The Expression and Function of the NKRP1 Receptor Family in C57BL/6 Mice

Abstract

NKRP1 receptors were discovered more than 20 years ago, but due to a lack of appropriate reagents, our understanding of them has remained limited. Using a novel panel of mAbs that specifically recognize mouse NKRP1A, D, and F molecules, we report here that NKRP1D expression is limited to a subpopulation of NK cells, but in contrast to Ly49 receptors appears to be expressed in a normal codominant manner. NKRP1D− and NKRP1D+ NK cells are functionally distinct, NKRP1D+ cells showing reduced expression of various Ly49 receptors, elevated expression of CD94/NKG2 receptors, and higher IFN-γ secretion and cytotoxicity than NKRP1D− cells. Furthermore, NKRP1D+ NK cells were unable to kill transfected cells expressing high levels of Clr-b molecules, but readily killed MHC class-I-deficient blast cells that express only low levels of Clr-b. NKRP1A and NKRP1F were expressed at low levels on all splenic and bone marrow NK cells, but mAb-induced cross-linking of NKRP1A and NKRP1F caused no significant enhancement or inhibition of NK cell cytotoxicity and no detectable production of IFN-γ. NKRP1A, D, and F expression could not be detected on NKT cells, all of which express NKRP1C, and although some activated T cells expressed NKRP1C and perhaps low levels of NKRP1A, no significant expression of NKRP1D or F could be detected. NKRP1 molecules expressed on NK cells or transfectants were down-regulated by cross-linking with mAbs or cell surface ligands, and using this phenomenon as a functional assay for NKRP1-ligand interaction revealed that NKRP1F can recognize CLR-x.

Functional characterization of a conserved pair of NKR‐P1 receptors expressed by NK cells and T lymphocytes in liver and gut

“…NKR-P1F contains a transmembrane arginine that indicates that it may interact with an ITAM-containing adaptor such as FcRγ [32], but previous attempts to demonstrate an activating function for mouse NKR-P1F has been inconclusive [31]. As shown in Figure 2A, we observed a distinct Ca 2+ -response in NK cells in response to NKR-P1F cross-linking, but weaker than NKR-P1A.…”

“…NKR-P1F has a charged amino acid in the transmembrane domain that allows association with immunoreceptor tyrosine-based activation motif (ITAM)-bearing adapters supporting activating function, and an immunoreceptor tyrosinebased inhibitory motif (ITIM) in the intracellular part of NKR-P1G indicates inhibitory function. Antibodies toward mouse NKR-P1F have been described but have yielded inconclusive results in functional assays [31], therefore, it is still unclear if it is a functional activating receptor, and the native NKR-P1G receptor has remained uncharacterized to date. This paper presents the generation of monoclonal antibodies (mAbs) toward NKR-P1F and NKR-P1G, which have allowed us to study the protein expression and functional properties of the whole NKR-P1 family in rat.…”

Genetic Investigation of MHC-Independent Missing-Self Recognition by Mouse NK Cells Using an In Vivo Bone Marrow Transplantation Model

“…Elevated Ly49 receptor expression has been observed on NK cells from b 2 m 2/2 mice, which lack MHC-I ligands (35). Mechanistically, elevated NKR-P1B expression is likely posttranslational and due to a lack of receptor ligation or internalization following interaction with cognate ligand (on NK cells in cis or on neighboring cells in trans) (47,48 cell surface molecules (50). Therefore, these transplanted grafts promote disinhibition of both Ly49 + and NKG2/CD94 + NK subsets, which synergize to mediate rejection (51 These results suggest a model in which Clr-b expression may modulate surface expression of other Clr ligands.…”

Characterization of Alternatively Spliced Transcript Variants of CLEC2D Gene

“…This is the case for KLRB1 genes coding for the NKR-P1 family of receptors located in close proximity to CLEC2D genes coding for osteoclast inhibitory lectin molecules also named C-type lectin related (Clr) in mice and rats or lectin-like transcript 1 (LLT1) in humans. In mice, the inhibitory NKR-P1B/D was described to bind to Clrb, and the activating NKR-P1F was described to bind to Clrg and/or Clrx (2)(3)(4)(5). The functions of these interactions remain largely unknown.…”