Human leukocyte antigen-C and killer immunoglobulin-like receptors in reproductive medicine. / Antígeno leucocitario humano C y receptores tipo inmunoglobulina en medicina reproductiva.

Proper communication between natural killer cells and the human leukocyte antigens of the embryonic trophoblast at the maternal-fetal interface during pregnancy is essential for successful reproduction. However, specific combinations of embryonic human leukocyte antigen-C with killer immunoglobulin-like receptors on decidual natural killer cells (the immunological code of pregnancy) can be associated with obstetric morbidity and pregnancy loss. This article presents an updated review of the mechanisms underlying the interaction between embryonic human leukocyte antigen-C and maternal killer immunoglobulin-like receptors and their relevance to the physiology and pathophysiology of human reproduction.

Una adecuada comunicación entre las células asesinas naturales en la interfase materno-fetal con las moléculas de los antígenos de histocompatibilidad del trofoblasto embrionario es clave en el éxito de la reproducción. Sin embargo, combinaciones de determinados antígenos leucocitarios humanos tipo C embrionarios con los receptores tipo inmunoglobulina presentes en las células asesinas naturales deciduales (el código inmunológico del embarazo), pueden asociarse con morbilidad obstétrica y pérdidas gestacionales. En este artículo se presenta una revisión actualizada de los mecanismos subyacentes a la interacción entre el antígeno de histocompatibilidad tipo C embrionario y los receptores tipo inmunoglobulina maternos, y su relevancia tanto en la fisiología como en la fisiopatología de la reproducción humana.

Missing or altered self: human NK cell receptors that recognize HLA-C.

Natural killer (NK) cells are fast-acting and versatile lymphocytes that are critical effectors of innate immunity, adaptive immunity, and placental development. Controlling NK cell function are the interactions between killer-cell immunoglobulin-like receptors (KIRs) and their HLA-A, HLA-B and HLA-C ligands. Due to the extensive polymorphism of both KIR and HLA class I, these interactions are highly diversified and specific combinations correlate with protection or susceptibility to a range of infectious, autoimmune, and reproductive disorders. Evolutionary, genetic, and functional studies are consistent with the interactions between KIR and HLA-C being the dominant control mechanism of human NK cells. In addition to their recognition of the C1 and C2 epitopes, increasing evidence points to KIR having a previously unrecognized selectivity for the peptide presented by HLA-C. This selectivity appears to be a conserved feature of activating KIR and may partly explain the slow progress made in identifying their HLA class I ligands. The peptide selectivity of KIR allows NK cells to respond, not only to changes in the surface expression of HLA-C, but also to the more subtle changes in the HLA-C peptidome, such as occur during viral infection and malignant transformation. Here, we review recent advances in understanding of human-specific KIR evolution and how the inhibitory and activating HLA-C receptors allow NK cells to respond to healthy cells, diseased cells, and the semi-allogeneic cells of the fetus.

Resurrecting KIR2DP1: A Key Intermediate in the Evolution of Human Inhibitory NK Cell Receptors That Recognize HLA-C.

