DESCRIPTION: This is a revised application to study the role of elements of innate immunity in the pathogenesis of periodontal disease. Specifically, a novel model of P- and E-selectin deficient mice (P/E(-/-)) will be utilized to investigate the role of innate immunity, specifically, Toll-like receptors (TLR), in periodontal disease. Previous studies have shown that P/E(-/-) mice develop a progressive periodontitis that is initiated shortly after tooth eruption, and is characterized by an oral flora that is increased in mass and pathogenicity, gingival inflammation, increased expression of the bone resorptive cytokine IL-1, and extensive bone loss. Moreover, antibiotic treatment completely prevents bone loss. It is suggested that this model offers advantages over other systems, including the naturally occurring nature of the disease, the rapidity of periodontal destruction, the ability to control and manipulate the oral flora and the host immune response, and the availability of a vast array of reagents and genetically-engineered strains. The investigators will test the hypothesis that periodontal destruction can be ameliorated by modulating TLRs, their signaling pathways, and the cytokines that they induce. The proposed study is divided into four Specific Aims: 1) to identify the periodontal pathogens that are responsible for disease in P/E(-/-) mice; these studies will utilize 16S rRNA sequencing to characterize the oral flora in P/E(-/-), P/E(+/+) , and antibiotic treated mice; 2) to determine the immune mechanisms activated by pathogens in P/E(-/-) mice. Cell infiltrates, cytokines and Toll-like receptors (TLRs) will be characterized in vivo and in vitro; 3) to determine the function of TLRs in cytokine and co-stimulatory molecule expression in response to pathogens. Dominant negative constructs of TLR signal transducing molecules will be used to inhibit TLR responses and the effect on pathogen-induced cytokine responses determined. Also, the role of TLRs in skewing the immune response towards a Th1 and Th2 profile will be assessed; 4) to determine the roles of TLRs and cytokines in periodontal bone destruction. Knockout mice and modulation of IL-1, IL-6 and IL-10 will be used to establish the role of these factors in periodontal bone loss. The long-term goal of these studies is to determine the role of innate immunity in periodontitis and to apply this information to the development of immune modulators that ameliorate disease.