Phenotype and function of natural killer cells in systemic lupus erythematosus: excess interferon-γ production in patients with active disease

Rheumatoid arthritis and systemic lupus erythematosus: Pathophysiological mechanisms related to innate immune system

Rheumatoid arthritis and systemic lupus erythematosus are two highly prevalent autoimmune diseases that generate disability and low quality of life. The innate immune system, a long-forgotten issue in autoimmune diseases, is becoming increasingly important and represents a new focus for the treatment of these entities. This review highlights the role that innate immune system plays in the pathophysiology of rheumatoid arthritis and systemic lupus erythematosus. The role of the innate immune system in rheumatoid arthritis and systemic lupus erythematosus pathophysiology is not only important in early stages but is essential to maintain the immune response and to allow disease progression. In rheumatoid arthritis, genetic and environmental factors are involved in the initial stimulation of the innate immune response in which macrophages are the main participants, as well as fibroblast-like synoviocytes. In systemic lupus erythematosus, all the cells contribute to the inflammatory response, but the complement system is the major effector of the inflammatory process. Detecting alterations in the normal function of these cells, besides its contribution to the understanding of the pathophysiology of autoimmune diseases, could help to establish new treatment strategies for these diseases.

Autoantibodies to Killer Cell Immunoglobulin-Like Receptors in Patients With Systemic Lupus Erythematosus Induce Natural Killer Cell Hyporesponsiveness

Natural killer (NK) cell cytotoxicity toward self-cells is restrained by the inhibitory HLA class I-binding receptors CD94/NKG2A and the killer cell immunoglobulin-like receptors (KIRs). CD94/NKG2A and KIRs are also essential for NK cell education, which is a dynamic functional maturation process where a constitutive binding of inhibitory receptors to cognate HLA class I molecules is required for NK cells to maintain their full cytotoxic capacity. Previously, we described autoantibodies to CD94/NKG2A in patients with systemic lupus erythematosus (SLE). In this study we analyzed sera from 191 patients with SLE, 119 patients with primary Sjögren's syndrome (pSS), 48 patients with systemic sclerosis (SSc), and 100 healthy donors (HD) for autoantibodies to eight different KIRs. Anti-KIR autoantibodies were identified in sera from 23.0% of patients with SLE, 10.9% of patients with pSS, 12.5% of patients with SSc, and 3.0% of HD. IgG from anti-KIR-positive SLE patients reduced the degranulation and cytotoxicity of NK cells toward K562 tumor cells. The presence of anti-KIR-autoantibodies reacting with >3 KIRs was associated with an increased disease activity (p < 0.0001), elevated serum levels of IFN-α (p < 0.0001), nephritis (p = 0.001), and the presence of anti-Sm (p = 0.007), and anti-RNP (p = 0.003) autoantibodies in serum. Together these findings suggest that anti-KIR autoantibodies may contribute to the reduced function of NK cells in SLE patients, and that a defective NK cell function may be a risk factor for the development of lupus nephritis.

Interferon pathway in SLE: one key to unlocking the mystery of the disease

SLE is characterised by an activation of the interferon (IFN) system, which leads to an increased expression of IFN-regulated genes. The reasons behind the IFN signature in SLE are (1) the existence of endogenous IFN inducers, (2) activation of several IFN-producing cell types, (3) production of many different IFNs, (4) a genetic setup promoting IFN production and (5) deficient negative feedback mechanisms. The consequences for the immune system is a continuous stimulation to an immune response, and for the patient a number of different organ manifestations leading to typical symptoms for SLE. In the current review, we will present the existing knowledge of the IFN system and pathway activation in SLE. We will also discuss how this information can contribute to our understanding of both the aetiopathogenesis and some organ manifestations of the disease. We will put forward some issues that are unresolved and should be clarified in order to make a proper stratification of patients with SLE, which seems important when selecting a therapy aiming to downregulate the IFN system.

Molecular and Cellular Bases of Immunosenescence, Inflammation, and Cardiovascular Complications Mimicking "Inflammaging" in Patients with Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an archetype of systemic autoimmune disease, characterized by the presence of diverse autoantibodies and chronic inflammation. There are multiple factors involved in lupus pathogenesis, including genetic/epigenetic predisposition, sexual hormone imbalance, environmental stimulants, mental/psychological stresses, and undefined events. Recently, many authors noted that "inflammaging", consisting of immunosenescence and inflammation, is a common feature in aging people and patients with SLE. It is conceivable that chronic oxidative stresses originating from mitochondrial dysfunction, defective bioenergetics, abnormal immunometabolism, and premature telomere erosion may accelerate immune cell senescence in patients with SLE. The mitochondrial dysfunctions in SLE have been extensively investigated in recent years. The molecular basis of normoglycemic metabolic syndrome has been found to be relevant to the production of advanced glycosylated and nitrosative end products. Besides, immunosenescence, autoimmunity, endothelial cell damage, and decreased tissue regeneration could be the results of premature telomere erosion in patients with SLE. Herein, the molecular and cellular bases of inflammaging and cardiovascular complications in SLE patients will be extensively reviewed from the aspects of mitochondrial dysfunctions, abnormal bioenergetics/immunometabolism, and telomere/telomerase disequilibrium.

Combined genetic and transcriptome analysis of patients with SLE: distinct, targetable signatures for susceptibility and severity

OBJECTIVES

Systemic lupus erythematosus (SLE) diagnosis and treatment remain empirical and the molecular basis for its heterogeneity elusive. We explored the genomic basis for disease susceptibility and severity.

METHODS

mRNA sequencing and genotyping in blood from 142 patients with SLE and 58 healthy volunteers. Abundances of cell types were assessed by CIBERSORT and cell-specific effects by interaction terms in linear models. Differentially expressed genes (DEGs) were used to train classifiers (linear discriminant analysis) of SLE versus healthy individuals in 80% of the dataset and were validated in the remaining 20% running 1000 iterations. Transcriptome/genotypes were integrated by expression-quantitative trail loci (eQTL) analysis; tissue-specific genetic causality was assessed by regulatory trait concordance (RTC).

RESULTS

SLE has a 'susceptibility signature' present in patients in clinical remission, an 'activity signature' linked to genes that regulate immune cell metabolism, protein synthesis and proliferation, and a 'severity signature' best illustrated in active nephritis, enriched in druggable granulocyte and plasmablast/plasma-cell pathways. Patients with SLE have also perturbed mRNA splicing enriched in immune system and interferon signalling genes. A novel transcriptome index distinguished active versus inactive disease-but not low disease activity-and correlated with disease severity. DEGs discriminate SLE versus healthy individuals with median sensitivity 86% and specificity 92% suggesting a potential use in diagnostics. Combined eQTL analysis from the Genotype Tissue Expression (GTEx) project and SLE-associated genetic polymorphisms demonstrates that susceptibility variants may regulate gene expression in the blood but also in other tissues.

CONCLUSION

Specific gene networks confer susceptibility to SLE, activity and severity, and may facilitate personalised care.

