LXR signaling couples sterol metabolism to proliferation in the acquired immune response.

Cholesterol is essential for membrane synthesis; however, the mechanisms that link cellular lipid metabolism to proliferation are incompletely understood. We demonstrate here that cellular cholesterol levels in dividing T cells are maintained in part through reciprocal regulation of the LXR and SREBP transcriptional programs. T cell activation triggers induction of the oxysterol-metabolizing enzyme SULT2B1, consequent suppression of the LXR pathway for cholesterol transport, and promotion of the SREBP pathway for cholesterol synthesis. Ligation of LXR during T cell activation inhibits mitogen-driven expansion, whereas loss of LXRbeta confers a proliferative advantage. Inactivation of the sterol transporter ABCG1 uncouples LXR signaling from proliferation, directly linking sterol homeostasis to the antiproliferative action of LXR. Mice lacking LXRbeta exhibit lymphoid hyperplasia and enhanced responses to antigenic challenge, indicating that proper regulation of LXR-dependent sterol metabolism is important for immune responses. These results implicate LXR signaling in a metabolic checkpoint that modulates cell proliferation and immunity.

Merocytic Dendritic Cells Compose a Conventional Dendritic Cell Subset with Low Metabolic Activity.

Conventional dendritic cells (cDCs) are arguably the most potent APCs that induce the activation of naive T cells in response to pathogens. In addition, at steady-state, cDCs help maintain immune tolerance. Two subsets of cDCs have been extensively characterized, namely cDC1 and cDC2, each contributing differently to immune responses. Recently, another dendritic cell (DC) subset, termed merocytic DCs (mcDCs), was defined. In contrast to both cDC1 and cDC2, mcDCs reverse T cell anergy, properties that could be exploited to potentiate cancer treatments. Yet, whether mcDCs represent an unconventional DC or a cDC subset remains to be defined. In this article, we further characterize mcDCs and find that they bear true characteristics of cDC subsets. Indeed, as for cDCs, mcDCs express the cDC-restricted transcription factor Zbtb46 and display very potent APC activity. In addition, mcDC population dynamics parallels that of cDC1 and cDC2 in both reconstitution kinetic studies and parabiotic mice. We next investigated their relatedness to cDC1 and cDC2 and demonstrate that mcDCs are not dependent on cDC1-related Irf8 and Batf3 transcription factors, are dependent on Irf4, a cDC2-specific transcription factor, and express a unique transcriptomic signature. Finally, we find that cDC1, cDC2, and mcDCs all present with different metabolic phenotypes, in which mcDCs exhibit the lowest glucose uptake activity and mcDC survival is the least affected by glycolysis inhibition. Defining the properties of mcDCs in mice may help identify a functionally equivalent subset in humans leading to the development of innovative cancer immunotherapies.

Development of a patient-reported outcome measure for patients who have recovered from a subarachnoid hemorrhage: the "questionnaire for the screening of symptoms in aneurysmal subarachnoid hemorrhage" (SOS-SAH).

BACKGROUND: Patients who have been successfully treated for an aneurysmal subarachnoid hemorrhage (aSAH) often retain multiple health complaints, including mood disorders, cognitive complaints, fatigue, and problems with social participation. These problems are not always fully addressed during hospital visits or in current outcome measures, such as the modified Rankin score and the Glasgow Outcome Scale. Here, we present the development of the "Questionnaire for the Screening of Symptoms in aneurysmal Subarachnoid Hemorrhage" (SOS-SAH), which screens for the self-reported symptoms of patients with mild disabilities. METHODS: During the development of the SOS-SAH we adhered to the PROM-cycle framework for the selection and implementation of patient-reported outcome measures (PROMs). The SOS-SAH was developed in an iterative process informed by a literature study. Patients and healthcare professionals were involved in the development process through participating in a working group, interviews, and a cognitive validation study. RESULTS AND CONCLUSIONS: Relevant patient-reported outcomes (PROs) were identified for patients with aSAH. The SOS-SAH was developed primarily using domains and items from existing PROMs and, if necessary, by developing new items. The SOS-SAH consists of 40 items and covers 14 domains: cognitive abilities, hypersensitivity to stimuli, anxiety, depression, fatigue, social roles, personality change, language, vision, taste, smell, hearing, headache, and sexual function. It also includes a proxy measurement for use by family members to assess cognitive functioning and personality change.

Loss of GTPase of immunity-associated protein 5 (Gimap5) promotes pathogenic CD4+ T-cell development and allergic airway disease.

