Detection of interleukin 1α and 1β in rabbit tissues during endotoxemia using sensitive radioimmunoassays

Interleukin 1 (IL-1) is a primary mediator of a wide variety of immunologic and inflammatory responses, including reactions to microbial infections. To study this cytokine in an animal model, we have developed specific and sensitive radioimmunoassays for the quantitation of rabbit IL- 1α and IL-1β. The sensitivity (limit of detection at 95% confidence level) of our assay for IL-1α and 1β was 20-40 and 40-80 pg/ml, respectively. Recovery of IL-1 from tissues ranged from 75 to 107%, with a mean of 95% for IL-1α and 89% (range 19-98) for IL-1β. We employed these assays in in vivo and in vitro studies. In an in vivo model, we measured the amount of rabbit IL-1α and 1β protein present in brain, kidney, liver, lung, muscle, and spleen at various times after the injection of endotoxin. IL-1 was found in all tissues studied but largely in the spleen; IL-1 levels were transient, reaching peak levels by 4 h after injection of endotoxin and rapidly decreasing to low levels by 24 h. In similar in vitro studies, IL-1α levels reached peak elevation 6 h after addition of endotoxin, whereas IL-1β was maximal at 24 h. IL-1α was detected in all tissues; IL-1β was observed primarily in lung, kidney, and spleen. These studies establish the presence of IL-1 in various tissues during endotoxemia.