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The role of mitochondrial biogenesis during naive to effector differentiation of CD8+ T cells remains ill explored. In this study, we describe a critical role for early mitochondrial biogenesis in supporting cytokine production of nascent activated human naive CD8+ T cells. Specifically, we found that prior to the first round of cell division activated naive CD8+ T cells rapidly increase mitochondrial mass, mitochondrial respiration, and mitochondrial reactive oxygen species (mROS) generation, which were all inter-linked and important for CD8+ T cell effector maturation. Inhibition of early mitochondrial biogenesis diminished mROS dependent IL-2 production - as well as subsequent IL-2 dependent TNF, IFN-γ, perforin, and granzyme B production. Together, these findings point to the importance of mitochondrial biogenesis during early effector maturation of CD8+ T cells.

Intrinsic complement C3 activity is integral to human T helper type 1 (Th1) and cytotoxic T cell responses. Increased or decreased intracellular C3 results in autoimmunity and infections, respectively. The mechanisms regulating intracellular C3 expression remain undefined. We identified complement, including C3, as among the most significantly enriched biological pathway in tissue-occupying cells. We generated C3-reporter mice and confirmed that C3 expression was a defining feature of tissue-immune cells, including T cells and monocytes, occurred during transendothelial diapedesis, and depended on integrin lymphocyte-function-associated antigen 1 (LFA-1) signals. Immune cells from patients with leukocyte adhesion deficiency type 1 (LAD-1) had reduced C3 transcripts and diminished effector activities, which could be rescued proportionally by intracellular C3 provision. Conversely, increased C3 expression by T cells from arthritis patients correlated with disease severity. Our study defines integrins as key controllers of intracellular complement, demonstrates that perturbations in the LFA-1-C3-axis contribute to primary immunodeficiency, and identifies intracellular C3 as biomarker of severity in autoimmunity.

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.

The histidine nucleotide-binding protein, Hint2, is a mitochondrial phosphoramidase expressed in liver, brown fat, pancreas, and muscle. The livers of Hint2 knockout ( Hint2−/−) mice accumulate triglycerides and show a pattern of mitochondrial protein lysine hyperacetylation. The extent and nature of the lysine acetylation changes and the response of Hint2−/−mice to nutritional challenges that elicit a modification of protein acetylation have not been investigated. To compare the adaptation of Hint2−/−and control ( Hint2+/+) mice with episodes of fasting and high-fat diet (HFD), we subjected animals to either feeding ad libitum or fasting for 24 h, and to either a HFD or control diet for 8 wk. Triglyceride content was higher in Hint2−/−than in Hint2+/+livers, whereas plasma triglycerides were fourfold lower. Malonyl-CoA levels were increased twofold in Hint2−/−livers. After 24 h fasting, Hint2−/−displayed a decrease in body temperature, commensurate with a decrease in mass of brown fat and downregulation of uncoupling protein 1. HFD-treated Hint2−/−livers showed more steatosis, and plasma insulin and cholesterol were higher than in Hint+/+mice. Several proteins identified as substrates of sirtuin 3 and 5 and active in intermediary and ketone metabolism were hyperacetylated in liver and brown fat mitochondria after both HFD and fasting regimens. Glutamate dehydrogenase activity was downregulated in fed and fasted livers, and this was attributed to an increase in acetylation and ADP-ribosylation. The absence of Hint2 deregulates the posttranslational modification of several mitochondrial proteins, which impedes the adaptation to episodes of nutritional stress.

Serum acetate increases upon systemic infection. Acutely, assimilation of acetate expands the capacity of memory CD8+ T cells to produce IFN-γ. 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 (1) directly activating glutaminase, thereby augmenting glutaminolysis, cellular respiration, and survival, and (2) 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-acetate-induces distinct immunometabolic programs within the same cell type.

