Gata6+ Pericardial Cavity Macrophages Relocate to the Injured Heart and Prevent Cardiac Fibrosis.

Macrophages play an important role in structural cardiac remodeling and the transition to heart failure following myocardial infarction (MI). Previous research has focused on the impact of blood-derived monocytes on cardiac repair. Here we examined the contribution of resident cavity macrophages located in the pericardial space adjacent to the site of injury. We found that disruption of the pericardial cavity accelerated maladaptive post-MI cardiac remodeling. Gata6+ macrophages in mouse pericardial fluid contributed to the reparative immune response. Following experimental MI, these macrophages invaded the epicardium and lost Gata6 expression but continued to perform anti-fibrotic functions. Loss of this specialized macrophage population enhanced interstitial fibrosis after ischemic injury. Gata6+ macrophages were present in human pericardial fluid, supporting the notion that this reparative function is relevant in human disease. Our findings uncover an immune cardioprotective role for the pericardial tissue compartment and argue for the reevaluation of surgical procedures that remove the pericardium.

Tissue-resident and memory properties of human T-cell and NK-cell subsets.

Efficient immune responses to invading pathogens are the result of the complex but coordinated synergy between a variety of cell types from both the innate and adaptive arms of the immune system. While adaptive and innate immune responses are highly complementary, some cells types within these two systems perform similar functions, underscoring the need for redundancy and increased flexibility. In this review, we will discuss the striking shared features of immunological memory and tissue residency recently discovered between T cells, a component of the adaptive immune system, and natural killer (NK) cells, members generally assigned to the innate compartment. Specifically, we will focus on the T-cell and NK-cell diversity at the single-cell level, on the discrete function of specific subsets, and on their anatomical location. Finally, we will discuss the implication of such diversity in the generation of long-term memory.

Human liver-resident CD56(bright)/CD16(neg) NK cells are retained within hepatic sinusoids via the engagement of CCR5 and CXCR6 pathways.

RATIONALE: The liver-specific natural killer (NK) cell population is critical for local innate immune responses, but the mechanisms that lead to their selective homing and the definition of their functionally relevance remain enigmatic. OBJECTIVES: We took advantage of the availability of healthy human liver to rigorously define the mechanisms regulating the homing of NK cells to liver and the repertoire of receptors that distinguish liver-resident NK (lr-NK) cells from circulating counterparts. FINDINGS: Nearly 50% of the entire liver NK cell population is composed of functionally relevant CD56(bright) lr-NK cells that localize within hepatic sinusoids. CD56(bright) lr-NK cells express CD69, CCR5 and CXCR6 and this unique repertoire of chemokine receptors is functionally critical as it determines selective migration in response to the chemotactic stimuli exerted by CCL3, CCL5 and CXCL16. Here, we also show that hepatic sinusoids express CCL3(pos) Kupffer cells, CXCL16(pos) endothelial cells and CCL5(pos) T and NK lymphocytes. The selective presence of these chemokines in sinusoidal spaces creates a unique tissue niche for lr-CD56(bright) NK cells that constitutively express CCR5 and CXCR6. CD56(bright) lr-NK cells co-exist with CD56(dim) conventional NK (c-NK) cells that are, interestingly, transcriptionally and phenotypically similar to their peripheral circulating counterparts. Indeed, CD56(dim) c-NK cells lack expression of CD69, CCR5, and CXCR6 but express selectins, integrins and CX3CR1. CONCLUSION: Our findings disclosing the phenotypic and functional differences between lr-Nk cells and c-NK cells are critical to distinguish liver-specific innate immune responses. Hence, any therapeutic attempts at modifying the large population of CD56(bright) lr-NK cells will require modification of hepatic CCR5 and CXCR6.

Dopamine inhibits the effector functions of activated NK cells via the upregulation of the D5 receptor.

