Toll-like receptors and their dual role in periodontitis: a review

Innate immunity is the first line of host defense and represents inherited resistance to infection. Innate immunity works through toll-like receptors (TLRs), which recognize the conserved molecular patterns on pathogenic bacteria known as pathogen-associated molecular patterns. The periodontium is a unique environment in which oral microorganisms are in constant contact with the host immune system. The TLRs present on gingival epithelial cells are continuously stimulated, resulting in production of cytokines and defensins that help to maintain oral health. If the epithelial barrier is breached, allowing invasion of bacteria into the underlying connective tissue, the TLRs on other resident and non-resident cells of the periodontium become activated. This leads to an exaggerated release of pro-inflammatory cytokines and other biological mediators, which may cause host tissue destruction. The present review examines the role of TLRs and their signaling in periodontal health and disease.