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* Department of Clinical Immunology and Biochemical Genetics, Royal Perth Hospital, Perth, Australia;
School of Surgery and Pathology, University of Western Australia, Crawley, Australia; and
Division of Immunology and Genetics, John Curtin School of Medical Research, Australian National University, Canberra, Australia
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Abstract |
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Introduction |
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TopAbstractIntroductionMethods and MaterialsResultsDiscussionReferences |
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-3 domain of all HLA molecules. The CD94/NKG2 receptors recognize class I HLA molecules indirectly by binding HLA-E that is surface expressed when it binds class I HLA signal sequence peptides. These families of receptors either inhibit function through immunotyrosine-based inhibitory motifs (ITIMs) or activate function through adaptor molecules (DAP-12) that associate with a charged residue in the transmembrane domain. The inhibitory receptors in these receptor families provide the mechanism by which NK cell effector function is prevented against cells expressing normal levels of class I HLA molecules, yet is permitted against cells expressing reduced levels of class I HLA molecules, such as on virally infected or tumor cells. The activating receptors provide a mechanism by which NK cell function is stimulated. Although HLA-E is known to be the ligand for the activating CD94/NKG2C receptor (3), there is doubt as to the effectiveness of class I HLA molecules as ligands for activating KIR (4).
KIR2DL4 (CD158d) is a member of the KIR gene family yet is unique in its genomic organization, expression, and function compared with other KIR (5). KIR2DL4 is considered a framework KIR gene, being present in almost all genomes. It is expressed in a codominant manner contrasting with at least some other KIR that may be monoallelically expressed (6). KIR2DL4 is reported to be expressed at the mRNA level, by all or most NK cells (7, 8, 9), contrasting with the expression of other KIR that is clonally distributed (7). Using polyclonal antisera, KIR2DL4 protein has been variously reported to be present on the surface of all peripheral NK cells (10) or restricted to uterine NK cells (11). Functionally, KIR2DL4 has been reported to be an inhibitory receptor for peripheral NK cells (12) and uterine NK cells (11), but ligation of KIR2DL4 with mAb results in activation of IFN-
secretion and cytotoxicity in peripheral NK cells (13). These different functional activities of KIR2DL4 are consistent with the fact that KIR2DL4 has both an ITIM in its cytoplasmic domain and a charged residue in the transmembrane domain. Both these domains in KIR2DL4 have been shown to be functional using chimeric receptors (14, 15). These data suggest KIR2DL4 may mediate different functions under different circumstances.
Any study of KIR2DL4 must take into account KIR2DL4 gene polymorphisms. We have previously reported two genetic variants of the transmembrane exon of the KIR2DL4 gene (16, 17). One allele (10A) produces only a single mRNA that appears to code for a classical membrane bound receptor that includes an inhibitory ITIM motif in its cytoplasmic tail. The alternate allele (9A) has a deletion of 1 adenine in a series of 10 adenines at the end of the transmembrane exon.4 The 9A allele produces a small amount of mRNA that includes the transmembrane exon (9ATr). However, the frame shift caused by the deletion results in a stop codon 4 codons into exon 7, the first cytoplasmic exon, suggesting a protein with a truncated cytoplasmic tail. The protein product from this mRNA could conceivably be expressed on the membrane but would lack the inhibitory ITIM motif. The other mRNA transcript produced by the 9A allele (9A 
TM) is more abundant but omits the transmembrane exon, making it unlikely that any translated protein could be expressed on the membrane. Because the 9A and 10A alleles of KIR2DL4 each have a population frequency of 50% (16), this suggests balancing selection and functional importance. Apparent differences in expression and function reported for this receptor could be explained by different groups having studied subjects with different transmembrane genotypes. This study reports on the expression and function of KIR2DL4 on NK cells in individuals expressing the 9A and/or 10A alleles. We show that KIR2DL4 cell surface expression is restricted to individuals with at least one 10A allele and that KIR2DL4 is constitutively expressed by only the minor CD56bright peripheral blood NK cell subset but can be induced on a majority of NK cells following in vitro culture. Furthermore, we show KIR2DL4 transmembrane genotype influences activation of cytotoxic function.
