IL-12-induced up-regulation of NKRP1A expression in human NK cells and consequent NKRP1A-mediated down-regulation of NK cell activation

Distinct cellular immune responses in children en route to type 1 diabetes with different first-appearing autoantibodies

Previous studies have revealed heterogeneity in the progression to clinical type 1 diabetes in children who develop islet-specific antibodies either to insulin (IAA) or glutamic acid decarboxylase (GADA) as the first autoantibodies. Here, we test the hypothesis that children who later develop clinical disease have different early immune responses, depending on the type of the first autoantibody to appear (GADA-first or IAA-first). We use mass cytometry for deep immune profiling of peripheral blood mononuclear cell samples longitudinally collected from children who later progressed to clinical disease (IAA-first, GADA-first, ≥2 autoantibodies first groups) and matched for age, sex, and HLA controls who did not, as part of the Type 1 Diabetes Prediction and Prevention study. We identify differences in immune cell composition of children who later develop disease depending on the type of autoantibodies that appear first. Notably, we observe an increase in CD161 expression in natural killer cells of children with ≥2 autoantibodies and validate this in an independent cohort. The results highlight the importance of endotype-specific analyses and are likely to contribute to our understanding of pathogenic mechanisms underlying type 1 diabetes development.

Lectin-like Transcript-1 (LLT1) Expression in Oral Squamous Cell Carcinomas: Prognostic Significance and Relationship with the Tumor Immune Microenvironment

Lectin-like transcript-1 (LLT1) expression is detected in different cancer types and is involved in immune evasion. The present study investigates the clinical relevance of tumoral and stromal LLT1 expression in oral squamous cell carcinoma (OSCC), and relationships with the immune infiltrate into the tumor immune microenvironment (TIME). Immunohistochemical analysis of LLT1 expression was performed in 124 OSCC specimens, together with PD-L1 expression and the infiltration of CD20+, CD4+, and CD8+ lymphocytes and CD68+ and CD163+-macrophages. Associations with clinicopathological variables, prognosis, and immune cell densities were further assessed. A total of 41 (33%) OSCC samples showed positive LLT1 staining in tumor cells and 55 (44%) positive LLT1 in tumor-infiltrating lymphocytes (TILs). Patients harboring tumor-intrinsic LLT1 expression exhibited poorer survival, suggesting an immunosuppressive role. Conversely, positive LLT1 expression in TILs was significantly associated with better disease-specific survival, and also an immune-active tumor microenvironment highly infiltrated by CD8+ T cells and M1/M2 macrophages. Furthermore, the combination of tumoral and stromal LLT1 was found to distinguish three prognostic categories (favorable, intermediate, and adverse; p = 0.029, Log-rank test). Together, these data demonstrate the prognostic relevance of tumoral and stromal LLT1 expression in OSCC, and its potential application to improve prognosis prediction and patient stratification.

Alteration of PBMC transcriptome profile after interaction with multipotent mesenchymal stromal cells under "physiological" hypoxia

Multipotent mesenchymal stromal cells (MSCs) have demonstrated a pronounced immunosuppressive activity, the manifestation of which depends on the microenvironmental factors, including O2 level. Here we examined the effects of MSCs on transcriptomic profile of allogeneic phytohemagglutinin-stimulated peripheral blood mononuclear cells (PBMCs) after interaction at ambient (20%) or "physiological" hypoxia (5%) O2. As revealed with microarray analysis, PBMC transcriptome at 20% O2 was more affected, which was manifested as differential expression of more than 300 genes, whereas under 5% O2 220 genes were changed. Most of genes at 20% O2 were downregulated, while at hypoxia most of genes were upregulated. Altered gene patterns were only partly overlapped at different O2 levels. A set of altered genes at hypoxia only was of particular interest. According to Gene Ontology a part of above genes was responsible for adhesion, cell communication, and immune response. At both oxygen concentrations, MSCs demonstrated effective immunosuppression manifested as attenuation of T cell activation and proliferation as well as anti-inflammatory shift of cytokine profile. Thus, MSC-mediated immunosuppression is executed with greater efficacy at a "physiological" hypoxia, since the same result has been achieved through a change in the expression of a fewer genes in target PBMCs.

Key Genes Associated with Tumor-Infiltrating Non-regulatory CD4- and CD8-Positive T Cells in Microenvironment of Hepatocellular Carcinoma

The immune microenvironment in hepatocellular carcinoma (HCC), especially T-cell infiltration, plays a key role in the prognosis and drug sensitivity of HCC. Our study aimed to analyze genes related to non-regulatory CD4+ and CD8+ T cell in HCC. Data of HCC samples were downloaded from The Cancer Genome Atlas (TCGA) database. According to stromal and immune score retrieved by Estimation of Stromal and Immune cells in Malignant Tumor tissues using Expression data (ESTIMATE) algorithm, differentiated expressed genes (DEGs) between high and low stromal/immune scoring groups were collected. Using Cibersort algorithm, abundance of immune cells was calculated and genes related with CD4+ and CD8+ T cells were selected. Protein-protein interaction (PPI) networks and networks of microRNA (miRNA)-target gene interactions were illustrated, in which CD4+ and CD8+ T cell-related core genes were selected. Finally, Cox regression test and Kaplan-Meier (K-M) survival analysis were conducted. Totally, 1579 DEGs were identified, where 103 genes and 407 genes related with CD4+ and CD8+ T cell were selected, respectively. Each of 30 core genes related to CD4+ T cells and CD8+ T cells were selected by PPI network. Four genes each related with the two types of T cells had a significant impact on prognosis of HCC patients. Amongst, KLRB1 and IL18RAP were final two genes related to both two kinds of T cells and associated with overall survival of the HCC patients.

Structure of the human NK cell NKR-P1:LLT1 receptor:ligand complex reveals clustering in the immune synapse

Signaling by the human C-type lectin-like receptor, natural killer (NK) cell inhibitory receptor NKR-P1, has a critical role in many immune-related diseases and cancer. C-type lectin-like receptors have weak affinities to their ligands; therefore, setting up a comprehensive model of NKR-P1-LLT1 interactions that considers the natural state of the receptor on the cell surface is necessary to understand its functions. Here we report the crystal structures of the NKR-P1 and NKR-P1:LLT1 complexes, which provides evidence that NKR-P1 forms homodimers in an unexpected arrangement to enable LLT1 binding in two modes, bridging two LLT1 molecules. These interaction clusters are suggestive of an inhibitory immune synapse. By observing the formation of these clusters in solution using SEC-SAXS analysis, by dSTORM super-resolution microscopy on the cell surface, and by following their role in receptor signaling with freshly isolated NK cells, we show that only the ligation of both LLT1 binding interfaces leads to effective NKR-P1 inhibitory signaling. In summary, our findings collectively support a model of NKR-P1:LLT1 clustering, which allows the interacting proteins to overcome weak ligand-receptor affinity and to trigger signal transduction upon cellular contact in the immune synapse.

NKR-P1 is an inhibitory receptor on the surface of natural killer cells, and its engagement with the ligand LLT1 on activated monocytes and B cells triggers NK cell self-tolerance and other immunological processes. Here authors set up a comprehensive, structure-based model of NKR-P1-LLT1 interaction that involves NKR-P1 homodimer formation and subsequent bridging of two LLT1 molecules.

