Allergic contact dermatitis and Langerhans cells: comments on recent developments.

Among the most interesting medical developments of the twentieth century is the revelation that the skin is an organ of major immunologic importance (about 95 percent of resident cells in the epidermis [keratinocytes and Langerhans cells] can serve immunologic functions). Allergic contact-type dermatitis and its underlying mechanism, allergic contact-type sensitization, have been a highly useful model in uncovering the facts that are the basis for this statement. The comments in this article deal with a few randomly selected findings that have been reported in the literature during the past twenty years. They include the probable role of the Birbeck granules in the process of antigen presentation by Langerhans cells; photomodulation of important immunologic reactions by ultraviolet radiation; a previously unrecognized form of contact allergy, apparently present only at clinically active sites of atopic dermatitis (and engendered by small protein antigens rather than by small molecular ["simple chemical"] compounds); and the first factual evidence that epidermal Langerhans cells may be subject to control by intraepidermally located parts of the peripheral nervous system.