Elevated levels of antibodies to polyuridylic acid detected and quantitated in systemic scleroderma patients by solid phase radioimmunoassay.

A solid support radioimmunoassay has been developed to detect immunoglobulin specific circulating antibodies to polyuridylic acid (Pol U), single-stranded RNA (ss RNA), and single-stranded DNA (ss DNA) in scleroderma and other connective tissue diseases. The assay system uses flex-vinyl microtiter plates on which bovine methyl albumin, the respective polynucleotide, a 1:80 dilution of patient serum, and tritiated high affinity anti-IgG, -IgA, or -IgM are layered. The individual wells containing the sandwich assay are then counted for the presence of labeled immunoglobulins and the results are reported in microgram/ml. Of the 30 scleroderma patients tested, only patients with diffuse systemic scleroderma had antibody levels reactive to Poly U > 4.0 microgram/ml and to ss RNA < 3.0 microgram/ml. Patients with linear scleroderma or morphea had antibody levels to Poly U < 3.0 microgram/ml and very little antibody to ss DNA or ss RNA in their sera. Partial cross reactivity to Poly U was found only in SLE patients with high levels of Ab to ss DNA. Insignificant levels of Poly U antibody were found in patients with other connective tissue diseases and in normal controls. High levels of serum antibody in patients which reacted with Poly U suggest active diffuse systemic scleroderma.