Production and characterization of a new monoclonal antibody to colorectal carcinoma.

This study describes a new murine monoclonal antibody (MoAb) 5C1 raised against human colorectal carcinoma, which gave a differential reaction on formalin-fixed sections of the gastrointestinal tract. The MoAb 5C1 of immunoglobulin M (IgM) isotype reacted with both the cytoplasm and membrane of all normal colonic epithelia, and with all benign colonic polyps and all premalignant colonic lesions. However, there was a decreased expression of the 5C1 antigen in most cases of colonic malignancy and it was this feature that makes MoAb 5C1 unique. The distribution of the 5C1 epitope in normal gastrointestinal tract is limited to a few epithelial cells in the mid-portion of the small intestine but this distribution increased progressively down the digestive tract until it was found on greater than 90% of normal epithelial cells (in membrane and cytoplasm) of the colon. In addition, the 5C1 epitope was present on mucin secreting cells from normal organs of the gastrointestinal, reproductive and pulmonary tract and benign and malignant tissues of the colon. On Western blots, MoAb 5C1 was found to detect a heterogeneous population of molecules with molecular weights greater than 100 kDa with the strongest staining bands found between 230 and 300 kDa. MoAb 5C1 does not detect carcino-embryonic antigens (CEA), human milk fat globules (HMFG), human lymphocyte antigens (HLA) or ABO blood group antigens. The combination of its presence in mucin secreting cells and its broad molecular weight bands suggest that the antigen detected is a mucin.