Expression and ultrastructural localization of HMB-45 antigen.
HMB-45 is a monoclonal antibody specific for melanoma cells and premature developing melanocytes. We examined the expression and specific subcellular binding sites of HMB-45 in various types of melanocytes including epidermal melanocytes from fetuses and infants with or without tyrosinase-negative oculocutaneous albinism (type IA), melanin-producing and non-producing melanoma cell lines (G361 and MeWo), and in vivo melanoma cells (melanotic and amelanotic malignant melanoma). Subcellular HMB-45 binding was examined by using post-embedding immunogold electron microscopy with rapid freezing and freeze substitution fixation methods without the use of chemical fixatives to preserve the intracytoplasmic delicate antigen property of HMB-45. HMB-45 antigen was detected not only in in vivo melanoma cells and normal fetal melanocytes, but also in melanocytes in the other conditions. Post-embedding immunogold electron microscopy revealed that HMB-45 antigen was exclusively localized to stages I and II melanosomes in the cytoplasm of neoplastic melanocytes, but was detected mainly on stages II and III melanosomes in the melanocytes from fetuses and infants. In tyrosinase-negative oculocutaneous albinism, only stages I and II melanosomes were detected in the cytoplasm, but both stages of melanosomes were HMB-45 positive. We conclude that HMB-45 appears mainly on the immature melanosomes during melanogenesis in both neoplastic and non-neoplastic melanocytes regardless of their tyrosinase activity, but the intracytoplasmic localization of HMB-45 antigen is different by each condition of melanocytes.
Kikuchi
A
A
Department of Dermatology, Keio University School of Medicine, Tokyo, Japan.
Shimizu
H
H
Nishikawa
T
T
D000293:Adolescent; D000951:Antigens, Neoplasm / Q000032:analysis*; D002454:Cell Differentiation / Q000502:physiology; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007124:Immunoenzyme Techniques; D008544:Melanocytes / Q000737:chemistry* / Q000648:ultrastructure; D008545:Melanoma / Q000737:chemistry* / Q000648:ultrastructure; D058950:Melanoma-Specific Antigens; D016253:Microscopy, Immunoelectron; D009363:Neoplasm Proteins / Q000032:analysis*; D012867:Skin / Q000196:embryology; D012878:Skin Neoplasms / Q000737:chemistry* / Q000648:ultrastructure; D014407:Tumor Cells, Cultured
D000951:Antigens, Neoplasm; D058950:Melanoma-Specific Antigens; D009363:Neoplasm Proteins