Immunological studies in seronegative spondyloarthropathies.

Immunological parameters including the serum levels of major classes of immunoglobulins and complement C3, screening of six commonly encountered autoantibodies (including rheumatoid factor) and screening for circulating immune complexes were carried out in patients with different presentations of seronegative spondyloarthropathies. Compared with 27 controls, the mean serum levels of IgG were significantly elevated (p less than 0.001) in 19 patients with ankylosing spondylitis (AS), 15 with Reiter's disease (RD) and nine with 'unclassified' seronegative spondarthritis. Serum IgA was significantly elevated (p less than 0.01) in Reiter's disease but not in the other two groups of patients. One patient with 'unclassified' seronegative spondarthritis showed complete absence of IgA and IgM in his serum. Serum C3 levels were estimated in 26 AS patients, 14 RD patients and nine unclassified seronegative spondarthritis patients. The values did not differ significantly from those in 27 controls. Autoantibodies were not detected in any of 29 patients with AS, 15 with RD and 10 patients with unclassified seronegative spondarthritis. Circulating immune complexes were detected by latex agglutination-inhibition technique in 5.9% of 85 controls, 61% of 18 patients with ankylosing spondylitis (p less than 0.001), 67% of 15 patients with Reiter's disease (p less than 0.05) and 78% of nine patients with unclassified seronegative spondarthritis (p less than 0.001). The findings would suggest an ongoing antigenic challenge in these diseases in which tissues may be damaged by deposits of antigen-antibody complexes.