Demonstration of Electrophoretic Heterogeneity of Serum β2‐Microglobulin in Systemic Lupus Erythematosus and Rheumatoid Arthritis: Evidence against Autoantibodies to β2‐Microglobulin

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Abstract
A sensitive crossed radioimmunoelectrophoretic method (CRIE), originally developed to study lymphocyte-associated β2-microglobulin (β2m), was applied in the study of serum β2m in patients with systemic lupus erythemutosus (SLE) and rheumatoid arthritis (RA). In six of seven patients with SLE and nineteen of twenty-seven patients with RA a considerable elec-trophoretic heterogeneity of serum β2m was found. In addition to the normally seen symmetric β2m precipitate, a β2 precipitate exhibiting complete immunochemical identity was found in the α-electrophoretic region. Binding of isolated I25l-labelled β2m to the abnormal precipitate was demonstrated in crossed immunoelectrophoresis. After gel filtration of sera exhibiting the above-mentioned β2m binding, all β2m was eluted in low molecular weight fractions corresponding to free β2m. By application of appropriate antisera and a glycoprotein-binding lectin in intermediate gels in CRIE, it was shown that the possible β2m-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 < 0.01) in such patients. Thus our data exelude the possibility that autoantibodies to β2m were present in serum from patients with SLE and RA.

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