Progress in our understanding of the pathogenesis of severe sepsis has been constant over the past two decades, and is now beginning to lead to new therapeutic approaches. During the previous funding period, we demonstrated that targeted (but not systemic) expression of first generation adenoviral (Ad) vectors expressing IL-10 could improve outcome in several murine models of sepsis. Importantly, the use of Ad has provided a unique tool to modulate dendritic cell (DC) phenotype, deliver IL-10 locally, and modify the sepsis response. Although we (and others) have demonstrated that the loss of DCs from lymphoid tissues is a consequence of sepsis, its causative relationship to outcome has not been confirmed until recently. In preliminary studies, we have demonstrated that myeloid and lymphoid DC depletion is associated with an adverse outcome in murine sepsis, whereas modifying the phenotype of DCs both in vivo and ex vivo by autocrine production of IL-10 can improve outcome. This continuing renewal seeks to identify the mechanistic basis for these observations, as well as the overall importance of DCs in the sepsis response. Our overarching hypothesis is that modulation of DC function bv adenoviral delivery of IL-10 can improve outcome in sepsis bv altering the interactions between DCs and T-cell and natural killer (NK) cell populations in Iymphatic tissues. The two specific aims are focused on determining whether modifying DC number and function with Ad expressing IL-10 impacts outcome through alterations in the induction of T-cell apoptosis. The generation of regulatory T cell populations, and NK and NK-Tcell interactions. Using a murine model of generalized peritonitis (cecal ligation and puncture), and transgenic mice that can be depleted of CD11c+ cells, or transgenic mice lacking IL-10 or CD25<7, as well as reconstitution experiments with Ad-transduced DCs, we intend to explore the mechanisms by which modification of DC status and function alters outcome to sepsis. Not only will these studies provide valuable preclinical information about the feasibility of ex vivo Ad transfections schemes in sepsis and acute inflammation, but will also provide essential information about the role of the DC in the successful host response to sepsis.