KIR2DP1 is an inactive member of the human lineage III KIR family, which includes all HLA-C-specific receptor genes. The lethal, and only, defect in KIR2DP1 is a nucleotide deletion in codon 88. Fixed in modern humans, the deletion is also in archaic human genomes. KIR2DP1 is polymorphic, with dimorphism at specificity-determining position 44. By repairing the deletion, we resurrected 11 alleles of KIR2DP1F , the functional antecedent of KIR2DP1 We demonstrate how K44-KIR2DP1F with lysine 44 recognized C1+HLA-C, whereas T44-KIR2DP1F recognized C2+HLA-C. Dimorphisms at 12 other KIR2DP1F residues modulate receptor avidity or signaling. KIR2DP1 and KIR2DL1 are neighbors in the centromeric KIR region and are in tight linkage disequilibrium. Like KIR2DL1, KIR2DP1 contributed to CenA and CenB KIR haplotype differences. Encoded on CenA, C1-specific K44-KIR2DP1F were stronger receptors than the attenuated C2-specific T44-KIR2DP1F encoded on CenB The last common ancestor of humans and chimpanzees had diverse lineage III KIR that passed on to chimpanzees but not to humans. Early humans inherited activating KIR2DS4 and an inhibitory lineage III KIR, likely encoding a C1-specific receptor. The latter spawned the modern family of HLA-C receptors. KIR2DP1F has properties consistent with KIR2DP1F having been the founder gene. The first KIR2DP1F alleles encoded K44-C1 receptors; subsequently KIR2DP1F alleles encoding T44-C2 receptors evolved. The emergence of dedicated KIR2DL2/3 and KIR2DL1 genes encoding C1 and C2 receptors, respectively, could have led to obsolescence of KIR2DP1F Alternatively, pathogen subversion caused its demise. Preservation of KIR2DP1F functional polymorphism was a side effect of fixation of the deletion in KIR2DP1F by micro gene conversion.

HLA reduces killer cell Ig-like receptor expression level and frequency in a humanized mouse model.

NK cells use NK cell receptors to be able to recognize and eliminate infected, transformed, and allogeneic cells. Human NK cells are prevented from killing autologous healthy cells by virtue of inhibitory NKRs, primarily killer cell Ig-like receptors (KIR) that bind "self" HLA class I molecules. Individual NK cells stably express a selected set of KIR, but it is currently disputed whether the fraction of NK cells expressing a particular inhibitory KIR is influenced by the presence of the corresponding HLA ligand. The extreme polymorphism of the KIR and HLA loci, with wide-ranging affinities for individual KIR and HLA allele combinations, has made this issue particularly hard to tackle. In this study, we used a transgenic mouse model to investigate the effect of HLA on KIR repertoire and function in the absence of genetic variation inside and outside the KIR locus. These H-2K(b-/-) and H-2D(b-/-) mice lacked ligands for inhibitory Ly49 receptors and were transgenic for HLA-Cw3 and a KIR B haplotype. In this reductionist system, the presence of HLA-Cw3 reduced the frequency of KIR2DL2(+) cells, as well as the surface expression levels of KIR2DL2. In addition, in the presence of HLA-Cw3, the frequency of NKG2A(+) cells and the surface expression levels of NKG2A were reduced. In line with these findings, both transgene-encoded KIR and endogenous NKG2A contributed to the rejection of cells lacking HLA-Cw3. These findings support the idea that HLA influences the human KIR repertoire.

Potential implication of activating killer cell immunoglobulin-like receptor and HLA in onset of pulmonary tuberculosis.

Killer cell immunoglobulin-like receptor (KIR) and human leucocyte antigen (HLA) play crucial role in maintaining immune homoeostasis and controlling immune responses. To investigate the influence of KIR and HLA-C ligands on the risk of pulmonary tuberculosis (PTB), we studied 200 patients who were confirmed to have PTB and 200 healthy controls on the different frequencies of KIR and HLA-C ligands. Genotyping of these genes was conducted by sequence-specific primer polymerase chain reaction (SSP-PCR) method. Gene frequencies were compared between PTB group and the control group by χ(2) test, and P < 0.05 was regarded as statistically significant. As a result, the frequency of KIR genotype A/B was increased in PTB than controls but A/A was decreased. Moreover, striking differences were observed in the frequencies of HLA-Cw*08 between the two groups. Besides, the frequencies of '2DL2/3 with C1' in PTB were increased compared with control group. In addition, individuals with no KIR2DS3 and no Cw*08 were higher in controls than in PTB. KIR2DS1 was increased in PTB when HLA-C group 2 alleles were missing. In conclusion, KIR and HLA-C gene polymorphisms were related to susceptibility to PTB.

