Role Of Natural Killer Research Articles

NKT cells in liver diseases.

Natural killer T cells are innate-like and tissue-resident lymphocytes, which recognize lipid antigens and are enriched in the liver. Natural killer T cells play important roles in infections, tumors, autoimmune diseases, and metabolic diseases. In this study, we summarize recent findings on biology of natural killer T cells and their roles in hepatitis B virus and hepatitis C virus infection, autoimmune liver diseases, alcoholic liver disease, nonalcoholic fatty liver disease, and hepatocellular carcinoma. Controversial results from previous studies are discussed, and indicate the dynamic alteration in the role of natural killer T cells during the progression of liver diseases, which might be caused by changes in natural killer T subsets, factors skewing cytokine responses, and intercellular crosstalk between natural killer T cells and CD1d-expressing cells or bystander cells.

The Role of Natural Killer T Cells in Cancer-A Phenotypical and Functional Approach.

Natural killer T (NKT) cells are a subset of CD1d-restricted T cells at the interface between the innate and adaptive immune system. NKT cells can be subdivided into functional subsets that respond rapidly to a wide variety of glycolipids and stress-related proteins using T- or natural killer (NK) cell-like effector mechanisms. Because of their major modulating effects on immune responses via secretion of cytokines, NKT cells are also considered important players in tumor immunosurveillance. During early tumor development, T helper (TH)1-like NKT cell subsets have the potential to rapidly stimulate tumor-specific T cells and effector NK cells that can eliminate tumor cells. In case of tumor progression, NKT cells may become overstimulated and anergic leading to deletion of a part of the NKT cell population in patients via activation-induced cell death. In addition, the remaining NKT cells become hyporesponsive, or switch to immunosuppressive TH2-/T regulatory-like NKT cell subsets, thereby facilitating tumor progression and immune escape. In this review, we discuss this important role of NKT cells in tumor development and we conclude that there should be three important focuses of future research in cancer patients in relation with NKT cells: (1) expansion of the NKT cell population, (2) prevention and breaking of NKT cell anergy, and (3) skewing of NKT cells toward TH1-like subsets with antitumor activity.

ADCC-Mediated CD56dim NK Cell Responses Are Associated with Early HBsAg Clearance in Acute HBV Infection

Hepatitis B virus (HBV) affects up to 400 million people worldwide and accounts for approximately one million deaths per year from liver pathologies. Current treatment regimens are effective in suppressing viremia but usually have to be taken indefinitely, warranting research into new therapeutic approaches. Acute HBV infection in adults almost universally results in resolution of viremia, with the exception of immunocompromised persons, suggesting that the immune response can functionally cure or even eradicate HBV infection. Because immunophenotypic and functional studies have implicated a role for Natural Killer (NK) cells in HBV clearance during acute infection, we hypothesized that a distinct NK-cell profile exists in acute HBV infection that could provide information for the mechanism of HBV clearance. Using multivariate flow cytometry, we evaluated the expression of key activating and inhibitory receptors on NK cells, and their ability to respond to classic target cell lines. Multivariate analysis revealed selective perturbation of the CD56 dim NK-cell subset during acute infection, displaying low levels of NKp46+, NKp30+, CD160+ and CD161+ cells. Intriguingly, the CD56 dim NK-cell profile predicted time to HBV surface antigen (HBsAg) clearance from the blood, and distinct NK-cell profiles predicted early (NKp30, CD94, CD161) and late clearance (KIR3DL1, CD158a, perforin, NKp46). Finally, functional analysis demonstrated that early and late clearance tracked with elevated degranulation (CD107a) or IFNγ production, respectively, in response to ADCC-mediated activation. In conclusion, the cytolytic CD56dim NK-cell subset is selectively activated in acute HBV infection and displays distinct phenotypic and functional profiles associated with efficient and early control of HBV, implicating antibody-mediated cytolytic NK-cell responses in the early control and functional cure of HBV infection.