Natural killer cells and immune-checkpoint inhibitor therapy: Current knowledge and new challenges

The discovery of immune checkpoints (ICs) and the development of specific blockers to relieve immune effector cells from this inhibiting mechanism has changed the view of anti-cancer therapy. In addition to cytotoxic T lymphocyte antigen 4 (CTLA4) and programmed death 1 (PD1), classical ICs of T lymphocytes and recently described also on a fraction of natural killer (NK) cells, several NK cell receptors, including killer immunoglobulin-like inhibitory receptors (KIRs) and NGK2A, have been recognized as checkpoint members typical of the NK cell population. This offers the opportunity of a dual-checkpoint inhibition approach, targeting classical and non-classical ICs and leading to a synergistic therapeutic effect. In this review, we will overview and discuss this new perspective, focusing on the most relevant candidates for this role among the variety of potential NK ICs. Beside listing and defining classical ICs expressed also by NK cells, or non-classical ICs either on T or on NK cells, we will address their role in NK cell survival, chronic stimulation or functional exhaustion, and the potential relevance of this phenomenon on anti-tumor immune response. Furthermore, NK ICs will be proposed as possible new targets for the development of efficient combined immunotherapy, not forgetting the relevant concerns that may be raised on NK IC blockade. Finally, the impact of epigenetic drugs in such a complex therapeutic picture will be briefly addressed.

LLT1-CD161 Interaction in Cancer: Promises and Challenges

The success of immune checkpoint therapy in cancer has changed our way of thinking, promoting the design of future cancer treatments that places the immune system at the center stage. The knowledge gained on immune regulation and tolerance helped the identification of promising new clinical immune targets. Among them, the lectin-like transcript 1 (LLT1) is the ligand of CD161 (NKR-P1A) receptor expressed on natural killer cells and T cells. LLT1/CD161 interaction modulates immune responses but the exact nature of the signals delivered is still partially resolved. Investigation on the role of LLT1/CD161 interaction has been hampered by the lack of functional homologues in animal models. Also, some studies have been misled by the use of non-specific reagents. Recent studies and meta-analyses of single cell data are bringing new insights into the function of LLT1 and CD161 in human pathology and notably in cancer. The advances made on the characterization of the tumor microenvironment prompt us to integrate LLT1/CD161 interaction into the equation. This review recapitulates the key findings on the expression profile of LLT1 and CD161, their regulation, the role of their interaction in cancer development, and the relevance of targeting LLT1/CD161 interaction.

NK Cell-Based Immunotherapy for Hematological Malignancies

Natural killer (NK) lymphocytes are an integral component of the innate immune system and represent important effector cells in cancer immunotherapy, particularly in the control of hematological malignancies. Refined knowledge of NK cellular and molecular biology has fueled the interest in NK cell-based antitumor therapies, and recent efforts have been made to exploit the high potential of these cells in clinical practice. Infusion of high numbers of mature NK cells through the novel graft manipulation based on the selective depletion of T cells and CD19+ B cells has resulted into an improved outcome in children with acute leukemia given human leucocyte antigen (HLA)-haploidentical hematopoietic transplantation. Likewise, adoptive transfer of purified third-party NK cells showed promising results in patients with myeloid malignancies. Strategies based on the use of cytokines or monoclonal antibodies able to induce and optimize NK cell activation, persistence, and expansion also represent a novel field of investigation with remarkable perspectives of favorably impacting on outcome of patients with hematological neoplasia. In addition, preliminary results suggest that engineering of mature NK cells through chimeric antigen receptor (CAR) constructs deserve further investigation, with the goal of obtaining an "off-the-shelf" NK cell bank that may serve many different recipients for granting an efficient antileukemia activity.

Hemophagocytic lymphohistiocytosis in an adult kidney transplant recipient successfully treated by plasmapheresis: A case report and review of the literature

RATIONALE

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease entity primarily described in children, but not less relevant in adults. It is characterized by a misdirected activation of the immune system, resulting in an uncontrolled cytokine release from macrophages and cytotoxic T-cells (CTLs). Primary HLH relies on a genetic predisposition, whereas secondary HLH develops in the context of infections, malignancies or autoimmune diseases. However, the awareness and therapeutic knowledge for HLH in adulthood is limited. Most therapy protocols are almost exclusively validated in pediatric cohorts and for primary HLH. Their transferability to adult individuals with mostly secondary HLH is doubtful. Especially the high liver and bone marrow toxicity of applied etoposide-based protocols is discussed controversially and connected to overwhelming infections and death.

PATIENT CONCERN

A 51-year old, male, kidney transplant recipient was admitted to our center suffering from diarrhea, fever, nausea, hyponatremia, kidney graft failure, disorientation, progressive hemodynamic instability, and multiorgan failure.

DIAGNOSES

Clinical and laboratory findings resembled those of a septic shock. Ferritin and soluble interleukin-2 receptor (sCD25) levels were disproportionally elevated. Only a mild hepatosplenomegaly was diagnosed in a CT scan. A T2-weighted, fluid-attenuated inversion recovery MRI showed marked, bilateral and periventricular white matter hyperintensities. The cerebrospinal fluid (CSF) analysis showed a moderately elevated protein content and cell count. There was no evidence of any bacterial, viral, or parasitic infection. The diagnosis of HLH was made.

INTERVENTIONS & OUTCOMES

The patient was successfully treated by a combined approach consisting of plasma exchange (PE), corticosteroids, anakinra, and cyclosporine (CsA).

LESSONS

HLH is an important differential diagnosis in critically ill patients. Its unspecific clinical picture complicates an early diagnosis and may be misclassified as sepsis. A combination of plasma exchange (PE), corticosteroids, anakinra, and cyclosporine (CsA) may be a promising and less toxic approach for HLH therapy in adults.

Rare causes of hyperbilirubinemia after lung transplantation: our experience at a single center

Background

Lung transplantation is the last treatment option for end-stage lung disease, and the number of lung transplantations has been steadily increasing. Hyperbilirubinemia is a rare complication after lung transplantation. The aim of this study was to review rare causes of hyperbilirubinemia after lung transplantation at our center.

Methods

In this single-center study, we retrospectively reviewed the records of 116 consecutive lung transplantation patients who underwent lung transplantation at Severance Hospital and Gangnam Severance Hospital of Yonsei University College of Medicine in South Korea between December 22, 2010 and January 1, 2016. Hyperbilirubinemia was defined as a total bilirubin level exceeding 5 mg/dL for at least 3 days after lung transplantation.

Results

Hyperbilirubinemia occurred in 33 patients (28.4%) who received lung transplants at our institution. Twenty-four cases involved common causes such as drug toxicity, biliary tract stone, sepsis, and bleeding. However, rare causes of hyperbilirubinemia including hemophagocytic lymphohistiocytosis (HLH), thrombotic microangiopathy (TMA), and ischemic cholangiopathy were observed in 9 (7.8%) patients during the study period. All patients with hyperbilirubinemia due to a rare cause died despite aggressive treatment.

Conclusion

Causes of hyperbilirubinemia after lung transplantation are varied, and the prognosis of patients with hyperbilirubinemia arising from rare causes was poor. Therefore, early evaluation and management of hyperbilirubinemia after lung transplantation is important to improve patient outcomes.

