Expression of KIR2DL1 on the entire NK cell population: a possible novel immunodeficiency syndrome

Decreased IL-6 and NK Cells in Early-Stage Lung Adenocarcinoma Presenting as Ground-Glass Opacity

Background

Lung ground-glass opacities (GGOs) are an early manifestation of lung adenocarcinoma. It is of great value to study the changes in the immune microenvironment of GGO to elucidate the occurrence and evolution of early lung adenocarcinoma. Although the changes of IL-6 and NK cells in lung adenocarcinoma have caught global attention, we have little appreciation for how IL-6 and NK cells in the lung GGO affect the progression of early lung adenocarcinoma.

Methods

We analyzed the RNA sequencing data of surgical specimens from 21 patients with GGO-featured primary lung adenocarcinoma and verified the changes in the expression of IL-6 and other important immune molecules in the TCGA and GEO databases. Next, we used flow cytometry to detect the protein expression levels of important Th1/Th2 cytokines in GGO and normal lung tissues and the changes in the composition ratio of tumor infiltrating lymphocytes (TILs). Then, we analyzed the effect of IL-6 on NK cells through organoid culture and immunofluorescence. Finally, we explored the changes of related molecules and pathway might be involved.

Results

IL-6 may play an important role in the tumor microenvironment of early lung adenocarcinoma. Further research confirmed that the decrease of IL-6 in GGO tissue is consistent with the changes in NK cells, and there seems to be a correlation between these two phenomena.

Conclusion

The IL-6 expression status and NK cell levels of early lung adenocarcinoma as GGO are significantly reduced, and the stimulation of IL-6 can up-regulate or activate NK cells in GGO, providing new insights into the diagnosis and pathogenesis of early lung cancer.

Role of KIR Receptor in NK Regulation during Viral Infections

Natural Killer (NK) cells are key effectors of the innate immune system which represent the first line of defense against viral infections. NK cell activation depends on the engagement of a complex receptor repertoire expressed on their surface, consisting of both activating and inhibitory receptors. Among the known NK cell receptors, the family of killer Ig-like receptors (KIRs) consists in activating/inhibitory receptors that interact with specific human leukocyte antigen (HLA) molecules expressed on target cells. In particular, the expression of peculiar KIRs have been reported to be associated to viral infection susceptibility. Interestingly, a significant association between the development and onset of different human pathologies, such as tumors, neurodegeneration and infertility, and a clonal KIRs expression on NK cells has been described in presence of viral infections, supporting the crucial role of KIRs in defining the effect of viral infections in different tissues and organs. This review aims to report the state of art about the role of KIRs receptors in NK cell activation and viral infection control.

Individualized genetic makeup that controls natural killer cell function influences the efficacy of isatuximab immunotherapy in patients with multiple myeloma

BACKGROUND

Phase IIb clinical trial with isatuximab (Isa)-lenalidomide (Len)-dexamethasone (Dex) showed an improved progression-free survival (PFS) in patients with relapsed or refractory multiple myeloma (RRMM), but the efficacy varied by patient. Antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) cells plays a crucial role in arbitrating antitumor activities of therapeutic-antibodies. We tested if patient-specific genetic makeup known to set NK cell functional threshold influence response to Isa-Len-Dex therapy.

METHODS

We characterized 57 patients with RRMM receiving Isa-Len-Dex for polymorphisms of killer-cell immunoglobulin-like receptors (KIR), human leukocyte antigen (HLA) class I, and FCGR3A loci. In vitro ADCC assay, coincubating primary NK cells expressing specific KIR repertoire with multiple myeloma cell lines (MM cells) expressing selected HLA class I ligands, was used to confirm the identified genetic correlatives of clinical response.

RESULTS

Patients with KIR3DL2+ and its cognate-ligand HLA-A3/11+ had superior PFS than patients missing this combination (HR=0.43; p=0.02), while patients carrying KIR2DL1+ and HLA-C2C2+ compared with to patients missing this pair showed short PFS (HR=3.54; p=0.05). Patients with KIR3DL2+ and HLA-A3/11+ plus high-affinity FCGR3A-158V allele showed the most prolonged PFS (HR=0.35; p=0.007). Consistent with these clinical data, mechanistic experiments demonstrated that NK cells expressing KIR3DL2 trigger greater ADCC when MM cells express HLA-A3/11. Inversely, NK cells expressing KIR2DL1 do not kill if MM cells express the HLA-C2C2 ligand. NK cells expressing high-affinity FCGR3A-158VV-induced greater ADCC compared with those with low-affinity FCGR3A-158FF.

CONCLUSIONS

Our results suggest that KIR3DL2+ and HLA-A3/11+ with FCGR3A-158V markers lead to enhanced Isa-dependent NK-mediated cytolysis against MM cells and results in improved PFS in patients with RRMM treated by Isa-Len-Dex. Moreover, the presence of KIR2DL1+ and HLA-C2C2+ identifies patients who may have a lower response to Isa-Len-Dex therapy linked to a reduced NK-mediated ADCC. These biomarkers could potentially identify, via precision medicine, patients more likely to respond to Isa-Len-Dex immunotherapy.

TRIAL REGISTRATION NUMBER

NCT01749969.

The effect of KIR and HLA polymorphisms on dengue infection and disease severity in northeastern Thais

Killer cell immunoglobulin-like receptors (KIRs) are cell surface receptors on natural killer (NK) cells and subsets of T cells. The interaction between KIRs and their cognate ligands (Human leukocyte antigen class I molecules, HLA class I) modulates the immune response of NK cells, in particular through clearance of virus-infected cells. Here, we investigated the effect of KIRs and HLA ligands on dengue infections and disease severity. The KIRs and HLA ligands were identified in 235 healthy controls (HC) and 253 dengue patients (DEN) using polymerase chain reaction with sequence specific primer (PCR-SSP); moreover, DEN was classified to 100 dengue fever (DF) and 153 dengue haemorrhagic fever (DHF). Risks were expressed as odds ratios (ORs) and 95% confidence intervals (CIs) with significance set at a two-tailed P value of < 0.05. The Bonferroni correction was applied for multiple comparisons. Twelve significant associations were observed in dengue infections and disease severity; however, two outcomes survived after the Bonferroni correction. Of these, HLA-A11 was associated with an increased risk to develop dengue disease (OR 2.41, 95% CI 1.62-3.60, P^c = 0.004), while KIR3DS1⁺ Bw4 was a protective genotype to developing DHF (OR 0.28, 95% CI 0.16-0.48, P^c < 0.001). This study revealed an important role of KIR and HLA ligands in innate immune responses to dengue viral infections and, in particular, their effect on clinical outcomes and disease severity.

Natural killer cell receptor variants and chronic hepatitis B virus infection in the Vietnamese population

OBJECTIVES

Genes of host immunity play an important role in disease pathogenesis and are determinants of clinical courses of infections, including hepatitis B virus (HBV). Killer-cell immunoglobulin-like receptor (KIR), expressed on the surface of natural killer cells (NK), regulate NK cell cytotoxicity by interacting with human leukocyte antigen (HLA) class I molecules and are candidates for influencing the course of HBV. This study evaluated whether variations in KIR gene content and HLA-C ligands are associated with HBV and with the development of liver cirrhosis and hepatocellular carcinoma.

METHODS

A Vietnamese study cohort (HBV n = 511; controls n = 140) was genotyped using multiplex sequence-specific polymerase chain reaction (PCR-SSP) followed by melting curve analysis.

RESULTS

The presence of the functional allelic group of KIR2DS4 was associated with an increased risk of chronic HBV (OR = 1.86, p^corr = 0.02), while KIR2DL2+HLA-C1 (OR = 0.62, p^corr = 0.04) and KIR2DL3+HLA-C1 (OR = 0.48, p^corr = 0.04) were associated with a decreased risk. The pair KIR2DL3+HLA-C1 was associated with liver cirrhosis (OR = 0.40, p^corr = 0.01). The presence of five or more activating KIR variants was associated with hepatocellular carcinoma (OR = 0.53, p^corr = 0.04).

