Although ReA is considered a sterile disease with no microorganisms found in the joints, immune complexes with Yersinia antigens, Yersinia-specific antibodies of the IgM, IgG, and IgA classes, and LPS have been found in serum and synovial fluid from patients diagnosed with Yersinia-induced ReA, even several years after infection [28]. This evidence concerns the gene CD79A and infection.