Several lines of evidence indicate that dopamine (DA) plays a key role in the cross-talk between the nervous and immune systems. In this study, we disclose a novel immune-regulatory role for DA: inhibition of effector functions of activated NK lymphocytes via the selective upregulation of the D5 dopaminergic receptor in response to prolonged cell stimulation with rIL-2. Indeed, engagement of this D1-like inhibitory receptor following binding with DA suppresses NK cell proliferation and synthesis of IFN-γ. The inhibition of IFN-γ production occurs through blocking the repressor activity of the p50/c-REL dimer of the NF-κB complex. Indeed, the stimulation of the D5 receptor on rIL-2-activated NK cells inhibits the binding of p50 to the microRNA 29a promoter, thus inducing a de novo synthesis of this miRNA. In turn, the increased levels of microRNA 29a were inversely correlated with the ability of NK cells to produce IFN-γ. Taken together, our findings demonstrated that DA switches off activated NK cells, thus representing a checkpoint exerted by the nervous system to control the reactivity of these innate immune effectors in response to activation stimuli and to avoid the establishment of chronic and pathologic inflammatory processes.

Engagement of NKp30 on Vδ1 T cells induces the production of CCL3, CCL4, and CCL5 and suppresses HIV-1 replication.

Natural cytotoxicity receptors (NCRs) were originally identified as specific natural killer cell activating receptors that, on binding to their endogenous ligands, trigger the killing of tumor cell targets. We recently described the differentiation of a novel subset of NCR(+) Vδ1 T cells characterized by a remarkably high cytolytic potential against cancer cells. Here we demonstrate that the engagement of NKp30, one of the NCRs expressed de novo on Vδ1 T cells after stimulation, triggers the production of high levels of CCL3/MIP-1α, CCL4/ MIP-1ß, and CCL5/RANTES but not of CXCL12/SDF-1. In turn, this NKp30-induced secretion of cc-chemokines is able to significantly suppress the replication of a CCR5 tropic strain of HIV-1 in CD4(+)/CCR5(+) infected PM1 cell lines. This experimental evidence disclosing an unanticipated antiviral function of NCR(+) Vδ1 T cells opens new avenues for understanding the pathogenic role and for manipulating the function of γδ T cells in HIV-1 infection.

Sialic acid-binding Ig-like lectin-7 interacts with HIV-1 gp120 and facilitates infection of CD4pos T cells and macrophages.

BACKGROUND: Sialic acid-binding Ig-like lectin-7 (Siglec-7) expression is strongly reduced on natural killer (NK) cells from HIV-1 infected viremic patients. To investigate the mechanism(s) underlying this phenomenon, we hypothesized that Siglec-7 could contribute to the infection of CD4pos target cells following its interaction with HIV-1 envelope (Env) glycoprotein 120 (gp120). RESULTS: The ability of Siglec-7 to bind gp120 Env in a sialic acid-dependent manner facilitates the infection of both T cells and monocyte-derived macrophages (MDMs). Indeed, pre-incubation of HIV-1 with soluble Siglec-7 (sSiglec-7) increases the infection rate of CD4pos T cells, which do not constitutively express Siglec-7. Conversely, selective blockade of Siglec-7 markedly reduces the degree of HIV-1 infection in Siglec-7pos MDMs. Finally, the sSiglec-7 amount is increased in the serum of AIDS patients with high levels of HIV-1 viremia and inversely correlates with CD4pos T cell counts. CONCLUSIONS: Our results show that Siglec-7 binds HIV-1 and contributes to enhance the susceptibility to infection of CD4pos T cells and MDMs. This phenomenon plays a role in HIV-1 pathogenesis and in disease progression, as suggested by the inverse correlation between high serum level of sSiglec-7 and the low CD4pos T cell count observed in AIDS patients in the presence of chronic viral replication.

The role of natural killer cells in autoimmune liver disease: a comprehensive review.

