On the mechanism of hemolytic plaque inhibition

Abstract

Equations are presented which and can be used to describe the inhibition of γG plaques by hapten. Two types of experimental situations are considered. In the first the Red Blood Cell epitope density is large enough so that intramolecular reaction is favorable, and the reaction with antibody is considered irreversible during the time of the experiment. In the second case the epitopes are considered to be sparsely distributed so that only univalent attachment is possible. Since antibody site epitope interaction occurs rapidly ( ⪆1 sec ) on the time scale of diffusion, local equilibrium is assumed to apply in this case. We show that these models lead to different types of inhibition results. In the first instance a differential plot of the inhibition curve will reflect the affinity distribution as is often assumed. The reason involves the fact that only the interaction between antibody and free hapten is controlled by affinity, the interaction between antibody and Red Blood Cell (RBC) being irreversible. Consequently the interaction with RBC cannot effect the shape of the inhibition curve. In the second model, however, the interaction with RBC bound hapten and free hapten are both controlled by affinity. The model predicts that at a fixed secretion rate inhibition occurs abruptly, In this case, therefore, the breadth of the inhibition curve reflects the spread in the secretion rate distribution.