Recent advances in diagnostic and therapeutic guidelines for primary and secondary hemophagocytic lymphohistiocytosis

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome characterized by excessive activation of macrophages and T cells resulting from defective cytotoxicity. It is potentially life threatening due to the large amounts of cytokines released by the activated macrophages and lymphocytes secondary to a hyperinflammatory response. It has a high fatality in children with an incidence of approximately 1.2cases/million per year.

METHOD

The literature was extensively searched in PubMed, MEDLINE and Google scholar.

RESULTS

A variable and nonspecific symptomatology can delay the diagnosis and hence requires a high index of suspicion in both primary and secondary HLH.

Enhanced Th1/Th17 Functions of CD161+ CD8+ T Cells in Mucosal Tissues of Rhesus Macaques

Expression of the C-type lectin-like receptor CD161 by human T cells is associated with type-17 responses, which play critical regulatory roles in immunity and inflammation at mucosal sites. However, the functions of CD161-expressing T cells in macaques, the pre-clinical model of several human diseases, remain unknown. This study examined the phenotypic and functional characteristics of CD161⁺ T cells in peripheral blood, mucosal tissues and lymph nodes of rhesus macaques. Majority of CD161-expressing T cells in peripheral blood and lung/intestinal mucosal tissues of rhesus macaques were found to be CD8⁺CD4^– in phenotype. There was a significant enrichment of CD161⁺CD8⁺ T cells in the lungs and colonic mucosa (16.1%±6.6 and 16.8%±5.7) in comparison to peripheral blood (4.2%±1.2) and mesenteric lymph nodes (1.3%±0.8). Regardless of the tissue compartment, CD161⁺CD8⁺ T cells mainly comprised of γδ T cells and TCR Vα7.2⁺ MAIT cells (up to 80%), and displayed Th1 and Th17 cytokine responses to mitogen stimulation. Mucosal CD161⁺CD8⁺ T cells were characterized by very high expression of CD69, a recent activation marker that is preferentially expressed on tissue resident cells. Furthermore, lung and colonic mucosal CD161⁺CD8⁺ T cells showed enhanced IFN-γ, IL-17, and Perforin production in comparison to those in blood. Thus, macaque CD161⁺CD8⁺ T cells represent mucosal tissue-homing innate-like CD8⁺ T-cell populations with Th1/Th17 type cytokine and cytotoxic effector functions that can potentially enhance the recruitment of adaptive immune cells and control initial pathogen burden/dissemination in tissues. Analysis of their role in early immune responses to mucosal pathogens will be valuable in the design of vaccines and therapeutics.

Functional characterization of a conserved pair of NKR-P1 receptors expressed by NK cells and T lymphocytes in liver and gut

Natural killer cell receptor protein 1 (NKR-P1) molecules are C-type lectin-like receptors modulating cellular responses toward target cells expressing C-type lectin-like related (Clr) molecules. Although the function of the prototypic rat NKR-P1A receptor and its inhibitory counterpart NKR-P1B are known, little is known about NKR-P1F and NKR-P1G apart from their promiscuity for Clr ligands. Here we generated mAbs against both receptors for phenotypic and functional analyses in rat tissues. NKR-P1F induced redirected lysis and robust Ca(2+) signaling in NK cells, which were prevented by simultaneous engagement of NKR-P1G. NKR-P1G also inhibited NK-cell lysis of Clr transfectants. NKR-P1F was expressed by most NK cells and NKR-P1A(+) T cells in all tissues analyzed, and by many NKR-P1A(-) intestinal T cells, while NKR-P1G was expressed by subsets of these cells with highest prevalence in gut and liver. In the intraepithelial compartment, the proportion of NKR-P1A(+) and NKR-P1F(+) cells was high at birth and thereafter declined, while NKR-P1B(+) and NKR-P1G(+) cells increased with age. Expression levels were also modulated by cytokines, with an increase of NKR-P1B and NKR-P1G induced by inflammatory cytokines, and a reduction of NKR-P1A by TGF-β. The physiological impact of NKR-P1 receptors might thus be dependent on age, tissue, and inflammatory status.

Gamma Delta T-lymphocytes in Hepatitis C and Chronic Liver Disease

Discovered 30 years ago, gamma delta (γδ) T-lymphocytes remain an intriguing and enigmatic T-cell subset. Although in humans they comprise a small fraction of the total circulating T-lymphocyte pool, they represent an important T-cell subset in tissues such as the liver, with roles bridging the innate and adaptive immune systems. The associations of γδ T-lymphocytes with chronic liver disease have been explored – however, there remain conflicting data as to whether these T-cells are pathogenic or protective. In patients with some forms of liver disease, their expansion in the periphery and especially in the liver may indeed help pathogen clearance, while in other conditions their presence may, in contrast, contribute to disease progression. γδ T-cells can also express CD161, a C-type lectin, and such cells have been found to be involved in the pathogenesis of inflammatory disease. CD161+ T-cells of diverse subsets are known to be enriched in the livers of patients with chronic hepatitis C. This article serves to provide a review of the γδ T-cell population and its role in hepatitis C and other chronic liver diseases, and also explores a potential role of the CD161+ γδ T-cells in liver diseases.

Complexity and Diversity of the NKR-P1:Clr (Klrb1:Clec2) Recognition Systems

The NKR-P1 receptors were identified as prototypical natural killer (NK) cell surface antigens and later shown to be conserved from rodents to humans on NK cells and subsets of T cells. C-type lectin-like in nature, they were originally shown to be capable of activating NK cell function and to recognize ligands on tumor cells. However, certain family members have subsequently been shown to be capable of inhibiting NK cell activity, and to recognize proteins encoded by a family of genetically linked C-type lectin-related ligands. Some of these ligands are expressed by normal, healthy cells, and modulated during transformation, infection, and cellular stress, while other ligands are upregulated during the immune response and during pathological circumstances. Here, we discuss historical and recent developments in NKR-P1 biology that demonstrate this NK receptor–ligand system to be far more complex and diverse than originally anticipated.

Hemophagocytic syndromes--an update

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome and not an independent disease. HLH represents the extreme end of a severe uncontrolled hyperinflammatory reaction that can occur in many underlying conditions. Genetic forms of HLHs are due to defects in transport, processing and function of cytotoxic granules in natural killer cells and cytotoxic T lymphocytes, and are not restricted to manifestation in childhood. Acquired forms of HLH are encountered in infections, autoinflammatory and autoimmune diseases, malignancies, acquired immune deficiency. Functional tests allow for differentiation between genetic and acquired HLH. Treatment aims at suppressing hypercytokinemia and eliminating activated and infected cells. It includes immunomodulatory and immunosuppressive agents, cytostatics, T-cell and cytokine antibodies. In genetic HLH cure can only be achieved with hematopoietic stem cell transplantation. Reduced-intensity conditioning regimens have considerably improved survival.

Genetically coupled receptor–ligand pair NKp80-AICL enables autonomous control of human NK cell responses

Human NK cells contain Golgi complex–associated intracellular stores of AICL, a ligand of the activating NK receptor NKp80. Upon exposure to inflammatory cytokines, AICL surfaces on NK cells, rendering them susceptible to NKp80-mediated bystander NK cytolysis.

