The MHV68 M2 Protein Drives IL-10 Dependent B Cell Proliferation and Differentiation

Murine gammaherpesvirus 68 (MHV68) establishes long-term latency in memory B cells similar to the human gammaherpesvirus Epstein Barr Virus (EBV). EBV encodes an interleukin-10 (IL-10) homolog and modulates cellular IL-10 expression; however, the role of IL-10 in the establishment and/or maintenance of chronic EBV infection remains unclear. Notably, MHV68 does not encode an IL-10 homolog, but virus infection has been shown to result in elevated serum IL-10 levels in wild-type mice, and IL-10 deficiency results in decreased establishment of virus latency. Here we show that a unique MHV68 latency-associated gene product, the M2 protein, is required for the elevated serum IL-10 levels observed at 2 weeks post-infection. Furthermore, M2 protein expression in primary murine B cells drives high level IL-10 expression along with increased secretion of IL-2, IL-6, and MIP-1α. M2 expression was also shown to significantly augment LPS driven survival and proliferation of primary murine B cells. The latter was dependent on IL-10 expression as demonstrated by the failure of IL10−/− B cells to proliferate in response to M2 protein expression and rescue of M2-associated proliferation by addition of recombinant murine IL-10. M2 protein expression in primary B cells also led to upregulated surface expression of the high affinity IL-2 receptor (CD25) and the activation marker GL7, along with down-regulated surface expression of B220, MHC II, and sIgD. The cells retained CD19 and sIgG expression, suggesting differentiation to a pre-plasma memory B cell phenotype. These observations are consistent with previous analyses of M2-null MHV68 mutants that have suggested a role for the M2 protein in expansion and differentiation of MHV68 latently infected B cells—perhaps facilitating the establishment of virus latency in memory B cells. Thus, while the M2 protein is unique to MHV68, analysis of M2 function has revealed an important role for IL-10 in MHV68 pathogenesis—identifying a strategy that appears to be conserved between at least EBV and MHV68

TLR9-induced interferon β is associated with protection from gammaherpesvirus-induced exacerbation of lung fibrosis

Abstract Background We have shown previously that murine gammaherpesvirus 68 (γHV68) infection exacerbates established pulmonary fibrosis. Because Toll-like receptor (TLR)-9 may be important in controlling the immune response to γHV68 infection, we examined how TLR-9 signaling effects exacerbation of fibrosis in response to viral infection, using models of bleomycin- and fluorescein isothiocyanate-induced pulmonary fibrosis in wild-type (Balb/c) and TLR-9-/- mice. Results We found that in the absence of TLR-9 signaling, there was a significant increase in collagen deposition following viral exacerbation of fibrosis. This was not associated with increased viral load in TLR-9-/- mice or with major alterations in T helper (Th)1 and Th2 cytokines. We examined alveolar epithelial-cell apoptosis in both strains, but this could not explain the altered fibrotic outcomes. As expected, TLR-9-/- mice had a defect in the production of interferon (IFN)-β after viral infection. Balb/c fibroblasts infected with γHV68 in vitro produced more IFN-β than did infected TLR-9-/- fibroblasts. Accordingly, in vitro infection of Balb/c fibroblasts resulted in reduced proliferation rates whereas infection of TLR-9-/- fibroblasts did not. Finally, therapeutic administration of CpG oligodeoxynucleotides ameliorated bleomycin-induced fibrosis in wild-type mice. Conclusions These results show a protective role for TLR-9 signaling in murine models of lung fibrosis, and highlight differences in the biology of TLR-9 between mice and humans.http://deepblue.lib.umich.edu/bitstream/2027.42/112877/1/13069_2011_Article_57.pd

Murine Gamma-herpesvirus Immortalization of Fetal Liver-Derived B Cells Requires both the Viral Cyclin D Homolog and Latency-Associated Nuclear Antigen

Human gammaherpesviruses are associated with the development of lymphoproliferative diseases and B cell lymphomas, particularly in immunosuppressed hosts. Understanding the molecular mechanisms by which human gammaherpesviruses cause disease is hampered by the lack of convenient small animal models to study them. However, infection of laboratory strains of mice with the rodent virus murine gammaherpesvirus 68 (MHV68) has been useful in gaining insights into how gammaherpesviruses contribute to the genesis and progression of lymphoproliferative lesions. In this report we make the novel observation that MHV68 infection of murine day 15 fetal liver cells results in their immortalization and differentiation into B plasmablasts that can be propagated indefinitely in vitro, and can establish metastasizing lymphomas in mice lacking normal immune competence. The phenotype of the MHV68 immortalized B cell lines is similar to that observed in lymphomas caused by KSHV and resembles the favored phenotype observed during MHV68 infection in vivo. All established cell lines maintained the MHV68 genome, with limited viral gene expression and little or no detectable virus production - although virus reactivation could be induced upon crosslinking surface Ig. Notably, transcription of the genes encoding the MHV68 viral cyclin D homolog (v-cyclin) and the homolog of the KSHV latency-associated nuclear antigen (LANA), both of which are conserved among characterized γ2-herpesviruses, could consistently be detected in the established B cell lines. Furthermore, we show that the v-cyclin and LANA homologs are required for MHV68 immortalization of murine B cells. In contrast the M2 gene, which is unique to MHV68 and plays a role in latency and virus reactivation in vivo, was dispensable for B cell immortalization. This new model of gammaherpesvirus-driven B cell immortalization and differentiation in a small animal model establishes an experimental system for detailed investigation of the role of gammaherpesvirus gene products and host responses in the genesis and progression of gammaherpesvirus-associated lymphomas, and presents a convenient system to evaluate therapeutic modalities

Global mRNA Degradation during Lytic Gammaherpesvirus Infection Contributes to Establishment of Viral Latency

During a lytic gammaherpesvirus infection, host gene expression is severely restricted by the global degradation and altered 3′ end processing of mRNA. This host shutoff phenotype is orchestrated by the viral SOX protein, yet its functional significance to the viral lifecycle has not been elucidated, in part due to the multifunctional nature of SOX. Using an unbiased mutagenesis screen of the murine gammaherpesvirus 68 (MHV68) SOX homolog, we isolated a single amino acid point mutant that is selectively defective in host shutoff activity. Incorporation of this mutation into MHV68 yielded a virus with significantly reduced capacity for mRNA turnover. Unexpectedly, the MHV68 mutant showed little defect during the acute replication phase in the mouse lung. Instead, the virus exhibited attenuation at later stages of in vivo infections suggestive of defects in both trafficking and latency establishment. Specifically, mice intranasally infected with the host shutoff mutant accumulated to lower levels at 10 days post infection in the lymph nodes, failed to develop splenomegaly, and exhibited reduced viral DNA levels and a lower frequency of latently infected splenocytes. Decreased latency establishment was also observed upon infection via the intraperitoneal route. These results highlight for the first time the importance of global mRNA degradation during a gammaherpesvirus infection and link an exclusively lytic phenomenon with downstream latency establishment