EXPRESSION OF CD26 DIPEPTIDYL-PEPTIDASE-IV IN BENIGN AND MALIGNANT PIGMENT-CELL LESIONS OF THE SKIN/

The T-cell activation antigen CD26 or dipeptidyl-peptidase IV (DPP-TV) belongs to a group of membrane-bound proteases that are variably expr essed by melanoma cell lines. In vitro studies have suggested that los s of CD26 is associated with tumour progression. To correlate its expr ession with the histological stage of tumour progression of malignant melanoma (MM), we studied the distribution of CD26/DPP-IV in paraffin sections of a series of 110 benign and malignant pigment-cell lesions of the skin using a cocktail of anti-CD26 monoclonal antibodies and th e three-step ABC method. Only two of 44 benign lesions focally express ed CD26 in their junctional compartment, rn MM, expression of CD26 was not related to any of the known histological prognostic factors, but was associated with the stage of tumour progression; thus, CD26 was ex pressed in the in situ or invasive radial growth phase in 34% of MM, w hereas only 12% of MM expressed CD26 in the vertical growth phase, No CD26 expression occurred in metastatic melanomas. These data suggest t hat this proteinase plays a part in the early invasion of MM. Thus, CD 26 may serve in the binding to, and enzymatic degradation, components of the extracellular matrix of the papillary dermis, Loss of CD26 in t he vertical growth phase may contribute to the insufficient inactivati on of regulatory peptides and unlimited action of growth factors.