Immune complexes in progressive systemic sclerosis and mixed connective tissue disease

Area of Science:

• Immunology
• Rheumatology
• Clinical Chemistry

Background:

• Circulating immune complexes (CICs) are implicated in autoimmune diseases.
• Progressive systemic sclerosis (PSS) and mixed connective tissue disease (MCTD) are systemic autoimmune disorders.

Purpose of the Study:

• To investigate the presence and levels of CICs in patients with PSS and MCTD.
• To compare the sensitivity of different assays for CIC detection.
• To explore the relationship between CIC levels and disease activity.

Main Methods:

• Sera from PSS and MCTD patients were analyzed for CICs using Clq precipitins, cryoglobulins, and radioimmunoassays (Raji cell and Clq).
• The Raji cell assay was identified as the most sensitive method for CIC detection.

Main Results:

• The Raji cell assay detected CICs in 82% of MCTD patients and 55% of PSS patients.
• Median CIC levels were significantly higher in MCTD (79 µg eq AHG/ml) compared to PSS (20 µg eq AHG/ml).
• In MCTD, CIC levels correlated with disease activity, unlike in PSS.

Conclusions:

• The Raji cell assay is a sensitive tool for detecting CICs in PSS and MCTD.
• Elevated CIC levels, particularly those correlating with disease activity, may be more characteristic of MCTD than PSS.
• Ribonucleoprotein (RNP) antigen was not found in the detected immune complexes.