During immune challenge, T lymphocytes engage pathways of anabolic metabolism to meet the demands of clonal expansion and development of effector functions. Here we report a critical role for the non-essential amino acid serine in effector T cell responses. Upon activation, T cells upregulate enzymes of the serine, glycine, one-carbon (SGOC) metabolic network, and rapidly increase processing of serine into one-carbon metabolism. We show that T cell proliferation is highly dependent on extracellular serine, and that serine is required for optimal T cell expansion even in glucose concentrations sufficient to support T cell activation, bioenergetics, and effector function. Restricting dietary serine impairs pathogen-driven expansion of T cells in vivo, without affecting overall immune cell homeostasis. Mechanistically, we demonstrate that serine supplies glycine and one-carbon units for de novo nucleotide biosynthesis in proliferating T cells, and that one-carbon units from formate can rescue T cells from serine deprivation. Our data implicate serine as a key immunometabolite that directly modulates adaptive immunity by controlling T cell proliferative capacity.

Antibacterial antibody responses that target surfaces of live bacteria or secreted toxins are likely to be relevant in controlling bacterial pathogenesis. The ability to specifically quantify bacterial-surface-binding antibodies is therefore highly attractive as a quantitative correlate of immune protection. Here, binding of antibodies from various body fluids to pure-cultured live bacteria is made visible with fluorophore-conjugated secondary antibodies and measured by flow cytometry. We indicate the necessary controls for excluding nonspecific binding and also demonstrate a cross-adsorption technique for determining the extent of cross-reactivity. This technique has numerous advantages over standard ELISA and western blotting techniques because of its independence from scaffold binding, exclusion of cross-reactive elements from lysed bacteria and ability to visualize bacterial subpopulations. In addition, less than 10(5) bacteria and less than 10 μg of antibody are required per sample. The technique requires 3-4 h of hands-on experimentation and analysis. Moreover, it can be combined with automation and mutliplexing for high-throughput applications.

Citrobacter rodentium infection is a mouse model for the important human diarrheal infection caused by enteropathogenic E. coli (EPEC). The pathogenesis of both species is very similar and depends on their unique ability to form intimately epithelium-adherent microcolonies, also known as “attachment/effacement” (A/E) lesions. These microcolonies must be dynamic and able to self-renew by continuous re-infection of the rapidly regenerating epithelium. It is unknown whether sustained epithelial A/E lesion pathogenesis is achieved through re-infection by planktonic bacteria from the luminal compartment or local spread of sessile bacteria without a planktonic phase. Focusing on the earliest events as C. rodentium becomes established, we show here that all colonic epithelial A/E microcolonies are clonal bacterial populations, and thus depend on local clonal growth to persist. In wild-type mice, microcolonies are established exclusively within the first 18 hours of infection. These early events shape the ongoing intestinal geography and severity of infection despite the continuous presence of phenotypically virulent luminal bacteria. Mechanistically, induced resistance to A/E lesion de-novo formation is mediated by TLR-MyD88/Trif-dependent signaling and is induced specifically by virulent C. rodentium in a virulence gene-dependent manner. Our data demonstrate that the establishment phase of C. rodentium pathogenesis in vivo is restricted to a very short window of opportunity that determines both disease geography and severity., Author summary The so-called “attaching and effacing” (A/E) pathogens enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC) cause serious human diarrheal infections by adhering to and damaging the intestinal epithelium. Previous work on the mouse A/E pathogen Citrobacter rodentium has established that host adaptive immune response and intestinal microbiota cooperate to control the epithelial infection and colonization with this pathogen. We found that this is complemented by a rapid pathogen-induced mucosal innate immune response that is essential to prevent excessive pathogenesis before adaptive immunity takes effect. Its effectiveness is demonstrated by the fact that it normally limits the duration during which the bacteria can induce epithelial lesions to the first 18 hours of infection. Later, luminal virulent bacteria can no longer induce new A/E lesions, but those induced already in the first 18 hours of infection persist through localized epithelial re-infection. Severity of the disease at the peak of infection is consequently shaped by the early events of the first 18 hours. This information may be important for the development of effective therapies and vaccines.