CD161 defines the subset of FoxP3+ T cells capable of producing proinflammatory cytokines

Regulatory FoxP3+CD4+ T cells (Treg) are vital for maintaining the balance between tolerance, adequate immune response, and autoimmunity. Despite this immunoregulatory role, it has been shown that Treg may also produce proinflammatory cytokines. Here we present a distinct population of Treg, defined by CD161 expression, as the major source of FoxP3+ Treg-derived proinflammatory cytokines. CD161+ Treg can be followed throughout development, from thymus and cord blood to healthy child and adult samples. CD161+ Treg display anergy, are suppressive in cocultures with conventional T cells (Tconv), and possess a predominantly demethylated Treg-specific demethylated region of the FOXP3 locus. In addition to the production of interleukin (IL) 17A, interferon γ, and IL-2, CD161+FoxP3+ cells share markers with Tconv, including expression of the transcription factors retinoic acid-related orphan receptor Cv2 (RORCv2) and T-cell-specific T-box transcription factor (Tbet). Expression of CD161 and enrichment for cytokine production are stable characteristics of CD161+ Treg upon both short- and longer-term culture in vitro. Additionally, CD161+ Treg are highly enriched within the inflammatory environment of childhood arthritis, suggesting a role in disease. Our data therefore demonstrate that CD161+FoxP3+ T cells are a novel Treg subset, found in health and disease, which display high proinflammatory potential but also exhibit hallmark Treg characteristics.

Human NK cells at early stages of differentiation produce CXCL8 and express CD161 molecule that functions as an activating receptor

Human natural killer (NK) cell development is a step-by-step process characterized by phenotypically identified stages. CD161 is a marker informative of the NK cell lineage commitment, whereas CD56, CD117, and CD94/NKG2A contribute to define discrete differentiation stages. In cells undergoing in vitro differentiation from CD34+ umbilical cord blood (UCB) progenitors, LFA-1 expression allowed to discriminate between immature noncytolytic CD161+CD56+LFA-1− and more differentiated cytolytic CD161+CD56+LFA-1+ NK cells. CD161+CD56+LFA-1− NK cells produce large amounts of CXCL8 after phorbol myristate acetate (PMA) or cytokine treatment. Remarkably, CXCL8 mRNA expression was also detected in fresh stage III immature NK cells isolated from tonsils and these cells expressed CXCL8 protein on PMA stimulation. Within in vitro UCB-derived CD161+CD56+LFA-1− NK cells, CXCL8 release was also induced on antibody-mediated cross-linking of NKp44 and CD161. Such unexpected activating function of CD161 was confined to the CD161+CD56+LFA-1− subset, because it did not induce cytokine release or CD107a expression in CD161+CD56+LFA-1+ cells or in mature peripheral blood NK cells. Anti-CXCL8 neutralizing antibody induced a partial inhibition of NK cell differentiation, which suggests a regulatory role of CXCL8 during early NK cell differentiation. Altogether, these data provide novel information that may offer clues to optimize NK cell maturation in hematopoietic stem cell transplantation.

Induction of lectin-like transcript 1 (LLT1) protein cell surface expression by pathogens and interferon-γ contributes to modulate immune responses

CD161 is a C-type lectin-like receptor expressed on human natural killer (NK) cells and subsets of T cells. CD161 has been described as an inhibitory receptor that regulates NK cell-mediated cytotoxicity and IFN-γ production. Its role on T cells has remained unclear. Studies have shown that triggering of CD161 enhances NK T cell proliferation and T cell-IFN-γ production while inhibiting TNF-α production by CD8(+) T cells. Lectin-like transcript 1 (LLT1), the ligand of CD161, was found to be expressed on Toll-like receptor (TLR)-activated plasmacytoid and monocyte-derived dendritic cells (DC) and on activated B cells. Using newly developed anti-LLT1 mAbs, we show that LLT1 is not expressed on the surface of circulating B and T lymphocytes, NK cells, monocytes, and dendritic cells but that LLT1 is up-regulated upon activation. Not only TLR-stimulated dendritic cells and B cells but also T cell receptor-activated T cells and activated NK cells up-regulate LLT1. Interestingly, IFN-γ increases LLT1 expression level on antigen-presenting cells. LLT1 is also induced on B cells upon viral infection such as Epstein-Barr virus or HIV infection and in inflamed tonsils. Finally, expression of LLT1 on B cells inhibits NK cell function but costimulates T cell proliferation or IFN-γ production, and coengagement of CD161 with CD3 increases IL-17 secretion. Altogether, our results point toward a role for LLT1/CD161 in modulating immune responses to pathogens.

Deciphering the role of Epstein-Barr virus in the pathogenesis of T and NK cell lymphoproliferations

Epstein-Barr virus (EBV) is a highly successful herpesvirus, colonizing more than 90% of the adult human population worldwide, although it is also associated with various malignant diseases. Primary infection is usually clinically silent, and subsequent establishment of latency in the memory B lymphocyte compartment allows persistence of the virus in the infected host for life. EBV is so markedly B-lymphotropic when exposed to human lymphocytes in vitro that the association of EBV with rare but distinct types of T and NK cell lymphoproliferations was quite unexpected. Whilst relatively rare, these EBV-associated T and NK lymphoproliferations can be therapeutically challenging and prognosis for the majority of patients is dismal. In this review, we summarize the current knowledge on the role of EBV in the pathogenesis of these tumours, and the implications for treatment.

CD161(high)CD8+T cells bear pathogenetic potential in multiple sclerosis

To identify differentially expressed genes in multiple sclerosis, microarrays were used in a stringent experimental setting-leukapheresis from disease-discordant monozygotic twins and gene expression profiling in CD4(+) and CD8(+) T-cell subsets. Disease-related differences emerged only in the CD8(+) T-cell subset. The five differentially expressed genes identified included killer cell lectin-like receptor subfamily B, member 1, also known as natural killer receptor protein 1a/CD161, presented by the International Multiple Sclerosis Genetics Consortium as one of the non-MHC candidate loci. Flow cytometric analysis on peripheral blood of healthy donors and patients with multiple sclerosis and rheumatoid arthritis confirmed an upregulation of CD161 at the protein level, showing also a significant excess of CD161(high)CD8(+) T cells in multiple sclerosis. This subset prevalently included chemokine (C-C motif) receptor 6(+), cytokine-producing, effector-memory T cells with proinflammatory profiles. It also included all circulating interleukin-17(+)CD8(+) T cells. In the CD161(high)CD8(+) subset, interleukin-12 facilitated proliferation and interferon-γ production, with CD161 acting as a co-stimulatory receptor. CD161(+)CD8(+)CD3(+) T cells producing interferon-γ were part of intralesional immune infiltrates and ectopic B cell follicles in autopsy multiple sclerosis brains. Variations of CD161 expression on CD8(+) T cells identify a subset of lymphocytes with proinflammatory characteristics that have not been previously reported in multiple sclerosis and are likely to contribute to disease immunopathology.

