Characterization of the colorectal antigen IOR-C2.

A colorectal antigen (IOR-C2) was characterized by a monoclonal antibody produced against the colon cancer cell line SW1116. By immunohistochemical staining the antigen was abundant and strongly expressed in epithelium of normal colon whereas colorectal carcinomas showed a more variable and heterogenous reactivity to the antibody (IOR-C2). Radioimmunoprecipitates of SW1116 cell homogenates showed a 160-200 kD band in SDS gels. Physicochemical characterization indicate that at least two IOR-C2 reactive sites are present on the antigen tested and that it is mainly an 0-linked glycoprotein carbohydrate chain which can also be N-linked to the protein. The expression of IOR-C2 mimics that of the colon associated antigen (CAA) and NCC-CO-450 antigen but is distinct from these with regard to its expression in carcinomas as well as its physicochemical characteristics.