Showing papers in "Journal of Experimental Medicine in 2016"

Immunometabolism governs dendritic cell and macrophage function

Abstract: Recent studies on intracellular metabolism in dendritic cells (DCs) and macrophages provide new insights on the functioning of these critical controllers of innate and adaptive immunity. Both cell types undergo profound metabolic reprogramming in response to environmental cues, such as hypoxia or nutrient alterations, but importantly also in response to danger signals and cytokines. Metabolites such as succinate and citrate have a direct impact on the functioning of macrophages. Immunogenicity and tolerogenicity of DCs is also determined by anabolic and catabolic processes, respectively. These findings provide new prospects for therapeutic manipulation in inflammatory diseases and cancer.

TREM2-mediated early microglial response limits diffusion and toxicity of amyloid plaques

Abstract: Triggering receptor expressed on myeloid cells 2 (TREM2) is a microglial receptor that recognizes changes in the lipid microenvironment, which may occur during amyloid β (Aβ) accumulation and neuronal degeneration in Alzheimer's disease (AD). Rare TREM2 variants that affect TREM2 function lead to an increased risk of developing AD. In murine models of AD, TREM2 deficiency prevents microglial clustering around Aβ deposits. However, the origin of myeloid cells surrounding amyloid and the impact of TREM2 on Aβ accumulation are a matter of debate. Using parabiosis, we found that amyloid-associated myeloid cells derive from brain-resident microglia rather than from recruitment of peripheral blood monocytes. To determine the impact of TREM2 deficiency on Aβ accumulation, we examined Aβ plaques in the 5XFAD model of AD at the onset of Aβ-related pathology. At this early time point, Aβ accumulation was similar in TREM2-deficient and -sufficient 5XFAD mice. However, in the absence of TREM2, Aβ plaques were not fully enclosed by microglia; they were more diffuse, less dense, and were associated with significantly greater neuritic damage. Thus, TREM2 protects from AD by enabling microglia to surround and alter Aβ plaque structure, thereby limiting neuritic damage.

The glycolytic enzyme PKM2 bridges metabolic and inflammatory dysfunction in coronary artery disease

Abstract: Abnormal glucose metabolism and enhanced oxidative stress accelerate cardiovascular disease, a chronic inflammatory condition causing high morbidity and mortality. Here, we report that in monocytes and macrophages of patients with atherosclerotic coronary artery disease (CAD), overutilization of glucose promotes excessive and prolonged production of the cytokines IL-6 and IL-1β, driving systemic and tissue inflammation. In patient-derived monocytes and macrophages, increased glucose uptake and glycolytic flux fuel the generation of mitochondrial reactive oxygen species, which in turn promote dimerization of the glycolytic enzyme pyruvate kinase M2 (PKM2) and enable its nuclear translocation. Nuclear PKM2 functions as a protein kinase that phosphorylates the transcription factor STAT3, thus boosting IL-6 and IL-1β production. Reducing glycolysis, scavenging superoxide and enforcing PKM2 tetramerization correct the proinflammatory phenotype of CAD macrophages. In essence, PKM2 serves a previously unidentified role as a molecular integrator of metabolic dysfunction, oxidative stress and tissue inflammation and represents a novel therapeutic target in cardiovascular disease.

Type I interferon-mediated monogenic autoinflammation: The type I interferonopathies, a conceptual overview.

Abstract: Type I interferon is a potent substance. As such, the induction, transmission, and resolution of the type I interferon–mediated immune response are tightly regulated. As defined, the type I interferonopathies represent discrete examples of a disturbance of the homeostatic control of this system caused by Mendelian mutations. Considering the complexity of the interferon response, the identification of further monogenic diseases belonging to this disease grouping seems likely, with the recognition of type I interferonopathies becoming of increasing clinical importance as treatment options are developed based on an understanding of disease pathology and innate immune signaling. Definition of the type I interferonopathies indicates that autoinflammation can be both interferon and noninterferon related, and that a primary disturbance of the innate immune system can “spill over” into autoimmunity in some cases. Indeed, that several non-Mendelian disorders, most particularly systemic lupus erythematosus and dermatomyositis, are also characterized by an up-regulation of type I interferon signaling suggests the possibility that insights derived from this work will have relevance to a broader field of clinical medicine.

