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

Immunoglobulin A-alpha-1-antitrypsin complex (IgA-AT) is a nonimmune complex formed by disulphide bonding between an active thiol group available on the cysteine residue of alpha heavy chains of IgA and a cysteine in position 232 of alpha l-antitrypsin in single polypeptide chain. The level of the complex can easy be determined using the ELISA method and findings are expressed in arbitrary units. In the healthy adults' sera the IgA-AT complex level is lower than 0.4 arbitrary unit. The elevated levels of the complex were found in a number of rheumatic diseases. In 50% of SLE patients, its levels are increased, particularly in those with current central nervous system involvement. Similarly, in approximately 50% sera derived from RA patients they are also found to be higher. Their presence correlates with anatomical progression of the disease. IGA-AT complex is found in RA (in 90% of cases) but not in the osteoarthritis synovial fluid. Our findings can be applied in clinical praxis in differential diagnosis of early rheumatoid arthritis and osteoarthritis. The IGA-AT complex can be also found in ankylosing spondylitis. The complex has been determined in a relatively large number of IgA myeloma sera. In 30% of the cases its levels were 10-fold higher than the upper limit for healthy adults.