Integrated Analysis of Single-Cell and Bulk RNA Sequencing Data Reveals Memory-like NK Cell Subset Associated with Mycobacterium tuberculosis Latency

Natural killer (NK) cells are innate-like lymphocytes that belong to the family of type-1 innate lymphoid cells and rapidly respond to virus-infected and tumor cells. In this study, we have combined scRNA-seq data and bulk RNA-seq data to define the phenotypic and molecular characteristics of peripheral blood NK cells. While the role of NK cells in immune surveillance against virus infections and tumors has been well established, their contribution to protective responses to other intracellular microorganisms, such as Mycobacterium tuberculosis (Mtb), is still poorly understood. In this study, we have combined scRNA-seq data and bulk RNA-seq data to illuminate the molecular characteristics of circulating NK cells in patients with active tuberculosis (TB) disease and subjects with latent Mtb infection (LTBI) and compared these characteristics with those of healthy donors (HDs) and patients with non-TB other pulmonary infectious diseases (ODs). We show here that the NK cell cluster was significantly increased in LTBI subjects, as compared to patients with active TB or other non-TB pulmonary diseases and HD, and this was mostly attributable to the expansion of an NK cell population expressing KLRC2, CD52, CCL5 and HLA-DRB1, which most likely corresponds to memory-like NK2.1 cells. These data were validated by flow cytometry analysis in a small cohort of samples, showing that LTBI subjects have a significant expansion of NK cells characterized by the prevalence of memory-like CD52+ NKG2C+ NK cells. Altogether, our results provide some new information on the role of NK cells in protective immune responses to Mtb.

NKG2A discriminates natural killer cells with a suppressed phenotype in pediatric acute leukemia

Natural killer (NK) cells are important for early tumor immune surveillance. In patients with hematological cancers, NK cells are generally functional deficient and display dysregulations in their receptor repertoires. Acute leukemia is the most common cancer in children, and we here performed a comparative phenotypic profiling of NK cells from B-cell precursor acute lymphoblastic leukemia (BCP-ALL) patients to identify aberrant NK cell phenotypes. NK cell phenotypes, maturation, and function were analyzed in matched bone marrow and blood NK cells from BCP-ALL patients at diagnosis, during treatment, and at end of treatment and compared with age-matched pediatric control subjects. Expression of several markers were skewed in patients, but with large interindividual variations. Undertaking a multiparameter approach, we found that high expression levels of NKG2A was the single predominant marker distinguishing NK cells in BCP-ALL patients compared with healthy control subjects. Moreover, naïve CD57-NKG2A NK cells dominated in BCP-ALL patients at diagnosis. Further, we found dysregulated expression of the activating receptor DNAM-1 in resident bone marrow CXCR6+ NK cells. CXCR6+ NK cells lacking DNAM-1 expressed NKG2A and had a tendency for lower degranulation activity. In conclusion, high expression of NKG2A dominates NK cell phenotypes from pediatric BCP-ALL patients, indicating that NKG2A could be targeted in therapies for this patient group.

Single-cell transcriptomics of peripheral blood mononuclear cells indicates impaired immune and inflammatory responses in alcohol-associated hepatitis

Alcohol-associated hepatitis (AH) is often diagnosed at advanced stages, and severe AH usually carries poor prognosis and high short-term mortality. In addition, it is challenging to understand the molecular mechanisms of immune dysregulation and inflammation in AH due to the cellular complexity and heterogeneity. Using single-cell RNA sequencing, previous studies found that AH causes dysfunctional innate immune response in monocytes, involving activation of pattern recognition receptors (PRRs) and cytokine signaling pathways. To better understand the coordinated systemic immune response in AH patients, we performed combined single-cell transcriptome, cell-surface protein, and lymphocyte antigen receptor analysis of peripheral blood mononuclear cell (PBMC) samples. Our results showed inflammatory cytokines and chemokines were highly expressed in AH, including IL-2, IL-32, CXC3R1 and CXCL16 in monocytes and NK cells, whereas HLA-DR genes were reduced in monocytes. In addition, we also found altered differentiation of T-helper cells (TH1 and TH17), which could further lead to neutrophil recruitment and macrophage activation. Lastly, our results also suggest impaired NK-cell activation and differentiation in AH with reduced gene expression of KLRC2 and increased gene expression of KLRG1. Our findings indicate different mechanisms may be involved in impaired immune and inflammatory responses for the cellular subtypes of the PBMCs in AH.

Post-Acute Myocardial Infarction Heart Failure Core Genes and Relevant Signaling Pathways

ABSTRACT

There is increasing concern about heart failure after myocardial infarction and the current clinical treatment measures for ventricular remodeling. Herein, we present the results of differential gene analysis, pathway enrichment analysis, and characteristic gene screening. Our study identifies 4 core genes ( KLRC2 , SNORD105 , SNORD45B , and RNU5A-1 ) associated with post-acute myocardial infarction (AMI) heart failure. The authors discuss the significance of the identified core genes, their potential implications in immune dysfunction and heart failure, and their relevance to disease regulatory genes. The study concludes by emphasizing the importance of clinical relevance in molecular research and suggests potential therapeutic targets for post-AMI heart failure.

A novel immune-related gene signature for predicting immunotherapy outcomes and survival in clear cell renal cell carcinoma

Clear cell renal carcinoma (ccRCC) is one of the most common cancers worldwide. In this study, a new model of immune-related genes was developed to predict the overall survival and immunotherapy efficacy in patients with ccRCC. Immune-related genes were obtained from the ImmPort database. Clinical data and transcriptomics of ccRCC samples were downloaded from GSE29609 and The Cancer Genome Atlas. An immune-related gene-based prognostic model (IRGPM) was developed using the least absolute shrinkage and selection operator regression algorithm and multivariate Cox regression. The reliability of the developed models was evaluated by Kaplan-Meier survival curves and time-dependent receiver operating characteristic curves. Furthermore, we constructed a nomogram based on the IRGPM and multiple clinicopathological factors, along with a calibration curve to examine the predictive power of the nomogram. Overall, this study investigated the association of IRGPM with immunotherapeutic efficacy, immune checkpoints, and immune cell infiltration. Eleven IRGs based on 528 ccRCC samples significantly associated with survival were used to construct the IRGPM. Remarkably, the IRGPM, which consists of 11 hub genes (SAA1, IL4, PLAUR, PLXNB3, ANGPTL3, AMH, KLRC2, NR3C2, KL, CSF2, and SEMA3G), was found to predict the survival of ccRCC patients accurately. The calibration curve revealed that the nomogram developed with the IRGPM showed high predictive performance for the survival probability of ccRCC patients. Moreover, the IRGPM subgroups showed different levels of immune checkpoints and immune cell infiltration in patients with ccRCC. IRGPM might be a promising biomarker of immunotherapeutic responses in patients with ccRCC. Overall, the established IRGPM was valuable for predicting survival, reflecting the immunotherapy response and immune microenvironment in patients with ccRCC.

Activating NKG2C Receptor: Functional Characteristics and Current Strategies in Clinical Applications

The interest in NK cells and their cytotoxic activity against tumour, infected or transformed cells continuously increases as they become a new efficient and off-the-shelf agents in immunotherapies. Their actions are balanced by a wide set of activating and inhibitory receptors, recognizing their complementary ligands on target cells. One of the most studied receptors is the activating CD94/NKG2C molecule, which is a member of the C-type lectin-like family. This review is intended to summarise latest research findings on the clinical relevance of NKG2C receptor and to examine its contribution to current and potential therapeutic strategies. It outlines functional characteristics and molecular features of CD94/NKG2C, its interactions with HLA-E molecule and presented antigens, pointing out a key role of this receptor in immunosurveillance, especially in the human cytomegalovirus infection. Additionally, the authors attempt to shed some light on receptor's unique interaction with its ligand which is shared with another receptor (CD94/NKG2A) with rather opposite properties.