BACKGROUND: GTPase of immunity-associated protein 5 (GIMAP5) is essential for lymphocyte homeostasis and survival. Recently, human GIMAP5 single nucleotide polymorphisms have been linked to an increased risk for asthma, whereas loss of Gimap5 in mice has been associated with severe CD4+ T cell-driven immune pathology. OBJECTIVE: We sought to identify the molecular and cellular mechanisms by which Gimap5 deficiency predisposes to allergic airway disease. METHODS: CD4+ T-cell polarization and development of pathogenic CD4+ T cells were assessed in Gimap5-deficient mice and a human patient with a GIMAP5 loss-of-function (LOF) mutation. House dust mite-induced airway inflammation was assessed by using a complete Gimap5 LOF (Gimap5sph/sph) and conditional Gimap5fl/flCd4Cre/ert2 mice. RESULTS: GIMAP5 LOF mutations in both mice and human subjects are associated with spontaneous polarization toward pathogenic TH17 and TH2 cells in vivo. Mechanistic studies in vitro reveal that impairment of Gimap5-deficient TH cell differentiation is associated with increased DNA damage, particularly during TH1-polarizing conditions. DNA damage in Gimap5-deficient CD4+ T cells could be controlled by TGF-ß, thereby promoting TH17 polarization. When challenged with house dust mite in vivo, Gimap5-deficient mice displayed an exacerbated asthma phenotype (inflammation and airway hyperresponsiveness), with increased development of TH2, TH17, and pathogenic TH17/TH2 cells. CONCLUSION: Activation of Gimap5-deficient CD4+ T cells is associated with increased DNA damage and reduced survival that can be overcome by TGF-ß. This leads to selective survival of pathogenic TH17 cells but also TH2 cells in human subjects and mice, ultimately promoting allergic airway disease.

Loss of Phagocytic and Antigen Cross-Presenting Capacity in Aging Dendritic Cells Is Associated with Mitochondrial Dysfunction.

Impaired functionality of dendritic cells (DCs) significantly contributes to decreased adaptive immune responses in aged hosts. The expression of MHC-peptide on the DC surface is the critical first step in T cell priming, but few studies have addressed the effect of aging on Ag acquisition, processing, and presentation by DCs. In this study, we show that aged murine DCs were less efficient in the cross-presentation of cell-associated Ag and subsequently in the cross-priming of CD8(+) T cells than were their young counterparts. The decreased cross-presentation was associated with a reduction in the frequency of CD8α DCs and merocytic (CD8α(-)CD11b(-))DCs that could endocytose cell-associated Ag, as well as the number and the size of the endocytosed particles in the DC that did internalize cell-associated materials. Mechanistically, phagocytic capacity has been associated with mitochondrial activity and membrane potential (Δψm). Aged DCs exhibited profound signs of mitochondrial dysfunction, illustrated by lower Δψm, reduced ATP turnover and coupling efficiency, decreased baseline oxidative phosphorylation, and greater proton leak and reactive oxygen species (ROS) production. Mimicking the aged metabolic phenotype in young DCs by pharmacologic manipulation indicated that the reductions in Δψm and ATP impeded the phagocytic capacity whereas ROS interfered with a later step in the cross-presentation process. Conversely, in vitro scavenging of ROS partially restored cross-presentation by aged DCs. Taken together, these data suggest that improvement of aged DC functionality might be feasible in the elderly by targeting metabolic dysfunction or its downstream sequelae, thereby opening new avenues for enhancing vaccine efficiency in this population.

Antigen cross-presentation by dendritic cell subsets: one general or all sergeants?

Antigen cross-presentation describes the process through which dendritic cells (DCs) acquire exogenous antigens for presentation on MHC class I molecules. The ability to cross-present has been thought of as a feature of specialized DC subsets. Emerging data, however, suggest that the cross-presenting ability of each DC subset is tuned by and dependent on several factors, such as DC location and activation status, and the type of antigen and inflammatory signals. Thus, we argue that capacity of cross-presentation is not an exclusive trait of one or several distinct DC subtypes, but rather a common feature of the DC family in both mice and humans. Understanding DC subset activation and antigen-presentation pathways might yield improved tools and targets to exploit the unique cross-presenting capacity of DCs in immunotherapy.

STING-mediated DNA sensing promotes antitumor and autoimmune responses to dying cells.

