Expression of a colorectal antigen defined by a new monoclonal antibody, CO-TL1.

A murine monoclonal antibody (MoAb CO-TL1, IgG1) has been raised by differential screening of hybridoma supernatants on sections of human large and small intestines, followed by screening on colon adenomas as well as on colorectal carcinomas. In both paraffin sections and cryostat sections, the antibody stained strongly all cell types in adult, neonatal and fetal human colorectal epithelium, that is, the goblet cells, the columnar cells and the endocrine cells. No staining was observed in the remaining parts of the normal gastrointestinal tract and other tissues. As revealed by immuno electron microscopy the epitope was present in the apical and basolateral cell membranes, the Golgi complex, secretory vesicles of goblet and columnar cells, and also in granules of the endocrine cells. The epitope in colorectal tissue sections was resistant to the deglycosylation enzymes neuramidase, diastase and hyaluronidase indicating its proteinaceous nature. This colorectal antigen remained expressed in 100% of colorectal adenomas (n = 39) and 86% (n = 29) of colorectal carcinomas. The expression was reduced in undifferentiated carcinomas. The CO-TL1 antibody detected also most other gastrointestinal adenocarcinomas and a few carcinomas of the ovary, uterus, breast, gallbladder and pancreas. However, it never detected carcinomas derived from the thyroid, lung, liver, bladder, kidney, prostate, testis, serous membranes of body cavities and skin. A wild-type variant protein of > 300 kDa of the colorectal antigen was identified in normal colorectal epithelium. In colorectal tumours, however, two tumour variant forms were found of 160-200 and 115-140 kDa, respectively. Our data indicate that this new MoAb CO-TL1 can be considered as a useful marker, which identifies normal colorectal epithelium and gastrointestinal tumours and especially colorectal tumours with high accuracy and excludes tumours originated from thyroid, lung, liver, bladder, kidney, prostate, testis, mesothelium and skin.