CONCLUSIONS

KIR gene content variation and combinations KIR-HLA influence the outcome of HBV infection.

HIV-1-induced cytokines deplete homeostatic innate lymphoid cells and expand TCF7-dependent memory NK cells

Human immunodeficiency virus 1 (HIV-1) infection is associated with heightened inflammation and excess risk of cardiovascular disease, cancer and other complications. These pathologies persist despite antiretroviral therapy. In two independent cohorts, we found that innate lymphoid cells (ILCs) were depleted in the blood and gut of people with HIV-1, even with effective antiretroviral therapy. ILC depletion was associated with neutrophil infiltration of the gut lamina propria, type 1 interferon activation, increased microbial translocation and natural killer (NK) cell skewing towards an inflammatory state, with chromatin structure and phenotype typical of WNT transcription factor TCF7-dependent memory T cells. Cytokines that are elevated during acute HIV-1 infection reproduced the ILC and NK cell abnormalities ex vivo. These results show that inflammatory cytokines associated with HIV-1 infection irreversibly disrupt ILCs. This results in loss of gut epithelial integrity, microbial translocation and memory NK cells with heightened inflammatory potential, and explains the chronic inflammation in people with HIV-1.

KIR Polymorphism Modulates the Size of the Adaptive NK Cell Pool in Human Cytomegalovirus-Infected Individuals

Acute infection with human CMV (HCMV) induces the development of adaptive NKG2C⁺ NK cells. In some cases, large expansions of this subset, characterized by coexpression of HLA-C-specific KIR, are stably maintained during the life-long latent phase of infection. The factors that control these unusual expansions in vivo are currently unknown. In this study, the role of KIR polymorphism and expression in this process was analyzed. It is shown that strong NKG2C⁺ NK cell expansions are dominated by single KIR clones, whereas moderate expansions are frequently polyclonal (p < 0.0001). Importantly, the choice of KIR was not arbitrary but biased toward usage of HLA-C-specific KIR encoded by the centromeric part of group A (cenA) haplotypes. Consideration of KIR allelic variation and gene copy number revealed that the cenA effect was predominantly due to the HLA-C2-specific KIR2DL1 receptor; presence of KIR2DL1 on NKG2C⁺ NK cells led to significantly larger clonal expansions than the cenB-encoded KIR2DL2 (p = 0.002). Expansion of NKG2C⁺KIR2DL1⁺ NK cells was always accompanied by the cognate ligand HLA-C2. Moreover, in these donors the frequency of NKG2C⁺ NK cells correlated with the concentration of anti-HCMV IgG (r = 0.62, p = 0.008), suggesting direct relevance of NKG2C⁺KIR2DL1⁺ NK cells for virus control. Altogether, the study suggests that the homeostasis of NKG2C⁺ NK cells in HCMV infection is at least partly controlled by coexpression of cognate inhibitory KIR. In particular, the strong interaction of KIR2DL1 and HLA-C2 ligands seems to promote large and stable expansion of adaptive NK cells in HCMV infection.

Role of Immunogenetics in the Outcome of HCMV Infection: Implications for Ageing

The outcome of host-virus interactions is determined by a number of factors, some related to the virus, others to the host, such as environmental factors and genetic factors. Therefore, different individuals vary in their relative susceptibility to infections. Human cytomegalovirus (HCMV) is an important pathogen from a clinical point of view, as it causes significant morbidity and mortality in immunosuppressed or immunosenescent individuals, such as the transplanted patients and the elderly, respectively. It is, therefore, important to understand the mechanisms of virus infection control. In this review, we discuss recent advances in the immunobiology of HCMV-host interactions, with particular emphasis on the immunogenetic aspects (human leukocyte antigens, HLA; killer cell immunoglobulin-like receptors, KIRs; immunoglobulin genetic markers, GM allotypes) to elucidate the mechanisms underlying the complex host-virus interaction that determine various outcomes of HCMV infection. The results, which show the role of humoral and cellular immunity in the control of infection by HCMV, would be valuable in directing efforts to reduce HCMV spurred health complications in the transplanted patients and in the elderly, including immunosenescence. In addition, concerning GM allotypes, it is intriguing that, in a Southern Italian population, alleles associated with the risk of developing HCMV symptomatic infection are negatively associated with longevity.

Natural killer cells attenuate cytomegalovirus-induced hearing loss in mice

Congenital cytomegalovirus (CMV) infection is the most common non-hereditary cause of sensorineural hearing loss (SNHL) yet the mechanisms of hearing loss remain obscure. Natural Killer (NK) cells play a critical role in regulating murine CMV infection via NK cell recognition of the Ly49H cell surface receptor of the viral-encoded m157 ligand expressed at the infected cell surface. This Ly49H NK receptor/m157 ligand interaction has been found to mediate host resistance to CMV in the spleen, and lung, but is much less effective in the liver, so it is not known if this interaction is important in the context of SNHL. Using a murine model for CMV-induced labyrinthitis, we have demonstrated that the Ly49H/m157 interaction mediates host resistance in the temporal bone. BALB/c mice, which lack functional Ly49H, inoculated with mCMV at post-natal day 3 developed profound hearing loss and significant outer hair cell loss by 28 days of life. In contrast, C57BL/6 mice, competent for the Ly49H/m157 interaction, had minimal hearing loss and attenuated outer hair cell loss with the same mCMV dose. Administration of Ly49H blocking antibody or inoculation with a mCMV viral strain deleted for the m157 gene rendered the previously resistant C57BL/6 mouse strain susceptible to hearing loss to a similar extent as the BALB/c mouse strain indicating a direct role of the Ly49H/m157 interaction in mCMV-dependent hearing loss. Additionally, NK cell recruitment to sites of infection was evident in the temporal bone of inoculated susceptible mouse strains. These results demonstrate participation of NK cells in protection from CMV-induced labyrinthitis and SNHL in mice.

Cytomegalovirus (CMV) transmission from an infected mother to her fetus is a leading cause of permanent hearing loss in children, but the contributing processes are not clear. In this report, we utilized a mouse model, which recapitulates many features of congenital CMV mediated childhood hearing loss, to demonstrate that natural killer cells (NK), a component of early host immune response to infection, play a critical protective role in CMV-induced hearing loss. Specifically, we determined that NK cells interact with CMV infected cells through binding of the NK cell receptor, Ly49H, with a virally-encoded protein, m157, expressed on the cell surface of CMV infected inner ear cells, to mediate the protective effect. Findings from this study provide insight into the host immune response during CMV-induced hearing loss in mice.

A constant companion: immune recognition and response to cytomegalovirus with aging and implications for immune fitness

Approximately 50% of individuals aged 6-49 years in the United States are infected with cytomegalovirus (CMV), with seroprevalence increasing with age, reaching 85-90% by 75-80 years according to Bate et al. (Clin Infect Dis 50 (11): 1439-1447, 2010) and Pawelec et al. (Curr Opin Immunol 24:507-511, 2012). Following primary infection, CMV establishes lifelong latency with periodic reactivation. Immunocompetent hosts experience largely asymptomatic infection, but CMV can cause serious illness in immunocompromised populations, such as transplant patients and the elderly. Control of CMV requires constant immune surveillance, and recent discoveries suggest this demand alters general features of the immune system in infected individuals. Here, we review recent advances in the understanding of the immune response to CMV and the role of CMV in immune aging and fitness, while highlighting the importance of potential confounding factors that influence CMV studies. Understanding how CMV contributes to shaping "baseline" immunity has important implications for a host's ability to mount effective responses to diverse infections and vaccination.

