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Temperature Effect on IgE Binding to CD23 Versus FcRI ¹

Bing-Hung Chen^*, Michelle A. Kilmon^*, Check Ma^*, Timothy H. Caven^*, Yee Chan-Li^*, Anne E. Shelburne^*, Robert M. Tombes, Eric Roush and Daniel H. Conrad^2,*

Departments of ^* Microbiology and Immunology and Biology, Virginia Commonwealth University, Richmond, VA 23298; and Biacore, Inc., Piscataway, NJ 08854

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 FcRI. A similar human CD23 construct was also shown to inhibit binding of human IgE to human FcRI. In both systems, the inhibition was found to be temperature dependent; a 10-fold molar excess of lz-CD23 gave 90–98% inhibition at 4°C, dropping to 20–30% inhibition at 37°C. Surface plasmon resonance analysis of lz-CD23 binding to an IgE-coated sensor chip suggested that the effective concentration of lz-CD23 was lower at the higher temperatures. Analysis of ¹²⁵I-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 FcRI⁺-rat basophilic leukemia cells at 37°C compared with 4°C. 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.

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				M. A. Kilmon, A. E. Shelburne, Y. Chan-Li, K. L. Holmes, and D. H. Conrad CD23 Trimers Are Preassociated on the Cell Surface Even in the Absence of Its Ligand, IgE J. Immunol., January 15, 2004; 172(2): 1065 - 1073. [Abstract] [Full Text] [PDF]