The host immune system responds to invading pathogens by detecting pathogen-associated molecular patterns (PAMPs) through an array of receptors called pattern recognition receptors (PRRs). The role of extracellular PRRs and their ligands are very well characterized in the pathogenesis of periodontal disease. Bacterial nucleic acids represent a group of PAMPs that are mainly recognized through intracellular PRRs, including Toll like receptor 9, AIM2 (absent in melanoma-2) for inflammasome and DAI. Recent data regarding the contribution of DNA and intracellular DNA receptors has changed our view of disease pathogenesis in a variety of conditions. This may be true for periodontal infections and in fact, studies conducted in our laboratory also support this hypothesis. Our preliminary studies identified increased expression of TLR9, AIM2 and DAI in periodontally diseased tissues compared to healthy sites. Furthermore, we also reported differential expression of a single nucleotide polymorphism (SNP) in the TLR9 promoter in periodontally-diseased versus -healthy subjects. Moreover, we also showed that periodontal bDNA-initiated inflammatory pathways are operant both in myeloid and non-myeloid cells of importance for periodontal pathology. Periodontal disease is not only limited to gingival tissues but also is associated with various systemic diseases. Identification of periodontal bDNA in distant sites suggests that bDNA-initiated inflammatory pathways may not be only important in periodontal pathology but also contribute to periodontal disease adverse effects on systemic health. Hence, it is important to determine the biological mechanisms involved in periodontal bDNA-initiated signaling pathways and their interactions with other PAMPs and PRRs to understand their importance in the pathogenesis of periodontitis and systemic diseases. We believe, cumulative effect of DNA in the tissues may either directly promotes a hyper-inflammatory state and/or interferes with other PAMPs and signaling pathways modifying the immune responses. This proposal is designed to extend our previous studies to primary human and mouse macrophages determine the role of periodontal bDNA and its receptors with regard to induction of cytokines, tolerance/cross and synergy.