The Expression of Human Cytomegalovirus MicroRNA MiR-UL148D during Latent Infection in Primary Myeloid Cells Inhibits Activin A-triggered Secretion of IL-6

The successful establishment and maintenance of human cytomegalovirus (HCMV) latency is dependent on the expression of a subset of viral genes. Whilst the exact spectrum and functions of these genes are far from clear, inroads have been made for protein-coding genes. In contrast, little is known about the expression of non-coding RNAs. Here we show that HCMV encoded miRNAs are expressed de novo during latent infection of primary myeloid cells. Furthermore, we demonstrate that miR-UL148D, one of the most highly expressed viral miRNAs during latent infection, directly targets the cellular receptor ACVR1B of the activin signalling axis. Consistent with this, we observed upregulation of ACVR1B expression during latent infection with a miR-UL148D deletion virus (ΔmiR-UL148D). Importantly, we observed that monocytes latently infected with ΔmiR-UL148D are more responsive to activin A stimulation, as demonstrated by their increased secretion of IL-6. Collectively, our data indicates miR-UL148D inhibits ACVR1B expression in latently infected cells to limit proinflammatory cytokine secretion, perhaps as an immune evasion strategy or to postpone cytokine-induced reactivation until conditions are more favourable. This is the first demonstration of an HCMV miRNA function during latency in primary myeloid cells, implicating that small RNA species may contribute significantly to latent infection.

Influence of KIR genes and their HLA ligands in susceptibility to dengue in a population from southern Brazil

Killer cell immunoglobulin-like receptors (KIR) form a group of regulatory molecules that specifically recognise human leukocyte antigen (HLA) class I molecules, modulating the cytolytic activity of natural killer cells. The purpose of this study was to investigate the influence of KIR genes and their class I HLA ligands in susceptibility to dengue fever in a population from southern Brazil through a case-control study. One hundred four subjects with confirmed diagnoses of dengue participated in this study, along with a control group of 172 individuals from the same geographic area. HLA and KIR genotyping was performed by polymerase chain reaction with sequence-specific oligonucleotide probes (PCR-SSOP) and with sequence-specific primer (PCR-SSP) techniques, respectively. Data analysis showed significant differences for the KIR2DS1 (54.8% vs 40.7%, P = 0.03), KIR2DS5 (50.0% vs 36.0%, P = 0.03) and KIR2DL5 (76.0% vs 56.4%, P = 0.001) genes. With regard to KIR-ligand pairs, positive associations with dengue were observed in KIR3DS1-Bw4 (45.2% vs 29.7%, P = 0.01), KIR3DL1-Bw4 (80.7% vs 65.1%, P < 0.001), KIR2DL1-C2 (75.0% vs 62.2%, P = 0.03) and KIR2DS1-C2 (40.4% vs 25.6%, P = 0.01) interactions, and a negative association in KIR2DL3-C1/C1 (18.2% vs 33.1%, P = 0.01). Furthermore, the analysis of KIR haplogroups showed a possible protective factor against dengue fever in individuals with the AA genotype. Taken together, these results suggest the existence of genetic predisposition to dengue fever in the population from southern Brazil.

Two novel human cytomegalovirus NK cell evasion functions target MICA for lysosomal degradation

NKG2D plays a major role in controlling immune responses through the regulation of natural killer (NK) cells, αβ and γδ T-cell function. This activating receptor recognizes eight distinct ligands (the MHC Class I polypeptide-related sequences (MIC) A andB, and UL16-binding proteins (ULBP)1-6) induced by cellular stress to promote recognition cells perturbed by malignant transformation or microbial infection. Studies into human cytomegalovirus (HCMV) have aided both the identification and characterization of NKG2D ligands (NKG2DLs). HCMV immediate early (IE) gene up regulates NKGDLs, and we now describe the differential activation of ULBP2 and MICA/B by IE1 and IE2 respectively. Despite activation by IE functions, HCMV effectively suppressed cell surface expression of NKGDLs through both the early and late phases of infection. The immune evasion functions UL16, UL142, and microRNA(miR)-UL112 are known to target NKG2DLs. While infection with a UL16 deletion mutant caused the expected increase in MICB and ULBP2 cell surface expression, deletion of UL142 did not have a similar impact on its target, MICA. We therefore performed a systematic screen of the viral genome to search of addition functions that targeted MICA. US18 and US20 were identified as novel NK cell evasion functions capable of acting independently to promote MICA degradation by lysosomal degradation. The most dramatic effect on MICA expression was achieved when US18 and US20 acted in concert. US18 and US20 are the first members of the US12 gene family to have been assigned a function. The US12 family has 10 members encoded sequentially through US12-US21; a genetic arrangement, which is suggestive of an 'accordion' expansion of an ancestral gene in response to a selective pressure. This expansion must have be an ancient event as the whole family is conserved across simian cytomegaloviruses from old world monkeys. The evolutionary benefit bestowed by the combinatorial effect of US18 and US20 on MICA may have contributed to sustaining the US12 gene family.

HLA and killer cell immunoglobulin-like receptors influence the natural course of CMV infection

BACKGROUND

Natural killer (NK) cells provide a major defense against cytomegalovirus (CMV) infection through the interaction of their surface receptors, including the activating and inhibitory killer immunoglobulin-like receptors (KIRs), and human leukocyte antigens (HLA) class I molecules. This study assessed whether the KIR and HLA repertoire may influence the risk of developing symptomatic or asymptomatic disease after primary CMV infection in the immunocompetent host.

METHODS

Sixty immunocompetent patients with primary symptomatic CMV infection were genotyped for KIR and their HLA ligands, along with 60 subjects with a previous asymptomatic infection as controls.

RESULTS

The frequency of the homozygous A haplotype (only KIR2DS4 as activating KIR) was higher in symptomatic patients than controls (30% vs 12%, respectively; odds ratio [OR] = 3.24; P = .01). By logistic regression, the risk of developing symptomatic disease was associated with the homozygous A haplotype and the HLABw4(T) allele. Combining the 2 independent variables, we found that 37 out of 60 (62%) symptomatic patients but only 18 out of 60 (30%) of controls possessed the homozygous A haplotype or the HLABw4(T) allele with a highly significant OR (OR = 3.75, P < .0005).

CONCLUSIONS

Immunocompetent subjects carrying the homozygous A haplotype or the HLABw4(T) allele are at higher risk of developing symptomatic disease after primary CMV infection.

Genetics of microscopic polyangiitis in the Japanese population

The epidemiology of ANCA-associated vasculitis is substantially different between Caucasians and Japanese, which may be related to differences in genetic backgrounds. In this review, I discussed our findings on the genetics of microscopic polyangiitis (MPA) in Japanese. Analysis of HLA genes revealed a significant increase in the HLA-DRB1*09:01-DQB1*03:03 haplotype MPA. This is one of the most frequent haplotypes in Japanese, but is nearly absent in Caucasians, and has been shown to be associated with multiple autoimmune diseases. Analysis of KIR genes revealed significant decreases in the carrier frequency of an activating receptor KIR2DS3 in MPA. When KIRs were analyzed in combination with HLA ligands, the proportion of individuals carrying KIR3DL1 and HLA-Bw4 but not KIR3DS1, the most inhibitory of all KIR3DS1/3DL1/HLA-B combinations, was significantly increased in MPA. These results suggested that decreased activation of NK and/or T cells may cause a predisposition to MPA. LILRA2 is an activating receptor involved in granulocyte and macrophage activation. LILRA2 SNP rs2241524 G >A, which disrupts the intron 6 splice acceptor site, was significantly associated with MPA. The risk allele produces an LILRA2 isoform lacking three amino acids in the linker region. These findings, when confirmed by larger-scale studies, will shed light on the molecular mechanisms of MPA. (*English Translation of J Jpn Coll Angiol 2009; 49: 31-37.).