Consistent beneficial effects of killer cell immunoglobulin-like receptor 2DL3 and group 1 human leukocyte antigen-C following exposure to hepatitis C virus.

UNLABELLED: Natural killer cells are a key component in the immune control of viral infections. Their functions are controlled by inhibitory receptors for major histocompatability complex (MHC) class I, including the killer cell immunoglobulin-like receptors (KIR). KIR2DL3 in combination with its cognate human leukocyte antigen (HLA)-C ligand has been shown to be associated with spontaneous resolution of viremia following hepatitis C virus (HCV) infection. In order to determine if this gene combination is advantageous across all potential outcomes following HCV exposure, we studied individuals with apparent resistance to HCV infection who remain seronegative and aviremic despite long-term injection drug use and also individuals chronically infected with HCV who successfully clear HCV with treatment. Homozygosity for KIR2DL3 in combination with group 1 HLA-C allotypes was more frequent in exposed seronegative aviremic individuals as compared to those with chronic HCV (25.0% versus 9.7%, P = 0.003, odds ratio [OR] = 3.1, 95% confidence interval [CI] = 1.3-7.1) in a model similar to that found for those spontaneously resolving HCV. In individuals undergoing treatment for HCV, those with KIR2DL3 and group 1 HLA-C were more likely to make a sustained virological response (SVR) (P = 0.013, OR = 2.3, 95% CI = 1.1-4.5). KIR and HLA-C protection in both treatment response and spontaneously resolving HCV was validated at the allelic level, in which KIR2DL3-HLA-Cw*03 was associated with SVR (P = 0.004, OR = 3.4, 95% CI = 1.5-8.7) and KIR2DL3/KIR2DL3-HLA-Cw*03 was associated with spontaneous resolution of HCV infection (P = 0.01, OR = 2.3, 95% CI = 1.2-4.4). CONCLUSION: KIR and HLA-C genes are consistently beneficial determinants in the outcome of HCV infection. This advantage extends to the allelic level for both gene families.

HLA-C is necessary for optimal human immunodeficiency virus type 1 infection of human peripheral blood CD4 lymphocytes.

The hypothesis that open conformers of HLA-C on target cells might directly exert an effect on their infectability by human immunodeficiency virus (HIV) has been suggested previously. This was tested by exploiting the peculiar specificity of monoclonal antibody (mAb) L31 for HLA-C open conformers to show that normal levels of Env-driven fusion were restored in HLA-C transfectants of a major histocompatibility complex-deleted (fusion-incompetent) cell line. The physiological relevance of this finding is now confirmed in this report, where small interfering RNA (siRNA) technology was used to silence HLA-C expression in peripheral blood lymphocytes (PBLs) from 11 healthy donors. Infectability by HIV (strains IIIB and Bal and primary isolates) was significantly reduced (P=0.016) in silenced cells compared with cells that maintained HLA-C expression in 10 of the 11 PBL donors. Normal infectability was resumed, together with HLA-C expression, when the effect of siRNA interference waned after several days in culture. Additional confirmation of the HLA-C effect was obtained in several assays employing HLA-C-positive and -negative cell lines, a number of HIV strains and also pseudoviruses. In particular, viruses pseudotyped with env genes from HIV strains AC10 and QH0692.42 were assayed on siRNA-silenced lymphocytes from three healthy donors: the differences in infection with pseudoviruses were even higher than those observed in infections with normal viruses.

Sharing kidneys across donor-service area boundaries with sensitized candidates can be influenced by HLA C.

