16 α-Hydroxyestrone induced adduct generate high affinity autoantibodies in SLE

Increased 16 α-hydroxyestrone (16 α-OHE₁) and autoantibodies against histone H1 (H₁) have been well described in systemic lupus erythematosus (SLE), but the combination effects of 16 α-OHE₁ and H₁ remains unclear. Here, we tried to assess the affinity and binding specificity of SLE autoantibodies against the 16 α-OHE₁-H₁ adduct. IgG was induced against this adduct and was also used as immunochemical probe for the estimation of 16 α-OHE₁ in the serum of SLE patients.

The affinity and binding specificities of SLE autoantibodies against 16 α-OHE₁-H₁ were determined by direct binding and inhibition ELISA as well as quantitative precipitation titration in 60 patients and 30 control subjects.

Purified SLE autoantibodies showed greater recognition to 16 α-OHE₁-H₁ over H₁ (p < 0.05) or 16 α-OHE₁ (p < 0.001). The relative affinity of SLE autoantibodies for 16 α-OHE₁-H₁, H₁ and 16 α-OHE₁ was 1.41 × 10^-7, 1.31 × 10^-6, and 1.03 × 10^-6, respectively. The concentration of 16 α-OHE₁ in the sera of SLE patients was significantly higher than controls (p < 0.05) as estimated by anti-16 α-OHE₁-H₁ antibodies.

High affinity of 16 α-OHE₁-H₁ with SLE autoantibodies might suggest an antigenic role of this adduct in the production of these autoantibodies. The anti-16 α-OHE₁-H₁ antibody is a good immunochemical probe to measure 16 α-OHE₁ in different SLE sera.