Immunology and photocarcinogenesis. New light on an old problem.

Renewed interest in experimental photocarcinogenesis was stimulated by the observation that skin cancers induced in mice by ultraviolet radiation are highly antigenic. Most of these cancers are rejected by the immune system on transplantation into a normal, genetically identical animal. This finding raised the question of how these tumors could survive and grow progressively in the primary host without inducing immunologic rejection. Studies addressing this question produced the unexpected finding that mice that had been exposed to ultraviolet radiation, but that had not yet developed primary skin cancers, were also unable to reject transplants of these highly antigenic tumors. Thus exposing the animals to ultraviolet radiation produced a systemic alteration in the animals that interfered with the immunologic rejection of ultraviolet radiation-induced skin cancers implanted at nonirradiated sites. The failure of tumor rejection was associated with the presence of suppressor lymphocytes in the lymphoid organs of ultraviolet-irradiated mice. A question raised by the finding of suppressor lymphocytes in ultraviolet-irradiated mice is how exposure of the skin to ultraviolet radiation leads to this alteration in immune regulation. Evidence for some of the steps in this process has been accumulating for the past few years. It has been found that ultraviolet-irradiated mice have at least two other immunologic alterations; one involves the response to antigens applied topically at irradiated sites, and the other involves the response to certain antigens applied on nonirradiated skin.(ABSTRACT TRUNCATED AT 250 WORDS)