Keratinocytes: Gatekeeper in innate defense

Keratinocytes, as a major cell type of skin epidermis, function as a gatekeeper to effectively prevent pathogen entry or long-term survival on the skin. Multiple pattern recognition receptors (PRRs) such as toll-like receptors (TLRs) are expressed on keratinocytes, which enables keratinocyte recognition of microbial invasion. The activation of PRRs in keratinocytes in turn triggers the release of soluble effectors, such as the antimicrobial peptides that rapidly repel microbial assault. This short communication focuses on describing the expression profile of PRRs in keratinocytes and antimicrobial intermediates produced by keratinocytes after PRR activation, and highlights protective roles of keratinocytes in innate defense. The skin is the primary interface between the host and environmental damage such as microbes. A myriad of microbes colonize on skin and make contact with keratinocytes in the epidermis.However, despite the abundant colonization by microbes, skin normally isn't infected or inflamed. Therefore, keratinocytes, the predominant cell type in the epidermis of skin, not only play an important role in maintaining the physical barrier between the host and the environment, but also participate in cutaneous immune responses to protect skin from infection (Kupper and Fuhlbrigge, 2004; Robert and Kupper, 1999). This short communication will describe how Toll-like receptors are activated to release antimicrobial peptides against pathogens in keratinocytes, thus maintaining skin homeostasis.