The strength with which a multivalent antibody binds a multivalent antigen is termed the

• A. Affinity
• B. Avidity
• C. Reactivity
• D. Valence

Answer: (B)

Avidity is the overall binding strength that results when a multivalent antibody interacts with a multivalent antigen. When multiple binding sites engage simultaneously, the combined interactions stabilize the complex far more than any single site would alone, making the overall binding much stronger under physiological conditions. This differs from affinity, which describes the strength of a single antigen–antibody paratope–epitope interaction; avidity reflects the cumulative effect of multiple engagements. Valence refers to how many binding sites a molecule has, which influences potential avidity but is not the binding strength by itself. Reactivity is a general term for the ability to bind, not the strength of the multivalent interaction.