Antibodies to and elevations of beta 2 microglobulin in the serum of ankylosing spondylitis patients.

Antibodies to beta 2 microglobulin are found in systemic lupus erythematosus patients and are important in the lymphocytotoxic reactions of sera from such patients. In this study, beta 2 microglobulin antibodies were measured with the use of an enzyme-linked immunosorbent assay with purified beta 2 microglobulin antigen and peroxidase-labeled anti-human IgG or IgM. IgG antibodies to beta 2 microglobulin were found in 68% of 22 patients with ankylosing spondylitis. This incidence was higher than the 5% in 80 controls (P less than 0.01) and similar to the 71% incidence found in 35 patients with systemic lupus erythematosus. Eleven (27%) of 41 patients with rheumatoid arthritis had elevated levels of antibodies to beta 2 microglobulin (P less than 0.01). The mean antibody levels expressed in enzyme units were 0.125 for patients with ankylosing spondylitis, 0.157 for those with systemic lupus erythematosus, 0.101 for those with rheumatoid arthritis, and 0.067 for controls. IgM anti-beta 2 microglobulin was not significantly different from controls. A competitive binding assay with enzyme-labeled beta 2 microglobulin was used to determine serum beta 2 microglobulin. These values were also found to be elevated in 48% of patients in all 3 disease categories (P less than 0.01). Beta 2 microglobulin antibodies and serum beta 2 microglobulin did not correlate with each other, renal diseases or antinuclear antibodies in patients with systemic lupus erythematosus, with rheumatoid factor or severity of articular disease in patients with rheumatoid arthritis, or with peripheral arthritis or iritis in those with ankylosing spondylitis. Although antibodies to beta 2 microglobulin might reflect a general disturbance of immune regulation in patients with systemic lupus erythematosus, their presence in those with ankylosing spondylitis, a disease closely associated with a specific HLA allotype and not usually associated with formation of autoantibody, suggests that they might play a role in the pathogenesis of the latter disease.