Multiple regions of the murine coronavirus spike glycoprotein influence neurovirulence

The spike (S) glycoprotein of mouse hepatitis virus (MHV) is a major determ inant of neurovirulence. Using targeted recombination we previously demonst rated that the S gene of the highly neurovirulent MHV-4 conferred a dramati c increase in neurovirulence to the mildly neurovirulent MHV-A59. To identi fy the genetic determinants of neurovirulence within the MHV-4 spike, we ge nerated isogenic recombinant viruses containing various MHV-4/MHV-A59 chime ric spike genes, and studied their phenotypes in vivo. The MHV-4/MHV-A59 ch imeric spike genes consisted of either reciprocal exchanges between the S1 and S2 spike subunits, or smaller exchanges specifically in the hypervariab le region (HVR) of S1. The chimeric spike gene containing recombinants all exhibited efficient replication in vitro, yet many were severely attenuated for virulence in vivo. Furthermore, these attenuated recombinants exhibite d decreased titers of infectious virus in the brain relative to the parenta l recombinant viruses containing the full-length MHV-4 or MHV-A59 spike gen es. This is the first report that compares the neurovirulence and pathogene sis of isogenic viruses with defined alterations in the MHV spike protein. From these studies, it appears that the interactions of multiple regions of the MHV spike, including the HVR, act in concert to allow for efficient in fection of and virulence in the murine central nervous system.