The immunohistochemical localization of
melanoma-associated
antigen p94 kd200 was investigated in frozen sections of 3 congenital
nevi, 4 benign
intradermal nevi, 1 regressing
nevus, 1
blue nevus, 1
dysplastic nevus, 1
lentigo maligna, 1 superficial spreading
melanoma and 2 metastatic
melanomas. The original
avidin-
biotin complex
lectin method (Hsu SM, Raine L, Fanger H: Am. J. Clin. Pathol., 75: 734-738, 1981) was modified to detect the
antigen. The sections were exposed to the
monoclonal antibody to p94 kd200 (Hybritech Inc.), the linking
biotin-labelled anti-mouse
IgG, the
avidin-
biotin peroxidase complex and the
3-amino-9-ethylcarbazole solution in an incubator at 37 degrees C and 100% humidity. We found that the percentage of cells expressing p94 kd200 varied between 0 and 100% in congenital
nevi, between 80 and 100% in benign
intradermal nevi, between 0 and 20% in the regressing, blue and
dysplastic nevi, and in the
lentigo maligna, 80 to 100% in the superficial spreading
melanoma, and between 0 and 40% in the metastatic
melanomas. Positive cells were found to be hypomelanotic (did not have heavy
melanin content). The intensity of labelling or the degree of
antigen expression on benign and malignant hypomelanotic cells was also found to vary. These findings 1) reinforce the concept of quantitative rather than qualitative antigenic differences in benign and malignant cells 2) suggest that kd200 is lost with increasing pigment production 3) offer a potentially significant tool to investigate the antigenic changes during cell differentiation.