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AN ORGAN WHICH CAN BE GROWN |
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Different steps to construct different epidermis |
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RECONSTRUCTING THE EPIDERMIS
The very first model - A model which tans - A model on the watch - EpiskinTM, the marketed kit
The importance of the superficial layer of the epidermis in the application of cosmetics is at the origin of the production of the first models, with a differentiated horny layer playing its primordial barrier role. These models are obtained in three stages: the seeding of human keratinocytes onto an inert support material, proliferation of the keratinocytes in an immersed culture and exposure of the culture to the air to cause differentiation of these cells and thus form the horny layer.
L'Oral researchers achieved a technological feat by including melanocytes in these models....then Langerhans cells, thus creating a model possessing the three fundamental cellular types that living epidermis contains.
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 The very first model
The first model of this type, the Prunieras-Rgnier model, was realized in 1979.
From a skin biopsy from aesthetic surgery, the epidermis was separated from the dermis by enzymatic treatment. The keratinocytes were isolated from the epidermis cultured and seeded on an inert de-epidermised dermis (DED). The parts of the basal membrane were conserved, which favoured optimal reconstruction of a multi-layered epidermis surmounted by a horny layer.
This first model illustrated for the first time the capacity of keratinocytes to divide and then differentiate to form a horny layer close to that of human skin.
Histological sections of human skin (A.) and reconstruct epidermis (B). Formation of functionnal stratum corneum.
M. Prunieras and M. Rgnier joined the L'Oral group in 1983 where they continued their work.
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A model which tans
By separately isolating melanocytes and keratinocytes from skin biopsies, and then putting these two cell types in culture as before, the Rgnier-Schmidt model produces a pigmented epidermis model. By then integrating melanocytes from African, European or Asiatic skin, L'Oral researchers produce pigmented epidermis models corresponding to the various phenotypes representing the skins of the world. These models are also capable of "tanning" (melanogenesis) under the influence of UV radiation. Thus a model is available which tans like normal skin and therefore allows the effects of UVA and UVB to be studied, the pigmentation or depigmentation properties of new molecules to be demonstrated, and also the efficacy of new sun filters produced by L'Oral chemists to be tested.
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A model on the watch
Within a European programme, M. Rgnier and R. Schmidt, working with INSERM (medical research center), then succeeded in creating examples of the epidermis containing Langerhans cells. These cells actively participate in immune defence by recognising foreign bodies which have penetrated the cutaneous barrier. This model represents a major scientific advance which was for a long time considered as impossible because, once isolated, the Langerhans cells are unable to multiply in vitro.
The researchers got around the problem by isolating the precursors of the Langerhans cells from the blood: in contact with the keratinocytes and melanocytes in the reconstructed epidermis, these precursors differentiate into Langerhans cells.
This model thus includes three epidermal cellular types and shows the same characteristics as human skin: the Langerhans cells are located in the Malphigian mucous layer, their morphology changes and their number decreases when the epidermis is exposed to solar radiation, thus reproducing the phenomenon of photo-immuno-suppression. In addition, these Langerhans cells respond to products known to provoke allergies, which demonstrates the usefulness of the model for detecting the sensitising ability of certain products.
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EpiskinTM, the marketed kit
The model developed by E. Tinnois consists of a dermal support formed from collagens. Keratinocytes, deposited on the support material, divide for three days in the culture medium, then differentiate in the air exposed culture. At the end, the epidermis consists of a mitotic layer, a mucous Malphigian layer and a functional horny layer.
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