Natural Killer (NK) cells are important players of the innate arm of the immune system and provide an early defense against pathogens and tumor-transformed cells. Peripheral blood NK (PB-NK) cells were first identified because of their ability to spontaneously kill tumor-cell targets in vitro without the need for specific antigen priming, which is the reason that they were named 'natural killer' cells. The characterization of NK cells in human tissues and body organs represented another important step forward to better understand their physiology and physiopathology. In this regard, many reports revealed over the past decade a differential anatomic distribution of NK cell subsets in several sites such as the intestine, lung, cervix, placenta and liver as well as in secondary lymphoid organs such as spleen, lymph nodes and tonsils. Among all these tissues, the liver is certainly unique as its parenchyma contains an unusually high number of infiltrating immune cells with 30-50% of total lymphocytes being NK cells. Given the constant liver intake of non-self antigens from the gastrointestinal tract via the portal vein, hepatic NK (H-NK) cells must retain a certain degree of tolerance in the context of their immune-surveillance against dangers to the host. Indeed, the breakdown of the tolerogenic state of the liver-associated immune system has been shown to induce autoimmunity. However, the role of NK cells during the course of autoimmune liver diseases is still being debated mainly because a complete characterization of H-NK cells normally resident in healthy human liver has not yet been fully disclosed. Furthermore, the differences in phenotype and functions between human and mouse H-NK cells often preclude translation of results obtained from murine models into experimental approaches to be performed in humans. Here, we provide an extensive characterization of the phenotype of H-NK cells physiologically resident in the human liver by both mentioning data available in literature and including a set of original results recently developed in our laboratory. We then review our current knowledge in regard to the contribution of H-NK cells in regulating local immune homeostasis and tolerance as well as in inducing the development of liver autoimmunity.

Differentiation of human peripheral blood Vδ1+ T cells expressing the natural cytotoxicity receptor NKp30 for recognition of lymphoid leukemia cells.

The success of cancer immunotherapy depends on productive tumor cell recognition by killer lymphocytes. γδ T cells are a population of innate-like lymphocytes endowed with strong, MHC-unrestricted cytotoxicity against tumor cells. This notwithstanding, we recently showed that a large proportion of human hematologic tumors is resistant to γδ peripheral blood lymphocytes (PBLs) activated with specific agonists to the highly prevalent Vγ9Vδ2 TCR. Although this probably constitutes an important limitation to current γδ T cell-mediated immunotherapy strategies, we describe here the differentiation of a novel subset of Vδ2(-) Vδ1(+) PBLs expressing natural cytotoxicity receptors (NCRs) that directly mediate killing of leukemia cell lines and chronic lymphocytic leukemia patient neoplastic cells. We show that Vδ1(+) T cells can be selectively induced to express NKp30, NKp44 and NKp46, through a process that requires functional phosphatidylinositol 3-kinase (PI-3K)/AKT signaling on stimulation with γ(c) cytokines and TCR agonists. The stable expression of NCRs is associated with high levels of granzyme B and enhanced cytotoxicity against lymphoid leukemia cells. Specific gain-of-function and loss-of-function experiments demonstrated that NKp30 makes the most important contribution to TCR-independent leukemia cell recognition. Thus, NKp30(+) Vδ1(+) T cells constitute a novel, inducible and specialized killer lymphocyte population with high potential for immunotherapy of human cancer.

The decreased expression of Siglec-7 represents an early marker of dysfunctional natural killer-cell subsets associated with high levels of HIV-1 viremia.

HIV-1 has developed several strategies to evade natural killer (NK)-cell antiviral functions. One of these mechanisms is the HIV-1-induced expansion of highly dysfunctional NK-cell subsets. Here, we analyze a large cohort of HIV-1-infected patients in early or chronic phases of infection, both cross-sectionally and longitudinally. We demonstrate that a striking decrease in the surface expression of sialic acid-binding immunoglobulin-like lectin 7 (Siglec-7) represents the earliest marker of the aberrant NK-cell dysregulation, which precedes the down-modulation of CD56 mostly occurring in patients with chronic HIV-1 viremia. The combined detection of Siglec-7 and CD56 allows the identification of 2 new pathologic NK-cell subsets expanded preferentially in early (Siglec-7-/CD56+) or chronic (Siglec-7-/CD56-) stages of HIV-1 infection. Remarkably, these phenotypic abnormalities were directly associated with progressive and distinct impairments of NK-cell functions. The aforementioned NK-cell aberrancies could be observed only in the presence of high levels of viral replication and not in patients with low or undetectable HIV-1 viremia, such as long-term nonprogressors or patients having undergone antiretroviral therapy. High frequencies of Siglec-7-/CD56+ and Siglec-7-/CD56- pathologic NK cells reflect the immune and clinical status of HIV-1 infection and can also track the effectiveness of therapy.

Peri-tumoural CD3+ Inflammation and Neutrophil-to-Lymphocyte Ratio Predict Overall Survival in Patients Affected by Colorectal Liver Metastases Treated with Surgery.