Phenotypic and functional characteristics of highly differentiated CD57+NKG2C+ NK cells in HIV-1-infected individuals

Natural killer (NK) cells are important anti-viral effector cells. The function and phenotype of the NK cells that constitute an individual's NK cell repertoire can be influenced by ongoing or previous viral infections. Indeed, infection with human cytomegalovirus (HCMV) drives the expansion of a highly differentiated NK cell population characterized by expression of CD57 and the activating NKG2C receptor. This NK cell population has also been noted to occur in HIV-1-infected individuals. We evaluated the NK cells of HIV-1-infected and HIV-1-uninfected individuals to determine the relative frequency of highly differentiated CD57+NKG2C+ NK cells and characterize these cells for their receptor expression and responsiveness to diverse stimuli. Highly differentiated CD57+NKG2C+ NK cells occurred at higher frequencies in HCMV-infected donors relative to HCMV-uninfected donors and were dramatically expanded in HIV-1/HCMV co-infected donors. The expanded CD57+NKG2C+ NK cell population in HIV-1-infected donors remained stable following antiretroviral therapy. CD57+NKG2C+ NK cells derived from HIV-1-infected individuals were robustly activated by antibody-dependent stimuli that contained anti-HIV-1 antibodies or therapeutic anti-CD20 antibody, and these NK cells mediated cytolysis through NKG2C. Lastly, CD57+NKG2C+ NK cells from HIV-1-infected donors were characterized by reduced expression of the inhibitory NKG2A receptor. The abundance of highly functional CD57+NKG2C+ NK cells in HIV-1-infected individuals raises the possibility that these NK cells could play a role in HIV-1 pathogenesis or serve as effector cells for therapeutic/cure strategies.

CMV reactivation initiates long-term expansion and differentiation of the NK cell repertoire

Introduction

NK cells play an important role in suppression of viral replication and are critical for effective control of persistent infections such as herpesviruses. Cytomegalovirus infection is associated with expansion of 'adaptive-memory' NK cells with a characteristic CD56dimCD16bright NKG2C+ phenotype but the mechanisms by which this population is maintained remain uncertain.

Methods

We studied NK cell reconstitution in patients undergoing haemopoietic stem cell transplantation and related this to CMV reactivation.

Results

NK cells expanded in the early post-transplant period but then remained stable in the absence of viral reactivation. However, CMV reactivation led to a rapid and sustained 10-fold increase in NK cell number. The proportion of NKG2C-expressing cells increases on all NK subsets although the kinetics of expansion peaked at 6 months on immature CD56bright cells whilst continuing to rise on the mature CD56dim pool. Phenotypic maturation was observed by acquisition of CD57 expression. Effective control of viral reactivation was seen when the peripheral NK cell count reached 20,000/ml.

Discussion

These data show that short term CMV reactivation acts to reprogramme hemopoiesis to drive a sustained modulation and expansion of the NK cell pool and reveal further insight into long term regulation of the innate immune repertoire by infectious challenge.

In vivo CRISPR screens reveal the landscape of immune evasion pathways across cancer

The immune system can eliminate tumors, but checkpoints enable immune escape. Here, we identify immune evasion mechanisms using genome-scale in vivo CRISPR screens across cancer models treated with immune checkpoint blockade (ICB). We identify immune evasion genes and important immune inhibitory checkpoints conserved across cancers, including the non-classical major histocompatibility complex class I (MHC class I) molecule Qa-1b/HLA-E. Surprisingly, loss of tumor interferon-γ (IFNγ) signaling sensitizes many models to immunity. The immune inhibitory effects of tumor IFN sensing are mediated through two mechanisms. First, tumor upregulation of classical MHC class I inhibits natural killer cells. Second, IFN-induced expression of Qa-1b inhibits CD8+ T cells via the NKG2A/CD94 receptor, which is induced by ICB. Finally, we show that strong IFN signatures are associated with poor response to ICB in individuals with renal cell carcinoma or melanoma. This study reveals that IFN-mediated upregulation of classical and non-classical MHC class I inhibitory checkpoints can facilitate immune escape.

High frequencies of adaptive NK cells are associated with absence of coronary plaque in cytomegalovirus infected people living with HIV

The objective of this study was to evaluate whether adaptive NKG2C+CD57+ natural killer (adapNK) cell frequencies are associated with pre-clinical coronary atherosclerosis in participants of the Canadian HIV and Aging Cohort Study. This cross-sectional study included 194 Canadian HIV and Aging Cohort Study participants aged ≥ 40 years of which 128 were cytomegalovirus (CMV)+ people living with HIV (PLWH), 8 were CMV-PLWH, 37 were CMV mono-infected individuals, and 21 were neither human immunodeficiency virus nor CMV infected. Participants were evaluated for the frequency of their adapNK cells and total plaque volume (TPV). TPV was assessed using cardiac computed tomography. Participants were classified as free of, or having, coronary atherosclerosis if their TPV was "0" and ">0," respectively. The frequency of adapNK cells was categorized as low, intermediate or high if they constituted <4.6%, between ≥4.6% and 20% and >20%, respectively, of the total frequency of CD3-CD56dim NK cells. The association between adapNK cell frequency and TPV was assessed using an adjusted Poisson regression analysis. A greater proportion of CMV+PLWH with TPV = 0 had high adapNK cell frequencies than those with TPV > 0 (61.90% vs 39.53%, P = .03) with a similar non-significant trend for CMV mono-infected participants (46.15% vs 34.78%). The frequency of adapNK cells was negatively correlated with TPV. A high frequency of adapNK cells was associated with a relative risk of 0.75 (95% confidence intervals 0.58, 0.97, P = .03) for presence of coronary atherosclerosis. This observation suggests that adapNK cells play a protective role in the development of coronary atherosclerotic plaques.

Identification of immune hub genes participating in the pathogenesis and progression of Vogt-Koyanagi-Harada disease

Background

Vogt-Koyanagi-Harada (VKH) disease is an autoimmune inflammatory disorder characterized by bilateral granulomatous uveitis. The objective of this study was to identify immune hub genes involved in the pathogenesis and progression of VKH disease.

Methods

High throughput sequencing data were downloaded from the Gene Expression Omnibus (GEO) and an immune dataset was downloaded from ImmPort. Immune differentially expressed genes (DEGs) were obtained from their intersection in the GEO and ImmPort datasets. Immune hub genes for VKH disease were selected through differential expression analyses, including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), Disease Ontology (DO), protein-protein interaction (PPI) network, and clustering analyses. Confidence in the immune hub genes was subsequently validated using box plots and receiver operating characteristic (ROC) curves.

Results

A total of 254 DEGs were screened and after the intersection with ImmPort, 20 genes were obtained as immune DEGs. Functional enrichment analysis indicated that the key genes were mainly involved in several types of immune pathways (such as the lymphocyte mediated and leukocyte mediated immune responses, natural killer cell mediated cytotoxicity, and antigen binding) and immunodeficiency diseases. Following PPI network analysis, the top seven genes in cluster 1 were selected as potential immune hub genes in VKH. After evaluating the accuracy of the hub genes, one gene (GNLY) was excluded because its expression level was statistically similar in VKH patients and healthy controls. Finally, six immune hub genes, namely KLRC2, KLRC3 SH2D1B, GZMB, KIR2DL3, and KIR3DL2 were identified as playing important roles in the occurrence and development of VKH disease.

Conclusion

Six immune hub genes (KLRC2, KLRC3 SH2D1B, GZMB, KIR2DL3, and KIR3DL2) identified by our bioinformatics analyses may provide new diagnostic and therapeutic targets for VKH disease.

Impact of an Immune Modulator Mycobacterium-w on Adaptive Natural Killer Cells and Protection Against COVID-19

The kinetics of NKG2C+ adaptive natural killer (ANK) cells and NKG2A+inhibitory NK (iNK) cells with respect to the incidence of SARS-CoV-2 infection were studied for 6 months in a cohort of healthcare workers following the administration of the heat-killed Mycobacterium w (Mw group) in comparison to a control group. In both groups, corona virus disease 2019 (COVID-19) correlated with lower NKG2C+ANK cells at baseline. There was a significant upregulation of NKG2C expression and IFN-γ release in the Mw group (p=0.0009), particularly in those with a lower baseline NKG2C expression, along with the downregulation of iNK cells (p<0.0001). This translated to a significant reduction in the incidence and severity of COVID-19 in the Mw group (incidence risk ratio-0.15, p=0.0004). RNA-seq analysis at 6 months showed an upregulation of the ANK pathway genes and an enhanced ANK-mediated antibody-dependent cellular cytotoxicity (ADCC) signature. Thus, Mw was observed to have a salutary impact on the ANK cell profile and a long-term upregulation of ANK-ADCC pathways, which could have provided protection against COVID-19 in a non-immune high-risk population.

