Presence of circulating immune complexes in Reiter's syndrome and ankylosing spondylitis

Circulating immune complexes (ICs) were sought in the sera of patients with Reiter's syndrome (RS) and ankylosing spondylitis (AS) because (i) the presence of these complexes would support the hypothesis that these diseases are immunologically mediated, and (ii) characterization of the antigen in the complex could provide an important clue toward understanding pathogenesis. Three separate assays were used: the Raji, the conglutinin, and the solid phase anti-C3. All three assays detected complexes in the majority of patients with RS. The Raji was the most sensitive assay, detecting complexes in 67% (20 of 30) patients with RS. Seventy-seven percent of RS patients had detectable complexes by at least one of the three assays. For AS, complexes were present in 69% of the sera studied by the Raji assay. The conglutinin assay gave concordant results. By contrast, the anti-C3 assay did not detect complexes in AS sera. Identification of the antigen in these complexes would elucidate the pathogenesis of these diseases.