GLYCOSYLPHOSPHATIDYLINOSITOL (GPI)-ANCHORED MEMBRANE-PROTEINS ARE CONSTITUTIVELY DOWN-REGULATED IN PSORIATIC SKIN

Hyperproliferation of keratinocytes (KCs) in psoriasis has been found to be associated with excessive activation of a phospholipase C (PLC)/ protein kinase C (PKC) signal transduction system. The molecular speci es of PLCs which are activated in psoriasis have not been thoroughly i nvestigated. It was envisaged that if glycosylphosphatidylinositol (GP I)-specific PLC was activated in the membrane of psoriatic epidermal c ells, it would render these cells devoid of those proteins which are a nchored to the cell membrane through their GPI moiety. In order to tes t this possibility, four GPI proteins (CD16, CD55, CD58, and CD59) wer e determined immunohistochemically in normal and psoriatic skin. In no rmal skin, CD55 and CD59 were strongly expressed on epithelium and vas cular structures, whereas CD16 and CD58 were strongly expressed only o n epithelium. The expression of all four GPI proteins was decreased in non-lesional psoriatic skin and virtually abolished in lesional psori atic skin. A control transmembrane protein, CD16, was strongly express ed in normal and non-lesional psoriatic skin, and its expression was n ot significantly decreased in psoriatic lesions. The absence or reduct ion of GPI proteins was not seen in the lesions of several other infla mmatory and proliferative diseases studied.