BACKGROUND: Systemic and local inflammation plays an important role in many cancers and colorectal liver metastases (CRLM). While the role of local immune response mediated by CD3+ tumour-infiltrating lymphocytes is well-established, new evidence on systemic inflammation and cancer, such as neutrophil-lymphocyte ratio (NLR), is emerging. The aim of this study is to seek an association between the CD3+ lymphocytes and NLR with patients' prognosis and possibly stratifying it accordingly. METHODS: From January 2005 to January 2013, 128 consecutive patients affected by CRLM and treated with chemotherapy and surgery were included in the study. Different cutoff levels were calculated with ROC curves for each of the biomarkers, and their relative outcome in terms of overall survival (OS) and recurrence-free survival (RFS) was determined. Associating the two biomarkers, three risk groups were determined: low risk (two protective biomarkers), intermediate risk (one protective biomarker) and high risk (no protective biomarker). RESULTS: After a median follow-up of 45 months, median OS and RFS were 44 and 9 months, respectively. For OS, 29 (22.66%), 59 (46.09%) and 40 (31.25%) patients were in the low, intermediate and high-risk groups, respectively. Adjusted Cox regression analysis showed an increased risk of death in the intermediate group (HR 2.67 p = 0.007 95% CI 1.31-5.42) and high-risk group (HR 2.86 p = 0.005 95% CI 1.37-5.99) compared to the low-risk group (reference). CONCLUSION: Systemic and local immune response index allows stratification of patients in different OS and RFS risk groups.

A Metagenomics Study on Hirschsprung's Disease Associated Enterocolitis: Biodiversity and Gut Microbial Homeostasis Depend on Resection Length and Patient's Clinical History.

Objectives: Since 2010, several researches demonstrated that microbiota dynamics correlate and can even predispose to Hirschsprung (HSCR) associated enterocolitis (HAEC). This study aims at assessing the structure of the microbiota of HSCR patients in relation to extent of aganglionosis and HAEC status. Methods: All consecutive HSCR patients admitted to Gaslini Institute (Genova, Italy) between May 2012 and November 2014 were enrolled. Institutional review board (IRB) approval was obtained. Stools were sampled and 16S rDNA V3-V4 regions were sequenced using the Illumina-MiSeq. Taxonomy assignments were performed using QIIME RDP. Alpha diversity indexes were analyzed by Shannon and Simpson Indexes, and Phylogenetic Diversity. Results: We enrolled 20 patients. Male to female ratio was 4:1. Six patients suffered from Total Colonic Aganglionosis (TCSA). Considering sample site (i.e., extent of aganglionosis), we confirmed the known relationship between sample site and both biodiversity and composition of intestinal microbiota. Patients with TCSA showed lower biodiversity and increased Proteobacteria/Bacteroidetes relative abundance ratio. When addressing biodiversity, composition and dynamics of TCSA patients we could not find any significant relationship with regard to HAEC occurrences. Conclusions: The composition of HAEC predisposing microbiota is specific to each patient. We could confirm that total colon resections can change the composition of intestinal microbiota and to dramatically reduce microbial diversity. The subsequent reduction of system robustness could expose TCSA patients to environmental microbes that might not be part of the normal microbiota. Future long-term studies should investigate both patients and their family environment, as well as their disease history.

Increased Infiltration of Natural Killer and T Cells in Colorectal Liver Metastases Improves Patient Overall Survival.

INTRODUCTION: Cancer heterogeneity and degree of intra-tumoral immune cells represent variables affecting overall survival (OS). The present study investigated the impact of natural killer (NK) and T cells infiltrating colorectal liver metastases (CLM) in patients undergoing hepatectomy after neoadjuvant chemotherapy. METHODS: The frequencies of intra-tumoral, marginal, and peritumoral CD3+ T and NKp46+ NK cells were determined for 121 patients. OS was assessed in relation to prognostic factors. RESULTS: At univariate analysis, several variables, including T and N of the primary tumor, metachronous CLM, radiological response, and higher density of intra-tumoral CD3+ T cell (>1%/mm2) and of NKp46+ NK cells (>1 cell/mm2), were associated with OS. Only increased frequencies of intra-tumoral CD3+ T cells (p = 0.005) and NKp46+ NK cells (p = 0.004) correlated with OS at multivariate analysis. The logistic regression revealed that metachronous CLM (OR = 2.781; p = 0.002), the use of an epidermal growth factor receptor inhibitor (OR = 3.891; p = 0.001), and radiological response (OR = 3.219; p = 0.001) were associated with higher infiltration of these cells. CONCLUSIONS: High frequencies of NK and T cells in response to chemotherapy predict OS in CLM patients. These findings provide important insights that can help physicians to choose the best treatment option and adopt more predictive follow-up strategies for patients with CLM.

