Persistent infection of neural cell lines by human coronaviruses

Human coronaviruses (HCV) have been associated mainly with infections of the respiratory tract. Accumulating evidence from in vitro and in vivo observations is consistent with the neurotropism of these viruses in humans. To verify the possibility of a persistent infection within the central nervous system (CNS), various human cell lines of neural origin were tested for their ability to maintain chronic infection by both known strains of HCV, OC43 and 229E. Production of infectious progeny virions was monitored by an immunoperoxydase assay on a susceptible cell line and viral RNA was observed after RT-PCR. Astrocytic cell lines U-373 MG and U-87 MG did not sustain a persistent HCV-229E infection, even though they were susceptible to an acute infection by this virus. On the other hand, these two cell lines could maintain a persistent infection by HCV-OC43 for as many as 25 cell passages (about 130 days of culture). Relatively stable titers of infectious viral particles, as well as apparently constant amounts of viral RNA were detected throughout the persistent infection of U-87 MG cells. However, persistent infection of U-373 MG cells was accompanied by the detection of infectious viral particles from passage 0 to passage 13 and then from passage 20 to the end of the experiment. This gap in the production of infectious virions was correlated by a drop in the apparent amount of viral RNA detected at passages 15 and 20. These results confirm the ability of HCV-OC43 to persistently infect cells of an astrocytic lineage and, together with our previous observations of HCV infection of primary cultures of human astrocytes and the detection of HCV RNA in human brains, are consistent with the possibility that this human coronavirus could persist in the human CNS by targeting astrocytes.