Localized juvenile periodontitis (LJP) is a periodontal disease which primarily affects peripubertal children of African descent. Over 95 percent of the LJP patient population is colonized with the facultative Gram negative rod Actinobacillus actinomycetmcomitans (Aa). In LJP, virulent strains of Aa invade the epithelial cells, and colonize the oral mucosa, and induce a hyperinflammatory response. A bacterial virulence factor which encodes a secreted leukotoxin inhibits bactericidal activity by the PMNs, allowing colonization. For the initial colonization and subsequent invasion, however, the bacteria must first evade the initial line of host defense in the oral cavity. This primary part of oral innate immunity is based in the response of the epithelial cells by the production of antimicrobial agents and inflammatory mediators. Little is known about how the periodontal epithelium responds to the presence of bacteria in general, and Aa in particular. Furthermore, while LJP is a disease with a large genetic component which only manifests with localized periodontal infections, the deficiencies in the host defense capabilities of this epithelium have not been examined. Thus, a more complete analysis of the innate immune response of the gingival epithelium to Aa will allow for a better understanding of the etiology of this disease. The long-range goal of our research is to better understand the dynamic host defense systems in the mucosal epithelium. The objective of these studies is to determine how a pathogenic bacterium evades the innate immune response in individuals which are predisposed to this infection. Our central hypothesis is that the gingival epithelium provides an active host defense tissue. A combination of deficiencies in this host defense and bacterial virulence factors can lead to severe infection. By characterizing the response of the epithelial cells to the pathogen, and identifying differences in cells from diseased versus normal individuals, we will be able to better address the issues of early detection and treatment. This would include strategies to modulate the endogenous antimicrobial peptide expression to prevent serious bacterial infections. To achieve this we propose to: 1. Characterize the specific pattern recognition receptors to Aa in the gingival epithelium. 2. Define the host defense gene expression of the cultured gingival epithelium in response to Aa. 3. Determine innate immune gene expression in the oral epithelium from healthy and LJP patients. For this study we will focus on the role of pattern recognition receptors such as CD14 and Toll- like receptors, antimicrobial peptide and production of proinflammatory cytokines. Our approach, which includes studying the interactions of the epithelium with live bacteria and the use of microarrays, will provide a detailed picture of the host defense capabilities of the oral cavity. Characterization of variability in the expression of specific natural antibiotics such as beta-defensins or stimulants of neutrophil antibacterial function such as chemotactic and proinflammatory cytokines, which may prevent colonization of periodontal tissues by this persistent bacterium, may allow for early identification of the susceptible individuals or provide an alternative treatment approach for this patient category. The result from this study will allow us to develop novel strategies to prevent attachment and colonization of disease-causing bacteria.