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Methods and Materials |
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Blood samples for expression of KIR2DL4 on peripheral NK cells were obtained from randomly selected donors attending the Australian Red Cross Blood Service in Perth and Canberra. Whole blood was obtained by venipuncture and collected into heparinized tubes. For some experiments, whole blood was treated with NH4Cl to lyse erythrocytes and immediately used for analysis by flow cytometry. For other experiments, mononuclear cells were obtained by Ficoll-Hypaque (Pharmacia, Uppsala, Sweden) density gradient centrifugation, stored frozen in aliquots in liquid nitrogen, and thawed as required.
mAbs and immunofluorescence flow cytometry
An IgG1 mAb (No. 33) and IgM mAb (No. 64) to KIR2DL4 were produced as previously described (13) and kindly provided by Drs. E. Long and S. Rajagopolan (Laboratory of Immunogenetics, National Institutes of Health, Bethesda, MD). These Abs were used in the Perth laboratory in conjunction with a FITC-conjugated goat anti-mouse Ig(H + L) (Caltag Laboratories, Burlingame, CA) for staining of peripheral NK cells. In the Perth laboratory, the following mAbs were obtained from commercial sources: PE-Cy5-conjugated CD3 (UCHT1, IgG1) and PE-conjugated CD56 (N901, IgG1), both from BD PharMingen (San Jose, CA). In the Canberra laboratory, the following Abs were obtained from commercial sources: PE-conjugated CD56 (IgG2a) from Chemicon Europe (Chandlers Ford, UK); FITC-conjugated CD3 and FITC-conjugated CD19 from BD PharMingen. The NKG2D mAb 149804 (IgG1) was a kind gift from Dr. J. P. Houchins (R&D Systems, Minneapolis, MN). In the Canberra laboratory, mAb 64 was detected using biotinylated goat anti-mouse IgM (Chemicon, Boronia, Australia) and streptavidin-Cy-Chrome (BD PharMingen). Reagents were incubated with cells for 30 min on ice, centrifuged, and washed twice between incubations. All reagents were titrated and used at optimum concentrations. Cells were analyzed using either a BD Biosciences FACScan (San Jose, CA) in Canberra or a Coulter EPICS XL-MCL flow cytometer (Beckman Coulter, Fullerton, CA) in Perth. Lymphocytes were gated electronically on the basis of forward and side scatter parameters. NK cells were identified as CD3- CD19- lymphocytes.
Isolation and culture of NK cells
PBMC were labeled with mAbs as described above, and NK cells were sorted using a BD Biosciences FACStar gating electronically on lymphocytes and selecting cells that were CD3-FITC- and CD19-FITC-. For sorting CD56bright or CD56dim NK subsets, NK cells were first isolated from PBMC using the RosetteSep (Stemcell Technologies, Vancouver, Canada) method of negative selection adapted for use with frozen PBMC (18) before labeling with CD56-PE. Sorted NK subsets were expanded in culture using previously described methods (19). Briefly, NK cell proliferation was initiated using gamma-irradiated MM-170 malignant melanoma cells or JY B-lymphoblastoid cells (19) with medium containing 200 U/ml rIL-2 (generously provided by Dr. G. Zurawski, DNAX Research Institute of Cellular and Molecular Biology, Palo Alto, CA). In some experiments, sorted NK cells were labeled with CFSE (Molecular Probes, Eugene, OR) before culture to monitor cell division (20). Proliferating NK cells were maintained after day 8 by subculturing as required in medium containing 50 U/ml rIL-2. Cultured cells were verified as NK cells (CD3-CD94+) before functional analysis.
