The conglutinin binding activity in sera of the patients with systemic lupus erythematosus (SLE) was measured and following results were obtained. 1. The sera from SLE, progressive systemic sclerosis, mixed connective tissue diseases and Behcet's disease patients had higher conglutinin binding activity than normal human sera. 2. The conglutinin binding activity in SLE showed good correlation with C1q or ds-DNA binding activity (p<0.1) and level of serum CH50, but had poor correlation with staining patterns of antinuclear antibody or clinical nephropathy. 3. Increased activity was found in 33% of SLE sera by the conglutinin radioimmunoassay and 84% of SLE sera by the C1q radioimmunoassay. 4. SLE patients with high conglutinin binding activity were classified into three groups. In the first groups patients has clinically active stage due to SLE, in the second groups patients had no clinical activity during more than several months, and in the third groups patients had no clinical activity due to SLE but had the other clinical manifestations, such as, liver damage. 5. The binding activity in the sera of the SLE patients who had low serum complement levels was not measured by the counglutinin radioimmunoassay.
systemic lupus erythematosus