Light micrograph of pemphigus vulgaris in skin tissue. This skin disease causes blistering of the outer (epidermal) layer of the skin and mucous membranes. It is an autoimmune disorder in which the immune system produces antibodies against specific proteins in the skin and mucous membrane. These antibodies produce a reaction that leads to a separation of epidermal cells (acantholysis). The exact cause of the development of antibodies against the body's own tissues (autoantibodies) is unknown.