Mutations in PI3K110δ cause impaired natural killer cell function partially rescued by rapamycin treatment

Heterozygous gain-of-function mutations in PI3K110δ lead to lymphadenopathy, lymphoid hyperplasia, EBV and cytomegalovirus viremia, and sinopulmonary infections. The known role of natural killer (NK) cell function in the control of EBV and cytomegalovirus prompted us to investigate the functional and phenotypic effects of PI3K110δ mutations on NK cell subsets and cytotoxic function. Mutations in patients were identified by using whole-exome or targeted sequencing. We performed NK cell phenotyping and functional analysis of patients' cells using flow cytometry, standard Cr51 cytotoxicity assays, and quantitative confocal microscopy. PI3K110δ mutations led to an altered NK cell developmental phenotype and cytotoxic dysfunction. Impaired NK cell cytotoxicity was due to decreased conjugate formation with susceptible target cells and abrogated activation of cell machinery required for target cell killing. These defects were restored partially after initiation of treatment with rapamycin in 3 patients. We describe novel NK cell functional deficiency caused by PI3K110δ mutation, which is a likely contributor to the severe viremia observed in these patients. Rapamycin treatment partially restores NK cell function, providing a further rationale for its use in patients with this disease.

Meet the First Authors.

Meet the First Authors.

Broad Impairment of Natural Killer Cells from Operationally Tolerant Kidney Transplanted Patients.

The role of natural killer (NK) cells in organ transplantation is controversial. This study aims to decipher their role in kidney transplant tolerance in humans. Previous studies highlighted several modulated genes involved in NK cell biology in blood from spontaneously operationally tolerant patients (TOLs; drug-free kidney-transplanted recipients with stable graft function). We performed a phenotypic, functional, and genetic characterization of NK cells from these patients compared to kidney-transplanted patients with stable graft function under immunosuppression and healthy volunteers (HVs). Both operationally TOLs and stable patients harbored defective expression of the NKp46 activator receptor and lytic molecules perforin and granzyme compared to HVs. Surprisingly, NK cells from operationally TOLs also displayed decreased expression of the CD16 activating marker (in the CD56Dim NK cell subset). This decrease was associated with impairment of their functional capacities upon stimulation, as shown by lower interferon gamma (IFNγ) production and CD107a membranous expression in a reverse antibody-dependent cellular cytotoxicity (ADCC) assay, spontaneous lysis assays, and lower target cell lysis in the 51Cr release assay compared to HVs. Conversely, despite impaired K562 cell lysis in the 51Cr release assay, patients with stable graft function harbored a normal reverse ADCC and even increased amounts of IFNγ+ NK cells in the spontaneous lysis assay. Altogether, the strong impairment of the phenotype and functional cytotoxic capacities of NK cells in operationally TOLs may accord with the establishment of a pro-tolerogenic environment, despite remaining highly activated after transplantation in patients with stable graft function.

Differential inhibitory and activating NK cell receptor levels and NK/NKT-like cell functionality in chronic and recovered stages of chikungunya.

The role of natural killer (NK; CD3-CD56+)/NKT (CD3+CD56+)-like cells in chikungunya virus (CHIKV) disease progression/recovery remains unclear. Here, we investigated the expression profiles and function of NK and NKT-like cells from 35 chronic chikungunya patients, 30 recovered individuals, and 69 controls. Percentage of NKT-like cells was low in chronic chikungunya patients. NKp30+, CD244+, DNAM-1+, and NKG2D+ NK cell percentages were also lower (MFI and/or percentage), while those of CD94+ and NKG2A+ NKT-like cells were higher (MFI and/or percentage) in chronic patients than in recovered subjects. IFN-γ and TNF-α expression on NKT-like cells was high in the chronic patients, while only IFN-γ expression on NK cells was high in the recovered individuals. Furthermore, percentage of perforin+NK cells was low in the chronic patients. Lower cytotoxic activity was observed in the chronic patients than in the controls. CD107a expression on NK and NKT-like cells post anti-CD94/anti-NKG2A blocking was comparable among the patients and controls. Upregulated inhibitory and downregulated activating NK receptor expressions on NK/NKT-like cells, lower perforin+ and CD107a+NK cells are likely responsible for inhibiting the NK and NKT-like cell function in the chronic stage of chikungunya. Therefore, deregulation of NKR expression might underlie CHIKV-induced chronicity.

