FCER2

FCER2 Full Name

Fc fragment of IgE, low affinity II, receptor for (CD23)

FCER2 Introduction

FCER2, widely known as CD23, is the low-affinity receptor for the Fc region of IgE antibodies (Fc fragment of IgE, low affinity II). Unlike the high-affinity IgE receptor (FcεRI) which belongs to the immunoglobulin superfamily, CD23 is unique as a C-type (calcium-dependent) lectin. It is primarily expressed on activated B cells and monocytes. Physiologically, CD23 functions as a pivotal regulator of IgE production and B-cell survival. It exists in two dynamic states: a membrane-bound trimer (mCD23) and various soluble fragments (sCD23) generated by proteolytic cleavage (shedding) via ADAM10. The membrane-bound form acts as part of a negative feedback loop to limit IgE synthesis. Conversely, the soluble fragments, particularly when trimeric, can bind to CD21 (complement receptor 2) and IgE, promoting IgE synthesis and preventing B-cell apoptosis. This dual mechanism allows CD23 to act as a "molecular switch" in the allergic response, balancing the production of allergic antibodies.

Figure 1. Structure of the FcεRI a-chain (A), CD23 (B) and its complex with IgE. (Source: Okayama Y, et al. 2020)

The dysregulation of CD23 is central to the pathology of allergic diseases and lymphoproliferative disorders. In allergic asthma and rhinitis, the "brake" mechanism of CD23 is often defective, leading to uncontrolled high levels of serum IgE and hypersensitivity. Beyond allergy, CD23 is a critical biomarker in Chronic Lymphocytic Leukemia (CLL). In CLL, leukemic B cells often overexpress CD23, and high levels of soluble CD23 in the blood are correlated with tumor burden, rapid disease progression, and poor prognosis. Consequently, sCD23 is utilized clinically as a prognostic factor and a marker for monitoring disease activity in leukemia patients.

Alternate Names for FCER2

FCER2; Fc fragment of IgE, low affinity II, receptor for (CD23); CD23; FCE2; CD23A; IGEBF; CLEC4J; BLAST-2; low affinity immunoglobulin epsilon Fc receptor; CD23 antigen; fc-epsilon-RII; lymphocyte IgE receptor; immunoglobulin E-binding factor; C-type lectin domain family 4, member J;

• Immunohistochemistry Antibodies for Pathology
• Immunohistochemistry Antibodies for Pathology

• 1. McDonnell JM, et al. IgE, IgE Receptors and Anti-IgE Biologics: Protein Structures and Mechanisms of Action. Annu Rev Immunol. 2023 Apr 26;41:255-275.
  2. Okayama Y, et al. Roles of omalizumab in various allergic diseases. Allergol Int. 2020 Apr;69(2):167-177.