HLA-specific and non-HLA-specific human NK receptors

Distribution of killer cell immunoglobulin-like receptors in the Greek population

The interaction between killer cell immunoglobulin-like receptors (KIR) expressed on natural killer (NK) cells, and human leukocyt antigen (HLA) molecules expressed on target cells is known to regulate the cytolytic activity. A wide range of KIR genotypes is observed in the population, as the number of KIR loci can vary. In the present study we have determined the frequencies and combinations of 13 KIR genes and two CD94:NKG2 receptor genes and their distribution in the two haplotype groups in a panel of 233 unrelated healthy Greek Caucasians. We have typed genomic DNA for the presence of the putative KIR loci KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL4, KIR3DL1, KIR3DL2, KIR3DL3, KIR2DS1, KIR2DS2, KIR2DS3, KIR2DS4, KIR2DS5, and KIR3DS1 using modified polymerase chain reaction sequence-specific primers. The frequency of KIR loci combined with the linkage disequilibrium values suggest that the Greek population shares several general features with other Caucasoid populations studied before, but still distinguishes itself by the increased or decreased frequency of several alleles. The majority of the 45 different KIR genotypes seen in Greeks have been observed in Caucasoid populations studied before. Nevertheless, two of these genotypes, although met in other populations, have not been found in Caucasians before. One individual possesses a novel profile with no KIR inhibitory gene. The A haplotypes remain the most prevalent, with AA1 being the most common genotype, and the number of inhibitory KIRs being more variable than the number of noninhibitory KIRs in most haplotypes.

Early signaling via inhibitory and activating NK receptors

This review focuses on recent findings on the structural features of inhibitory NK cell receptors containing immunoreceptor tyrosine-based inhibition motif (ITIM) and of NK cell activating receptors, both in human and mouse. First, the study of the inhibitory killer cell immunoglobulin-like receptors (KIR) unveiled the presence of intracytoplasmic ITIM and their capacity to recruit protein tyrosine phosphatases such as SHP-1 in vivo. A brief summary of the known SHP-1 targets may help us to understand the inhibition mediated by the KIR. The characterization of ITIM thus allowed the definition of a large group of inhibitory cell surface receptors. The second part of the review describes the known NK cell activating receptors. Most of them require association with ITAM-containing polypeptides in order to mediate cell activation.

2B4: an NK cell activating receptor with unique specificity and signal transduction mechanism

2B4 is a cell surface glycoprotein of the Ig-superfamily structurally related to CD2-like molecules such as CD2, CD48, CD58, CD84, Ly-9, and SLAM. Engagement of 2B4 on NK cells with specific antibodies or with its ligand CD48 enhances NK cell-mediated cytotoxicity. 2B4 is also expressed on both CD8+ T cells and myeloid cells, but its function in these cells remains unknown. Signal transduction through 2B4 involves recruitment of the SH2-containing adapter molecule SAP to cytoplasmic tyrosines. SAP is deficient in patients affected by X-linked lymphoproliferative disorder (XLP), which is triggered following EBV infection. Thus, an interruption of signaling through 2B4 and related molecules may impair NK cell recognition of virally infected cells and contribute to XLP.

Molecular and functional characterization of IRp60, a member of the immunoglobulin superfamily that functions as an inhibitory receptor in human NK cells

In this study we describe the functional and molecular characterization of IRp60 (inhibitory receptor protein 60), an inhibitory receptor expressed on all human NK cells. The IRp60 molecule has been identified by the generation of three novel monoclonal antibodies (mAb). Cross-linking of IRp60 by specific mAb strongly inhibits the spontaneous cytotoxicity of NK cells as well as the NK-mediated cytolytic activity induced via different non-HLA-specific or HLA-specific activating receptors. IRp60 is a 60-kDa glycoprotein that, upon sodium pervanadate treatment, becomes tyrosine phosphorylated and associates with the SH2-containing phosphatases SHP-1 and SHP-2. The IRp60 gene is located on human chromosome 17 and encodes a molecule belonging to the immunoglobulin (Ig) superfamily characterized by a single V-type Ig-like domain in the extracellular portion. The cytoplasmic tail contains three classical immunoreceptor tyrosine-based inhibitory motifs. Southern blot analysis revealed cross-hybridization with monkey and mouse genomic DNA, thus suggesting that IRp60 may be conserved among different species. Moreover, based on the use of different anti-IRp60 mAb, we could identify two IRp60 allelic variants. Since IRp60 is also expressed by other cell types, including T cell subsets, monocytes and granulocytes, it may play a more general role in the negative regulation of different leukocyte populations.