Production of intraepidermal microabscesses by topical application of leukotriene B4.

Leukotriene B4 is a highly potent leukocyte chemotactic compound. It has been identified in chamber fluid and scale from psoriatic skin lesions, in which epidermal neutrophil infiltration is reported to be one of the earliest pathologic events. The ability of leukotriene B4 to reproduce the inflammatory events of psoriasis, by topical application to the skin of normal human volunteers, was thus studied. Persistent visible inflammatory reactions were elicited by application of amounts of leukotriene B4 as low as 5 ng, and the maximum diameters of the reactions were dose-related up to at least 500 ng. The visible reactions appeared 12-24 h after initial application of leukotriene B4, and persisted for several days, leaving brownish pigmentation and scaling at 7 days. Histologic examination showed intraepidermal neutrophil microabscesses at 24 h, but these had resolved by 48 h. A mixed, perivascular neutrophil and mononuclear cell infiltrate was seen in the dermis at 24 h, becoming predominantly mononuclear after 24 h. Nonspecific chemical irritant contact dermatitis was excluded by the absence of reactions to high doses of two chemically similar metabolites of arachidonic acid which lack significant in vitro chemokinetic activity. These experiments provide further evidence for the role of leukotriene B4 in the pathogenesis of psoriasis, and may lead to the development of an experimental model of the inflammatory events in psoriasis, and of a simple in vivo test of neutrophil function.