Genetic dissection of NK cell responses

The association of Natural Killer (NK) cell deficiencies with disease susceptibility has established a central role for NK cells in host defence. In this context, genetic approaches have been pivotal in elucidating and characterizing the molecular mechanisms underlying NK cell function. To this end, homozygosity mapping and linkage analysis in humans have identified mutations that impact NK cell function and cause life-threatening diseases. However, several critical restrictions accompany genetic studies in humans. Studying NK cell pathophysiology in a mouse model has therefore proven a useful tool. The relevance of the mouse model is underscored by the similarities that exist between cell-structure-sensing receptors and the downstream signaling that leads to NK cell activation. In this review, we provide an overview of how human and mouse quantitative trait locis (QTLs) have facilitated the identification of genes that modulate NK cell development, recognition, and killing of target cells.

Control of human viral infections by natural killer cells

Natural killer (NK) cells are effector cells of the innate immune system and are important in the control of viral infections. Their relevance is reflected by the multiple mechanisms evolved by viruses to evade NK cell-mediated immune responses. Over recent years, our understanding of the interplay between NK cell immunity and viral pathogenesis has improved significantly. Here, we review the role of NK cells in the control of four important viral infections in humans: cytomegalovirus, influenza virus, HIV-1, and hepatitis C virus.

Natural killer cell functional defects in pediatric patients with severe and recurrent herpesvirus infections

Natural killer (NK) cells play a critical role in the host defense against herpesviruses. Although herpesviruses are ubiquitous in human populations, only a minority of people experience severe recurrent infections. We hypothesize that uncharacterized NK cell functional deficits predispose individuals to more significant or frequent herpesvirus infections and reactivations. To investigate this hypothesis, we broadly analyzed NK cell phenotype and functional responses in a cohort of predominantly pediatric patients with recurrent and/or severe herpesvirus infections and compared them to a healthy control population. Our results identified no global differences in cytolysis, degranulation, interferon-γ production, or surface receptor upregulation following cytokine stimulation. However, abnormal NK cell functional responses were observed in nearly one-third of patients (including 3 with hyporesponsiveness to activating signals and 1 with markedly decreased CD11b expression associated with reduced cytotoxicity and degranulation), which might contribute to those individuals' susceptibility to herpesvirus infections.

Interplay between human cytomegalovirus and intrinsic/innate host responses: a complex bidirectional relationship

The interaction between human cytomegalovirus (HCMV) and its host is a complex process that begins with viral attachment and entry into host cells, culminating in the development of a specific adaptive response that clears the acute infection but fails to eradicate HCMV. We review the viral and cellular partners that mediate early host responses to HCMV with regard to the interaction between structural components of virions (viral glycoproteins) and cellular receptors (attachment/entry receptors, toll-like receptors, and other nucleic acid sensors) or intrinsic factors (PML, hDaxx, Sp100, viperin, interferon inducible protein 16), the reactions of innate immune cells (antigen presenting cells and natural killer cells), the numerous mechanisms of viral immunoevasion, and the potential exploitation of events that are associated with early phases of virus-host interplay as a therapeutic strategy.

The immune response to human CMV

This review will summarize and interpret recent literature regarding the human CMV immune response, which is among the strongest measured and is the focus of attention for numerous research groups. CMV is a highly prevalent, globally occurring infection that rarely elicits disease in healthy immunocompetent hosts. The human immune system is unable to clear CMV infection and latency, but mounts a spirited immune-defense targeting multiple immune-evasion genes encoded by this dsDNA β-herpes virus. Additionally, the magnitude of cellular immune response devoted to CMV may cause premature immune senescence, and the high frequencies of cytolytic T cells may aggravate vascular pathologies. However, uncontrolled CMV viremia and life-threatening symptoms, which occur readily after immunosuppression and in the immature host, clearly indicate the essential role of immunity in maintaining asymptomatic co-existence with CMV. Approaches for harnessing the host immune response to CMV are needed to reduce the burden of CMV complications in immunocompromised individuals.

IL-10 restricts activation-induced death of NK cells during acute murine cytomegalovirus infection

IL-10 is an immunomodulatory cytokine that acts to antagonize T cell responses elicited during acute and chronic infections. Thus, the IL-10R signaling pathway provides a potential therapeutic target in strategies aimed at combating infectious diseases. In this study, we set out to investigate whether IL-10 expression had an effect on NK cells. Murine CMV infection provides the best characterized in vivo system to evaluate the NK cell response, with NK cells being critical in the early control of acute infection. Blockade of IL-10R during acute murine CMV infection markedly reduced the accumulation of cytotoxic NK cells in the spleen and lung, a phenotype associated with a transient elevation of virus DNA load. Impaired NK cell responsiveness after IL-10R blockade was attributed to elevated levels of apoptosis observed in NK cells exhibiting an activated phenotype. Therefore, we conclude that IL-10 contributes to antiviral innate immunity during acute infection by restricting activation-induced death in NK cells.

'Immunogenetics of Aging': report on the activities of the 15th International HLA and Immunogenetics Working Group and 15th International HLA and Immunogenetics Workshop

'Immunogenetics of Aging' is a component that was first included in the 14th International HLA and Immunogenetics Workshop (IHIWS) and developed further within the 15th Workshop. The aim of this component was to assess the impact of human leukocyte antigen (HLA) genes, cytokine genes, and some innate immunity genes such as killer-cell immunoglobulin-like receptors (KIRs) and mannose-binding lectin 2 (MBL2) in successful aging and their contribution to the better understanding of immune dysfunction in old age. Within the 15th IHIWS new populations were included in the analysis. Additional cytokine gene polymorphisms were assessed and innate immunity genes were analyzed for possible relevance in longevity. The results showed that longevity might be associated with anti-inflammatory cytokine gene profiles, decreased frequency of interleukin-10 (IL-10) and transforming growth factor-B1 haplotypes associated with a low level of gene expression, and increased frequency of haplotypes determining a high level of expression. Extended tumor necrosis factor-A and IL-12B genotypes were also likely relevant to longevity. Data also showed that innate immunity genes are associated with susceptibility to infections in the elderly and showed that these genes might be an important genetic marker in aging. Decreased frequencies of KIR2DS5 and A1B10 haplotypes, and an increased proportion of MBL2-deficient haplotypes were found in the group with higher cytomegalovirus-specific IgG antibody levels. Together, these studies emphasize the relevance of genes regulating immune functions in maintaining human longevity and stress the importance of further clarifying their impact on successful aging.

The impact of Ly49-NK cell-dependent recognition of MCMV infection on innate and adaptive immune responses

Clinical and experimental data indicate that a subset of innate lymphocytes, natural killer (NK) cells, plays a crucial role in the response against herpesviruses, especially cytomegaloviruses (CMV). Indeed, in mice, NK cells, due to the expression of germline encoded Ly49 receptors, possess multiple mechanisms to recognize CMV infection. Classically, this results in NK cell activation and the destruction of the infected cells. More recently, however, this unique host-pathogen interaction has permitted the discovery of novel aspects of NK cell biology, implicating them in the regulation of adaptive immune responses as well as in the development of immunological memory. Here, we will concisely review the newly acquired evidence pertaining to NK cell Ly49-dependent recognition of MCMV-infected cell and the ensuing NK cell regulatory responses.

