Analysis of the expression of intercellular adhesion molecule-1 and MUC18 on benign and malignant melanocytic lesions using monoclonal antibodies directed against distinct epitopes and recognizing denatured, non-glycosylated antigen.

Intercellular adhesion molecule (ICAM)-1 and mucin isotype MUC18 were originally identified as melanoma progression antigens by monoclonal antibodies (MAb) generated in a search for molecules expressed by melanomas but not detectable on benign naevi. As MAb detect single epitopes whose accessibility may be modulated, a new panel of antibodies directed against distinct epitopes and reacting with denatured nonglycosylated antigen as well as native antigen were used to examine expression of these molecules on melanocytic lesions. The antibodies were analysed in a binding inhibition assay and divided into groups defining independent epitopes. Three anti-ICAM-1 and four anti-MUC18 antibodies representing these groups were then tested on frozen sections of 10 benign naevi and 10 melanoma lymph-node metastases. The anti-ICAM-1 antibodies demonstrated concordant reactivities on both the malignant and benign lesions and reacted with all samples suggesting that antibodies that detect differences in ICAM-1 expression between these two lesions detect altered epitopes. Three of the four antibodies directed to MUC18 showed concordant reactivities and indicated that this molecule was expressed in nine melanomas and three naevi. However, one antibody (MUC18BA.3) reacted strongly with all lesions indicating either crossreactivity with another melanocyte molecule or the expression of a different form of MUC18 on naevi.