All-Atom Simulations Reveal a Key Interaction Network in the HLA-E/NKG2A/CD94 Immune Complex Fine-Tuned by the Nonameric Peptide

Natural killer (NK) cells, an important part of the innate immune system, can clear a wide variety of pathological challenges, including tumor, senescent, and virally infected cells. They express various activating and inhibitory receptors on their surface, and the balance of interactions between them and specific ligands displayed on the surface of target cells is critical for NK cell cytolytic function and target cell protection. The CD94/NKG2A heterodimer is one of the inhibitory receptors that interacts with its trimeric ligand consisting of HLA-E, β2m, and a nonameric peptide. Here, multi-microsecond-long all-atom molecular dynamics simulations of eight immune complexes elucidate the subtleties of receptor (NKG2A/CD94)-ligand (HLA-E/β2m/peptide) molecular recognition that mediate the NK cell protection from a geometric and energetic perspective. We identify key differences in the interactions between the receptor and ligand complexes, which are via an entangled network of hydrogen bonds fine-tuned by the ligand-specific nonameric peptide. We further reveal that the receptor protein NKG2A regulates the NK cell activity, while its CD94 partner forms the majority of the energetically important interactions with the ligand. This knowledge rationalizes the atomistic details of the fundamental NK cell protection mechanism and may enable a variety of opportunities in rational-based drug discovery for diverse pathologies including viral infections and cancer and elimination of senescent cells associated with potential treatment of many age-related diseases.

Expression of NKG2A inhibitory receptor on cytotoxic lymphocytes as an indicator of severity in Corona Virus Disease 2019 (COVID-19) patients

NK group 2 member A (NKG2A) receptor transduces inhibitory signaling; suppressing NK and T-cell cytokine secretion and cytotoxic function. This study aimed to assess the expression of NKG2A inhibitory receptor on natural killer (NK) cells and CD8+ T lymphocytes in COVID-19 patients and correlate the results with disease severity defined according to the criteria established by the world health organization, in a trial to understand the immunological response towards COVID-19 infection. The study enrolled 30 COVID-19 patients classified into 2 groups that comprised 15 subjects each; moderate and severe based on clinical, radiological, and laboratory findings. Ten age and sex matched apparently healthy individuals were included in this study as a control group. About 1 ml EDTA anti-coagulated blood samples were collected for measuring expression of NKG2A/CD159a on CD56+ CD3- NK and CD3+CD8+ T cells by flow cytometry. Results revealed that COVID-19 patients had significantly lower NK and CD8+ T cell counts compared to healthy subjects. Severe cases had significantly lower CD8+ T counts compared to moderate ones. Percentages of NK and CD8+T cells expressing NKG2A receptor were significantly higher in cases compared to controls. Comparison between severe and moderate cases revealed that although the percentages of NK cells expressing NKG2A receptor were not significantly higher in severe cases, the mean fluorescence intensity was significantly higher. The percentages of CD8 +T cells expressing NKG2A receptor were significantly higher in severe cases with higher mean fluorescence intensity. In conclusion, our results indicate that elevated NKG2A expression on cytotoxic lymphocytes correlates with disease severity in COVID-19 patients, and may serve as a potential marker for prognosis. Additionally, the blockade of NKG2A should be investigated as means of enhancing NK cell and cytotoxic T cells antiviral immunity in patients with severe COVID-19 infection.

Setting traps for NKG2A gives NK cell immunotherapy a fighting chance

The equilibrium of signaling through activating and inhibitory receptors dictates whether a given NK cell will execute cellular cytotoxicity. In this issue of the JCI, Kamiya et al. describe a novel approach to efficiently inhibiting surface expression of the inhibitory receptor CD94/NK group 2 member A (NKG2A) through retention of the protein in the endoplasmic reticulum. In adoptive transfer experiments into tumor-bearing immunodeficient mice, NKG2Anull NK cells were significantly more effective at eliminating HLA-E-expressing tumor cells than NKG2A+ NK cells. This study provides proof of concept for a new immunotherapeutic approach using NKG2Anull NK cells.

Increased frequency of human leukocyte antigen-E inhibitory receptor CD94/NKG2A-expressing peritoneal natural killer cells in patients with endometriosis

OBJECTIVE

To analyze the frequency of peritoneal natural killer (NK) cells expressing the human leukocyte antigen (HLA)-E receptor CD94/NKG2A in patients with endometriosis.

DESIGN

Case-control study.

SETTING

University hospital.

PATIENT(S)

Stage III and stage IV endometriosis, according to the revised American Society for Reproductive Medicine classification, was laparoscopically and histologically confirmed in 11 and 9 patients, respectively; 13 subjects without endometriosis were selected for the control group.

INTERVENTION(S)

Collection of peripheral venous blood, peritoneal fluid, endometriotic tissue, and normal endometrium in subjects undergoing laparoscopy.

MAIN OUTCOME MEASURE(S)

Surface expression levels of CD94/NKG2A and CD94/NKG2C were detected by three-color cytofluorometric analysis. Semiquantitative HLA-E messenger RNA expression analysis was performed in endometriotic lesions and in eutopic endometrium. NK cell-mediated cytotoxic activity toward HLA-E positive target, DT360 cell line, was also determined.

RESULT(S)

In women with endometriosis, the percentage of CD94/NKG2A-positive peritoneal NK cells was significantly higher than in the control group. The CD94/NKG2A ligand, HLA-E, was detected at high levels in endometriotic tissue as messenger RNA transcript. Target cells bearing HLA-E were resistant to NK cell-mediated lysis in a CD94/NKG2A-dependent manner.

CONCLUSION(S)

Increased expression of CD94/NKG2A in peritoneal NK cells may mediate the resistance of endometriotic tissue to NK cell-mediated lysis, thus contributing to the progression of the disease.

CD94-NKG2A recognition of human leukocyte antigen (HLA)-E bound to an HLA class I leader sequence

The recognition of human leukocyte antigen (HLA)-E by the heterodimeric CD94-NKG2 natural killer (NK) receptor family is a central innate mechanism by which NK cells monitor the expression of other HLA molecules, yet the structural basis of this highly specific interaction is unclear. Here, we describe the crystal structure of CD94-NKG2A in complex with HLA-E bound to a peptide derived from the leader sequence of HLA-G. The CD94 subunit dominated the interaction with HLA-E, whereas the NKG2A subunit was more peripheral to the interface. Moreover, the invariant CD94 subunit dominated the peptide-mediated contacts, albeit with poor surface and chemical complementarity. This unusual binding mode was consistent with mutagenesis data at the CD94-NKG2A-HLA-E interface. There were few conformational changes in either CD94-NKG2A or HLA-E upon ligation, and such a "lock and key" interaction is typical of innate receptor-ligand interactions. Nevertheless, the structure also provided insight into how this interaction can be modulated by subtle changes in the peptide ligand or by the pairing of CD94 with other members of the NKG2 family. Differences in the docking strategies used by the NKG2D and CD94-NKG2A receptors provided a basis for understanding the promiscuous nature of ligand recognition by NKG2D compared with the fidelity of the CD94-NKG2 receptors.

NKG2C is a major triggering receptor involved in the V[delta]1 T cell-mediated cytotoxicity against HIV-infected CD4 T cells

BACKGROUND

Gammadelta T cells share with natural killer (NK) cells many effector capabilities and cell-surface proteins, including the NKG2 receptor family. A subset of gammadelta T cells that express the variable Vdelta1 region plays a critical role in immune regulation, tumour surveillance and viral infection. Dramatic expansion of Vdelta1 T cells has been observed in HIV disease.

OBJECTIVE

To determine if NKG2C expression on Vdelta1 T cells during HIV-1 infection is correlated with CD4 cell count and involved in lysis of CD4 T cells.