Infektionskrankheiten sind weltweit die führende Todesursache noch vor kardiovaskulären und neoplastischen Erkrankungen. Die Einführung von Impfstoffen war deshalb ein wichtiger Meilenstein in der Medizingeschichte. Ziel ist es immer einen avirulenten, nicht-invasiven, nicht-replizierenden Impfstoff zu entwickeln, der eine spezifische, langlebige adaptive Immunantwort induzieren kann. Während die frühe Impfstoffentwicklung primär empirisch war, ist seither das detaillierte immunologische Verständnis erfolgreicher Immunantworten immer wichtiger geworden. Es bildet die Grundlage für die Entwicklung neuer Impfstoffe gegen komplexe Erreger, welche z. T. auch bei natürlicher Infektion keinen lebenslangen Infektionsschutz induzieren. Eine spezielle Patientengruppe stellen die primär und sekundär immunsupprimierten Patienten dar, welche ein deutlich erhöhtes Infektionsrisiko haben und deshalb konsequent geimpft werden sollten. In diesen Fällen sind Totimpfstoffe auch unter Therapie möglich, während Lebendimpfstoffe kontraindiziert sind oder nur in ausgewählten Situationen durchgeführt werden sollten. Zur Verbesserung der Impfantwort zielen neue Studien darauf ab bestehende Impfschemen zu optimieren. So können durch die Zugabe von Adjuvantien, durch eine Veränderung der Dosis oder des Dosisintervalls sowie des Applikationsortes höhere Antikörpertiter und antigen-spezifische T-Zellen induziert werden. Hierbei sind jedoch nicht nur die absolute Höhe des Antikörpertiters und die Anzahl spezifischer T-Zellen relevant sondern auch deren Qualität, Interaktion und Wirkungsort. Besonderes Interesse hat dabei die mukosale Immunantwort geweckt, wie z. B. mukosale T-Zellen und IgA. Inwiefern diese entscheidend für den Impfschutz sind, wird derzeit noch kontrovers diskutiert. In dieser Übersichtsarbeit erörtern wir die praxisrelevanten immunologischen Grundlagen einer erfolgreichen Impfantwort. Wir zeigen auf, wie Impfantworten modifiziert werden können, und fassen aktuelle Impfempfehlungen bei immunsupprimierten und -defizienten Patienten zusammen.

We are all born germ-free. Following birth we enter into a lifelong relationship with microbes residing on our body's surfaces. The lower intestine is home to the highest microbial density in our body, which is also the highest microbial density known on Earth (up to 10(12) /g of luminal contents). With our indigenous microbial cells outnumbering our human cells by an order of magnitude our body is more microbial than human. Numerous immune adaptations confine these microbes within the mucosa, enabling most of us to live in peaceful homeostasis with our intestinal symbionts. Intestinal epithelial cells not only form a physical barrier between the bacteria-laden lumen and the rest of the body but also function as multi-tasking immune cells that sense the prevailing microbial (apical) and immune (basolateral) milieus, instruct the underlying immune cells, and adapt functionally. In the constant effort to ensure intestinal homeostasis, the immune system becomes educated to respond appropriately and in turn immune status can shape the microbial consortia. Here we review how the dynamic immune-microbial dialogue underlies maturation and regulation of the immune system and discuss recent findings on the impact of diet on both microbial ecology and immune function.

Infections disturb homeostasis and often induce a switch to catabolic organismal metabolism. During catabolism, increased systemic availability of glucose, fatty acids and ketone bodies is observed, and recent evidence indicates that these metabolites might serve an immunomodulatory function. However, whereas our understanding of direct pathogen recognition by the host immune system is quite detailed, much less is known about the immunobiology of the metabolic host response to infection. In this review article we briefly discuss how pathogens induce ‘dys-homeostasis’ systemically, locally, and within cells, and provide examples of how such changes can shape immune-functionality during the course of an infection.

