Final answer:
A multivalent antigen has many epitopes, which can be identical or different, allowing multiple antibodies to bind to those different epitopes on the same antigen. This characteristic can result in cross-reactivity, where antibodies bind to epitopes on different antigens.
Step-by-step explanation:
A multivalent antigen is one that has many epitopes; the epitopes can be either identical or different. Antigens are macromolecules that can elicit an immune response while epitopes, also known as antigenic determinants, are the specific parts of the antigen where antibodies or T-cell receptors bind. A single complex antigen, such as a bacterial flagellum protein, can have a plethora of epitopes, each with unique three-dimensional structures that determine the specificity of the antibody binding.
Different antibodies can recognize and bind to these different epitopes on the same antigen, demonstrating the immune system's ability to fine-tune its response to a wide array of pathogens. Cross-reactivity occurs when antibodies raised against a specific epitope can also bind to similar epitopes on different antigens, showcasing the sophisticated and sometimes unpredictable nature of immune recognition.