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

Regulation of TREM2 on BV2 inflammation through PI3K/AKT/mTOR pathway

This work sought to determine how lipopolysaccharide (LPS)-induced pro-inflammatory factor production in BV2 microglia was influenced by myeloid cell 2 (TREM2) expressions. LPS (0.1, 1, and 10 µg/mL) induced inflammation in BV2 cells, MTT and QPCR were used to detect the occurrence of inflammation; TREM2 activation and inhibition vectors were used to activate and inhibit TREM2; Cell Proliferation was detected using CCK-8 and cell cloning experiments. LY294002 was used to inhibit the activity of PI3K/AKT signal pathway; Western blot and ELISA were used to detect cell polarization and signal pathway changes. CCK-8 and cell clone experiments found that the activation of TERM2 can promote the proliferation of BV2 cells; and the activation of TERM2 can promote the expression of IL6, IL1β, TNFα and the expression of M2 cell phenotype molecules Arg-1 and CD206. The effect of adding LY294002 signaling pathway by TERM2 activation was inhibited, indicating that TERM2 can affect the occurrence of inflammation by regulating the activity of PI3K/AKT signaling pathway. Finally, Western blotting and ELISA showed that activation of TERM2 can promote the expression of Arg-1 and CD206 in BV2 cells, and promote the transformation of BV2 cells to M2 polarization. TERM2 can affect the inflammatory response in microglia through the PI3K/AKT signaling pathway, suggesting that TERM2 may be a target for the treatment of inflammatory response in glial cells. This study provides a treatment plan for alleviating the impact of inflammation on central nervous system.

The presence of cytotoxic CD4 and exhausted-like CD8+ T-cells is a signature of active tuberculosis

Chronic infections induce CD4+ T-cells with cytotoxic functions (CD4 CTLs); at present, it is still unknown whether latent tuberculosis (LTB) and active tuberculosis (ATB) induce CD4 CTLs. Plasma and cells from four patient groups-uninfected contact (UC), LTB, and ATB (divided as sensitive [DS-TB]- or resistant [DR-TB]-drug)-were evaluated by flow cytometry, q-PCR, and proteomics. The data showed that ATB patients had an increased frequency of CD4+ T-cells and a decreased frequency of CD8+ T-cells. The latter displays an exhausted-like profile characterized by CD39, CD279, and TIM-3 expression. ATB had a high frequency of CD4 + perforin+ cells, suggesting a CD4 CTL profile. The expression (at the transcriptional level) of granzyme A, granzyme B, granulysin, and perforin, as well as the genes T-bet (Tbx21) and NKG2D (Klrk1), in enriched CD4+ T-cells, confirmed the cytotoxic signature of CD4+ T-cells during ATB (which was stronger in DS-TB than in DR-TB). Moreover, proteomic analysis revealed the presence of HSP70 (in DS-TB) and annexin A5 (in DR-TB), which are molecules that have been associated with favoring the CD4 CTL profile. Finally, we found that lipids from Mycobacterium tuberculosis increased the presence of CD4 CTLs in DR-TB patients. Our data suggest that ATB is characterized by exhausted-like CD8+ T-cells, which, together with a specific microenvironment, favor the presence of CD4 CTLs.

Investigation into Cardiac Myhc-α 334-352-Specific TCR Transgenic Mice Reveals a Role for Cytotoxic CD4 T Cells in the Development of Cardiac Autoimmunity

Myocarditis is one of the major causes of heart failure in children and young adults and can lead to dilated cardiomyopathy. Lymphocytic myocarditis could result from autoreactive CD4+ and CD8+ T cells, but defining antigen specificity in disease pathogenesis is challenging. To address this issue, we generated T cell receptor (TCR) transgenic (Tg) C57BL/6J mice specific to cardiac myosin heavy chain (Myhc)-α 334-352 and found that Myhc-α-specific TCRs were expressed in both CD4+ and CD8+ T cells. To investigate if the phenotype is more pronounced in a myocarditis-susceptible genetic background, we backcrossed with A/J mice. At the fourth generation of backcrossing, we observed that Tg T cells from naïve mice responded to Myhc-α 334-352, as evaluated by proliferation assay and carboxyfluorescein succinimidyl ester staining. The T cell responses included significant production of mainly pro-inflammatory cytokines, namely interferon (IFN)-γ, interleukin-17, and granulocyte macrophage-colony stimulating factor. While the naïve Tg mice had isolated myocardial lesions, immunization with Myhc-α 334-352 led to mild myocarditis, suggesting that further backcrossing to increase the percentage of A/J genome close to 99.99% might show a more severe disease phenotype. Further investigations led us to note that CD4+ T cells displayed the phenotype of cytotoxic T cells (CTLs) akin to those of conventional CD8+ CTLs, as determined by the expression of CD107a, IFN-γ, granzyme B natural killer cell receptor (NKG)2A, NKG2D, cytotoxic and regulatory T cell molecules, and eomesodermin. Taken together, the transgenic system described in this report may be a helpful tool to distinguish the roles of cytotoxic cardiac antigen-specific CD4+ T cells vs. those of CD8+ T cells in the pathogenesis of myocarditis.

The Role of NKG2D and Its Ligands in Autoimmune Diseases: New Targets for Immunotherapy

Natural killer (NK) cells and CD8+ T cells can clear infected and transformed cells and generate tolerance to themselves, which also prevents autoimmune diseases. Natural killer group 2 member D (NKG2D) is an important activating immune receptor that is expressed on NK cells, CD8+ T cells, γδ T cells, and a very small percentage of CD4+ T cells. In contrast, the NKG2D ligand (NKG2D-L) is generally not expressed on normal cells but is overexpressed under stress. Thus, the inappropriate expression of NKG2D-L leads to the activation of self-reactive effector cells, which can trigger or exacerbate autoimmunity. In this review, we discuss the role of NKG2D and NKG2D-L in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), type I diabetes (T1DM), inflammatory bowel disease (IBD), and celiac disease (CeD). The data suggest that NKG2D and NKG2D-L play a pathogenic role in some autoimmune diseases. Therefore, the development of strategies to block the interaction of NKG2D and NKG2D-L may have therapeutic effects in some autoimmune diseases.

Coordinated Priming of NKG2D Pathway by IL-15 Enhanced Functional Properties of Cytotoxic CD4+CD28- T Cells Expanded in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder, and numerous aberrations of T cell responses have been reported and were implicated in its pathophysiology. Recently, CD4-positive T cells with cytotoxic potential were shown to be involved in autoimmune disease progression and tissue damage. However, the effector functions of this cell type and their potential molecular mechanisms in SLE patients remain to be elucidated. In this study, we find that cytotoxic CD4+CD28- T cells are expanded in SLE patients with flow cytometry analysis, and the percentage of CD4+CD28- T cells positively correlates with the Systemic Lupus International Collaborating Clinics/ACR Damage Index (SDI). Furthermore, our study suggests that interleukin-15 (IL-15) promotes the expansion, proliferation, and cytotoxic function of CD4+CD28- T cells in SLE patients through activation of the Janus kinase3-STAT5 pathway. Further study indicates that IL-15 not only mediates the upregulation of NKG2D, but also cooperates with the NKG2D pathway to regulate the activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. Together, our study demonstrated that proinflammatory and cytolytic CD4+CD28- T cells expand in SLE patients. The pathogenic potential of these CD4+CD28- T cells is driven by the coupling of the IL-15/IL-15R signaling pathway and the NKG2D/DAP10 signaling pathway, which may open new avenues for therapeutic intervention to prevent SLE progression.

The role of CD4+ T cells in tumor and chronic viral immune responses

Immunotherapies are mainly aimed to promote a CD8+ T cell response rather than a CD4+ T cell response as cytotoxic T lymphocytes (CTLs) can directly kill target cells. Recently, CD4+ T cells have received more attention due to their diverse roles in tumors and chronic viral infections. In antitumor and antichronic viral responses, CD4+ T cells relay help signals through dendritic cells to indirectly regulate CD8+ T cell response, interact with B cells or macrophages to indirectly modulate humoral immunity or macrophage polarization, and inhibit tumor blood vessel formation. Additionally, CD4+ T cells can also exhibit direct cytotoxicity toward target cells. However, regulatory T cells exhibit immunosuppression and CD4+ T cells become exhausted, which promote tumor progression and chronic viral persistence. Finally, we also outline immunotherapies based on CD4+ T cells, including adoptive cell transfer, vaccines, and immune checkpoint blockade. Overall, this review summarizes diverse roles of CD4+ T cells in the antitumor or protumor and chronic viral responses, and also highlights the immunotherapies based on CD4+ T cells, giving a better understanding of their roles in tumors and chronic viral infections.

