Transitional B Cells and TLR9 Responses Are Defective in Selective IgA Deficiency

Area of Science:

• Immunology
• Cell Biology

Background:

• Selective IgA deficiency (IgAD) is the most common primary antibody deficiency.
• Individuals with IgAD face increased risks of autoimmunity, atopic diseases, and infections.
• Toll-like receptor 9 (TLR9) plays a role in B cell differentiation into IgA-producing plasma cells.

Purpose of the Study:

• To analyze T and B cell phenotypes and functions in IgAD individuals after TLR9 stimulation.
• To investigate the impact of CpG-TLR9 stimulation on B cell subsets and IgA production in IgAD.

Main Methods:

• Analysis of T and B cell populations ex vivo in IgAD patients.
• In vitro CpG-TLR9 stimulation to assess B cell responses and IgA production.
• Flow cytometry to identify transitional B cells (CD19+CD24hiCD38hi) and class-switched memory B cells (CD20+CD27+IgD-).

Main Results:

• IgAD individuals exhibited lower numbers of transitional B cells and class-switched memory B cells ex vivo.
• T cell populations and in vitro induced T effector/regulatory cells were comparable to healthy controls.
• CpG stimulation exacerbated transitional B cell defects and failed to induce IgA production in IgAD patients.

Conclusions:

• A defect in TLR9 responses contributes to B cell dysregulation in Selective IgA deficiency.
• Impaired TLR9 signaling leads to decreased IgA production in IgAD.
• This highlights a critical role for TLR9 in IgA homeostasis and IgAD pathogenesis.