In vitro reproduction of clinical hallmarks of eczematous dermatitis in organotypic skin models

Dermatitis is a group of highly pruritic chronic inflammatory skin diseases which represents a major public-health problem worldwide. The prevalence of dermatitis has increased in recent years affecting up to 20% of the general population. Acute skin lesions are characterized by extensive degrees of intercellular edema of the epidermis (spongiosis) and a marked perivenular inflammatory cell infiltrate in the dermis. Keratinocytes within eczematous lesions exhibit a modified expression of proinflammatory cytokines, chemokines and cell-surface molecules. The pathophysiological puzzle of dermatitis is far from being elucidated completely, but skin infiltration of activated memory/effector T cells are thought to play the pivotal role in the pathogeneses. The aim of this study was the set-up of organotypic models mimicking the symptoms of eczematous dermatitis to provide a tool for therapeutic research in vitro. Therefore activated T cells (ATs) were integrated in organotypic skin and epidermis equivalents (SE, EE). These models enabled the reproduction of several clinical hallmarks of eczematous dermatitis: (1) T cells induce keratinocyte apoptosis, which leads to a reduced expression of the adhesion molecule E-cadherin (E-cad) and disruption of the epidermal barrier. (2) Expression of intercellular adhesion molecule-1 (ICAM-1) allows the attachment of leukocytes to epidermal cells. (3) Upregulation of neurotrophin-4 (NT-4) in the epidermis is thought to mediate pruritus in lesions by supporting nerve outgrowth. (4) Elevated levels of pro-inflammatory cytokines (IL-1 alpha and IL-6) and chemokines (IL-8, IP-10, TARC, MCPA, RANTES and eotaxin) amplify the inflammatory response and lead to an influx of secondary immunocells into the skin. The therapeutics dexamethasone and FK506 markedly reduce cytokines/ chemokines production and epidermal damaging in these models. These data underline that activated memory/effector T cells induce eczematous changes in this HaCaT cell based organotypic skin equivalent. Furthermore it can be concluded that these models make it possible to investigate targets of therapeutics in skin.