Cytotoxicity assays
Cytotoxicity was measured in a 4-h 51Cr release assay using 5000 51Cr-labeled target cells as described previously (19). The FcRII+ mouse mastocytoma cell line P815 was used as the target cell. The E:T ratio was 2:1. mAb concentrations that were optimal in the assay were usually one-tenth of that giving maximum staining by flow cytometry.
cDNA production
Total cellular RNA was extracted from 2 x 106 cells using Trizol reagent (Life Technologies, Gaitherburg, MD) according to the manufacturer’s instructions. First strand cDNA was synthesised from 5 µg of total RNA using oligo(dT)12–18 primer and 200 U of Superscript II reverse transcriptase (Invitrogen, Carlsbad, CA). The reaction was incubated for 1 h at 42°C and then terminated by heating to 65°C for 15 min. Samples were digested with 1 U of RNase H (Roche Diagnostic Australia, Castle Hill, Australia) to remove the complementary RNA strand.
Cloning and transfections
KIR2DL4 transcripts were amplified using a forward primer specific for exon 3 (D0) of KIR2DL4 and a reverse primer specific for exon 8 of KIR2DL4 (10). PCR products were ligated into pGEM-T EasyVectorII (Promega, Annandale, Australia) and cloned into JM109 cells. Individual clones were sequenced to determine the transmembrane type and Ig domain sequences. Clones representing different transmembrane types and Ig domain sequences were excised from pGEM-T using BglII and SalI (Promega) and inserted into the pDisplay expression vector (Invitrogen) immediately downstream and in frame with the hemagglutinin (HA) tag sequence. The expression constructs were cloned in TOP10F'OneShotTM bacteria (Invitrogen). Equal amounts of cloned pDisplay containing different KIR2DL4 inserts were transfected into 293T Phoenix cells (courtesy of Dr. D. Eisen, Institute of Child Health Research, Perth, Western Australia) using LipoFectamine-2000 (Invitrogen) and the expression tested using anti-HA ascites (courtesy of Dr. E. Ingley Medical Research Foundation, Royal Perth Hospital, Perth, Australia), KIR2DL4 mAbs 33 or 64, and IgG or IgM isotype controls (Beckman Coulter) followed by a FITC-conjugated anti-mouse Ig (H + L) (Caltag Laboratories). Untransfected cells and control transfections using the pDisplay vector without a KIR2DL4 insert were included. Transfection efficiency was monitored by cotransfection with a pCDNA3.1/lacZ (courtesy of Dr. Degli-Esposti, Department of Microbiology, QEII Medical Center, Perth, Western Australia) and staining of transfected cells with the fluorescent LacZ substrate resorufin D-galactosylpyranoside (Sigma-Aldrich, Sydney, Australia). KIR2DL4 expression was compared in cells with equal levels of LacZ expression 48 h after transfection. Fig. 1 shows the cDNAs used, the allele from which they were derived, the structure of the protein predicted from the cDNA, and the GenBank accession number corresponding to the cDNA sequence.
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Exons 6 through 7 were amplified from genomic DNA using primers and method previously described (16). PCR products were sequenced in both directions using M13F and M13R primers and big-dye primer chemistry to determine the transmembrane genotype. Individuals homozygous for the 9A genotype and 10A genotype were in all cases shown to have a series of 9 and 10As, respectively, and the entire sequence was homozygous. The sequence of heterozygotes was homozygous until the 9th A (forward primer) or 9th T (reverse primer), after which it became heterozygous.
