Leukotriene B4-induced accumulation of polymorphonuclear leukocytes in psoriatic skin.

The intraepidermal penetration of polymorphonuclear leukocytes is anearly event in the pathogenesis of psoriasis. In the present study wequantified these cells in biopsies from lesionai epidermis of chronicstable plaque psoriasis. In this phase intraepidermal penetration ofpolymorphonuclear leukocytes was shown in 41% of the lesions. Themicropustules of Kogoj were seen in 10% of the lesions. Pronouncedparakeratosis was associated with the presence of polymorphonuclearleukocytes. Microabscesses of Munro were located exclusively withinareas of parakeratosis.The absence of polymorphonuclear leukocytes in the majority of skinbiopsies from chronic stable plaque psoriasis is compatible with thecyclic pattern of the migration of these cells into the skin. Intraepidermal penetration of polymorphonuclear leukocytes (PMNexocytosis) is reputed to be a classical feature of the psoriaticlesion.1 In the early phase of the lesion this phenomenon dominatesthe histological picture. In the established lesion the situation isless clear. According to some authors PMN invasion is one of theessential hall-marks.2»3 However, others^t^ state that PMN accumu-lation in the epidermis is less impressive in this later phase. Fig. 1. Typical histologic appearance of intraepidermal •accumulation of PMN.(a) Micropustule of Kogoj(b) Sporadic intraepidermal PMN(c) Microabscess of Munro