Characterization and identification of interleukin 1 receptors on bovine neutrophils

Interleukin 1 (IL-1) has been shown to modulate various functional activities of neutrophils, presumably by first binding to cell surface IL-1 receptors. In this study, we characterized and identified IL-1 receptors on bovine neutrophils using direct and competitive receptor binding studies and affinity cross-linking analysis. The results of direct binding studies demonstrated that bovine neutrophils bound 125I-labeled bovine IL-1 by a single affinity binding site (Kd = 4.6 nM, 5600 binding sites per cell). Competitive receptor binding studies demonstrated that unlabeled recombinant bovine IL-1 beta, murine IL-1 alpha, and human IL-1 beta competitively blocked neutrophil binding of 125I-labeled bovine IL-1 beta. In contrast, the IL-1 receptor antagonist (IL-1ra) demonstrated no detectable binding to bovine neutrophils as judged by direct and competitive receptor binding assays. Affinity cross-linking of 125I-labeled bovine IL-1 beta to neutrophils was used to identify cell surface IL-1 receptors. Two specific cross-linked products were observed with molecular sizes of 89 kd (a deduced receptor size of 71.5 kd) and more than 200 kd. The latter may indicate a complex of IL-1 receptor-associated signal-transducing components, IL-1 receptors, and IL-1. The presence of 100 nM unlabeled bovine, murine, or human IL-1 during the receptor binding and cross-linking reactions prevented the formation of cross-linked complexes of 125I-labeled bovine IL-1 beta and its receptor. In contrast, the IL-1ra failed to inhibit the formation of cross-linked complexes of 125I-labeled bovine IL-1 beta and its receptor.