Anti-T4-Tyrosinase Monoclonal Antibodies—Specific Markers for Pigmented Melanocytes

Abstract

Tyrosinase (EC 1.14.18.1) is the enzyme essential to pigment formation in mammals; this enzyme is specifically localized in melanocytes, which occur primarily in the skin, hair bulbs, and eyes. Three hybridomas, TMH-1, TMH-2, and TMH-3, which produce monoclonal antibodies directed against tyrosinase, were obtained by fusion of SP2/0 myeloma cells and lymphocytes of rats hyperimmunized with purified melanosomal tyrosinase. These three monoclonal antibodies bound specifically to the mature, T4 form of tyrosinase, and did not bind to either of the precursor forms (T1 or T2) of the enzyme, which demonstrates that further posttranslational modifications of this enzyme occur which had not previously been detected. Epitope mapping studies have shown that at least two different immunologic determinants on tyrosinase are recognized by these antibodies. All three antibodies showed positive immunofluorescence staining of pigmented murine melanocytes from various sources, including B16 melanoma growing in vivo and in vitro, epidermal melanocytes, and retinal melanocytes. The antibodies did not cross-react with unpigmented cells, including K1735 amelanotic melanoma cells, albino murine skin or eye tissue, fibrosarcoma cells, rat fibroblasts, or epidermal keratinocytes. These monoclonal antibodies are sensitive, highly specific probes for pigmented mammalian melanocytes.