Leukotriene B₄ fails to induce penetration of lymorphonuclear leukocytes into psoriatic lesions

The intraepidermal accumulation of polymorphonuclear leukocytes following the epicutaneous application of leukotriene B₄ (LTB₄) was studied in lesional and clinically uninvolved skin of five patients with chronic stable plaque psoriasis. The lesions were found to be wholly unresponsive to LTB₄, doses of 100 ng failing to produce either micropustules or exocytosis. This phenomenon was sharply localized; the response immediately adjacent to the lesion being identical to that in more distant uninvolved skin. We speculate that both the reduced response to LTB₄ in the psoriatic patient and also the tolerance to LTB₄ seen after repeated applications, result from the induction of a P₄₅₀-linked hydroxylase.