Receptor for interleukin-12. This subunit is the signaling component coupling to the JAK2/STAT4 pathway. Promotes the proliferation of T-cells as well as NK cells. Induces the promotion of T-cells towards the Th1 phenotype by strongly enhancing IFN-gamma production. Heterodimer/heterooligomer; disulfide-linked. The functional high affinity IL12 receptor is composed of I12RB1 and IL12RB2. Il12RB2 binds JAK2 (via its N-terminal) through a membrane-proximal region of the cytoplasmic domain. Interaction, in vitro and in vivo, with SOCS3 (via its SH2 domain) inhibits the STAT4-mediated activation. Binds STAT4 through a membrane-distal C-terminal region. Isoform 2 is expressed at similar levels in both naive and activated T-cells. Maximum levels in Th1 cells between day 3 and day 8 of activation. In vitro, up-regulated by IFN-alpha. The WSXWS motif appears to be necessary for proper protein folding and thereby efficient intracellular transport and cell-surface receptor binding. The box 1 motif is required for JAK interaction and/or activation. On IL12 binding, phosphorylated on C-terminal tyrosine residues by JAK2. Phosphorylation on Tyr-800 is required for STAT4 binding and activation, and for SOCS3 binding. Heterozygotic variants Gly-313 and Arg-720 are associated with atopy, an immunological condition that can lead to clinical symptoms such as allergic rhinitis, sinusitis, asthma and eczema. Belongs to the type I cytokine receptor family. Type 2 subfamily.