A point mutation in the IL-12Rβ2 gene underlies the IL-12 unresponsiveness of Lps-defective C57BL/10ScCr mice

Lps-defective C57BL/10ScCr (Cr) mice are homozygous for a deletion encompassing Toll-like receptor 4 that makes them refractory to the biological activity of LPS. In addition, these mice exhibit an inherited IL-12 unresponsiveness resulting in impaired IFN-gamma responses to different microorganisms. By positional cloning methods, we show here that this second defect of Cr mice is due to a mutation in a single gene located on mouse chromosome 6, in close proximity to the Ig kappa locus. The gene is IL-12R beta2. Cr mice carry a point mutation creating a stop codon that is predicted to cause premature termination of the translated IL-12R beta2 after a lysine residue at position 777. The truncated beta2 chain can still form a heterodimeric IL-12R that allows phosphorylation of Janus kinase 2, hut, unlike the wild-type IL-12R, can no longer mediate phosphorylation of STAT4. Because the phosphorylation of STAT4 is a prerequisite for the IL-12-mediated induction of IFN-gamma, its absence in Cr mice is responsible for their defective IFN-gamma response to microorganisms.