Ultraviolet A inhibits histamine release from human peripheral leukocytes.

Irradiation of human peripheral leukocytes with ultraviolet A (UVA) induced a significant and dose-dependent reduction of anti-IgE or Ca-ionophore-stimulated histamine release without consistent influence upon C5a-induced release reactions. This effect was equally demonstrable in atopics and controls. In the presence of the radical scavenger superoxide dismutase, the UVA-induced inhibition of anti-IgE-induced histamine release was abolished. Under the conditions used, UVB exposure did not result in relevant changes of in vitro histamine release.