelial expression of NOS 2 mRNA occurs as part of the host response to HRV infection in vitro and in vivo. Given the antiviral effects of NO, we speculate that increased host production of NO may play an important role in host defense during HRV infections.