Oxidized mitochondrial nucleoids released by neutrophils drive type I interferon production in human lupus.

Abstract: Autoantibodies against nucleic acids and excessive type I interferon (IFN) are hallmarks of human systemic lupus erythematosus (SLE). We previously reported that SLE neutrophils exposed to TLR7 agonist autoantibodies release interferogenic DNA, which we now demonstrate to be of mitochondrial origin. We further show that healthy human neutrophils do not complete mitophagy upon induction of mitochondrial damage. Rather, they extrude mitochondrial components, including DNA (mtDNA), devoid of oxidized (Ox) residues. When mtDNA undergoes oxidation, it is directly routed to lysosomes for degradation. This rerouting requires dissociation from the transcription factor A mitochondria (TFAM), a dual high-mobility group (HMG) protein involved in maintenance and compaction of the mitochondrial genome into nucleoids. Exposure of SLE neutrophils, or healthy IFN-primed neutrophils, to antiribonucleotide protein autoantibodies blocks TFAM phosphorylation, a necessary step for nucleoid dissociation. Consequently, Ox nucleoids accumulate within mitochondria and are eventually extruded as potent interferogenic complexes. In support of the in vivo relevance of this phenomenon, mitochondrial retention of Ox nucleoids is a feature of SLE blood neutrophils, and autoantibodies against Ox mtDNA are present in a fraction of patients. This pathway represents a novel therapeutic target in human SLE.

GPR91 senses extracellular succinate released from inflammatory macrophages and exacerbates rheumatoid arthritis

Abstract: When SUCNR1/GPR91-expressing macrophages are activated by inflammatory signals, they change their metabolism and accumulate succinate. In this study, we show that during this activation, macrophages release succinate into the extracellular milieu. They simultaneously up-regulate GPR91, which functions as an autocrine and paracrine sensor for extracellular succinate to enhance IL-1β production. GPR91-deficient mice lack this metabolic sensor and show reduced macrophage activation and production of IL-1β during antigen-induced arthritis. Succinate is abundant in synovial fluids from rheumatoid arthritis (RA) patients, and these fluids elicit IL-1β release from macrophages in a GPR91-dependent manner. Together, we reveal a GPR91/succinate-dependent feed-forward loop of macrophage activation and propose GPR91 antagonists as novel therapeutic principles to treat RA.

Unique pathological tau conformers from Alzheimer’s brains transmit tau pathology in nontransgenic mice

Abstract: Filamentous tau aggregates are hallmark lesions in numerous neurodegenerative diseases, including Alzheimer's disease (AD). Cell culture and animal studies showed that tau fibrils can undergo cell-to-cell transmission and seed aggregation of soluble tau, but this phenomenon was only robustly demonstrated in models overexpressing tau. In this study, we found that intracerebral inoculation of tau fibrils purified from AD brains (AD-tau), but not synthetic tau fibrils, resulted in the formation of abundant tau inclusions in anatomically connected brain regions in nontransgenic mice. Recombinant human tau seeded by AD-tau revealed unique conformational features that are distinct from synthetic tau fibrils, which could underlie the differential potency in seeding physiological levels of tau to aggregate. Therefore, our study establishes a mouse model of sporadic tauopathies and points to important differences between tau fibrils that are generated artificially and authentic ones that develop in AD brains.

Widespread transneuronal propagation of α-synucleinopathy triggered in olfactory bulb mimics prodromal Parkinson's disease

Abstract: Parkinson's disease (PD) is characterized by the progressive appearance of intraneuronal Lewy aggregates, which are primarily composed of misfolded α-synuclein (α-syn). The aggregates are believed to propagate via neural pathways following a stereotypical pattern, starting in the olfactory bulb (OB) and gut. We hypothesized that injection of fibrillar α-syn into the OB of wild-type mice would recreate the sequential progression of Lewy-like pathology, while triggering olfactory deficits. We demonstrate that injected α-syn fibrils recruit endogenous α-syn into pathological aggregates that spread transneuronally over several months, initially in the olfactory network and later in distant brain regions. The seeded inclusions contain posttranslationally modified α-syn that is Thioflavin S positive, indicative of amyloid fibrils. The spreading α-syn pathology induces progressive and specific olfactory deficits. Thus, we demonstrate that propagating α-syn pathology triggered in the OB is functionally detrimental. Collectively, we have created a mouse model of prodromal PD.

