Response of human skin equivalents to Sarcoptes scabiei

Studies have shown that molecules in an extract made from bodies of the ectoparasitic mite, Sarcoptes scabiei De Geer, modulate cytokine secretion from cultured human keratinocytes and fibroblasts. In vivo, in the parasitized skin, these cells interact with each other by contact and cytokine mediators and with the matrix in which they reside. Therefore, these cell types may function differently together than they do separately. In this study, we used a human skin equivalent (HSE) model to investigate the influence of cellular interactions between keratinocytes and fibroblasts when the cells were exposed to active/burrowing scabies mites, mite products, and mite extracts. The HSE consisted of an epidermis of stratified stratum corneum, living keratinocytes, and basal cells above a dermis of fibroblasts in a collagen matrix. HSEs were inoculated on the surface or in the culture medium, and their cytokine secretions on the skin surface and into the culture medium were determined by enzyme-linked immunosorbent assay. Active mites on the surface of the HSE induced secretion of cutaneous T cell-attracting chemokine, thymic stromal lymphopoietin, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor antagonist (IL-1ra), IL-6, IL-8, monocyte chemoattractant protein-1, granulocyte/macrophage colony-stimulating factor, and macrophage colony-stimulating factor. The main difference between HSEs and monocultured cells was that the HSEs produced the proinflammatory cytokines IL-1alpha and IL-1beta and their competitive inhibitor IL-1ra, whereas very little of these mediators was previously found for cultured keratinocytes and fibroblasts. It is not clear how the balance between these cytokines influences the overall host response. However, IL-1ra may contribute to the depression of an early cutaneous inflammatory response to scabies in humans. These contrasting results illustrate that cell interactions are important in the host's response to burrowing scabies mites.