Keratinocytes

Abstract

Keratinocytes form a multilayered epidermis that separates the inner body from the outer environment. The outermost epidermal layer of the body is constantly exposed to external pathogens, and keratinocytes are the first line of defense against invading pathogens. Keratinocytes sense pathogens through innate immune receptors and produce various cytokines, chemokines, and antimicrobial proteins, which have antimicrobial activity against diverse pathogens including gram-positive and -negative bacteria, fungi, and viruses. The epidermal barrier function is disrupted in atopic dermatitis or can be disrupted by environmental proteases. Barrier disruption increases the accessibility of the allergens to the keratinocytes, facilitating keratinocyte activation by pathogens or allergens. Among the environmental allergens, house dust mite allergens are important for the development of allergic diseases and activate the NLRP3 inflammasome of keratinocytes. Activated keratinocytes produce cytokines that can promote a cascade of antigen recognition and allergic inflammation. Thus, in addition to their role in innate immunity, epidermal keratinocytes initiate the onset or exacerbation of allergic reactions.