CD56+ immune cell infiltration and MICA are decreased in breast lobules with fibrocystic changes

PurposeWhile the role of natural killer (NK) cells in breast cancer therapy has been investigated, little information is known about NK cell function and presence in nonmalignant and premalignant breast tissue. Here, we investigate and quantify NK cell marker CD56 and activating ligand MICA in breast tissue with benign breast disease.MethodsSerial tissue sections from 88 subjects, 44 with benign breast disease (BBD) who remained cancer-free, and 44 with BBD who later developed cancer, were stained with H&E, anti-MICA, and anti-CD56. Up to ten representative lobules were identified on each section. Using digital image analysis, MICA and CD56 densities were determined for each lobule, reported as percent of pixels in the lobule that registered as stained by each antibody. Analyses were performed on a per-subject and per-lobule basis.ResultsPer-subject multivariate analyses showed associations of CD56 and MICA with age: CD56 was increased in older subjects (p = 0.03), while MICA was increased in younger subjects (p = 0.005). Per-lobule analyses showed that CD56 and MICA levels were both decreased in lobules with fibrocystic change, with median levels of CD56 and MICA staining, respectively, at 0.31 and 7.0% in fibrocystic lobules compared to 0.76 and 12.2% in lobules without fibrocystic change (p < 0.001 for each). Among fibrocystic lobules, proliferative/atypical lobules showed significantly lower expression compared to nonproliferative lobules for MICA (p = 0.02) but not for CD56 (p = 0.80).ConclusionLevels of CD56+ NK cells and activating ligand MICA were decreased in breast lobules with fibrocystic change, and MICA levels showed a significant stepwise decrease with increasing histopathologic abnormality. MICA levels were also significantly decreased in older subjects, who generally have higher risk of developing cancer. These findings advance a model in which MICA promotes cytotoxic activity in CD56+ NK cells to protect against tumorigenesis in breast lobules, and suggest further research is warranted.

Fatal accelerated rejection with a prominent natural killer cell infiltrate in a heart transplant recipient with peripartum cardiomyopathy

Accelerated rejection is uncommon after cardiac transplantation. The mechanism is hypothesized to be mediated by cytotoxic T cells and anti-HLA antibodies resulting from a memory response to the donor allograft in sensitized patients. A role for Natural Killer (NK) cell in cellular rejection has also been suggested. We report a case of fulminant accelerated rejection in a heart transplant recipient, with a history of peripartum cardiomyopathy (PPMC). The patient had no pre-transplant donor specific antibody and flow cytometric T and B cell crossmatches were negative. Autopsy revealed left ventricular subendocardial and intramyocardial hemorrhage with diffuse lymphocytic infiltrates and myocyte damage (Grade 3R rejection). Immunohistochemistry revealed a large proportion (50–70%) of mature CD16+ NK cells with cytotoxic potential in the interstitium and the intra capillary compartments. This case highlights the need for evaluating the potential role of NK cells in accelerated rejection in heart transplant recipients.

The Role of Natural Killer T Cells in Acute Kidney Injury: Angel or Evil?

Acute kidney injury (AKI) is manifested by inflammation, and an early feature in the pathogenesis is the accumulation of immune cells in the kidney. Natural killer T (NKT) cells, a peculiar T cells subtype, serve as a bridge between innate and adaptive immunity. Due to the difference between type I and type II subsets, NKT cells were supposed to play a dual role in IR-related tissue injury. Furthermore, membrane receptors and clinical immunosuppressive agents remain involved in the modulation of NKT cell function. Therefore, regulation of the amount and viability of NKT cells becomes a potential strategy in amelioration of AKI. This review will highlight the recent insights gained into the role and mechanisms of NKT cells in AKI.

The Expression of Activating Receptor Gene of Natural Killer Cells (KLRC3) in Patients with Type 1 Diabetes Mellitus (T1DM).

