How systemic metabolic alterations during acute infections impact immune cell function remains poorly understood. We found that acetate accumulates in the serum within hours of systemic bacterial infections and that these increased acetate concentrations are required for optimal memory CD8(+) T cell function in vitro and in vivo. Mechanistically, upon uptake by memory CD8(+) T cells, stress levels of acetate expanded the cellular acetyl-coenzyme A pool via ATP citrate lyase and promoted acetylation of the enzyme GAPDH. This context-dependent post-translational modification enhanced GAPDH activity, catalyzing glycolysis and thus boosting rapid memory CD8(+) T cell responses. Accordingly, in a murine Listeria monocytogenes model, transfer of acetate-augmented memory CD8(+) T cells exerted superior immune control compared to control cells. Our results demonstrate that increased systemic acetate concentrations are functionally integrated by CD8(+) T cells and translate into increased glycolytic and functional capacity. The immune system thus directly relates systemic metabolism with immune alertness.

SummaryT lymphocytes are a critical component of the adaptive immune system mediating protection against infection and malignancy, but also implicated in many immune pathologies. Upon recognition of specific antigens T cells clonally expand, traffic to inflamed sites and acquire effector functions, such as the capacity to kill infected and malignantly transformed cells and secrete cytokines to coordinate the immune response. These processes have significant bioenergetic and biosynthetic demands, which are met by dynamic changes in T-cell metabolism, specifically increases in glucose uptake and metabolism; mitochondrial function; amino acid uptake, and cholesterol and lipid synthesis. These metabolic changes are coordinate by key cellular kinases and transcription factors. Dysregulated T-cell metabolism is associated with impaired immunity in chronic infection and cancer and conversely with excessive T-cell activity in autoimmune and inflammatory pathologies. Here we review the key aspects of T-cell metabolism relevant to their immune function, and discuss evidence for the potential to therapeutically modulate T-cell metabolism in disease.

Glycolysis is linked to the rapid response of memory CD8 T cells, but the molecular and subcellular structural elements enabling enhanced glucose metabolism in nascent activated memory CD8 T cells are unknown. We found that rapid activation of protein kinase B (PKB or AKT) by mammalian target of rapamycin complex 2 (mTORC2) led to inhibition of glycogen synthase kinase 3β (GSK3β) at mitochondria-endoplasmic reticulum (ER) junctions. This enabled recruitment of hexokinase I (HK-I) to the voltage-dependent anion channel (VDAC) on mitochondria. Binding of HK-I to VDAC promoted respiration by facilitating metabolite flux into mitochondria. Glucose tracing pinpointed pyruvate oxidation in mitochondria, which was the metabolic requirement for rapid generation of interferon-γ (IFN-γ) in memory T cells. Subcellular organization of mTORC2-AKT-GSK3β at mitochondria-ER contact sites, promoting HK-I recruitment to VDAC, thus underpins the metabolic reprogramming needed for memory CD8 T cells to rapidly acquire effector function.

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Natural killer cells lacking expression of CD56 (CD56neg NK cells) have been described in chronic HIV and hepatitis C virus infection. Features and functions of CD56neg NK cells in the context of latent infection with CMV and / or EBV with age are not known. In a cohort of healthy donors >60 years of age, we found that co-infection with CMV and EBV drives expansion of CD56neg NK cells. Functionally, CD56neg NK cells displayed reduced cytotoxic capacity and IFN-γ production, a feature that was enhanced with CMV / EBV co-infection. Further, the frequency of CD56neg NK cells correlated with accumulation of end-stage-differentiated T cells and a reduced CD4 / CD8 T cell ratio, reflecting an immune risk profile. CD56neg NK cells had a mature phenotype characterized by low CD57 and KIR expression and lacked characteristics of cell senescence. No changes in their activating NK cell receptor expression, and no upregulation of the negative co-stimulation receptors PD-1 or TIM-3 were observed. In all, our data identify expansion of dysfunctional CD56neg NK cells in CMV+EBV+ elderly individuals suggesting that these cells may function as shape-shifters of cellular immunity and argue for a previously unrecognized role of EBV in mediating immune risk in the elderly.

