Potency of hexavalent and decavalent anaphylactogens: affinity enhancement by epitope clusters.

Two deca-L-lysine conjugates, one carrying ten, the other carrying six D-benzylpenicilloyl haptenic groups as epitope models, were used as elicitors of passive cutaneous anaphylaxis in guinea pigs. It was found that equal haptenic doses yielded virtually indistinguishable responses, i.e., the potencies were close to 10:6. Interpretation of these data appears possible by using established immunochemical concepts of preequilibria and equilibria in free solution as starting point. The discussion is simplified due to the fact that the two conjugates being decavalent and hexavalent, respectively, in free solution, are both hexavalent on cell membranes. It was found that the clusters of haptenic groups displayed by the conjugates enhance the affinity for antibody binding and that the haptenic densities are directly related to potencies. Epitope clusters of enhanced affinity interacting with cell-bound antibody may be significant and useful in a number of ways.