ULTRAVIOLET-A RADIATION (320-400 NM) PROTECTS HAIRLESS MICE FROM IMMUNOSUPPRESSION INDUCED BY ULTRAVIOLET-B RADIATION (280-320 NM) OR CIS-UROCANIC ACID

T cell-mediated immune function, here measured as the contact hypersen sitivity reaction, is readily suppressed by moderate exposure of mice to ultraviolet B (UVB) or solar-simulated radiation (SSUV), or by topi cal application of cis-urocanic acid. The effect of ultraviolet A (UVA ) radiation on immune function has been unclear. Here we have demonstr ated that when UVA radiation from a fluorescent tube source was rigoro usly filtered to remove contaminating UVB radiation, it was immunologi cally innocuous at physiologically relevant doses. Furthermore, we hav e found that mice exposed to UVA radiation, either immediately after, or up to 24 h before, immunosuppressive treatment with either UVB radi ation, SSUV or cis-urocanic acid, became refractory to the immunosuppr ession and retained more normal contact hypersensitivity. A greater UV A exposure reversed the immunosuppression more effectively. The result s suggest that there are immunologically significant interactions betw een UV wavebands, and that UVA exposure may induce a relatively long-l ived immunoprotective photoproduct, as yet unidentified, that can inhi bit the activity of epidermal cis-urocanic acid and thus provide prote ction from photo immune suppression.