Cytotoxic Function and Cytokine Production of Natural Killer Cells and Natural Killer T-Like Cells in Systemic Lupus Erythematosis Regulation with Interleukin-15

Natural killer cells and NKT-like cells are the first line immune defense against tumor and virus infection. Deficient NK and NKT-like cell effector function may contribute to increased susceptibility to infection in SLE patients. We sought to examine the perforin and granzyme B expression, interferon-gamma (IFN-γ), and tumor-necrosis factor-alpha (TNF-α) production and CD107a degranulation of NK and NKT-like cells from SLE patients and their regulation by IL-15. We established that (1) perforin expression on SLE NK cells was decreased but unrelated to disease activity; (2) the MFI of granzyme B was increased in NK cells from SLE patients with active disease, associated with increased percentages of granzyme B⁺ CD56^bright NK cells; (3) NK cells from active SLE patients, both CD56^dim and CD56^bright NK subsets, produced higher IFN-γ compared to controls; (4) CD56^dim, but not CD56^bright NK cells from active SLE patients, produced lower TNF-α, compared to inactive SLE patients and controls; (5) CD107a degranulation of SLE NK cells was comparable to controls; (6) IL-15 enhanced perforin/granzyme B expression, IFN-γ/TNF-α production, and CD107a degranulation of NK cells from SLE patients; and (7) similar observations were found for CD56⁺CD3⁺ NKT-like cells. Taken together, we demonstrated the differential expression of the heightened granzyme B and decreased TNF-α in NK and NKT-like cells in SLE patients. Higher granzyme B expression of NK and NKT-like cells in active SLE patients, further enhanced by circulating IL-15, may contribute to the maintenance of inflammation in SLE.

Innate lymphoid cell disturbance with increase in ILC1 in systemic lupus erythematosus

The innate lymphoid cell (ILC) is a group of effector cells with diverse important cellular functions in both health and disease states. In comparison with healthy controls, there were increases in circulating ILC in SLE patients. The proportion of ILC1 significantly increased with significant decreases of ILC2 in SLE patients and ILC3 in SLE patients with moderate to severe activity. IL-12, IL-18, IL-25, IL-33, IL-23, IL-1β and IFN-γ were significantly increased in SLE patients. Moreover, IL-12, IL-18 and IL-1β but not IFN-γ correlated significantly with SLEDAI. Successful treatments rapidly reduced them and with certain normalization of the ILC subsets. In addition to increases in ILC1 numbers, ~ 80% of the ILC1 in SLE patients were positive for synthesis of IFN-γ. Plasma from SLE patients were shown to be potent in inducing ILC1. Thus, increased circulating ILC1 might contribute to the pathogenesis of SLE through mounting type 1 immune response.

Natural killer cell expression of Ki67 is associated with elevated serum IL-15, disease activity and nephritis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder whose pathology involves multiple immune cell types, including B and T lymphocytes as well as myeloid cells. While it is clear that autoantibody-producing B cells, as well as CD4⁺ T cell help, are key contributors to disease, little is known regarding the role of innate lymphoid cells such as natural killer (NK) cells in the pathogenesis of SLE. We have characterized the phenotype of NK cells by multi-color flow cytometry in a large cohort of SLE patients. While the overall percentage of NK cells was similar or slightly decreased compared to healthy controls, a subset of patients displayed a high frequency of NK cells expressing the proliferation marker, Ki67, which was not found in healthy donors. Although expression of Ki67 on NK cells correlated with Ki67 on other immune cell subsets, the frequency of Ki67 on NK cells was considerably higher. Increased frequencies of Ki67⁺ NK cells correlated strongly with clinical severity and active nephritis and was also related to low NK cell numbers, but not overall leukopenia. Proteomic and functional data indicate that the cytokine interleukin-15 promotes the induction of Ki67 on NK cells. These results suggest a role for NK cells in regulating the immune-mediated pathology of SLE as well as reveal a possible target for therapeutic intervention.

Autoantibodies to killer cell immunoglobulin-like receptor 3DL1 in patients with systemic lupus erythematosus

A genetic variant of the killer immunoglobulin-like receptor 3DL1 (KIR3DL1) has been found in patients with systemic lupus erythematosus (SLE). Herein, we investigated the presence of autoantibodies to KIR3DL1 in a cohort of patients with SLE. We tested sera from 28 patients with SLE, 11 patients with rheumatoid arthritis (RA) and 17 healthy control subjects for anti-KIR3DL1 activity by an enzyme-linked immunosorbent assay (ELISA) using recombinant KIR3DL1-enhanced green fluorescent protein (EGFP) and EGFP proteins. Anti-KIR3DL1 antibodies were detected in 22 (79%) of the 28 patients with SLE, whereas they were present in only three (27%) of the 11 patients with RA examined. Notably, 10 (91%) of the 11 samples from patients with SLE prior to therapy had anti-KIR3DL1 antibodies. None of the samples from healthy donors were positive for the antibodies. Here, we report the presence of anti-KIR3DL1 antibodies in the sera of patients with SLE for the first time. Anti-KIR3DL1 autoantibodies may be involved in the pathogenesis of autoimmune diseases.

Natural killer cells in inflammation and autoimmunity

First described 40 years ago, natural killer (NK) cells represent the founding members of the innate lymphoid cell (ILC) family. They were initially defined by their ability to kill cancer cells of hematopoietic origin. More recently, NK cells are recognized not only for their ability to kill infected or malignant cells, but also for mediating cytotoxicity against a range of normal immune cells. They thereby play an important physiological role in controlling immune responses and maintaining homeostasis. Besides cytotoxic activity, NK cells activation is accompanied by secretion of pro-inflammatory cytokines. Hence, NK cells have the potential to act both in driving inflammation and in restricting adaptive immune responses that may otherwise lead to excessive inflammation or even autoimmunity. Here, we highlight how NK cell activity is linked to inflammasome activation and review new molecular insights to the roles of NK cells in inflammation and autoimmunity. Furthermore, in light of new insights to NK cell differentiation and memory, we deliberate on how distinct NK cell subsets may impact immunoregulatory functions. Hypothetically, memory-like or adaptive NK cells could drive NK cell-mediated autoreactive diseases. Together, new findings underscore the complex yet important physiological roles of NK cells in both promoting inflammation and exerting immunoregulation and maintenance of immune homeostasis. Insights raise intriguing questions as to how NK cells themselves maintain self-tolerance.

Downregulation of CD3ζ in NK Cells from Systemic Lupus Erythematosus Patients Confers a Proinflammatory Phenotype

Cytotoxic function and cytokine profile of NK cells are compromised in patients with systemic lupus erythematosus (SLE). CD3ζ, an important molecule for NK cell activation, is downregulated in SLE T cells and contributes to their altered function. However, little is known about the role of CD3ζ in SLE NK cells. We studied CD3ζ levels and its contribution to cytotoxic, degranulation, and cytokine production capacity of NK cells from patients with SLE. Furthermore, we studied the human NK cell line, NKL, in which manipulation of CD3ζ levels was achieved using small interfering RNA and NK cells from Rag2 mice deficient in CD3ζ. We found reduced CD3ζ expression in NK cells from SLE patients independent of disease activity. Downregulation of CD3ζ expression in NK cells is mediated, at least in part, by Caspase 3, the activity of which is higher in NK cells from patients with SLE compared with NK cells from healthy donors. CD3ζ levels correlated inversely with natural cytotoxicity and the percentage of cells capable of producing the proinflammatory cytokines IFN-γ and TNF. In contrast, CD3ζ levels showed a direct correlation with levels of Ab-dependent cellular cytotoxicity. Experiments performed in CD3ζ-silenced NKL and CD3ζ-deficient NK cells from Rag2 mice confirmed the dependence of NK cell function on CD3ζ levels. Our results demonstrate a differential role for CD3ζ in natural cytotoxicity and Ab-dependent cellular cytotoxicity. We conclude that downregulated CD3ζ confers a proinflammatory phenotype to SLE NK cells and contributes to their altered function in patients with SLE.

