Disruption of the gene encoding the γHV68 v-GPCR leads to decreased efficiency of reactivation from latency

Murine gammaherpesvirus 68 (γHV68; MHV68) infection of mice has been a useful model for characterizing the role of conserved herpesvirus genes in pathogenesis. One of the well conserved genes among γ2-herpesvirus, gene 74, encodes a viral G-protein coupled receptor (v-GPCR). To examine the role of the γHV68 v-GPCR in pathogenesis we have generated a mutant virus in which 440 base pairs of the gene 74 open reading frame have been deleted (γHV68v-GPCRΔ440). This deletion did not affect the growth of the virus in single or multiple rounds of replication in vitro, nor acute replication in vivo as assessed by plaque assay of spleens and lungs on days 4, 7 and 9 post-infection (p.i.). The ability of the v-GPCR mutant virus to establish latency and to reactivate from latency was quantitated on days 16 and 42 p.i. While there was no detectable difference in the ability of the mutant virus to either establish latency or reactivate from latency on day 16 p.i., as compared to wild-type γHV68 and marker rescue virus, there was a significant decrease in the efficiency of virus reactivation by day 42 p.i. Notably, mice infected with the mutant virus lacking the v-GPCR contained a higher frequency of viral genome positive cells in the peritoneum by day 42 p.i. than mice infected with either wild type or marker rescue virus. However, analysis of virus reactivation demonstrated that approximately the same frequency of cells reactivated virus from mice infected with either the γHV68 v-GPCR mutant, wild-type virus, or marker rescue virus. From these experiments we conclude that the γHV68 v-GPCR is dispensable for acute virus replication in vivo, but does play a role in reactivation from latency.