Reverse vaccinology 2.0: Human immunology instructs vaccine antigen design

Abstract: Traditionally, vaccines have been developed by cultivating infectious agents and isolating the inactivated whole pathogen or some of its purified components. 20 years ago, reverse vaccinology enabled vaccine discovery and design based on information deriving from the sequence of microbial genomes rather than via the growth of pathogens. Today, the high throughput discovery of protective human antibodies, sequencing of the B cell repertoire, and the increasing structural characterization of protective antigens and epitopes provide the molecular and mechanistic understanding to drive the discovery of novel vaccines that were previously impossible. We are entering a “reverse vaccinology 2.0” era.

Pyroptosis triggers pore-induced intracellular traps (PITs) that capture bacteria and lead to their clearance by efferocytosis

Abstract: Inflammasomes activate caspase-1 in response to cytosolic contamination or perturbation. This inflammatory caspase triggers the opening of the GSDMD pore in the plasma membrane, resulting in lytic cell death called pyroptosis. We had previously assumed that pyroptosis releases intracellular bacteria to the extracellular space. Here, we find that viable bacteria instead remain trapped within the cellular debris of pyroptotic macrophages. This trapping appears to be an inevitable consequence of how osmotic lysis ruptures the plasma membrane, and may also apply to necroptosis and some forms of nonprogrammed necrosis. Although membrane tears release soluble cytosolic contents, they are small enough to retain organelles and bacteria. We call this structure the pore-induced intracellular trap (PIT), which is conceptually parallel to the neutrophil extracellular trap (NET). The PIT coordinates innate immune responses via complement and scavenger receptors to drive recruitment of and efferocytosis by neutrophils. Ultimately, this secondary phagocyte kills the bacteria. Hence, caspase-1-driven pore-induced cell death triggers a multifaceted defense against intracellular bacteria facilitated by trapping the pathogen within the cellular debris. Bona fide intracellular bacterial pathogens, such as Salmonella, must prevent or delay pyroptosis to avoid being trapped in the PIT and subsequently killed by neutrophils.

Control of Foxp3 stability through modulation of TET activity.

Abstract: Ten-eleven translocation (TET) enzymes oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine and other oxidized methylcytosines, intermediates in DNA demethylation. In this study, we examine the role of TET proteins in regulating Foxp3, a transcription factor essential for the development and function of regulatory T cells (T reg cells), a distinct lineage of CD4(+) T cells that prevent autoimmunity and maintain immune homeostasis. We show that during T reg cell development in the thymus, TET proteins mediate the loss of 5mC in T reg cell-specific hypomethylated regions, including CNS1 and CNS2, intronic cis-regulatory elements in the Foxp3 locus. Similar to CNS2-deficient T reg cells, the stability of Foxp3 expression is markedly compromised in T reg cells from Tet2/Tet3 double-deficient mice. Vitamin C potentiates TET activity and acts through Tet2/Tet3 to increase the stability of Foxp3 expression in TGF-β-induced T reg cells. Our data suggest that targeting TET enzymes with small molecule activators such as vitamin C might increase induced T reg cell efficacy.

What does PD-L1 positive or negative mean?

Abstract: Expression of the programmed death-1 (PD-1) ligand 1 (PD-L1) is used to select patients and analyze responses to anti–PD-1/L1 antibodies. The expression of PD-L1 is regulated in different ways, which leads to a different significance of its presence or absence. PD-L1 positivity may be a result of genetic events leading to constitutive PD-L1 expression on cancer cells or inducible PD-L1 expression on cancer cells and noncancer cells in response to a T cell infiltrate. A tumor may be PD-L1 negative because it has no T cell infiltrate, which may be reversed with an immune response. Finally, a tumor that is unable to express PD-L1 because of a genetic event will always be negative for PD-L1 on cancer cells.

