TLR9 ligand sequestration by chemokine CXCL4 negatively affects central B cell tolerance

Area of Science:

• Immunology
• Molecular Biology
• Autoimmunity

Background:

• Central B cell tolerance is critical for preventing autoimmunity and is mediated by B cell receptor signaling upon self-antigen recognition.
• The role of Toll-like receptors (TLRs) in B cell tolerance, particularly TLR9, remains incompletely understood.

Purpose of the Study:

• To investigate the role of TLR9 and its adaptor MyD88 in the regulation of central B cell tolerance.
• To determine the impact of CXCL4, a chemokine implicated in systemic sclerosis (SSc), on TLR9 function and B cell tolerance.

Main Methods:

• Utilized humanized mice with genetic defects in MyD88, TLR7, or TLR9 expression.
• Assessed the impact of CXCL4 on TLR9 ligand binding and endosomal localization in B cells.
• Evaluated the development of autoreactive B cell clones and the establishment of central tolerance in vivo.

Main Results:

• TLR9 and MyD88 signaling are essential for maintaining central B cell tolerance and eliminating developing autoreactive B cell clones.
• CXCL4 impairs TLR9 function by sequestering TLR9 ligands, preventing their access to endosomal compartments.
• In vivo production of CXCL4 disrupts TLR9-mediated B cell responses and hinders the establishment of central B cell tolerance.

Conclusions:

• TLR9 plays a vital early tolerogenic role in establishing central B cell tolerance.
• Defective TLR9 function in B cells contributes to the loss of tolerance, as observed in systemic sclerosis.
• Restoring TLR9 function in B cells from SSc patients could be a potential therapeutic strategy to re-establish B cell tolerance.