To identify the possible role of natural killer (NK) cells in the pathogenesis of type 1 diabetes mellitus (T1DM) through studying the expression of the KLRC3 gene, which encodes the NK cell activating receptor (NKG2E). This study was conducted at Alexandria University Children's Hospital from April to October 2015. The study was conducted with 30 newly diagnosed T1DM patients (15 males and 15 females), aged 7-13 years (10.6±1.8 years) and 20 non-diabetic subjects served as age- and sex-matched controls. The patients were further sub-divided into two groups; group I included patients who first presented with classical symptoms of DM (polyuria, polydipsia, and polyphagia) without diabetes ketoacidosis (DKA) and group II included patients who first presented with DKA. The expression of the KLRC3 gene was measured in each group using the real-time polymerase chain reaction. KLRC3 gene expression was significantly downregulated in T1DM cases compared to healthy controls (p = 0.001). Expression was more downregulated in group I patients (p = 0.008). Moreover, there was higher mean value of glycated heamoglobin and lower C-peptide levels in group I than group II. Serum pancreatic amylase showed no significant difference between the two groups. KLRC3 gene expression was downregulated in patients with T1DM compared to healthy controls. Downregulation of expression was greater in DKA patients compared to those who presented with classical symptoms. Expression of KLRC3 in T1DM might play a role in the pathogenesis of T1DM and could be a predictor of its severity.

Impaired liver regeneration is associated with reduced cyclin B1 in natural killer T cell-deficient mice

BackgroundIt has been shown that the proportion of natural killer T cells is markedly elevated during liver regeneration and their activation under different conditions can modulate this process. As natural killer T cells and liver injury are central in liver regeneration, elucidating their role is important.MethodsThe aim of the current study is to explore the role of natural killer T cells in impaired liver regeneration. Concanvalin A was injected 4 days before partial hepatectomy to natural killer T cells- deficient mice or to anti CD1d1-treated mice. Ki-67 and proliferating cell nuclear antigen were used to measure hepatocytes proliferation. Expression of hepatic cyclin B1 and proliferating cell nuclear antigen were evaluated by Western Blot and liver injury was assessed by ALT and histology.ResultsNatural killer T cells- deficient or mice injected with anti CD1d antibodies exhibited reduced liver regeneration. These mice were considerably resistant to ConA-induced liver injury. In the absence of NKT cells hepatic proliferating cell nuclear antigen and cyclin B1 decreased in mice injected with Concanvalin A before partial hepatectomy. This was accompanied with reduced serum interleukin-6 levels.ConclusionsNatural killer T cells play an important role in liver regeneration, which is associated with cyclin B1 and interleukin-6.

NOX2-dependent immunosuppression in chronic myelomonocytic leukemia.

Chronic myelomonocytic leukemia (CMML) is a myeloproliferative and myelodysplastic neoplasm with few treatment options and dismal prognosis. The role of natural killer (NK) cells and other antileukemic lymphocytes in CMML is largely unknown. We aimed to provide insight into the mechanisms of immune evasion in CMML with a focus on immunosuppressive reactive oxygen species (ROS) formed by the myeloid cell NADPH oxidase-2 (NOX2). The dominant population of primary human CMML cells was found to express membrane-bound NOX2 and to release ROS, which, in turn, triggered extensive PARP-1-dependent cell death in cocultured NK cells, CD8+ T effector memory cells, and CD8+ T effector cells. Inhibitors of ROS formation and scavengers of extracellular ROS prevented CMML cell-induced lymphocyte death and facilitated NK cell degranulation toward Ab-coated, primary CMML cells. In patients with CMML, elevation of immature cell counts (CD34+) in blood was associated with reduced expression of several NK cell-activating receptors. We propose that CMML cells may use extracellular ROS as a targetable mechanism of immune escape.

