Significance and pathogenesis of basal keratinocyte herniations in psoriasis.

Using transmission electron microscopy, we studied, quantitatively, basal keratinocyte herniations (BKH) in relation to the other basement membrane zone changes in psoriatic lesions of varying clinical activity, and in psoriasiform skin diseases. BKH appears to correlate with disease activity. They do not occur passively as a result of the formation of gaps in the basal lamina. BKH in active psoriasis are associated with electron-lucent areas suggestive of proteolytic enzyme release. Their apparent association with Langerhans cells, neutrophils, macrophages, and endothelial cells may point to these cells as the source of proteolytic enzymes in psoriasis. BKH may prove to be a useful marker for clinical psoriasis.