Demonstration of electrophoretic heterogeneity of serum beta 2-microglobulin in systemic lupus erythematosus and rheumatoid arthritis: evidence against autoantibodies to beta 2-microglobulin.

A sensitive crossed radioimmunoelectrophoretic method (CRIE), originally developed to study lymphocyte-associated beta 2-microglobulin (beta 2m), was applied in the study of serum beta 2m in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). In six of seven patients with SLE and nineteen of twenty-seven patients with RA a considerable electrophoretic heterogeneity of serum beta 2m was found. In addition to the normally seen symmetric beta 2m precipitate, a beta 2m precipitate exhibiting complete immunochemical identity was found in the alpha-electrophoretic region. Binding of isolated 125I-labelled beta 2m to the abnormal precipitate was demonstrated in crossed immunoelectrophoresis. After gel filtration of sera exhibiting the above-mentioned beta 2m binding, all beta 2m was eluted in low molecular weight fractions corresponding to free beta 2m. By application of appropriate antisera and a glycoprotein-binding lectin in intermediate gels in CRIE, it was shown that the possible beta 2m-binding ligand is not an antibody, not a major constituent of normal human serum, and not unmodified HLA alloantigen. The abnormality was not restricted to patients with high disease activity but was found more frequently and was more pronounced (mean score 1.6 arbitrary units against 0.57 arbitrary units, P less than 0.01) in such patients. Thus our data exclude the possibility that autoantibodies to beta 2m were present in serum from patients with SLE and RA.