| The identification and characterization of the receptors that dictate target specificity and regulate natural killer (NK) cell functions are fundamental to a better understanding of NK cell biology and the role that these cells play in immunity and disease. One approach to dissect the complexities of NK cell-target recognition is to exploit genetic differences among inbred strains of mice. We observed that NK cells derived from BALB/c mice fail to efficiently kill Chinese hamster ovary (CHO) cells when compared to NK cells from the C57BU6(B6) strain, despite equivalent capacity to kill other targets. We determined that differences at this locus, termed Chok, are manifested in vivo through a perforin-dependent mechanism. Using a CXB recombinant inbred mouse panel, we mapped this phenotypically defined locus to the natural killer gene complex (NKC) on mouse chromosome 6, a region known to contain multiple clustered gene families selectively expressed on NK cells. NK cells derived from two NKC congenic mouse strains were used to confirm our localization of Chok. BALB.B6- Cmv1r, a congenic strain in which the Cmv1 locus and other NKC loci from the B6 strain had been backcrossed onto the BALB/c background, displayed efficient lysis of CHO cells, establishing that this congenic strain possesses the B6 allele of Chok.;The localization of Chok to the NKC suggested that the Chok gene product, like other NKC-encoded molecules, may either activate or inhibit NK cell function. Efficient CHO cell lysis by BALB/c NK cells in a lectin-facilitated lysis assay indicated that the B6 allele of Chok encodes an activation receptor. We generated a monoclonal antibody (mAb) against the B6 Chok gene product by immunizing BALB/c mice with NK cells derived from the congenic BALB.B6-Cmvlr, and screening for mAbs that block B6-NK mediated CHO lysis. This monoclonal reagent facilitated the identification of the Chok antigen as Ly-49D, a member of the Ly-49 family of NK cell receptors. Gene transfer experiments established that Ly-49D is sufficient to confer functional CHO cell target specificity to BALB/c NK cells. These studies demonstrate, for the first time, a mouse NK cell receptor that directly activates natural killing. |
