Abstract Seasonal influenza epidemics result in 3-5 million severe illnesses and 300,000-500,000 deaths globally each year [1]. In the United States, the financial burden of seasonal influenza alone is nearly $90 billion annually [2]. Seasonal influenza viruses mutate and evolve rapidly necessitating the annual reformulation of influenza vac- cines, which are merely predictions to the upcoming circulating strains. Influenza vaccine efficacies vary widely from approximately 10-60%; the 2017-2018 influenza season has been particularly severe, and low vaccine efficacy underscores the critical need for improved influenza vaccine strategies. A universal influenza vaccine would theoretically provide efficacious and durable protection against multiple influenza viruses and is a top priority of the NIAID [1]. Identified steps to improving influenza vaccines include exploring the incorporation of adjuvants and altering the route of administration to maximize mucosal innate immune responses that subse- quently influence adaptive immunity [1]. Host-encoded interferons (IFNs) are critical factors that mediate innate protection as well as modulate the adaptive immune response to viruses. Type III IFNs (IFNλs) are now appre- ciated to be the predominant IFNs produced during influenza virus infection, however there is limited infor- mation about the host pathways that regulate IFNλ expression. Lack of such knowledge is a barrier to improv- ing vaccine strategies to control virus infections and transmission in susceptible populations. We recently demonstrated that the host-encoded serine-threonine kinase, Tpl2, enhances IFNλ production and host protec- tion against influenza virus infection. Therefore, the objective of this application is to gain a better understand- ing of how Tpl2 coordinates the innate immune response to influenza virus. This will be examined in two Aims. In Aim 1, the mechanisms by which viruses induce Tpl2 kinase activity and intracellular signaling pathways to promote IFNλ and amplify the anti-viral IFN response will be delineated. In Aim 2, the epithelial cell-intrinsic functions of Tpl2 during influenza virus infection will be elucidated. Experimental approaches will utilize primary murine lung epithelial cells, genetically altered mouse strains including lung epithelial cell-specific ablation of Tpl2, and unbiased genome-wide transcriptomic analysis. The results of the proposed studies will lead to a more complete understanding of how lung epithelial cells generate protective mucosal responses to respiratory viruses. Information obtained from these studies will help to improve vaccine strategies for respiratory viruses and can likely be translated to other mucosotropic infectious diseases where IFNλs have prominent roles in immunoprotection.