Human anti-interleukin 1 alpha antibodies.

Autoantibodies to the cytokine interleukin (IL)-1 alpha are frequently found in sera of apparently healthy humans. We have developed a sensitive radioimmunoassay (RIA) and an indirect enzyme-linked immunosorbent assay (ELISA) for the detection of human serum antibodies to IL-1 alpha at concentrations below 10 pmol/l. The RIA is based on coprecipitation of 125I-labelled human recombinant IL-1 alpha (rIL-1 alpha) by rabbit antibodies to human immunoglobulins. The ELISA is based on recovery of added rIL-1 alpha to serum samples and takes advantage of the fact that free human autoantibodies to IL-1 alpha in a dose dependent manner reduce recovery of added rIL-1 alpha. The assays correlate exceedingly well (r = 0.99, P less than 0.001). Their inter- and intraassay coefficients of variation were less than 30% and less than 5% (RIA) and less than 20% and less than 10% (ELISA). Both assays were used to measure the presence of anti-IL-1 alpha antibodies in sera of patients with various autoimmune diseases. Autoantibodies to IL-1 alpha were detectable in up to 75% of these sera, but the frequencies and titers varied considerably between individuals with different diseases.