Defective helper T cell function in IgM rheumatoid factor synthesis in patients with ankylosing spondylitis

Despite chronic inflammation and the presence of hypergammaglobulinemia, rheumatoid factor (RF) is rarely found in the blood of patients with ankylosing spondylitis (AS). We used ELISA to compare spontaneous and pokeweed mitogen (PWM)-induced IgG, IgM and IgM rheumatoid factor (IgM-RF) production in normals and in patients with rheumatoid arthritis (RA) and AS. The IgG and IgM synthesis in these three groups did not differ. However, the IgM-RF level in PWM-induced mononuclear cell cultured supernatants of AS was significantly decreased, compared with normal and RA patients. Furthermore, mixing experiments by co-culture of normal T or B cells with patient's B or T cells in the presence of PWM revealed a deficiency of the helper T cell function in patients with AS. These results illustrate the cellular mechanism of the seronegativity of the rheumatoid factor in patients with ankylosing spondylitis.