Antigenic stimulation during ultraviolet therapy in man does not result in immunological tolerance

People receiving therapy with either 8-methoxypsoralen plus long wavelength ultraviolet radiation (PUVA) or medium wavelength ultraviolet radiation (UVB) have been studied to see whether their unresponsiveness to the contact sensitizer dinitrochlorobenzene (DNCB) is a form of immunological tolerance. It was confirmed that both PUVA and UVB therapy impair sensitization by DNCB:4/13 PUVA-treated and 9/29 UVB-treated psoriatic subjects became sensitized by a dose of DNCB which sensitizes 100% of untreated patients. Subjects unsuccessfully sensitized during PUVA therapy could subsequently be sensitized perfectly normally. Subjects unsuccessfully sensitized during UVB therapy showed slight impairment of subsequent sensitization which was not statistically significant, and which was probably a persistent effect of UVB exposure. In conclusion, the temporary unresponsiveness seen in human subjects exposed to antigens during PUVA or UVB therapy is not due to immunological tolerance.