Antibodies of different specificities are self-binding: implication for antibody diversity

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Antibodies of the S107/T15 germline family have unique variable region structures enabling specific complex formation.
• Self-binding antibodies, or autobodies, are crucial for understanding antibody diversity and immune regulation.
• Previous studies focused on the immunochemical properties of autobodies, necessitating further investigation into mutant forms.

Purpose of the Study:

• To investigate the self-binding properties of mutant antibodies U4 (DNA-binding) and U10 (unspecified specificity).
• To elucidate the molecular mechanisms underlying the self-binding of these mutant antibodies.
• To explore the role of variable region structures in antibody self-binding and repertoire diversity.

Main Methods:

• Comparative analysis of wild-type (TEPC15) and mutant (U4, U10) antibodies from the S107/T15 germline family.
• Investigation of self-binding inhibition using free hapten (phosphorylcholine), DNA, and free nucleotides.
• Peptide mapping using variable region-derived peptides to identify self-binding loci.

Main Results:

• Mutant antibodies U4 and U10, like the germline TEPC15 antibody, demonstrate self-binding.
• Self-binding of the anti-DNA antibody U4 is inhibited by DNA and nucleotides, unlike TEPC15 which is inhibited by phosphorylcholine.
• A specific peptide from the variable heavy chain (CDR2/FR3) of the TEPC15 germline structure inhibited self-binding in U4 and U10.

Conclusions:

• Antibody self-binding is a feature present in both wild-type and mutant antibodies within the S107/T15 germline family.
• Variable region sequence structures play a critical role in determining antibody self-binding specificities.
• The study reveals a novel mechanism of antibody repertoire diversity controlled by variable sequence structures, leading to self-binding or non-self-binding antibodies with identical specificities.