IL-12 drives functional plasticity of human group 2 innate lymphoid cells

Abstract: Group 2 innate lymphoid cells (ILC2) include IL-5– and IL-13–producing CRTh2+CD127+ cells that are implicated in early protective immunity at mucosal surfaces. Whereas functional plasticity has been demonstrated for both human and mouse ILC3 subsets that can reversibly give rise to IFN-γ–producing ILC1, plasticity of human or mouse ILC2 has not been shown. Here, we analyze the phenotypic and functional heterogeneity of human peripheral blood ILC2. Although subsets of human CRTh2+ ILC2 differentially express CD117 (c-kit receptor), some ILC2 surface phenotypes are unstable and can be modulated in vitro. Surprisingly, human IL-13+ ILC2 can acquire the capacity to produce IFN-γ, thereby generating plastic ILC2. ILC2 cultures demonstrated that IFN-γ+ ILC2 clones could be derived and were stably associated with increased T-BET expression. The inductive mechanism for ILC2 plasticity was mapped to the IL-12–IL-12R signaling pathway and was confirmed through analysis of patients with Mendelian susceptibility to mycobacterial disease due to IL-12Rβ1 deficiencies that failed to generate plastic ILC2. We also detected IL-13+IFN-γ+ ILC2 ex vivo in intestinal samples from Crohn’s disease patients. These results demonstrate cytokine production plasticity for human ILC2 and further suggest that environmental cues can dictate ILC phenotype and function for these tissue-resident innate effector cells.

Tumor macrophages are pivotal constructors of tumor collagenous matrix.

Abstract: Tumor-associated macrophages (TAMs) promote tumor development, invasion, and dissemination by various mechanisms. In this study, using an orthotopic colorectal cancer (CRC) model, we found that monocyte-derived TAMs advance tumor development by the remodeling of its extracellular matrix (ECM) composition and structure. Unbiased transcriptomic and proteomic analyses of (a) TAM-abundant and -deficient tumor tissues and (b) sorted tumor-associated and -resident colonic macrophage subpopulations defined a distinct TAM-induced ECM molecular signature composed of an ensemble of matricellular proteins and remodeling enzymes they provide to the tumor microenvironment. Remarkably, many of these ECM proteins are specifically increased in human CRC versus healthy colon. Specifically, we demonstrate that although differentiating into TAMs, monocytes up-regulate matrix-remodeling programs associated with the synthesis and assembly of collagenous ECM, specifically collagen types I, VI, and XIV. This finding was further established by advanced imaging showing that TAMs instruct the deposition, cross-linking, and linearization of collagen fibers during tumor development, especially at areas of tumor invasiveness. Finally, we show that cancer-associated fibroblasts are significantly outnumbered by TAMs in this model and that their expression of collagen XIV and I is reduced by TAM deficiency. Here, we outline a novel TAM protumoral function associated with building of the collagenous ECM niche.

Human USP18 deficiency underlies type 1 interferonopathy leading to severe pseudo-TORCH syndrome.

Abstract: Pseudo-TORCH syndrome (PTS) is characterized by microcephaly, enlarged ventricles, cerebral calcification, and, occasionally, by systemic features at birth resembling the sequelae of congenital infection but in the absence of an infectious agent. Genetic defects resulting in activation of type 1 interferon (IFN) responses have been documented to cause Aicardi-Goutieres syndrome, which is a cause of PTS. Ubiquitin-specific peptidase 18 (USP18) is a key negative regulator of type I IFN signaling. In this study, we identified loss-of-function recessive mutations of USP18 in five PTS patients from two unrelated families. Ex vivo brain autopsy material demonstrated innate immune inflammation with calcification and polymicrogyria. In vitro, patient fibroblasts displayed severely enhanced IFN-induced inflammation, which was completely rescued by lentiviral transduction of USP18. These findings add USP18 deficiency to the list of genetic disorders collectively termed type I interferonopathies. Moreover, USP18 deficiency represents the first genetic disorder of PTS caused by dysregulation of the response to type I IFNs. Therapeutically, this places USP18 as a promising target not only for genetic but also acquired IFN-mediated CNS disorders.

