B700 and B50 are melanoma-specific antigens originally isolated from B16 murine melanoma. B700, which elicits a strong tumor rejection response, is present on all murine melanomas tested to date. We now demonstrate the presence of B50 in the other murine melanomas and find that the 2 molecules are non-covalently complexed with each other within the cells. We also show that hosts immunized with intact, irradiated melanoma cells produce antibodies that specifically recognize the B700 and B50 tumor antigens. These results suggest that B50 may also participate in the host response to melanoma growth.
Previous observations indicated the absence of demonstrable 5'-nucleotidase activity in six of seven cultured murine melanoma cell lines. It could not be determined from those studies whether the enzyme was absent, or whether an inhibitor was present. The current studies indicate that no inhibitor can be demonstrated, therefore the enzyme is absent.
The activity of 5'-nucleotidase and ouabain-sensitive Na/K ATPase was determined in seven different mouse melanoma cell lines. Ouabain-sensitive Na/K ATPase activity was found in NP40-treated cell homogenates of all cell lines. However, 5'-nucleotidase activity was found in only one mouse melanoma cell line--JB/RH. The absence of expression of 5'-nucleotidase activity in the other six cell lines is not associated with pigmentation in melanoma cells, nor is the gene switched off in all transformed melanocytes of C57BL/6 origin.
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