Suppression of immediate-type hypersensitivity elicitation in the skin prick test by ultraviolet B irradiation

Reproducibility of skin prick testing (SPT) and its modulation by ultraviol et B (UVB) radiation is of clinical interest. Sensitized atopic volunteers (groups A and B, n=21) were prick tested with common commercial allergen so lutions (undiluted, diluted 1:10 and diluted 1:100) before, 24 h after one and 24 h after three suberythematous UVB irradiations. Volunteers in group A (n=8) received local UVB irradiation of prick test areas, whereas volunte ers in group B (n=13) received whole body UVB irradiation, with prick test areas covered. In group A, the wheal intensities, expressed as the ratio al lergen wheal size to histamine wheal size, were decreased by 28% (1:10 dilu tion) (P=0.01) and 45% (1:100 dilution) (P=0.02) after one UVB irradiation. Flare intensities were decreased by 48% (1:10 dilution) (P=0.03) after thr ee UVB irradiations. In group B, the wheal and flare responses tended to de crease. Possible mechanisms of this short-term suppressive effect of UVB ir radiation on SPT reactions include a direct effect on mast cells. It is con cluded that UV irradiation, even a single exposure, prior to skin testing m ay compromise the validity of SPT testing.