title: The murine gammaherpesvirus 68 M2 gene is required for efficient reactivation from latently infected B cells.
abstract: Murine gammaherpesvirus 68 (gammaHV68) infection of mice provides a tractable small-animal model system for assessing the requirements for the establishment and maintenance of gammaherpesvirus latency within the lymphoid compartment. The M2 gene product of gammaHV68 is a latency-associated antigen with no discernible homology to any known proteins. Here we focus on the requirement for the M2 gene in splenic B-cell latency. Our analyses showed the following. (i) Low-dose (100 PFU) inoculation administered via the intranasal route resulted in a failure to establish splenic B-cell latency at day 16 postinfection. (ii) Increasing the inoculation dose to 4 x 10(5) PFU administered via the intranasal route partially restored the establishment of B-cell latency at day 16, but no virus reactivation was detected upon explant into tissue cultures. (iii) Although previous data failed to detect a phenotype of the M2 mutant upon high-dose intraperitoneal inoculation, decreasing the inoculation dose to 100 PFU administered intraperitoneally revealed a splenic B-cell latency phenotype at day 16 that was very similar to the phenotype observed upon high-dose intranasal inoculation. (iv) After low-dose intraperitoneal inoculation, fractionated B-cell populations showed that the M2 mutant virus was able to establish latency in surface immunoglobulin D-negative (sIgD(-)) B cells; by 6 months postinfection, equivalent frequencies of M2 mutant and marker rescue viral genome-positive sIgD(-) B cells were detected. (v) Like the marker rescue virus, the M2 mutant virus also established latency in splenic naive B cells upon low-dose intraperitoneal inoculation, but there was a significant lag in the decay of this latently infected reservoir compared to that seen with the marker rescue virus. (vi) After low-dose intranasal inoculation, by day 42 postinfection, latency was observed in the spleen, although at a frequency significantly lower than that in the marker rescue virus-infected mice; by 3 months postinfection, nearly equivalent levels of viral genome-positive cells were observed in the spleens of marker rescue virus- and M2 mutant virus-infected mice, and these cells were exclusively sIgD(-) B cells. Taken together, these data convincingly demonstrate a role for the M2 gene product in reactivation from splenic B cells and also suggest that disruption of the M2 gene leads to dose- and route-specific defects in the efficient establishment of splenic B-cell latency.
authors.affiliation: Center for Emerging Infectious Diseases, Yerkes National Primate Research Center, School of Medicine, Emory University, Atlanta, GA 30329, USA.
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Herskowitz
authors.forename: Jeremy
authors.initials: J
authors.lastname: Herskowitz
authors.forename: Meagan A
authors.initials: MA
authors.lastname: Jacoby
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Speck
mesh_terms: D000281:Administration, Intranasal; D000818:Animals; D001402:B-Lymphocytes / Q000821:virology*; D018142:Gammaherpesvirinae / Q000235:genetics* / Q000502:physiology; D005814:Genes, Viral / Q000502:physiology*; D006566:Herpesviridae Infections / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D013154:Spleen / Q000821:virology; D014774:Virulence; D014775:Virus Activation / Q000502:physiology*; D017735:Virus Latency / Q000502:physiology*; D014779:Virus Replication