Common IgA and IgM rheumatoid factor idiotypes in autoimmune diseases

Area of Science:

• Immunology
• Rheumatology
• Serology

Background:

• Rheumatoid factors (RFs) are autoantibodies, primarily IgM, IgG, or IgA, targeting the Fc region of immunoglobulin G.
• RFs are associated with autoimmune diseases like rheumatoid arthritis and Sjögren's syndrome, but also occur in other conditions and healthy individuals.
• The idiotype of an antibody is its unique antigen-binding site, and anti-idiotypic antibodies target these specific sites.

Purpose of the Study:

• To investigate the cross-reactivity of anti-idiotypic antibodies against various rheumatoid factors.
• To determine if RF idiotype conservation is linked to disease category, antibody clonality, or isotype.
• To explore the implications of RF cross-reactivity for the germline antibody repertoire.

Main Methods:

• Production of anti-idiotypic antibodies in rabbits against monoclonal and polyclonal IgM and IgA rheumatoid factors.
• Testing the cross-reactivity of these anti-idiotypic antibodies against RFs from patients with essential mixed cryoglobulinaemia, rheumatoid arthritis, systemic sicca syndrome, and systemic lupus erythematosus.

Main Results:

• Variable, but significant, cross-reactivity was observed for each anti-idiotypic antibody tested.
• The observed cross-reactivity was not restricted by the disease category of the RF.
• Cross-reactivity was independent of the clonality (monoclonal vs. polyclonal) or isotype (IgM, IgA) of the rheumatoid factor.

Conclusions:

• The findings suggest a high degree of conservation among rheumatoid factor genes within the germline antibody repertoire.
• This conservation implies shared structural features or V gene usage across different RFs, irrespective of clinical presentation.
• Understanding RF idiotype conservation may offer insights into autoimmune disease pathogenesis and B cell repertoire development.