NK cell receptor/H2-Dk-dependent host resistance to viral infection is quantitatively modulated by H2q inhibitory signals

The cytomegalovirus resistance locus Cmv3 has been linked to an epistatic interaction between two loci: a Natural Killer (NK) cell receptor gene and the major histocompatibility complex class I (MHC-I) locus. To demonstrate the interaction between Cmv3 and H2^k, we generated double congenic mice between MA/My and BALB.K mice and an F₂ cross between FVB/N (H-2^q) and BALB.K (H2^k) mice, two strains susceptible to mouse cytomegalovirus (MCMV). Only mice expressing H2^k in conjunction with Cmv3^MA/My or Cmv3^FVB were resistant to MCMV infection. Subsequently, an F₃ cross was carried out between transgenic FVB/H2-D^k and MHC-I deficient mice in which only the progeny expressing Cmv3^FVB and a single H2-D^k class-I molecule completely controlled MCMV viral loads. This phenotype was shown to be NK cell–dependent and associated with subsequent NK cell proliferation. Finally, we demonstrated that a number of H2^q alleles influence the expression level of H2^q molecules, but not intrinsic functional properties of NK cells; viral loads, however, were quantitatively proportional to the number of H2^q alleles. Our results support a model in which H-2^q molecules convey Ly49-dependent inhibitory signals that interfere with the action of H2-D^k on NK cell activation against MCMV infection. Thus, the integration of activating and inhibitory signals emanating from various MHC-I/NK cell receptor interactions regulates NK cell–mediated control of viral load.

Effective natural killer (NK) cell responses against virally infected cells are regulated by NK cell receptors that specifically recognize target cells. In the current study, we validated the specific interaction taking place between NK cell receptors and MHC class I molecules on the surface of infected cells, resulting in resistance to cytomegalovirus. Genetic dissection of this mechanism of interaction revealed that the NK cell response occurs exclusively through the triggering of the activating Ly49P receptor by the MHC class I H2-D^k molecule. We observed, in this context, that NK cells were incapable of clearing the virus when target cells also expressed MHC class I H2^q molecules, which strongly and quantitatively inhibit NK cells. Our findings reveal that the interplay between inhibitory and activating NK cell receptors and their MHC class I ligands generate signals that shape the outcome of infection.

Human cytomegalovirus immunity and immune evasion

Human cytomegalovirus (HCMV) infection induces both innate immune responses including Natural Killer cells as well as adaptive humoral and cell mediated (CD4+ helper, CD8+ cytotoxic and γδ T cell) responses which lead to the resolution of acute primary infection. Despite such a robust primary immune response, HCMV is still able to establish latency. Long term memory T cell responses are maintained at high frequency and are thought to prevent clinical disease following periodic reactivation of the virus. As such, a balance is established between the immune response and viral reactivation. Loss of this balance in the immunocompromised host can lead to unchecked viral replication following reactivation of latent virus, with consequent disease and mortality. HCMV encodes multiple immune evasion mechanisms that target both the innate and acquired immune system. This article describes the current understanding of Natural killer cell, antibody and T cell mediated immune responses and the mechanisms that the virus utilizes to subvert these responses.

Human cytomegalovirus UL141 promotes efficient downregulation of the natural killer cell activating ligand CD112

Human cytomegalovirus (HCMV) UL141 induces protection against natural killer cell-mediated cytolysis by downregulating cell surface expression of CD155 (nectin-like molecule 5; poliovirus receptor), a ligand for the activating receptor DNAM-1 (CD226). However, DNAM-1 is also recognized to bind a second ligand, CD112 (nectin-2). We now show that HCMV targets CD112 for proteasome-mediated degradation by 48 h post-infection, thus removing both activating ligands for DNAM-1 from the cell surface during productive infection. Significantly, cell surface expression of both CD112 and CD155 was restored when UL141 was deleted from the HCMV genome. While gpUL141 alone is sufficient to mediate retention of CD155 in the endoplasmic reticulum, UL141 requires assistance from additional HCMV-encoded functions to suppress expression of CD112.

Associations between genes for killer immunoglobulin-like receptors and their ligands in patients with solid tumors

Killer immunoglobulin-like receptor (KIR) and human leukocyte antigen (HLA) genotypes were analyzed from panels of lung (non-small-cell lung cancer [NSCLC] and small-cell lung cancer [SCLC]), colon, and kidney cancer patients and compared with normal control subjects. No significant differences were noted between KIR gene frequencies in patients compared with normal subjects. When combinations of KIR genes and their HLA ligands were considered, there were significant decreases in frequencies of both KIR2DL2 and KIR2DL3 in homozygotes for their ligand HLA-C1, and an increase in the frequency of KIR3DL1 and its ligand HLA-Bw4 in kidney cancer patients compared with controls. Both associations were partly attributable to changes in ligand frequencies alone. NSCLC patients showed a significant increase in the frequency of KIR2DL1 and its ligand HLA-C2 and a corresponding decrease in frequency of KIR2DL3 and its ligand HLA-C1 in homozygotes. In NSCLC, the Ile80 form of HLA-Bw4 was decreased in KIR3DL1+ HLA-Bw4+ patients, whereas in SCLC the Ile80 form was increased and the Thr80 form decreased in KIR3DS1+ HLA-Bw4+ patients. These findings are consistent with increased co-expression of high-affinity inhibitory KIRs and their ligands, potentially resulting in decreased natural killer cell function, and hence with natural killer cells having a protective role in lung and kidney cancer but not colon cancer.

Cytomegalovirus infection in pediatric rheumatic diseases: a review

Human cytomegalovirus (HCMV) is familiar to pediatric rheumatologists mainly as a cause of opportunistic disease in pharmacologically immune suppressed patients. However, HCMV also has a variety of immuno-modulatory effects, through which it may influence the course of rheumatic conditions. In this article we discuss the interplay between HCMV and the immune system, and review the clinical manifestations, diagnosis, and treatment of HCMV infection in children with rheumatic disease.

Natural Killer cells: keepers of pregnancy in the turnstile of the environment

During early pregnancy, an orchestrated endocrine-immunological scenario of maternal adaptation toward tolerance of the semiallogeneic fetus is required. Mechanisms preventing fetal loss by protecting the immune privilege of the gravid uterus, i.e. Galectin-1 or regulatory T cells, have recently been identified. Further, the presence of a unique population of Natural Killer (NK) cells, in humans identified by their CD56(+++)Galectin (Gal)-1(+)CD16(-) phenotype in the uterine lining (decidua), has been proposed to be a pivotal aspect of maternal adaptation to pregnancy. Decidual NK (dNK) cells comprise the largest population of immune cells during the first trimester in human decidua and control trophoblast invasion and vascular remodeling through their ability to secrete an array of angiogenesis-regulating molecules, chemokines and cytokines. A wealth of environmental factors, such as smoking, altered nutrition, pollution or stress has been proposed to peril not only pregnancy, but also fetal development. Further, published evidence supports that NK cells act as sentinel cells and environmental challenges can change their phenotype, e.g. via epigenetic pathways. We here review the effect of environmental factors, largely stress perception, on NK cells and its implication for pregnancy, fetal development and general health. As NK cells may not only be passive responders to the environment, but can also be 'educated and licensed', we propose novel strategies aiming to take advantage of the versatility of NK cells in maintaining immunosurveillance and tissue homeostasis.

Inhibitory NK receptor recognition of HLA-G: regulation by contact residues and by cell specific expression at the fetal-maternal interface

The non-classical HLA-G protein is distinguished from the classical MHC class I molecules by its expression pattern, low polymorphism and its ability to form complexes on the cell surface. The special role of HLA-G in the maternal-fetal interface has been attributed to its ability to interact with specific receptors found on maternal immune cells. However this interaction is restricted to a limited number of receptors. In this study we elucidate the reason for this phenomenon by comparing the specific contact residues responsible for MHC-KIR interactions. This alignment revealed a marked difference between the HLA-G molecule and other MHC class I molecules. By mutating these residues to the equivalent classical MHC residues, the HLA-G molecule regained an ability of interacting with KIR inhibitory receptors found on NK cells derived either from peripheral blood or from the decidua. Functional NK killing assays further substantiated the binding results. Furthermore, double immunofluorescent staining of placental sections revealed that while the conformed form of HLA-G was expressed in all extravillous trophoblasts, the free heavy chain form of HLA-G was expressed in more distal cells of the column, the invasion front. Overall we suggest that HLA-G protein evolved to interact with only some of the NK inhibitory receptors thus allowing a control of inhibition, while permitting appropriate NK cell cytokine and growth factor production necessary for a viable maternal fetal interface.

