Enzyme immunoassay of complement-binding rheumatoid factors.

Area of Science:

• Immunology
• Rheumatology
• Biochemistry

Background:

• Rheumatoid factors (RFs) are autoantibodies implicated in autoimmune diseases.
• Quantifying complement-binding RFs is crucial for understanding disease pathogenesis.
• Existing methods may not fully capture the complexity of RF activity.

Purpose of the Study:

• To develop and validate a novel enzyme immunoassay (EIA) for detecting complement-binding rheumatoid factors (RFs).
• To measure complement-binding RF levels in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).
• To compare RF levels between patient groups and healthy controls, and correlate findings with disease activity.

Main Methods:

• An enzyme immunoassay was developed using heat-aggregated human IgG-coated polystyrene tubes.
• Patient sera were heat-inactivated, incubated with aggregated IgG, and then exposed to fresh human complement.
• Bound C3 complement was quantified using an indirect enzyme immunoassay.

Main Results:

• Significantly elevated levels of complement-binding RFs were observed in both RA and SLE patients compared to healthy controls (P < 0.0005).
• Active SLE cases showed higher mean levels of complement-binding RFs than inactive cases (P < 0.05).
• In RA, complement-binding RF levels correlated with non-agglutinating IgM RF (r=0.56) and IgG RF (r=0.70) but not with the traditional Waaler-Rose titre.

Conclusions:

• The developed EIA is effective for determining complement-binding RFs.
• Complement-binding RFs are prevalent in RA and SLE, suggesting their involvement in these autoimmune conditions.
• The assay provides a valuable tool for assessing RF activity and potentially disease status in RA and SLE.