Structural and affinity studies of IgM polyreactive natural autoantibodies

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Natural polyreactive autoantibodies (NAA) are part of the normal B cell repertoire.
• NAA are known for binding multiple, dissimilar antigens.
• Previous assumptions suggested NAA bind antigens with low affinity and are encoded by germline genes.

Purpose of the Study:

• To investigate the binding avidities and structural characteristics of murine monoclonal NAA.
• To compare the binding kinetics and gene usage of NAA with immune antibodies.
• To explore the structural basis of polyreactivity in NAA.

Main Methods:

• Surface Plasmon Resonance (SPR) for determining binding avidities.
• Structural analysis of five murine monoclonal NAA.
• Amino acid sequencing and molecular modeling of antibody variable domains.

Main Results:

• All five NAA bound diverse antigens with kinetic constants comparable to immune antibodies.
• NAA expressed a restricted set of V(H), V(L), and D gene segments, with some shared genes.
• Antibody structures showed typical germline configurations and paratope side chain distributions similar to immune antibodies.
• No distinctive particularity in the CDR3 region length or charge was observed in NAA compared to immune antibodies.

Conclusions:

• NAA bind antigens with high affinity, similar to immune antibodies.
• Restricted V gene usage and germline configuration contribute to NAA characteristics.
• The structural features of NAA paratopes resemble those of immune antibodies, challenging the role of CDR3 in polyreactivity.