Activation of Blood CD3+CD56+CD8+ T Cells during Pregnancy and Multiple Sclerosis

A striking common feature of most autoimmune diseases is their female predominance, with at least twice as common among women than men in relapsing–remitting multiple sclerosis (MS), the prevailing MS clinical form with onset at childbearing age. This fact, together with the protective effect on disease activity during pregnancy, when there are many biological changes including high levels of estrogens and progesterone, puts sex hormones under the spotlight. The role of natural killer (NK) and NKT cells in MS disease beginning and course is still to be elucidated. The uterine NK (uNK) cells are the most predominant immune population in early pregnancy, and the number and function of uNK cells infiltrating the endometrium are sex-hormones’ dependent. However, there is controversy on the role of estrogen or progesterone on circulating NK (CD56dim and CD56bright) and NKT cells’ subsets. Here, we show a significantly increased activation of CD3+CD56+CD8+ cells in pregnant MS women (MSP) compared with non-pregnant MS women (NPMS) (p < 0.001) and even with respect to healthy pregnant women (HP, p < 0.001), remaining increased even after delivery. The dynamics of expression of early activation marker CD69 on CD3+CD56+CD8+ cells showed a progressive statistically significant increase along the gestation trimesters (T) and at postpartum (PP) with respect to NPMS (1T: p = 0.018; 2T: p = 0.004; 3T: p < 0.001; PP: p = 0.001). In addition, early activation expression of CD69 on CD3+CD56+CD8+ cells was higher in MSP than HP in the first two trimesters of gestation (p = 0.004 and p = 0.015, respectively). NPMS showed significantly increased cytotoxic/regulatory NK ratio compared with healthy controls (p < 0.001). On the other hand, gender studies showed no differences between MS women and men in NK and CD3+CD56+CD8+ cells’ subsets. Our findings may add on the understanding of the regulatory axis in MS during pregnancy. Further studies on specific CD8+ NKT cells function and their role in pregnancy beneficial effects on MS are warranted to move forward more effective MS treatments.

The role of natural killer T cells in a mouse model with spontaneous bile duct inflammation.

Natural killer T (NKT) cells are activated by lipid antigens presented by CD1d molecules and represent a major lymphocyte subset of the liver. NOD.c3c4 mice spontaneously develop biliary inflammation in extra‐ and intrahepatic bile ducts. We demonstrated by flow cytometry that invariant NKT (iNKT) cells were more abundant in the thymus, spleen, and liver of NOD.c3c4 mice compared to NOD mice. iNKT cells in NOD.c3c4 mice displayed an activated phenotype. Further, NOD and NOD.Cd1d ‐/‐ mice were irradiated and injected with NOD.c3c4 bone marrow, and injection of NOD.c3c4 bone marrow resulted in biliary infiltrates independently of CD1d expression in recipient mice. Activation or blocking of NKT cells with α‐galactosylceramide or anti‐CD1d antibody injections did not affect the biliary phenotype of NOD.c3c4 mice. NOD.c3c4.Cd1d ‐/‐ mice were generated by crossing NOD.Cd1d ‐/‐ mice onto a NOD.c3c4 background. NOD.c3c4.Cd1d ‐/‐ and NOD.c3c4 mice developed the same extent of biliary disease. This study demonstrates that iNKT cells are more abundant and activated in the NOD.c3c4 model. The portal inflammation of NOD.c3c4 mice can be transferred to irradiated recipients, which suggests an immune‐driven disease. Our findings imply that NKT cells can potentially participate in the biliary inflammation, but are not the primary drivers of disease in NOD.c3c4 mice.

Natural killer T cells in atherosclerosis.

Atherosclerosis is a chronic inflammatory disorder that develops in response to hyperlipidaemia. Cells from both the innate and adaptive immune systems contribute to the development of atherosclerotic lesions. The role of natural killer T (NKT) cells in response to microbial pathogens and inflammatory disorders such as atherosclerosis has received increasing attention in the past 10-15 years. Endogenous self-lipid antigens and exogenous lipid antigens, including those on microorganisms can activate NKT cells. CD1d molecules on antigen-presenting cells present these lipids to the T-cell receptor on NKT cells, which results in the rapid production of cytokines and cytotoxic proteins. NKT cells can also be activated in a CD1d-independent manner. Numerous studies have shown that NKT cells can promote atherogenesis. Various NKT cell sublineages have been described, but the participation of each in atherogenesis requires further characterization. In this Review, we provide an overview of NKT cells in the immune system, discuss CD1 molecules and lipid antigen presentation, and describe the interaction of the CD1d-NKT cell network with gut microbiota and its effect in modulating the activity or levels of NKT cells, which might in turn influence atherosclerosis. Although the exact mechanisms by which NKT cells promote atherosclerosis have not been fully elucidated, several potential mechanisms are proposed.

