Binding Affinity of Human Autoantibodies: Studies of Cryoglobulin IgM Rheumatoid Factors and IgG Autoantibodies to Albumin

The binding affinity of cryoglobulin IgM rheumatoid factors (RF) for human IgG and of human IgG anti-albumin autoantibodies for HSA was measured by the molecular sieving technique. The binding affinities of the two autoantibodies were consistently low (10⁴-10⁵ I/M) as compared to the affinities of corresponding hyperimmune animal antibodies (10⁶-10⁸ I/M). The findings were discussed in relation to theories on human autoimmunity. The existence of strict autotolerance at the T cell level and of autoreactivity at the low affinity B cell level was considered to be best compatible with the findings of this study and with the major known facts of autoimmunity.