Given the size difference between small molecule antigens and antibodies is it ever possible for multiple antibodies to bind to the same antigen if they recognize different domains on that antigen? When the antigen is a protein rather than a small molecule is it more likely that multiple antibodies can bind?
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2$\begingroup$ Does this answer your question? Can more than one antibody bind the same antigen $\endgroup$– tyersomeJan 9, 2020 at 20:39
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Not only is it possible for multiple antibodies to bind a single antigen, when that happens, it's more likely to trigger a full immune response.
Here's a description of the concept from a company that sells antibodies for research. To help understand the quote, you'll need to know that the portion of an antigen that an antibody binds is called an epitope.
Because an antigen can have multiple different epitopes, a number of antibodies can bind to the protein. When two or more antigen binding sites are identical, an antibody can form a stronger bond with the antigen than if only one of the antibody’s sites is bound. Antigens with multiple identical binding sites are called multivalent, and antibodies are able to bind it more strongly.
Here is an article that describes, among other things, the importance of clustering in B-cells when multiple B-cell receptors bind to a single multivalent antigen.
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$\begingroup$ Thanks! Does that only work for large antibodies though? I'm worried that the relative size of a small molecule compared to the antibody means that even with multiple epitopes only one antibody will be able to bind it. I reached out to novus and they were unable to give an answer $\endgroup$– IkeJun 27, 2018 at 18:44
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$\begingroup$ @ike that's going to depend on the antigen. Is this for something you're working on in a lab? $\endgroup$– De NovoJun 27, 2018 at 18:53
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$\begingroup$ Yes--We're looking to work with aflatoxin, a small molecule produced by Aspergillus flavus that has multiple antibodies which recognize it. $\endgroup$– IkeJun 27, 2018 at 19:18
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$\begingroup$ Oh yes, that's an intercalating agent. I wouldn't be surprised if you got more than one antibody binding to one molecule of aflatoxin, but you'd have to test it. Are you trying to measure a quantitative signal? $\endgroup$– De NovoJun 27, 2018 at 19:25
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$\begingroup$ it's more of a binary on/off as to whether both bind or not. $\endgroup$– IkeJun 27, 2018 at 20:29