Novel aspects of in vitro IL-2 or IFN-α enhanced NK cytotoxicity of healthy individuals based on NKG2D and CD161 NK cell receptor induction

As IL-2 and IFN-α modulate NK cell activity it was of interest to investigate the expression of newly defined NK cell receptors and augmented NK cell activity in healthy individuals after cytokine in vitro treatment. Peripheral blood lymphocytes (PBL) obtained from 31 healthy volunteers treated for 18 h with 200 IU/ml IL-2 and 250 IU/ml IFN-α were evaluated for NK cell cytotoxicity. Expression of NKG2D, CD161, CD158a, CD158b receptors was analyzed on CD3⁻CD16+ NK cells, cytotoxic CD16(bright) and regulatory CD16(dim) subsets by FACS flow. The found induced significant in vitro enhancement of NK cell activity by both cytokines is supported by specific cytokine induction in PBL of pSTAT1 and pSTAT5, determined by Western blotting, as well as induction of IRF-1 transcription. Both cytokines induce significant up-regulation of NKG2D expression while only IFN-α induced significant up-regulation of CD161, with no alteration in KIR expression by either cytokine on CD3⁻CD16+ NK cells. Investigated cytokines did not induce change in NK cell bright and dim subset distribution. Moreover, we find that, not only cytokine receptor induction on the CD3⁻CD16+ NK cells, but also simultaneous increase in their percentage and/or density on CD16(bright) and CD16(dim) subsets, represent good indicators of receptor cytokine-susceptibility. As the role of NK cells has been shown in the loss of tolerance, infection and cancer, the data obtained in this study may be of help in NK cell profiling, by giving referent values of cytokine-induced novel NK cell receptor expression either in evaluation of these diseases or in immunomonitoring during cytokine immunotherapy.

Changes to the natural killer cell repertoire after therapeutic hepatitis B DNA vaccination

BACKGROUND

Improvements to the outcome of adaptive immune responses could be achieved by inducing specific natural killer (NK) cell subsets which can cooperate with dendritic cells to select efficient T cell responses. We previously reported the induction or reactivation of T cell responses in chronic hepatitis B patients vaccinated with a DNA encoding hepatitis B envelope proteins during a phase I clinical trial.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined changes in the peripheral NK cell populations occurring during this vaccine trial using flow cytometry analysis. Despite a constant number of NK cells in the periphery, a significant increase in the CD56(bright) population was observed after each vaccination and during the follow up. Among the 13 different NK cell markers studied by flow cytometry analysis, the expression of CD244 and NKG2D increased significantly in the CD56(bright) NK population. The ex vivo CD107a expression by CD56(bright) NK cells progressively increased in the vaccinated patients to reach levels that were significantly higher compared to chronically HBV-infected controls. Furthermore, modifications to the percentage of the CD56(bright) NK cell population were correlated with HBV-specific T cell responses detected by the ELISPOT assay.

CONCLUSIONS/SIGNIFICANCE

These changes in the CD56(bright) population may suggest a NK helper effect on T cell adaptive responses. Activation of the innate and adaptive arms of the immune system by DNA immunization may be of particular importance to the efficacy of therapeutic interventions in a context of chronic infections.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00988767.

Functional consequences of interactions between human NKR-P1A and its ligand LLT1 expressed on activated dendritic cells and B cells

Lectin-like transcript-1 (LLT1) (also named osteoclast inhibitory lectin or CLEC2D) is a ligand for the human NKR-P1A (CD161) receptor, present on NK cells and T cells. To further understand the physiological relevance of this interaction, we developed mAbs against LLT1, characterized the expression pattern of LLT1, and explored the functional consequence of LLT1 engagement of the NKR-P1A receptor on NK cells and T cells. LLT1 is expressed on TLR-activated plasmacytoid dendritic, TLR-activated monocyte-derived dendritic cells, and on B cells stimulated through TLR9, surface Ig, or CD40. Interactions between NKR-P1A on NK cells and LLT1 on target cells inhibit NK cell-mediated cytotoxicity and cytokine production and can inhibit TNF-alpha production by TCR-activated NKR-P1A(+) CD8(+) T cells. In contrast, NKR-P1A failed to inhibit or augment the TCR-dependent activation of NKR-P1A-bearing CD4(+) T cells. Expression of LLT1 on activated dendritic cells and B cells suggests that it might regulate the cross-talk between NK cells and APCs.

CD161 expression on hepatitis C virus-specific CD8+ T cells suggests a distinct pathway of T cell differentiation

Hepatitis C virus (HCV) causes chronic infection accompanied by a high risk of liver failure and hepatocellular carcinoma. CD8+ T cell responses are important in the control of viremia. However, the T cell response in chronic infection is weak both in absolute numbers and in the range of epitopes targeted. In order to explore the biology of this response further, we analyzed expression of a panel of natural killer cell markers in HCV compared with other virus-specific T cell populations as defined by major histocompatibility complex class I tetramers. We found that CD161 was significantly expressed on HCV-specific cells (median 16.8%) but not on CD8+ T cells specific for human immunodeficiency virus (3.3%), cytomegalovirus (3.4%), or influenza (3.4%). Expression was seen in acute, chronic, and resolved disease and was greatest on intrahepatic HCV-specific T cells (median 57.6%; P < 0.05). Expression of CD161 was also found on hepatitis B virus-specific CD8+ T cells. In general, CD161+CD8+ T cells were found to be CCR7- "effector memory" T cells that could produce proinflammatory cytokines (interferon-gamma and tumor necrosis factor-alpha) but contained scanty amounts of cytolytic molecules (granzyme B and perforin) and proliferated poorly in vitro. Expression of CD161 on CD8+ T cells was tightly linked to that of CXCR6, a chemokine with a major role in liver homing.

CONCLUSION

We propose that expression of CD161 indicates a unique pattern of T cell differentiation that might help elucidate the mechanisms of HCV immunity and pathogenesis.

Malignant glioma cells counteract antitumor immune responses through expression of lectin-like transcript-1

Glioblastoma, one of the most lethal tumors, is paradigmatic for tumor-associated immunosuppression. Lectin-like transcript-1 (LLT1) is a newly identified ligand for the inhibitory natural killer (NK) cell receptor CD161. Here, we report that glioma cells express LLT1 mRNA and protein in vitro and in vivo, whereas expression levels in normal brain are low. LLT1 expression in human gliomas increases with the WHO grade of malignancy. We further show that transforming growth factor-beta (TGF-beta) up-regulates the expression of LLT1 in glioma cells. Small interfering RNA (siRNA)-mediated down-regulation of LLT1 in LNT-229 and LN-428 cells promotes their lysis by NK cells. Thus, LLT1 acts as a mediator of immune escape and contributes to the immunosuppressive properties of glioma cells.

Familial and acquired hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition of severe hyperinflammation caused by the uncontrolled proliferation of activated lymphocytes and histiocytes secreting high amounts of inflammatory cytokines. Cardinal signs and symptoms are prolonged fever, hepatosplenomegaly and pancytopenia. Characteristic biochemical markers include elevated triglycerides, ferritin and low fibrinogen. HLH occurs on the basis of various inherited or acquired immune deficiencies. Impaired function of natural killer (NK) cells and cytotoxic T-cells (CTL) is shared by all forms of HLH. Genetic HLH occurs in familial forms (FHLH) in which HLH is the primary and only manifestation, and in association with the immune deficiencies Chédiak-Higashi syndrome 1 (CHS 1), Griscelli syndrome 2 (GS 2) and x-linked lymphoproliferative syndrome (XLP), in which HLH is a sporadic event. Most patients with acquired HLH have no known underlying immune deficiency. Both acquired and genetic forms are triggered by infections, mostly viral, or other stimuli. HLH also occurs as a complication of rheumatic diseases (macrophage activation syndrome) and of malignancies. Several genetic defects causing FHLH have recently been discovered and have elucidated the pathophysiology of HLH. The immediate aim of therapy in genetic and acquired HLH is suppression of the severe hyperinflammation, which can be achieved with immunosuppressive/immunomodulatary agents and cytostatic drugs. Patients with genetic forms have to undergo stem cell transplantation to exchange the defective immune system with normally functioning immune effector cells. In conclusion, awareness of the clinical symptoms and of the diagnostic criteria of HLH is crucial in order not to overlook HLH and to start life-saving therapy in time.

