[New knowledge of the skin's horny layer may improve understanding of skin diseases]

The aetiology of many skin diseases is to be sought in the multiplicity of interactions between mechanisms generally present in the body, such as the inflammatory response and immune systems, and mechanisms present in the skin. In the case of organ-specific skin diseases, it is reasonable to suppose the underlying disturbance to affect structures and molecular processes unique to the skin. The stratum corneum represents the culmination of epidermal differentiation and consists of very resistant and cohesive cells surrounded by an intracellular space filled with lamellar lipids, thus forming a highly effective and resistant physico-chemical barrier between the interior of the body and the external environment. As the stratum corneum is continuously produced, a prerequisite of its well-regulated thickness is an equally well regulated shedding of cells from the skin surface. This is preceded by proteolytic degradation of intracellular cohesive structures--i.e. desmosomes. We have recently discovered a new serine proteinase, stratum corneum chymotryptic enzyme (SCCE), which may be involved in this process. SCCE has been purified, cloned and expressed in mammalian cells.