Natural cytotoxicity receptors: broader expression patterns and functions in innate and adaptive immune cells.

Natural cytotoxicity receptors (NCRs) have been classically defined as activating receptors delivering potent signals to Natural Killer (NK) cells in order to lyze harmful cells and to produce inflammatory cytokines. Indeed, the elicitation of NK cell effector functions after engagement of NCRs with their ligands on tumor or virus infected cells without the need for prior antigen recognition is one of the main mechanisms that allow a rapid clearance of target cells. The three known NCRs, NKp46, NKp44, and NKp30, comprise a family of germ-line encoded Ig-like trans-membrane (TM) receptors. Until recently, NCRs were thought to be NK cell specific surface molecules, thus making it possible to easily distinguish NK cells from phenotypically similar cell types. Moreover, it has also been found that the surface expression of NKp46 is conserved on NK cells across mammalian species. This discovery allowed for the use of NKp46 as a reliable marker to identify NK cells in different animal models, a comparison that was not possible before due to the lack of a common and comprehensive receptor repertoire between different species. However, several studies over the recent few years indicated that NCR expression is not exclusively confined to NK cells, but is also present on populations of T as well as of NK-like lymphocytes. These insights raised the hypothesis that the induced expression of NCRs on certain T cell subsets is governed by defined mechanisms involving the engagement of the T cell receptor (TCR) and the action of pro-inflammatory cytokines. In turn, the acquisition of NCRs by T cell subsets is also associated with a functional independence of these Ig-like TM receptors from TCR signaling. Here, we review these novel findings with respect to NCR-mediated functions of NK cells and we also discuss the functional consequences of NCR expression on non-NK cells, with a particular focus on the T cell compartment.

Induction of RET dependent and independent pro-inflammatory programs in human peripheral blood mononuclear cells from Hirschsprung patients.

Hirschsprung disease (HSCR) is a rare congenital anomaly characterized by the absence of enteric ganglia in the distal intestinal tract. While classified as a multigenic disorder, the altered function of the RET tyrosine kinase receptor is responsible for the majority of the pathogenesis of HSCR. Recent evidence demonstrate a strong association between RET and the homeostasis of immune system. Here, we utilize a unique cohort of fifty HSCR patients to fully characterize the expression of RET receptor on both innate (monocytes and Natural Killer lymphocytes) and adaptive (B and T lymphocytes) human peripheral blood mononuclear cells (PBMCs) and to explore the role of RET signaling in the immune system. We show that the increased expression of RET receptor on immune cell subsets from HSCR individuals correlates with the presence of loss-of-function RET mutations. Moreover, we demonstrate that the engagement of RET on PBMCs induces the modulation of several inflammatory genes. In particular, RET stimulation with glial-cell line derived neurotrophic factor family (GDNF) and glycosyl-phosphatidylinositol membrane anchored co-receptor α1 (GFRα1) trigger the up-modulation of genes encoding either for chemokines (CCL20, CCL2, CCL3, CCL4, CCL7, CXCL1) and cytokines (IL-1ß, IL-6 and IL-8) and the down-regulation of chemokine/cytokine receptors (CCR2 and IL8-Rα). Although at different levels, the modulation of these "RET-dependent genes" occurs in both healthy donors and HSCR patients. We also describe another set of genes that, independently from RET stimulation, are differently regulated in healthy donors versus HSCR patients. Among these "RET-independent genes", there are CSF-1R, IL1-R1, IL1-R2 and TGFß-1, whose levels of transcripts were lower in HSCR patients compared to healthy donors, thus suggesting aberrancies of inflammatory responses at mucosal level. Overall our results demonstrate that immune system actively participates in the physiopathology of HSCR disease by modulating inflammatory programs that are either dependent or independent from RET signaling.

