Temperature Effect on IgE Binding to CD23 Versus FcεRI

Abstract

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 FcεRI. A similar human CD23 construct was also shown to inhibit binding of human IgE to human FcεRI. 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 FcεRI+-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.

CD23 Trimers Are Preassociated on the Cell Surface Even in the Absence of Its Ligand, IgE

“…Thus, only the upper portion of the stalk separates at 37°C, and the lower region of the stalk, near the transmembrane domain, remains tightly associated at all times. Note that these data also fit well with our recent finding that IgE and CD23 interact better at 4 than 37°C and confirm the increased instability of CD23 at physiological temperatures (44). Association of the trimers of CD23 was further investigated using FRET.…”

General mechanism for modulating immunoglobulin effector function

“…In support of this notion, stabilizing the trimeric form of soluble CD23 through a leucine zipper motif linked to the N-terminus of the receptor (lz-CD23) allows for enhanced detection of sialylated IgG binding in a solid-phase ELISA format at physiological temperature relative to the extracellular region of CD23 alone (Fig. S5), as has been reported for IgE (26). However, in contrast to IgE, binding of sialylated IgG to trimeric CD23 is not enhanced at 4°C.…”

Crystal structure of IgE bound to its B-cell receptor CD23 reveals a mechanism of reciprocal allosteric inhibition with high affinity receptor FcεRI

“…Clearly this is not, as previously thought, due to overlapping binding sites, but to an allosteric linkage between the two distant sites. The idea that the open and closed conformations might interact differently with FcεRI and CD23 was in fact anticipated by Conrad et al (24) after their surprising discovery that CD23 bound more strongly to IgE at 4°C than 37°C, whereas the opposite was true for FcεRI. They hypothesized that a change in the relative proportion of these open and closed conformational states might account for this temperature effect, and it will certainly be revealing to explore further the temperature dependence of the kinetics and thermodynamics of these receptor interactions as well as the conformational dynamics of the IgE molecule, particularly with respect to the Cε3 domains.…”

“…The fact that sCD23 can compete with FcεRI binding, albeit at high concentrations (23), was thought to be due to overlap of the two receptor binding sites. This competition was observed at considerably lower concentrations of a trimeric sCD23 molecule, presumably owing to the avidity effect (10,11), and subsequently an intriguing effect of temperature upon the relative affinities of IgE for FcεRI and CD23 was discovered (24). We now report the crystal structure of the complex between the head domain of CD23 [termed derCD23 because it corresponds to the sCD23 fragment generated by the house dust mite allergenic protease Der p 1 (25)] and Fcε3-4.…”