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Results |
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In addition to the transmembrane polymorphism, we have previously reported the existence of two common alleles of exons 3 and 4 encoding the Ig domains of KIR2DL4. Before using mAb 33 as a reagent for the investigation of KIR2DL4 expression, the reactivity of mAb 33 for the receptors encoded by each of the two common alleles of the Ig domains was tested. cDNAs Ig1-Tm10A and Ig2-Tm10A of the two common Ig domain alleles (alleles 1F and 2F, respectively, in the paper of Witt et al. (16)) were cloned into the pDisplay expression vector, which added an HA tag to the N-terminal end of the protein. This allowed the use of an anti-HA Ab to check expression of the different KIR2DL4 proteins after transfection of 293T cells. Both cDNAs had 10A sequences in the transmembrane exon and were therefore expected to code for full length receptors. The transfected 293T cells were then stained with an anti-HA Ab and mAb 33. The receptors encoded by both alleles were equally well stained with anti-HA Ab (data not shown). As shown in Fig. 2, the receptors encoded by both alleles were also stained equally well with mAb 33, indicating that mAb 33 is a valid reagent with which to investigate KIR2DL4 expression on peripheral NK cells. Identical results were obtained with KIR2DL4 mAb 64. These mAb have been shown previously not to react with other members of the KIR family (13).
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To determine whether the receptors produced by different transmembrane alleles of KIR2DL4 can be expressed on the membrane, 293T cells were transfected with full length cDNA having a transmembrane domain, long cytoplasmic tail, and the Ig domains of alleles 1F or 2F (Ig1-Tm10A and Ig2-Tm10A), a cDNA postulated to encode a truncated receptor having the Ig domains of allele 2 (Ig2-Tm9ATr), or a cDNA having the Ig domains of allele 2 but lacking a transmembrane domain (Ig2-Tm9ADel). Transcripts representing a truncated receptor and having the Ig domains of allele Ig1 do not occur naturally, but such a transcript was discovered during cloning of the Ig1 transcripts, probably created by in vitro polymerase slippage. This artificial transcript having the Ig domains of allele Ig1 but postulated to encode a truncated cytoplasmic tail (Ig1-Tm10ATr) was also transfected. Transfected cells were tested with anti-HA Ab and KIR2DL4 mAb 33. Fig. 3 shows that the protein encoded by the transcript postulated to encode a truncated receptor (Ig2-Tm9ATr) is expressed but relatively weakly compared with that encoded by the full length transcript (Ig2-Tm10A), whereas the receptor encoded by the transcript lacking the transmembrane exon (Ig2-Tm9ADel) is not detectable. Cells transfected with the cDNA encoding a truncated receptor of the 1F allele (Ig1-Tm10ATr) produced by in vitro artifact stained with the same intensity as cells transfected with cDNA encoding the naturally occurring truncated receptor derived from the Ig2 allele (data not shown). Identical results were obtained using either anti-HA Ab (Fig. 3) or KIR2DL4 mAb 33 (data not shown).
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The transfection data suggested that individuals with different transmembrane genotypes may differ in their expression of KIR2DL4. Having established that the KIR2DL4 mAbs react with receptors encoded by both common Ig domain alleles, we examined KIR2DL4 expression on peripheral NK cells from 27 individuals. Interestingly, when expressed, positive staining for KIR2DL4 was weak and observed only on the minor CD56bright population of NK cells. Representative data (Fig. 4) show that expression of KIR2DL4 on CD56bright NK cells varied between different individuals (Fig. 4, A and B), and in some cases KIR2DL4 was not detectable (Fig. 4C). Staining of CD56dim NK cells was not observed in any of the 27 subjects tested. To determine whether the presence of KIR2DL4-positive NK cells correlates with transmembrane genotype, the proportion of KIR2DL4-positive cells among CD56bright NK cells of 27 individuals was determined and related to their transmembrane genotype (Fig. 5). Although Fig. 4 shows that there is a shift of the entire CD56bright population when Ab to KIR2DL4 is used, we assessed staining intensity by measuring the proportion of cells with an intensity greater than an arbitrary fluorescence cutoff. The results in Fig. 5 are therefore likely to be an underestimate of the proportion of CD56bright NK cells expressing KIR2DL4. The data show that most subjects with the 10A/10A or 9A/10A genotypes had at least 10% of CD56bright cells staining for KIR2DL4, whereas there was little or no KIR2DL4 staining for any of the subjects homozygous for the 9A allele. Age and sex did not appear to correlate with low numbers of KIR2DL4 expressing cells in those subjects who had the 9A/10A or 10A/10A genotype. Health status is also unlikely to be relevant to low staining as all subjects tested were healthy blood donors.
