A single dose of UV radiation suppresses delayed type hypersensitivity responses to alloantigens and prolongs heart allograft survival in mice

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Abstract
The systemic effect of ultraviolet (UV) irradiation on delayed type hypersensitivity (DTH), contact hypersensitivity (CHS) and allograft rejection was investigated in BALB/c mice which had been exposed to a single 1 h treatment with UV radiation (27 kJ/m2) from FS40 sunlamps (60% UVB). After UV irradiation (3–5 days), mice were treated on an unirradiated site with either a subcutaneous injection of allogeneic spleen cells or a topical application of the contact sensitizer oxazolone (OX). The DTH response to allogeneic cells and the CHS response to OX elicited 6 days after immunization were significantly lower in UV-treated mice than in normal mice. Spleen cells from these animals were transferred intravenously into X-irradiated (600R) recipients which were immediately challenged with antigen and the DTH or CHS response elicited was determined 24 h later. Recipients of equal numbers of cells from sensitized and normal animals (6106 from each donor) exhibited positive DTH or CHS responses to the antigen used to sensitize the donor. In contrast, recipients of equal numbers of cells from animals sensitized and UV suppressed to the same antigen showed a suppressed DTH or CHS response. This suppression was antigen-specific. Treatment of cells from UV suppressed animals, prior to transfer, with complement and cytotoxic anti-Lyt 2 or anti-Thy 12 monoclonal antibodies abrogated the suppressive ability of these cells, in contrast to cytotoxic treatment with anti-L3T4 or anti-Lyt 1 monoclonal antibodies which had no significant effect. The suppressor cells therefore had the phenotype Thy 12+, Lyt 2+, L3T4-, Lyt 1-. In a separate series of experiments BALB/c mice, either untreated or given 1 h of UV irradiation 3–5 days previously, were given a heart or skin allograft from a C3H/He donor. The primarily vascularized cardiac allografts survived significantly longer in UV-irradiated than in normal recipients (median survival time 13 days vs 10 days, P= 0035), but the survival of C3H/He skin allografts was unaltered in UV mice. No identification of suppressor populations was carried out in the heart allograft recipients. These experiments provide the basis for investigations of the possible role of UV-induced antigen-specific suppressor cells in modulating responses to alloantigens.