Mapping of NKp46(+) Cells in Healthy Human Lymphoid and Non-Lymphoid Tissues.

Understanding Natural Killer (NK) cell anatomical distribution is key to dissect the role of these unconventional lymphocytes in physiological and disease conditions. In mouse, NK cells have been detected in various lymphoid and non-lymphoid organs, while in humans the current knowledge of NK cell distribution at steady state is mainly restricted to lymphoid tissues. The translation to humans of findings obtained in mice is facilitated by the identification of NK cell markers conserved between these two species. The Natural Cytotoxicity Receptor (NCR) NKp46 is a marker of the NK cell lineage evolutionary conserved in mammals. In mice, NKp46 is also present on rare T cell subsets and on a subset of gut Innate Lymphoid Cells (ILCs) expressing the retinoic acid receptor-related orphan receptor γt (RORγt) transcription factor. Here, we documented the distribution and the phenotype of human NKp46(+) cells in lymphoid and non-lymphoid tissues isolated from healthy donors. Human NKp46(+) cells were found in splenic red pulp, in lymph nodes, in lungs, and gut lamina propria, thus mirroring mouse NKp46(+) cell distribution. We also identified a novel cell subset of CD56(dim)NKp46(low) cells that includes RORγt(+) ILCs with a lineage(-)CD94(-)CD117(bright)CD127(bright) phenotype. The use of NKp46 thus contributes to establish the basis for analyzing quantitative and qualitative changes of NK cell and ILC subsets in human diseases.

Engagement of Siglec-7 receptor induces a pro-inflammatory response selectively in monocytes.

Sialic acid binding immunoglobulin-like lectin-7 (Siglec-7) is a trans-membrane receptor carrying immunoreceptor tyrosine based inhibitory motifs (ITIMs) and delivering inhibitory signals upon ligation with sialylated glycans. This inhibitory function can be also targeted by several pathogens that have evolved to express sialic acids on their surface to escape host immune responses. Here, we demonstrate that cross-linking of Siglec-7 by a specific monoclonal antibody (mAb) induces a remarkably high production of IL-6, IL-1α, CCL4/MIP-1ß, IL-8 and TNF-α. Among the three immune cell subsets known to constitutively express Siglec-7, the production of these pro-inflammatory cytokines and chemokines selectively occurs in monocytes and not in Natural Killer or T lymphocytes. This Siglec-7-mediated activating function is associated with the phosphorylation of the extracellular signal-regulated kinase (ERK) pathway. The present study also shows that sialic acid-free Zymosan yeast particles are able to bind Siglec-7 on monocytes and that this interaction mimics the ability of the anti Siglec-7 mAb to induce the production of pro-inflammatory mediators. Indeed, blocking or silencing Siglec-7 in primary monocytes greatly reduced the production of inflammatory cytokines and chemokines in response to Zymosan, thus confirming that Siglec-7 participates in generating a monocyte-mediated inflammatory outcome following pathogen recognition. The presence of an activating form of Siglec-7 in monocytes provides the host with a new and alternative mechanism to encounter pathogens not expressing sialylated glycans.

Pathologic natural killer cell subset redistribution in HIV-1 infection: new insights in pathophysiology and clinical outcomes.

Several lines of evidence indicate that the interaction of HIV-1 with NK cells markedly affects host immune responses and leads to a defective control of the virus. Until recently, it was generally believed that the absolute number of total circulating NK cells was decreased during the course of chronic and active phases of HIV-1 infection and that this explained, at least in part, the defective NK cell antiviral activities. However, scientific advances made over recent years have changed this concept and have clarified that HIV-1 viremia is associated with a pathologic redistribution rather than an absolute decrease in the number of circulating NK cells. In particular, the expansion of dysfunctional Siglec-7(neg) and/or CD56(neg) NK cell subsets expressing an aberrant repertoire of activating and inhibitory receptors has been associated with functional impairments of NK cells and with clinical outcomes of HIV-1 disease. Indeed, these pathologic NK cell populations often comprise the majority of NK cells in the presence of high levels of chronic HIV-1 viremia. The reasons for these NK cell aberrancies remain unknown, as freshly purified CD4(neg) NK cells are not productively infected by HIV-1. Disclosing the cellular and molecular mechanisms underlying such dysfunctions represents an important challenge of biomedical research, also considering that the presence of a rare KIR3DS1(pos) NK cell population represents a protective factor against HIV-1 disease progression. In this review, we will summarize the recent updates regarding NK cell pathophysiology during the course of HIV-1 infection.