Senescent T cells: Beneficial and detrimental roles

As the thymus involutes during aging, the T-cell pool has to be maintained by the periodic expansion of preexisting T cells during adulthood. A conundrum is that repeated episodes of activation and proliferation drive the differentiation of T cells toward replicative senescence, due to telomere erosion. This review discusses mechanisms that regulate the end-stage differentiation (senescence) of T cells. Although these cells, within both CD4 and CD8 compartments, lose proliferative activity after antigen-specific challenge, they acquire innate-like immune function. While this may confer broad immune protection during aging, these senescent T cells may also cause immunopathology, especially in the context of excessive inflammation in tissue microenvironments.

Extremely Differentiated T Cell Subsets Contribute to Tissue Deterioration During Aging

There is a dramatic remodeling of the T cell compartment during aging. The most notorious changes are the reduction of the naive T cell pool and the accumulation of memory-like T cells. Memory-like T cells in older people acquire a phenotype of terminally differentiated cells, lose the expression of costimulatory molecules, and acquire properties of senescent cells. In this review, we focus on the different subsets of age-associated T cells that accumulate during aging. These subsets include extremely cytotoxic T cells with natural killer properties, exhausted T cells with altered cytokine production, and regulatory T cells that gain proinflammatory features. Importantly, all of these subsets lose their lymph node homing capacity and migrate preferentially to nonlymphoid tissues, where they contribute to tissue deterioration and inflammaging.

NKG2D Ligands in Liquid Biopsy: The Importance of Soluble and Vesicle-Bound Proteins for Immune Modulation

The identification of biomarkers allowing diagnostics, prognostics and patient classification is still a challenge in oncological research for patient management. Improvements in patient survival achieved with immunotherapies substantiate that biomarker studies rely not only on cellular pathways contributing to the pathology, but also on the immune competence of the patient. If these immune molecules can be studied in a non-invasive manner, the benefit for patients and clinicians is obvious. The immune receptor Natural Killer Group 2 Member D (NKG2D) represents one of the main systems involved in direct recognition of tumor cells by effector lymphocytes (T and Natural Killer cells), and in immune evasion. The biology of NKG2D and its ligands comprises a complex network of cellular pathways leading to the expression of these tumor-associated ligands on the cell surface or to their release either as soluble proteins, or in extracellular vesicles that potently inhibit NKG2D-mediated responses. Increased levels of NKG2D-ligands in patient serum correlate with tumor progression and poor prognosis; however, most studies did not test the biochemical form of these molecules. Here we review the biology of the NKG2D receptor and ligands, their role in cancer and in patient response to immunotherapies, as well as the changes provoked in this system by non-immune cancer therapies. Further, we discuss the use of NKG2D-L in liquid biopsy, including methods to analyse vesicle-associated proteins. We propose that the evaluation in cancer patients of the whole NKG2D system can provide crucial information about patient immune competence and risk of tumor progression.

Cytotoxic CD4+ T cells in cancer: Expanding the immune effector toolbox

Cytotoxic T cells are important effectors of anti-tumor immunity. While tumor killing is ascribed to CD8⁺ T cell function, pre-clinical and clinical studies have identified intra-tumoral CD4⁺ T cells that possess cytotoxic programs and can directly kill cancer cells. Cytotoxic CD4⁺ T cells are found in other disease settings including infection and autoimmunity. Here, we review the phenotypic and functional characteristics of cytotoxic CD4⁺ T cells in non-cancer and cancer contexts. We conduct a comparative examination of cytolytic mechanisms of cytotoxic CD4⁺ T cells across disease states and synthesize features that define these cells independent of context. We discuss regulatory mechanisms driving ontogeny and effector function and evidence for the clinical relevance of cytotoxic CD4⁺ T cells in cancer. In this context, we highlight important gaps in understanding in the biology of cytotoxic CD4⁺ T cells as well as the potential use of these cells in immunotherapies for specific cancers.

The HHV-6A Proteins U20 and U21 Target NKG2D Ligands to Escape Immune Recognition

The coevolution of the human immune system and herpesviruses led to the emergence and diversification of both cellular danger molecules recognized by immune cells on the one hand and viral countermeasures that prevent the expression of these proteins on infected cells on the other. There are eight ligands for the activating receptor NKG2D in humans - MICA, MICB, ULBP1-6. Several of them are induced and surface-expressed on herpesvirus-infected cells to serve as danger signals to activate the immune system. Therefore, these ligands are frequently targeted for suppression by viral immune evasion mechanisms. Mechanisms to downregulate NKG2D ligands and thereby escape immune recognition have been identified in all other human herpesviruses (HHV), except for HHV-6A. In this study, we identify two HHV-6A encoded immunoevasins, U20 and U21, which suppress the expression of the NKG2D ligands ULBP1 and ULBP3, respectively, during infection. Additionally, MICB is targeted by a so far unexplored viral protein. Due to the diminished NKG2D ligand surface expression on infected cells, recognition of HHV-6A infected cells by innate immune cells is impaired. Importantly, our study indicates that immune escape mechanisms between the related herpesviruses HHV-6A and HHV-6B are evolutionary conserved as the same NKG2D ligands are targeted. Our data contribute an additional piece of evidence for the importance of the NKG2D receptor - NKG2D ligand axis during human herpesvirus infections and sheds light on immune evasion mechanisms of HHV-6A.

Immune Phenotyping of Patients With Acute Vogt-Koyanagi-Harada Syndrome Before and After Glucocorticoids Therapy

Previous studies have established that disturbed lymphocytes are involved in the pathogenesis of Vogt-Koyanagi-Harada (VKH) syndrome. Accordingly, glucocorticoids (GCs), with their well-recognized immune-suppressive function, have been widely used for treatment of VKH patients with acute relapses. However, the systemic response of diverse immune cells to GC therapy in VKH is poorly characterized. To address this issue, we analyzed immune cell subpopulations and their phenotype, as well as cytokine profiles in peripheral blood from VKH patients (n=25) and health controls (HCs, n=21) by flow cytometry and luminex technique, respectively. For 16 patients underwent GC therapy (methylprednisolone, MP), the aforementioned measurements as well as the transcriptome data from patients before and after one-week’s GC therapy were also compared to interrogate the systemic immune response to GC therapy. Lymphocyte composition in the blood was different in VKH patients and HCs. VKH patients had significantly higher numbers of T cells with more activated, polarized and differentiated phenotype, more unswitched memory B cells and monocytes, as compared to HCs. MP treatment resulted in decreased frequencies of T cells and NK cells, inhibited NK cell activation and T cell differentiation, and more profoundly, a marked shift in the distribution of monocyte subsets. Collectively, our findings suggest that advanced activation and differentiation, as well as dysregulated numbers of peripheral lymphocytes are the major immunological features of VKH, and GC therapy with MP not only inhibits T cell activation directly, but also affects monocyte subsets, which might combinatorically result in the inhibition of the pathogenic immune response.

NK cell receptor NKG2D enforces proinflammatory features and pathogenicity of Th1 and Th17 cells

NKG2D is a danger sensor expressed on different subsets of innate and adaptive lymphocytes. Despite its established role as a potent activator of the immune system, NKG2D-driven regulation of CD4+ T helper (Th) cell-mediated immunity remains unclear. In this study, we demonstrate that NKG2D modulates Th1 and proinflammatory T-bet+ Th17 cell effector functions in vitro and in vivo. In particular, NKG2D promotes higher production of proinflammatory cytokines by Th1 and T-bet+ Th17 cells and reinforces their transcription of type 1 signature genes, including Tbx21. Conditional deletion of NKG2D in T cells impairs the ability of antigen-specific CD4+ T cells to promote inflammation in vivo during antigen-induced arthritis and experimental autoimmune encephalomyelitis, indicating that NKG2D is an important target for the amelioration of Th1- and Th17-mediated chronic inflammatory diseases.

The Role of the NKG2D in Vitiligo

Vitiligo is an acquired multifactorial disease that affects melanocytes and results in skin depigmentation. In this review, we examine the role of cells stress and self-reactive T cells responses. Given the canonical and non-canonical functions of NKG2D, such as authenticating stressed target and enhance TCR signaling, we examine how melanocyte stress leads to the expression of ligands that are recognized by the activating receptor NKG2D, and how its signaling results in the turning of T cells against self (melanocyte suicide by proxy). We also discuss how this initiation phase is followed by T cell perpetuation, as NKG2D signaling results in self-sustained long-lasting T cells, with improved cytolytic properties.