Crucial role for CD69 in allergic inflammatory responses: CD69-Myl9 system in the pathogenesis of airway inflammation

CD69 has been known as an early activation marker of lymphocytes; whereas, recent studies demonstrate that CD69 also has critical functions in immune responses. Early studies using human samples revealed the involvement of CD69 in various inflammatory diseases including asthma. Moreover, murine disease models using Cd69^-/- mice and/or anti-CD69 antibody (Ab) treatment have revealed crucial roles for CD69 in inflammatory responses. However, it had not been clear how the CD69 molecule contributes to the pathogenesis of inflammatory diseases. We recently elucidated a novel mechanism, in which the interaction between CD69 and its ligands, myosin light chain 9, 12a and 12b (Myl9/12) play a critical role in the recruitment of activated T cells into the inflammatory lung. In this review, we first summarize CD69 function based on its structure and then introduce the evidence for the involvement of CD69 in human diseases and murine disease models. Then, we will describe how we discovered CD69 ligands, Myl9 and Myl12, and how the CD69-Myl9 system regulates airway inflammation. Finally, we will discuss possible therapeutic usages of the blocking Ab to the CD69-Myl9 system.

Revisiting the Functional Impact of NK Cells

Immune responses are critical for the maintenance of homeostasis but can also upset the equilibrium, depending on the context and magnitude of the response. Natural killer (NK) cells are well known for their important roles in antiviral and antitumor immune responses, and they are currently used, mostly under optimized forms, as immunotherapeutic agents against cancer. Nevertheless, with accumulating examples of deleterious effects of NK cells, it is paramount to consider their negative contributions. Here, we critically review and comment on the literature surrounding undesirable aspects of NK cell activity, focusing on situations where they play a harmful rather than a protective role.

NK cells in autoimmune diseases: Linking innate and adaptive immune responses

The pathogenesis of autoimmunity remains to be fully elucidated, although the contribution of genetic and environmental factors is generally recognized. Despite autoimmune conditions are principally due to T and B lymphocytes, NK cells also appear to play a role in the promotion and/or maintenance of altered adaptive immune responses or in peripheral tolerance mechanisms. Although NK cells are components of the innate immune system, they shows characteristics of the adaptive immune system, such as the expansion of pathogen-specific cells, the generation of long-lasting "memory" cells able to persist upon cognate antigen encounter, and the possibility to induce an increased secondary recall response to re-challenge. Human NK cells are generally identified as CD56+CD3-, conversely CD56+CD3+ cells represent a mixed population of NK-like T (NK T) cells and antigen-experienced T cells showing the up-regulation of several NK cell markers. CD56dim constitute about 90% of NK cells in the peripheral blood, they are mature and involved in cytotoxicity responses; CD56bright instead are more immature, mostly involved in cytokine production, having only a limited role in cytolytic responses, keen to leave the blood vessels as the principal population observed in lymph nodes. NK cells have been identified also in non-lymphoid tissues since, in pathologic conditions, they can quickly reach the target organs. A cross-talk between NK with dendritic cells and T cells is established throughout different receptor-ligand bindings. Several studies support the correlation between NK cell number and/or functional alterations, such as a defective cytotoxic activity and several autoimmune conditions. Among the different autoimmune pathologies and even within the same disease, NK cell function is significantly different either promoting or even protecting against the onset of the autoimmune condition. In this Review, we discuss recent literature supporting the role played by NK cells, as a bridge between innate and adaptive immunity, in the onset of autoimmune diseases.

Altered natural killer cell cytokine profile in type 2 autoimmune hepatitis

Type 2 autoimmune hepatitis (AIH-2) is a rare disease presenting in early childhood. The immunopathogenetic mechanisms are poorly characterized, although a defect of regulatory T cells (Treg) has been shown. There is virtually no information on innate immune responses and natural killer (NK) cells in particular. We have performed an extended immunophenotypic and functional analysis of NK cells in children with AIH-2. We show that NK cell frequency is reduced in this setting and that the balance between NK activating and inhibitory receptors is skewed toward activation. More importantly, NK cells display an altered cytokine pattern characterized by increased IFNγ and reduced IL2 production which could contribute to impaired Treg function. Exposure of mononuclear cells to IL2 resulted in normalization of NK IFNγ production. Thus, our findings support treatment of AIH-2 with low-dose IL2, which would result in normalization of NK cell function and expansion of the Treg cell subset.

Analysis of the regulatory function of natural killer cells from patients with systemic lupus erythematosus

Natural killer (NK) cells participate in the regulation of the immune response. However, the immunomodulatory function of NK cells in systemic lupus erythematosus (SLE) is not well understood. The aim of this study was to evaluate the regulatory function of NK cells in SLE patients and to identify the NK cells involved in the pathogenesis of this complex disease. We analysed the expression of NK receptors and co-stimulatory molecules in peripheral NK cells (CD3^- CD56⁺ ) from SLE patients, as well as the numbers of human leucocyte antigen D-related (HLA-DR)/CD11c⁺ NK cells. In addition, NK cell regulatory function was assessed by the detection of NK cell-mediated dendritic cell (DC) lysis. We found that SLE patients showed increased numbers of immunoglobulin-like transcript 2 (ILT2)⁺ , CD86⁺ and CD134⁺ NK cells. Furthermore, NK cells from SLE patients induced higher levels of DC lysis. We were able to identify a new subset of NK cells co-expressing CD11c and HLA-DR. These atypical NK cells were increased in SLE patients when compared with controls. We have identified an expanded new subset of NK cells in SLE patients. This is the first study, to our knowledge, which demonstrates that NK cells in SLE patients have an altered phenotype with a high expression of receptors characteristic of dendritic cells. Our results suggest that the impairment in the regulatory function of NK cells, together with the increased number of DC-like NK cells, could play an important role in the development of SLE and highlight the importance of NK cells as a future therapeutic target.

Activating and inhibitory receptors on natural killer cells in patients with systemic lupus erythematosis-regulation with interleukin-15

Natural killer (NK) cells may play an important role in the pathogenesis of SLE. Interleukin(IL)-15, an NK-enhancing cytokine, is over-expressed in SLE patients. In the present study, we examined the effect of IL-15 on NK cytotoxicity of SLE patients, and the expression of various activating and inhibitory NK receptors on NK cells from SLE patients in relation to disease activity. We also sought to determine how IL-15 would affect the NK receptor expression on NK cells from SLE patients. PBMCs were collected from 88 SLE patients with inactive disease activity (SLEDAI score<6) and active disease activity (SLEDAI score≥6), 26 age-matched healthy adults were used as controls. PBMC were incubated in the presence or absence of IL-15 (10ng/ml) for eighteen hours. CD3-CD56+ lymphoctes were gated using flow cytometry and further divided into CD56dim and CD56bright subsets according to the MFI of CD56. We observed that 1. Serum IL-15 was elevated in SLE patients, and higher in active disease than in inactive disease; 2. NK cytotoxicity of SLE patients was deficient compared to controls and showed an impaired response to IL-15 compared to controls; 3.CD69, CD94, NKG2A, NKp30, and CD158b on NK cells from SLE patients were higher than controls, and could be further enhanced by IL-15; 4. NKp46 expression from SLE patients was higher than controls, but down-regulated by IL-15; 5.Deficient NKG2D and NKAT-2 expression were found on NK cells from SLE patients, which were enhanced by IL-15; 6. A unique NKp46- subset and CD158b+ subsets were observed in NK cells from SLE patients but not controls. 7. Unlike controls, CD158k on NK cells from SLE patients failed to respond to IL-15. Taken together, we demonstrated the aberrant NCR and iNKR expression on NK cells and their distinct response to IL-15 in SLE patients. As IL-15 predominantly aggravates the aberrant NKR expression found in SLE, IL-15 antagonist may have therapeutic benefits in SLE patients.

