The inhibition spectrum of solar urticaria suppresses the wheal–flare response following intradermal injection with photo‐activated autologous serum but not with compound 48/80

Abstract

The inhibition spectrum (IS) in solar urticaria was identified mainly in Japanese patients with solar urticaria, although the mechanism of action of the IS has not been elucidated. Because an intradermal injection of action spectrum (AS)-irradiated serum in a case of solar urticaria induced a wheal response, we studied the responsiveness of the intradermal injection after an IS irradiation. An AS in this patient was composed of visible light shorter than 500 nm, while an IS was composed of visible light longer than 530 nm. When the IS was exposed immediately after the AS irradiation, the wheal response was inhibited. However, when the IS was exposed before the AS irradiation, the wheal response was not inhibited. An intradermal injection of her serum produced no reaction, whereas an intradermal injection of her serum pre-irradiated with visible light induced a wheal flare response. Further examination revealed that the in vivo wheal-inducing activity of her serum irradiated with visible light could be attenuated by post-IS irradiation at the injection site, while the wheal-inducing activity of her visible light-irradiated serum was not inhibited by irradiation of the activated serum with the IS. The wheal-flare response induced by compound 48/80 and histamine was not altered by IS irradiation at the site of skin tests. These findings indicate that photoallergens in the patient's serum that are activated by visible light irradiation are responsible for the development of her symptoms and that the IS may suppress the wheal response by inhibiting the binding of the photoallergens to mast cells, not by inactivating the photoallergens and stabilizing mast cells.