Sequence of changes in psoriatic epidermis. Immunocompetent cell redistribution precedes altered expression of keratinocyte differentiation markers.

Recent studies suggest that the immune system is involved in the pathogenesis of psoriasis. We studied the expression and distribution of immunocompetent cells and of some chosen differentiation antigens of keratinocytes at various stages of lesion development, using indirect and amplified immunofluorescence, and avidin-biotin-peroxidase method. Serial cryostat sections were collected so as to allow comparative studies of adjacent parts of each biopsy sample with various immunocytochemical markers. Our results indicate that focal intra-epidermal infiltration of otherwise unaltered epidermis with lymphocytes, mostly of the T-helper phenotype, was the first perceptible change occurring in patients with eruptive psoriasis. Modification of the Langerhans' cell staining was observed in these initial subclinical lesions. A significant reduction of the cell frequency was noted in psoriatic papules and plaques. Changes in the epidermal antigen expression could be observed in the developed lesions only. The simultaneous appearance of histologic signs of psoriasis and the modification of keratinocyte antigens indicates that both events are related to the epidermis hyperproliferation, possibly induced by focal inflammatory reaction.