A Gut Feeling The mammalian gut is colonized by many nonpathogenic, commensal microbes. In order to prevent the body from mounting inappropriate immune responses to these microbes, plasma cells in the gut produce large amounts of immunoglobulin A (IgA) specific for commensal bacteria. Because of the difficulties of uncoupling IgA production from microbial colonization, how commensal bacteria shape the gut IgA response is not well understood. Hapfelmeier et al. (p. 1705 ; see the Perspective by Cerutti ) have now devised a way to get around this problem by developing a reversible system of gut bacterial colonization in mice. Commensal-specific IgA responses were able to persist for long periods of time in the absence of microbial colonization and required the presence of high microbial loads in the gut for their induction. IgA responses upon bacterial reexposure did not resemble the synergistic prime-boost effect seen in classical immunological memory responses but rather exhibited an additive effect that matched the current bacterial content present in the gut. The body thus constantly adapts the commensal-specific immune response to the microbial species present in the gut, which contrasts with the systemic immune response, which persists in the absence of pathogenic microbes.

Background & Aims Little is known about the pathogenic mechanisms of autoimmune pancreatitis (AIP), an increasingly recognized, immune-mediated form of chronic pancreatitis. Current treatment options are limited and disease relapse is frequent. We investigated factors that contribute to the development of AIP and new therapeutic strategies. Methods We used quantitative polymerase chain reaction, immunohistochemical, and enzyme-linked immunosorbent analyses to measure the expression of cytokines and chemokines in tissue and serum samples from patients with and without AIP. We created a mouse model of human AIP by overexpressing lymphotoxin (LT)α and β specifically in acinar cells ( Ela1-LTab mice). Results Messenger RNA levels of LTα and β were increased in pancreatic tissues from patients with AIP, compared with controls, and expression of chemokines ( CXCL13 , CCL19, CCL21 , CCL1 , and B-cell–activating factor ) was increased in pancreatic and serum samples from patients. Up-regulation of these factors was not affected by corticosteroid treatment. Acinar-specific overexpression of LTαβ (Ela1-LTαβ) in mice led to an autoimmune disorder with various features of AIP. Chronic inflammation developed only in the pancreas but was sufficient to cause systemic autoimmunity. Acinar-specific overexpression of LTαβ did not cause autoimmunity in mice without lymphocytes ( Ela1-LTab/Rag1 −/− ); moreover, lack of proinflammatory monocytes ( Ela1-LTab/Ccr2 −/− ) failed to prevent AIP but prevented early pancreatic tissue damage. Administration of corticosteroids reduced pancreatitis but did not affect production of autoantibodies, such as antipancreatic secretory trypsin inhibitor in Ela1-LTab mice. In contrast, inhibition of LTβR signaling reduced chemokine expression, renal immune-complex deposition, and features of AIP in Ela1-LTab mice. Conclusions Overexpression of LTαβ specifically in acinar cells of mice causes features of AIP. Reagents that neutralize LTβR ligands might be used to treat patients with AIP.

Adiponectin, which plays a pivotal role in metabolic liver diseases, is reduced in concentration in patients with NASH (non-alcoholic steatohepatitis). The aim of the present study was to determine adiponectin concentrations in patients with different forms and stages of chronic liver diseases. Serum adiponectin concentrations were measured in 232 fasting patients with chronic liver disease: 64 with NAFLD (non-alcoholic fatty liver disease), 123 with other chronic liver disease (e.g. viral hepatitis, n=71; autoimmune disease, n=18; alcohol-induced liver disease, n=3; or elevated liver enzymes of unknown origin, n=31) and 45 with cirrhosis. Circulating adiponectin levels were significantly lower in patients with NAFLD in comparison with patients with other chronic liver disease (4.8±3.5 compared with 10.4±6.3 μg/ml respectively; P