Inflammatory Gene Expression Profile and Defective Interferon-γ and Granzyme K in Natural Killer Cells From Systemic Juvenile Idiopathic Arthritis Patients.

Systemic juvenile idiopathic arthritis (JIA) is an immunoinflammatory disease characterized by arthritis and systemic manifestations. The role of natural killer (NK) cells in the pathogenesis of systemic JIA remains unclear. The purpose of this study was to perform a comprehensive analysis of NK cell phenotype and functionality in patients with systemic JIA. Transcriptional alterations specific to NK cells were investigated by RNA sequencing of highly purified NK cells from 6 patients with active systemic JIA and 6 age-matched healthy controls. Cytokines (NK cell-stimulating and others) were quantified in plasma samples (n = 18). NK cell phenotype and cytotoxic activity against tumor cells were determined (n = 10), together with their interferon-γ (IFNγ)-producing function (n = 8). NK cells from the systemic JIA patients showed an altered gene expression profile compared to cells from the healthy controls, with enrichment of immunoinflammatory pathways, increased expression of innate genes including TLR4 and S100A9, and decreased expression of immune-regulating genes such as IL10RA and GZMK. In the patients' plasma, interleukin-18 (IL-18) levels were increased, and a decreased ratio of IFNγ to IL-18 was observed. NK cells from the patients exhibited specific alterations in the balance of inhibitory and activating receptors, with decreased killer cell lectin-like receptor G1 and increased NKp44 expression. Although NK cells from the patients showed increased granzyme B expression, consistent with intact cytotoxicity and degranulation against a tumor cell line, decreased granzyme K expression in CD56bright NK cells and defective IL-18-induced IFNγ production and signaling were demonstrated. NK cells are active players in the inflammatory environment typical of systemic JIA. Although their cytotoxic function is globally intact, subtle defects in NK-related pathways, such as granzyme K expression and IL-18-driven IFNγ production, may contribute to the immunoinflammatory dysregulation in this disease.

Natural killer cell subpopulations are associated with MRI activity in a relapsing-remitting multiple sclerosis patient cohort from Australia

Background: The importance of the innate immune system in multiple sclerosis (MS) is increasingly recognized and the role of natural killer (NK) cells in controlling autoimmunity may be an important modulator of disease activity. Objective: To examine NK subsets in MS patients on different treatments and to evaluate the role of NK subsets as indicators for disease activity. Methods: We measured NK subset levels in blood obtained from 110 relapsing-remitting MS patients. Patients were either off treatment or on treatment with natalizumab, fingolimod, glatiramer acetate or beta-interferon. Disease activity was defined according to ‘No Evidence of Disease Activity’ (NEDA) criteria within an observation period of up to 2.4 years. The mean NK subset levels were compared among treatment groups using multivariate analysis of variance (ANOVA) and association analysis with disease activity performed using multi-factor logistic regression. Results: Our analysis revealed differences in NK cells and subsets on treatment compared to off treatment (p < 0.0005). A high proportion of bright NK cells were significantly associated with stable magnetic resonance imaging (MRI) imaging after adjusting for treatment effects (p < 0.05). Conclusion: The independent association of NK subsets with MRI stability needs to be confirmed in prospective studies to test their usefulness in predicting disease activity in MS patients.

Human anti-pig NK cell and CD8+ T-cell responses in the presence of regulatory dendritic cells.

