Presentation of antigen to suppressor cells by a dimethylbenz (a) anthracene-resistant, Ia-positive, Thy-1-negative, I-J-restricted epidermal cell.

The epidermal layer of the skin contains class II major histocompatibility (MHC)-positive antigen-presenting cells (APC), the most well characterized population being Langerhans' cells (LC). The chemical carcinogen 7,12 dimethylbenz (a) anthracene (DMBA) depletes about two-thirds of these cells from murine epidermis, and contact sensitizers applied to DMBA-treated skin induce specific immunological tolerance. This tolerance results from epidermal cells migrating to local lymph nodes within 3-6 hr after contact with antigen where they present the antigen to suppressor cells. Here we demonstrate that this epidermal cell which activates suppressor cells is a class II MHC-positive. Thy-1-negative, I-J-restricted APC. Hence at least two types of class II MHC-positive epidermal cells migrate to local lymph nodes and present antigen to lymphocytes; LC, which are sensitive to the effects of DMBA and activate helper lymphocytes, and another, which is resistant to DMBA and activates suppressor cells in an I-J-restricted manner. During the early stages of carcinogenesis any antigen present in the epidermis would be presented only by the cells which activate suppressor lymphocytes, resulting in tolerance induction. This may enable neoplastic cells to avoid the initiation of anti-tumour immunity.