Altered expression of signalling lymphocyte activation molecule receptors in T-cells from lupus nephritis patients-a potential biomarker of disease activity

Objectives. The aim was to investigate whether the signalling lymphocyte activation molecule (SLAM) signalling pathways contribute to LN and whether SLAM receptors could be valuable biomarkers of disease activity.

Methods. Peripheral blood mononuclear cells from 30National Research Ethics Service SLE patients with biopsy-proven LN were analysed by flow cytometry. Clinical measures of disease activity were assessed. The expression of the SLAM family receptors on T-cell subpopulations [CD4, CD8 and double negative (DN) T cells] was measured and compared between lupus patients with active renal disease and those in remission.

Results. The frequency of CD8 T cells expressing SLAMF3, SLAMF5 and SLAMF7 was significantly lower in LN patients who were in remission. In contrast, these subsets were similar in patients with active renal disease and in healthy individuals. Patients with active nephritis had an increased percentage of circulating monocytes, consistent with a potential role played by these cells in glomerular inflammation. Changes in the frequency of DN T cells positive for SLAMF2, SLAMF4 and SLAMF7 were observed in lupus patients irrespective of the disease activity. We detected alterations in the cellular expression of the SLAM family receptors, but these changes were less obvious and did not reveal any specific pattern. The percentage of DN T cells expressing SLAMF6 could predict the clinical response to B-cell depletion in patients with LN.

Conclusion. Our study demonstrates altered expression of the SLAM family receptors in SLE T lymphocytes. This is consistent with the importance of the SLAM-associated pathways in lupus pathogenesis.

Decreased ex vivo production of interferon-gamma is associated with severity and poor prognosis in patients with lupus

Background

Lupus pathogenesis is closely associated with interferon gamma (IFN-γ), which plays a central role in innate and adaptive immunity. The aim of this study was to evaluate the ex vivo production of IFN-γ after stimulation of peripheral blood mononuclear cells with phytohemagglutinin (PHA) in patients with lupus, according to disease activity.

Methods

This study included 118 patients with lupus who had undergone IFN-γ-releasing assays (IGRAs) to screen for tuberculosis. Data on IFN-γ production in negative (nil) and positive (mitogen with PHA) controls were collected and analysed. The difference (mitogen minus nil) was used to calculate ex vivo IFN-γ production. Disease activity was evaluated using the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2 K). Poor hospitalisation outcome was defined as in-hospital mortality or intensive care unit admission. Associations among disease activity, poor hospitalisation outcome, and ex vivo IFN-γ production were assessed.

Results

The level of ex vivo IFN-γ production was significantly lower in patients with active systemic lupus erythematosus (SLE) (n = 64) than in those with inactive SLE (n = 54) (median 0.92 vs. 11.06 IU/mL, p < 0.001). Ex vivo IFN-γ production was correlated with the SLEDAI-2 K (r = − 0.587, p < 0.001). Results of multivariate logistic regression analysis showed that ex vivo IFN-γ production ≤ 7.19 IU/mL was an independent predictor for discriminating active and inactive lupus. In addition, patients with ex vivo IFN-γ production ≤ 0.40 IU/mL had more frequent poor hospitalisation outcomes than those with ex vivo IFN-γ production > 0.40 (40.0% vs. 9.3%, p = 0.001). The proportion of indeterminate IGRA results was higher in patients with active lupus than in those with inactive lupus (45.3% vs. 0.0%, p < 0.001) because of decreased ex vivo IFN-γ production.

Conclusions

Ex vivo IFN-γ production is a useful biomarker for assessing disease activity and predicting poor clinical outcomes of SLE.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1404-z) contains supplementary material, which is available to authorized users.

Hepatitis B vaccine non response: A predictor of latent autoimmunity?

Unresponsiveness to Hepatitis B virus (HBV) vaccine has been associated with interleukins involved with Th1 functioning including Interleukin-8 (IL-18) and Interferon-γ (IFN-γ). IL-18 and IFN-γ have also been implicated in the onset of different types of immune-mediate inflammatory conditions such as Type 1 Diabetes (T1D), Celiac disease (CD), rheumatoid arthritis (RA), obesity and systemic lupus erythematosus (SLE). Taking into account that HBV vaccination is provided in the 1st year of life worldwide, I propose that all babies should be tested for anti-HBs response after completion of the vaccine series. And I suggest that children with undetectable anti-HBs titers after recommended immunization schedule as well as the additional booster doses should be followed up over time because they may be at risk of developing a number of autoimmune disorders. In this light, the non-responsiveness to HBV vaccine might be a predictor of latent autoimmunity. For that reason, research studies are needed in order to verify the existence of potential IL-18 and IFN-γ gene polymorphisms to utilize as biomarkers of latent autoimmunity. As a final point, administration of neutralizing antibodies against IFN-γ and/or IL-18 might represent a future target for immune-modulatory therapeutic approach to halt or even reverse autoimmune phenomena.

CD69: from activation marker to metabolic gatekeeper

CD69 is a membrane-bound, type II C-lectin receptor. It is a classical early marker of lymphocyte activation due to its rapid appearance on the surface of the plasma membrane after stimulation. CD69 is expressed by several subsets of tissue resident immune cells, including resident memory T (TRM) cells and gamma delta (γδ) T cells, and is therefore considered a marker of tissue retention. Recent evidence has revealed that CD69 regulates some specific functions of selected T-cell subsets, determining the migration-retention ratio as well as the acquisition of effector or regulatory phenotypes. Specifically, CD69 regulates the differentiation of regulatory T (Treg) cells as well as the secretion of IFN-γ, IL-17, and IL-22. The identification of putative CD69 ligands, such as Galectin-1 (Gal-1), suggests that CD69-induced signaling can be regulated not only during cognate contacts between T cells and antigen-presenting cells in lymphoid organs, but also in the periphery, where cytokines and other metabolites control the final outcome of the immune response. Here, we will discuss new aspects of the molecular signaling mediated by CD69 and its involvement in the metabolic reprogramming regulating TH-effector lineages.

Unraveling the expression of microRNA-27a* & NKG2D in peripheral blood mononuclear cells and natural killer cells of pediatric systemic lupus erythematosus patients

BACKGROUND AND AIM

The activity of natural killer (NK) cells is known to be decreased in systemic lupus erythematosus (SLE) patients. Nevertheless, the exact contribution of NK cells in the pathogenesis of SLE is still inconclusive. MicroRNAs (miRNAs), are small noncoding RNA molecules that play a fundamental role in regulating NK cell function. The objective of this study was to investigate the expression of miRNAs that might potentially target an essential activating receptor, NKG2D in peripheral blood mononuclear cells (PBMCs) and NK cells of SLE patients.

METHODS

In silico analysis revealed miR-27a* to potentially target NKG2D messenger RNA (mRNA), hence PBMCs and NK cells were isolated from blood samples of SLE patients and healthy controls. Next, the cells were transfected using mimics and antagomirs, after which miRNA/mRNA were quantified using real time quantitative reverse transcription polymerase chain reaction.