Gut dysbiosis impairs recovery after spinal cord injury

Abstract: The trillions of microbes that exist in the gastrointestinal tract have emerged as pivotal regulators of mammalian development and physiology. Disruption of this gut microbiome, a process known as dysbiosis, causes or exacerbates various diseases, but whether gut dysbiosis affects recovery of neurological function or lesion pathology after traumatic spinal cord injury (SCI) is unknown. Data in this study show that SCI increases intestinal permeability and bacterial translocation from the gut. These changes are associated with immune cell activation in gut-associated lymphoid tissues (GALTs) and significant changes in the composition of both major and minor gut bacterial taxa. Postinjury changes in gut microbiota persist for at least one month and predict the magnitude of locomotor impairment. Experimental induction of gut dysbiosis in naive mice before SCI (e.g., via oral delivery of broad-spectrum antibiotics) exacerbates neurological impairment and spinal cord pathology after SCI. Conversely, feeding SCI mice commercial probiotics (VSL#3) enriched with lactic acid-producing bacteria triggers a protective immune response in GALTs and confers neuroprotection with improved locomotor recovery. Our data reveal a previously unknown role for the gut microbiota in influencing recovery of neurological function and neuropathology after SCI.

Specific niches for lung-resident memory CD8+ T cells at the site of tissue regeneration enable CD69-independent maintenance.

Abstract: CD8+ tissue-resident memory T cells (TRM cells) reside permanently in nonlymphoid tissues and provide a first line of protection against invading pathogens. However, the precise localization of CD8+ TRM cells in the lung, which physiologically consists of a markedly scant interstitium compared with other mucosa, remains unclear. In this study, we show that lung CD8+ TRM cells localize predominantly in specific niches created at the site of regeneration after tissue injury, whereas peripheral tissue-circulating CD8+ effector memory T cells (TEM cells) are widely but sparsely distributed in unaffected areas. Although CD69 inhibited sphingosine 1-phosphate receptor 1-mediated egress of CD8+ T cells immediately after their recruitment into lung tissues, such inhibition was not required for the retention of cells in the TRM niches. Furthermore, despite rigid segregation of TEM cells from the TRM niche, prime-pull strategy with cognate antigen enabled the conversion from TEM cells to TRM cells by creating de novo TRM niches. Such damage site-specific localization of CD8+ TRM cells may be important for efficient protection against secondary infections by respiratory pathogens.

Psoriatic T cells recognize neolipid antigens generated by mast cell phospholipase delivered by exosomes and presented by CD1a.

Abstract: Psoriasis is a chronic inflammatory skin disease associated with a T helper 17 response. Yet, it has proved challenging to identify relevant peptide-based T cell antigens. Antigen-presenting Langerhans cells show a differential migration phenotype in psoriatic lesions and express constitutively high levels of CD1a, which presents lipid antigens to T cells. In addition, phospholipase A2 (PLA2) is highly expressed in psoriatic lesions and is known to generate neolipid skin antigens for recognition by CD1a-reactive T cells. In this study, we observed expression of a cytoplasmic PLA2 (PLA2G4D) in psoriatic mast cells but, unexpectedly, also found PLA2G4D activity to be extracellular. This was explained by IFN-α–induced mast cell release of exosomes, which transferred cytoplasmic PLA2 activity to neighboring CD1a-expressing cells. This led to the generation of neolipid antigens and subsequent recognition by lipid-specific CD1a-reactive T cells inducing production of IL-22 and IL-17A. Circulating and skin-derived T cells from patients with psoriasis showed elevated PLA2G4D responsiveness compared with healthy controls. Overall, these data present an alternative model of psoriasis pathogenesis in which lipid-specific CD1a-reactive T cells contribute to psoriatic inflammation. The findings suggest that PLA2 inhibition or CD1a blockade may have therapeutic potential for psoriasis.

Ubiquitin in the activation and attenuation of innate antiviral immunity.

Abstract: Viral infection activates danger signals that are transmitted via the retinoic acid–inducible gene 1–like receptor (RLR), nucleotide-binding oligomerization domain-like receptor (NLR), and Toll-like receptor (TLR) protein signaling cascades. This places host cells in an antiviral posture by up-regulating antiviral cytokines including type-I interferon (IFN-I). Ubiquitin modifications and cross-talk between proteins within these signaling cascades potentiate IFN-I expression, and inversely, a growing number of viruses are found to weaponize the ubiquitin modification system to suppress IFN-I. Here we review how host- and virus-directed ubiquitin modification of proteins in the RLR, NLR, and TLR antiviral signaling cascades modulate IFN-I expression.