Adaptive immune responses to Ags released by dying cells play a critical role in the development of autoimmunity, allograft rejection, and spontaneous as well as therapy-induced tumor rejection. Although cell death in these situations is considered sterile, various reports have implicated type I IFNs as drivers of the ensuing adaptive immune response to cell-associated Ags. However, the mechanisms that underpin this type I IFN production are poorly defined. In this article, we show that dendritic cells (DCs) can uptake and sense nuclear DNA-associated entities released by dying cells to induce type I IFN. Remarkably, this molecular pathway requires STING, but not TLR or NLR function, and results in the activation of IRF3 in a TBK1-dependent manner. DCs are shown to depend on STING function in vivo to efficiently prime IFN-dependent CD8(+) T cell responses to tumor Ags. Furthermore, loss of STING activity in DCs impairs the generation of follicular Th cells and plasma cells, as well as anti-nuclear Abs, in an inducible model of systemic lupus erythematosus. These findings suggest that the STING pathway could be manipulated to enable the rational design of immunotherapies that enhance or diminish antitumor and autoimmune responses, respectively.

Dendritic Cells in Systemic Lupus Erythematosus: From Pathogenic Players to Therapeutic Tools.

System lupus erythematosus (SLE) is a multifactorial systemic autoimmune disease with a wide variety of presenting features. SLE is believed to result from dysregulated immune responses, loss of tolerance of CD4 T cells and B cells to ubiquitous self-antigens, and the subsequent production of anti-nuclear and other autoreactive antibodies. Recent research has associated lupus development with changes in the dendritic cell (DC) compartment, including altered DC subset frequency and localization, overactivation of mDCs and pDCs, and functional defects in DCs. Here we discuss the current knowledge on the role of DC dysfunction in SLE pathogenesis, with the focus on DCs as targets for interventional therapies.

Nab2 regulates secondary CD8+ T-cell responses through control of TRAIL expression.

CD4(+) Th cells are pivotal for the generation and maintenance of CD8(+) T-cell responses. "Helped" CD8(+) T cells receive signals during priming that prevent the induction of the proapoptotic molecule TNF-related apoptosis-inducing ligand (TRAIL) during reactivation, thereby enabling robust secondary expansion. Conversely, "helpless" CD8(+) T cells primed in the absence of Th induce TRAIL expression after restimulation and undergo activation-induced cell death. In the present study, we investigated the molecular basis for the differential regulation of TRAIL in helped versus helpless CD8(+) T cells by comparing their transcriptional profiles, and have identified a transcriptional corepressor, NGFI-A binding protein 2 (Nab2), that is selectively induced in helped CD8(+) T cells. Enforced expression of Nab2 prevents TRAIL induction after restimulation of primary helpless CD8(+) T cells, and expression of a dominant-negative form of Nab2 in helped CD8(+) T cells impairs their secondary proliferative response that is reversible by TRAIL blockade. Finally, we observe that the CD8(+) T-cell autocrine growth factor IL-2 coordinately increases Nab2 expression and decreases TRAIL expression. These findings identify Nab2 as a mediator of Th-dependent CD8(+) T-cell memory responses through the regulation of TRAIL and the promotion of secondary expansion, and suggest a mechanism through which this operates.

The value of the Charlson Co-morbidity Index in aneurysmal subarachnoid haemorrhage.

BACKGROUND: Several studies have included different co-morbid conditions in prediction models for stroke patients. For subarachnoid haemorrhage (SAH), it is not known whether the Charlson Co-morbidity Index (CCI) is associated with outcome. We evaluated if this index was associated with outcome in patients with ruptured intracerebral aneurysms. METHODS: The data of all consecutive aneurysmal SAH (aSAH) patients treated at the Radboudumc, Nijmegen, The Netherlands and entered in the database were retrospectively analysed. Clinical condition at admission was recorded using the WFNS (World Federation of Neurological Surgeons Grading System) grade was collected, as were the age and treatment modality. The burden of co-morbidity was retrospectively registered using the CCI. Outcome was dichotomised on the modified Rankin Scale (mRS; 0-2, favourable outcome; 3-6, unfavourable outcome). A binary logistic regression analysis was performed. RESULTS: Between 6th May 2008 and 31st July 2013, 457 patients were admitted because of non-traumatic SAH (aSAH). Seventy-seven (16.8 %) patients had no aneurysm. Of the 380 patients with aSAH, information on co-morbid conditions was available for 371 patients. Thirty-six of those 371 had no treatment because of: bad clinical condition in 34 (9.2 %), a non-treatable dissecting aneurysm in 1 (0.3 %) and the explicit wishes of another. Co-morbidity was present in 113 (31.5 %) patients. Binary logistic regression analysis revealed no added value of using the CCI in predicting the outcome (p = 0.91). CONCLUSIONS: This study reports that the CCI is not associated with the outcome classified on the mRS at 6 months in patients after aSAH. The CCI has no added value in case-mix correction.

