Immunoglobulin A--alpha-1-antitrypsin complex in rheumatic diseases

Area of Science:

• Biochemistry
• Immunology
• Clinical Diagnostics

Background:

• The Immunoglobulin A-alpha-1-antitrypsin (IgA-AT) complex is a nonimmune complex formed via disulfide bonding.
• Its formation involves IgA's cysteine residue and alpha-1-antitrypsin's cysteine at position 232.
• IgA-AT complex levels are quantifiable using ELISA and expressed in arbitrary units.

Purpose of the Study:

• To investigate the diagnostic utility of IgA-AT complex levels in rheumatic diseases.
• To explore the correlation between IgA-AT complex levels and disease progression.
• To assess the potential of IgA-AT complex in differential diagnosis.

Main Methods:

• Quantification of IgA-AT complex levels in patient sera and synovial fluid using ELISA.
• Comparison of IgA-AT complex levels in healthy adults, patients with SLE, RA, osteoarthritis, ankylosing spondylitis, and IgA myeloma.

Main Results:

• Healthy adults typically have IgA-AT complex levels below 0.4 arbitrary units.
• Elevated IgA-AT complex levels were observed in 50% of SLE patients, especially those with central nervous system involvement.
• Approximately 50% of RA patients showed higher IgA-AT levels, correlating with disease progression; the complex was found in 90% of RA cases.
• IgA-AT complex was absent in osteoarthritis synovial fluid but present in ankylosing spondylitis.
• In IgA myeloma, 30% of cases exhibited IgA-AT levels 10-fold higher than the healthy adult upper limit.

Conclusions:

• Elevated IgA-AT complex levels are indicative of several rheumatic conditions, including SLE and RA.
• The IgA-AT complex shows promise for the differential diagnosis of early rheumatoid arthritis versus osteoarthritis.
• The complex is also found in ankylosing spondylitis and significantly elevated in a subset of IgA myeloma patients.