NKG2D-ligands: Putting everything under the same umbrella can be misleading

NKG2D is a key receptor for the activation of immune effector cells, mainly Natural Killer cells and T lymphocytes, in infection, cancer and autoimmune diseases. Since the detection of ligands for NKG2D in sera of cancer patients is, in many human models, indicative of prognosis, a large number of studies have been undertaken to improve understanding of the biology regulating this receptor and its ligands, with the aim of translating this knowledge into clinical practice. Although it is becoming clear that the NKG2D system can be used as a tool for diagnosis and manipulated for therapy, some questions remain open due to the complexity associated with the existence of a large number of ligands, each one of them displaying distinct biological properties. In this review, we have highlighted some key aspects of this system that differ between humans and mice, including the properties of NKG2D, as well as the genetic and biochemical complexity of NKG2D-ligands. All of these features affect the characteristics of the immune response exerted by NKG2D-expressing cells and are likely to be important factors in the clearance of a tumour or the development of autoimmunity. Implementation of more global analyses, including information on genotype, transcription and protein properties (cellular vs released to the blood stream) of NKG2D-ligands expressed in patients will be necessary to fully understand the links between this system and disease progression.

Human Cytomegalovirus Antigen Presentation by HLA-DR+ NKG2C+ Adaptive NK Cells Specifically Activates Polyfunctional Effector Memory CD4+ T Lymphocytes

Natural killer (NK) cells play a dual role in the defense against viral pathogens by directly lysing infected cells as well as by regulating anti-viral T cell immunity. Infection by human cytomegalovirus (HCMV) promotes a persistent expansion of NKG2C+ adaptive NK cells which have been shown to display enhanced antibody-dependent responses against infected targets and associated to viral control in transplanted patients. Based on gene expression data showing increased transcription of CIITA and several genes related to the MHC class II pathway in adaptive NK cells, we explored their putative capacity for antigen presentation to CD4+ T cells. Phenotypic analysis confirmed a preferential steady-state expression of HLA-DR by circulating NKG2C+ adaptive NK cells in healthy individuals. Expression of HLA-DR in NKG2C+ adaptive NK cells was variable and unrelated to the expression of activation (i.e., CD69 and CD25) or differentiation (i.e., FcRγ chain, CD57) markers, remaining stable over time at the individual level. Incubation of purified NK cells with HCMV complexed with serum specific antibodies induced an up-regulation of surface HLA-DR concomitant to CD16 loss whereas no changes in CD80/CD86 co-stimulatory ligands were detected. In addition, surface CX3CR1 decreased upon antigen-loading while HLA-DR+ NK cells maintained a CCR7-, CXCR3^low homing profile. Remarkably, HCMV-loaded purified NK cells activated autologous CD4+ T cells in an HLA-DR dependent manner. The fraction of T lymphocytes activated by antigen-loaded NK cells was smaller than that stimulated by monocyte-derived dendritic cells, corresponding to CD28-negative effector-memory CD4+ T cells with cytotoxic potential. Antigen presentation by NK cells activated a polyfunctional CD4+ T cell response characterized by degranulation (CD107a) and the secretion of Th1 cytokines (IFNγ and TNFα). Overall, our data discloses the capacity of NKG2C+ adaptive NK cells to process and present HCMV antigens to memory CD4+ cytotoxic T cells, directly regulating their response to the viral infection.

The Role of Natural Killer Group 2, Member D in Chronic Inflammation and Autoimmunity

Current medicine and medical science puts great effort into elucidating the basis of chronicity and finding appropriate treatments for inflammatory diseases; however, the mechanisms driving aberrant immune responses are mostly unknown and deserve further study. Of particular interest is the identification of checkpoints that regulate the function and differentiation of pro-inflammatory cells during pathogenesis, along with means of their modulation for therapeutic purposes. Natural killer group 2, member D (NKG2D) is a potent activator of the immune system, known as a sensor for “induced-self” ligands, i.e., cellular danger signals that, in the context of chronic inflammation and autoimmunity, can be presented by cells being exposed to an inflammatory cytokine milieu, endoplasmic reticulum stress, or cell death. Engagement by such ligands can be translated by NKG2D into activation or co-stimulation of NK cells and different subsets of T cells, respectively, thus contributing to the regulation of the inflammatory response. In this review, we discuss the current knowledge on the contribution of the NKG2D–NKG2DL signaling axis during intestinal inflammation, type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, where the role of NKG2D has been associated either by aberrant expression of the receptor and its ligands and/or by functional data in corresponding mouse models.

The NKG2D/NKG2DL Axis in the Crosstalk Between Lymphoid and Myeloid Cells in Health and Disease

Natural killer group 2, member D (NKG2D) receptor is a type II transmembrane protein expressed by both innate and adaptive immune cells, including natural killer (NK) cells, CD8+ T cells, invariant NKT cells, γδ T cells, and some CD4+ T cells under certain pathological conditions. NKG2D is an activating NK receptor that induces cytotoxicity and production of cytokines by effector cells and supports their proliferation and survival upon engagement with its ligands. In both innate and T cell populations, NKG2D can costimulate responses induced by other receptors, such as TCR in T cells or NKp46 in NK cells. NKG2D ligands (NKG2DLs) are remarkably diverse. Initially, NKG2DL expression was typically attributed to stressed, infected, or transformed cells, thus signaling “dysregulated-self.” However, many reports indicated their expression under homeostatic conditions, usually in the context of cell activation and/or proliferation. Myeloid cells, including macrophages and dendritic cells (DCs), are among the first cells sensing and responding to pathogens and tissue damage. By secreting a plethora of soluble mediators, by presenting antigens to T cells and by expressing costimulatory molecules, myeloid cells play vital roles in inducing and supporting responses of other immune cells in lymphoid organs and tissues. When activated, both macrophages and DCs upregulate NKG2DLs, thereby enabling them with additional mechanisms for regulating lymphocyte responses. In this review, we will focus on the expression of NKG2D by innate and adaptive lymphocytes, the regulation of NKG2DL expression on myeloid cells, and the contribution of the NKG2D/NKG2DL axis to the crosstalk of myeloid cells with NKG2D-expressing lymphocytes. In addition, we will highlight pathophysiological conditions associated with NKG2D/NKG2DL dysregulation and discuss the putative involvement of the NKG2D/NKG2DL axis in the lymphocyte/myeloid cell crosstalk in these diseases.

NKG2D: A Master Regulator of Immune Cell Responsiveness

NKG2D is an activating receptor that is mostly expressed on cells of the cytotoxic arm of the immune system. Ligands of NKG2D are normally of low abundance, but can be induced in virtually any cell in response to stressors, such as infection and oncogenic transformation. Engagement of NKG2D stimulates the production of cytokines and cytotoxic molecules and traditionally this receptor is, therefore, viewed as a molecule that mediates direct responses against cellular threats. However, accumulating evidence indicates that this classical view is too narrow. During NK cell development, engagement of NKG2D has a long-term impact on the expression of NK cell receptors and their responsiveness to extracellular cues, suggesting a role in NK cell education. Upon chronic NKG2D engagement, both NK and T cells show reduced responsiveness of a number of activating receptors, demonstrating a role of NKG2D in induction of peripheral tolerance. The image that emerges is that NKG2D can mediate both inhibitory and activating signals, which depends on the intensity and duration of ligand engagement. In this review, we provide an overview of the impact of NKG2D stimulation during hematopoietic development and during acute and chronic stimulation in the periphery on responsiveness of other receptors than NKG2D. We propose that NKG2D interprets the context of the immunological environment through detection of cellular cues and in response sets the appropriate activation threshold for a large number of immune receptors. This perspective is of particular importance for future therapies that aim to exploit NKG2D signaling to fight tumors or infection.

HHV-6A Infection of Endometrial Epithelial Cells Induces Increased Endometrial NK Cell-Mediated Cytotoxicity

Background: We have recently reported the presence of Human herpesvirus-6A (HHV-6A) DNA in the 43% of endometrial epithelial cells from primary idiopathic infertile women, with no positivity in fertile women. To investigate the possible effect of HHV-6A infection in endometrial (e)NK cells functions, we examined activating/inhibitory receptors expressed by eNK cells and the corresponding ligands on endometrial cells during HHV-6A infection.

Methods: Endometrial biopsies and uterine flushing samples during the secretory phase were obtained from 20 idiopathic infertile women and twenty fertile women. HHV-6A infection of endometrial epithelial cells was analyzed by Real-Time PCR, immunofluorescence and flow cytometry. eNKs receptors and endometrial ligands expression were evaluated by immunofluorescence and flow cytometry.