Significant functional heterogeneity among KIR2DL1 alleles and a pivotal role of arginine 245

Killer immunoglobulin-like receptors (KIRs) play an essential role in the regulation of natural killer cell functions. KIR genes are highly polymorphic in nature, showing both haplotypic and allelic variations among people. We demonstrated in both in vitro and in vivo models a significant heterogeneity in function among different KIR2DL1 alleles, including their ability to inhibit YT-Indy cells from degranulation, interferon gamma production, and cytotoxicity against target cells expressing the HLA-Cw6 ligand. Subsequent experiments showed that the molecular determinant was an arginine residue at position 245 (R245) in its transmembrane domain that mechanistically affects both the efficiency of inhibitory signaling and durability of surface expression. Specifically, in comparison with R245-negative alleles, KIR2DL1 that included R245 recruited more Src-homology-2 domain-containing protein tyrosine phosphatase 2 and beta-arrestin 2, showed higher inhibition of lipid raft polarization at immune synapse, and had less down-regulation of cell-surface expression upon interaction with its ligand. Thus, our findings provide novel insights into the molecular determinant of KIR2DL1 and conceivably a fundamental understanding of KIR2DL1 allelic polymorphism in human disease susceptibility, transplant outcome, and donor selection.

Lack of killer immunoglobulin-like receptor 2DS2 (KIR2DS2) and KIR2DL2 is associated with poor responses to therapy of recurrent hepatitis C virus in liver transplant recipients

Killer immunoglobulin-like receptors (KIRs) expressed on natural killer and natural killer T cells are involved in activation of these cells and can influence antiviral immunity in the liver. This study investigated the association between KIR genetic diversity and sustained virologic response (SVR) to Peginterferon and Ribavirin (Peg/RBV) therapy in liver transplant (LT) recipients with hepatitis C virus (HCV) recurrence. We tested KIR genotypes in 44 HCV-infected LT recipients treated with Peg/RBV for 48 weeks. Patients were categorized as having KIR genotypes A/A or B/x and analyzed for association with SVR. Fifteen of 44 (34%) patients had SVR. Only 2 of 18 (11%) who lacked KIR2DS2/KIR2DL2 achieved SVR compared to 13 of 26 (50%) who carried these two genes (odds ratio: 8.0, 95% confidence interval: 1.5-42.0, P = 0.008). The association between lack of KIR2DS2/KIR2DL2 and SVR remained significant after exclusion of 10 patients with non-genotype 1 HCV. No correlation was found with other activating or inhibitory KIR genes. Absence of KIR2DS2 and/or KIR2DL2 is associated with failure of Peg/RBV therapy in patients with recurrent HCV after LT. These findings support the role of natural killer and natural killer T cells in HCV clearance after LT and might be generalizable to treatment of HCV infection outside the setting of LT.

Distribution of several activating and inhibitory receptors on CD3-CD16+ NK cells and their correlation with NK cell function in healthy individuals

The aim of this study was to estimate the distribution and density of a representative set of activating and inhibitory receptors on gated natural killer (NK) cells, as well as on their bright and dim subsets, and to correlate the receptor expression with NK cell activity for healthy individuals on CD3(-)CD16(+) NK cells. We show that in 43 healthy controls NK cell activity against K562 target cells was 37.34% (E:T, 80:1) by standard chromium release assay. The expression of receptors on NK cells and their subsets was analyzed by flow cytometry. The cytotoxic CD3(-)CD16(bright) NK subset constituted 78.97%, while the regulatory CD3(-)CD16(dim) NK subset constituted 21.03% of NK cells. We show the distribution of NKG2D, CD161, CD158a, and CD158b receptors on CD3(-)CD16(+) NK cells in peripheral blood lymphocytes (PBLs), on gated NK cells, and on the CD3(-)CD16(bright) and CD3(-)CD16(dim) subsets. Contrary to CD158a and CD158b killer immunoglobulin-like receptors (KIRs), there is a significant positive correlation of NKG2D and CD161 expression with NK cytotoxicity. We show the kinetics of change in CD3(-)CD16(+)NK/K562 conjugate composition, together with the stronger target binding capacity of CD16(bright) NK cells. Furthermore, we show that after coculture of PBLs with K562 the expression of CD107a, a degranulation marker, on CD3(-)CD16(+)NK cells and subsets is time dependent and significantly higher on the cytotoxic CD3(-)CD16(bright) NK subset. The novel data obtained regarding expression of NK cell activating and inhibitory receptors for healthy individuals may aid in detecting changes that are associated with various diseases.

The Yin and Yang of HLA and KIR in human disease

Killer cell immunoglobulin-like receptors (KIR) are expressed on natural killer (NK) cells and subsets of T cells. The KIR genes are polymorphic and the KIR gene complex is polygenic with varying numbers of inhibitory and activating receptors. HLA class I molecules serve as ligands for the KIR. Interactions of the independently segregating KIR and HLA loci are important for recognition of targets by NK cells as well as NK cell 'licensing'. Several disease association studies indicate a role for interactions between these loci in infectious diseases, autoimmune/inflammatory disorders, cancer and reproduction. Emerging functional data supports a mechanism based on a continuum of inhibition to activation through various compound KIR-HLA genotypes in diseases.

Natural killer cell evasion by an E3 ubiquitin ligase from Kaposi's sarcoma-associated herpesvirus

Viruses exploit the ubiquitin system by targeting cell-surface receptors recognized by immune cells for internalization, thereby evading recognition. We have characterized the KSHV (Kaposi's sarcoma-associated herpesvirus)-encoded E3 ubiquitin ligases, K3 and K5. We find their activities not only prevent recognition by cytotoxic T-lymphocytes, but also promote evasion of NK (natural killer) cells. NK cells recognize and lyse virus-infected cells expressing ligands for activatory receptors such as NKG2D (NK group 2D). K5 down-regulates cell-surface expression of the NKG2D ligands MICA/B (MHC class I-related chains A and B) by ubiquitination of MIC cytoplasmic tail lysine residues. Ubiquitination results in redistribution of MICA from the plasma membrane to an intracellular compartment, but does not result in an increased rate of degradation. Furthermore, K5 down-regulates cell-surface expression of another NK cell activatory receptor ligand, AICL (activation-induced C-type lectin). This activity requires the K5 RING (really interesting new gene)-CH domain and AICL cytoplasmic tail lysine residues. MICA and AICL down-regulation by K5 reduces NK cell-mediated cytotoxicity towards target cells, thus providing KSHV with an NK cell evasion mechanism.

Blocking NK cell inhibitory self-recognition promotes antibody-dependent cellular cytotoxicity in a model of anti-lymphoma therapy

Human NK cells lyse Ab-coated target cells through the process of Ab-dependent cellular cytotoxicity (ADCC). Improving ADCC responses is desirable because it is thought to be an important antitumor mechanism for some Abs. NK cell inhibitory receptors, such as killer cell Ig-like receptors, engage with MHC class I molecules on self-cells to block NK cell activation. Accordingly, we enhanced ADCC responses by blocking NK cell inhibitory receptors, thus perturbing induction of the self-recognition signal. In a cell line model of anti-lymphoma therapy, the combination of rituximab with an Ab that blocks inhibitory self-recognition yielded increased NK cell-mediated target cell lysis when compared with rituximab alone. To validate this proof-of-concept, we then used a more representative approach in which an individual's fresh primary NK cells encountered autologous, EBV-transformed B cells. In this system, rituximab and a combination of Abs that block NK cell inhibitory receptors yielded improved NK cell-mediated lysis over rituximab alone. The results show, for the first time, that disruption of inhibitory self-recognition can efficiently promote ADCC in a human model, applying an autologous system in which physiologic checkpoints are in place. This method provides an alternative approach to potentiate the therapeutic benefit of antitumor Abs that mediate ADCC.