METHODS

gammadelta T cells from viraemic HIV-infected patients were examined. Expression of NK cell markers was analyzed by flow cytometry. The cytolytic activity of Vdelta1 T cells was determined by either Cr-release assays or degranulation assays against HLA-E-transfected 721.221 cells or HIV-infected CD4 primary T cells.

RESULTS

The expression of C-type lectin NKG2 receptors was sharply modulated on gammadelta T cells in patients with HIV infection. A profound decrease of Vdelta1 T cells bearing inhibitory NKG2A receptors corresponded to a drastic expansion of a distinct population of Vdelta1 T cells expressing a functional activating NKG2C receptor. Engagement of HLA-E, the ligand of both NKG2A and NKG2C, which is specifically induced on HIV-infected CD4 T cells, substantially enhanced the Vdelta1 T cell-mediated cytotoxicity.

CONCLUSIONS

These results raise the possibility that induction of NKG2C expression on Vdelta1 T cells plays a key role in the destruction of HIV-infected CD4 T cells during HIV disease.

Small intestinal CD8+TCRgammadelta+NKG2A+ intraepithelial lymphocytes have attributes of regulatory cells in patients with celiac disease

Intraepithelial lymphocytes (IELs) bearing the gammadelta TCR are more abundant in the small intestinal mucosa of patients with celiac disease (CD) compared with healthy individuals. However, their role in disease pathogenesis is not well understood. Here, we investigated the functional attributes of TCRgammadelta+ IELs isolated from intestinal biopsies of patients with either active celiac disease (ACD) or those on a gluten-free diet (GFD). We found that compared with individuals with ACD, individuals on GFD have a higher frequency of CD8+TCRgammadelta+ IELs that express the inhibitory NK receptor NKG2A and intracellular TGF-beta1. TCR triggering as well as cross-linking of NKG2A increased both TGF-beta1 intracellular expression and secretion in vitro. Coculture of sorted TCRgammadelta+NKG2A+ IELs, IL-15-stimulated TCRalphabeta+ IELs, and HLA-E+ enterocytes resulted in a decreased percentage of cytotoxic CD8+TCRalphabeta+ IELs expressing intracellular IFN-gamma and granzyme-B and surface NKG2D. This inhibition was partially abrogated by blocking either TGF-beta alone or both NKG2A and HLA-E. Thus, our data indicate that suppression was at least partially mediated by TGF-beta secretion as a result of engagement of NKG2A with its ligand, HLA-E, on enterocytes and/or TCRalphabeta+ IELs. These findings demonstrate that human small intestinal CD8+TCRgammadelta+ IELs may have regulatory potential in celiac disease.

The heterodimeric assembly of the CD94-NKG2 receptor family and implications for human leukocyte antigen-E recognition

The CD94-NKG2 receptor family that regulates NK and T cells is unique among the lectin-like receptors encoded within the natural killer cell complex. The function of the CD94-NKG2 receptors is dictated by the pairing of the invariant CD94 polypeptide with specific NKG2 isoforms to form a family of functionally distinct heterodimeric receptors. However, the structural basis for this selective pairing and how they interact with their ligand, HLA-E, is unknown. We describe the 2.5 A resolution crystal structure of CD94-NKG2A in which the mode of dimerization contrasts with that of other homodimeric NK receptors. Despite structural homology between the CD94 and NKG2A subunits, the dimer interface is asymmetric, thereby providing a structural basis for the preferred heterodimeric assembly. Structure-based sequence comparisons of other CD94-NKG2 family members, combined with extensive mutagenesis studies on HLA-E and CD94-NKG2A, allows a model of the interaction between CD94-NKG2A and HLA-E to be established, in which the invariant CD94 chain plays a more dominant role in interacting with HLA-E in comparison to the variable NKG2 chain.

Natural killer cells in perinatally HIV-1-infected children exhibit less degranulation compared to HIV-1-exposed uninfected children and their expression of KIR2DL3, NKG2C, and NKp46 correlates with disease severity

NK cells play an integral role in the innate immune response by targeting virally infected and transformed cells with direct killing and providing help to adaptive responses through cytokine secretion. Whereas recent studies have focused on NK cells in HIV-1-infected adults, the role of NK cells in perinatally HIV-1-infected children is less studied. Using multiparametric flow cytometric analysis, we assessed the number, phenotype, and function of NK cell subsets in the peripheral blood of perinatally HIV-1-infected children on highly active antiretroviral therapy and compared them to perinatally exposed but uninfected children. We observed an increased frequency of NK cells expressing inhibitory killer Ig-like receptors in infected children. This difference existed despite comparable levels of total NK cells and NK cell subpopulations between the two groups. Additionally, NK cell subsets from infected children expressed, with and without stimulation, significantly lower levels of the degranulation marker CD107, which correlates with NK cell cytotoxicity. Lastly, increased expression of KIR2DL3, NKG2C, and NKp46 on NK cells correlated with decreased CD4+ T-lymphocyte percentage, an indicator of disease severity in HIV-1- infected children. Taken together, these results show that HIV-1-infected children retain a large population of cytotoxically dysfunctional NK cells relative to perinatally exposed uninfected children. This reduced function appears concurrently with distinct NK cell surface receptor expression and is associated with a loss of CD4+ T cells. This finding suggests that NK cells may have an important role in HIV-1 disease pathogenesis in HIV-1-infected children.

Features and distribution of CD8 T cells with human leukocyte antigen class I-specific receptor expression in chronic hepatitis C

CD8(+) T cells represent a sizable component of the liver inflammatory infiltrate in chronic hepatitis C and are thought to contribute to immune-mediated tissue injury. Because chronic stimulation may promote the expression by CD8(+) T cells of distinct human leukocyte antigen class I-specific natural killer cell receptors (NKRs) susceptible to both inhibiting effector functions and promoting cell survival, we examined the distribution and characteristics of CD8(+) T cells with such receptors in chronic hepatitis C patients. NKR CD8(+) T cells were detectable in liver and peripheral blood from hepatitis C virus (HCV)-infected patients but were not major subsets. However, the frequency of NKG2A(+) CD8(+) in the liver and in a lesser extent in the peripheral blood was positively correlated to histological activity in HCV-infected patients. No such correlation was found with KIR(+) T cells in liver in HCV-infected patients and with the both NKR CD8(+) T cells in hepatitis B virus (HBV) infected patients. Circulating CD8(+) T cells expressing KIRs exhibited phenotypic features of memory T cells with exacerbated expression of the senescence marker CD57 in patients. NKG2A(+)CD8(+) T cells were committed T cells that appeared less differentiated than KIR(+)CD8(+) T cells. In HCV-infected patients, their content in perforin was low and similar to that observed in NKG2A(-)CD8(+) T cells; this scenario was not observed in healthy subjects and HBV-infected patients. Both NKG2A and KIRs could inhibit the response of HCV-specific CD8(+) T cells ex vivo.

CONCLUSION

These results support the concept that an accumulation in the liver parenchyma of NKR(+)CD8(+) T cells that have functional alterations could be responsible for liver lesions. They provide novel insights into the complexity of liver-infiltrating CD8(+) T cells in chronic hepatitis C and reveal that distinct subsets of antigen-experienced CD8(+) T cells are differentially sensitive to the pervasive influence of HCV.

High expression of NKG2A/CD94 and low expression of granzyme B are associated with reduced cord blood NK cell activity

Human umbilical cord blood (CB) has recently been used as a source of stem cells in transplantation. NK cells derived from CB are the key effector cells involved in graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL). It was reported that the activity of CB NK cells was lower than that of adult peripheral blood (PB) NK cells. In this study, we analyzed the expression of some NK cell receptors and cytotoxicity-related molecules in CB and PB NK cells. The expressions of activating NK receptors, CD16, NKG2D and NKp46, did not show significant difference between CB and PB NK cells. But the expression of inhibitory receptor NKG2A/CD94 was significantly higher on CB NK cells. As to the effector function molecules, granzyme B was expressed significantly lower in CB NK cells, but the expressions of intracellular perforin, IFN-gamma, TNF-alpha and cell surface FasL and TRAIL did not show difference between CB and PB NK cells. The results indicated that the high expression of NKG2A/CD94 and low expression of granzyme B may be related with the reduced activity of CB NK cells.