Results: We observed the presence of HHV-6A infection (DNA, protein) of endometrial epithelial cells in the 40% of idiopathic infertile women. The eNK from all the subgroups expressed high levels of NKG2D and NKG2A receptors. Functional studies showed that NKG2D activating receptor and FasL are involved in the acquired cytotoxic function of eNK cells during HHV-6A infection of endometrial epithelial cells. In the presence of HHV-6A infection, eNK cells increased expression of CCR2, CXCR3 and CX3CR1 chemokine receptors (p = 0.01) and endometrial epithelial cells up-modulated the corresponding ligands: MCP1 (Monocyte chemotactic protein 1, CCL2), IP-10 (Interferon gamma-induced protein 10, CXCL10) and Eotaxin-3 (CCL26).

Conclusion: Our results, for the first time, showed the implication of eNK cells in controlling HHV-6A endometrial infection and clarify the mechanisms that might be implicated in female idiopathic infertility.

Impact of cytomegalovirus reactivation on relapse and survival in patients with acute leukemia who received allogeneic hematopoietic stem cell transplantation in first remission

Cytomegalovirus (CMV)-reactivation is associated with graft-vs-leukemia (GVL) effect by stimulating natural-killer or T-cells, which showed leukemia relapse prevention after hematopoietic stem cell transplantation (HSCT). We enrolled patients with acute myeloid leukemia (n = 197) and acute lymphoid leukemia (n = 192) who underwent allogeneic-HSCT in first remission. We measured RQ-PCR weekly to detect CMV-reactivation and preemptively used ganciclovir (GCV) when the titer increased twice consecutively, but GCV was sometimes delayed in patients without significant graft-vs-host disease (GVHD) by reducing immunosuppressive agents. In the entire group, CMV-reactivation showed poor overall survival (OS). To evaluate subsequent effects of CMV-reactivation, we excluded early relapse and deaths within 100 days, during which most of the CMV-reactivation occurred. Untreated CMV-reactivated group (n = 173) showed superior OS (83.8% vs. 61.7% vs. 74.0%, p < 0.001) with lower relapse rate (10.1% vs 22.1% vs. 25.5%, p = 0.004) compared to GCV-treated CMV-reactivated group (n = 122) and CMV-undetected group (n = 42). After excluding chronic GVHD, untreated CMV-reactivated group still showed lower relapse rate (9.4% vs. 24.1% vs. 30.2%, p = 0.006). Multivariate analysis showed adverse-risk karyotype and patients in other than untreated CMV-reactivated group were independent factors for relapse prediction. Our data showed possible GVL effect of CMV-reactivation and minimizing antiviral therapy may benefit for relapse prevention in acute leukemia.

The role of toll-like receptor 4 in tumor microenvironment

Tumors are closely related to chronic inflammation, during which there are various changes in inflammatory sites, such as immune cells infiltration, pro-inflammation cytokines production, and interaction between immune cells and tissue cells. Besides, substances, released from both tissue cells attacked by exogenous etiologies, also act on local cells. These changes induce a dynamic and complex microenvironment favorable for tumor growth, invasion, and metastasis. The toll-like receptor 4 (TLR4) is the first identified member of the toll-like receptor family that can recognize pathogen-associated molecular patterns (PAMPs) and damage-associated molecular pattern (DAMPs). TLR4 expresses not only on immune cells but also on tumor cells. Accumulating evidences demonstrated that the activation of TLR4 in tumor microenvironment can not only boost the anti-tumor immunity but also give rise to immune surveillance and tumor progression. This review will summarize the expression and function of TLR4 on dendritic cells (DCs), tumor-associated macrophages (TAMs), T cells, myeloid-derived suppressor cells (MDSCs), tumor cells as well as stromal cells in tumor microenvironment. Validation of the multiple role of TLR4 in tumors could primarily pave the road for the development of anti-tumor immunotherapy.

An Approach for a Synthetic CTL Vaccine Design against Zika Flavivirus Using Class I and Class II Epitopes Identified by Computer Modeling

The threat posed by severe congenital abnormalities related to Zika virus (ZKV) infection during pregnancy has turned development of a ZKV vaccine into an emergency. Recent work suggests that the cytotoxic T lymphocyte (CTL) response to infection is an important defense mechanism in response to ZKV. Here, we develop the rationale and strategy for a new approach to developing cytotoxic T lymphocyte (CTL) vaccines for ZKV flavivirus infection. The proposed approach is based on recent studies using a protein structure computer model for HIV epitope selection designed to select epitopes for CTL attack optimized for viruses that exhibit antigenic drift. Because naturally processed and presented human ZKV T cell epitopes have not yet been described, we identified predicted class I peptide sequences on ZKV matching previously identified DNV (Dengue) class I epitopes and by using a Major Histocompatibility Complex (MHC) binding prediction tool. A subset of those met the criteria for optimal CD8+ attack based on physical chemistry parameters determined by analysis of the ZKV protein structure encoded in open source Protein Data File (PDB) format files. We also identified candidate ZKV epitopes predicted to bind promiscuously to multiple HLA class II molecules that could provide help to the CTL responses. This work suggests that a CTL vaccine for ZKV may be possible even if ZKV exhibits significant antigenic drift. We have previously described a microsphere-based CTL vaccine platform capable of eliciting an immune response for class I epitopes in mice and are currently working toward in vivo testing of class I and class II epitope delivery directed against ZKV epitopes using the same microsphere-based vaccine.

Killer cells in atherosclerosis

Cytotoxic lymphocytes (killer cells) play a critical role in host defence mechanisms, protecting against infections and in tumour surveillance. They can also exert detrimental effects in chronic inflammatory disorders and in autoimmune diseases. Tissue cell death and necrosis are prominent features of advanced atherosclerotic lesions including vulnerable/unstable lesions which are largely responsible for most heart attacks and strokes. Evidence for accumulation of killer cells in both human and mouse lesions together with their cytotoxic potential strongly suggest that these cells contribute to cell death and necrosis in lesions leading to vulnerable plaque development and potentially plaque rupture. Killer cells can be divided into two groups, adaptive and innate immune cells depending on whether they require antigen presentation for activation. Activated killer cells detect damaged or stressed cells and kill by cytotoxic mechanisms that include perforin, granzymes, TRAIL or FasL and in some cases TNF-α. In this review, we examine current knowledge on killer cells in atherosclerosis, including CD8 T cells, CD28- CD4 T cells, natural killer cells and γδ-T cells, mechanisms responsible for their activation, their migration to developing lesions and effector functions. We also discuss pharmacological strategies to prevent their deleterious vascular effects by preventing/limiting their cytotoxic effects within atherosclerotic lesions as well as potential immunomodulatory therapies that might better target lesion-resident killer cells, to minimise any compromise of the immune system, which could result in increased susceptibility to infections and reductions in tumour surveillance.

NKG2D: A versatile player in the immune system

NKG2D is known as a potent activating receptor of the immune system. It is expressed on a multitude of immune cells, including NK cells and different subsets of T cells. NKG2D recognizes various MHC I-like ligands that are induced on target cells exposed to stressors such as viral infection, DNA damage and oncological transformation. NKG2D drives or facilitates cytotoxic and cytokine responses towards cells expressing its ligands to eliminate the threat. Therefore, NKG2D is usually classified as a sensor that translates cellular stress into activation signals for immune cells. However, more recently it has become evident that NKG2D plays a role beyond direct killing of target cells. Lack of NKG2D affects development of NK cells in the bone marrow, resulting in hyperreactive NK cells. NKG2D deficiency on CD8 T cells affects the ability of effector cells to produce cytokines in response to T cell receptor engagement and reduces their capacity to establish immunological memory. Although NKG2D is not expressed on B cells subsets, lack of this receptor in hematopoietic precursors affects B cell development. Homing of mature B2 cells is altered in NKG2D-deficient mice and they have a strong reduction in peripheral B1a cell numbers, resulting in increased susceptibility to bacterial infections. The exact molecular mechanisms via which NKG2D mediates these versatile functions is still being explored, but appears to depend on the control of activation thresholds, either in hematopoietic precursors or mature immune cell subsets. In this review, we will elaborate on the underappreciated developmental and regulatory roles of NKG2D.

MICA and NKG2D: Is There an Impact on Kidney Transplant Outcome?

