Abnormal maturation pathway of keratinocytes in psoriatic skin.

We compared the maturation pathway of normal and psoriatic epidermis using three different markers: (1) Involucrin, which is normally detected in the stratum granulosum in normal skin, was detected in all but the basal layer of involved psoriatic skin; (2) an antigen, recognized by the murine monoclonal antibody psi 3, was present in all but the basal layer of involved psoriatic skin but was absent from uninvolved and normal skin; (3) fibronectin, which normally localizes in the dermis and the epidermal-dermal junction, was also detected intra- and extracellularly in the psoriatic epidermis. These results indicate that the alterations in keratinocyte maturation found in psoriasis do not arise from a truncation of the normal maturation pathway but rather reflect the onset of an abnormal pathway of differentiation characterized by the expression of psi 3 antigen and fibronectin and the premature appearance of involucrin.