ANTIBODIES TO BETA-2 MICROGLOBULIN IN SERA OF PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 33  (4) , 535-541
Abstract
Antibodies to .beta.2 microglobulin were detected in the sera of patients with systemic lupus erythematosus (SLE). Using a Farr-type ammonium sulfate precipitation assay, test sera were reacted with 125I.beta.2 microglobulin, and immunoglobulins were precipitated by 50% saturated ammonium sulfate. Increased .beta.2 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 .beta.2 microglobulin. Direct validation was done by reacting 125I.beta.2 microglobulin with 4 SLE sera having increased 125I.beta.2 microglobulin binding activity, and subjecting the reactants to sucrose density gradient ultracentrifugation. Two peaks were obtained, one corresponding to free .beta.2 microglobulin, and the other to 7S material complexed to .beta.2 microglobulin. Normal sera demonstrated only 1 peak corresponding to unbound .beta.2 microglobulin. Assays of .beta.2 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 .beta.2 microglobulin was demonstrated to be IgG. Sera with abnormal .beta.2 microglobulin binding activity had higher titers of antinuclear antibody compared to those lacking such activity (t = 3.18; P < 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.