Autoantibody subclass predominance is not driven by aberrant class switching or impaired B cell development

Area of Science:

• Immunology
• Autoimmunity
• B cell biology

Background:

• A subset of autoimmune diseases features predominant pathogenic immunoglobulin G4 (IgG4) autoantibodies, termed IgG4-AIDs.
• The underlying mechanisms driving IgG4 subclass predominance in these conditions remain largely unknown.
• This study investigates potential causes, including B cell maturation and class switching abnormalities.

Purpose of the Study:

• To investigate whether dysregulated B cell maturation or aberrant class switching leads to the overrepresentation of IgG4-producing B cells and plasma cells in IgG4-AIDs.
• To compare the B cell compartment in patients with IgG4-AIDs versus those with IgG1-3-AIDs and healthy individuals.

Main Methods:

• Flow cytometry was used to analyze the B cell compartment in patients with four different IgG4-AIDs, two IgG1-3-AIDs, and healthy donors.
• Analysis focused on the relative subset abundance across all maturation stages and the quantification of specific cell populations.

Main Results:

• B cell maturation stages showed normal subset abundance in IgG4-AIDs, with a potential treatment-related reduction in immature and naive CD5+ cells.
• IgG4-producing B cell and plasma cell numbers were comparable to controls.
• A significant, subclass-independent 8-fold increase in circulating CD20-CD138+ cells was observed in IgG4-AID patients, lacking autoreactivity.

Conclusions:

• The findings suggest that aberrant B cell development is not the primary driver for IgG4 subclass predominance in these autoimmune diseases.
• The results support an antigen-driven mechanism for the specific autoantibody subclass.
• Despite diverse clinical presentations, IgG4-AIDs share a common underlying immune profile.