The United Network for Organ Sharing (UNOS) implemented the virtual crossmatch system in UNet as a way to improve the likelihood of a negative crossmatch when kidneys are shared with HLA-sensitized candidates across donor service area (DSA) boundaries. The role of HLA C in that process is not universally appreciated. We recently experienced an unexpected positive flow T and B cell crossmatch for an imported, HLA zero-mismatched kidney because of donor-specific HLA C antibodies and transplanted it into the backup candidate. HLA C locus antigens were not typed by the OPO's laboratory that sent the kidney so the UNet virtual crossmatch could not "strike" our candidate from the UNOS match run. HLA C locus typing data of donors for kidneys our DSA imported from other DSAs revealed that C typing was not performed in 23% (14/60) and was discrepant with our molecular type for 10% (6/60) and was concordant in 67% (40/60) of cases. The rate of positive donor-specific crossmatches was higher (83%) for HLA C discrepantly typed donors than for concordantly typed donors (44%). Sensitization for HLA C (42%) is less frequent than for A (80%) or B (83%) locus antigens but the immunogenicity of C locus antigens in patients who make C locus antibodies is equivalent in black and white patients. Finally, the transplant rate of imported kidneys into class I-sensitized candidates was 24%, and C locus-sensitized candidates comprised 55% of those transplanted.

Host genetic determinants of spontaneous hepatitis C clearance.

Acute infection with the hepatitis C virus (HCV) induces a wide range of innate and adaptive immune responses. A total of 20-50% of acutely HCV-infected individuals permanently control the virus, referred to as 'spontaneous hepatitis C clearance', while the infection progresses to chronic hepatitis C in the majority of cases. Numerous studies have examined host genetic determinants of hepatitis C infection outcome and revealed the influence of genetic polymorphisms of human leukocyte antigens, killer immunoglobulin-like receptors, chemokines, interleukins and interferon-stimulated genes on spontaneous hepatitis C clearance. However, most genetic associations were not confirmed in independent cohorts, revealed opposing results in diverse populations or were limited by varying definitions of hepatitis C outcomes or small sample size. Coordinated efforts are needed in the search for key genetic determinants of spontaneous hepatitis C clearance that include well-conducted candidate genetic and genome-wide association studies, direct sequencing and follow-up functional studies.

Killer Ig-like receptor ligand mismatch directs NK cell expansion in vitro.

NK cell alloreactivity is governed largely through failure to detect self-HLA class I ligands by the clonally distributed inhibitory killer Ig-like receptors (KIR) expressed on the NK cell surface. In this study, we investigated the extent to which HLA class I-KIR interactions influence human NK cell proliferation in the allogeneic setting. NK cells were cultured with feeder cells either matched or mismatched for inhibitory KIR ligands, the latter lacking one or more ligands present in the NK cell donor. In postculture cytotoxicity assays, the ability of polyclonal NK cells to kill KIR ligand-mismatched targets was enhanced by exposure to appropriately mismatched feeder cells in prior culture. This corresponded with an increased frequency of postculture donor NK cells expressing a given inhibitory KIR if the allogeneic feeder cells used in the culture lacked its ligand. Similar skewing of KIR distribution was seen in clonally expanded NK cells. Finally, a flow cytometry-based proliferation assay was used to show KIR-specific NK cell division in response to missing self. The findings demonstrate that KIR distribution among a population of alloresponding peripheral blood NK cells is shaped by the HLA class I environment.

Genetic and antibody-mediated reprogramming of natural killer cell missing-self recognition in vivo.

Natural killer (NK) cells are lymphocytes of the innate immune system able to recognize and kill tumors lacking self-MHC class I molecules. This "missing-self" recognition is mediated by the lack of engagement of MHC class I-specific inhibitory NK cell receptors that include the killer cell Ig-like receptors (KIR) in humans and Ly49 molecules in mice. A promising immunotherapeutic strategy against MHC class I(+) cancer cells is to block NK cell inhibitory receptors using monoclonal antibodies (mAb). However, interactions between MHC class I molecules and their inhibitory receptors are also required for the acquisition of NK cell functional competence, a process referred as to "education." In addition, inhibitory receptors are involved in self-tolerance on educated NK cells. Here, we developed a preclinical mouse model in which all NK cells are educated by a single transgenic inhibitory receptor, human KIR2DL3, through the engagement with its HLA-Cw3 ligand. This approach revealed that NK cells could be reprogrammed to control the development of mouse syngenic tumors in vivo. Moreover, in vivo anti-KIR mAb treatment induced the killing of HLA(+) target cells without breaking self-tolerance. Finally, the long-term infusion of anti-KIR mAb neither abolished NK cell education nor tumor cell recognition. Therefore, these results strongly support the use of inhibitory receptor blockade in cancer patients.

