Rat serum antibodies binding to high-molecular-weight glycoprotein(s) on syngeneic colon carcinomas, demonstrated by competition with rat monoclonal antibody.

Sera from rats immunized to syngeneic 1,2-dimethylhydrazine colon carcinomas were analyzed for their ability to inhibit the binding of a syngeneic rat IgM monoclonal antibody (10B12) specific for high-molecular-weight glycoprotein(s) from rat colon carcinoma. Immunization with irradiated tumour cells or with tumour tissue extracts resulted in the appearance of a strong inhibiting activity. Sera of animals with established growing tumours and of females shortly after partus also inhibited binding of the monoclonal antibody, while unimmunized animals or animals immunized with irrelevant antigens had no inhibiting antibodies in their sera. Dimethylhydrazine-treated animals showed an increased titer of antibodies binding to the high-molecular-weight glycoprotein, but showed no inhibition of binding of the 10B12 monoclonal antibody. The syngeneic 10B12 rat antibody obviously does not reflect a rare event captured from a hyperimmune animal by the hybridoma technique but rather represents an antibody specificity frequently appearing in the immune response to tumours expressing the high-molecular-weight glycoprotein.