A radioimmunoassay for human interleukin-1 alpha: measurement of IL-1 alpha produced in vitro by human blood mononuclear cells stimulated with endotoxin.

A specific radioimmunoassay (RIA) for human interleukin-1 alpha (IL-1 alpha) which detects less than 25-50 pg/ml IL-1 alpha is described. Although human IL-1 alpha shares structural homology, receptors and multiple biological properties with IL-1 beta, this RIA does not detect human IL-1 beta or other human cytokines. We recovered nearly 100% of IL-1 alpha added to fresh human heparinized blood or freshly voided urine; in contrast, using a specific RIA for IL-1 beta, recovery of IL-1 beta added to fresh blood is approximately 50% reduced by nonspecific factors. In the present study, we employed this RIA to measure the amount of total (extracellular and cell-associated) immunoreactive IL-1 alpha produced by human blood mononuclear cells stimulated in vitro by different concentrations of endotoxin. Using ultrafiltered culture medium to reduce endotoxin content, there was no detectable (less than 50 pg/ml) IL-1 alpha produced after 24 hours. Endotoxin (0.5 ng/ml) induced a mean concentration of 900 pg/ml (range 180-1660 pg/ml). At higher concentrations of endotoxin (500 ng/ml), a mean of 6,990 pg/ml (range 415-11,900 pg/ml) was produced. These levels were comparable to the amount of IL-1 beta produced under similar culture conditions. The results indicate that IL-1 alpha can be measured independently of IL-1 beta in human body fluids and from human mononuclear cells.