RESULTS

The results of this study showed that miR-27a* is overexpressed in the PBMCs and NK cells of SLE patients. In contrast, NKG2D was found to be downregulated in PBMCs and NK cells of SLE patients. Forcing the expression of miR-27a* in PBMCs and NK cells enhances the expression of NKG2D in SLE patients. Furthermore, the ligand of NKG2D, ULBP2, was found to be downregulated in the PBMCs of SLE patients.

CONCLUSION

The altered expression of the triad, miR-27a* as well as NKG2D and ULBP2, is thought to be characteristic for NK cells in SLE patients. Hence, the ability of miR-27a* to alter the expression of NKG2D may provide a new groundwork for understanding the role of miRNAs in NK cells of SLE patients.

A Cytomegalovirus Peptide-Specific Antibody Alters Natural Killer Cell Homeostasis and Is Shared in Several Autoimmune Diseases

Human cytomegalovirus (hCMV), a ubiquitous beta-herpesvirus, has been associated with several autoimmune diseases. However, the direct role of hCMV in inducing autoimmune disorders remains unclear. Here we report the identification of an autoantibody that recognizes a group of peptides with a conserved motif matching the Pp150 protein of hCMV (anti-Pp150) and is shared among patients with various autoimmune diseases. Anti-Pp150 also recognizes the single-pass membrane protein CIP2A and induces the death of CD56(bright) NK cells, a natural killer cell subset whose expansion is correlated with autoimmune disease. Consistent with this finding, the percentage of circulating CD56(bright) NK cells is reduced in patients with several autoimmune diseases and negatively correlates with anti-Pp150 concentration. CD56(bright) NK cell death occurs via both antibody- and complement-dependent cytotoxicity. Our findings reveal that a shared hCMV-induced autoantibody is involved in the decrease of CD56(bright) NK cells and may thus contribute to the onset of autoimmune disorders.

Effect of Interleukin-15 on CD11b, CD54, and CD62L Expression on Natural Killer Cell and Natural Killer T-Like Cells in Systemic Lupus Erythematosus

Adhesion molecules may play an important role in systemic lupus erythematosus (SLE) pathogenesis. We investigated the effect of interleukin- (IL-) 15 on CD11b, CD54, and CD62L expression on natural killer (NK) cells, T cells, and CD56⁺CD3⁺ NKT-like cells from SLE subjects and healthy controls. SLE patients had decreased circulating NK cells and NKT-like cells compared to controls. NK cells from SLE patients showed higher CD11b and CD62L expression compared to controls. IL-15 enhanced CD11b and CD54 but downregulated CD62L expression on NK cells from SLE patients. Similar observations were found for T cells and NKT-like cells. NK cells from SLE patients expressed higher CD56 than controls; both could be further enhanced by IL-15. IL-15 also enhanced CD56 expression of NKT-like cells from SLE patients. A greater degree of IL-15 induced downregulation of CD62L on NKT-like cells noted in SLE patients compared to controls. The percentage of CD11b expressing NK cells and the % inhibition of CD62L expression on NKT-like cells by IL-15 correlated with serum anti-dsDNA levels in SLE patients, respectively. Taken together, we demonstrated the dysfunctional NK and NKT-like cells in SLE patients with regard to CD11b and CD62L expression and their response to IL-15.

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

Background

The 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).

Methods

Peripheral 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.

Results

In 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 CD56^dim 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.

Conclusions

NK cell numbers correlate inversely with GPA activity. Reduced CD56^dim 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 material

The online version of this article (doi:10.1186/s13075-016-1098-7) contains supplementary material, which is available to authorized users.

Human CD56bright NK Cells: An Update

Human NK cells can be subdivided into various subsets based on the relative expression of CD16 and CD56. In particular, CD56(bright)CD16(-/dim) NK cells are the focus of interest. They are considered efficient cytokine producers endowed with immunoregulatory properties, but they can also become cytotoxic upon appropriate activation. These cells were shown to play a role in different disease states, such as cancer, autoimmunity, neuroinflammation, and infection. Although their phenotype and functional properties are well known and have been extensively studied, their lineage relationship with other NK cell subsets is not fully defined, nor is their precise hematopoietic origin. In this article, we summarize recent studies about CD56(bright) NK cells in health and disease and briefly discuss the current controversies surrounding them.

The complement receptor 3 (CD11b/CD18) agonist Leukadherin-1 suppresses human innate inflammatory signalling

Complement receptor 3 (CR3, CD11b/CD18) is a multi‐functional receptor expressed predominantly on myeloid and natural killer (NK) cells. The R77H variant of CD11b, encoded by the ITGAM rs1143679 polymorphism, is associated robustly with development of the autoimmune disease systemic lupus erythematosus (SLE) and impairs CR3 function, including its regulatory role on monocyte immune signalling. The role of CR3 in NK cell function is unknown. Leukadherin‐1 is a specific small‐molecule CR3 agonist that has shown therapeutic promise in animal models of vascular injury and inflammation. We show that Leukadherin‐1 pretreatment reduces secretion of interferon (IFN)‐γ, tumour necrosis factor (TNF) and macrophage inflammatory protein (MIP)‐1β by monokine‐stimulated NK cells. It was associated with a reduction in phosphorylated signal transducer and activator of transcription (pSTAT)‐5 following interleukin (IL)‐12 + IL‐15 stimulation (P < 0·02) and increased IL‐10 secretion following IL‐12 + IL‐18 stimulation (P < 0·001). Leukadherin‐1 pretreatment also reduces secretion of IL‐1β, IL‐6 and TNF by Toll‐like receptor (TLR)‐2 and TLR‐7/8‐stimulated monocytes (P < 0·01 for all). The R77H variant did not affect NK cell response to Leukadherin‐1 using ex‐vivo cells from homozygous donors; nor did the variant influence CR3 expression by these cell types, in contrast to a recent report. These data extend our understanding of CR3 biology by demonstrating that activation potently modifies innate immune inflammatory signalling, including a previously undocumented role in NK cell function. We discuss the potential relevance of this to the pathogenesis of SLE. Leukadherin‐1 appears to mediate its anti‐inflammatory effect irrespective of the SLE‐risk genotype of CR3, providing further evidence to support its evaluation of Leukadherin‐1 as a potential therapeutic for autoimmune disease.

A cytotoxic anti-IL-3Rα antibody targets key cells and cytokines implicated in systemic lupus erythematosus

To date, the major target of biologic therapeutics in systemic lupus erythematosus (SLE) has been the B cell, which produces pathogenic autoantibodies. Recently, targeting type I IFN, which is elaborated by plasmacytoid dendritic cells (pDCs) in response to endosomal TLR7 and TLR9 stimulation by SLE immune complexes, has shown promising results. pDCs express high levels of the IL-3Rα chain (CD123), suggesting an alternative potential targeting strategy. We have developed an anti-CD123 monoclonal antibody, CSL362, and show here that it affects key cell types and cytokines that contribute to SLE. CSL362 potently depletes pDCs via antibody-dependent cell-mediated cytotoxicity, markedly reducing TLR7, TLR9, and SLE serum-induced IFN-α production and IFN-α-upregulated gene expression. The antibody also inhibits TLR7- and TLR9-induced plasmablast expansion by reducing IFN-α and IL-6 production. These effects are more pronounced than with IFN-α blockade alone, possibly because pDC depletion reduces production of other IFN subtypes, such as type III, as well as non-IFN proinflammatory cytokines, such as IL-6. In addition, CSL362 depletes basophils and inhibits IL-3 signaling. These effects were confirmed in cells derived from a heterogeneous population of SLE donors, various IFN-dependent autoimmune diseases, and healthy controls. We also demonstrate in vivo activity of CSL362 following its s.c. administration to cynomolgus monkeys. This spectrum of effects provides a preclinical rationale for the therapeutic evaluation of CSL362 in SLE.