This paper aims to present an overview of MICA and natural killer group 2 member D (NKG2D) genetic and functional interactions and their impact on kidney transplant outcome. Organ transplantation has gone from what can accurately be called a “clinical experiment” to a routine and reliable practice, which has proven to be clinically relevant, life-saving and cost-effective when compared with non-transplantation management strategies of both chronic and acute end-stage organ failures. The kidney is the most frequently transplanted organ in the world (transplant-observatory¹). The two treatment options for end-stage renal disease (ESRD) are dialysis and/or transplantation. Compared with dialysis, transplantation is associated with significant improvements in quality of life and overall longevity. A strong relationship exists between allograft loss and human leukocyte antigens (HLA) antibodies (Abs). HLA Abs are not the only factor involved in graft loss, as multiple studies have shown that non-HLA antigens are also involved, even when a patient has a good HLA matche and receives standard immunosuppressive therapy. A deeper understanding of other biomarkers is therefore important, as it is likely to lead to better monitoring (and consequent success) of organ transplants. The objective is to fill the void left by extensive reviews that do not often dive this deep into the importance of MICA and NKG2D in allograft acceptance and their partnership in the immune response. There are few papers that explore the relationship between these two protagonists when it comes to kidney transplantation. This is especially true for the role of NKG2D in kidney transplantation. These reasons give a special importance to this review, which aims to be a helpful tool in the hands of researchers in this field.

CD4 CTL, a Cytotoxic Subset of CD4+ T Cells, Their Differentiation and Function

CD4⁺ T cells with cytotoxic activity (CD4 CTL) have been observed in various immune responses. These cells are characterized by their ability to secrete granzyme B and perforin and to kill the target cells in an MHC class II-restricted fashion. Although CD4 CTLs were once thought to be an in vitro artifact associated with long-term culturing, they have since been identified in vivo and shown to play important roles in antiviral and antitumor immunity, as well as in inflammation. Functional characterization of CD4 CTL suggests their potential significance for therapeutic purposes. However, in order to develop effective CD4 CTL therapy it is necessary to understand the differentiation and generation of these cells. Although the mechanisms regulating development of various CD4⁺ Th subsets have been clarified in terms of the cytokine and transcription factor requirement, the CD4 CTL differentiation mechanism remains elusive. These cells are thought to be most closely related to Th1 cells secreting IFNγ and regulated by eomesodermin and/or T-bet transcription factors for their differentiation. However, our studies and those of others have identified CD4 CTLs within other CD4⁺ T cell subsets, including naïve T cells. We have identified class I-restricted T cell-associated molecule as a marker of CD4 CTL and, by using this marker, we detected a subset of naïve T cells that have the potential to differentiate into CD4 CTL. CD4 CTL develops at sites of infections as well as inflammation. In this review, we summarize recent findings about the generation of CD4 CTL and propose a model with several differentiation pathways.

NK1.1- CD4+ NKG2D+ T cells suppress DSS-induced colitis in mice through production of TGF-β

CD4⁺NKG2D⁺ T cells are associated with tumour, infection and autoimmune diseases. Some CD4⁺NKG2D⁺ T cells secrete IFN‐γ and TNF‐α to promote inflammation, but others produce TGF‐β and FasL to facilitate tumour evasion. Here, murine CD4⁺NKG2D⁺ T cells were further classified into NK1.1⁻CD4⁺NKG2D⁺ and NK1.1⁺CD4⁺NKG2D⁺ subpopulations. The frequency of NK1.1⁻CD4⁺NKG2D⁺ cells decreased in inflamed colons, whereas more NK1.1⁺CD4⁺NKG2D⁺ cells infiltrated into colons of mice with DSS‐induced colitis. NK1.1⁻CD4⁺NKG2D⁺ cells expressed TGF‐β and FasL without secreting IFN‐γ, IL‐21 and IL‐17 and displayed no cytotoxicity. The adoptive transfer of NK1.1⁻CD4⁺NKG2D⁺ cells suppressed DSS‐induced colitis largely dependent on TGF‐β. NK1.1⁻CD4⁺NKG2D⁺ cells did not expressed Foxp3, CD223 (LAG‐3) and GITR. The subpopulation was distinct from NK1.1⁺CD4⁺NKG2D⁺ cells in terms of surface markers and RNA transcription. NK1.1⁻CD4⁺NKG2D⁺ cells also differed from Th2 or Th17 cells because the former did not express GATA‐3 and ROR‐γt. Thus, NK1.1⁻CD4⁺NKG2D⁺ cells exhibited immune regulatory functions, and this T cell subset could be developed to suppress inflammation in clinics.

Cytotoxic effector functions of T cells are not required for protective immunity against fatal Rickettsia typhi infection in a murine model of infection: Role of TH1 and TH17 cytokines in protection and pathology

Endemic typhus caused by Rickettsia (R.) typhi is an emerging febrile disease that can be fatal due to multiple organ pathology. Here we analyzed the requirements for protection against R. typhi by T cells in the CB17 SCID model of infection. BALB/c wild-type mice generate CD4+ TH1 and cytotoxic CD8+ T cells both of which are sporadically reactivated in persistent infection. Either adoptively transferred CD8+ or CD4+ T cells protected R. typhi-infected CB17 SCID mice from death and provided long-term control. CD8+ T cells lacking either IFNγ or Perforin were still protective, demonstrating that the cytotoxic function of CD8+ T cells is not essential for protection. Immune wild-type CD4+ T cells produced high amounts of IFNγ, induced the release of nitric oxide in R. typhi-infected macrophages and inhibited bacterial growth in vitro via IFNγ and TNFα. However, adoptive transfer of CD4+IFNγ-/- T cells still protected 30-90% of R. typhi-infected CB17 SCID mice. These cells acquired a TH17 phenotype, producing high amounts of IL-17A and IL-22 in addition to TNFα, and inhibited bacterial growth in vitro. Surprisingly, the neutralization of either TNFα or IL-17A in CD4+IFNγ-/- T cell recipient mice did not alter bacterial elimination by these cells in vivo, led to faster recovery and enhanced survival compared to isotype-treated animals. Thus, collectively these data show that although CD4+ TH1 cells are clearly efficient in protection against R. typhi, CD4+ TH17 cells are similarly protective if the harmful effects of combined production of TNFα and IL-17A can be inhibited.

Cytotoxic CD4 T Cells-Friend or Foe during Viral Infection?

CD4 T cells with cytotoxic function were once thought to be an artifact due to long-term in vitro cultures but have in more recent years become accepted and reported in the literature in response to a number of viral infections. In this review, we focus on cytotoxic CD4 T cells in the context of human viral infections and in some infections that affect mice and non-human primates. We examine the effector mechanisms used by cytotoxic CD4 cells, the phenotypes that describe this population, and the transcription factors and pathways that lead to their induction following infection. We further consider the cells that are the predominant targets of this effector subset and describe the viral infections in which CD4 cytotoxic T lymphocytes have been shown to play a protective or pathologic role. Cytotoxic CD4 T cells are detected in the circulation at much higher levels than previously realized and are now recognized to have an important role in the immune response to viral infections.

Peginterferon Alfa-2a/Ribavirin treatment efficacy in chronic hepatitis C patients is related to natural killer group 2D gene rs1049174 GC polymorphism

Natural killer group 2D (NKG2D), as an activating receptor, plays pivotal role in viral infectious diseases. Several single nucleotide polymorphisms (SNPs) in the NKG2D gene have characterized that the rs1049174G/C SNP of NKG2D is in the spotlight of notice because of its role in activating of human T cells. This study aimed to investigate rs1049174G/C genetic polymorphism in Chronic Hepatitis C (CHC) patients. The study compromised 107 CHC patients with genotype 1a and 1b. All recruited patients were under treatment with Peginterferon Alfa-2a/Ribavirin according to standard protocol. After completing treatment, 67 patients showed sustained virologic response (SVR) and the rest of patients did not respond to the treatment and considered as non-responder (NR). Genotyping of NKG2D rs1049174G/C SNP was performed using PCR-RFLP method in SVR and NR patients. The NKG2D rs1049174 genotypes frequency for GG, GC and CC were 45, 41 and 14 % respectively. Genotypes distribution were significantly different between SVR and NR groups (p = 0.005). So that the patients with the homozygous GG genotype demonstrated a higher response to Peginterferon Alfa-2a/Ribavirin therapy against HCV infection (OR = 6.0, 95 %CI 1.71-21.08, p = 0.005). In conclusion, the rs1049174 GG genotype of NKG2D receptor is an effective factor in successfully treatment of CHC patients by Peginterferon Alfa-2a/Ribavirin.

