Fab fragments with long hinge regions are better able to reach multiple epitopes on an antigen; this increases immunoglobulin avidity because avidity is directly proportional to the number of Fab-antigen interactions.
Uworld QID 540: Affinity is the binding strength of the Fab variable region for a given antigenic epitope. Affinity is determined by the hypervariable amino acid sequence of the variable region.
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Uworld QID 540