Anti-estrogen antibodies in systemic lupus erythematosus: a quantitative evaluation of serum levels.

We measured the beta-estradiol binding capacity of serum gamma-globulins in four subject groups; 1) normal men, 2) normal women who had never taken oral contraceptives, 3) normal women who had a history of oral contraceptive use and, 4) patients with systemic lupus erythematosus (SLE). We used dextran-coated charcoal to strip endogenous estradiol from serum proteins, added 3H-estradiol, and measured its association with proteins in various electrophoretic fractions following zone separation on agarose gels. Most of the bound radioactivity was present in the albumin, beta and gamma-globulin fractions. Binding to gamma-globulins was elevated in SLE patients, and normal controls who had taken oral contraceptives, as opposed to other controls (p less than 0.005). Gamma-region radioactivity could be removed by protein-G adsorption prior to zone electrophoresis. Isoelectric focusing revealed a pattern of tritiated-E2 binding consistent with polyclonal B-cell activation in all groups. There was no correlation between the extent of gamma-region binding and the total serum immunoglobulin level for any of the groups studied, nor was there a correlation between E2 binding and anti-DNA titers in the SLE group. The average anti-estradiol antibody concentrations in SLE sera (assuming equimolar binding) was 105 ng/ml (95% CL = 92-118), whereas their average anti-DNA antibody concentration was in the microgram/ml range. Thus, quantitatively, the level of anti-estradiol antibodies is at least an order of magnitude lower than the anti-DNA antibodies characteristic of this disease.