Human coronaviruses (HuCV) cause common colds. Previous reports suggest that these infectious agents may be neurotropic in humans, as they are for some mammals. With the long-term aim of providing experimental evidence for the neurotropism of HuCV and the establishment of persistent infections in the nervous system, we have evaluated the susceptibility of various human neural cell lines to acute and persistent infection by HuCV-229E. Viral antigen, infectious virus progeny and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, and oligodendrocytic MO3.13 cell lines, were all susceptible to an acute infection by HuCV-229E. The CHME-5 immortalized fetal microglial cell line was not susceptible to infection by this virus. The MO3.13 and H4 cell lines also sustained a persistent viral infection, as monitored by detection of viral antigen and infectious virus progeny. Sequencing of the S1 gene from viral RNA after ∼130 days of infection showed two point mutations, suggesting amino acid changes during persistent infection of MO3.13 cells but none for H4 cells. Thus, persistent in vitro infection did not generate important changes in the S1 portion of the viral spike protein, which was shown for murine coronaviruses to bear hypervariable domains and to interact with cellular receptor. These results are consistent with the potential persistence of HuCV-229E in cells of the human nervous system, such as oligodendrocytes and possibly neurons, and the virus’s apparent genomic stability.

The 299£ prototype strain of human coronavirus (HCV-229£) has so far been mainly associated with infections of the respiratory tract. In the present study, we show evidence for infection of the central nervous system (CNS) by HCV-229E, both in vitro and in vivo. Various human cell lines of CNS origin were tested for their susceptibility to infection by HCV-229£. Production of viral antigens was monitored by indirect immunofluorescence with monoclonal antibodies and infectious progeny virions by plaque assay on the L132 human embryonic lung cell line. The SK-N-SH neuroblastoma and H4 neuroglioma cell lines were highly susceptible to infection. The U-87 MG and U-373 MG astrocytoma cell lines were also infectable by HCV-229E. We could also demonstrate infection of the M03.13 cell line, which was established by fusion of human oligodendrocytes with a thioguanineresistant mutant of the 1E671 (RD) human rhabdomyosarcoma cell line. An apparently more extensive infection of the M03.13 cells, when compared to the parental cells, supports the notion that human oligodendrocytes are differentially susceptible to infection by this virus. We also tested for HCV-229E gene expression in pathological brain specimens. For that purpose, we developed a reverse transcription-polymerase chain reaction (RT-PCR) assay to amplify a portion of the mRNA encoding the viral nucleocapsid protein. Using stringent laboratory conditions, viral RNA was detectable in brain tissue of 4 of 11 multiple sclerosis patients and none of 6 neurological and 5 normal controls. These results strongly suggest neurotropism on the part of HCV-229E and emphasize the importance of further studies on the possible involvement of human coronaviruses in neurological diseases such as multiple sclerosis.