affinity, control the strength of the interaction. These are high local
concentration of the antigen and the possibility of bivalent binding.
The initial binding of the antibody to the immobilized antigen is limited
by diffusion, but after the first antibody-epitope interaction occurs, the
formation of the second bond may be an intramolecular conversion if
sterically possible (Fig. 3.5). In addition , the high local concentration
of antigen increases the chance that any disassociated antibodies will
rebind to neighboring antigens. In essence, diffusion occurs, but the
high concentration of antigen acts as a trap to hold the antibody to the
solid phase. These factors combine to yield a high avidity.
This type of multimetric interaction can occur in cell staining,
immunoblotting, and many types of immuno assays.
DCX-83, p. 33-34. The apparent increase in affinity for antibodies bound to a substrate is confirmed
by Paul, Fundamentals of Immunology (FUND), p. 432-33. This standard reference work states:60
However, another effect also increases the effective affinity in
a two-phase system. This effect applies even for monovalent
antibodies (Fab fragments) or monovalent ligands. The effect arises
from the enormously high effective local concentration of binding sites
at the surface compared to the concentration if the same number of
sites were distributed in bulk solution. [Endnote omitted.]
Because of the possible enhanced affinity of the carrier-bound antibody, the person of ordinary
skill in the art would not be able to reasonably conclude that the affinity of the bound antibody was
necessarily about the same as that of the labeled antibody in solution from the overall sensitivity of
the assay.
On pages 101 to 102 of her brief Engvall also argues to the effect that those working in the
art would recognize that the antibodies used in Engvall’s example 1 had affinities “higher than 108
liters/mole” (emphasis added) and refers to Langone’s testimony to for support. However,
Engvall’s argument misses the mark. As we indicated above, the phrase “at least about 108
liters/mole” indicates the lower limit of the affinity constant for the invention. The evidence must
show that one having ordinary skill in the art would be led to the lower claimed limit for the affinity
constant of “at least about 10 liters/mole” from the examples not just to any affinity constant with8
some value higher than 10 . 8
60
See n. 5, supra.
37
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