Activating and inhibitory receptors on synovial fluid natural killer cells of arthritis patients: role of CD94/NKG2A in control of cytokine secretion

Natural killer (NK) cells are activated early during inflammatory events and contribute to the shaping of the ensuing adaptive immune response. To further understand the role for NK cells in inflammation, we investigated the phenotype and function of synovial fluid (SF) NK cells from patients with chronic joint inflammation, as well as from patients with transient inflammation of the knee following trauma. We confirm that synovial NK cells are similar to the well-characterized CD56(bright) peripheral blood (PB) NK-cell subset present in healthy individuals. However, compared to this PB subset the synovial NK cells express a higher degree of activation markers including CD69 and NKp44, the latter being up-regulated also on CD56(bright) NK cells in the PB of patients. Activated synovial NK cells produced interferon-gamma and tumour necrosis factor, and the production was further up-regulated by antibody masking of CD94/NKG2A, and down-regulated by target cells expressing human leucocyte antigen-E in complex with peptides known to engage CD94/NKG2A. We conclude that synovial NK cells have an activated phenotype and that CD94/NKG2A is a key regulator of synovial NK-cell cytokine synthesis.

The expression of human natural killer cell receptors in early life

Natural killer (NK) cells play an important role in tumour immunosurveillance and the early defence against viral infections. Recognition of altered cells (i.e. infected- or tumour-cells) is achieved through a multiple receptor recognition strategy which gives the NK cells inhibitory or activating signals depending on the ligands present on the target cell. NK cells originate from the bone marrow where they develop and proliferate. However, further maturation processes and homeostasis of NK cells in peripheral blood are not well understood. To determine the proportions of cells and the expression of NK cell receptors, mononuclear cells from children at three time points during early childhood were compared, i.e. cord blood (CB), 2 and 5 years of age. The proportion of NK cells was high in CB, but the interferon-gamma (IFN-gamma) production low compared to later in life. In contrast, the proportion of T cells was low in CB. This may indicate a deviation of the regulatory function of NK cells in CB compared to later in life, implying an importance of innate immunity in early life before the adaptive immune system matures. Additionally, we found that the proportion of LIR-1(+) NK cells increased with increasing age while CD94(+)NKG2C(-) (NKG2A(+)) NK cells and the level of expression of NKG2D, NKp30 and NKp46 decreased with age. These age related changes in NK cell populations defined by the expression of activating and inhibitory receptors may be the result of pathogen exposure and/or a continuation of the maturation process that begins in the bone marrow.

gammadelta-T cells expressing NK receptors predominate over NK cells and conventional T cells in the innate IFN-gamma response to Plasmodium falciparum malaria

Rapid production of interferon-gamma (IFN-gamma) in response to malaria by the innate immune system may determine resistance to infection, or inflammatory disease. However, conflicting reports exist regarding the identity of IFN-gamma-producing cells that rapidly respond to Plasmodium falciparum. To clarify this area, we undertook detailed phenotyping of IFN-gamma-producing cells across a panel of naive human donors following 24-h exposure to live schizont-infected red blood cells (iRBC). Here, we show that NK cells comprise only a small proportion of IFN-gamma-responding cells and that IFN-gamma production is unaffected by NK cell depletion. Instead, gammadelta-T cells represent the predominant source of innate IFN-gamma, with the majority of responding gammadelta-T cells expressing NK receptors. Malaria-responsive gammadelta-T cells more frequently expressed NKG2A compared to non-responding gammadelta-T cells, while non-responding gammadelta-T cells more frequently expressed CD158a/KIR2DL1. Unlike long-term gammadelta-T cell responses to iRBC, alphabeta-T cell help was not required for innate gammadelta-T cell responses. Diversity was observed among donors in total IFN-gamma output. This was positively associated with CD94 expression on IFN-gamma(+) NK-like gammadelta-T cells. Applied to longitudinal cohort studies in endemic regions, similar comparative phenotyping should allow assessment of the contribution of diverse cell populations and regulatory receptors to risk of infection and disease.

Thymic stromal lymphopoietin augments the cytolytic activity of the human natural killer cell line NK-92

Culturing the human natural killer cell line NK-92 for 24 h in the presence of thymic stromal lymphopoietin (TSLP) potentiated its cytotoxic capacity against the erythroleukemia cell line K562. Longer incubation times did not augment the NK activity any further. No synergistic effects with respect to either proliferation or cytotoxicity were observed when TSLP was mixed with suboptimal concentrations of IL-2. FACS analysis of the NK-92 cells indicated expression of TSLPR but not the other component of the TSLP receptor complex, namely IL-7Ralpha. Some of the surface molecules known to be involved in NK cell-mediated cytotoxicity were also monitored. None of the receptors analyzed altered their expression to any major extent upon culture in TSLP or IL-2. However, a limited number of NK-92 cells were observed that had a rather low CD94/NKG2A expression, which increased upon stimulation with TSLP or IL-2.

Natural killer cells of Parkinson's disease patients are set up for activation: a possible role for innate immunity in the pathogenesis of this disease

Neuroinflammation in Parkinson's disease (PD) involves activation of microglia, participation of several inflammatory cytokines, prostaglandins, complement and systemic activation of natural killer (NK) cells, suggesting that innate immunity has a role in the pathogenesis of this disease. In this study, we examined NK activity and the expression of its regulatory molecules in peripheral lymphocytes of PD patients and compared the results with those of healthy controls. Expression of the inhibitory NKG2A receptors was significantly lower in PD, causing PD patients to be susceptible in a condition for NK activation after NK cells bind to target cells via these receptors.

Expansion of natural killer cell receptor (CD94/NKG2A)-expressing cytolytic CD8 T cells and CD4+CD25+ regulatory T cells from the same cord blood unit

OBJECTIVE

Cord blood contains a significant number of precursor cells that differentiate to cytotoxic effector cells and immunoregulatory cells. We tried to expand inhibitory natural killer cell receptor CD94-expressing CD8 T cells with cytolytic activity and CD4(+)CD25(+) regulatory T cells from the same cord cell unit.

METHODS

Cytotoxic CD94-expressing CD8 T cells were expanded from CD4-depleted cord blood using an immobilized anti-CD3 monoclonal antibody and a cytokine and also CD4(+)CD25(+) regulatory T cells were expanded from a CD4-enriched fraction derived from the same cord blood unit using anti-CD3/CD28 monoclonal antibody-coated Dynabeads and cytokines.

RESULTS

We were able to obtain a more than 1000-fold expansion of CD94-expressing CD8 T cells and a more than 50-fold expansion of CD4(+)CD25(+) cells from the same cord blood unit. These expanded CD4(+)CD25(+) cells expressed FoxP3 mRNA at a level about 100-fold higher than that in isolated CD25(-) cells and could suppress allogeneic mixed lymphocyte culture by >80% (effector cells: CD4(+)CD25(+) cells = 2:1). Cytolytic activities of purified CD94-expressing cells detected by a 4-hour (51)Cr release assay against K562 were >60%. Coculture of CD94-expressing cells with expanded CD4(+)CD25(+) cells did not have any effect on cytolytic activities of purified CD94-expressing cells against K562 cells.

CONCLUSION

These expanded cytolytic CD94-expressing CD8 cells might be able to induce a graft-vs-leukemia effect without enhancing graft-vs-host disease, and CD4(+)CD25(+) cells might be able to suppress allogeneic responses, including graft-vs-host disease and graft rejection after cord blood transplantation.

Good news, bad news for missing-self recognition by NK cells: autoimmune control but viral evasion

In this issue of Immunity, Voigt et al. (2007) and Lu et al. (2007) extend the understanding of the consequences of missing-self recognition in immune evasion and immune cell regulation via NKRP-1 and CD94-NKG2A inhibitory receptors, respectively.

