Characterization of ior C5 colorectal tumor associated antigen

Established human colon cancer cell line SW1116 was used to generate ior C5 monoclonal antibody (mAb) by standard hybridoma technique. By immunohistochemical studies the antigen was abundant and strongly expressed in the epithelium of the gastrointestinal tract, mainly the small and large intestine, and the bronchus epithelial cell lining; no reaction was observed in the other normal tissues studies. Glandular epithelial derived tumors, especially colorectal cancers showed a more variable and heterogeneous reactivity to the antibody. Enzymatic and chemical treatments of colorectal cancer membrane extracts indicated that the antigen recognized by this mAb is an O-linked glycoprotein carbohydrate chain. Western blot studies on SW1116 cell membrane extracts showed that the ior C5 mAb recognized a glycoprotein complex composed of a major 145 kDa band and a minor 190 kDa band. The epitope recognized by this mAb can also be found in a high molecular weight glycoprotein obtained from normal colon. In blocking experiments using ior C5 and ior C2 mAb (previously report by us), it was shown that both mAbs compete for the same antigen site, although ion C5 shows a higher blocking efficiency. Additionally, ior C5 in contrast with ior C2 mAb, was capable of blocking the recognition of 17-1A mAb by a pool of human anti idiotypic antibodies generated against 17-1A mAb. Since, 17-1A and ior C5 mAbs recognized different antigens, the above result indicates that these anti idiotypic antibodies recognize a non paratopic idiotype shared by both 17-1A and ior C5 mAbs. The preferential staining of colorectal tumors and the restricted reactivity in normal human adult tissues make ior C5 mAb an eligible candidate for the radioimmunodetection of colorectal tumors.