Bacterial cell wall components released into the bloodstream are believed to be important in eliciting the inflammatory response that causes Gram-negative Sepsis. The bacterial outer membrane contains lipopolysaccharide (LPS), outer membrane proteins (OMPs), and phospholipids. LPS has been studied extensively as an important mediator in sepsis; the importance of OMPs in sepsis has not been systematically evaluated. Our preliminary data indicate that complexes containing three conserved OMPs and LPS are released from bacteria into human serum and are also released into the circulation of septic rats. We have identified the three proteins and have found that at least one of the proteins has biological activity. The major goals of this project are to further characterize release of the three OMPs in sepsis, to assess their roles in the pathogenesis of sepsis, and to evaluate anti-OMP immunity as a means of treating sepsis. The first specific aim is to assess release of OMPs and OMP/LPS complexes in humans with Gram- negative sepsis and in two models of experimental Gram-negative sepsis in rats. The second specific aim is to evaluate individual OMPs, OMP/LPS complexes, and OMPs on the surface of intact bacteria for biological activity in vitro on isolated immune cells, an in vivo by studying lethality, induction of cytokines in blood and organs, and pulmonary neutrophil sequestration in LPS resistant and LPS responsive mice. The third specific aim is to evaluate protective effects of active immunity on toxicity of OMP containing preparations in mice and in the rat infection models of sepsis. The applicant's long-term career objective is to become an independent investigator studying basic mechanisms of Gram- negative infection and sepsis. The career development plan is designed to expand the candidate's research knowledge base through hands-on research and educational activities. These will include course work (laboratory and didactic), attendance at and participation in laboratory meetings and research seminars, and formal and informal interactions with the Advisory Committee members. The ultimate goal of the candidate is to apply the fundamental knowledge of mechanisms involved in sepsis to develop anti-sepsis strategies that target bacterial toxins.