Recognition of a carbohydrate xenoepitope by human NKRP1A (CD161)

BACKGROUND

Many immunologically important interactions are mediated by leukocyte recognition of carbohydrates via cell surface receptors. Uncharacterized receptors on human natural killer (NK) cells interact with ligands containing the terminal Galalpha(1,3)Gal xenoepitope. The aim of this work was to isolate and characterize carbohydrate binding proteins from NK cells that bind alphaGal or other potential xenoepitopes, such as N-acetyllactosamine (NAcLac), created by the deletion of alpha1,3galactosyltransferase (GT) in animals.

METHODS AND RESULTS

Initial analysis suggested the human C-type lectin NKRP1A bound to a pool of glycoconjugates, the majority of which contained the terminal Galalpha(1,3)Gal epitope. This was confirmed by high level binding of cells expressing NKRP1A to mouse laminin, which contains a large number of N-linked oligosaccharides with the Galalpha(1,3)Gal structure. The consequence of removing the terminal alphaGal was then investigated. Elevated NAcLac levels were observed on thymocytes from GT-/- mice. Exposing NAcLac on laminin, by alpha-galactosidase treatment, resulted in a significant increase in NKRP1A binding.

CONCLUSIONS

NKRPIA binds to the alphaGal epitope. Moreover, exposing NAcLac by removal of alphaGal resulted in an increase in binding. This may be relevant in the later phases of xenotransplant rejection if GT-/- pigs, like GT-/- mice, display increased NAcLac expression.

Cutting edge: lectin-like transcript 1 is a ligand for the CD161 receptor

Human NK cells and subsets of T cells or NKT cells express the orphan C-type lectin receptor CD161 (NKR-P1A) of unknown function. In contrast to rodents that possess several NKR-P1 genes coding for either activating or inhibitory receptors, the nature of signals delivered by the single human NKR-P1A receptor is still to be clarified. In this article, we show that the lectin-like transcript 1 (LLT1) molecule is a ligand for the CD161 receptor. Engagement of CD161 on NK cells with LLT1 expressed on target cells inhibited NK cell-mediated cytotoxicity and IFN-gamma secretion. Conversely, LLT1/CD161 interaction in the presence of a TCR signal enhanced IFN-gamma production by T cells. These findings identify a novel ligand/receptor pair that differentially regulate NK and T cell functions.

Cutting Edge: Lectin-Like Transcript-1 Is a Ligand for the Inhibitory Human NKR-P1A Receptor

Increasingly, roles are emerging for C-type lectin receptors in immune regulation. One receptor whose function has remained largely enigmatic is human NKR-P1A (CD161), present on NK cells and subsets of T cells. In this study, we demonstrate that the lectin-like transcript-1 (LLT1) is a physiologic ligand for NKR-P1A. LLT1-containing liposomes bind to NKR-P1A+ cells, and binding is inhibited by anti-NKR-P1A mAb. Additionally, LLT1 activates NFAT-GFP reporter cells expressing a CD3zeta-NKR-P1A chimeric receptor; reciprocally, reporter cells with a CD3zeta-LLT1 chimeric receptor are stimulated by NKR-P1A. Moreover, LLT1 on target cells can inhibit NK cytotoxicity via interactions with NKR-P1A.

Familial and acquired hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition characterized by uncontrolled hyperinflammation on the basis of various inherited or acquired immune deficiencies. Cardinal symptoms are prolonged fever, hepatosplenomegaly and cytopenias. Central nervous system (CNS) symptoms are common. Biochemical markers include elevated triglyceride and ferritin, high levels of the alpha chain of the soluble interleukin-2 receptor and low fibrinogen. Impaired function of natural killer (NK) cells and cytotoxic T-cells (CTL) is a characteristic of all forms of HLH. Genetic HLH occurs in familial forms (FHLH), in which HLH is the primary and only manifestation, and in association with the immune deficiencies Chédiak-Higashi syndrome (CHS), Griscelli syndrome (GS) and X-linked lymphoproliferative syndrome (XLP), in which secondary HLH occurs sporadically. Most patients with acquired HLH have no known underlying immune deficiency. Both acquired and genetic forms are triggered by infections, mostly viruses, or other stimuli. HLH also occurs as a complication of rheumatic diseases (macrophage activation syndrome) and of malignancies. The recent discovery of several genetic defects causing FHLH as well as the identification of the genes responsible for CHS, GS and XLP have underscored the role of granule (perforin/granzymes)-mediated cytotoxicity in both the killing of infected cells and the termination of the immune response. The immediate aim of therapy is suppression of the increased inflammatory response by immunosuppressive/immunomodulatory agents and cytotoxic drugs. Genetic cases can only be cured with stem cell transplantation. Awareness of the clinical symptoms and of diagnostic criteria for HLH is crucial to starting life-saving therapy in time.

Decrease in a specific killer cell immunoglobulin-like receptor on peripheral natural killer cells in women with recurrent spontaneous abortion of unexplained etiology

PROBLEM

The aim of this study was to investigate immunophenotypic characteristics of natural killer (NK) cells by assessing specific molecules expressed in women with recurrent spontaneous abortion (RSA) of unexplained etiology.

METHOD OF STUDY

Peripheral blood cells were obtained from 20 RSA women and 15 fertile controls. The expression of perforin, CD94, CD161, CD158a, CD158b, and CD244 on CD3- CD56+ NK cells was analyzed by flow cytometry.

RESULTS

A significant decrease in CD158a expression was demonstrated in RSA women (mean +/- SD, 22.9 +/- 8.7%) as compared with that in controls (33.6 +/- 15.7%) (P < 0.05). The percentage of NK cells showing dual expression of CD94 and CD161 was relatively higher in RSA women (55.1 +/- 10.2%) than in the controls (47.1 +/- 19.0%), but without statistically significant (P = 0.096). The expression of perforin, CD158b, or CD244 in RSA women did not differ from that in the controls.

CONCLUSIONS

A divergence of the specific NK cell repertoire might be related to the etiology of RSA.

Expression of CD94/NKG2-A on human T lymphocytes is induced by IL-12: implications for adoptive immunotherapy

NK cell receptors (NKRs) are expressed on a subset of human T cells, predominantly CD8(+), within which they can modulate TCR-mediated functions. In an attempt to identify the mechanisms leading to NKR expression, we analyzed the capacity of IL-12 to modulate the expression by T cells of the components of the CD94/NKG2-A inhibitory receptor, a member of the C-type lectin-like family of NKR. We show that IL-12 induces the expression of NKG2-A and/or CD94 by CD8(+) T cells in culture, and that this induction was mediated neither by IFN-gamma nor by IL-15. We also show, using the redirected killing assay, that IL-12-induced expression of both CD94 and NKG2-A led to the acquisition by T cells of a functional inhibitory receptor. Expression of the CD94/NKG2-A inhibitory receptor was also induced by IL-12 during T cell Ag stimulation so that in the presence of this cytokine a high proportion of melanoma-reactive CTL induced from PBL by melanoma peptide stimulation expressed this receptor. This study emphasizes the implication of IL-12 in the modulation of immune responses through NKR induction.

