Avidity (source code)
= Avidity
{wiki}
<Avidity> is the combined strength of multivalent attachment. An intact <IgG> can make two contacts when accessible <epitopes> have suitable spacing. <Molecular Biology of the Cell, 4th edition by Bruce Alberts and others>[Chapter 24, B Cells and Antibodies, A Typical Antibody Has Two Identical Antigen-Binding Sites; The Strength of an Antibody-Antigen Interaction Depends on Both the Number and the Affinity of the Antigen-Binding Sites: avidity]{ref} If one contact breaks while the other remains, the detached arm stays nearby and can bind again before the whole <antibody> escapes. That geometric advantage does not require changing either <paratope>'s intrinsic <antibody affinity>. Two arms binding two separate freely moving <antigens> do not automatically provide the same tethering advantage. <Epitope> spacing, accessibility and surface density matter; <avidity> is not obtained by adding two <dissociation constants>.
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