Cytomegalovirus Infection Leads to Development of High Frequencies of Cytotoxic Virus-Specific CD4+ T Cells Targeted to Vascular Endothelium

Cytomegalovirus (CMV) infection elicits a very strong and sustained intravascular T cell immune response which may contribute towards development of accelerated immune senescence and vascular disease in older people. Virus-specific CD8+ T cell responses have been investigated extensively through the use of HLA-peptide tetramers but much less is known regarding CMV-specific CD4+ T cells. We used a range of HLA class II-peptide tetramers to investigate the phenotypic and transcriptional profile of CMV-specific CD4+ T cells within healthy donors. We show that such cells comprise an average of 0.45% of the CD4+ T cell pool and can reach up to 24% in some individuals (range 0.01–24%). CMV-specific CD4+ T cells display a highly differentiated effector memory phenotype and express a range of cytokines, dominated by dual TNF-α and IFN-γ expression, although substantial populations which express IL-4 were seen in some donors. Microarray analysis and phenotypic expression revealed a profile of unique features. These include the expression of CX3CR1, which would direct cells towards fractalkine on activated endothelium, and the β2-adrenergic receptor, which could permit rapid response to stress. CMV-specific CD4+ T cells display an intense cytotoxic profile with high level expression of granzyme B and perforin, a pattern which increases further during aging. In addition CMV-specific CD4+ T cells demonstrate strong cytotoxic activity against antigen-loaded target cells when isolated directly ex vivo. PD-1 expression is present on 47% of cells but both the intensity and distribution of the inhibitory receptor is reduced in older people. These findings reveal the marked accumulation and unique phenotype of CMV-specific CD4+ T cells and indicate how such T cells may contribute to the vascular complications associated with CMV in older people.

Cytomegalovirus (CMV) is a member of the herpesvirus family and most humans carry chronic CMV infection. This drives the development of large expansions of CD8+ CMV-specific T cells, which increase further during ageing. CMV infection is associated with vascular disease and increased risk of mortality in older people, which may be related to damage from this CMV-specific immune response. Here we used a set of novel reagents called HLA class II tetramers to make a detailed study of CMV-specific CD4+ T cells. We show that CMV-specific CD4+ T cells are found at remarkably high frequencies within blood, representing up to a quarter of all such white cells. In addition they demonstrate a range of unique features. Firstly they carry a chemokine receptor that directs the cells to activated endothelial cells within blood vessels. Secondly, they express epinephrine receptors which would allow them to respond rapidly to stress. Finally, these CD4+ T cells are unique as they are strongly cytotoxic and equipped with the ability to directly kill virally-infected cells. HLA class II tetramers therefore reveal a profile of unique features which provide insight into how CMV-specific CD4+ T cells may be involved in vascular immunopathology.

T Cells Going Innate

Natural killer (NK) cell receptors (NKRs) play a crucial role in the homeostasis of antigen-experienced T cells. Indeed, prolonged antigen stimulation may induce changes in the receptor repertoire of T cells to a profile that features NKRs. Chronic antigen exposure, at the same time, has been shown to trigger the loss of costimulatory CD28 molecules with recently reported intensified antigen thresholds of antigen-experienced CD8(+) T cells. In transplantation, NKRs have been shown to assist allograft rejection in a CD28-independent fashion. We discuss here a role for CD28-negative T cells that have acquired the competency of the NKR machinery, potentially promoting allorecognition either through T cell receptor (TCR) crossreactivity or independently from TCR recognition. Collectively, NKRs can bring about innate-like T cells by providing alternative costimulatory pathways that gain relevance in chronic inflammation, potentially leading to resistance to CD28-targeting immunosuppressants.

Aberrant NKG2D expression with IL-17 production of CD4+ T subsets in patients with type 2 diabetes

Type 2 diabetes (T2D) is a systemic inflammatory disease. Although the natural killer group 2, member D (NKG2D) receptor, was not expressed normally on CD4+ T cells, the aberrant expression was found in pathological conditions such as in auto-immune diseases. However, the involvement of NKG2D in pathogenesis of T2D is unclear. We hypothesize that there is an inflammatory CD4+ T cell subpopulation expressing NKG2D and producing interleukin (IL)-17 in T2D. NKG2D expression on CD4+ T cells and their subsets were analyzed by multi-color staining using flow cytometry. Lymphocytes were activated by phorbol-12-myristate-13-acetate (PMA) and ionomycin, and were stained for intracellular IL-17. To investigate the mechanism of IL-17 production, patients' lymphocytes were stimulated using specific anti-T cell receptor (TCR) alone, anti-NKG2D alone or a combination of the two antibodies. CD4+ T cells and particularly, CD4+CD28^nullT subset of T2D patients were highly expressed NKG2D and more prevalent compared to non-diabetic individuals (ND) (P=0.039 and P=0.022, respectively). Significantly higher percentages of CD4+CD28^nullNKG2D+T cells of patients produced IL-17 when compared to those of ND (P=0.024) and were positively correlated with the level of glycated hemoglobin A1c (HbA1c) (R²=0.386, P=0.041). Additionally, this cell population could be stimulated by specific monoclonal anti-NKG2D to produce IL-17. In conclusion, CD4+CD28^nullNKG2D+T cells were expanded in T2D, especially in patients with poor glycemic control. NKG2D may be one of the surrogate co-stimulatory receptors leading to irregular inflammatory function producing IL-17. An IL-17 producing CD4+CD28^nullNKG2D+T cells may potentially be involved in pathogenesis and drive severity of the disease with the glycemic dependence. This particular cell type could be targeted for prognostic or therapeutic purposes.

Cytomegalovirus-Associated CD4(+) CD28(null) Cells in NKG2D-Dependent Glomerular Endothelial Injury and Kidney Allograft Dysfunction

Emerging data suggest that expansion of a circulating population of atypical, cytotoxic CD4(+) T cells lacking costimulatory CD28 (CD4(+) CD28(null) cells) is associated with latent cytomegalovirus (CMV) infection. The purpose of the current study was to increase the understanding of the relevance of these cells in 100 unselected kidney transplant recipients followed prospectively for a median of 54 months. Multicolor flow cytometry of peripheral blood mononuclear cells before transplantation and serially posttransplantation was undertaken. CD4(+) CD28(null) cells were found predominantly in CMV-seropositive patients and expanded in the posttransplantation period. These cells were predominantly effector-memory phenotype and expressed markers of endothelial homing (CX3CR1) and cytotoxicity (NKG2D and perforin). Isolated CD4(+) CD27(-) CD28(null) cells proliferated in response to peripheral blood mononuclear cells previously exposed to CMV-derived (but not HLA-derived) antigens and following such priming incubation with glomerular endothelium resulted in signs of endothelial damage and apoptosis (release of fractalkine and von Willebrand factor; increased caspase 3 expression). This effect was mitigated by NKG2D-blocking antibody. Increased CD4(+) CD28(null) cell frequencies were associated with delayed graft function and lower estimated glomerular filtration rate at end follow-up. This study suggests an important role for this atypical cytotoxic CD4(+) CD28(null) cell subset in kidney transplantation and points to strategies that may minimize the impact on clinical outcomes.

Levels of regulatory T cells CD69(+)NKG2D(+)IL-10(+) are increased in patients with autoimmune thyroid disorders

Regulatory T (Treg) cells play an important role in the pathogenesis of autoimmune thyroid disorders (AITD). New subsets of CD4(+)CD69(+) and CD4(+)NKG2D(+) T lymphocytes that behave as regulatory cells have been recently reported. The role of these immunoregulatory lymphocytes has not been previously explored in AITD. We analyzed by multi-parametric flow cytometry different Treg cell subsets in peripheral blood from 32 patients with AITD and 19 controls, and in thyroid tissue from seven patients. The suppressive activity was measured by an assay of inhibition of lymphocyte activation. We found a significant increased percentage of CD4(+)CD69(+)IL-10(+), CD4(+)CD69(+)NKG2D(+), and CD4(+)CD69(+)IL-10(+)NKG2D(+) cells, in peripheral blood from GD patients compared to controls. The increase in CD4(+)CD69(+)IL-10(+) and CD4(+)CD69(+)IL-10(+)NKG2D(+) T cells was especially remarkable in patients with active Graves' ophthalmopathy (GO), and a significant positive correlation between GO activity and CD4(+)CD69(+)IL-10(+) or CD4(+)CD69(+)IL-10(+)NKG2D(+) cells was also found. In addition, these cells were increased in patients with a more severe and/or prolonged disease. Thyroid from AITD patients showed an increased proportion of CD69(+) regulatory T cells subpopulations compared to autologous peripheral blood. The presence of CD69(+), NKG2D(+), and IL-10(+) cells was confirmed by immunofluorescence microscopy. In vitro functional assays showed that CD69(+) Treg cells exerted an important suppressive effect on the activation of T effector cells in controls, but not in AITD patients. Our findings suggest that the levels of CD69(+) regulatory lymphocytes are increased in AITD patients, but they are apparently unable to down-modulate the autoimmune response and tissue damage.