Local antigen in nonlymphoid tissue promotes resident memory CD8+ T cell formation during viral infection

Abstract: Tissue-resident memory (Trm) CD8(+) T cells are functionally distinct from their circulating counterparts and are potent mediators of host protection against reinfection. Whether local recognition of antigen in nonlymphoid tissues during infection can impact the formation of Trm populations remains unresolved. Using skin infections with vaccinia virus (VacV)-expressing model antigens, we found that local antigen recognition had a profound impact on Trm formation. Activated CD8(+) T cells trafficked to VacV-infected skin in an inflammation-dependent, but antigen-independent, manner. However, after viral clearance, there was a subsequent ∼50-fold increase in Trm formation when antigen was present in the tissue microenvironment. Secondary antigen stimulation in nonlymphoid tissue caused CD8(+) T cells to rapidly express CD69 and be retained at the site of infection. Finally, Trm CD8(+) T cells that formed during VacV infection in an antigen-dependent manner became potent stimulators of localized antigen-specific inflammatory responses in the skin. Thus, our studies indicate that the presence of antigen in the nonlymphoid tissue microenvironment plays a critical role in the formation of functional Trm CD8(+) T cell populations, a finding with relevance for both vaccine design and prevention of inflammatory disorders.

RNase H2 catalytic core Aicardi-Goutières syndrome–related mutant invokes cGAS–STING innate immune-sensing pathway in mice

Abstract: The neuroinflammatory autoimmune disease Aicardi-Goutieres syndrome (AGS) develops from mutations in genes encoding several nucleotide-processing proteins, including RNase H2. Defective RNase H2 may induce accumulation of self-nucleic acid species that trigger chronic type I interferon and inflammatory responses, leading to AGS pathology. We created a knock-in mouse model with an RNase H2 AGS mutation in a highly conserved residue of the catalytic subunit, Rnaseh2a(G37S/G37S) (G37S), to understand disease pathology. G37S homozygotes are perinatal lethal, in contrast to the early embryonic lethality previously reported for Rnaseh2b- or Rnaseh2c-null mice. Importantly, we found that the G37S mutation led to increased expression of interferon-stimulated genes dependent on the cGAS-STING signaling pathway. Ablation of STING in the G37S mice results in partial rescue of the perinatal lethality, with viable mice exhibiting white spotting on their ventral surface. We believe that the G37S knock-in mouse provides an excellent animal model for studying RNASEH2-associated autoimmune diseases.

The macrophage IRF8/IRF1 regulome is required for protection against infections and is associated with chronic inflammation.

Abstract: IRF8 and IRF1 are transcriptional regulators that play critical roles in the development and function of myeloid cells, including activation of macrophages by proinflammatory signals such as interferon-γ (IFN-γ). Loss of IRF8 or IRF1 function causes severe susceptibility to infections in mice and in humans. We used chromatin immunoprecipitation sequencing and RNA sequencing in wild type and in IRF8 and IRF1 mutant primary macrophages to systematically catalog all of the genes bound by (cistromes) and transcriptionally activated by (regulomes) IRF8, IRF1, PU.1, and STAT1, including modulation of epigenetic histone marks. Of the seven binding combinations identified, two (cluster 1 [IRF8/IRF1/STAT1/PU.1] and cluster 5 [IRF1/STAT1/PU.1]) were found to have a major role in controlling macrophage transcriptional programs both at the basal level and after IFN-γ activation. They direct the expression of a set of genes, the IRF8/IRF1 regulome, that play critical roles in host inflammatory and antimicrobial defenses in mouse models of neuroinflammation and of pulmonary tuberculosis, respectively. In addition, this IRF8/IRF1 regulome is enriched for genes mutated in human primary immunodeficiencies and with loci associated with several inflammatory diseases in humans.

