Murine peritoneal macrophages support murine cytomegalovirus replication

Because there have been different conclusions regarding the susceptibility of murine macrophages to murine cytomegalovirus (MCMV) infection and replication, we have undertaken a detailed comparison of MCMV infection of macrophages with that of a permissive cell line, mouse embryo cells. Although both cell lines undergo productive infections with MCMV, there are marked differences in certain aspects of the viral replication which may account for some of the different conclusions regarding the MCMV cycle in macrophages. Although both cell lines produce MCMV after infection, the time course of the infection differed markedly between the cell types. Similarly, the proportion of infected macrophages that are releasing infection virions is much smaller than the proportion of a comparably infected mouse embryo cell culture. Tissue culture passage of MCMV first enhanced (after one passage) and then reduced the infectivity of the virus for macrophages in vitro. The delayed time course and lesser production at early intervals after infection of macrophage cultures could not be attributed to demonstrable inhibitors or to replication in contaminating fibroblasts in the macrophage cultures.