The human gammaherpesviruses (GHVs) Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are DNA tumor viruses that establish lifelong chronic infections of host lymphocytes and other cell types. Through the expression of viral gene products that alter normal cellular signaling pathways and counteract host immune responses, GHVs place the chronically infected host at risk for numerous malignancies. As it relates to the COBRE theme of defining the impact of microbial virulence factors on host inflammatory and immune responses, the overall objective of experiments described in this project is to better define mechanisms by which GHVs counteract innate host defense mechanisms in order to successfully colonize a host. Central to this objective is the utilization of murine gammaherpesvirus-68 (MHV68), a naturally occurring rodent pathogen that is genetically related to EBV and KSHV and recapitulates key aspects of human GHV infection as a tractable small-animal model to define the virus-host interaction in vivo. Extending our published and preliminary data, the current proposal specifically seeks to understand functions of the MHV68 latency-associated nuclear antigen (mLANA), a putative viral transcriptional repressor protein, as a critical modulator of antiviral transcriptional pathways or cellular immune responses activated by interferon alpha/Beta (IFN-I) signaling that would otherwise restrict GHV infection. This work will be accomplished in three integrated but independent specific aims: (1) define IFN-l-mediated control of GHV infection at mucosal barriers, (2) elucidate roles for mLANA-mediated transcriptional control in MHV68 pathogenesis, and (3) define mLANA-interferon regulatory factor 3 (IRF-3) interactions in MHV68 infection. The proposed experiments hold broad significance by addressing two critical gaps in our understanding of GHV pathogenesis: the functions of viral disease determinants in the success of GHV infection and the interactions of GHV with host innate immune response pathways. Moreover, by advancing understanding of the nature of host immune responses, which is fundamentally important to all infectious diseases, the proposed experiments may also hold relevance for diseases caused by diverse and unrelated intracellular pathogens.