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NK cells were purified by negative selection from subjects with different KIR2DL4 transmembrane genotypes and established in culture with IL-2 and irradiated feeder cells. After 16 to 20 days of culture, KIR2DL4 expression was assessed using indirect staining with the IgM mAb 64, biotinylated anti-mouse IgM and streptavidin-Cy-Chrome. In contrast to uncultured peripheral NK cells among which only a small percentage of all NK cells have detectable staining for KIR2DL4, a considerable proportion of cultured cells from 10A/10A or 9A/10A subjects stained positively for KIR2DL4 (Fig. 6). In contrast, for cultured cells from 9A/9A subjects, much weaker staining (donor 2458) or no staining (donor 27629) was observed. Thus, for individuals in whom genotype analysis predicts that KIR2DL4 will be poorly expressed, the culture conditions were unable to induce cell surface expression of KIR2DL4.
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NK cells that were cultured and tested for KIR2DL4 expression (Fig. 6) were also tested for cytotoxicity in a redirected lysis assay. As a positive control, cytotoxicity stimulated through NKG2D was assessed, because for all donors NKG2D was expressed on all NK cells and at similar levels regardless of KIR2DL4 genotype (data not shown). The data in Fig. 8 demonstrate that cultured NK cells from subjects of 10A/10A and 9A/10A genotype kill the FcRII+ target cell P815 in the presence of KIR2DL4 mAb 33, but cytotoxicity is weak compared with killing in the presence of NKG2D mAb. For cultured NK cells from donors of 9A/9A genotype, killing though KIR2DL4 was almost undetectable above the background killing induced by the control CD56 mAb. The KIR2DL4 genotype dependency of cytolytic activity was seen also for NK cells generated from the CD56bright and CD56dim subsets (data not shown).
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Discussion |
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In freshly isolated peripheral NK cells, KIR2DL4 expression was found exclusively on a proportion of the minor CD56bright subset. This was demonstrated with the KIR2DL4 mAbs 33 and 64 that were shown to react with the receptors encoded by the two most common Ig domain alleles of KIR2DL4, alleles 1 and 2 (16). Selective expression of KIR2DL4 on CD56bright NK cells has not been reported previously but may explain why some groups have found KIR2DL4 to be either not expressed or expressed weakly on peripheral NK cells (11). Expression of KIR2DL4 on CD56bright NK cells is weak relative to other membrane markers, and detection requires attention to the sensitivity of reagents and instrumentation. A second factor complicating the detection of KIR2DL4 on peripheral NK cells is the influence of the transmembrane genotype on membrane expression. KIR2DL4 expression was detectable only on the CD56bright cells of individuals with at least one 10A allele. When peripheral blood NK cells were stimulated to proliferate in culture, KIR2DL4 cell surface expression increased on the CD56bright NK cell subset from individuals with a 10A allele. Importantly, KIR2DL4 was induced on the CD56dim NK cell subset. This is a unique observation, because when studied, expression of other KIR is stable irrespective of the activation status of NK cells (6). It has been reported that KIR2DL4 mRNA is detectable in most peripheral NK cells (7, 9). In the study by Husain (9), resting CD56positive NK cells were analyzed by single-cell PCR, but whether these NK cells were CD56bright or CD56dim was not stated. In the studies by Valiante et al. (7) and Cantoni et al. (8), culture-generated NK cell clones were analyzed, and in this case NK cell proliferation would be expected to induce KIR2DL4 expression. It is also possible that mRNA for KIR2DL4 is present in all NK cells and that its translation into cell surface-expressed protein occurs once NK cell proliferation is initiated.
