B cells regulate murine gammaherpesvirus 68 latency

The dynamics of the establishment of, and reactivation from, gammaherpesvir uses latency has not been quantitatively analyzed in the natural host. Gamm aherpesvirus 68 (gamma HV68) is a murine gammaherpesvirus genetically relat ed to primate gammaherpesviruses that establishes a latent infection in inf ected mice. We used limiting dilution reactivation (frequency of cells reac tivating gamma HV68 in vitro) and limiting dilution PCR (frequency of cells carrying gamma HV68 genome) assays to compare gamma HV68 latency in normal (C57BL/6) and B-cell-deficient (MuMT) mice. After intraperitoneal (i.p.) i noculation, latent gamma HV68 was detected in the spleen, bone marrow, and peritoneal cells, Both B-cell-deficient and C57BL/6 mice established latent infection in peritoneal cells after either i.p. or intranasal (i.n.) inocu lation. In contrast, establishment of splenic latency was less efficient in B-cell-deficient than in C57BL/6 mice after i.n. inoculation. Analysis of reactivation efficiency (reactivation frequency compared to frequency of ce lls carrying gamma HV68 genome) revealed that (i) regardless of route or mo use strain, splenic cells reactivated gamma HV68 less efficiently than peri toneal cells, (ii) the frequency of cells carrying gamma HV68 genome was ge nerally comparable over the course of infection between C57BL/6 and B-cell- deficient mice, (iii) between 28 and 250 days after infection, cells from B -cell-deficient mice reactivated gamma HV68 10- to 100-fold more efficientl y than cells from C57BL/6 mice, (iv) at 7 weeks postinfection, B-cell-defic ient mice had more genome-positive peritoneal cells than C57BL/6 mice, and (v) mixing cells (ratio of 3 to 1) that reactivated inefficiently with tell s that reactivated efficiently did not significantly decrease reactivation efficiency. Consistent with a failure to normally regulate chronic gamma HV 68 infection, the majority of infected B-cell-deficient mice died between 1 00 and 200 days postinfection. We conclude that (i) B cells are not require d for establishment of gamma HV68 latency, (ii) there are organ-specific di fferences in the efficiency of gamma HV68 reactivation, (iii) B cells play a crucial role in regulating reactivation of gamma HV68 from latency, and ( iv) B cells are important for controlling chronic gamma HV68 infection.