Effect of sunlight and its component wavebands on contact hypersensitivity in mice and guinea pigs.

Exposure of mice to UVB (280-320 nm) radiation is known to suppress the development of contact hypersensitivity (CHS) to chemicals that are applied subsequently to unirradiated skin, and this suppression is associated with the generation of suppressor lymphocytes. In this study, the systemic effect of other wavebands of nonionizing radiation on the development of CHS has been tested. Large doses of visible (greater than 400 nm) radiation produced a small but consistent systemic suppression of CHS in mice. In contrast, a large dose of UVA (320-400 nm) radiation did not suppress CHS but, rather, enhanced this immune response. Exposure of both mice and guinea pigs to sunlight produced systemic suppression of CHS. The suppression could be transferred to normal syngeneic animals by injection of splenic lymphoid cells obtained from animals that exhibited suppression, indicating that suppressor cells are associated with sunlight-induced systemic suppression of CHS. The immunomodulatory effect of sunlight was partially abrogated by a Mylar filter or prior application of a sunscreen containing para-aminobenzoic acid to the exposed skin. Thus, wavelengths mainly in the UVB portion of sunlight (295-320 nm) are responsible for sunlight-induced suppression of CHS, although wavelengths in the visible region may also play a role.