Keratinocyte

A keratinocyte is the predominant cell type in the epidermis, the outermost layer of the skin, constituting 90% of the cells found there. Those keratinocytes found in the basal layer (stratum basale) of the skin are sometimes referred to as "basal cells" or "basal keratinocytes".

Function

The primary function of keratinocytes is the formation of a barrier against environmental damage by pathogenic bacteria, fungi, parasites, and viruses, heat, UV radiation and water loss. Once pathogens start to invade the upper layers of the epidermis, keratinocytes can react by producing proinflammatory mediators, particularly chemokines such as CXCL10 and CCL2 which attract leukocytes to the site of pathogen invasion.

Structure

A number of structural proteins (filaggrin, keratin), enzymes (proteases), lipids and antimicrobial peptides (defensins) contribute to maintain the important barrier function of the skin. Keratinization is part of the physical barrier formation (cornification), in which the keratinocytes produce more and more keratin and undergo terminal differentiation. The fully cornified keratinocytes that form the outermost layer are constantly shed off and replaced by new cells.