A quantitative radioimmunoassay for DNA-binding antibodies.

An RIA is described for the measurement of serum immunoglobulins capable of binding to double-stranded or single-stranded DNA. DNA attached to Sephadex G-50 by UV irradiation was used as a solid-phase immunoabsorbent for DNA-binding proteins from serum. GAH IgG (125l-labeled) and GAH IgM (131l-labeled) were used to detect the human immunoglobulins bound onto the washed DNA-Sephadex. The quantities of immunoglobulins bound were determined by comparison with a standard curve constructed by dilution of a plasma from a SLE patient containing known amount of bound, DNA-specific IgM and IgG. Another RIA was employed for measuring levels of IgG and IgM. In combination with measurements of the total serum IgM and IgG, the RIA allowed for the determination of the fraction of the total serum IgM or IgG that was specific for double- or single-stranded DNA. For pool of normal human sera the quantities were as follows: 0.04% of the total IgM and 0.001% of the total IgG bound double-stranded DNA; 0.22% of the total IgM and 0.05% of the total IgG bound single-stranded DNA. This capability is important because information regarding the quantitative measurement of antibodies to DNA and their class determination may be of significance in monitoring the status of subjects with SLE.