Epidermal lipids.

Synopsis From the time an epidermal cell leaves the basal layer to the time it is desquamated, the cell lipids change dramatically, both qualitatively and quantitatively. The most abundant lipid class in basal cells is phospholipid with the remaining lipid being accounted for by roughly equal proportions of cholesterol, non-esterified fatty acid, triacylglycerol and glycolipid: minor components include cholesteryl esters and ceramide. In contrast, approximately half of the lipid in a desquamated cell consists of ceramide, with the remainder consisting largely of cholesterol and non-esterified fatty acid. Immediately before desquamation, small concentrations of cholesteryl sulphate and glycolipid have been found and there is evidence that these polar lipids are important components of the water barrier and also contribute towards the physical integrity of the lower part of the stratum corneum. The change in lipid content as cornification proceeds is no less dramatic than the change in lipid composition. A basal cell contains about 10 pg lipid, whereas a desquamated stratum corneum cell contains approximately six times this amount. The change in lipid composition of a cell undergoing cornification results, therefore, largely from de novo synthesis of lipid, especially cholesterol, non-esterified fatty acid and ceramide. Les lipides de l'épiderme.