An approach to the immunophenotypic features of circulating CD4⁺NKG2D⁺ T cells in invasive cervical carcinoma

Background

NKG2D, an activating immunoreceptor, is primarily restricted to NK cells and CD8⁺ T cells. The existence of an atypical cytotoxic CD4⁺NKG2D⁺ T cell population has also been found in patients with autoimmune dysfunctions. Nonetheless, contradictory evidence has categorized this population with a regulatory rather than cytotoxic role in other situations. These confounding data have led to the proposal that two distinct CD4⁺NKG2D⁺ T cell subsets might exist. The immune response elicited in cervical cancer has been characterized by apparent contradictions concerning the role that T cells, in particular T-helper cells, might be playing in the control of the tumor growth. Interestingly, we recently reported a substantial increase in the frequency of CD4⁺NKG2D⁺ T cells in patients with cervical intraepithelial neoplasia grade-1. However, whether this particular population is also found in patients with more advanced cervical lesions or whether they express a distinctive phenotype remains still to be clarified. In this urgent study, we focused our attention on the immunophenotypic characterization of CD4⁺NKG2D⁺ T cells in patients with well-established cervical carcinoma and revealed the existence of at least two separate CD4⁺NKG2D⁺ T cell subsets defined by the co-expression or absence of CD28.

Results

Patients with diagnosis of invasive cervical carcinoma were enrolled in the study. A group of healthy individuals was also included. Multicolor flow cytometry was used for exploration of TCR alpha/beta, CD28, CD158b, CD45RO, HLA-DR, CD161, and CD107a. A Luminex-based cytokine kit was used to quantify the levels of pro- and anti-inflammatory cytokines. We found an increased percentage of CD4⁺NKG2D⁺ T cells in patients with cervical cancer when compared with controls. Accordingly with an increase of CD4⁺NKG2D⁺ T cells, we found decreased CD28 expression. The activating or degranulation markers HLA-DR, CD161, and CD107a were heterogeneously expressed. The levels of IL-1beta, IL-2, TNF-alpha, and IL-10 were negatively correlated with the percentages of CD4⁺NKG2D⁺ T cells in patients with cervical carcinoma.

Conclusions

Taken together, our results reveal the existence of two separate CD4⁺NKG2D⁺ T cell subsets defined by the co-expression or absence of CD28, the latter more likely to be present in patients with cervical cancer.

Mesenchymal stem cells suppress CD8+ T cell-mediated activation by suppressing natural killer group 2, member D protein receptor expression and secretion of prostaglandin E2, indoleamine 2, 3-dioxygenase and transforming growth factor-β

Bone marrow mesenchymal stem cells (BMSCs) inhibit immune cell responsiveness, and especially of T lymphocytes. We showed that BMSCs markedly inhibited the proliferation and cytokine production by CD8(+) T cells by a cell-to-cell contact phenomenon and secretion of soluble factors. BMSCs down-regulate the expression of natural killer group 2, member D protein (NKG2D) receptors on CD8(+) T cells when co-cultured with them. Moreover, CD8(+) T cells that express low levels of NKG2D had impaired proliferation after triggering by a mitogen. The major histocompatibility complex (MHC) class I chain-related (MIC) A/B molecule, which is a typical ligand for NKG2D, was expressed on BMSCs, and caused dampening of cell proliferation. Monoclonal antibody blocking experiments targeted to MIC A/B impaired CD8(+) T cell function, as evaluated by proliferation and cytokine production. In addition, the production of prostaglandin E2 (PGE2 ), indoleamine 2, 3-dioxygenase (IDO) and transforming growth factor (TGF)-β1 were increased when BMSCs were co-cultured with CD8(+) T cells. The addition of specific inhibitors against PGE2 , IDO and TGF-β partially restored the proliferation of CD8(+) T cells. Our results suggest that BMSCs suppress CD8(+) T cell-mediated activation by suppressing NKG2D expression and secretion of PGE2, IDO and TGF-β. Our observations further confirm the feasibility of BMSCs as a potential adoptive cellular therapy in immune-mediated diseases such as graft-versus-host disease (GVHD).

CD4(+) NKG2D(+) T cells induce NKG2D down-regulation in natural killer cells in CD86-RAE-1ε transgenic mice

The binding of NKG2D to its ligands strengthens the cross-talk between natural killer (NK) cells and dendritic cells, particularly at early stages, before the initiation of the adaptive immune response. We found that retinoic acid early transcript-1ε (RAE-1ε), one of the ligands of NKG2D, was persistently expressed on antigen-presenting cells in a transgenic mouse model (pCD86-RAE-1ε). By contrast, NKG2D expression on NK cells, NKG2D-dependent cytotoxicity and tumour rejection, and dextran sodium sulphate-induced colitis were all down-regulated in this mouse model. The down-regulation of NKG2D on NK cells was reversed by stimulation with poly (I:C). The ectopic expression of RAE-1ε on dendritic cells maintained NKG2D expression levels and stimulated the activity of NK cells ex vivo, but the higher frequency of CD4(+) NKG2D(+) T cells in transgenic mice led to the down-regulation of NKG2D on NK cells in vivo. Hence, high levels of RAE-1ε expression on antigen-presenting cells would be expected to induce the down-regulation of NK cell activation by a regulatory T-cell subset.

Oligoclonal expansions of mucosal T cells in Crohn's disease predominate in NKG2D-expressing CD4 T cells

Crohn's disease (CD) is an inflammatory pathology of the mucosal intestine that results from uncontrolled immune response towards commensal microbes. Clonal expansions of T cells have been found in patients with CD suggesting an antigen-specific stimulation of pathogenic T cells. Here we show, using T-cell receptor repertoire analysis by real-time PCR, that oligoclonal expansions are found in both CD8+ and CD4+ T cells in the blood and intestinal mucosa of CD patients. The majority of CD4+ T-cell-expanded clones are CD4+NKG2D+ T cells. These clonal expansions were found in both inflamed and neighboring healthy tissue and were persisting during the course of the disease. The presence of these CD4+NKG2D+ T-cell clones at the macroscopically normal edge of the surgical resection might be predictive of inflammation relapse post surgery.

CD4 CTL: living up to the challenge

During thymic development, thymocytes expressing a T cell receptor consisting of an alpha and beta chain (TCRαβ), commit to either the cytotoxic- or T helper-lineage fate. This lineage dichotomy is controlled by key transcription factors, including the T helper (Th) lineage master regulator, the Th-inducing BTB/POZ domain-containing Kruppel-like zinc-finger transcription factor, ThPOK, (formally cKrox or Zfp67; encoded by Zbtb7b), which suppresses the cytolytic program in major histocompatibility complex (MHC) class II-restricted CD4(+) thymocytes and the Runt related transcription factor 3 (Runx3), which counteracts ThPOK in MHC class I restricted precursor cells and promotes the lineage commitment of CD8αβ(+) cytolytic T lymphocytes (CTL). ThPOK continues to repress the CTL gene program in mature CD4(+) T cells, even as they differentiate into effector Th cell subsets. The Th cell fate however is not fixed and two recent studies showed that mature, antigen-stimulated CD4(+) T cells have the flexibility to terminate the expression of ThPOK and functionally reprogram to cytotoxic effector cells. This unexpected plasticity of CD4(+) T cells results in the post-thymic termination of the Th lineage fate and the functional differentiation of distinct MHC class II-restricted CD4(+) CTL. The recognition of CD4 CTL as a defined separate subset of effector cells and the identification of the mechanisms and factors that drive their reprogramming finally create new opportunities to explore the physiological relevance of these effector cells in vivo and to determine their pivotal roles in both, protective immunity as well as in immune-related pathology.

Substantial increase in the frequency of circulating CD4+NKG2D+ T cells in patients with cervical intraepithelial neoplasia grade 1

Background

The NKG2D receptor confers important activating signals to NK cells via ligands expressed during cellular stress and viral infection. This receptor has generated great interest because not only is it expressed on NK cells, but it is also seen in virtually all CD8⁺ cytotoxic T cells and is classically considered absent in CD4⁺ T cells. However, recent studies have identified a distinctive population of CD4⁺ T cells that do express NKG2D, which could represent a particular cytotoxic effector population involved in viral infections and chronic diseases. On the other hand, increased incidence of human papillomavirus-associated lesions in CD4⁺ T cell-immunocompromised individuals suggests that CD4⁺ T cells play a key role in controlling the viral infection. Therefore, this study was focused on identifying the frequency of NKG2D-expressing CD4⁺ T cells in patients with cervical intraepithelial neoplasia (CIN) 1. Additionally, factors influencing CD4⁺NKG2D⁺ T cell expansion were also measured.

