The appearance, density and distribution of melanocytes in human embryonic and fetal skin revealed by the anti-melanoma monoclonal antibody, HMB-45

Abstract

The presence, densities, and patterns of distribution of melanocytes in the epidermis of human embryos and fetuses, ranging in age from 40 d to 140 d estimated gestational age (EGA), were studied using the HMB-45 monoclonal antibody that recognizes an antigen in melanoma cells and fetal melanocytes. Immunostained sections of skin and epidermal sheets revealed dendritic melanocytes within the basal or intermediate layers of 50 d EGA and older skin. Melanocytes could not be identified by immunostaining or electron microscopy in younger (40-50 d EGA) epidermis or in cultured epidermal cells from these specimens. However, skin from a 45 d EGA embryo grown in organ culture for 11 d stained positively with HMB-45, suggesting that melanocytes are present at the age either in the epidermis or dermis of the explant. Double-labeling experiments using ATPase and HMB-45 confirmed the specificity of HMB-45 for melanocytes and demonstrated that melanocytes and Langerhans cells are nonoverlapping populations. Melanocytes were present in the embryonic epidermis in relatively high numbers (mean value of approximately 1050 cells/mm2); they increased in density to approximately 2300 cells/mm2 during the late first trimester and early second trimester, then declined during later stages of development to a density of approximately 800 cells/mm2, within the range of values for the newborn child and young adult. Equivalent numbers of melanocytes were recognized by silver staining and with the HMB-45 antibody in an 87 d EGA test sample, indicating that HMB-45 reacted with the total melanocytic population. Melanocytes appeared to be distributed in epidermal sheets in a regular pattern. Statistical tests used to evaluate the randomness of a population revealed a tendency toward a non-random distribution in specimens younger than 80 d EGA, just prior to appendage formation and epidermal stratification into multiple layers, however there was variability in the degree of randomness for any given age. The results of this study have closed the gap in timing between the conclusion of neural crest formation and migration (around 6 weeks) and the appearance of melanocytes in the skin between 40-50 d EGA.

Keratin expression and its significance in five cultured melanoma cell lines derived from primary, recurrent and metastasized melanomas

“…Keratin subunits have roles in the structure and formation of epithelial cells [3,4] and also in the reorganization of cells during mitosis [5][6][7]. On the other hand, human melanocytes are developmentally derived from neural crest cells and are localized in the basal cell layer of the epidermis [8]. The main functions of melanocytes are to produce melanin and to supply the melanin to the epidermis as a means of protection against ultraviolet irradiation.…”

Diagnostic Value of HMB-45 and Anti-Melan A Staining of Sentinel Lymph Nodes with Isolated Positive Cells

“…Presumably, this method uses monoclonal antibodies to a glycoprotein that is present in premelanosomes (11). In immunohistochemical assays, this antibody reacts with melanoma cells, junctional nevus cells, and fetal melanocytes but generally not with completely melanized normal adult melanocytes or with intradermal nevus cells (12)(13)(14). HMB-45 is nonreactive with almost all non-melanoma human malignancies, with the exception of rare tumors showing evidence of melanogenesis (e.g., pigmented schwannoma, clear cell sarcoma) or tumors associated with tuberous sclerosis complex (angiomyolipoma and lymphangiomyoma; 15,27).…”

Diagnosis of pulmonary lymphangioleiomyomatosis by HMB45 in surgically treated spontaneous pneumothorax

“…HMB45 binds to antigen present in the cytoplasm of neoplastic melanocytic cells [2,3], melanocytes in foetal skin at a gestational age of 50 days [16], and foetal and neonatal retinal pigment epithelium [17]. This distribution suggests that this MoAb binds cytoplasmic oncofoetal glycogen associated with immature melanosomes, and changes in immunoreactivity with maturation or malignant transformation may be a function of post-translational modification [17].…”