The structure of human CD23 and its interactions with IgE and CD21

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• The low-affinity immunoglobulin E (IgE) receptor, CD23, plays a critical role in regulating IgE synthesis, the antibody isotype central to allergic responses.
• CD23 interacts with both IgE and CD21, but the structural basis for these interactions and its role in IgE regulation remain incompletely understood.

Purpose of the Study:

• To determine the three-dimensional structure of the C-type lectin domain of CD23.
• To identify the residues involved in CD23 self-association and ligand binding.
• To elucidate the structural mechanisms underlying CD23's regulation of IgE synthesis.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy was employed to determine the structure of the CD23 C-type lectin domain in solution.
• Chemical shift perturbation analysis was used to map self-association interfaces and ligand binding sites for IgE and CD21.

Main Results:

• The three-dimensional structure of the CD23 C-type lectin domain was determined.
• Residues involved in trimerization and binding to IgE and CD21 were identified.
• CD23 was shown to bind both IgE and CD21 simultaneously, forming high molecular mass multimeric complexes, independent of calcium.

Conclusions:

• The structural insights explain how CD23 can mediate both up- and down-regulation of IgE synthesis.
• These findings provide a structural foundation for developing novel therapeutic inhibitors for allergic diseases.