Cardiolipin binding a light chain from lupus-prone mice

Area of Science:

• Immunology
• Molecular Biology
• Autoimmunity Research

Background:

• Autoantibodies in systemic lupus erythematosus (SLE) target conserved molecules like nucleic acids and phospholipids.
• Analysis of autoantibody variable gene sequences (VH and VL) reveals a limited repertoire.
• Monoclonal antibodies from lupus-prone mice were studied for cardiolipin reactivity.

Purpose of the Study:

• To investigate the role of heavy-chain variable (VH) and light-chain variable (VL) sequences in cardiolipin autoantibody binding.
• To determine if the light-chain variable sequence alone can confer antigen-binding specificity.

Main Methods:

• Sequencing of VH and VL regions of monoclonal antibodies A1.72 and A1.84.
• Recombinant expression of single-chain variable fragments (scFv) combining VL 72/84 with different VH sequences.
• Expression of the VL 72/84 sequence alone.
• Immunoaffinity purification using cardiolipin liposomes and measurement of dissociation constants (Kd).

Main Results:

• Antibodies A1.72 and A1.84 shared identical VL sequences (VL 72/84) but differed in VH sequences.
• The VL 72/84 sequence alone, and when combined with various VH sequences, conferred cardiolipin-binding activity.
• The dissociation constant of the isolated VL chain for cardiolipin was comparable to the intact antibody.

Conclusions:

• The light-chain variable (VL) sequence alone can mediate direct binding to cardiolipin.
• Antigen specificity for cardiolipin may reside exclusively within the VL sequence in certain autoantibodies.
• This challenges the traditional view of antigen binding requiring contributions from both VH and VL domains.