Micro-anatomy related antigen expression in melanocytic lesions

The in situ expression of antigens associated with melanosomes (gp-100), pi gmentation (PAA), tyrosinase (TRP-1), melanoma (MAA-1/MAA-2), and HLA-DR wa s investigated immunohistochemically in frozen archival specimens of common acquired melanocytic naevi, in dysplastic melanocytic naevi, and in lymph node metastases of melanoma. Expression of these antigens was also studied in established cultured normal human melanocytes, naevus-derived melanocyte s and melanoma cell lines of varying metastatic potential, by immunohistoch emistry and flow cytometry. Compared with normal melanocytes, melanocytic n aevi exhibited increased expression of gp-100, PAA, and TRP-1 in the lesion al cells at or very near the dermo-epidermal junction, but with diminishing expression towards the intra-dermal base of the lesions. In contrast, expr ession of MAA-1 and MAA-2 was observed in melanocytes throughout the dermal part of the naevi. Melanocytes located at the basal layer of the epidermis mere positive only for gp-100, PAA, and TRP-1 antigens. Dysplastic melanoc ytic naevi showed staining of gp-100, PAA, TRP-1, HLA-DR, MAA-1, and MAA-2 of junctional lesional melanocytes, but less intense than that of common ac quired naevi. These antigens were not detectable in the dermal part of the dysplastic naevi. Expression of these antigens in lymph node metastases of melanoma was either positive or negative. Similar results regarding antigen expression were observed in all cultured melanocytic cells, both by immuno histochemistry and by flow cytometry. The present data suggest that analysi s of these antigens may contribute to the discrimination of common acquired melanocytic naevi from their dysplastic counterparts. Furthermore, variati ons in the levels of expression in naevi may be consistently related to the micro-anatomy of the lesions, indicating that the microenvironment may hav e an influence on the expression levels of these antigens in different lesi onal melanocytes. Copyright (C) 2000 John Wiley & Sons, Ltd.