Identification and treatment of the Staphylococcus aureus reservoir in vivo

Abstract: Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is reaching epidemic proportions causing morbidity, mortality, and chronic disease due to relapses, suggesting an intracellular reservoir. Using spinning-disk confocal intravital microscopy to track MRSA-GFP in vivo, we identified that within minutes after intravenous infection MRSA is primarily sequestered and killed by intravascular Kupffer cells (KCs) in the liver. However, a minority of the Staphylococci overcome the KC's antimicrobial defenses. These bacteria survive and proliferate for many days within this intracellular niche, where they remain undetected by recruited neutrophils. Over time, the KCs lyse, releasing bacteria into the circulation, enabling dissemination to other organs such as the kidneys. Vancomycin, the antibiotic of choice to treat MRSA bacteremia, could not penetrate the KCs to eradicate intracellular MRSA. However, based on the intravascular location of these specific macrophages, we designed a liposomal formulation of vancomycin that is efficiently taken up by KCs and diminished the intracellular MRSA. Targeting the source of the reservoir dramatically protected the liver but also dissemination to other organs, and prevented mortality. This vancomycin formulation strategy could help treat patients with Staphylococcal bacteremia without a need for novel antibiotics by targeting the previously inaccessible intracellular reservoir in KCs.

B cell IFN-γ receptor signaling promotes autoimmune germinal centers via cell-intrinsic induction of BCL-6

Abstract: Dysregulated germinal center (GC) responses are implicated in the pathogenesis of human autoimmune diseases, including systemic lupus erythematosus (SLE). Although both type 1 and type 2 interferons (IFNs) are involved in lupus pathogenesis, their respective impacts on the establishment of autoimmune GCs has not been addressed. In this study, using a chimeric model of B cell-driven autoimmunity, we demonstrate that B cell type 1 IFN receptor signals accelerate, but are not required for, lupus development. In contrast, B cells functioning as antigen-presenting cells initiate CD4(+) T cell activation and IFN-γ production, and strikingly, B cell-intrinsic deletion of the IFN-γ receptor (IFN-γR) abrogates autoimmune GCs, class-switched autoantibodies (auto-Abs), and systemic autoimmunity. Mechanistically, although IFN-γR signals increase B cell T-bet expression, B cell-intrinsic deletion of T-bet exerts an isolated impact on class-switch recombination to pathogenic auto-Ab subclasses without impacting GC development. Rather, in both mouse and human B cells, IFN-γ synergized with B cell receptor, toll-like receptor, and/or CD40 activation signals to promote cell-intrinsic expression of the GC master transcription factor, B cell lymphoma 6 protein. Our combined findings identify a novel B cell-intrinsic mechanism whereby IFN signals promote lupus pathogenesis, implicating this pathway as a potential therapeutic target in SLE.

Identification of CD112R as a novel checkpoint for human T cells

Abstract: T cell immunoglobulin and ITIM domain (TIGIT) and CD226 emerge as a novel T cell cosignaling pathway in which CD226 and TIGIT serve as costimulatory and coinhibitory receptors, respectively, for the ligands CD155 and CD112. In this study, we describe CD112R, a member of poliovirus receptor–like proteins, as a new coinhibitory receptor for human T cells. CD112R is preferentially expressed on T cells and inhibits T cell receptor–mediated signals. We further identify that CD112, widely expressed on antigen-presenting cells and tumor cells, is the ligand for CD112R with high affinity. CD112R competes with CD226 to bind to CD112. Disrupting the CD112R–CD112 interaction enhances human T cell response. Our experiments identify CD112R as a novel checkpoint for human T cells via interaction with CD112.

Toxoplasma gondii TgIST co-opts host chromatin repressors dampening STAT1-dependent gene regulation and IFN-γ-mediated host defenses.

Abstract: An early hallmark of Toxoplasma gondii infection is the rapid control of the parasite population by a potent multifaceted innate immune response that engages resident and homing immune cells along with pro- and counter-inflammatory cytokines. In this context, IFN-γ activates a variety of T. gondii-targeting activities in immune and nonimmune cells but can also contribute to host immune pathology. T. gondii has evolved mechanisms to timely counteract the host IFN-γ defenses by interfering with the transcription of IFN-γ-stimulated genes. We now have identified TgIST (T. gondii inhibitor of STAT1 transcriptional activity) as a critical molecular switch that is secreted by intracellular parasites and traffics to the host cell nucleus where it inhibits STAT1-dependent proinflammatory gene expression. We show that TgIST not only sequesters STAT1 on dedicated loci but also promotes shaping of a nonpermissive chromatin through its capacity to recruit the nucleosome remodeling deacetylase (NuRD) transcriptional repressor. We found that during mice acute infection, TgIST-deficient parasites are rapidly eliminated by the homing Gr1(+) inflammatory monocytes, thus highlighting the protective role of TgIST against IFN-γ-mediated killing. By uncovering TgIST functions, this study brings novel evidence on how T. gondii has devised a molecular weapon of choice to take control over a ubiquitous immune gene expression mechanism in metazoans, as a way to promote long-term parasitism.

