THE SPIKE PROTEIN OF MURINE CORONAVIRUS MOUSE HEPATITIS-VIRUS STRAIN A59 IS NOT CLEAVED IN PRIMARY GLIAL-CELLS AND PRIMARY HEPATOCYTES

Mouse hepatitis virus strain A59 (MHV-A59) produces meningoencephaliti s and severe hepatitis during acute infection. Infection of primary ce lls derived from the central nervous system (CNS) and liver was examin ed to analyze the interaction of virus with individual cell types deri ved from the two principal sites of viral replication in vivo. In glia l cell cultures derived from C57BL/6 mice, MHV-A59 produces a producti ve but nonlytic infection, with no evidence of cell-to-cell fusion. In contrast, in continuously cultured cells, this virus produces a lytic infection with extensive formation of syncytia. The observation of fe w and delayed syncytia following MHV-A59 infection of hepatocytes more closely resembles infection of glial cells than that of continuously cultured cell lines. For MHV-A59, lack of syncytium formation correlat es with lack of cleavage of the fusion glycoprotein, or spike (S) prot ein. The absence of cell-to-cell fusion following infection of both pr imary cell types prompted us to examine the cleavage of the spike prot ein. Cleavage of S protein was below the level of detection by Western blot analysis in MHV-A59-infected hepatocytes and glial cells. Furthe rmore, no cleavage of this protein was detected in liver homogenates f rom C57BL/6 mice infected with MHV-A59. Thus, cleavage of the spike pr otein does not seem to be essential for entry and spread of the virus in vivo, as well as for replication in vitro.