Effects of methoxsalen plus near-ultraviolet radiation or mid-ultraviolet radiation on immunologic mechanisms.

Skin cancers induced in mice by UVB, i.e., 280-320 nm radiation, are highly antigenic. They grow progressively in UVB-irradiated hosts because of certain specific immunologic alterations that are induced in the mice. Comparative studies of the immunologic aspects of carcinogenesis by UVB or methoxsalen plus UVA, i.e., 320-400 nm radiation (PUVA), formed the basis for the following conclusions: 1) Skin cancers induced by PUVA in C3H/HeN mammary tumor virus-negative mice are not highly antigenic, in contrast to those induced by UVB; 2) PUVA-induced tumors also differ from those induced by UVB, in that they do not exhibit preferential growth in UVB-irradiated mice; 3) PUVA treatment of mice, unlike UVB, does not induce susceptibility to the transplantation of UVB-induced tumors; 4) both UVB and PUVA treatments suppress the induction of contact hypersensitivity by a mechanism that involves suppressor lymphocytes.