Perturbation of epidermal barrier function correlates with initiation of cytokine cascade in human skin

Abstract

An important function of skin is to serve as a barrier and thus provide protection from the external environment. The epidermal keratinocyte establishes this barrier by producing an intact stratum corneum. In the past, keratinocytes were appreciated only for this rather inert, passive structural responsibility and not for their potential dynamic contribution to inflammatory or immune-mediated reactions. Our purpose was to examine the cascade of molecular and cellular events that occur when the barrier function of human skin is abrogated by repeated tape stripping, which physically removes the stratum corneum without inducing any cytopathic effects on the underlying epidermal keratinocytes. Eight healthy human volunteers underwent repeated tape stripping and sequential punch biopsy specimens of skin obtained between 1 and 24 hours after tape stripping were analyzed for protein antigens by immunostaining of cryostat-cut sections. The presence or absence of various messenger RNAs (mRNAs) were detected by polymerase chain reaction. After repeated tape stripping, keratinocytes became activated within hours. The responses included up-regulation of keratin-16 expression and keratinocyte proliferation accompanied by production of a specific profile of cytokine and adhesion molecule mRNAs and proteins in both epidermal and dermal compartments. Polymerase chain reaction amplification of RNA species isolated from the epidermal portion of skin revealed increases 6 hours after tape stripping in mRNA coding for tumor necrosis factor-alpha, IL-8, IL-10, interferon gamma, intercellular adhesion molecule-1, transforming growth factor-alpha, and transforming growth factor-beta. There was no increase in tumor necrosis factor-alpha, IL-8, IL-10, or transforming growth factor-alpha mRNAs in the dermal samples. Immunostaining revealed that keratinocyte intercellular adhesion molecule-1 was increased 6 hours after stripping and was accompanied by endothelial cell expression of E-selectin (endothelial cell adhesion molecule-1) and vascular cell adhesion molecule-1. These molecular events, which occurred after 6 hours in tape-stripped skin, preceded any movement of inflammatory cells from the circulation into dermis or epidermis and hence reflect changes that occur in cells indigenous to normal human skin. None of these changes occurred in persons who underwent limited tape strippings without barrier perturbation. The results highlight the rapid and distinctive responses of epidermal keratinocytes and demonstrate that these cells can actively participate in a far greater number of homeostatic responses other than the production of the epidermal barrier.