Affinity and avidity determined by Law of Mass Action
Describes the strength of a single Ag-Ab bond.
As Ag and Ab come close together a chemical bond forms which is weak and can dissociate.
How well the Ab fits the Ag will determine stability of bond, “lock and key” fit has strongest affinity.
Ab may react with structurally similar Ags, results in cross reactivity.
Most antibodies have a high affinity for their antigens.
Describes the combined strength of multiple Ag-Ab bonds.
Initially bond is easily broken, but multiple bindings at the same time the dissociation is overcome by the sheer number of bonds remaining.
Avidity is influenced by both the valence of the antibody and the valence of the antigen.
Affinity versus Affinity
Affinity refers to the strength of binding between a single antigenic determinant and an individual antibody combining site whereas avidity refers to the overall strength of binding between multivalent antigens and antibodies.
IgM and IgG
Most frequently detected immunoglobulins.
IgM has low affinity but high avidity due to 10 binding sites.
IgG has 2 strong binding sites, high affinity and avidity.
Law of Mass Action
Governs the reversibility of the antigen-antibody reaction.
Reversible reaction, visible reaction occurs when the rate of binding exceeds the rate of dissociation.
As affinity and avidity increases, strengthens reaction.