Framework-mediated binding of foreign and self-glycans by IGHV4-34 antibodies

Area of Science:

• Immunology
• Structural Biology
• Autoimmune Diseases

Background:

• Cold agglutinin disease (CAD) is an autoimmune disorder causing red blood cell destruction.
• CAD is driven by self-reactive antibodies targeting I/i carbohydrate blood group antigens.
• The IGHV4-34 germline antibody is prevalent in CAD and features a conserved hydrophobic patch in framework 1 (FR1).

Purpose of the Study:

• To elucidate the structural and mechanistic role of the FR1 hydrophobic patch in IGHV4-34 antibodies.
• To understand how these antibodies bind to I/i carbohydrate antigens in CAD.
• To provide a structural rationale for the preservation of the self-reactive IGHV4-34 germline.

Main Methods:

• Analysis of structural data of IGHV4-34 antibodies bound to HIV envelope glycoprotein.
• Comparison of glycan structures on HIV and I/i antigens.
• Stereochemical analysis of antibody-glycan interactions.

Main Results:

• Structural data reveal direct interfaces between the FR1 hydrophobic patch and high mannose glycans on HIV.
• These interactions suggest a framework-centric, non-CDR binding mode.
• The findings offer a potential mechanism for IGHV4-34 antibodies engaging self-antigens like LacNAc.

Conclusions:

• The FR1 hydrophobic patch plays a direct role in antigen binding, not just conformational shaping.
• This mechanism explains how IGHV4-34 antibodies can bind to I/i antigens in CAD.
• The study provides a structural basis for the persistence of this self-reactive antibody lineage.