Regulation of activated CD4+ T cells by NK cells via the Qa-1-NKG2A inhibitory pathway

The ability of natural-killer cells to regulate adaptive immunity is not well understood. Here we define an interaction between the class Ib major histocompatibility complex (MHC) molecule Qa-1-Qdm on activated T cells responsible for adaptive immunity and CD94-NKG2A inhibitory receptors expressed by natural-killer cells by using Qa-1-deficient and Qa-1 knockin mice containing a point mutation that selectively abolishes Qa-1-Qdm binding to CD94-NKG2A receptors. The Qa-1-NKG2A interaction protected activated CD4+ T cells from lysis by a subset of NKG2A+ NK cells and was essential for T cell expansion and development of immunologic memory. Antibody-dependent blockade of this Qa-1-NKG2A interaction resulted in potent NK-dependent elimination of activated autoreactive T cells and amelioration of experimental autoimmune encephalomyelitis. These findings extend the functional reach of the NK system to include regulation of adaptive T cell responses and suggest a new clinical strategy for elimination of antigen-activated T cells in the context of autoimmune disease and transplantation.

Upregulation of CD94/NKG2A receptors and Qa-1b ligand during murine cytomegalovirus infection of salivary glands

Following acute infection, murine cytomegalovirus (MCMV) replicates persistently in the salivary glands, despite the vigorous response of activated CD8 T cells that infiltrate this gland. Virus-specific CD8 T lymphocytes isolated from this organ were found to express the inhibitory CD94/NKG2A receptor that, in some virus models, confers an inhibitory response to cytotoxic T lymphocytes (CTLs). In response to MCMV infection, expression of the CD94/NKG2A ligand, Qa-1b, increased dramatically in the submandibular gland (SMG) prior to upregulation of H-2Dd. However, there was no net negative impact on virus-specific T-cell function, as virus titres were similar in CD94- and CD94+ mice. CD94/NKG2A expression, also known to inhibit apoptosis, did not influence the numbers of accumulated T, NK and NK T cells. These data indicate that expression of inhibitory CD94/NKG2A receptors does not account for the failure of MCMV-specific CTLs to clear the SMG of infection.

A subpopulation of human peripheral blood NK cells that lacks inhibitory receptors for self-MHC is developmentally immature

How receptor acquisition correlates with the functional maturation of natural killer (NK) cells is poorly understood. We used quantitative real-time polymerase chain reaction (PCR) assays to compare NKG2 and killer immunoglobulin-like receptor (KIR) gene expression in NK cells from allogeneic transplant recipients and their donors. Marked differences were observed in the NK subsets of recipients who had 8-fold more CD56(bright) cells, diminished KIR expression (except 2DL4), and increased NKG2A. In normal blood not all CD56(dim) cells express KIR, and a novel subpopulation of cells committed to the NK-cell lineage was defined. These cells, which comprise 19.4% +/- 2.8% of the CD56(dim) NK population in healthy donors, express the activating NKG2D and NKG2E receptors but no KIR or NKG2A. Although the CD56(dim) NKG2A(-) KIR(-) NK cells lack "at least one" inhibitory receptor for autologous MHC class I, they are not fully responsive, but rather functionally immature cells with poor cytotoxicity and IFN-gamma production. Upon culture with IL-15 and a stromal cell line, CD56(dim) and CD56(bright) KIR(-) NK cells proliferate, express KIR, and develop cytotoxicity and cytokine-producing potential. These findings have implications for the function of NK cells reconstituting after transplantation and support a model for in vivo development in which CD56(bright) cells precede CD56(dim) cells.

Genomics and diversity of the common marmoset monkey NK complex

The common marmoset monkey (Callithrix jacchus) is a New World primate that is increasingly used in biomedical research as a model organism. Due to the occurrence of natural bone marrow chimerism, it represents a particularly useful primate model in immunological research. In this study, we describe the genomic organization of the CD94, NKG2, and LY49L genes in the NK complex (NKC) of the common marmoset based on complete sequencing of a bacterial artificial chromosome clonal contig. This region of the marmoset NKC is 1.5 times smaller than its human counterpart, but the genes are colinear and orthologous. One exception is the activating NKG2CE gene, which is probably an ancestral form of the NKG2C- and NKG2E-activating receptor genes of humans and great apes. The two completely sequenced marmoset bacterial artificial chromosome clones are derived from distinct haplotypes, which differ by 200 sites in the overlapping sequence. Analyses of NKC genes in nine additional marmoset individuals revealed a moderate degree of polymorphism of the CD94, NKG2A, NKG2CE, and NKG2D genes. Furthermore, expression analyses identified several alternatively spliced transcripts, particularly of the CD94 gene. Several products of alternative splicing of NKC genes are highly conserved among primates. Alternative transcriptional start sites were found, but these probably do not lead to a change of the translational start site or result in longer or shorter cytoplasmic regions of these type II membrane receptors.

Differential induction of CD94 and NKG2 in CD4 helper T cells. A consequence of influenza virus infection and interferon-gamma?

Influenza A virus causes worldwide epidemics and pandemics and the investigation of memory T helper (Th) cells that help maintain serological memory following infection is important for vaccine design. In this study we investigated CD94 and NKG2 gene expression in memory CD4 T-cell clones established from the spleens of C57BL/10 (H-2(b)) and BALB/c (H-2(d)) mice infected with influenza A virus (H3N2). CD94 and NKG2A/C/E proteins form heterodimeric membrane receptors that are involved in virus recognition. CD94 and NKG2 expression have been well characterized in natural killer (NK) and cytotoxic T cells. Despite CD94 being potentially an important marker for Th1 cells involved in virus infection, however, there has been little investigation of its expression or function in the CD4 T-cell lineage and no studies have looked at in-vivo-generated Th cells or memory cells. We show in this study that in-vivo-generated CD4 Th1 cells, but not Th2 cells, exhibited full-length CD94 and NKG2A gene expression following activation with viral peptide. For NKG2A, a novel 'short' (possibly redundant) truncated isoform was detectable in a Th2 cell clone. Another member of the NK receptor family, NKG2D, but not NKG2C or E, was also differentially expressed in Th1 cells. We show here that CD94 and NKG2A may exist as multiple isoforms with the potential to distinguish helper T-cell subsets.

Phenotypic and functional changes of cytotoxic CD56pos natural T cells determine outcome of acute hepatitis C virus infection

Innate CD56(pos) natural killer (NK) and natural T (NT) cells comprise important hepatic antiviral effector lymphocytes whose activity is fine-tuned through surface NK receptors (NKRs). Dysregulation of NKRs in patients with long-standing hepatitis C virus (HCV) infection has been shown, but little is known regarding NKRs in acute infection. Treatment-naïve patients with acute HCV (n = 22), including 10 with spontaneous recovery, were prospectively studied. CD56(pos) NT levels were reduced early in acute HCV infection and did not fluctuate over time. In resolving HCV infection, NT cells with a more activated phenotype (lower CD158A and higher natural cytotoxicity receptor expression) at baseline predated spontaneous recovery. Moreover, NKG2A expression on CD56(+) NT cells correlated directly with circulating HCV RNA levels. Deficient interleukin-13 (IL-13) production by NT cells and reduced IL-2-activated killing (LAK) at baseline were associated with the ultimate development of persistence. These results indicate a previously unappreciated role for NT cells in acute HCV infection and identify a potential target for pharmacologic manipulation.

Reconstitution of Natural Killer Cell Receptor Repertoires after Unmanipulated HLA-Mismatched/Haploidentical Blood and Marrow Transplantation: Analyses of CD94:NKG2A and Killer Immunoglobulin-Like Receptor Expression and Their Associations with Clinical Outcome

The effect of natural killer (NK) cell alloreactivity on the outcome of haploidentical hematopoietic stem cell transplantation (HSCT), with or without in vitro T cell depletion, remains controversial. Killer immunoglobulin-like receptors (KIRs) recognize human leukocyte antigen C and B epitopes on target cells, thereby regulating NK cell activity. To examine the recovery of CD94:NKG2A and KIR (CD158a, CD158b, and CD158e) expression by NK cells, we used flow cytometry to evaluate samples from 24 patients and their donors before and in the year following unmanipulated HLA-haploidentical/mismatched blood and marrow transplantation. Linear regression analysis demonstrated that NKG2A recovery was inversely correlated with CD158b recovery in the year following transplant. The doses of T cell subgroups CD4+ and CD8+ were inversely associated with CD158a and CD158e expression during the 2 months following transplantation. Moreover, patients with grades II-IV acute graft-versus-host disease (aGVHD) or who received "high" doses of T cells (>1.37 x 10(8)/kg) showed delayed recovery of KIRs during the 2 months following transplantation. Univariate analysis showed that patients with high CD94 expression by day 60 (>90%) or who received donors with high CD94 expression (>80%) were associated with higher transplantation-related mortality (P = .006 or .067, respectively) and poorer leukemia-free survival (P = .012 or .094, respectively). Thus, the occurrence of aGVHD or the receipt of high doses of T cells in the allograft altered KIR reconstitution. Furthermore, high levels of CD94 expression in donors or in recipients by day 60 might be a good predictor for poor prognosis.