Modulation of natural killer cells by human cytomegalovirus

Human cytomegalovirus (HCMV) causes lifelong, persistent infections and its survival is under intense, continuous selective pressure from the immune system. A key aspect of HCMV's capacity for survival lies in immune avoidance. In this context, cells undergoing productive infection exhibit remarkable resistance to natural killer (NK) cell-mediated cytolysis in vitro. To date, six genes encoding proteins (UL16, UL18, UL40, UL83, UL141 and UL142) and one encoding a microRNA (miR-UL112) have been identified as capable of suppressing NK cell recognition. Even though HCMV infection efficiently activates expression of ligands for the NK cell activating receptor NKG2D, at least three functions (UL16, UL142 and miR-UL112) act in concert to suppress presentation of these ligands on the cell surface. Although HCMV downregulates expression of endogenous MHC-I, it encodes an MHC-I homologue (UL18) and also upregulates the expression of cellular HLA-E through the action of UL40. The disruption of normal intercellular connections exposes ligands for NK cell activating receptors on the cell surface, notably CD155. HCMV overcomes this vulnerability by encoding a function (UL141) that acts post-translationally to suppress cell surface expression of CD155. The mechanisms by which HCMV systematically evades (or, more properly, modulates) NK cell recognition constitutes an area of growing understanding that is enhancing our appreciation of the basic mechanisms of NK cell function in humans.

Antiviral NK cell responses in HIV infection: I. NK cell receptor genes as determinants of HIV resistance and progression to AIDS

NK cells play an important role in controlling viral infections. They can kill virus-infected cells directly as well as indirectly via antibody-dependent, cell-mediated cytotoxicity. They need no prior sensitization and expansion for this killing. NK cells are also considered as important regulators of antiviral immune responses. They do so by secreting a multitude of soluble mediators and by directly interacting with other immune cells, e.g., dendritic cells. NK cells do not possess a single well-defined receptor to recognize antigens on target cells. Instead, they express an array of inhibitory and activating receptors and coreceptors, which bind to their cognate ligands expressed on the surface of target cells. These ligands include classical and nonclassical MHC class I antigens, MHC-like proteins, and a variety of other self- and virus-derived molecules. They may be expressed constitutively and/or de novo on the surface of virus-infected cells. NK cell receptors (NKRs) of the killer-cell Ig-like receptor (KIR) family, like their MHC class I ligands, are highly polymorphic. Several recent studies suggest that epistatic interactions between certain KIR and MHC class I genes may determine innate resistance of the host to viral infections, including HIV. In the first part of this review article, we provide an overview of the current state of knowledge of NK cell immunobiology and describe how NKR genes, alone and in combination with HLA genes, may determine genetic resistance/susceptibilty to HIV infection and the development of AIDS in humans.

Lineage-specific transition of histone signatures in the killer cell Ig-like receptor locus from hematopoietic progenitor to NK cells

The clonal distribution and stable expression of killer cell Ig-like receptor (KIR) genes is epigenetically regulated. To assess the epigenetic changes that occur during hemopoietic development we examined DNA methylation and chromatin structure of the KIR locus in early hemopoietic progenitor cells and major lymphocyte lineages. In hemopoietic progenitor cells, KIR genes exhibited the major hallmarks of epigenetic repression, which are dense DNA methylation, inaccessibility of chromatin to Micrococcus nuclease digest, and a repressive histone signature, characterized by strong H3K9 dimethylation and reduced H4K8 acetylation. In contrast, KIR genes of NK cells showed active histone signatures characterized by absence of H3K9 dimethylation and presence of H4K8 acetylation. Histone modifications correlated well with the competence of different lymphocyte lineages to express KIR; whereas H4K8 acetylation was high in NK and CD8+ T cells, it was almost absent in CD4+ T cells and B cells and, in the latter case, replaced by H3K9 dimethylation. In KIR-competent lineages, active histone signatures were also observed in silent KIR genes and in this case found in combination with dense DNA methylation of the promoter and nearby regions. The study suggests a two-step model of epigenetic regulation in which lineage-specific acquisition of euchromatic histone marks is a prerequisite for subsequent gene-specific DNA demethylation and expression of KIR genes.

The human cytomegalovirus MHC class I homolog UL18 inhibits LIR-1+ but activates LIR-1- NK cells

The inhibitory leukocyte Ig-like receptor 1 (LIR-1, also known as ILT2, CD85j, or LILRB1) was identified by its high affinity for the human CMV (HCMV) MHC class I homolog gpUL18. The role of this LIR-1-gpUL18 interaction in modulating NK recognition during HCMV infection has previously not been clearly defined. In this study, LIR-1(+) NKL cell-mediated cytotoxicity was shown to be inhibited by transduction of targets with a replication-deficient adenovirus vector encoding UL18 (RAd-UL18). Fibroblasts infected with an HCMV UL18 mutant (DeltaUL18) also exhibited enhanced susceptibility to NKL killing relative to cells infected with the parental virus. In additional cytolysis assays, UL18-mediated protection was also evident in the context of adenovirus vector transduction and HCMV infection of autologous fibroblast targets using IFN-alpha-activated NK bulk cultures derived from a donor with a high frequency of LIR-1(+) NK cells. A single LIR-1(high) NK clone derived from this donor was inhibited by UL18, while 3 of 24 clones were activated. CD107 mobilization assays revealed that LIR-1(+) NK cells were consistently inhibited by UL18 in all tested donors, but this effect was often masked in the global response by UL18-mediated activation of a subset of LIR-1(-) NK cells. Although Ab-blocking experiments support UL18 inhibition being induced by a direct interaction with LIR-1, the UL18-mediated activation is LIR-1 independent.

HIV modulates the expression of ligands important in triggering natural killer cell cytotoxic responses on infected primary T-cell blasts

The ability of natural killer (NK) cells to kill virus-infected cells depends on the presence of ligands for activation receptors on the target cells. We found the presence of few, if any, NKp30 and NK46 ligands on T cell blasts infected with HIV, although NKp44 ligands were found on infected cells. HIV does induce the NKG2D ligands ULBP-1, -2, and -3. These ligands are involved in triggering NK cells to kill autologous HIV-infected cells, because interfering with the interaction between NKG2D, but not NKp46, on NK cells and its ligands on HIV-infected cells drastically reduced the lysis of infected cells. Interfering with the binding of the NK-cell coreceptors NTB-A and 2B4 to their ligands also decreased destruction by NK cells. The coreceptor ligands, NTB-A and CD48, were also found to be down-regulated during the course of HIV infection. Thus, ligands for NK-cell receptors are modulated during the course of HIV infection, which may greatly alter NK cells' ability to kill the infected cells.

Influence of interleukin IL-2 and IL-12 + IL-18 on surface expression of immunoglobulin-like receptors KIR2DL1, KIR2DL2, and KIR3DL2 in natural killer cells

Natural killer (NK) cells express killer cell inhibitory receptors (KIRs) that recognize polymorphic class I MHC molecules. In the present study, we analyze the modulatory effect of IL-2 alone or a combination of IL-12 with IL-18 on surface expression of killer cell immunoglobulin-like receptors KIR2DL1, KIR2DL2, and KIR3DL2 in NK cells. Thus, it was found that IL-2 causes a significant increase in the proportion of cells with given studied receptors. Stimulation by a mixture of IL-12 and IL-18 caused significant increase in the fraction of cells with the KIR2DL1 and KIR2DL2, however no significant change in the percentage of cells with KIR3DL2 receptor on their surface was observed. The results of the study show the presence of KIRs on both resting and activated NK cells, this may suggest that KIRs have also an important role in the regulatory processes after activation of this subpopulation of cells.