Jinx, an MCMV susceptibility phenotype caused by disruption of Unc13d: a mouse model of type 3 familial hemophagocytic lymphohistiocytosis.

Mouse cytomegalovirus (MCMV) susceptibility often results from defects of natural killer (NK) cell function. Here we describe Jinx, an N-ethyl-N-nitrosourea-induced MCMV susceptibility mutation that permits unchecked proliferation of the virus, causing death. In Jinx homozygotes, activated NK cells and cytotoxic T lymphocytes (CTLs) fail to degranulate, although they retain the ability to produce cytokines, and cytokine levels are markedly elevated in the blood of infected mutant mice. Jinx was mapped to mouse chromosome 11 on a total of 246 meioses and confined to a 4.60-million basepair critical region encompassing 122 annotated genes. The phenotype was ascribed to the creation of a novel donor splice site in Unc13d, the mouse orthologue of human MUNC13-4, in which mutations cause type 3 familial hemophagocytic lymphohistiocytosis (FHL3), a fatal disease marked by massive hepatosplenomegaly, anemia, and thrombocytopenia. Jinx mice do not spontaneously develop clinical features of hemophagocytic lymphohistiocytosis (HLH), but do so when infected with lymphocytic choriomeningitis virus, exhibiting hyperactivation of CTLs and antigen-presenting cells, and inadequate restriction of viral proliferation. In contrast, neither Listeria monocytogenes nor MCMV induces the syndrome. In mice, the HLH phenotype is conditional, which suggests the existence of a specific infectious trigger of FHL3 in humans.

Plasmacytoid dendritic cells protect against atherosclerosis by tuning T-cell proliferation and activity.

RATIONALE: Unlike conventional dendritic cells, plasmacytoid DCs (PDC) are poor in antigen presentation and critical for type I interferon response. Though proposed to be present in human atherosclerotic lesions, their role in atherosclerosis remains elusive. OBJECTIVE: To investigate the role of PDC in atherosclerosis. METHODS AND RESULTS: We show that PDC are scarcely present in human atherosclerotic lesions and almost absent in mouse plaques. Surprisingly, PDC depletion by 120G8 mAb administration was seen to promote plaque T-cell accumulation and exacerbate lesion development and progression in LDLr⁻/⁻ mice. PDC depletion was accompanied by increased CD4⁺ T-cell proliferation, interferon-γ expression by splenic T cells, and plasma interferon-γ levels. Lymphoid tissue PDC from atherosclerotic mice showed increased indoleamine 2,3-dioxygenase (IDO) expression and IDO blockage abrogated the PDC suppressive effect on T-cell proliferation. CONCLUSIONS: Our data reveal a protective role for PDC in atherosclerosis, possibly by dampening T-cell proliferation and activity in peripheral lymphoid tissue, rendering PDC an interesting target for future therapeutic interventions.

B7-mediated costimulation of CD4 T cells constrains cytomegalovirus persistence.

Cytomegalovirus (CMV) utilizes multiple strategies to modulate immunity and promote lifelong, persistent/latent infection, including suppressing T cell activation pathways. Here we examined the role of B7 costimulatory ligands in establishing immune détente from both the host and virus perspectives. Mice lacking both B7.1 and B7.2 showed reduced early expansion of CMV-specific CD4 T cells, consequently allowing for enhanced levels of persistent virus replication. In turn, a CMV mutant lacking expression of the m138 and m147.5 gene products, which restrict B7.1 and B7.2 expression in infected antigen-presenting cells, induced a more robust CD4 T cell response and showed decreased persistence. Together, these data reveal a requirement for B7-mediated signaling in regulating the CMV-specific CD4 T cell response and establishing host-virus equilibrium.

Prolonged antigen storage endows merocytic dendritic cells with enhanced capacity to prime anti-tumor responses in tumor-bearing mice.

