Immunology and skin disorders

Concepts of the function of skin have changed in the last decade from that of a barrier against microbiologic and chemical invasion to include its important role in immunity. This transition began with the recognition that skin could serve as a sensitive target of immunologic injury, typified by diseases such as lupus erythematosus and cutaneous vasculitis. Recently, a more complicated picture has emerged as investigators have established a role for skin in the initiation and regulation of immune responsiveness. Considerable effort in this area has focused on Langerhans cells and Thy‐1⁺ dendritic epidermal cells, both of which reside as bone marrow‐derived immigrants in normal epidermis. Not only do these cells contribute to immune processes in skin, but their function, in turn, is modified by the keratinocytes that surround them. More importantly, pharmacologic and physical manipulation of one cell or one structure in skin often has impact on its neighbors. This phenomenon may be documented by the wide‐reaching cutaneous effects of ultraviolet radiation, bone marrow transplantation, and drugs such as cyclosporine. Our changing concepts of the function of skin also create for us a model for the current evolution in science; our problem and our fortune lie in the mutual interdependence of cells, tissues, systems, and disciplines.