Rhinovirus infection in neuronal cells and brain

Abstract

Traditionally, rhinovirus is considered to cause common cold or mild upper respiratory tract infection. Recently, rhinovirus is frequently reported to cause lower respiratory tract infection and exacerbation of underlying chronic lung diseases. Moreover, there is accumulating evidence that rhinovirus is associated with extrapulmonary manifestations. A previous study showed that 23% of critically ill patients with rhinovirus infection had seizure. The aim of this study was to systematically investigate rhinovirus infection of the central nervous system (CNS) in vitro and in vivo. In chapter 4, we assessed the infection of rhinovirus in neuronal cell lines. First, rhinovirus 1A, a minor group rhinovirus, was found to replicate in three different neuronal cell lines (SK-N-SH, NT2 and SF268). In multicycle growth assay by RT-qPCR and plaque assay, rhinovirus 1A replicated best in the neuroblastoma cell line SK-N-SH. Infection in SK-N-SH was confirmed by viral antigen detection with immunofluorescent assay, and cytopathic effect was observed as early as day 1 post-infection. Second, we compared the replication of minor and major group rhinoviruses in SK-N-SH. In the multicycle growth assay of SK-N-SH cells, the viral load on day 3 post-infection was significantly higher for the minor group rhinovirus 1A than those of the major group rhinoviruses A16 and B14. In chapter 5, the host cytokine response and mode of cell death were assessed. Rhinovirus 1A infection induced the expression of proinflammatory cytokines in neuronal cells, including IL-1β, IL-6 and TNF-α. As shown in the TUNEL assay, rhinovirus 1A infection induced apoptosis in SK-N-SH. In chapters 6 and 7, a mouse model was used to investigate rhinovirus infection in the central nervous system. Enterovirus D68, a neurotropic virus previously known as rhinovirus 87, was used as a positive control in the mouse experiments. Intracerebral inoculation of rhinovirus 1A resulted in >10% body weight loss. When compared with the neuropathic enterovirus D68, intracerebral inoculation of rhinovirus 1A resulted in a higher viral load and a more prolonged infection, but a lower level of cytokine expression in brain tissues. Mice with intracerebral inoculation of rhinovirus A16 or B14 did not exhibit any weight loss or symptoms. Intranasal inoculation of rhinovirus 1A resulted in pneumonia, but there was no evidence of central nervous system infection after intranasal inoculation of rhinovirus 1A. In summary, although rhinovirus can infect neuronal cells and induce proinflammatory response in vitro and in vivo, infection via the respiratory route did not result in CNS invasion. Our results corroborate with the clinical findings in which rhinovirus is seldom identified in the cerebrospinal fluid or brain tissue of patients with rhinovirus infection. However, the ability of rhinovirus to infect neuronal cells suggests that rhinovirus may indeed infect CNS in immunocompromised patients.