The observation that KIR2DL4 is constitutively expressed on CD56bright NK cells may account for the observation that KIR2DL4 mAb selectively stimulates IFN- production from freshly isolated peripheral blood NK cells yet little cytotoxicity (13). This effector phenotype is characteristic of CD56bright peripheral blood NK cells (23). Uterine NK cells are predominantly CD56bright (24), and it may be that they are derived from CD56bright peripheral blood NK cells. The expression of KIR2DL4 on uterine NK cells (11) and its selective expression on CD56bright peripheral blood NK cells are consistent with this notion. It also has been shown that human CD56bright NK cells harvested from peripheral blood adhere to endothelium of murine uterine tissue sections (25). However, our data with cultured NK cells show that CD56dim NK cells acquire KIR2DL4 and show enhanced expression of CD56. Cultured NK cells express activation markers such as CD45R0 (26), markers that are seen on uterine NK cells (27). Thus, it is also possible that uterine NK cells are derived from the CD16- subset of CD56dim peripheral blood NK cells (23) after activation. That KIR specific for HLA-C alleles are expressed on uterine NK cells (27) yet apparently not on CD56bright peripheral blood NK cells (28) is consistent with the notion that a proportion of uterine NK cells are derived from CD56dim peripheral blood NK cells.
In the present study, redirected lysis assays showed that KIR2DL4 behaves like an activating receptor for cytotoxicity. These findings are consistent with a previous report (13) using cultured NK cells. We observed for NK cells from individuals with at least one 10A allele that the cytotoxic activity stimulated through KIR2DL4 is weak compared with that stimulated through the activating receptor NKG2D. This was the case for 10A homozygote and heterozygote individuals. This weak cytotoxic activity may reflect competing activation signals generated by an adaptor molecule and inhibitory signals produced by the inhibitory ITIM in the cytoplasmic tail. However, interestingly for some heterozygotes, cytotoxicity was weaker than expected given that the level of KIR2DL4 membrane expression was similar to that of homozygotes (data not shown). Peripheral blood NK cells from 9A/9A subjects have little if any membrane expression of KIR2DL4, which was not increased after culture. These cells also had barely detectable cytotoxicity. The present studies did not examine the influence of transmembrane genotype on IFN- secretion, but this is clearly of interest in view of the data of Rajagopalan and Long (13) and the role of NK cell-derived IFN- in modifying uterine arteries (reviewed by Croy et al. (29)).
Whether KIR2DL4 can behave as an inhibitory receptor under any circumstances is still not clear. The single ITIM in KIR2DL4 has been demonstrated to be functional when uncoupled from the transmembrane arginine (14, 15), and it seems unlikely that this inhibitory potential would be retained in a functional form if it were never used. Whereas we and others (13, 15), using peripheral NK cells and anti-KIR2DL4 Ab in redirected lysis assays, have demonstrated activating activity for KIR2DL4, others using HLA-G expressing cells as the target (11, 12) and uterine NK cells (11) have provided evidence that KIR2DL4 may have an inhibitory function. These contrasting data suggest that KIR2DL4 may be capable of both functions under different circumstances. However, it is clear that the KIR2DL4 receptor encoded by the 9A transmembrane allele cannot mediate an inhibitory function given the absence of a cytoplasmic tail containing an ITIM.