Medulloblastoma (MB) comprises four molecularly and genetically distinct subgroups of embryonal brain tumors that develop in the cerebellum. MB mostly affects infants and children and is difficult to treat because of frequent dissemination of tumor cells within the leptomeningeal space. A potential promoter of cell dissemination is the c-Met proto-oncogene receptor tyrosine kinase, which is aberrantly expressed in many human tumors including MB. Database analysis showed that c-Met is highly expressed in the sonic hedgehog (SHH) subgroup and in a small subset of Group 3 and Group 4 MB tumors. Using a cell-based three-dimensional cell motility assay combined with live-cell imaging, we investigated whether the c-Met ligand HGF could drive dissemination of MB cells expressing high levels of c-Met, and determined downstream effector mechanisms of this process. We detected variable c-Met expression in different established human MB cell lines, and we found that in lines expressing high c-Met levels, HGF promoted cell dissemination and invasiveness. Specifically, HGF-induced c-Met activation enhanced the capability of the individual cells to migrate in a JNK-dependent manner. Additionally, we identified the Ser/Thr kinase MAP4K4 as a novel driver of c-Met-induced invasive cell dissemination. This increased invasive motility was due to MAP4K4 control of F-actin dynamics in structures required for migration and invasion. Thus, MAP4K4 couples growth factor signaling to actin cytoskeleton regulation in tumor cells, suggesting that MAP4K4 could present a promising novel target to be evaluated for treating growth factor-induced dissemination of MB tumors of different subgroups and of other human cancers.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-0784-2) contains supplementary material, which is available to authorized users.

Serum acetate increases upon systemic infection. Acutely, assimilation of acetate expands the capacity of memory CD8 + T cells to produce IFN-. Whether acetate modulates memory CD8 + T cell metabolism and function during pathogen re-encounter remains unexplored. Here we show that at sites of infection high acetate concentrations are being reached, yet memory CD8 + T cells shut down the acetate assimilating enzymes ACSS1 and ACSS2. Acetate, being thus largely excluded from incorporation into cellular metabolic pathways, now had different effects, namely (i) directly activating glutaminase, thereby augmenting glutaminolysis, cellular respiration and survival, and (ii) suppressing TCR-triggered calcium-flux, and consequently cell activation and effector cell function. In vivo, high acetate abundance at sites of infection improved pathogen clearance while reducing immunopathology. This indicates that, during different stages of the immune response, the same metabolite -acetateinduces distinct immunometabolic programs within the same cell type.

Whether screening the metabolic activity of immune cells facilitates discovery of molecular pathology remains unknown. Here we prospectively screened the extracellular acidification rate (ECAR) as a measure of glycolysis and the oxygen consumption rate (OCR) as a measure of mitochondrial respiration in B cells from patients with primary antibody deficiency (PAD). The highest OCR values were detected in three study participants with persistent polyclonal B cell lymphocytosis (PPBL). Exome sequencing identified germline mutations in SDHA, which encodes succinate dehydrogenase subunit A, in all three patients with PPBL. SDHA gain-of-function led to accumulation of fumarate in PPBL B cells, which engaged the KEAP1-Nrf2 system to drive the transcription of genes encoding inflammatory cytokines. In a single patient trial, blocking the activity of the cytokine IL-6 in vivo prevented systemic inflammation and ameliorated clinical disease. Overall, our study has identified pathological mitochondrial retrograde signaling as a disease modifier in PAD. 3 Primary immunodeficiency disorders (PIDs) are rare genetic syndromes arising from defects in the immune system 1. The majority of PID patients display primary antibody deficiency (PAD) that can develop due to B cell intrinsic defects 2. The causes and genetic background of PADs are complex and pathogenic mutations have been identified only in a minority of cases 3, 4, 5. PADs present with a spectrum of clinical problems, ranging from infections to autoinflammation, autoimmunity, lymphoproliferation and enteropathy. Non-infectious complications are typically unaffected by immunoglobulin replacement therapy and contribute to excess mortality 6. The spectrum of clinical presentation is broad even in patients harboring the same pathogenic mutations, pointing to disease modifiers shaping clinical features 6. Cellular metabolism governs immune cell function 7, 8, 9. Specifically, various facets of glycolysis and glutaminolysis impact the function of B cells 10, 11, 12, 13. Glutaminolysis can contribute to ATP production, and glutamine-derived α-ketoglutarate (α-KG) serves as an anaplerotic source of tricarboxylic acid (TCA) cycle metabolites 14. Mitochondrial oxidative phosphorylation (OxPhos) produces most of the ATP required for anabolic processes in immune cells 15. Non-bioenergetic features of mitochondria also regulate immune cell function. Production of mitochondrial reactive oxygen species (mROS) has been linked to the activation of the transcription factor NFAT in CD4 + T cells and to inhibition of the B cell antigen receptor (BCR) signaling in B cells 16, 17. In T cells, mitochondrial function and epigenetic remodeling are interlinked via pyruvate oxidation and conversion of pyruvate-derived citrate to acetyl-CoA, which is required for histone acetylation 18, 19. Metabolites of the TCA cycle can also directly activate (a-KG), or inhibit (fumarate, succinate) dioxygenases involved in histone and DNA demethylation, thus modulating transcriptional activity. This process of m...