Gammaherpesvirus Colonization of the Spleen Requires Lytic Replication in B Cells

Abstract

Gammaherpesviruses infect lymphocytes and cause lymphocytic cancers. Murid herpesvirus-4 (MuHV-4), Epstein-Barr virus, and Kaposi's sarcoma-associated herpesvirus all infect B cells. Latent infection can spread by B cell recirculation and proliferation, but whether this alone achieves systemic infection is unclear. To test the need of MuHV-4 for lytic infection in B cells, we flanked its essential ORF50 lytic transactivator with sites and then infected mice expressing B cell-specific Cre (CD19-Cre). The floxed virus replicated normally in Cre mice. In CD19-Cre mice, nasal and lymph node infections were maintained; but there was little splenomegaly, and splenic virus loads remained low. Cre-mediated removal of other essential lytic genes gave a similar phenotype. CD19-Cre spleen infection by intraperitoneal virus was also impaired. Therefore, MuHV-4 had to emerge lytically from B cells to colonize the spleen. An important role for B cell lytic infection in host colonization is consistent with the large CD8 T cell responses made to gammaherpesvirus lytic antigens during infectious mononucleosis and suggests that vaccine-induced immunity capable of suppressing B cell lytic infection might reduce long-term virus loads. Gammaherpesviruses cause B cell cancers. Most models of host colonization derive from cell cultures with continuous, virus-driven B cell proliferation. However, vaccines based on these models have worked poorly. To test whether proliferating B cells suffice for host colonization, we inactivated the capacity of MuHV-4, a gammaherpesvirus of mice, to reemerge from B cells. The modified virus was able to colonize a first wave of B cells in lymph nodes but spread poorly to B cells in secondary sites such as the spleen. Consequently, viral loads remained low. These results were consistent with virus-driven B cell proliferation exploiting normal host pathways and thus having to transfer lytically to new B cells for new proliferation. We conclude that viral lytic infection is a potential target to reduce B cell proliferation.

Lytic Replication and Reactivation from B Cells Is Not Required for Maintaining Gammaherpesvirus Latency in vivo

“…Cre-lox recombination provides an elegant system for conditional deletion, but the deletion must be efficient and specific. It is notable that our findings differ from those of a previous study (67), however nuances of the two studies may explain the apparently conflicting results. Contrary to our results, a virus in which both ORF49 and ORF50 were floxed (MHV-F50) was significantly attenuated following both IN and IP infection of CD19-Cre mice.…”

Deletion of immune evasion genes provides an effective vaccine design for tumor-associated herpesviruses

“…MHV-68 then establishes a steady, low level persistent infection 4-6 weeks later. Early amplification and long-term maintenance of latency involves viral reactivation to re-infect naïve B-cells [71][72][73] . This cyclic infection to maintain viral persistence has also been proposed for EBV 74 .…”

Stem cell transplantation impairs dendritic cell trafficking and herpesvirus immunity

“…Mice develop a striking splenomegaly 2-3 weeks after infection with increased numbers of B cells and CD4 + and CD8 + T cells (76). The development of MHV-68-induced splenomegaly depends on CD4 + T cells (76) and viral lytic replication in the B cells (77,78). Infected DCs can pass the virus to B cells (79).…”