Skin and keratinocytes

The differentiation of the epidermal cells in a basal layer of dividing cells and an upper layer or layers of cells which become keratinised and eventually sloughed off appears a relatively simple system and it is made even simpler by the ability to grow keratinocytes in culture. 

Such an in vitro system can be used not only to study the differentiation of skin and diseases which affect the skin but may also be used to test drugs which affect human epidermis and possibly to produce large amounts of epidermal cells which could be used in skin grafting. 

Described below is a method for growing keratinocytes from skin biopsies using a feeder layer (Rheinwald and Green, 1975). The feeder cells may be 3T3 and BHK21 cells treated with gamma rays or with mitomycin C as described in 7.1.4. 

If the cultures are not subcultured when they become confluent then cells are shed from an upper layer while the basal layer continues to divided (Green, 1977). Thus the situation closely resembles the stratum corneum in vivo where the basal cells multiply and the non-basal cells undergo differentiation. 

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Because UVR does not penetrate below the skin, systemic effects must occur indirectly via mediators produced in the skin. Target cells in the skin include Langer-hans cells (dendritic cells in the skin) and keratinocytes (Figure 32.7). As indicated in Section 32.5.5, exposure to contact sensitizers causes increased expression of MHC II molecules on Langerhans cells and increased expression of intracellular adhesion... 

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