CA 125--epitopes and molecular size.

CA 125 has two main immunogenic areas reactive with mouse and rat monoclonal antibodies. These areas are defined by the antibodies OC 125 and M11, respectively. Antibodies related to the main groups are named OC 125-like and M 11-like antibodies. The OC 125-like antibodies can be subgrouped into four sets, whereas the M 11-like antibodies segregate into many closely related binding specificities. One M 11-like antibody, ZR38, is not fully inhibited by any other M 11-like antibody and therefore represents a distinct subgroup. A single antibody, OV 197, is related to some OC 125-like antibodies, but not to OC 125. However, OC 125 enhances binding of OV 197 to its epitope. A new antibody, 7C 12, induces conformation changes, affecting binding of some M 11-like and some OC 125-like antibodies. CA 125 exists as very large molecules that can be partly disrupted by SDS and heat. The form found in serum might be a degradation product from a larger molecule found in the abdominal and other serous cavities.