A novel trafficking signal within the HLA-C cytoplasmic tail allows regulated expression upon differentiation of macrophages.

MHC class I molecules (MHC-I) present peptides to CTLs. In addition, HLA-C allotypes are recognized by killer cell Ig-like receptors (KIR) found on NK cells and effector CTLs. Compared with other classical MHC-I allotypes, HLA-C has low cell surface expression and an altered intracellular trafficking pattern. We present evidence that this results from effects of both the extracellular domain and the cytoplasmic tail. Notably, we demonstrate that the cytoplasmic tail contains a dihydrophobic (LI) internalization and lysosomal targeting signal that is partially attenuated by an aspartic acid residue (DXSLI). In addition, we provide evidence that this signal is specifically inhibited by hypophosphorylation of the adjacent serine residue upon macrophage differentiation and that this allows high HLA-C expression in this cell type. We propose that tightly regulated HLA-C surface expression facilitates immune surveillance and allows HLA-C to serve a specialized role in macrophages.

Distinct KIR/HLA compound genotypes affect the kinetics of human antiviral natural killer cell responses.

Genetic studies suggest a role for killer cell immunoglobulin-like receptor/HLA (KIR/HLA) compound genotypes in the outcome of viral infections, but functional data to explain these epidemiological observations have not been reported. Using an in vitro model of infection with influenza A virus (IAV), we attribute functional differences in human NK cell activity to distinct KIR/HLA genotypes. Multicolor flow cytometry revealed that the HLA-C-inhibited NK cell subset in HLA-C1 homozygous subjects was larger and responded more rapidly in IFN-gamma secretion and CD107a degranulation assays than its counterpart in HLA-C2 homozygous subjects. The differential IFN-gamma response was also observed at the level of bulk NK cells and was independent of KIR3DL1/HLA-Bw4 interactions. Moreover, the differential response was not caused by differences in NK cell maturation status and phenotype, nor by differences in the type I IFN response of IAV-infected accessory cells between HLA-C1 and HLA-C2 homozygous subjects. These results provide functional evidence for differential NK cell responsiveness depending on KIR/HLA genotype and may provide useful insights into differential innate immune responsiveness to viral infections such as IAV.

Influence of killer cell immunoglobulin-like receptor genotypes on acute graft-vs-host disease after unrelated hematopoietic stem cell transplantation in Koreans.

Interactions between killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen class I ligands influence the development of the natural killer cell repertoire and the responses to infection, cancer, and allogeneic tissue. In this study, the association of KIR genes with acute graft-vs-host disease (GVHD) was investigated in 44 pairs of leukemia patients and their unrelated donors for hematopoietic stem cell transplantation (HSCT). Donors with more than 12 KIR genes showed significantly decreased frequencies of severe acute GVHD compared with donors with less than 11 KIR genes (P < 0.05). The distribution of KIR genotypes was not different between severe and mild acute GVHD in patients and donors, respectively. These results suggest that the number of KIR genes in donors could influence the occurrence of acute GVHD after unrelated HSCT.

Impact of recipient HLA-C in liver transplant: a protective effect of HLA-Cw*07 on acute rejection.

