Humans develop gingivitis and periodontitis in response to the challenges produced by microbial dental plaque. Individuals vary in their susceptibility to both gingivitis (superficial inflammation) and periodontitis (extensive inflammation causing bone and tooth loss). The etiology of periodontal disease is not fully understood;however, it is accepted that variance in the human host response to microbial plaque will relate to the host's innate, inflammatory or immune defense systems. Single nucleotide polymorphisms (SNPs) exist in the human genes encoding many molecules pertinent to the host-microbe interaction. Periodontal inflammation (gingivitis and periodontitis) begins with the perturbation of the epithelial cells by bacteria via receptors, including Toll-like Receptors (TLRs). Our preliminary data indicates that the pro-inflammatory cytokines and chemokines produced in response to bacterial and cytokine perturbations differ between individuals and these differences may relate to carriage of a specific TLR4 polymorphism. Our general hypothesis is that individual response characteristics of gingival epithelial cells to foreign challenges, relate to their cellular TLR genotype which influences susceptibility to gingivitis and periodontitis. Thus we will address the following aims utilizing multiple primary human gingival epithelial cells (HGECs), clinical studies and genotype and phenotype analyses. The first aim is to characterize molecularly the inter-patient differences in TLR expression in HGECs using qPCR, gene expression profiling, protein assays and immunoreactivity and to correlate this to the TLR genotype. Secondly, functional analysis of genetically- modified HGECs (using siRNA knock-downs and over-expression) will elucidate the role of TLR4 and the Asp299Gly and other SNPs in epithelial LPS hypo-responsiveness. Thirdly, we aim to translate this work by determining clinically if TLR4 polymorphisms and hypo-responsiveness correlate with the severity of experimental gingivitis and if they can differentiate periodontitis cases and controls. Finally, we aim to challenge HGECs and other cell types, monocytes, gut epithelia and endothelial cells to assess LPS responsiveness relevant to the etiopathology of TLR4 associated diseases such as inflammatory bowel disease, atheroma and asthma. Characterization of response differences and determination of related SNPs may lead to new therapeutics or diagnostics in a range of infectious and inflammatory diseases.