A role for KIR2DL4 in pregnancy is yet to be established. There is evidence that HLA-G is a ligand for KIR2DL4 (8, 10, 11), and HLA-G was originally reported to be expressed uniquely on trophoblasts (30). The absence of a fully functional KIR2DL4 receptor on peripheral blood NK cells in 25% of the population raises doubts as to the importance of KIR2DL4 in pregnancy. Indeed, we have not found any deviation from control frequencies for the KIR2DL4 transmembrane genotypes in problems associated with pregnancy including pre-eclampsia (16) and recurrent miscarriage (our manuscript in preparation). An essential function for KIR2DL4 in successful pregnancy is also questionable with the recent description of a multiparous woman lacking a KIR2DL4 gene (31). It is also the case that HLA-G binds the inhibitory LILRB1 and LILRB2 receptors and is indirectly monitored via HLA-E binding of the CD94/NKG2 receptors, providing alternative means for HLA-G recognition in addition to KIR2DL4. The LILRB1 and CD94/NKG2 receptors as well as other KIR also monitor HLA-C, the only classical class I HLA molecule expressed on trophoblast cells (32). Clearly multiple NK cell receptors and ligands may be involved in regulating the interaction between mother and fetus.
The maintenance of the 9A and 10A alleles of KIR2DL4 at gene frequencies of 0.5 in humans is indicative of balancing selection. In other cases of balancing selection (e.g., 
-thalassemia) homozygosity for the wild-type allele and heterozygosity are advantageous genotypes under different circumstances. Homozygosity for the mutant allele is generally disadvantageous, but the mutant allele is maintained in the population due to circumstances that select for the heterozygous genotype. If the 9A allele can be considered the mutant, then this model predicts that homozygosity for the 9A allele will be disadvantageous under some circumstances. The 9A and 10A alleles of KIR2DL4 are present in chimpanzees (33) and pigmy chimps (34), demonstrating that these alleles have been in existence for a long time. It remains to be determined what role if any this polymorphism of the KIR2DL4 gene has in terms of a selective advantage. Nonetheless, our study has clearly shown that this polymorphism influences both receptor expression and the activation of NK cell cytotoxicity.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Campbell Witt, Department of Clinical Immunology and Biochemical Genetics, Royal Perth Hospital, Wellington Street, Perth, Western Australia, 6000. E-mail address: Campbell.Witt{at}health.wa.gov.au
3 Abbreviations used in this paper: KIR, killer Ig-like receptors; LILR, leukocyte Ig-like receptors; ITIM, immunotyrosine-based inhibitory motifs; HA, hemagglutinin.
4 In different alleles, the end of exon 6 in the genomic sequence consists of either 9 or 10 adenines. However, because the first nucleotide of exon 7 is also an adenine, the 9A and 10A genomic sequences result in a series of 10As and 11As, respectively, in the mRNA. Furthermore, in some alleles, the last genomic adenine may be replaced with a guanine.
Received for publication November 21, 2002. Accepted for publication June 5, 2003.
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production but not cytotoxicity by the killer cell Ig-like receptor KIR2DL4 (CD158d) in resting NK cells. J. Immunol. 167:1877.This article has been cited by other articles:
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  J.P. Goodridge, L.J. Lathbury, E. John, A.K. Charles, F.T. Christiansen, and C.S. Witt The genotype of the NK cell receptor, KIR2DL4, influences INF{gamma} secretion by decidual natural killer cells Mol. Hum. Reprod., August 1, 2009; 15(8): 489 - 497. [Abstract] [Full Text] [PDF]
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 E. Morel and T. Bellon HLA Class I Molecules Regulate IFN-{gamma} Production Induced in NK Cells by Target Cells, Viral Products, or Immature Dendritic Cells through the Inhibitory Receptor ILT2/CD85j J. Immunol., August 15, 2008; 181(4): 2368 - 2381. [Abstract] [Full Text] [PDF]
