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Specificity of anti-carcinoembryonic antigen monoclonal antibodies and their effects on CEA-mediated adhesion
1McGill Cancer Center, Montreal, Quebec, Canada.
Abstract:
The carcinoembryonic antigen (CEA) domain specificities of a library of monoclonal anti-CEA antibodies were determined to investigate the mechanisms of homophilic binding involved in CEA-mediated intercellular adhesion. Using an indirect immunofluorescence cell surface staining technique, the reactivities of these antibodies were tested systematically on Chinese hamster ovary cells stably transfected with constructs of CEA gene family members CEA, nonspecific cross-reacting antigen, CGM6, and biliary glycoprotein, as well as on stable Chinese hamster ovary transfectants expressing truncated CEA and CEA/nerve cell adhesion molecule chimeric proteins. Epitopes for these antibodies were thus localized on the CEA molecule as follows: monoclonal antibody groups 1, 2, and 6 react with epitopes in the N-terminal domain of CEA, whereas groups 3, 5a, 5b, and 9 react with determinants found in the internal repeating domains located in the C-terminal part of the CEA molecule. Groups 4 and 8 appear to react with a repeating epitope in the internal domains of CEA and in all CEA subfamily members. Fab fragments of monoclonal antibody group 1 block aggregation of CEA transfectant cells, indicating that a region in the N domain is involved in CEA homophilic interaction. Fab fragments of monoclonal antibody group 9 recognize an epitope dependent on the B2 and A3 domains and stimulate aggregation. These results support the recently reported CEA-CEA homophilic reciprocal binding model in which anti-parallel molecules are bound by 2 bonds between the N domain of one molecule and the A3B3 domain of the interacting partner.
Insights
Researchers investigated carcinoembryonic antigen (CEA) homophilic binding mechanisms using monoclonal antibodies. They found specific CEA domains, particularly the N-terminal and internal repeating domains, are crucial for intercellular adhesion.
Area of Science:
- Cell Biology
- Immunology
- Molecular Biology
Background:
- Carcinoembryonic antigen (CEA) is implicated in cell adhesion.
- Understanding CEA's role in intercellular adhesion requires detailed analysis of its binding mechanisms.
Purpose of the Study:
- To investigate the domain specificities of monoclonal anti-CEA antibodies.
- To elucidate the mechanisms of homophilic binding in CEA-mediated intercellular adhesion.
Main Methods:
- Systematic testing of monoclonal anti-CEA antibody reactivities on transfected Chinese hamster ovary cells.
- Utilizing indirect immunofluorescence cell surface staining.
- Localization of antibody epitopes on CEA and its related family members.
Main Results:
- Antibody groups 1, 2, and 6 bind to N-terminal CEA epitopes; groups 3, 5a, 5b, and 9 bind to C-terminal internal repeating domain epitopes.
- Groups 4 and 8 recognize a repeating epitope in internal domains shared by CEA subfamily members.
- Fab fragments of group 1 antibodies block cell aggregation, implicating the N domain in homophilic interaction.
- Fab fragments of group 9 antibodies bind to epitopes dependent on B2 and A3 domains and stimulate aggregation.
Conclusions:
- The N-terminal domain of CEA is involved in CEA homophilic interactions.
- Specific internal domains (B2 and A3) are recognized by antibodies that stimulate aggregation.
- Results support a model of anti-parallel CEA-CEA binding involving the N domain and A3B3 domain.