Regulation of IgE Production Requires Oligomerization of CD23

Abstract

Here we describe the production of a rabbit polyclonal Ab (RAS1) raised against the stalk of murine CD23. RAS1 inhibits release of CD23 from the surface of both M12 and B cells resulting in an increase of CD23 on the cell surface. Despite this increase, these cells are unable to bind IgE as determined by FACS. CD23 has previously been shown to bind IgE with both a high (4–10 × 107 M−1) and low (4–10 × 106 M−1) affinity. Closer examination by direct binding of 125I-IgE revealed that RAS1 blocks high affinity binding while having no effect on low affinity binding. These data support the model proposing that oligomers of CD23 mediate high affinity IgE binding. These experiments suggest that RAS1 binding to cell surface CD23 results in a shift from oligomers to monomers, which, according to the model, only bind IgE with low affinity. These experiments also suggest that high affinity binding of IgE is required for IgE regulation by CD23 and is demonstrated by the fact that treatment of Ag/Alum-immunized mice treated with RAS1 results in a significant increase in IgE production similar to the levels seen in CD23-deficient mice. These mice also had significantly decreased levels of serum soluble CD23 and Ag-specific IgG1. RAS1 had no effect on IgE or Ag-specific IgG1 production in CD23-deficient mice.

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

“…1), maximize the propensity for cross-linking of mIgE on B cells committed to IgE synthesis by trimeric sCD23, and also mCD23 on B cells by IgE or IgE-allergen complexes. We have hypothesized that through such interactions, the former leading to upregulation of IgE synthesis and the latter to down-regulation, CD23 contributes to the mechanism of IgE homeostasis (43), and this notion has received experimental support from studies with monomeric and oligomeric sCD23 species (7,8,16,44). The structure of the complex is also consistent with the cocross-linking of mCD21 and mIgE by trimeric sCD23 (proposed to enhance IgE up-regulation), because CD21 binds to the "tail" sequence that is, although only partially present in derCD23, located adjacent to the connection to the stalk (Fig.…”

Necessity of the stalk region for immunoglobulin E interaction with CD23

“…12 The importance of this oligomerization in CD23 function has been illustrated in that a rabbit polyclonal antibody raised against the stalk region of murine CD23, both blocked highaffinity/avidity interaction with IgE and reversed the controlling action of CD23 on IgE production. 13 To determine the importance of oligomerization of CD23 in IgE binding, this laboratory 14 generated a soluble mouse CD23 (lz-CD23) that is composed of a modified leucine motif (lz) 15,16 attached to the N terminus of the entire extracellular region of CD23. This chimeric lz-CD23 construct was shown to be superior to monomeric CD23 in its capacity to bind IgE.…”

CD23-Bound IgE Augments and Dominates Recall Responses through Human Naive B Cells

“…Up to 80% of circulating B cells express CD23 at relatively high surface levels, illustrating a potentially important role in immunity (5). In fact, describing CD23 as having low affinity for IgE is misleading because oligomers of CD23 can bind IgE with equal affinity as the high-affinity IgE receptor (FcεRI) (7). Thus, CD23 + B cells circulate preloaded with CD23-bound IgE (5).…”