Rheumatoid factor isotypes and circulating immune complexes in rheumatoid arthritis

Area of Science:

• Immunology
• Rheumatology
• Biochemistry

Background:

• Rheumatoid arthritis (RA) is characterized by inflammation and the presence of autoantibodies.
• Rheumatoid factors (RF) and immune complexes (IC) are key players in RA pathogenesis.
• Quantifying RF and IC in different body fluids can offer insights into disease activity.

Purpose of the Study:

• To quantify IgM, IgG, and IgA rheumatoid factors (RF) and C1q or conglutinin binding immune complexes (IC) in serum and synovial fluid of RA patients.
• To correlate RF and IC levels with clinical and radiographic features of RA.
• To compare RF and IC levels between seropositive RA (SPRA), seronegative RA (SNRA), and osteoarthrosis patients.

Main Methods:

• Solid phase enzyme immunoassays were employed for quantification.
• Serum and synovial fluid samples from RA and osteoarthrosis patients were analyzed.
• Levels of IgM, IgG, and IgA RF, as well as C1q and conglutinin binding IC, were measured.

Main Results:

• Elevated serum RF isotypes were prevalent in SPRA patients, less so in SNRA patients.
• Synovial fluid RF levels were generally higher in SPRA than SNRA patients, except for IgG-RF.
• Both C1q and conglutinin binding IC were significantly higher in synovial fluid than serum of RA patients.
• Elevated IgG-RF in synovial fluid and C1q-binding IC correlated with radiographic indices and erythrocyte sedimentation rate.
• Extraarticular manifestations were more frequent with elevated IgM-RF or conglutinin binding IC.

Conclusions:

• IgG-RF in synovial fluid and C1q-binding IC are closely linked to local disease features in RA.
• RF and IC quantification in synovial fluid provides valuable information for understanding RA.
• These biomarkers may aid in assessing disease activity and predicting clinical outcomes.