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Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

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CD22 serves as a receptor for soluble IgM.

Takahiro Adachi¹, Satoru Harumiya, Hiromu Takematsu

¹Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan. tadachi.imm@mri.tmd.ac.jp

European Journal of Immunology

|September 30, 2011

Summary

Soluble IgM (sIgM) activates CD22 (Siglec-2) on B-cells, suggesting sIgM is a natural ligand. This interaction creates a negative feedback loop, regulating B-cell activation.

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Antibody Binding Specificity for Kappa (Vκ) Light Chain-containing Human (IgM) Antibodies: Polysialic Acid (PSA) Attached to NCAM as a Case Study

Published on: June 29, 2016

Area of Science:

Immunology
Glycobiology
Cell Signaling

Background:

CD22 (Siglec-2) is a B-cell receptor recognizing sialic acid, crucial for B-cell regulation.
Its exact function in B-cell signaling remains incompletely understood.
CD22 negatively regulates the B-cell antigen receptor (BCR) pathway.

Purpose of the Study:

To investigate the role of soluble IgM (sIgM) in CD22 activation.
To identify natural ligands for CD22.
To elucidate the mechanism of CD22-mediated negative feedback in B-cell activation.

Main Methods:

In vitro assays to assess CD22 activation by sIgM-antigen complexes.
Analysis of glycan structures on sIgM.
Comparison of CD22 function to FcγRIIB.

Main Results:

CD22 is efficiently activated in trans by complexes of antigen and sIgM.
Glycan ligands present on sIgM mediate this activation.
sIgM acts as a natural trans ligand for CD22.
CD22 functions as an sIgM receptor, inducing negative feedback on B-cell activation.

Conclusions:

Soluble IgM (sIgM) is identified as a natural trans ligand for CD22.
CD22 acts as an sIgM receptor, establishing a negative feedback loop for B-cell activation.
This mechanism parallels the inhibitory function of FcγRIIB.