Pathogenic Inflammation and Its Therapeutic Targeting in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE, lupus) is a highly complex and heterogeneous autoimmune disease that most often afflicts women in their child-bearing years. It is characterized by circulating self-reactive antibodies that deposit in tissues, including skin, kidneys, and brain, and the ensuing inflammatory response can lead to irreparable tissue damage. Over many years, clinical trials in SLE have focused on agents that control B- and T-lymphocyte activation, and, with the single exception of an agent known as belimumab which targets the B-cell survival factor BAFF, they have been disappointing. At present, standard therapy for SLE with mild disease is the agent hydroxychloroquine. During disease flares, steroids are often used, while the more severe manifestations with major organ involvement warrant potent, broad-spectrum immunosuppression with cyclophosphamide or mycophenolate. Current treatments have severe and dose-limiting toxicities and thus a more specific therapy targeting a causative factor or signaling pathway would be greatly beneficial in SLE treatment. Moreover, the ability to control inflammation alongside B-cell activation may be a superior approach for disease control. There has been a recent focus on the innate immune system and associated inflammation, which has uncovered key players in driving the pathogenesis of SLE. Delineating some of these intricate inflammatory mechanisms has been possible with studies using spontaneous mouse mutants and genetically engineered mice. These strains, to varying degrees, exhibit hallmarks of the human disease and therefore have been utilized to model human SLE and to test new drugs. Developing a better understanding of the initiation and perpetuation of disease in SLE may uncover suitable novel targets for therapeutic intervention. Here, we discuss the involvement of inflammation in SLE disease pathogenesis, with a focus on several key proinflammatory cytokines and myeloid growth factors, and review the known outcomes or the potential for targeting these factors in SLE.

Cardif (MAVS) Regulates the Maturation of NK Cells

Cardif, also known as IPS-1, VISA, and MAVS, is an intracellular adaptor protein that functions downstream of the retinoic acid-inducible gene I family of pattern recognition receptors. Cardif is required for the production of type I IFNs and other inflammatory cytokines after retinoic acid-inducible gene I-like receptors recognize intracellular antigenic RNA. Studies have recently shown that Cardif may have other roles in the immune system in addition to its role in viral immunity. In this study, we find that the absence of Cardif alters normal NK cell development and maturation. Cardif(-/-) mice have a 35% loss of mature CD27(-)CD11b(+) NK cells in the periphery. In addition, Cardif(-/-) NK cells have altered surface marker expression, lower cytotoxicity, decreased intracellular STAT1 levels, increased apoptosis, and decreased proliferation compared with wild-type NK cells. Mixed chimeric mice revealed that the defective maturation and increased apoptotic rate of peripheral Cardif(-/-) NK cells is cell intrinsic. However, Cardif(-/-) mice showed enhanced control of mouse CMV (a DNA β-herpesvirus) by NK cells, commensurate with increased activation and IFN-γ production by these immature NK cell subsets. These results indicate that the skewed differentiation and altered STAT expression of Cardif(-/-) NK cells can result in their hyperresponsiveness in some settings and support recent findings that Cardif-dependent signaling can regulate aspects of immune cell development and/or function distinct from its well-characterized role in mediating cell-intrinsic defense to RNA viruses.

Association of killer cell immunoglobulin-like receptor and human leucocyte antigen-Cw gene combinations with systemic lupus erythematosus

Killer cell immunoglobulin-like receptors (KIRs) are a diverse family of activating and inhibitory receptors expressed on natural killer (NK) cells and T cells, the genes of which show extreme polymorphism. Some KIRs bind to human leucocyte antigen (HLA) class I subgroups, and genetic interactions between KIR genes and their ligand HLA have been shown to be associated with several autoimmune diseases. The present study aimed to investigate whether the combinations of KIR genes and HLA-Cw ligands associate with the susceptibility of systemic lupus erythematosus (SLE). Polymerase chain reaction using sequence-specific primers was used to determine the genotypes of KIR genes and HLA-Cw alleles. We found that the frequencies of HLA-Cw07 were statistically significantly higher in the patient group than those in the control group (P = 0·009). KIR2DS1(+) HLA(-) Cw(Lys) was more common in subjects with SLE compared to control subjects (P = 0·015). In addition, the frequency of KIR2DS1 was increased in SLE when KIR2DL1/HLA-Cw are absent, and the difference was significant (P = 0·001). KIR genotype and HLA ligand interaction may potentially influence the threshold for NK (and/or T) cell activation mediated through activating receptors, thereby contributing to the pathogenesis of SLE.

Functional anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies in patients with systemic lupus erythematosus

OBJECTIVE

Recently we serendipitously identified a patient with systemic lupus erythematosus (SLE) who was positive for autoantibodies to CD94/natural killer receptor group 2A (NKG2A). The present study was undertaken to investigate the occurrence and function of autoantibodies targeting lectin-like NK cell receptors in SLE.

METHODS

Sera from 203 SLE patients and 90 healthy individuals were analyzed, by flow cytometry, for Ig binding to Ba/F3 cells transfected with CD94/NKG2A, CD94/NKG2C, or NKG2D. Autoantibodies identified were characterized with regard to interference with HLA-E binding, effect on NK cell activation in response to HLA-E-transfected K562 cells, and capacity to facilitate antibody-dependent cell-mediated cytotoxicity (ADCC). Levels of autoantibodies were determined in longitudinally sampled sera, and correlations with disease activity (SLE Disease Activity Index 2000) and severity (Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index) were investigated.

RESULTS

Anti-CD94/NKG2A autoantibodies were identified in 7 SLE patients. The autoantibodies from 6 patients inhibited binding of HLA-E to CD94/NKG2A, whereas those from the seventh patient augmented this binding. Autoantibodies from 2 patients also reacted with the activating receptor CD94/NKG2C, with inhibition of the binding of HLA-E to CD94/NKG2C observed in 1 case and enhancement of this binding in the other. None of the sera contained anti-NKG2D autoantibodies. The levels of anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies correlated with disease activity and with a more severe SLE phenotype. Mechanistically, anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies both interfered with HLA-E-mediated regulation of NK cell activation and facilitated the elimination of target cells expressing CD94/NKG2A or CD94/NKG2C through ADCC.

CONCLUSION

Anti-CD94/NKG2A and anti-CD94/NKG2C autoantibodies occur in a subset of patients with clinically active SLE. Given their capacity to deplete certain NK cell subsets and interfere with particular NK cell function, such autoantibodies may promote the pathogenesis of SLE.