Chicken CD69 and CD94/NKG2-like genes in a chromosomal region syntenic to mammalian natural killer gene complex

In mammals, natural killer (NK) cell C-type lectin receptors were encoded in a gene cluster called natural killer gene complex (NKC). The NKC is not reported in chicken yet. Instead, NK receptor genes were found in the major histocompatibility complex. In this study, two novel chicken C-type lectin-like receptor genes were identified in a region on chromosome 1 that is syntenic to mammalian NKC region. The chromosomal locations were validated with fluorescent in situ hybridization. Based on 3D structure modeling, sequence homology, chromosomal location, and phylogenetic analysis, one receptor is the orthologue of mammalian cluster of differentiation 69 (CD69), and the other is highly homologous to CD94 and NKG2. Like CD94/NKG2 gene found in teleostean fishes, chicken CD94/NKG2 has the features of both human CD94 and NKG2A. Unlike mammalian NKC, these two chicken C-type lectin receptors are not closely linked but separated by 42 million base pairs according to the chicken draft genome sequence. The arrangement of several other genes that are located outside the mammalian NKC is conserved among chicken, human, and mouse. The chicken NK C-type lectin-like receptors in the NKC syntenic region indicate that this chromosomal region existed before the divergence between mammals and aves.

Natural Regulation of Immunity to Minor Histocompatibility Antigens

MHC-matched hemopoietic stem cell transplantation is commonly used for the treatment of some forms of leukemia. Conditioning regimens before transplant act to reduce the burden of leukemic cells and the graft-vs-leukemia (GvL) effect can eliminate residual disease. The GvL effect results largely from the recognition of minor histocompatibility Ags by donor T cells on recipient tissues. These Ags are generally widely expressed and also provoke graft-vs-host (GvH) disease. Manipulation of immunity to promote GvL while curtailing GvH would greatly improve clinical outcome. To develop strategies that may achieve this, the parameters which control immunity to minor histocompatibility Ags need to be defined. In this study, we have analyzed responses to the mouse HY minor histocompatibility Ag using hemopoietic cell and skin grafts as surrogate GvL and GvH targets, respectively. We show that natural regulation of CD8 T cell responses to HY operates at multiple levels. First, CD4 T cell help is required for primary CD8 responses directed at hemopoietic cells. However, although CD4 T cells of H2(k) mouse strains recognize HY, they provide ineffective help associated with a proportion of recipients developing tolerance. This was further investigated using TCR-transgenic mice which revealed H2(k)-restricted HY-specific CD4 T cells are highly susceptible to regulation by CD25(+) regulatory T cells which expand in tolerant recipients. A second level of regulation, operating in the context of skin grafts, involves direct inhibition of CD8 T cell responses by CD94/NKG2 engagement of the nonclassical MHC class I molecule Qa1.

Cutting Edge: Distinct NK receptor profiles are imprinted on CD8 T cells in the mucosa and periphery during the same antigen challenge: role of tissue-specific factors

NK cell receptors (NKRs) modulate T lymphocyte responses by modifying the Ag activation threshold. However, what governs their expression on T cells remains unclear. In this study we show that different NKRs are imprinted on CD8 T cells in the gut mucosa and periphery during the same Ag challenge. After a viral, bacterial, and tumor challenge, most CD8 peritoneal exudate lymphocytes expressed NKG2A but not 2B4. In contrast, most CD8 intraepithelial lymphocytes exhibited 2B4 but not NKG2A. Our data suggest that tissue-specific factors may determine the pattern of NKR expression. In the gut, CD70 licensing appears to promote 2B4 induction on mucosal CD8 T cells. Conversely, retinoic acid produced by the intestinal dendritic cells may suppress NKG2A expression. Thus, tissue-specific factors regulate NKR expression and may confer T cells with differing effector functions in a tissue and site-specific manner.

Telomere length in human natural killer cell subsets

Natural killer (NK) cells are cytotoxic cells that play a critical role in the innate immune response against infections and tumors. In the elderly, the cytotoxic function of NK cells is often compromised. Telomeres progressively shorten with each cell division and with age in most somatic cells eventually leading to chromosomal instability and cellular senescence. We studied the telomere length in NK cell subsets isolated from peripheral blood using "flow FISH," a method in which the hybridization of telomere probe in cells of interest is measured relative to internal controls in the same tube. We found that the average telomere length in human NK cells decreased with age as was previously found for human T lymphocytes. Separation of adult NK cells based on CD56 and CD16 expression revealed that the telomere length was significantly shorter in CD56(dim)CD16(+) (mature) NK cells compared to CD56(bright)CD16(-) (immature) NK cells from the same donor. Furthermore, sorting of NK cells based on expression of activation markers, such as NKG2D and LFA-1, revealed that NK cells expressing these markers have significantly shorter telomeres. Telomere fluorescence was very heterogeneous in NK cells expressing CD94, killer inhibitory receptor (KIR), NKG2A, or CD161. Our observations indicate that telomeric DNA in NK cells is lost with cell division and with age similar to what has been observed for most other hematopoietic cells. Telomere attrition in NK cells is a plausible cause for diminished NK cell function in the elderly.

Expression and function of NKG2D in CD4+ T cells specific for human cytomegalovirus

The human NKG2D killer lectin-like receptor (KLR) is coupled by the DAP10 adapter to phosphoinositide 3-kinase (PI3 K) and specifically interacts with different stress-inducible molecules (i.e. MICA, MICB, ULBP) displayed by some tumour and virus-infected cells. This KLR is commonly expressed by human NK cells as well as TCRgammadelta(+) and TCRalphabeta(+)CD8(+) T lymphocytes, but it has been also detected in CD4(+) T cells from rheumatoid arthritis and cancer patients. In the present study, we analysed NKG2D expression in human cytomegalovirus (HCMV)-specific CD4(+) T lymphocytes. In vitro stimulation of peripheral blood mononuclear cells (PBMC) from healthy seropositive individuals with HCMV promoted variable expansion of CD4(+)NKG2D(+) T lymphocytes that coexpressed perforin. NKG2D was detected in CD28(-) and CD28(dull )subsets and was not systematically associated with the expression of other NK cell receptors (i.e. KIR, CD94/NKG2 and ILT2). Engagement of NKG2D with specific mAb synergized with TCR-dependent activation of CD4(+) T cells, triggering proliferation and cytokine production (i.e. IFN-gamma and TNF-alpha). Altogether, the data support the notion that NKG2D functions as a prototypic costimulatory receptor in a subset of HCMV-specific CD4(+) T lymphocytes and thus may have a role in the response against infected HLA class II(+) cells displaying NKG2D ligands.

Complexity in the cattle CD94/NKG2 gene families

Natural killer cell responses are controlled to a large extent by the interaction of an array of inhibitory and activating receptors with their ligands. The mostly nonpolymorphic CD94/NKG2 receptors in both humans and mice were shown to recognize a single nonclassical MHC class I molecule in each case. In this paper, we describe the CD94/NKG2 gene family in cattle. NKG2 and CD94 sequences were amplified from cDNA derived from four animals. Four CD94 sequences, ten NKG2A, and three NKG2C sequences were identified in total. In contrast to human, we show that cattle have multiple distinct NKG2A genes, some of which show minor allelic variation. All of the sequences designated NKG2A have two tyrosine-based inhibitory motifs in the cytoplasmic domain and one putative gene has, in addition, a charged residue in the transmembrane domain. NKG2C appears to be essentially monomorphic in cattle. All of the NKG2A sequences are similar apart from NKG2A-01, which, in contrast, shares the majority of its carbohydrate recognition domain with NKG2-C. Most of the genes appear to generate multiple alternatively spliced forms. These findings suggest that the CD94/NKG2A heterodimers in cattle, in contrast to other species, are binding several different ligands. Because NKG2C is not polymorphic, this raises questions as to the combined functional capacity of the CD94/NKG2 gene families in cattle.

