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.

Suppression of graft-versus-host reactivity in the mouse popliteal node by UVB radiation.

A single exposure of recipient (C57BL6 X C3H-) F1 (B6C3F1) mice to UVB radiation suppressed the graft-versus-host (GVH) reaction to injected C3H- lymphoid cells, as measured by the popliteal lymph node weight gain assay. Several observations provided evidence to suggest that this effect of UVB radiation is nonspecific and involves an alteration of the host lymphoid cell component of the reaction. First, the nonspecific trauma of mild thermal injury also suppressed the GVH reaction. Second, although treatment of mice with rose bengal and visible radiation suppresses contact hypersensitivity while treatment with eosin and visible radiation does not, both types of phototoxic treatment suppressed the GVH reaction. Third, implantation of spleens from normal B6C3F1 mice into UVB-treated or thermally injured recipient mice at the time of injection of graft cells overcame the suppression of the GVH reaction. Finally, treatment of donor B6C3F1 mice with UVB radiation did not suppress the host-versus-graft reaction in recipient C3H- mice, which suggests that radiation does not alter the stimulatory function of B6C3F1 cells. These findings are all consistent with a hypothesis that UVB radiation suppresses GVH reactivity by reducing the host component of this immune response through diversion of cells from the site of the reaction. Thus an alteration of cell trafficking appears to be an additional pathway by which UVB radiation can produce immunosuppression.

Spectral power distributions of radiation sources used in phototherapy and photochemotherapy.

Much attention is focused on the amount of radiant energy emitted by treatment systems used in phototherapy and photochemotherapy; however, another important property of a radiation source, the spectral power distribution (SPD), has often been ignored. Measurement of the SPDs of various radiation sources produced unexpected findings. The SPDs of fluorescent bulbs promoted specifically for use in psoralen and ultraviolet A (PUVA) therapy was fairly uniform. However, of three blacklight bulbs that also may be used for PUVA therapy, each had a different SPD, and one of these bulbs emitted more than 90% of its energy in the ultraviolet (UV) wave band at wavelengths greater than 360 nm. The wavelengths emitted by sunlamp fluorescent bulbs and an Alpine UV lamp, both of which are used for phototherapy, were predominantly less than 320 nm. A fluorescent bulb recently introduced for phototherapy had an SPD that was different from that of a PUVA bulb and from that of a sunlamp bulb, with a high emission in the 300- to 340-nm wave band. These findings indicate that consideration of both the SPD and the irradiance of a radiation source is necessary to determine its suitability for phototherapy or photochemotherapy.