Circulating CD21low B cells in common variable immunodeficiency resemble tissue homing, innate-like B cells

Area of Science:

• Immunology
• Cell Biology

Background:

• B cell subset homeostasis is crucial for immune function.
• Disturbances in B cell populations are observed in various immune deficiencies, such as common variable immunodeficiency (CVID).

Purpose of the Study:

• To characterize the unique CD21-low B cell population found in CVID patients.
• To investigate the phenotype, function, and potential origin of CD21-low B cells.

Main Methods:

• Flow cytometry to analyze B cell surface markers (CD21, IgM, IgD).
• Gene expression profiling to compare CD21-low B cells with conventional B cell subsets.
• Functional assays to assess B cell receptor signaling and proliferation.

Main Results:

• CD21-low B cells are expanded in a subgroup of CVID patients.
• These cells are polyclonal, unmutated IgM(+)IgD(+), with a distinct gene expression profile.
• CD21-low B cells show signs of activation but have defective calcium signaling and proliferation; they express altered chemokine receptors, promoting tissue homing.

Conclusions:

• CD21-low B cells represent a distinct human B cell population with innate-like characteristics.
• Their phenotype and homing properties suggest a role in immune surveillance and inflammatory conditions.
• These cells may represent a human equivalent of murine B1 B cells.