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I understand that when some antigen (e.g., virus, bacteria, etc.) is recognized in the body, antibodies specific to this antigen are produced that, in turn, bind to the antigen and effectively neutralize them as a potential threat to the organism.

Are all the antibodies that are produced against a specific antigen necessarily identical? Either within a single organism (e.g., a single person), or between different organisms (e.g., between different people, different species, etc.)? If two people get sick with the same disease, develop antibodies, and recover, are these antibodies the same? If a human and some other animal get sick with the same disease, will the antibodies each develop match?

Key to the operation of the antibodies is their specific recognition/binding of the antigen. I assume that the structure and composition of the antibody is tuned to bind to specific exposed moieties on the antigen. I can imagine that there are many different potential binding sites on the antigen to target and many possible combinations of ways to recognize those sites by the antibodies. I would think that it would be a remarkable coincidence (highly unlikely) if separate organisms both, independently, happened to develop the same “molecular strategy” for recognizing a particular antigen. This outcome seems to be implied in this question, How are antibodies specific for a disease detected in the blood if everybody produces a different antibody for the same antigen?

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Alright, there are two major questions:

(a) Are all the antibodies that are produced against a specific antigen necessarily identical?

Not in most cases. Antigens can either be monovalent or polyvalent, meaning that they can either have one epitope or various different epitopes (an epitope is the site of the antigen that binds to a T-cell receptor or a B-cell receptor). Most antigens are polyvalent, which implies that a single antigen may interact with several different T and B cell lineages. Each B cell lineage is only able to produce and export one type of antibody. Because the antigen will interact with different lineages, it will promote the production of different types of antibodies. These multiple antibodies produced against one antigen are called polyclonal antibodies, since they arise from multiple clonal lineages. When the antigen only has one kind of epitope, it will induce the production of only one type of antibody, which are called monoclonal antibodies, because they arise from only one clonal lineage.

(b) Do the antibodies produced against a certain antigen differ between members of the same species or between species?

Yes, in both cases. There is an important genetic variability surrounding immunoglobulins and T cell receptors.

Reference: Karp, G. (2009). Molecular and Cellular Biology: Methods and Concepts. Wiley. New York.

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