Immunohistochemical localization of Toll‐like receptors 1–10 in periodontitis

Background/aim: In periodontitis, bacteria and pathogen‐associated molecular patterns are sensed by Toll‐like receptors (TLRs), which initiate intracellular signaling cascades that may lead to host inflammation. In this study, the expression and distribution of TLRs (TLR‐1 to TLR‐10) were immunohistochemically detected in gingival epithelium and connective tissue. Methods: Immunohistochemistry was used for the localization of TLRs in gingival tissue samples from 10 patients with chronic periodontitis and 10 healthy controls; these samples were obtained during routine periodontal flap operations and during extraction operations performed for retained wisdom teeth, respectively. For the evaluation, epithelial layers were stratified to basal, spinous, and superficial layers, and the percentages of TLR‐positive cells were determined. Results: Both healthy and periodontitis gingival tissues expressed all TLRs except TLR‐10. In patients with periodontitis, epithelial cells showed increased TLR expression towards the basal layer. Healthy controls showed more variable cellular TLR expression and distribution between the layers of epithelium. In the connective tissue, consistently higher TLR expression was found within the periodontitis group compared to the healthy group. Conclusions: For the first time, the cellular expression and distribution of TLR‐1 to TLR‐10 have been studied in periodontitis, indicating that TLR‐1 to TLR‐9 are differentially expressed both in connective tissue and epithelial layers. Except for TLR‐7 and TLR‐8, all the other TLRs showed statistically significant differences between patients with periodontitis and healthy controls, suggesting their involvement in the pathogenesis of periodontitis.