Toll-like receptors in skin infections and inflammatory diseases

The skin is the ultimate example of the function of innate immunity, it alerts the host of danger by many systems including sensing pathogen-associated molecule patterns (PAMPs) through Toll-like receptors and other pattern recognition receptors (PRRs), yet normally provides defense without inflammation. 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. As a consequence of their pivotal role, TLR responses need to be tightly controlled by associated negative regulators or negative feedback loops to prevent detrimental effects from TLRs overactivation. This review focuses on describing the involvement of TLRs in the development of skin infections and inflammatory diseases, and highlights the potential application of TLR agonists or antagonists in these skin diseases.