The CD94/NKG2 family of receptors: from molecules and cells to clinical relevance

Immune responses must be tightly regulated to avoid hyporesponsiveness on one hand or excessive inflammation and the development of autoimmunity (hyperresponsiveness) on the other hand. This balance is attained through the throttling of activating signals by inhibitory signals that ideally leads to an adequate immune response against an invader without excessive and extended inflammatory signals that promote the development of autoimmunity. The CD94/NKG2 family of receptors is composed of members with activating or inhibitory potential. These receptors are expressed predominantly on NK cells and a subset of CD8+ T cells, and they have been shown to play an important role in regulating responses against infected and tumorigenic cells. In this review, we discuss the current knowledge about this family of receptors, including ligand and receptor interaction, signaling, membrane dynamics, regulation of gene expression and their roles in disease regulation, infections, and cancer, and bone marrow transplantation.

Natural killer cell and hepatic cell interaction via NKG2A leads to dendritic cell-mediated induction of CD4 CD25 T cells with PD-1-dependent regulatory activities

Natural killer (NK) cells have the ability to control dendritic cell (DC)-mediated T cell responses. However, the precise mechanisms by which NK receptor-mediated regulation of NK cells determines the magnitude and direction of DC-mediated T cell responses remain unclear. In the present study, we applied an in vitro co-culture system to examine the impact of NK cells cultured with hepatic cells on DC induction of regulatory T cells. We found that interaction of NK cells and non-transformed hepatocytes (which express HLA-E) via the NKG2A inhibitory receptor resulted in priming of DCs to induce CD4(+) CD25(+) T cells with regulatory properties. NKG2A triggering led to characteristic changes of the cytokine milieu of co-cultured cells; an increase in the transforming growth factor (TGF)-beta involved in the generation of this specific type of DC, and a decrease in the tumour necrosis factor-alpha capable of antagonizing the effect of TGF-beta. The regulatory cells induced by NK cell-primed DCs exert their suppressive actions through a negative costimulator programmed death-1 (PD-1) mediated pathway, which differs from freshly isolated CD4(+) CD25(+) T cells. These findings provide new insight into the role of NK receptor signals in the DC-mediated induction of regulatory T cells.

CD94/NKG2A inhibits NK cell activation by disrupting the actin network at the immunological synapse

An adequate immune response is the result of the fine balance between activation and inhibitory signals. The exact means by which inhibitory signals obviate activation signals in immune cells are not totally elucidated. Human CD94/NKG2A is an ITIM-containing inhibitory receptor expressed by NK cells and some CD8+ T cells that recognize HLA-E. We show that the engagement of this receptor prevents NK cell activation by disruption of the actin network and exclusion of lipid rafts at the point of contact with its ligand (inhibitory NK cell immunological synapse, iNKIS). CD94/NKG2A engagement leads to recruitment and activation of src homology 2 domain-bearing tyrosine phosphatase 1. This likely explains the observed dephosphorylation of guanine nucleotide exchange factor and regulator of actin, Vav1, as well as ezrin-radixin-moesin proteins that connect actin filaments to membrane structures. In contrast, NK cell activation by NKG2D induced Vav1 and ezrin-radixin-moesin phosphorylation. Thus, CD94/NKG2A prevents actin-dependent recruitment of raft-associated activation receptors complexes to the activating synapse. This was further substantiated by showing that inhibition of actin polymerization abolished lipid rafts exclusion at the iNKIS, whereas cholesterol depletion had no effect on actin disruption at the iNKIS. These data indicate that the lipid rafts exclusion at the iNKIS is an active process which requires an intact cytoskeleton to maintain lipid rafts outside the inhibitory synapse. The net effect is to maintain an inhibitory state in the proximity of the iNKIS, while allowing the formation of activation synapse at distal points within the same NK cell.

Evidence of NK cell dysfunction in SIV-infected rhesus monkeys: impairment of cytokine secretion and NKG2C/C2 expression

Defects in the adaptive immune response have been extensively characterized in human immunodeficiency virus type-1 (HIV-1)-infected individuals; however, much less is known about the function of natural killer (NK) cells during the course of HIV-1 infection. In the present study, we demonstrate that the NK cells from simian immunodeficiency virus (SIV)-infected rhesus monkeys are significantly impaired in their ability to secrete IFN-gamma, TNF-alpha, and IL-2, while NK cell function in SIV-infected long-term non-progressor monkeys is similar to that of normal monkeys. These findings suggest that abnormal NK cell activity may contribute to the global immune dysfunction observed in HIV-1-infected individuals. NK cell function is modulated by several families of cell surface receptors, including the CD94/NKG2 family. We evaluated the messenger RNA levels of these inhibitory and activating NKG2 molecules in SIV-infected rhesus monkeys. These experiments demonstrate that the activating molecules NKG2C and NKG2C2 are significantly down-regulated in peripheral blood mononuclear cells of SIV-infected rhesus monkeys, suggesting that the dysregulation of these molecules may contribute to the abnormal NK cell function observed in the setting of infection.

NKG2C+ NK cells are enriched in AIDS patients with advanced-stage Kaposi's sarcoma

Kaposi's sarcoma (KS) is an AIDS-defining condition in individuals with human immunodeficiency virus type 1 infection. We investigated the phenotype and function of the NKG2C+ NK cell population in individuals with AIDS and Kaposi's sarcoma. The staging of AIDS KS patients according to the AIDS Clinical Trial Group criteria revealed that patients with the S1 disease stage have a significantly higher proportion of NKG2C+ cells than those with the S0 disease stage. NKG2C+ cells from S1-stage patients are highly enriched for the expression of KIR3DL1, are depleted of NKp46, and respond poorly to major histocompatibility complex class I-positive target cells. These data demonstrate a link between NK cell phenotype and function and disease prognosis in AIDS.

Binding of sialyl Lewis X antigen to lectin-like receptors on NK cells induces cytotoxicity and tyrosine phosphorylation of a 17-kDa protein

BACKGROUND

Natural killer (NK) cells mediate cytotoxicity through cell-surface receptors including lectin-like receptors. We have investigated whether sialyl Lewis X (sLe(X)) antigen, Neu5Acalpha2,3Galbeta1,4(Fucalpha1,3) GlcNAc-R, can bind to the lectin-like receptors on human NK-derived KHYG cells, using transferrin secreted by human hepatoma-derived HepG2 cells (Hep-TF), whose N-glycans are rich in alpha1,3-fucosylated bi-, tri-, and tetra-antennary type complexes, and commercially available human transferrin (Nor-TF), which is comprised of bi-antennary N-glycans without alpha1,3-fucosylation.

RESULTS

High sLeX-expressing erythroleukemia-derived K562 cells isolated from fucosyltransferase-3-transfected cells were 2.5-fold more susceptible than wild-type K562 cells to KHYG cells. Fluorescein isothiocyanate (FITC)-labeled Hep-TF bound 1.8-fold more strongly to KHYG cells than did FITC-labeled Nor-TF; the binding was suppressed by treatment with anti-NKG2D, anti-NKG2C, anti-CD94 and anti-CD161 antibodies. FITC-labeled Hep-TF bound more strongly to human monocyte-derived U937 cells transfected with NKG2D and CD94 than to wild-type U937 cells. Moreover, tyrosine phosphorylation of a 17-kDa protein in the KHYG cells was enhanced by incubation on a Hep-TF coated plate and treatment with an anti-NKG2D antibody, but not by a Nor-TF coated plate and an anti-CD94 antibody.

CONCLUSION

The interaction of sLe(X) antigen with lectin-like receptors on NK cells induces cytotoxicity that is mediated through a tyrosine-phosphorylated 17-kDa protein.