Increased killer inhibitory receptor KIR2DL1 expression among natural killer cells in women with pelvic endometriosis

OBJECTIVE

To investigate the host immunologic response to endometriosis in terms of killer inhibitory receptor (KIR) expression by natural killer (NK) cells.

DESIGN

Case-control study of immunologic markers.

SETTING

University hospital.

PATIENT(S)

We compared cells from Japanese women with laparoscopically diagnosed endometriosis to cells from 40 women with other laparoscopic diagnoses.

INTERVENTION(S)

Peripheral venous blood sampling and laparoscopic peritoneal fluid collection.

MAIN OUTCOME MEASURE(S)

Flow cytometry was used to assess expression of KIR by NK cells in the cell samples.

RESULT(S)

The percentage of cells that expressed KIR2DL1 among NK (KIR2DL1(+)NK) cells in peritoneal fluid and peripheral blood was significantly higher in women with endometriosis than in controls. The proportion of KIR2DL1(+)NK cells in peripheral blood NK cells before and 1 month after laparoscopic surgery did not differ significantly.

CONCLUSION(S)

The proportion of KIR2DL1(+)NK cells was increased in peritoneal fluid and peripheral blood in women with endometriosis; this difference is probably related to NK cell suppression in endometriosis. This increase in KIR2DL1 expression by NK cells may represent a risk factor in the pathogenesis of endometriosis.

Differentially induced expression of C-type lectins in activated lymphocytes

The human NK gene complex encodes for the leucocyte C-type lectins, CD69, AICL (activation-induced C-type lectin), LLT1 (lectin-like transcript), CD161/NKR-P1A, CD94, and for NKG-2 molecules. These gene products have been implicated in the regulation of the function of natural killer (NK) cells and other lymphocytes. In this study the expression of C-type lectins during the early activation of PMA-stimulated peripheral blood lymphocytes was examined. To investigate the influence of de novo protein synthesis on activation-dependent expression of C-type lectins, cells were cultured in presence of cycloheximide (CHX) and mRNA levels were analyzed by semi-quantitative reverse transcription-polymerase chain reaction. Upregulated levels of CD69, AICL, and LLT1, but less pronounced changes of CD161/NKR-P1A and CD94 mRNA were found at early time points of cellular activation. CD69 was superinduced by CHX at the nuclear precursor transcript and the mRNA level suggesting that regulation of transcriptional activity and mRNA stability contribute to extent of CD69 mRNA accumulation. CHX treatment resulted also in an overexpression of AICL, LLT1, and CD161/NKR-P1A mRNAs. Conversely, CHX blocked CD94 mRNA expression in PMA-stimulated cells, demonstrating that this process is dependent on new protein synthesis. Expression kinetics in context with susceptibility to CHX indicate that the mechanisms responsible for upregulated CD69, AICL, and LLT1 expression are distinct from those which control CD161/NKR-P1A or CD94 expression. J. Cell. Biochem. Suppl. 36: 201-208, 2001.

Human natural killer cell receptors and signal transduction

Natural killer (NK) cells express numerous receptors, which continually engage with ligands on cell surfaces. Until 1995, only a handful of these receptors were characterized and the molecular basis of NK cell activation was obscure. Recently, considerable advances have been made in characterizing the receptor repertoire on human NK cells. Both activating and inhibitory receptors can transduce positive or negative signals to regulate NK cell cytotoxicity and cytokine release responses. The inhibitory receptors normally predominate in this balance of signals. Certain tumor cells and virally infected cells that lack major histocompatibility complex (MHC) class I molecules, however, can rapidly trigger NK cell activation. The basis of this activation is the loss of negative signals that are normally transmitted by MHC class I-binding inhibitory receptors, and the corresponding domination of activating receptor signals. While ligand specificity for a number of the recently described receptors is still a mystery, their signal transduction properties have begun to be defined. The dynamic crosstalk between these receptors ultimately governs the NK cell activation state. Although the complexities of NK cell signalling are only marginally understood, several overall themes have been defined by characterizing the roles of distinct pathways during NK cell responses.

Effect of granulocyte colony-stimulating factor mobilization on phenotypical and functional properties of immune cells

Some phenotypic and functional properties of lymphocytes from bone marrow or peripheral blood stem cell donors were compared in a randomized study. Lymphocyte subsets were analyzed by immunocytometry in blood harvested from bone marrow donors (n = 27) and from peripheral blood stem cell donors before and after granulocyte colony-stimulating factor mobilization (n = 23) and in bone marrow and peripheral blood stem cell grafts. Granulocyte colony-stimulating factor mobilization increased the blood T and B, but not NK, lymphocyte counts. All lymphocyte counts were approximately 10-fold higher in peripheral blood stem cell grafts than in bone marrow grafts. Analysis of CD25, CD95, HLA-DR, and CD45RA expression shows that T-cell activation level was lower after granulocyte colony-stimulating factor mobilization. Similarly, granulocyte colony-stimulating factor reduced by twofold to threefold the percentage of interferon-gamma, interleukin-2, and tumor necrosis factor-alpha-secreting cells within the NK, NK-T, and T-cell subsets and severely impaired the potential for interferon-gamma production at the single-cell level. mRNA levels of both type 1 (interferon-gamma, interleukin-2) and type 2 (interleukin-4, interleukin-13) cytokines were approximately 10-fold lower in peripheral blood stem cell grafts than in bone marrow grafts. This reduced potential of cytokine production was not associated with a preferential mobilization of so-called "suppressive" cells (CD3+CD4-CD8-, CD3+CD8+CD56+, or CD3+TCRVA24+CD161+), nor with a modulation of killer cell receptors CD161, NKB1, and CD94 expression by NK, NK-T, or T cells. Our data demonstrate in a randomized setting that quantitative as well as qualitative differences exist between a bone marrow and a peripheral blood stem cell graft, whose ability to produce type 1 and type 2 cytokines is impaired.

Evidence for a role of gammadelta T cells in demyelinating diseases as determined by activation states and responses to lipid antigens

In this report we review current information on the phenotypic and functional properties of gammadelta T cells in demyelinating disorders. The results support the conclusion that although gammadelta T cells show evidence of activation in patients with either multiple sclerosis (MS) or Guillain Barrè syndrome (GBS), differences exist in the phenotypic and functional properties of these cells between the two diseases. In particular, our data indicate that in patients with MS the Vdelta2 subset is activated and that these cells can be induced to secrete high levels of proinflammatory cytokines. In contrast, in patients with GBS, the Vdelta1 subset is expanded and can be induced to secrete cytokines more associated with a humoral response.

