Under physiologic conditions of pH and ionic strength, the I* anti-D appears to react with intact Rh(D) red cells and their Rh(D) stroma according to reversible, second-order kinetics.

At equilibrium the influence of hydrogen ion concentration in the pH range 6.4 to 8.4 on the I* anti-D system is slight. Beyond this pH range the profound depression of the I* anti-D system is consistent with marked conformational changes in the I* anti-D molecule.

The effect of lowered ionic strength on the kinetics of the nonspecific reaction between I* anti-D and rh(d) stroma appears electrostatically controlled if a first-order reaction is assumed. In contrast, the specific reaction between intact Rh(D) red cells or Rh(D) stroma appears to follow a reversible, second-order reaction when the ionic strength of the system is lowered. Consequently, the electrostatic effect of ionic strength on the I* anti-D system seems to be exerted predominantly at the specific Rh(D) site in the case of the intact Rh(D) red cell, but both specifically and nonspecifically in the case of Rh(D) stroma. These results are considered in view of the known effects of pH and ionic strength on other immunologic systems and their components.

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