Autoantibody activity of cryoglobulins and sera in systemic lupus erythematosus. Association of IgM class rheumatoid factors with Raynaud's syndrome.

A total of 218 samples obtained during a follow-up study of 36 patients with systemic lupus erythematosus (SLE) were tested for the presence of cryoglobulins. Cold-insoluble precipitates were found in 81% for the patients (29 patients, 114 samples). The protein concentration of the cryoglobulins correlated significantly with the disease activity. Autoantibody activity was determined in the dissolved cryoglobulins and in corresponding serum samples by enzyme-linked immunosorbent assays (ELISA). IgM-RF could be demonstrated more often in the cryoglobulins than in the sera (75% vs. 14%), whereas IgA-RF were seen in 28% of both cryoglobulins and sera. Anti-ssDNA and anti-poly(A) antibodies of both IgG and IgM classes were found more often in the sera than in the corresponding cryoprecipitates. In 7 samples from 5 patients an increase in the IgG-anti-ssDNA activity was seen after DNase digestion of the cryoglobulins. Patients with Raynaud's syndrome had a significantly higher level of cryoprecipitating IgM class rheumatoid factors than other patients. There was also an association between the IgG-anti-poly(A) antibody levels in the cryoglobulins and the activity of the disease. There was no difference with regard to the composition of the cryoglobulins, between patients with nephritis and those without an overt renal disease. Thus, the presence of cryoglobulins in SLE indicates active disease, but not necessarily renal involvement. IgM rheumatoid factors may play a role in the pathogenesis of Raynaud's syndrome of SLE patients.