Properties of epidermal proteins against microorganisms

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One of the biological functions of skin is the protection of living body against microorganisms, ultraviolet rays and so on. Cell membrane of the stratum corneum, the outside layer of the skin, is thick cell envelope composed several proteins and called cornified envelope. So it is a physical barrier. On the other hand, there must be some proteins which have anti-microorganism activity in the skin. We have investigated the properties of cystatin α and bactericidal/permeability-increasing protein (BPI)-like protein in skin. Cystatin α is a cysteine protease inhibitor, belonging to cystatin super family 1, in keratohyalin granules and the cornified envelope. The cornified envelope also inhibited the activity of cysteine protease. Cystatin α inhibited activities of cysteine proteases produced by poliovirus and Staphylococcus aureus V8, and growth of the virus and bacteria. Cystatin α would play a role as a barrier against microorganisms on the skin surface. BPI-like protein located in the cytoplasm of the inner root sheath cells in human and rat skin. And it inhibited endotoxin activity. A lot of bacteria locate in the inner root sheath as well as in sweat gland. Therefore, BPI-like protein could inhibit growth Gram-negative bacteria that produce endotoxin in the skin.