Chronic HIV-1 viremia reverses NKG2A/NKG2C ratio on natural killer cells in patients with human cytomegalovirus co-infection.

BACKGROUND: The HIV-1-induced expansion of highly dysfunctional natural killer (NK) cell subsets represents a strategy to evade NK cell antiviral functions. In this context, the loss of NKG2A NK cells in chronic viremic HIV-1-infected individuals has also been associated with a dramatic expansion of NKG2C NK cells. The viral trigger associated with high frequencies of NK cell subsets expressing NKG2C is still being debated. OBJECTIVE: To confirm that human cytomegalovirus (HCMV) infection is necessary for the expansion of NKG2C NK cells and to assess whether this phenomenon affects NKG2A/NKG2C ratio on NK cells in patients coinfected with HIV-1 and HCMV. DESIGN: We measured the expression of NKG2A and NKG2C on NK cells from 70 healthy donors, 21 early, 96 chronic and 27 long-term nonprogressor's (LTNPs) HIV-1-infected patients using a multicolor flow cytometric approach. HCMV infection was detected by titrating the serum levels of specific circulating antibodies. RESULTS: A significant expansion of NKG2C NK cells could be detected only in HCMV-infected patients. This phenotypic feature, together with the HIV-1-mediated downmodulation of NKG2A, pathologically reverses the ratio of NKG2A/NKG2C uniquely on NK cells from chronic viremic HIV-1-infected patients with a concomitant HCMV infection. The normalization of NKG2A/NKG2C ratio to values more than one occurred only after 24 months of suppression of HIV-1 replication following antiretroviral therapy. CONCLUSION: The inversion of NKG2A/NKG2C ratio characterizes advanced stages of HIV-1 disease in patients showing a concomitant HCMV infection. This NK cell immune parameter renders this cohort of patients distinguishable from LTNPs and early HIV-1-infected individuals.

Cutting edge: impaired glycosphingolipid trafficking and NKT cell development in mice lacking Niemann-Pick type C1 protein.

Niemann-Pick type C1 (NPC1) is a late endosomal/lysosomal transmembrane protein involved in the cellular transport of glycosphingolipids and cholesterol that is mutated in a majority of patients with Niemann-Pick C neurodegenerative disease. We found that NPC1-deficient mice lacked Valpha14-Jalpha18 NKT cells, a major population of CD1d-restricted T cells that is conserved in humans. NPC1-deficient mice also exhibited marked defects in the presentation of Sphingomonas cell wall Ags to NKT cells and in bacterial clearance in vivo. A synthetic fluorescent alpha-glycosylceramide analog of the Sphingomonas Ag trafficked to the lysosome of wild-type cells but accumulated in the late endosome of NPC1-deficient cells. These findings reveal a blockade of lipid trafficking between endosome and lysosome as a consequence of NPC1 deficiency and suggest a common mechanism for the defects in lipid presentation and development of Valpha14-Jalpha18 NKT cells.

Lysosomal glycosphingolipid recognition by NKT cells.

NKT cells represent a distinct lineage of T cells that coexpress a conserved alphabeta T cell receptor (TCR) and natural killer (NK) receptors. Although the TCR of NKT cells is characteristically autoreactive to CD1d, a lipid-presenting molecule, endogenous ligands for these cells have not been identified. We show that a lysosomal glycosphingolipid of previously unknown function, isoglobotrihexosylceramide (iGb3), is recognized both by mouse and human NKT cells. Impaired generation of lysosomal iGb3 in mice lacking beta-hexosaminidase b results in severe NKT cell deficiency, suggesting that this lipid also mediates development of NKT cells in the mouse. We suggest that expression of iGb3 in peripheral tissues may be involved in controlling NKT cell responses to infections and malignancy and in autoimmunity.