Abstract
Gammaherpesviruses infect most vertebrate species and are associated with B cell lymphomas. Manipulation of B cell differentiation is critical for natural infection and lymphomagenesis driven by gammaherpesviruses. Specifically, human Epstein-Barr virus (EBV) and murine gammaherpesvirus 68 (MHV68) drive differentiation of infected naive B cells into the germinal center to achieve exponential increase in the latent viral reservoir during the establishment of chronic infection. Infected germinal center B cells are also the target of viral lymphomagenesis, as most EBV-positive B cell lymphomas bear the signature of the germinal center response. All gammaherpesviruses encode a protein kinase, which, in the case of Kaposi's sarcoma-associated herpesvirus (KSHV) and MHV68, is sufficient and necessary, respectively, to drive B cell differentiation in vivo. In this study, we used the highly tractable MHV68 model of chronic gammaherpesvirus infection to unveil an antagonistic relationship between MHV68 protein kinase and interferon regulatory factor 1 (IRF-1). IRF-1 deficiency had minimal effect on the attenuated lytic replication of the kinase-null MHV68 in vivo. In contrast, the attenuated latent reservoir of the kinase-null MHV68 was partially to fully rescued in IRF-1-/- mice, along with complete rescue of the MHV68-driven germinal center response. Thus, the novel viral protein kinase-IRF-1 antagonism was largely limited to chronic infection dominated by viral latency and was less relevant for lytic replication during acute infection and in vitro. Given the conserved nature of the viral and host protein, the antagonism between the two, as defined in this study, may regulate gammaherpesvirus infection across species. IMPORTANCE Gammaherpesviruses are prevalent pathogens that manipulate physiological B cell differentiation to establish lifelong infection. This manipulation is also involved in gammaherpesvirus-driven B cell lymphomas, as differentiation of latently infected B cells through the germinal center response targets these for transformation. In this study, we define a novel antagonistic interaction between a conserved gammaherpesvirus protein kinase and a host antiviral and tumor suppressor transcription factor. The virus-host antagonism unveiled in this study was critically important to shape the magnitude of gammaherpesvirus-driven germinal center response. In contrast, the virus-host antagonism was far less relevant for lytic viral replication in vitro and during acute infection in vivo, highlighting the emerging concept that nonoverlapping mechanisms shape the parameters of acute and chronic gammaherpesvirus infection.