An integral feature of gammaherpesvirus infections is the ability to establish lifelong latency in B cells. During latency, the viral genome is maintained as an extrachomosomal episome, with stable maintenance in dividing cells mediated by the viral proteins Epstein-Barr nuclear antigen 1 (EBNA-1) for Epstein-Barr virus and latencyassociated nuclear antigen (LANA) for Kaposi's sarcoma-associated herpesvirus. It is believed that the expression of episome maintenance proteins is turned off in the predominant long-term latency reservoir of resting memory B cells, suggesting that chronic gammaherpesvirus infection is primarily dormant. However, the kinetics of LANA/ EBNA-1 expression in individual B-cell subsets throughout a course of infection has not been examined. The infection of mice with murine gammaherpesvirus 68 (MHV68, ␥HV68) provides a model to determine the specific cellular and molecular events that occur in vivo during lifelong gammaherpesvirus latency. In work described here, we make use of a heterologously expressed enzymatic marker to define the types of B cells that express the LANA homolog (mLANA) during chronic MHV68 infection. Our data demonstrate that mLANA is expressed in a stable fraction of B cells throughout chronic infection, with a prominent peak at 28 days. The expression of mLANA was detected in naïve follicular B cells, germinal-center B cells, and memory B cells throughout infection, with germinalcenter and memory B cells accounting for more than 80% of the mLANA-expressing cells during the maintenance phase of latency. These findings suggest that the maintenance phase of latency is an active process that involves the ongoing proliferation or reseeding of latently infected memory B cells.Gammaherpesviruses such as Epstein-Barr virus (EBV), Kaposi's sarcoma-associated virus (KSHV, HHV-8), and murine gammaherpesvirus 68 (MHV68, ␥HV68) are associated with lymphoproliferative diseases and a variety of malignancies of both epithelial and lymphoid origin. The strict species specificity exhibited by gammaherpesviruses has limited research on the human viruses primarily to in vitro studies. MHV68 is genetically colinear to the human gammaherpesviruses and exhibits many similar pathogenic features (54, 62). MHV68 is a natural pathogen of rodents (6, 9, 44), making the inoculation of mice with MHV68 a useful small-animal model to study gammaherpesvirus infection in vivo.A hallmark of gammaherpesvirus infections is the establishment of lifelong latency in B cells. During latency, the viral genome is maintained as an extrachromosomal episome, viral gene expression is highly restricted, and no new progeny virions are generated. The stable maintenance of the episome in dividing cells requires regulated plasmid DNA replication and the efficient partitioning of replicated genomes to daughter cells. These processes are mediated by critical episome maintenance protein Epstein-Barr nuclear antigen 1 (EBNA-1) for EBV and latency-associated nuclear antigen (LANA) for KSHV. EBNA-1 and LANA facilitate the re...

The human gammaherpesviruses Epstein-Barr virus (EBV)and Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 ) are ubiquitous human pathogens that are associated with the development of numerous types of malignancies, including B cell lymphomas. Murine gammaherpesvirus 68 (MHV68) is genetically related to EBV and KSHV and causes lymphoma and lymphoproliferative disease in mice, providing a useful small-animal model for mechanistic in vivo studies of the virus-host relationship. Both the human and murine viruses subvert the antiviral immune response to establish lifelong latent infections in mature B cells. However, it is not clearly understood how these viruses gain access to specific mature B cell subsets or whether latent infection of these subsets is actively maintained over time. One intriguing possibility is that gammaherpesviruses gain entry to the circulating mature B cell compartment via infection of B cell progenitors. Mature B cells arise via a highly regulated, multistep developmental process that results in the daily generation of thousands of new cells. Thus, any developing B cell subsets could provide a potential access point for recurrent entry of the virus into the long-lived mature B cell reservoir.

No abstract