We have isolated a murine
monoclonal antibody, called psi-3, which immunolabels maturing keratinocytes in psoriatic skin but not in normal epidermis. The staining is cytoplasmic and is not extractable with 1%
Triton X-100, which suggests that the
psi-3 antigen is a structural component of the keratinocyte. Neither basal cells nor invading inflammatory cells are stained in psoriatic skin and the
antigen appears to be associated specifically with maturing and not proliferating keratinocytes. Keratinocytes cultured in vitro from skin from nonpsoriatic individuals display the
antigen in a granular pattern in differentiated cells. The
antigen is also expressed after tape-stripping of normal skin and, therefore, represents an inducible product of normal keratinocytes. The
antigen is destroyed by
proteinase K and appears to be a
protein. On discontinuous
sodium dodecyl sulfate-gel electrophoresis, the
antigen has been found to have a molecular weight of 135,000. The
psi-3 antigen is interpreted as a new keratinocyte product expressed in
psoriasis, culture, wound healing, and certain other pathologic skin conditions. The synthesis of such a new
antigen would not be expected if keratinocyte maturation in
psoriasis is a truncated version of the normal system and supports the hypothesis that psoriatic keratinocytes are following an alternative pathway. Results using experimental injury suggest that the psoriatic pathway is normally expressed during wound healing.