Human natural killer cell deficiencies

PURPOSE OF REVIEW

Human natural killer cell deficiencies are a relevant clinical entity that provides insight into the role of natural killer cells in host defense, as well as the basic biology of natural killer cells. Since previously reviewing these disorders, significant developments warrant their reconsideration.

RECENT FINDINGS

Human natural killer cell deficiencies can occur as part of a more pervasive immunodeficiency syndrome or, rarely, in isolation. The most informative examples of the former are in the context of a known genetic defect, because the deficiency of natural killer cell development or activity can be attributed to the specific gene function. Since last reviewed, there are five human gene mutations that are now appreciated to affect natural killer cells, and additional new insights into natural killer cell biology have been obtained through seven others. Six new reports of isolated natural killer cell deficiencies, as well as a suggested classification scheme, are also reviewed.

SUMMARY

Appreciation of human genetic syndromes that include natural killer cell deficiencies, as well as new cases of isolated natural killer cell deficiencies, continue to advance the understanding of natural killer cell biology and solidify the role of natural killer cells in defense against human herpesviral infection.

KIR and disease: a model system or system of models?

The discovery of an unexpected level of diversity among the killer cell immunoglobulin-like receptors has led to a search for their role in human disease. Due to their polymorphism and also that of their human leukocyte antigen class I ligands, these studies are difficult to perform and complex to interpret. Nevertheless, as the number of data sets increase, consistent trends and themes are beginning to emerge in both viral and inflammatory disorders. In this review, we summarize the findings from a number of disease association studies and discuss these in the context of the activating and inhibitory roles of the members of this gene family.

Tumor and viral recognition by natural killer cells receptors

Natural killer (NK) cells destroy hazardous cells such as tumors and virus-infected cells immediately without the need for prior antigen stimulation. The activation of NK cells largely depends on the recently identified natural cytotoxic receptors (NCRs), which include three members: NKp46, NKp44 and NKp30. The NCRs are unique in their expression pattern that is almost conclusively confined to NK cells, and in their broad specificity towards a wide range of targets. However, very little is known about the ligands identity of the NCRs and so far the only ligands known are two virally derived molecules: the hemagglutinin protein of influenza viruses that directly binds and activates two of the NCRs; NKp46 and NKp44, and the human cytomegalovirus tegument protein, pp65, which binds the NKp30 receptor and inhibits its activation thus promoting survival of the virus. In this review we describe the function of the NCRs in various pathological conditions with a special emphasis on tumor targeting.

Les cellules natural killer : acquisitions récentes et implication en pathologie humaine

INTRODUCTION

Natural killer cells are cytotoxic lymphocytes of innate immunity. These last ten years our knowledge about the mechanisms that regulates NK cell function has greatly improved. Our purpose is to present a review of these new acquisitions and their potential implications in human disease.

CURRENT KNOWLEDGE AND KEY POINTS

NK cell function is regulated by a repertoire of NK cell receptors and is diversified by recognition of MHC class I by a multigenic and multi-allelic family of NK receptors. Analysis of NK cell repertoire has been used to investigate features that characterize NK cells in pathological situations. Apart from their direct cytotoxic potential to eliminate target cells, recently identification of mechanisms that control NK cell mediated cytokine production and cross talk with dendritic cells emphasize the role of NK cells in the regulation of acquired immune response.

FUTURE PROSPECTS AND PROJECTS

These findings have lead to a better knowledge of the importance of the NK cells in several human diseases. It has been shown that NK cells are actors of the immunosurveillance of tumoral and infectious challenges. Allo or auto reactivity of the NK cell compartment have also been suggested in autoimmune diseases, infertility or foetal loss and transplantation. Ongoing research on NK cells in the fields of human diseases is increasing and will clarify the utility of the evaluation of the NK cell compartment and their receptors in clinical practice.

Homozygosity for human leucocyte antigen-C ligands of KIR2DL1 is associated with increased risk of relapse after human leucocyte antigen-C-matched unrelated donor haematopoietic stem cell transplantation

Human leucocyte antigen (HLA)-C molecules regulate the function of natural killer cells and may be subdivided into two groups, C(1) and C(2), based on their specificity for inhibitory killer immunoglobulin-like receptors. We analysed the impact of the HLA-C genotype on outcome of HLA-C-matched unrelated donor haematopoietic stem cell transplantation (URD-HSCT) recipients. HLA-C(2) homozygous patients (n = 18) had lower probability of overall survival (P = 0.01) and disease-free survival (P = 0.02), resulting from increased relapse rate (P = 0.02) when compared with both HLA-C(1) homozygous (n = 43) and HLA-C(1),C(2) heterozygous (n = 50) subgroups. Patients lacking HLA-C(1) should, therefore, be considered at increased risk of relapse following HLA-C-matched URD-HSCT.

The impact of variation at the KIR gene cluster on human disease

Leukocyte behavior is controlled by a balance of inhibitory and stimulatory signals generated on ligand binding to a complex set of receptors located on the cell surface. The killer cell immunoglobulin-like receptor (KIR) genes encode one such, family of receptors expressed by natural killer (NK) cells, key components of the innate immune system that participate in early responses against infected or transformed cells through production of cytokines and direct cytotoxicity. KIRs are also expressed on a subset of T cells, where they contribute to the intensity of acquired immune responses. Recognition of self HLA class I ligands by inhibitory KIR allows NK cells to identify normal cells, preventing an NK cell-mediated response against healthy autologous cells. Activation of NK cells through stimulatory receptors is directed toward cells with altered expression of class I, a situation characteristic of some virally infected cells and tumor cells. The "missing self" model for NK cell activation was proposed to explain killing of cells that express little or no class I, while cells expressing normal levels of class I are spared. Studies performed over the last several years have revealed extensive diversity at the KIR gene locus, which stems from both its polygenic (variable numbers of genes depending on KIR haplotype) and multiallelic polymorphism. Given the role of KIR in both arms of the immune response, their specificity for HLA class I allotypes, and their extensive genomic diversity, it is reasonable to imagine that KIR gene variation affects resistance and susceptibility to the pathogenesis of numerous diseases. Consequently, the evolution of KIR locus diversity within and across populations may be a function of disease morbidity and mortality. Here we review a growing body of evidence purporting the influence of KIR polymorphism in human disease.

Characterization of a highly glycosylated form of the human cytomegalovirus HLA class I homologue gpUL18

Human cytomegalovirus (HCMV) gpUL18 is a HLA class I (HLA-I) homologue with high affinity for the inhibitory receptor LIR-1/ILT2. The previously described 67 kDa form of gpUL18 is shown here to be sensitive to endoglycosidase-H (EndoH). A novel form of gpUL18 with a molecular mass of approximately 160 kDa and resistance to EndoH was identified in cells infected with HCMV strain AD169 or the low passage HCMV isolates Merlin and Toledo. The 67 kDa EndoH-sensitive gpUL18 glycoform was detected earlier in a productive infection (from 24 h post-infection) than the slower-migrating EndoH-resistant glycoform (from 72 h post-infection). Deletion of the US2-US11 region from the HCMV genome was associated with a substantial up-regulation of endogenous HLA-I in infected cells, but had no obvious effect on the gpUL18 expression pattern. Vaccinia virus and adenovirus vectors were used to further analyse gpUL18 expression. Depending on the delivery vector system, differences in the electrophoretic motility of the EndoH-resistant >105 kDa form of gpUL18, but not the EndoH-sensitive 67 kDa form, were observed; post-translational modification of the higher molecular mass glycoform appears to be influenced by active virus infection and vector delivery. The EndoH-sensitive 67 kDa gpUL18 had a rapid turnover, while the maturation to the EndoH-resistant >105 kDa form was relatively slow and inefficient. However, synthesis of the EndoH-resistant >105 kDa form was enhanced with elevated levels of beta2-microglobulin. When expressed by using an adenovirus vector, both the EndoH-sensitive 67 kDa and the EndoH-resistant >105 kDa gpUL18 forms could be detected on the cell surface.