Temperature effect on IgE binding to CD23 versus FcεRI

A chimeric soluble CD23, consisting of the extracellular domain of mouse CD23 and a modified leucine zipper (lz-CD23), has been shown to inhibit IgE binding to the Fcis an element ofRI. A similar human CD23 construct was also shown to inhibit binding of human IgE to human Fcis an element ofRI. In both systems, the inhibition was found to be temperature dependent; a 10-fold molar excess of Iz-CD23,gave 90-98% inhibition at 4degreesC, dropping to 20-30% inhibition at 37degreesC. Surface plasmon resonance analysis of Iz-CD23 binding to an IgE-coated sensor chip suggested that the effective concentration of Iz-CD23 was lower at the higher temperatures. Analysis of I-125-IgE binding to CD23(+)-Chinese hamster ovary cells also indicated that increased temperature resulted in a lower percentage of IgE capable of interacting with CD23. In contrast, IgE interacts more effectively with Fcis an element ofRI(+)-rat basophilic leukemia cells at 37degreesC compared with 4degreesC. The results support the concept that the open and closed IgE structures found by crystallography interact differently with the two IgE receptors and suggest that temperature influences the relative percentage of IgE in the respective structural forms. Changes in CD23 oligomerization also plays a role in the decreased binding seen at physiological temperatures.