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 A. Iannello, O. Debbeche, S. Samarani, and A. Ahmad Antiviral NK cell responses in HIV infection: I. NK cell receptor genes as determinants of HIV resistance and progression to AIDS J. Leukoc. Biol., July 1, 2008; 84(1): 1 - 26. [Abstract] [Full Text] [PDF]
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S. M. Shahjahan Miah, T. L. Hughes, and K. S. Campbell KIR2DL4 Differentially Signals Downstream Functions in Human NK Cells through Distinct Structural Modules J. Immunol., March 1, 2008; 180(5): 2922 - 2932. [Abstract] [Full Text] [PDF]
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E. Estefania, R. Flores, N. Gomez-Lozano, H. Aguilar, M. Lopez-Botet, and C. Vilches Human KIR2DL5 Is an Inhibitory Receptor Expressed on the Surface of NK and T Lymphocyte Subsets J. Immunol., April 1, 2007; 178(7): 4402 - 4410. [Abstract] [Full Text] [PDF]
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K. Wendt, E. Wilk, S. Buyny, J. Buer, R. E. Schmidt, and R. Jacobs Gene and protein characteristics reflect functional diversity of CD56dim and CD56bright NK cells J. Leukoc. Biol., December 1, 2006; 80(6): 1529 - 1541. [Abstract] [Full Text] [PDF]
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T. Gonen-Gross, H. Achdout, T. I. Arnon, R. Gazit, N. Stern, V. Horejsi, D. Goldman-Wohl, S. Yagel, and O. Mandelboim The CD85J/Leukocyte Inhibitory Receptor-1 Distinguishes between Conformed and {beta}2-Microglobulin-Free HLA-G Molecules J. Immunol., October 15, 2005; 175(8): 4866 - 4874. [Abstract] [Full Text] [PDF]
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W. Leung, R. Iyengar, B. Triplett, V. Turner, F. G. Behm, M. S. Holladay, J. Houston, and R. Handgretinger Comparison of Killer Ig-Like Receptor Genotyping and Phenotyping for Selection of Allogeneic Blood Stem Cell Donors J. Immunol., May 15, 2005; 174(10): 6540 - 6545. [Abstract] [Full Text] [PDF]
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 L. Abi-Rached and P. Parham Natural selection drives recurrent formation of activating killer cell immunoglobulin-like receptor and Ly49 from inhibitory homologues J. Exp. Med., April 18, 2005; 201(8): 1319 - 1332. [Abstract] [Full Text] [PDF]
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A. Kikuchi-Maki, T. L. Catina, and K. S. Campbell Cutting Edge: KIR2DL4 Transduces Signals into Human NK Cells through Association with the Fc Receptor {gamma} Protein J. Immunol., April 1, 2005; 174(7): 3859 - 3863. [Abstract] [Full Text] [PDF]
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H.-I. Trompeter, N. Gomez-Lozano, S. Santourlidis, B. Eisermann, P. Wernet, C. Vilches, and M. Uhrberg Three Structurally and Functionally Divergent Kinds of Promoters Regulate Expression of Clonally Distributed Killer Cell Ig-Like Receptors (KIR), of KIR2DL4, and of KIR3DL3 J. Immunol., April 1, 2005; 174(7): 4135 - 4143. [Abstract] [Full Text] [PDF]
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J. van Bergen, A. Thompson, A. van der Slik, T. H. M. Ottenhoff, J. Gussekloo, and F. Koning Phenotypic and Functional Characterization of CD4 T Cells Expressing Killer Ig-Like Receptors J. Immunol., December 1, 2004; 173(11): 6719 - 6726. [Abstract] [Full Text] [PDF]
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 C.S. Witt, J. Goodridge, M.G. Gerbase-DeLima, S. Daher, and F.T. Christiansen Maternal KIR repertoire is not associated with recurrent spontaneous abortion Hum. Reprod., November 1, 2004; 19(11): 2653 - 2657. [Abstract] [Full Text] [PDF]
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A. Kikuchi-Maki, S.-i. Yusa, T. L. Catina, and K. S. Campbell KIR2DL4 Is an IL-2-Regulated NK Cell Receptor That Exhibits Limited Expression in Humans but Triggers Strong IFN-{gamma} Production J. Immunol., October 1, 2003; 171(7): 3415 - 3425. [Abstract] [Full Text] [PDF]
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