C595--a monoclonal antibody against the protein core of human urinary epithelial mucin commonly expressed in breast carcinomas.

Urinary mucins which express determinants for the anti-breast carcinoma monoclonal antibody, NCRC-11 (IgM), closely resemble the mammary mucins found in milk fat globules and carcinomas. An IgG3 monoclonal antibody, C595, was prepared against urinary mucins isolated on a NCRC-11 antibody affinity column, and this 'second generation' antibody was shown to have a very similar pattern of reactivity to the original NCRC-11 antibody. By immunohistology, the profile of reactivity of both antibodies with tumour and normal tissue specimens was virtually identical. Both antibodies reacted with epithelial mucins isolated from breast tumours or normal urine using an NCRC-11 antibody affinity column, although the antibodies were unreactive with other antigen preparations. Heterologous immunoradiometric assays ('sandwich' tests) confirmed that NCRC-11 and C595 epitopes were co-expressed on the same molecule. C595 antibodies inhibited the binding of radiolabelled NCRC-11 antibodies to antigen, suggesting that the two epitopes were in close topographical proximity. The protein core of the mammary mucins has recently been shown to consist predominantly of a repeated 20 amino acid sequence (Gendler et al., 1988). Peptides with this complete sequence and small fragments were synthesised, and the C595 antibody was found to recognise an epitope within this repeat. The ability to identify and synthesise monoclonal antibody-defined determinants, as well as those in the adjacent or overlapping sequences within the protein core of epithelial mucins, is viewed as a strategy for facilitating the production of antibodies of new and novel specificity to complement the panels of existing anti-breast cancer reagents.