Inducible expression of the gp49B inhibitory receptor on NK cells

Murine NK cells express inhibitory receptors belonging to the C-type lectin-like (Ly-49, CD94/NKG2) and Ig superfamily-related (gp49) receptors. The murine gp49B receptor displays structural homology with human killer inhibitory receptors, and was previously identified to be a receptor on mast cells and activated NK cells. The gp49B receptor is highly related to gp49A, a receptor with unknown function. In this study, using a novel mAb produced against soluble gp49B molecules that cross-reacts with gp49A, we examined the cellular distribution and function of these receptors. gp49 is constitutively expressed on cells of the myeloid lineage throughout development, as well as on mature cells. Importantly, gp49 is not expressed on spleen- and liver-derived lymphocytes, including NK cells, but its expression is induced in vitro on NK cells following IL-2 stimulation, or in vivo by infection with murine CMV. Molecular studies revealed that both the immunoreceptor tyrosine-based inhibitory motif-containing gp49B as well as immunoreceptor tyrosine-based inhibitory motif-less gp49A receptors are up-regulated on NK cells following murine CMV infection. When co-cross-linked with NK1.1, gp49B can inhibit NK1.1-mediated cytokine release by NK cells. Taken together, these studies demonstrate that the expression of gp49B on NK cells is regulated, providing the first example of an in vivo activation-induced NK cell inhibitory receptor, in contrast to the constitutively expressed Ly49 family.

Selective expansion of intraepithelial lymphocytes expressing the HLA-E-specific natural killer receptor CD94 in celiac disease

BACKGROUND & AIMS

Celiac disease is a gluten-induced enteropathy characterized by the presence of gliadin-specific CD4(+) T cells in the lamina propria and by a prominent intraepithelial T-cell infiltration of unknown mechanism. The aim of this study was to characterize the subset(s) of intraepithelial lymphocytes (IELs) expanding during active celiac disease to provide insights into the mechanisms involved in their expansion.

METHODS

Flow-cytometric analysis of isolated IELs and/or immunohistochemical staining of frozen sections were performed in 51 celiac patients and 50 controls with a panel of monoclonal antibodies against T-cell and natural killer (NK) receptors. In addition, in vitro studies were performed to identify candidate stimuli for NK receptor expression.

RESULTS

In normal intestine, different proportions of IELs, which were mainly T cells, expressed the NK receptors CD94/NKG2, NKR-P1A, KIR2D/3D, NKp46, Pen5, or CD56. During the active phase of celiac disease, the frequency of CD94(+) IELs, which were mostly alphabeta T cells, was conspicuously increased over controls. In contrast, the expression of other NK markers was not modified. Furthermore, expression of CD94 could be selectively induced in vitro by T-cell receptor activation and/or interleukin 15, a cytokine produced by intestinal epithelial cells.

CONCLUSIONS

The gut epithelium favors the development of T cells that express NK receptors. In active celiac disease, there is a specific and selective increase of IELs expressing CD94, the HLA-E-specific NK receptor that may be related to T-cell receptor activation and/or interleukin 15 secretion.

In vivo expression of natural killer cell inhibitory receptors by human melanoma-specific cytolytic T lymphocytes

Natural killer (NK) receptor signaling can lead to reduced cytotoxicity by NK cells and cytolytic T lymphocytes (CTLs) in vitro. Whether T cells are inhibited in vivo remains unknown, since peptide antigen-specific CD8(+) T cells have so far not been found to express NK receptors in vivo. Here we demonstrate that melanoma patients may bear tumor-specific CTLs expressing NK receptors. The lysis of melanoma cells by patient-derived CTLs was inhibited by the NK receptor CD94/NKG2A. Thus, tumor-specific CTL activity may be decreased through NK receptor triggering in vivo.

CD28-negative cytolytic effector T cells frequently express NK receptors and are present at variable proportions in circulating lymphocytes from healthy donors and melanoma patients

In humans, NK receptors are expressed by natural killer cells and some T cells, the latter of which are preferentially alphabetaTCR+ CD8+ cytolytic T lymphocytes (CTL). In this study we analyzed the expression of nine NK receptors (p58.1, p58.2, p70, p140, ILT2, NKRP1A, ZIN176, CD94 and CD94/NKG2A) in PBL from both healthy donors and melanoma patients. The percentages of NK receptor-positive T cells (NKT cells) varied strongly, and this variation was more important between individual patients than between individual healthy donors. In all the individuals, the NKT cells were preferentially CD28-, and a significant correlation was found between the percentage of CD28- T cells and the percentage of NK receptor+ T cells. Based on these data and the known activated phenotype of CD28- T cells, we propose that the CD28- CD8+ T cell pool represents or contains the currently active CTL population, and that the frequent expression of NK receptors reflects regulatory mechanisms modulating the extent of CTL effector function. Preliminary results indicate that some tumor antigen-specific T cells may indeed be CD28- and express NK receptors in vivo.

A novel negative regulator molecule, Cho-1, is involved in the cytotoxicity by human natural killer cells but not in cytotoxic T lymphocytes

We previously reported the cytotoxic negative regulatory molecule, Cho-1, that was expressed on the cell surface of rat fetal fibroblast cells in the cytotoxicity by natural killer (NK) cells. This molecule was IFN-gamma-inducible, but appeared to be different from MHC class I. It was expressed on NK-resistant cells but not on NK-sensitive murine target cells such as YAC-1. In this paper, first we determined whether Cho-1 could also act as the negative regulatory molecule in a human NK-resistant HEPM line. Our data strongly suggested that Cho-1 could act as such a negative regulatory molecule in human NK cytotoxicity. The immunoprecipitates made with HEPM cell lysate and anti-MHC class I monoclonal antibody (mAb) did not react against anti-Cho-1 mAb, indicating that Cho-I was different from MHC class I. Second, an assessment was made as to whether or not this molecule is involved in the cytotoxicity of CD8 (+) cytotoxic T lymphocytes (CTL) against human autologous tumor cells. The data indicated that although this cell surface molecule was expressed on certain tumor lines, it was not involved in the cytotoxic mechanism of CTL. Thus, Cho-1 appeared to be the novel regulatory molecule in the NK cytotoxic mechanism.

IL-12-Mediated NKRP1A Up-Regulation and Consequent Enhancement of Endothelial Transmigration of Vδ2+ TCRγδ+ T Lymphocytes from Healthy Donors and Multiple Sclerosis Patients

γδ T lymphocytes are thought to play a role in the pathogenesis of multiple sclerosis (MS) contributing to demyelinization and fibrosis in the central nervous system. In this study, we show that, in MS patients with active disease, the percentage of circulating Vδ2+ γδ T cells coexpressing NKRP1A is significantly increased compared with healthy donors. Vδ2+ and Vδ1+ T cells were sorted from MS patients and healthy volunteers and cloned. At variance with Vδ1+ clones, all Vδ2+ clones expressed NKRP1A, which was strongly up-regulated upon culture with IL-12; this effect was neutralized by specific anti-IL-12 Abs. No up-regulation of NKRP1A by IL-12 was noted on Vδ1+ clones. RNase protection assay showed that IL-12R β2 subunit transcript was significantly less represented in Vδ1+ than Vδ2+ clones. This finding may explain the different effect exerted by IL-12 on these clones. In transendothelial migration assays, Vδ2+ NKRP1A+ clones migrated more effectively than Vδ1+ clones, and this migratory potential was enhanced following culture with IL-12. Migration was strongly inhibited by the F(ab′)2 of an anti-NKRP1A Ab, suggesting that this lectin is involved in the migration process. We also show that, in freshly isolated PBMC from MS patients, the migrated population was enriched for Vδ2+ NKRP1A+ cells. We conclude that the expression of NKRP1A on Vδ2+ cells is associated with increased ability to migrate across the vascular endothelium and that this phenomenon may be regulated by IL-12 present in the microenvironment.