Dendritic cells (DC) play a major role in natural killer (NK) cell and cytotoxic T lymphocyte (CTL) activation leading to cell-mediated xenogeneic responses. In contrast, the use of in vitro differentiated regulatory DC may represent an attractive approach to protect porcine endothelial cells (pEC) from human cell-mediated immune responses. In this study, we evaluated the potential of human regulatory DC to reduce xenogeneic NK cell and CTL responses to pEC. Human monocytes were differentiated into DC with GM-CSF and IL-4 in the absence or presence of rapamycin or IL-10. The effect of regulatory DC on xenogeneic NK cell and CTL responses was evaluated by analyzing phenotype, IFNγ production, degranulation, and cytotoxicity by flow cytometry and cytotoxicity assays. Upon maturation with LPS, Rapa-DC and IL-10-DC displayed different phenotypes and cytokine production profiles. In contrast to untreated DC, both Rapa-DC and IL-10-DC induced significantly less IFNγ production and NK cell degranulation in response to pEC, but did not affect NK cell-mediated pEC lysis. Low production of IL-18 by Rapa-DC, and of IL-12 by IL-10-DC were linked to the deficient IFNγ production by NK cells as shown by partial reversion of IFNγ production upon cytokine reconstitution. In contrast to untreated DC efficiently generating xenoantigen-specific CTL, priming of CTL in the presence of IL-10-DC was impaired as shown by lower IFNγ production and cytotoxicity of CTL in response to pEC. Both Rapa-DC and IL-10-DC controlled human anti-porcine NK cell responses, in particular IFNγ production, whereas IL-10-DC presented stronger regulatory properties of anti-porcine CTL responses. These in vitro findings indicate that regulatory DC could be a useful tool to promote xenograft tolerance in vivo.

Active but not inactive granulomatosis with polyangiitis is associated with decreased and phenotypically and functionally altered CD56(dim) natural killer cells.

BackgroundThe role of natural killer (NK) cells in granulomatosis with polyangiitis (GPA) is poorly understood. We recently reported that peripheral blood NK cell percentages correlate with the suppression of GPA activity (cohort I). The purpose of the current study was to further characterize NK cell subsets, phenotype and function in a second GPA cohort (cohort II).MethodsPeripheral blood lymphocyte subsets were analyzed at a clinical diagnostic laboratory. Clinical data were extracted from medical records and patients were grouped according to their activity state (remission vs. active/non-remission). Separate analysis (cohort II, n = 22) and combined analysis (cohorts I and II, n = 34/57) of NK cell counts/percentages was performed. NK cell subsets and phenotypes were analyzed by multicolor flow cytometry. Cytotoxicity assays were performed using 51Cr-labeled K562 target cells.ResultsIn cohort II, NK cell counts were lower than the lower limit of normal in active GPA, despite normal percentages due to lymphopenia. NK cell counts, but not other lymphocyte counts, were significantly higher in remission. Combined analysis of cohorts I and II confirmed decreased NK cell counts in active GPA and increased percentages in long-term remission. Follow-up measurements of six patients revealed increasing NK cell percentages during successful induction therapy. Multicolor analysis from cohort II revealed that in active GPA, the CD56dim subset was responsible for decreased NK cell counts, expressed more frequently CD69, downregulated the Fc-receptor CD16 and upregulated the adhesion molecule CD54, the chemokine receptor CCR5 and the activating receptor NKG2C. In remission, these markers were unaltered or marginally altered. All other receptors investigated (NKp30, NKp44, NKp46, NKG2D, DNAM1, 2B4, CRACC, 41BB) remained unchanged. Natural cytotoxicity was not detectable in most patients with active GPA, but was restored in remission.ConclusionsNK cell numbers correlate inversely with GPA activity. Reduced CD56dim NK cells in active GPA have an activated phenotype, which intriguingly is associated with profound deficiency in cytotoxicity. These data suggest a function for NK cells in the pathogenesis and/or modulation of inflammation in GPA. NK cell numbers, phenotype (CD16, CD69, NKG2C) or overall natural cytotoxicity are promising candidates to serve as clinical biomarkers to determine GPA activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-1098-7) contains supplementary material, which is available to authorized users.