on- and off-rate of antibodies

[Will Fuller]

The on rate for most reactions (antibody-antigen, drug-receptor) is
usually constant and is determined by the rate of diffusion as this is
the limiting factor. The "tightness" of this interaction generally
determines the off rate. Hence the affinity determines the off rate and
the on rate is constant at a particular temperature.

Consider the equilibrium:


antigen                        on
+                   ----------------------->            antigen/antibody
complex
antibody        <----------------------
                                        off

on:    rate at which antibody and antigen come together, determined by
diffusion, independent of affinity

off:    rate of dissociation of the complex, determined by the affinity
of the antibody for the antigen

Therefore, higher affinity antbodies have the same on rate, but slower
off rates than lower affinity ones

Hope this helps