Evidence for histamine in the urticating hairs of Hylesia moths.

An urticarial dermatosis after contact with the urticating hairs of the adult female Hylesia moth may occur by several mechanisms including the intradermal injection of inflammatory mediators through the urticating hairs. Extracts were prepared from whole moths, urticating hairs, and other moth parts. Each of these extracts was subjected to a radioenzyme assay for histamine. Histamine was present in extracts made from whole moths and from urticating hairs. Extracts made from other moth parts contained no histamine. Cutaneous wheals occurred after intradermal injections of histamine and various concentrations of Hylesia extract (HE) into the backs of cynomolgus monkeys. This whealing response was suppressed by pretreatment of the animals with diphenhydramine hydrochloride, but not by pretreatment with indomethacin. Histologic examinations showed a perivascular lymphocytic infiltrate around dilated capillaries without evidence of mast cell degranulation in HE-injected sites but not in controls. These findings provide evidence that histamine may be the mediator responsible for the urticarial lesions seen after contact with Hylesia moths.