Toll-like receptors in dermatology: Review [Dermatolojide toll-benzeri reseptörler]

Toll-like receptors (TLRs) are important pattern-recognition receptors (PRR) involved in host defense against a variety of pathogenic microorganisms. TLRs represent of family of type 1 transmembrane proteins characterized by an extracellular leucine-rich repeat domain. TLRs also contain a transmembrane domain and a cytoplasmic tail domain that is homologous to the interleukin-1 receptor. Activation of TLRs leads to the production of cytokines, chemokines, antimicrobial peptides, and upregulation costimulatory and adhesion molecules involved in innate and adaptive immune responses. TLRs are expressed on a variety of cell types found in the skin, including keratinocytes and Langerhans cells in the epidermis, resident and trafficking immunesystem cells such as macrophages, dendritic cells, T and B cells, and mast cells in the dermis, endothelial cells of the skin microvasculature, and skin stromal cells such as fibroblasts and adipocytes. There have been an increasing number of reports demonstrating that TLRs play a key role in cutaneous host defense mechanisms against bacterial, fungal, and viral pathogens. The skin responds rapidly to invading microbes by producing antimicrobial peptides or other antimicrobial intermediates before cytokine release results in inflammation. To achieve maximal immune responses for clearing invading microbes, the activation of select PRRs in skin then initiates and shapes adaptive immune responses through the activation of dendritic cells and recruitment of T cell subsets. Importantly, cross-talk between TLRs can influence this system in several ways including augmenting or suppressing the immune response. They are key components of the innate immune response. In addition, TLRs have also been implicated in the pathophysiology of various inflammatory skin diseases. Recently, Toll-like receptors has gained considerable importance in dermatology and an evaluation was made on the new developments on this issue. Copyright © 2012 by Türkiye Klinikleri.