Publications

We have exploited strain-specific differences in the NK allorecognition repertoires to generate rat monoclonal antibodies against receptors involved in the control of allogeneic responses by rat NK cells. The monoclonal antibody STOK2 binds to a homodimeric glycoprotein that has been implicated as an inhibitory receptor for an MHC molecule in the PVG strain. In the present study, we haveidentified this glycoprotein as a novel rat Ly49 receptor (Ly49i2) containing an immunoreceptor tyrosine-based inhibitory motif. Ligation of the Ly49i2 receptor induces inhibitory signals, and Ly49i2 coprecipitates with the inhibitory tyrosine phosphatase SHP-1 in stably transfected RNK-16 cells. Moreover, it inhibits natural killing of lymphoblast targets and transfected fibroblast targets expressingthe classical MHC class Ia allele RT1-A1(c). Ly49i2, therefore, is an inhibitory receptor for specific MHC class Ia molecules, similar to inhibitory members of the mouse Ly49 family.

Previous studies of the rapid rejection of MHC-disparate lymphocytes in rats, named allogeneic lymphocyte cytotoxicity, have indicated that rat NK cells express activating receptors for nonclassical MHC class I allodeterminants from the RT1-C/E/M region. Using an expression cloning system that identifies activating receptors associated with the transmembrane adapter molecule DAP12, we have cloned a novel rat Ly-49 receptor that we have termed Ly-49 stimulatory receptor 3 (Ly-49s3). A newly generated anti-Ly-49s3 Ab, mAb DAR13, identified subpopulations of resting and IL-2-activated NK cells, but not T or B lymphocytes. Depletion of Ly-49s3-expressing NK cells drastically reduced alloreactivity in vitro, indicating that this subpopulation is responsible for a major part of the observed NK alloreactivity. DAR13-mediated blockade of Ly-49s3 inhibited killing of MHC-congenic target cells from the av1, n, lv1, and c haplotypes, but not from the u or b haplotypes. A putative ligand was mapped to the nonclassical MHC class I region (RT1-C/E/M) using intra-MHC recombinant strains. Relative numbers of Ly-49s3(+) NK cells were reduced, and surface levels of Ly-49s3 were lower, in MHC congenic strains expressing the putative Ly-49s3 ligand(s). In conclusion, we have identified a novel Ly-49 receptor that triggers rat NK cell-mediated responses.