De Novo Infection of B Cells during Murine Gammaherpesvirus 68 Latency

Abstract

The mechanisms by which gammaherpesviruses maintain latency are unclear. Here we used a murine gammaherpesvirus model to show that previously uninfected B cells in immunocompetent mice can acquire virus during latency. In vivo depletion of T cells allowed viral reactivation, as measured by increased viral loads, but not enhanced transfer of virus to new cells. In the absence of both immune T cells and antibody following the transfer of latently infected cells into naïve animals, there was robust infection of new B cells. These data confirm that both T cells and antibody contribute to the control of gammaherpesvirus latency, reactivation, and spread.The hallmark of herpesvirus (HV) infections is the establishment of latency, a lifelong condition characterized by persistent viral genome maintenance and restricted, low-level viral gene expression. The ability to reactivate from latency, reenter the lytic life cycle, and generate infectious virions is responsible for many of the secondary pathological consequences of HV infections, including autoimmunity, cancer, immunoproliferative disorders, recrudescent skin lesions, and transplant rejection (15,19). An unresolved issue in the field of herpesvirology is how latent infections are maintained in the host over time. In the case of alphaherpesvirus (␣HV) latency, the viral genomes reside in nonreplicating cells such as neurons, and so latency is likely propagated by the mere survival of latently infected cells, with periodic de novo infections following reactivation events. ␤HV and ␥HV infections are different, as they establish latency in immune system cells, which, unlike neurons, not only can proliferate but also can express high levels of major histocompatibility complex (MHC) class I and are targets for T cell immunity. Since long-term latency persists even in the presence of functional virus-specific immunity, it is crucial to understand how viral latency is propagated in an immunocompetent host in order to develop rational strategies to control ␥HV infections.Mechanisms for ␥HV latency persistence include viral immune evasion strategies; proliferation of latently infected B cells, in which latent viral episomes are replicated and transferred to the daughter cells; direct cell-to-cell transfer of infectious virus to naïve cells, in the absence of cell-free virus; and asymptomatic shedding of lytic virus, leading to the infection of new B cells. There is evidence in the literature for each of these mechanisms. For example, Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA-1) protein is associated with driving the proliferation of infected B cells (8). Furthermore, it has been shown that efficient EBV infection of epithelial cell lines requires cell-to-cell contact with virally infected cells in cocultures (3, 10), a process that is refractory to inhibition by blocking antibodies (Abs), suggesting that cell-free virus is not required for infection (22). In one study, long-term valacyclovir treatment did not affect the number of EBV DNA copies per B cell but did red...

Promotion of a Subdominant CD8 T Cell Response during Murine Gammaherpesvirus 68 Infection in the Absence of CD4 T Cell Help

“…Mice deficient in either CD8 or CD4 T cells succumb to infection, albeit with different kinetics, and both CD8 and CD4 T cells contribute to the long-term control of viral latency (2)(3)(4)(5). In some models of viral infection, CD4 T cells are critically important for helping CD8 T cells generate optimal memory cells.…”

γ-Herpesvirus Reactivation Differentially Stimulates Epitope-Specific CD8 T Cell Responses

“…This technique has been used to demonstrate that new naïve T cells can respond to persistent viral infections (4, 7). We have recently shown that busulfan treatment of γHV68-infected mice does not affect the latent viral load or impair the pre-existing humoral and cellular immunity (3). We allowed latently-infected mice to reconstitute for up to 28 weeks then measured the phenotype of the host and donor CD8 T cells (Figure 1B).…”

“…In our recent report, we demonstrated that depletion of the host T cell response by anti-Thy1.2 mAb injections led to substantial reactivation of latent virus, leading to enhanced infection of the donor B cells (3). It is unknown, however, whether viral reactivation also stimulates the recruitment of naïve T cells into the ongoing response.…”

“…One day later, 2 × 10 7 cells isolated from the bone marrow of naïve CD45.2 + Thy1.1 + mice were injected intraveneously (i.v.). Reconstitution in B cells was previously shown to be 63.32 ± 6.585, in CD4 T cells, 43.38 ± 5.658, and in CD8 T cells 33.06 ± 5.331 (3). Engraftment was in this range for the current studies.…”

“…The rodent pathogen murine γ-herpesvirus-68 (γHV68) is closely related to EBV and KSHV and infection of mice with γHV68 provides an experimental animal model to study γ-herpesvirus pathogenesis and immunity. As antiviral T cell activity is critical for the control of latent herpesvirus infections and the loss of T cell memory numbers or function can lead to viral reactivation and recurrent disease (1-3), it is of utmost importance to understand how antiviral CD8 T cell responses are maintained during γHV68 infection.…”