Mitogen activated protein kinases (MAPKs) including Erk, Jnk and p38 regulate diverse cellular functions, and are thought to be controlled by independent upstream activation cascades. Here we show that the sestrins bind to and co-ordinate simultaneous Erk, Jnk and p38 MAPK activation in T lymphocytes within a new immune-inhibitory complex (sestrin-MAPK Activation Complex; sMAC). Whereas sestrin ablation resulted in broad reconstitution of immune function in stressed T cells, inhibition of individual MAPKs only allowed partial functional recovery. T cells from old humans and mice were more likely to form the sMAC, and disruption of this complex restored antigen-specific functional responses in these cells. Correspondingly, sestrin deficiency or simultaneous inhibition of all three MAPKs enhanced vaccine responsiveness in old mice. Thus, disruption of sMAC provides a foundation for rejuvenating immunity during ageing.

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.

NK cells are the first line of defense against infected and transformed cells. Defective NK cell activity has been shown to increase susceptibility for viral infections and reduce tumor immune-surveillance. With age, the incidence of both infectious diseases and malignancy rises dramatically suggesting that impaired NK cell function might contribute to disease in these individuals. We found an increased frequency of NK cells with high expression of the inhibitory Killer Cell Lectin-like Receptor G1 (KLRG1) in individuals >70 years. The role of KLRG1 in ageing is not known and the mechanism of KLRG1-induced inhibition of NK cell function is not fully understood. Here we report that NK cells with high KLRG1 expression spontaneously activate the metabolic sensor AMP-activated protein kinase (AMPK) and that activation of AMPK negatively regulates NK cell function. Pre-existing AMPK activity is further amplified by ligation of KLRG1 in these cells, which leads to internalization of the receptor and allows interaction with AMPK. We show that KLRG1 activates AMPK by preventing its inhibitory de-phosphorylation by protein phosphatase PP2C rather than inducing de novo kinase activation. Finally, inhibition of either KLRG1 or AMPK prevented KLRG1-induced activation of AMPK and reduction in NK cell cytotoxicity, cytokine secretion, proliferation and telomerase expression. This novel signaling pathway links metabolic sensing, effector function and cell differentiation with inhibitory receptor signaling that may be exploited to enhance NK cell activity during ageing.

The in-depth understanding of skin resident memory CD8 T lymphocytes (T ) may help to uncover strategies for their manipulation during disease. We investigated isolated T from healthy human skin, which expressed the residence marker CD69, and compared them to circulating CD8 T cell populations from the same donors. There were significantly increased proportions of CD8 CD45RA CD27 T cells in the skin that expressed low levels of killer cell lectin-like receptor G1 (KLRG1), CD57, perforin and granzyme B. The CD8 T in skin were therefore phenotypically distinct from circulating CD8 CD45RA CD27 T cells that expressed high levels of all these molecules. Nevertheless, the activation of CD8 T with T cell receptor (TCR)/CD28 or interleukin (IL)-2 or IL-15 in vitro induced the expression of granzyme B. Blocking signalling through the inhibitory receptor programmed cell death 1 (PD)-1 further boosted granzyme B expression. A unique feature of some CD8 T cells was their ability to secrete high levels of tumour necrosis factor (TNF)-α and IL-2, a cytokine combination that was not seen frequently in circulating CD8 T cells. The cutaneous CD8 T are therefore diverse, and appear to be phenotypically and functionally distinct from circulating cells. Indeed, the surface receptors used to distinguish differentiation stages of blood T cells cannot be applied to T cells in the skin. Furthermore, the function of cutaneous T appears to be stringently controlled by environmental signals in situ.

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...

Latent Epstein-Barr virus (EBV) infection can clinically reactivate in immunosuppressed individuals causing lymphoproliferative disease and rarely hepatitis. In this study, we provide in vivo and in vitro evidence that Treponema pallidum infection can cause EBV reactivation with hepatitis in an immunocompetent patient. We report the diagnostic challenges and immunological findings of coinciding syphilis and EBV-associated hepatitis. Using an in vitro EBV-reactivation assay, we demonstrate that T pallidum reactivates latent EBV in a Toll-like receptor (TLR)2/B-cell receptor signaling-dependent manner. Epstein-Barr virus-associated reactivation or lymphoproliferation should be considered in infections with pathogens that activate TLR2.