Histologic distribution of staining by a monoclonal antibody (psi-3) in psoriasis and occurrence of psi-3 antigen in other cutaneous diseases.

psi-3 is a monoclonal antibody that recognizes a 135,000 molecular weight structural component of maturing keratinocytes in psoriasis (the psi-3 antigen) but fails to bind to any constituent of keratinocytes in normal epidermis. This paper describes the occurrence of the psi-3 antigen in a variety of dermatopathologic conditions using immunoperoxidase (biotin-avidin-peroxidase) and immunofluorescence methods which show excellent concordance. In 35 of 36 specimens of psoriasis vulgaris, psi-3 antibody consistently immunolabels the cytoplasm of keratinocytes above the basal layer. At the edges of psoriatic plaques, psi-3 antibody staining extends for a variable distance into lesion-free epidermis. A similar pattern has been found in a certain number of other conditions described in the paper, including squamous cell carcinoma and condyloma acuminatum, but not Darier's disease, basal cell carcinoma, nor lamellar ichthyosis. In all but one condition, the outermost or basal layer of cells is never stained. The only disease in which the lowermost cell layer is stained is a lichen planus-like lesion. The occurrence of psi-3 antigen cannot be correlated with any histologic feature of psoriasis such as acanthosis, loss of the granular layer, or hyperproliferation. The antigen appears to be a unique keratinocyte constituent which is expressed in certain pathologic conditions and which is not detected by any other histologic or immunophenotyping method. It is a potentially valuable addition to the panel of antibodies available for characterizing epithelial cells.