Collagen type II is recognized by a pathogenic antibody through germline encoded structures

Area of Science:

• Immunology
• Structural Biology
• Rheumatology

Background:

• Collagen type II (CII) is a primary target in autoimmune diseases like rheumatoid arthritis.
• Understanding CII epitope specificity is crucial for autoimmune disease research.

Purpose of the Study:

• To identify critical amino acid residues responsible for Collagen type II (CII) epitope specificity.
• To investigate the role of germline encoding in cartilage-specific autoimmunity.

Main Methods:

• Homology modeling of the CIIC1 antibody fragment (CIIC1scFv) complexed with its CII epitope.
• In silico molecular dynamics simulations and experimental validation using alanine replacements.
• Analysis of antibody binding affinity after reverting mutations to germline sequences.

Main Results:

• Identified crucial CII-binding sites within the CDR2 and CDR3 regions of both heavy and light antibody chains.
• Demonstrated that somatic mutations did not significantly alter CII binding.
• Revealed that the rigid collagen triple helix structure limits antibody interactions compared to globular antigens.

Conclusions:

• Potentially pathogenic cartilage-specific humoral autoimmunity might be encoded in the germline.
• The structural constraints of the collagen triple helix explain the limited impact of somatic mutations on CII recognition by autoantibodies.