Brain-resident memory T cells represent an autonomous cytotoxic barrier to viral infection

Abstract: Tissue-resident memory T cells (TRM) persist at sites of prior infection and have been shown to enhance pathogen clearance by recruiting circulating immune cells and providing bystander activation. Here, we characterize the functioning of brain-resident memory T cells (bTRM) in an animal model of viral infection. bTRM were subject to spontaneous homeostatic proliferation and were largely refractory to systemic immune cell depletion. After viral reinfection in mice, bTRM rapidly acquired cytotoxic effector function and prevented fatal brain infection, even in the absence of circulating CD8(+) memory T cells. Presentation of cognate antigen on MHC-I was essential for bTRM-mediated protective immunity, which involved perforin- and IFN-γ-dependent effector mechanisms. These findings identify bTRM as an organ-autonomous defense system serving as a paradigm for TRM functioning as a self-sufficient first line of adaptive immunity.

Changes in insulin and insulin signaling in Alzheimer's disease: cause or consequence?

Abstract: Individuals with type 2 diabetes have an increased risk for developing Alzheimer's disease (AD), although the causal relationship remains poorly understood. Alterations in insulin signaling (IS) are reported in the AD brain. Moreover, oligomers/fibrils of amyloid-β (Aβ) can lead to neuronal insulin resistance and intranasal insulin is being explored as a potential therapy for AD. Conversely, elevated insulin levels (ins) are found in AD patients and high insulin has been reported to increase Aβ levels and tau phosphorylation, which could exacerbate AD pathology. Herein, we explore whether changes in ins and IS are a cause or consequence of AD.

Anti-TNF drives regulatory T cell expansion by paradoxically promoting membrane TNF–TNF-RII binding in rheumatoid arthritis

Abstract: The interplay between inflammatory and regulatory pathways orchestrates an effective immune response that provides protection from pathogens while limiting injury to host tissue. Tumor necrosis factor (TNF) is a pivotal inflammatory cytokine, but there is conflicting evidence as to whether it boosts or inhibits regulatory T cells (T reg cells). In this study, we show that the therapeutic anti-TNF antibody adalimumab, but not the soluble TNF receptor etanercept, paradoxically promoted the interaction between monocytes and T reg cells isolated from patients with rheumatoid arthritis (RA). Adalimumab bound to monocyte membrane TNF from RA patients and unexpectedly enhanced its expression and its binding to TNF-RII expressed on T reg cells. As a consequence, adalimumab expanded functional Foxp3(+) T reg cells equipped to suppress Th17 cells through an IL-2/STAT5-dependent mechanism. Our data not only highlight the beneficial effect of membrane TNF on T reg cell numbers during chronic inflammation, but in addition reveal how a therapeutic antibody that is thought to act by simply blocking its target can enhance the regulatory properties of this proinflammatory cytokine.

Type I IFN promotes NK cell expansion during viral infection by protecting NK cells against fratricide

Abstract: Type I interferon (IFN) is crucial in host antiviral defense. Previous studies have described the pleiotropic role of type I IFNs on innate and adaptive immune cells during viral infection. Here, we demonstrate that natural killer (NK) cells from mice lacking the type I IFN-α receptor (Ifnar(-/-)) or STAT1 (which signals downstream of IFNAR) are defective in expansion and memory cell formation after mouse cytomegalovirus (MCMV) infection. Despite comparable proliferation, Ifnar(-/-) NK cells showed diminished protection against MCMV infection and exhibited more apoptosis compared with wild-type NK cells. Furthermore, we show that Ifnar(-/-) NK cells express increased levels of NK group 2 member D (NKG2D) ligands during viral infection and are susceptible to NK cell-mediated fratricide in a perforin- and NKG2D-dependent manner. Adoptive transfer of Ifnar(-/-) NK cells into NK cell-deficient mice reverses the defect in survival and expansion. Our study reveals a novel type I IFN-dependent mechanism by which NK cells evade mechanisms of cell death after viral infection.