A functional interleukin 12 receptor complex is composed of two ß-type cytokine receptor subunits, IL-12R ß1 (100 kDa) and IL-12R ß2 (130 kDa), each independently exhibiting a low affinity for IL-12. Co-expression leads to the formation of high-affinity IL-12-binding sites and reconstitution of IL-12-dependent signaling. IL-12R ß1 is a member of the hemopoietin receptor superfamily, bearing strong homology to gp130. IL-12 receptors are expressed primarily on activated T cells and natural killer (NK) cells, and activation of human PBMCs results in the up-regulation of IL-12R ß1 expression and IL-12 binding. Alternately, individuals that are genetically deficient in IL-12R ß1 produce greatly reduced IFN-? levels compared to healthy individuals. IL-12 induces tyrosine phosphorylation of a recently identified 85 kDa component of the IL-12 receptor complex that associates with the IL-12R ß1 subunit.Synonyms: IL-12 receptor beta, IL-12R-beta-1, IL-12RB1, IL12 receptor beta component, Interleukin-12 receptor beta-1 chain