The involvement of the human leukocyte antigen (HLA) in liver graft acceptance is controversial, but the frequency of acute rejection (AR) remains high in spite of the use of the modern immunosuppressive agents. The present study was aimed at determining whether an association exists between liver recipient HLA-C polymorphism and AR development that could influence graft acceptance. Four hundred and forty-six liver recipients and 473 controls were studied within the framework of a collaborative study carried out by the Spanish Transplant Immunotolerance Group (RED-GIT). HLA-A and -B were typed by the standard microlymphocytotoxicity technique, and HLA-C by polymerase chain reaction-sequence-specific oligonucleotide probes (PCR-SSOP). A statistically significant decrease in the HLA-Cw*07 allele frequency was found in liver recipients suffering AR episodes compared to those without AR (NAR). Studies regarding the possible influence of the Asn80 and Lys80 epitopes showed that the Asn80 epitope also could be associated with AR. However, further analysis considering Asn80 alleles others than HLA-Cw*07, confirmed that the apparent protective effect of the Asn80 epitope was actually from the HLA-Cw*07 allele. In conclusion, the HLA-Cw*07 allele carried by the liver recipient is negatively associated with AR development, and could be considered a predictive factor for liver graft acceptance.

[Progress on the study of HLA-Cw--review].

HLA-Cw belongs to classic HLA-I gene, HLA-Cw molecules have high polymorphism like HLA-A and B molecules. They distribute extensively on the surfaces of karyote, not only presenting endogenetic antigen to CD8+ T cells to induce specific killing effect, but also participating in immunologic reaction as the ligands of killer cell immunoglobulin-like receptor (KIR). Thus it has been valued for their relations to diseases and the functions in transplantation immunity, anti virus and anti-tumor immunity.

Cutting edge: engagement of CD160 by its HLA-C physiological ligand triggers a unique cytokine profile secretion in the cytotoxic peripheral blood NK cell subset.

CD160 is an Ig-like activating NK cell receptor expressed on the majority of circulating NK cells. This population corresponds to the nonproliferating, highly cytolytic, CD56dimCD16+ subset. CD160 engagement by HLA-C molecules mediates cytotoxic function. In this study, we report that upon specific activation by the physiological ligand HLA-C, or Ab cross-linking, CD160+ peripheral blood NK cells produce IFN-gamma, TNF-alpha, and IL-6. This unique CD160-mediated cytokine production differs from the one observed after CD16 engagement whose expression is also restricted to the CD56dim cytotoxic NK cell subset. As already reported for the CD160-mediated cytotoxic effector function, CD160-mediated cytokine production by peripheral blood-NK cells is negatively controlled by the killer Ig-like receptor CD158b. Thus, the CD160 receptor represents a unique triggering surface molecule expressed by cytotoxic NK cells that participates in the inflammatory response and determines the type of subsequent specific immunity.

Role of a KIR/HLA-C allorecognition system in pregnancy.

Decidual natural killer (NK) cells are thought to play a significant role in the allorecognition mechanisms during pregnancy. Through their activating and inhibitory receptors they may recognize selectively class I HLA alleles expressed on invading trophoblast and provide self-signals to control NK responses, thus regulating the maternal immune response at the fetomatenal interface. Killer immunoglobulin-like receptors (KIR) constitute one of the families of class I MHC receptors which are expressed on NK cells. Their repertoire includes both activating and inhibitory receptors, most of which recognize specific epitopes on HLA-C molecules and can either activate NK cell responses or abort activating signals and inhibit NK cell functions. Since KIRs are expressed on decidual NK cells and the HLA-C molecules that they recognize are also expressed on invading trophoblast, KIR receptors may play a regulatory role in pregnancy by interacting with their trophoblastic HLA-C counterparts and providing trophoblast damage evading signals (KIR/HLA-C allorecognition system). Our hypothesis that the KIR/HLA-C system might be ineffective in some unsuccessful pregnancies, has been investigated in women with unexplained spontaneous abortions. Our results suggest that a limited maternal repertoire of inhibiting KIRs (inhKIRs) and/or lack of maternal inhKIR-fetal HLA-C epitope matching may predispose to miscarriage.