PSEUDOTYPE VIRIONS FORMED BETWEEN MOUSE HEPATITIS-VIRUS AND LACTATE DEHYDROGENASE-ELEVATING VIRUS (LDV) MEDIATE LDV REPLICATION IN CELLS RESISTANT TO INFECTION BY LDV VIRIONS

Infection of cultures of peritoneal macrophages with both lactate dehydrogenase-elevating virus (LDV) and mouse hepatitis virus (MHV) resulted in the formation of pseudotype virions containing LDV RNA which productively infected cells that are resistant to infection by intact LDV virions but not to infection by MHV. These cells were mouse L-2 and 3T3-17Cl-1 cells as well as residual peritoneal macrophages from persistently LDV-infected mice. Productive LDV infection of these cells via pseudotype virions was inhibited by antibodies to the MHV spike protein or to the MHV receptor, indicating that LDV RNA entered the cells via particles containing the MHV envelope. Simultaneous exposure of L-2 cells to both LDV and MHV resulted in infection by MHV but not by LDV. The results indicate that an internal block to LDV replication is not the cause of the LDV nonpermissiveness of many cell types, including the majority of the macrophages in an adult mouse. Instead, LDV permissiveness is restricted to a subpopulation of mouse macrophages because only these cells possess a surface component that acts as an LDV receptor.