Antibodies to beta 2 microglobulin in the sera of patients with systemic lupus erythematosus.

The present study reports the detection of antibodies to β microglobulin in the sera of patients with systemic lupus erythematosus (SLE). Using a Farr-type ammonium sulphate precipitation assay, test sera were reacted with Iβ microglobulin, and immunoglobulins precipitated by 50% saturated ammonium sulphate. Increased β microglobulin binding activity (normal values: mean±2 sd = 35.5 ±7.8) was detected in 18 of 42 SLE sera. Anti-HLA sera did not reveal increased binding activity, suggesting that the antibody in SLE serum was directed toward free β microglobulin. Direct validation was done by reacting Iβ microglobulin with 4 SLE sera having increased Iβ microglobulin binding activity, and subjecting the reactants to sucrose density gradient ultracentrifugation. Two peaks were obtained, one corresponding to free β microglobulin, and the other to 7S material complexed to β microglobulin. Normal sera demonstrated only one peak corresponding to unbound β microglobulin. Assays of β microglobulin binding activity on protein fractions obtained by Sephadex G200 column chromatography also showed the presence of increased binding activity with 7S fractions. Using a double antibody assay, the 7S material reactive to β microglobulin was demonstrated to be IgG. It was also shown that sera with abnormal β microglobulin binding activity had higher titres of antinuclear antibody compared to those lacking such activity ( = 3.18; <0.01), indicating the pathogenetic relationship of this antibody to increased disease activity. This antibody may be responsible for some of the abnormalities of cell-mediated function previously described in SLE patients.