Results

Close to 50% of patients with CIN 1 contained at least one of the 37 HPV types detected by our genotyping system. A tendency for increased CD4⁺ T cells and CD8⁺ T cells and decreased NK cells was found in CIN 1 patients. The percentage of circulating CD4⁺ T cells co-expressing the NKG2D receptor significantly increased in women with CIN 1 versus control group. Interestingly, the increase of CD4⁺NKG2D⁺ T cells was seen in patients with CIN 1, despite the overall levels of CD4⁺ T cells did not significantly increase. We also found a significant increase of soluble MICB in CIN 1 patients; however, no correlation with the presence of CD4⁺NKG2D⁺ T cells was seen. While TGF-beta was significantly decreased in the group of CIN 1 patients, both TNF-alpha and IL-15 showed a tendency to increase in this group.

Conclusions

Taken together, our results suggest that the significant increase within the CD4⁺NKG2D⁺ T cell population in CIN 1 patients might be the result of a chronic exposure to viral and/or pro-inflammatory factors, and concomitantly might also influence the clearance of CIN 1-type lesion.

The enhanced effect of lupeol on the destruction of gastric cancer cells by NK cells

Lupeol, a triterpene, was reported to possess beneficial effects as a therapeutic and preventive agent for a range of disorders. Many studies have confirmed that lupeol possesses strong activities such as antioxidative, antiinflammatory, antiarthritic, antimutagenic, and antimalarial, both in vitro and in vivo, and at its effective therapeutic doses exhibit no toxicity to normal cells and tissues. Lupeol was observed to inhibit the proliferation of gastric tumour cells in a dose-dependent manner, as assessed by MTT assay, and induce the proliferation of NK cells, as assessed by flow cytometry and Western blotting. The killing effect of NK cells on gastric tumour cells was assessed by LDH. Our experiment demonstrated that lupeol at appropriate concentrations could promote the proliferation of NK cells, inhibit the proliferation of gastric cancer cell lines BGC823, N87 and HGC27, and increase the killing effect of NK cells on gastric cancer cells. We speculated that lupeol might increase the expression of PFP, IFN-γ, and CD107a via the activation of PI3K/Akt and Wnt/β-catenin signalling pathways. Lupeol could serve as a potential agent against gastric cancer; however, further in-depth in vivo studies are still required.

DNA demethylation and histone H3K9 acetylation determine the active transcription of the NKG2D gene in human CD8+ T and NK cells

The human activating receptor NKG2D is mainly expressed by NK, NKT, γδ T and CD8(+) T cells and, under certain conditions, by CD4(+) T cells. This receptor recognizes a diverse family of ligands (MICA, MICB and ULBPs 1-6) leading to the activation of effector cells and triggering the lysis of target cells. The NKG2D receptor-ligand system plays an important role in the immune response to infections, tumors, transplanted graft and autoantigens. Elucidation of the regulatory mechanisms of NKG2D is therefore essential for therapeutic purposes. In this study, we speculate whether epigenetic mechanisms, such as DNA methylation and histone acetylation, participate in NKG2D gene regulation in T lymphocytes and NK cells. DNA methylation in the NKG2D gene was observed in CD4(+) T lymphocytes and T cell lines (Jurkat and HUT78), while this gene was unmethylated in NKG2D-positive cells (CD8(+) T lymphocytes, NK cells and NKL cell line) and associated with high levels of histone H3 lysine 9 acetylation (H3K9Ac). Treatment with the histone acetyltransferase (HAT) inhibitor curcumin reduces H3K9Ac levels in the NKG2D gene, downregulates NKG2D transcription and leads to a marked reduction in the lytic capacity of NKG2D-mediated NKL cells. These findings suggest that differential NKG2D expression in the different cell subsets is regulated by epigenetic mechanisms and that its modulation by epigenetic treatments might provide a new strategy for treating several pathologies.

Influence of congenital human cytomegalovirus infection and the NKG2C genotype on NK-cell subset distribution in children

Human cytomegalovirus (HCMV) has been reported to reshape the NK-cell receptor (NKR) distribution, promoting an expansion of CD94/NKG2C(+) NK and T cells. The role of NK cells in congenital HCMV infection is ill-defined. Here we studied the expression of NKR (i.e., NKG2C, NKG2A, LILRB1, CD161) and the frequency of the NKG2C gene deletion in children with past congenital infection, both symptomatic (n = 15) and asymptomatic (n = 11), including as controls children with postnatal infection (n = 11) and noninfected (n = 20). The expansion of NKG2C(+) NK cells in HCMV-infected individuals appeared particularly marked and was associated with an increased number of LILRB1(+) NK cells in cases with symptomatic congenital infection. Increased numbers of NKG2C(+), NKG2A(+), and CD161(+) T cells were also associated to HCMV infection. The NKG2C deletion frequency was comparable in children with congenital HCMV infection and controls. Remarkably, the homozygous NKG2C(+/+) genotype appeared associated with increased absolute numbers of NKG2C(+) NK cells. Moreover, HCMV-infected NKG2C(+/+) children displayed higher absolute numbers of NKG2A(+) and total NK cells than NKG2C(+/-) individuals. Our study provides novel insights on the impact of HCMV infection on the homeostasis of the NK-cell compartment in children, revealing a modulatory influence of NKG2C copy number.

Human NKG2D-ligands: cell biology strategies to ensure immune recognition

Immune recognition mediated by the activating receptor NKG2D plays an important role for the elimination of stressed cells, including tumors and virus-infected cells. On the other hand, the ligands for NKG2D can also be shed into the sera of cancer patients where they weaken the immune response by downmodulating the receptor on effector cells, mainly NK and T cells. Although both families of NKG2D-ligands, major histocompatibility complex class I-related chain (MIC) A/B and UL16 binding proteins (ULBPs), are related to MHC molecules and their expression is increased after stress, many differences are observed in terms of their biochemical properties and cell trafficking. In this paper, we summarize the variety of NKG2D-ligands and propose that selection pressure has driven evolution of diversity in their trafficking and shedding, but not receptor binding affinity. However, it is also possible to identify functional properties common to individual ULBP molecules and MICA/B alleles, but not generally conserved within the MIC or ULBP families. These characteristics likely represent examples of convergent evolution for efficient immune recognition, but are also attractive targets for pathogen immune evasion strategies. Categorization of NKG2D-ligands according to their biological features, rather than their genetic family, may help to achieve a better understanding of NKG2D-ligand association with disease.

Regulation and gene expression profiling of NKG2D positive human cytomegalovirus-primed CD4+ T-cells

NKG2D is a stimulatory receptor expressed by natural killer (NK) cells, CD8⁺ T-cells, and γδ T-cells. NKG2D expression is normally absent from CD4⁺ T-cells, however recently a subset of NKG2D⁺ CD4⁺ T-cells has been found, which is specific for human cytomegalovirus (HCMV). This particular subset of HCMV-specific NKG2D⁺ CD4⁺ T-cells possesses effector-like functions, thus resembling the subsets of NKG2D⁺ CD4⁺ T-cells found in other chronic inflammations. However, the precise mechanism leading to NKG2D expression on HCMV-specific CD4⁺ T-cells is currently not known. In this study we used genome-wide analysis of individual genes and gene set enrichment analysis (GSEA) to investigate the gene expression profile of NKG2D⁺ CD4⁺ T-cells, generated from HCMV-primed CD4⁺ T-cells. We show that the HCMV-primed NKG2D⁺ CD4⁺ T-cells possess a higher differentiated phenotype than the NKG2D^– CD4⁺ T-cells, both at the gene expression profile and cytokine profile. The ability to express NKG2D at the cell surface was primarily determined by the activation or differentiation status of the CD4⁺ T-cells and not by the antigen presenting cells. We observed a correlation between CD94 and NKG2D expression in the CD4⁺ T-cells following HCMV stimulation. However, knock-down of CD94 did not affect NKG2D cell surface expression or signaling. In addition, we show that NKG2D is recycled at the cell surface of activated CD4⁺ T-cells, whereas it is produced de novo in resting CD4⁺ T-cells. These findings provide novel information about the gene expression profile of HCMV-primed NKG2D⁺ CD4⁺ T-cells, as well as the mechanisms regulating NKG2D cell surface expression.