Cancer-specific binding of a mouse MAb vs. Candida krusei cytochrome c : an antigen recognized by a cancer-associated human MAb HB4C5

More than 60 mouse monoclonal antibodies directed to cytochrome c from Candida krusei with different specificities were raised. Most of these monoclonal antibodies, except for three of them, did not cross-react with bovine cytochrome c. By the immunoblotting method, the monoclonal antibodies of clones HCC 5-13, 9-2, and 10-5 reacted with the Candida cytochrome c, which had been transferred onto nitrocellulose membrane, but those of clones HCC 1-22, 6-3, and 17-3 did not, although all these monoclonal antibodies strongly reacted with coated Candida cytochrome c on plastic immunoplates when examined by ELISA. On the contrary, monoclonal antibody activities of clones HCC 1-22, 6-3, and 17-3 in binding to the coated cytochrome c in ELISA were inhibited competitively by the addition of extra Candida cytochrome c, whereas those of clones HCC 5-13, 9-2, and 10-5 were not inhibited. Among these monoclonal antibodies, the antibody of clone HCC 6-3, which showed a good reactivity to added cytochrome c in inhibiting ELISA reaction but was not reactive with the transblotted cytochrome c on nitrocellulose, was found to be reactive with human lung cancer tissues specifically with no reactivity to normal tissues. The immunostaining of lung cancer tissue showed that this mouse monoclonal antibody to Candida cytochrome c reacted to the cytoplasmic fraction of the cancer cells specifically.