Expression of chimeric receptor CD4ζ by natural killer cells derived from human pluripotent stem cells improves in vitro activity but does not enhance suppression of HIV infection in vivo

Cell-based immunotherapy has been gaining interest as an improved means to treat human immunodeficiency virus (HIV)/AIDS. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) could become a potential resource. Our previous studies have shown hESC and iPSC-derived natural killer (NK) cells can inhibit HIV-infected targets in vitro. Here, we advance those studies by expressing a HIV chimeric receptor combining the extracellular portion of CD4 to the CD3ζ intracellular signaling chain. We hypothesized that expression of this CD4ζ receptor would more efficiently direct hESC- and iPSC-derived NK cells to target HIV-infected cells. In vitro studies showed the CD4ζ expressing hESC- and iPSC-NK cells inhibited HIV replication in CD4+ T-cells more efficiently than their unmodified counterparts. We then evaluated CD4ζ expressing hESC (CD4ζ-hESC)- and iPSC-NK cells in vivo anti-HIV activity using a humanized mouse model. We demonstrated significant suppression of HIV replication in mice treated with both CD4ζ-modified and -unmodified hESC-/iPSC-NK cells compared with control mice. However, we did not observe significantly increased efficacy of CD4ζ expression in suppression of HIV infection. These studies indicate that hESC/iPSC-based immunotherapy can be used as a unique resource to target HIV/AIDS.

NKG2D ligand overexpression in lupus nephritis correlates with increased NK cell activity and differentiation in kidneys but not in the periphery

NK cells are a major component of the immune system, and alterations in their activity are correlated with various autoimmune diseases. In the present work, we observed an increased expression of the NKG2D ligand MICA in SLE patients' kidneys but not healthy subjects. We also show glomerulus-specific expression of the NKG2D ligands Rae-1 and Mult-1 in various murine SLE models, which correlated with a higher number of glomerular-infiltrating NK cells. As the role of NK cells in the immunopathogenesis of SLE is poorly understood, we explored NK cell differentiation and activity in tissues and organs in SLE-prone murine models by use of diseased and prediseased MRL/MpJ and MRL/lpr mice. We report here that phenotypically iNK cells accumulate only in the spleen but not in BM or kidneys of diseased mice. Infiltrating NK cells in kidneys undergoing a lupus nephritic process showed a more mature, activated phenotype compared with kidney, as well as peripheral NK cells from prediseased mice, as determined by IFN-γ and STAT5 analysis. These findings and the presence of glomerulus-specific NKG2D ligands in lupus-prone mice identify a role for NK cells and NKG2D ligands in the lupus nephritic process, which could aid in understanding their role in human SLE.

Natural killer cells: In health and disease

Natural killer (NK) cells constitute our bodies' frontline defense system, guarding against tumors and launching attacks against infections. The activities of NK cells are regulated by the interaction of various receptors expressed on their surfaces with cell surface ligands. While the role of NK cells in controlling tumor activity is relatively clear, the fact that they are also linked to various other disease conditions is now being highlighted. Here, we present an overview of the role of NK cells during normal body state as well as under diseased state. We discuss the possible utilization of these powerful cells as immunotherapeutic agents in combating diseases such as asthma, autoimmune diseases, and HIV-AIDS. This review also outlines current challenges in NK cell therapy.

A CD8 T cell/indoleamine 2,3-dioxygenase axis is required for mesenchymal stem cell suppression of human systemic lupus erythematosus

OBJECTIVE

Allogeneic mesenchymal stem cells (MSCs) exhibit therapeutic effects in human autoimmune diseases such as systemic lupus erythematosus (SLE), but the underlying mechanisms remain largely unknown. The aim of this study was to investigate how allogeneic MSCs mediate immunosuppression in lupus patients.

METHODS

The effects of allogeneic umbilical cord-derived MSCs (UC-MSCs) on inhibition of T cell proliferation were determined. MSC functional molecules were stimulated with peripheral blood mononuclear cells from healthy controls and SLE patients and examined by real-time polymerase chain reaction. CD4+ and CD8+ T cells were purified using microbeads to stimulate MSCs in order to determine cytokine expression by MSCs and to further determine which cell subset(s) or which molecule(s) is involved in inhibition of MSC-mediated T cell proliferation. The related signaling pathways were assessed. We determined levels of serum cytokines in lupus patients before and after UC-MSC transplantation.

RESULTS

Allogeneic UC-MSCs suppressed T cell proliferation in lupus patients by secreting large amounts of indoleamine 2,3-dioxygenase (IDO). We further found that interferon-γ (IFNγ), which is produced predominantly by lupus CD8+ T cells, is the key factor that enhances IDO activity in allogeneic MSCs and that it is associated with IFNGR1/JAK-2/STAT signaling pathways. Intriguingly, bone marrow-derived MSCs from patients with active lupus demonstrated defective IDO production in response to IFNγ and allogeneic CD8+ T cell stimulation. After allogeneic UC-MSC transplantation, serum IDO activity increased in lupus patients.

CONCLUSION

We found a previously unrecognized CD8+ T cell/IFNγ/IDO axis that mediates the therapeutic effects of allogeneic MSCs in lupus patients.

Dynamic changes in the numbers of different subsets of peripheral blood NK cells in patients with systemic lupus erythematosus following classic therapy

Imbalance of natural killer (NK) cells is associated with the development of systemic lupus erythematosus (SLE). However, little is known about the dynamic changes on NK cells following therapy. This study aimed at examining the impact of classic therapies on the numbers of different subsets of NK cells in new-onset SLE patients. The numbers of different subsets of peripheral blood NK cells in 24 new-onset SLE patients before, 4 and 12 weeks post the classic therapies, and 7 healthy controls were determined by flow cytometry. The potential correlation between the numbers of NK cells and the values of clinical measures was analyzed. In comparison with that before treatment, the numbers of NK, NKG2C+, and KIR2DL3+ NK cells were significantly increased while the numbers of NKp46+ and NKG2A + NK cells significantly decreased at 4 and/or 12 weeks post the treatment only in the drug well-responding patients, but not in those poor responders (P < 0.05 for all). The numbers of NKG2C + NK cells were correlated positively with the levels of serum C3 while the numbers of KIR2DL3+ NK cells were correlated negatively with the scores of SLEDAI in these patients at 4 weeks post the treatment. The classic therapies modulated the numbers of some subsets of NK cells in drug well-responding SLE patients. The changes in the numbers of some subsets of NK cells may serve as biomarkers for evaluating the therapeutic responses of SLE.

Differential expression of natural killer activating and inhibitory receptors in patients with newly diagnosed systemic lupus erythematosus

AIM

Systemic lupus erythematosus (SLE) presents as the abnormal activation and over-proliferation of immune competent cells. Few studies have characterized the role of natural killer (NK) and NK T (NKT) cells in the pathogenesis of SLE, and therefore a consensus has not been reached as yet.

METHOD

Thirty-two patients with new-onset SLE and 15 healthy controls were recruited. Activated and inhibitory NK and NKT cells in peripheral blood were quantified by flow cytometry. The proportions of spontaneous and stimulated interferon (IFN)-γ(+) NK and NKT cells and CD107a(+) NK cells was examined. Finally, the potential relationship between the cell subsets and clinical indexes was analyzed.

RESULTS

The proportions of NK and NKT cells (P = 0.002 and 0.004, respectively) as well as the proportions of NKG2C(+) NK cells, inhibitory NK and NKT cell subsets (P = 0.016, P = 0.019, P = 0.049, and P = 0.028, respectively) in SLE patients were significantly lower than those in controls. In contrast, the proportions of activated NK cells and NKT cell subsets were significantly higher (P = 0.036, P = 0.034, P = 0.005, and P = 0.007, respectively). Moreover, the proportions of stimulated IFN-γ(+) NKT cells were significantly higher than in the controls, and the proportions of stimulated CD107a(+) NKT cells in SLE patients were significantly lower than in the controls (P = 0.032 and P = 0.02, respectively).

