Somatically mutated B cell pool provides precursors for insulin antibodies

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Antibodies to insulin arise from autoreactive B lymphocytes that evade normal immune system controls, a phenomenon termed "clonal ignorance."
• Understanding the genetic basis of these autoantibodies is key to understanding immune tolerance and autoimmunity.

Purpose of the Study:

• To investigate the genetic origins of insulin-binding antibodies produced by "clonally ignorant" B cells.
• To determine the specific roles of somatic mutation and germ-line V(H) gene structures in the development of anti-insulin activity.

Main Methods:

• Engineered monoclonal antibody (mAb) constructs with germ-line and mutated V(H) genes were created.
• The binding capabilities of these engineered mAbs to human and rodent insulin were assessed.
• The impact of specific mutations, particularly within CDRH2, on antibody binding was analyzed.

Main Results:

• Somatic mutations, especially those introducing aspartic acid in or near CDRH2, were found to be critical for insulin binding.
• Reverting the V(H) genes to their germ-line sequences abolished insulin binding and polyreactivity.
• A single mutation in CDRH2 was sufficient to confer anti-insulin activity on a previously non-binding antibody.

Conclusions:

• IgG insulin autoantibodies are likely not derived directly from unmutated germ-line precursors.
• Somatic mutation is a prerequisite for measurable insulin binding, indicating an origin from a pre-mutated B cell repertoire.
• Low-avidity interactions with insulin may influence the selection of these B cells, contributing to "clonal ignorance."