This project is designed to study the origin, membrane characteristics and function of the epidermal Langerhans cell (LC). The isolation of viable LC from guinea pig and human epidermis enables our laboratory to carry out experiments attempting to establish a continuous LC line. Moreover, the availability of viable LC suspensions will permit experiments designed to determine the origin and ontogeny of this cell. Of particular interest are studies designed to characterize the LC surface receptors for complement components and to determine if these receptors are of importance in the cell function. The question of whether LC have a "trophic" function for lymphoid cells will be evaluated by assessing its involvement in a variety of skin diseases in which a cell-mediated immunologic mechanism seems to be involved.