CONCLUSION

Lower proportions of NK and NKT cells, higher proportions of activated NK cells and activated NKT cells, lower proportions of inhibitory NK and NKT cells, higher NKT cell activity, and lower NKT cell degranulation may induce the autoimmune reaction involved in the pathogenesis of SLE.

NK cell autoreactivity and autoimmune diseases

Increasing evidences have pointed out the relevance of natural killer (NK) cells in organ-specific and systemic autoimmune diseases. NK cells bear a plethora of activating and inhibiting receptors that can play a role in regulating reactivity with autologous cells. The activating receptors recognize natural ligands up-regulated on virus-infected or stressed or neoplastic cells. Of note, several autoimmune diseases are thought to be linked to viral infections as one of the first event in inducing autoimmunity. Also, it is conceivable that autoimmunity can be triggered when a dysregulation of innate immunity occurs, activating T and B lymphocytes to react with self-components. This would imply that NK cells can play a regulatory role during adaptive immunity; indeed, innate lymphoid cells (ILCs), comprising the classical CD56(+) NK cells, have a role in maintaining or alternating tissue homeostasis secreting protective and/or pro-inflammatory cytokines. In addition, NK cells display activating receptors involved in natural cytotoxicity and the activating isoforms of receptors for HLA class I that can interact with healthy host cells and induce damage without any evidence of viral infection or neoplastic-induced alteration. In this context, the interrelationship among ILC, extracellular-matrix components, and mesenchymal stromal cells can be considered a key point for the control of homeostasis. Herein, we summarize evidences for a role of NK cells in autoimmune diseases and will give a point of view of the interplay between NK cells and self-cells in triggering autoimmunity.

Is CD69 an effective brake to control inflammatory diseases?

Early studies described CD69 as a leukocyte activation marker, and suggested its involvement in the activation of different leukocyte subsets as well as in the pathogenesis of chronic inflammation. However, recent investigations have showed that CD69 knockout mice exhibit an enhanced or reduced susceptibility to different experimental models of inflammatory diseases, including those mediated by T helper 17 (Th17) lymphocytes. In this regard, the expression of CD69, both in Th17 lymphocytes and by a subset of regulatory T cells, has an important role in the control of the immune response and the inflammatory phenomenon. Therefore, different evidence indicates that CD69 exerts a complex immunoregulatory role in humans, and that it could be considered as a target molecule for the therapy of immune-mediated diseases.

Anti-NKG2A autoantibodies in a patient with systemic lupus erythematosus

OBJECTIVES

To characterize a novel anti-NKG2A autoantibody detected in a patient with SLE during a severe flare, and in a cross-sectional study investigate the occurrence of such autoantibodies in patients with SLE and primary SS (pSS).

METHODS

Serum or IgG from patients with SLE, pSS and healthy volunteers were assayed for blocking of anti-NKG2A or HLA-E binding to peripheral blood mononuclear cells or CD94/NKG2A- and CD94/NKG2C-transfected Ba/F3 cells. The anti-NKG2A autoantibodies were evaluated for effect on NK cell degranulation in response to HLA-E-transfected K562 cells. IFN-α was determined by an immunoassay and disease activity by the SLEDAI score.

RESULTS

Anti-NKG2A autoantibodies, which blocked binding of HLA-E tetramers to CD94/NKG2A-transfected cells and impaired NKG2A-mediated inhibition of NK cell activation, were observed in a patient with SLE. The presence of anti-NKG2A autoantibodies was associated with high SLE disease activity (SLEDAI score 14 and 16) and increased serum IFN-α. Of 94 SLE, 60 pSS and 30 healthy donor sera, only the index patient serum contained anti-NKG2A autoantibodies.

CONCLUSION

The presence of autoantibodies targeting NKG2A is a rare event, but when such autoantibodies occur they may promote excessive NK cell function. This can contribute to the pathogenesis by increasing the killing of cells and the release of autoantigens. Our findings highlight the possible importance of NK cells in the SLE disease process.

The role of p38 MAPK in the aetiopathogenesis of psoriasis and psoriatic arthritis

The pathogenetic mechanisms responsible for the induction of immune-mediated disorders, such as psoriasis, remain not well characterized. Molecular signaling pathways are not well described in psoriasis, as well as psoriatic arthritis, which is seen in up to 40% of patients with psoriasis. Signaling pathway defects have long been hypothesized to participate in the pathology of psoriasis, yet their implication in the altered psoriatic gene expression still remains unclear. Emerging data suggest a potential pathogenic role for mitogen activated protein kinases p38 (p38 MAPK) extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK) in the development of psoriasis. The data are still limited, though, for psoriatic arthritis. This review discusses the current data suggesting a crucial role for p38 MAPK in the pathogenesis of these disorders.

Soluble MICA-NKG2D interaction upregulates IFN-γ production by activated CD3-CD56+ NK cells: potential impact on chronic graft versus host disease

A soluble isoform of MHC class I chain-related molecule A (soluble MICA), generated by proteolytic shedding from the membrane-bound MICA of various tumor cells, has been shown to downregulate both the expression of natural killer group 2-member D receptor and the cytotoxic function of effectors cells and was postulated as a mechanism for tumor immune evasion. Its effect on the expression of cytokines by the effector cells remained unexplored. Here we demonstrate that the sMICA molecules upregulate interferon gamma expression by interleukin-12/interleukin-18-activated CD3(-)CD56(+) natural killer cells, witnessing the pro-inflammatory effect of soluble MICA. Overall, these data are in line with our previous observations that the raised serum levels of soluble MICA, following allogeneic hematopoietic stem cell transplantation, confer susceptibility to and the presence of pre-transplantation anti-MICA antibodies in the patient's serum confer protection against chronic graft versus host disease.

Systemic lupus erythematosus immune complexes increase the expression of SLAM family members CD319 (CRACC) and CD229 (LY-9) on plasmacytoid dendritic cells and CD319 on CD56(dim) NK cells

Patients with systemic lupus erythematosus (SLE) display an activated type I IFN system due to unceasing IFN-α release from plasmacytoid dendritic cells (pDCs) stimulated by nucleic acid-containing immune complexes (ICs). NK cells strongly promote the IFN-α production by pDCs; therefore, we investigated surface molecules that could be involved in the pDC-NK cell cross-talk. In human PBMCs stimulated with RNA-containing ICs (RNA-ICs), the expression of the signaling lymphocyte activation molecule (SLAM) family receptors CD319 and CD229 on pDCs and CD319 on CD56(dim) NK cells was selectively increased. Upregulation of CD319 and CD229 on RNA-IC-stimulated pDCs was induced by NK cells or cytokines (e.g., GM-CSF, IL-3). IFN-α-producing pDCs displayed a higher expression of SLAM molecules compared with IFN-α⁻ pDCs. With regard to signaling downstream of SLAM receptors, pDCs expressed SHIP-1, SHP-1, SHP-2, and CSK but lacked SLAM-associated protein (SAP) and Ewing's sarcoma-activated transcript 2 (EAT2), indicating that these receptors may act as inhibitory receptors on pDCs. Furthermore, pDCs from patients with SLE had decreased expression of CD319 on pDCs and CD229 on CD56(dim) NK cells, but RNA-IC stimulation increased CD319 and CD229 expression. In conclusion, this study reveals that the expression of the SLAM receptors CD319 and CD229 is regulated on pDCs and NK cells by lupus ICs and that the expression of these receptors is specifically altered in SLE. These results, together with the observed genetic association between the SLAM locus and SLE, suggest a role for CD319 and CD229 in the SLE disease process.