Tumor cell vaccination with irradiated autologous tumor cells is a promising approach to activate tumor-specific T cell responses without the need for tumor Ag identification. However, uptake of dying cells by dendritic cells (DCs) is generally a noninflammatory or tolerizing event to prevent the development of autoreactive immune responses. In this study, we describe the mechanisms that confer the potent T cell priming capacity of a recently identified a population of DCs (merocytic DCs [mcDCs]) that potently primes both CD8(+) and CD4(+) T cells to cell-associated Ags upon uptake of apoptotic cells. mcDCs acquired cell-associated materials through a process of merocytosis that is defined by the uptake of small particles that are stored in nonacidic compartments for prolonged periods, sustained Ag presentation, and the induction of type I IFN. T cells primed by mcDCs to cell-associated Ags exhibit increased primary expansion, enhanced effector function, and increased memory formation. By using transgenic T cell transfer models and endogenous models, we show that treatment of tumor-bearing mice with mcDCs that have been exposed to dying tumor cells results in tumor suppression and increased host survival through the activation of naive tumor-specific CD8(+) T cells as well as the reinvigoration of tumor-specific T cells that had been rendered nonresponsive by the tumor in vivo. The potent capacity of mcDCs to prime both CD4(+) and CD8(+) T cells to cell-associated Ags under immunosuppressive conditions makes this DC subset an attractive target for tumor therapies as well as interventional strategies for autoimmunity and transplantation.

Cutting edge: merocytic dendritic cells break T cell tolerance to beta cell antigens in nonobese diabetic mouse diabetes.

In type 1 diabetes, the breach of central and peripheral tolerance results in autoreactive T cells that destroy insulin-producing, pancreatic beta cells. In this study, we identify a critical subpopulation of dendritic cells responsible for mediating both the cross-presentation of islet Ags to CD8(+) T cells and the direct presentation of beta cell Ags to CD4(+) T cells. These cells, termed merocytic dendritic cells (mcDCs), are more numerous in the NOD mouse and, when Ag-loaded, rescue CD8(+) T cells from peripheral anergy and deletion while stimulating islet-reactive CD4(+) T cells. When purified from the pancreatic lymph nodes of overtly diabetic NOD mice, mcDCs break peripheral T cell tolerance to beta cells in vivo and induce rapid onset type 1 diabetes in the young NOD mouse. Thus, the mcDC subset appears to represent the long-sought APC responsible for breaking peripheral tolerance to beta cell Ags in vivo.

Breaking T cell tolerance to beta cell antigens by merocytic dendritic cells.

In type 1 diabetes (T1D), a break in central and peripheral tolerance results in antigen-specific T cells destroying insulin-producing, pancreatic beta cells. Herein, we discuss the critical sub-population of dendritic cells responsible for mediating both the cross-presentation of islet antigen to CD8(+) T cells and the direct presentation of beta cell antigen to CD4(+) T cells. These cells, termed merocytic dendritic cells (mcDC), are more numerous in non-obese diabetic (NOD), and antigen-loaded mcDC rescue CD8(+) T cells from peripheral anergy and deletion, and stimulate islet-reactive CD4(+) T cells. When purified from the pancreatic lymph nodes of overtly diabetic NOD mice, mcDC can break peripheral T cell tolerance to beta cell antigens in vivo and induce rapid onset T cell-mediated T1D in young NOD mouse. Thus, the mcDC subset appears to represent the long-sought critical antigen-presenting cell responsible for breaking peripheral tolerance to beta cell antigen in vivo.

Naturally-aged microglia exhibit phagocytic dysfunction accompanied by gene expression changes reflective of underlying neurologic disease.

Age-associated microglial dysfunction contributes to the accumulation of amyloid-ß (Aß) plaques in Alzheimer's disease. Although several studies have shown age-related declines in the phagocytic capacity of myeloid cells, relatively few have examined phagocytosis of normally aged microglia. Furthermore, much of the existing data on aging microglial function have been generated in accelerated genetic models of Alzheimer's disease. Here we found that naturally aged microglia phagocytosed less Aß over time. To gain a better understanding of such dysfunction, we assessed differences in gene expression between young and old microglia that either did or did not phagocytose Aß. Young microglia had both phagocytic and neuronal maintenance signatures indicative of normal microglial responses, whereas, old microglia, regardless of phagocytic status, exhibit signs of broad dysfunction reflective of underlying neurologic disease states. We also found downregulation of many phagocytic receptors on old microglia, including TREM2, an Aß phagocytic receptor. TREM2 protein expression was diminished in old microglia and loss of TREM2+ microglia was correlated with impaired Aß uptake, suggesting a mechanism for phagocytic dysfunction in old microglia. Combined, our work reveals that normally aged microglia have broad changes in gene expression, including defects in Aß phagocytosis that likely underlies the progression to neurologic disease.