Cryoglobulinemia in autoimmune rheumatic diseases: Evidence of circulating monoclonal cryoglobulins in patients with primary Sjögren's syndrome

The incidence and nature of cryoglobulins, as well as their correlation with the clinical and serologic picture of Sjögren's syndrome (SS), were studied in the sera of 30 consecutive primary SS patients. Sera from 29 patients with systemic lupus erythematosus, 58 patients with rheumatoid arthritis, and 125 healthy blood donors were also studied. It was shown that one‐third of the patients with SS had cryoglobulinemia. These cryoglobulins were mixed monoclonal IgM immunoglobulins, whereas those observed in systemic lupus erythematosus and rheumatoid arthritis patients were mixed polyclonal. The nature of the cryoglobulins was demonstrated using high‐resolution electrophoresis combined with immunofixation. The presence of cryoglobulins in the sera of SS patients correlated with extraglandular disease and with antibodies to Ro (SS‐A) and IgM rheumatoid factor. SS patients with cryoglobulins had lower serum C4 levels than did patients without cryoglobulins. These findings suggest that SS expresses, in addition to polyclonal B cell hyperreactivity, a monoclonal process in the absence of lymphoid neoplasia. Further, they show that the extraglandular manifestations of the syndrome may be due to an immune complex‐mediated pathology.