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

A specific radioimmunoassay (RIA) for human interleukin-1α (IL-1α) which detects less than 25-50 pg/ml IL-1α is described. Although human IL-1α shares structural homology, receptors and multiple biological properties with IL-1β, this RIA does not detect human IL-1β or other human cytokines. We recovered nearly 100% of IL-1α added to fresh human heparinized blood or freshly voided urine; in contrast, using a specific RIA for IL-1β, recovery of IL-1β 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-1α 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-1α 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-1β produced under similar culture conditions. The results indicate that IL-1α can be measured independently of IL-1β in human body fluids and from human mononuclear cells.