Inflammatory monocytes activate memory CD8(+) T and innate NK lymphocytes independent of cognate antigen during microbial pathogen invasion

Effector memory CD8 T cell response elicits Hepatitis E Virus genotype 3 pathogenesis in the elderly

Genotype 3 Hepatitis E virus (HEV-3) is an emerging threat for aging population. More than one third of older infected patients develops clinical symptoms with severe liver damage, while others remain asymptomatic. The origin of this discrepancy is still elusive although HEV-3 pathogenesis appears to be immune-mediated. Therefore, we investigated the role of CD8 T cells in the outcome of the infection in immunocompetent elderly subjects. We enrolled twenty two HEV-3-infected patients displaying similar viral determinants and fifteen healthy donors. Among the infected group, sixteen patients experienced clinical symptoms related to liver disease while six remained asymptomatic. Here we report that symptomatic infection is characterized by an expansion of highly activated effector memory CD8 T (EM) cells, regardless of antigen specificity. This robust activation is associated with key features of early T cell exhaustion including a loss in polyfunctional type-1 cytokine production and partial commitment to type-2 cells. In addition, we show that bystander activation of EM cells seems to be dependent on the inflammatory cytokines IL-15 and IL-18, and is supported by an upregulation of the activating receptor NKG2D and an exuberant expression of T-Bet and T-Bet-regulated genes including granzyme B and CXCR3. We also show that the inflammatory chemokines CXCL9-10 are increased in symptomatic patients thereby fostering the recruitment of highly cytotoxic EM cells into the liver in a CXCR3-dependent manner. Finally, we find that the EM-biased immune response returns to homeostasis following viral clearance and disease resolution, further linking the EM cells response to viral burden. Conversely, asymptomatic patients are endowed with low-to-moderate EM cell response. In summary, our findings define immune correlates that contribute to HEV-3 pathogenesis and emphasize the central role of EM cells in governing the outcome of the infection.

The outcome of Genotype 3 Hepatitis E virus (HEV-3) infection differs among the elderly. Some patients develop severe forms of Hepatitis E while others remain asymptomatic. Nonetheless, parameters which can lead to severe versus silent infection are largely unknown. Therefore, we investigated immunological features of CD8 T cells in infected patients (aged ≥55) with similar viral determinants but distinct clinical outcomes. We show that drastic phenotypic changes were specifically observed within the effector memory (EM) compartment. Compared to asymptomatic patients, symptomatic ones display a strong activation of both HEV-3-specific and -nonspecific EM CD8 T cells associated with qualitative and quantitative alterations in cytokine production. In addition, EM cells are endowed with high cytotoxic capacity and have the ability to rapidly migrate to the liver. Finally, we report that the inflammatory response to HEV-3 infection shape EM cell activation and function in symptomatic elderly patients. In summary, our results present the first report demonstrating that the nature and the magnitude of EM CD8 T cell response play an important role in the outcome of HEV-3 infection in the elderly.

A Novel Experimental Approach for In Vivo Analyses of the Salivary Gland Microvasculature

Microvascular dysfunction plays a fundamental role in the pathogenesis of salivary gland disorders. Restoring and preserving microvascular integrity might therefore represent a promising strategy for the treatment of these pathologies. The mechanisms underlying microvascular dysfunction in salivary glands, however, are still obscure, partly due to the unavailability of adequate in vivo models. Here, we present a novel experimental approach that allows comprehensive in vivo analyses of the salivary gland microvasculature in mice. For this purpose, we employed different microscopy techniques including multi-photon in vivo microscopy to quantitatively analyze interactions of distinct immune cell subsets in the submandibular gland microvasculature required for their infiltration into the surrounding parenchyma and their effects on microvascular function. Confocal microscopy and multi-channel flow cytometry in tissue sections/homogenates complemented these real-time analyses by determining the molecular phenotype of the participating cells. To this end, we identified key adhesion and signaling molecules that regulate the subset- and tissue-specific trafficking of leukocytes into inflamed glands and control the associated microvascular leakage. Hence, we established an experimental approach that allows in vivo analyses of microvascular processes in healthy and diseased salivary glands. This enables us to delineate distinct pathogenetic factors as novel therapeutic targets in salivary gland diseases.

The downregulation of IL-18R defines bona fide kidney-resident CD8+ T cells

Stepwise induction of CD69 and CD103 marks distinct differentiation stages of mucosal Trms. But the majority of non-mucosal Trm lacks CD103 expression. The expression of CD69 alone cannot faithfully define Trm cells in heavily vascularized non-mucosal tissues, such as the kidney. Here, we found that a subset of kidney Trms downregulated IL-18 receptor during differentiation. Via global transcriptional analysis and parabiosis experiments, we have discovered that the downregulation of interleukin-18 receptor (IL-18R) is associated with the establishment of tissue residency. Together with the expression of CD69, IL-18R^lo exclusively identify tissue-resident cells whereas IL-18R^hi population contains both tissue-resident and migratory ones. Local cytokines including transforming growth factor β (TGF-β) and interferon α (IFN-α)/β as well as TGF-β-dependent suppression of transcription factor Tcf-1 are essential for IL-18R downregulation during kidney Trm differentiation. Together, we identified a convenient surface marker to distinguish bona fide kidney-resident CD8⁺ T cells as well as underlying molecular mechanisms controlling this differentiation process.

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CD8⁺ Trm cells downregulate IL-18 receptor during differentiation

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IL-18R^hi population is composed of both migratory and resident subsets

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IL-18R^lo population is exclusively tissue-resident

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TGF-β promotes, whereas IFN-α/β inhibits, IL-18R downregulation

Cytokine and Chemokine Signals of T-Cell Exclusion in Tumors

The success of cancer immunotherapy in solid tumors depends on a sufficient distribution of effector T cells into malignant lesions. However, immune-cold tumors utilize many T-cell exclusion mechanisms to resist immunotherapy. T cells have to go through three steps to fight against tumors: trafficking to the tumor core, surviving and expanding, and maintaining the memory phenotype for long-lasting responses. Cytokines and chemokines play critical roles in modulating the recruitment of T cells and the overall cellular compositions of the tumor microenvironment. Manipulating the cytokine or chemokine environment has brought success in preclinical models and early-stage clinical trials. However, depending on the immune context, the same cytokine or chemokine signals may exhibit either antitumor or protumor activities and induce unwanted side effects. Therefore, a comprehensive understanding of the cytokine and chemokine signals is the premise of overcoming T-cell exclusion for effective and innovative anti-cancer therapies.

Altered bioenergetics and mitochondrial dysfunction of monocytes in patients with COVID-19 pneumonia

In patients infected by SARS-CoV-2 who experience an exaggerated inflammation leading to pneumonia, monocytes likely play a major role but have received poor attention. Thus, we analyzed peripheral blood monocytes from patients with COVID-19 pneumonia and found that these cells show signs of altered bioenergetics and mitochondrial dysfunction, had a reduced basal and maximal respiration, reduced spare respiratory capacity, and decreased proton leak. Basal extracellular acidification rate was also diminished, suggesting reduced capability to perform aerobic glycolysis. Although COVID-19 monocytes had a reduced ability to perform oxidative burst, they were still capable of producing TNF and IFN-γ in vitro. A significantly high amount of monocytes had depolarized mitochondria and abnormal mitochondrial ultrastructure. A redistribution of monocyte subsets, with a significant expansion of intermediate/pro-inflammatory cells, and high amounts of immature monocytes were found, along with a concomitant compression of classical monocytes, and an increased expression of inhibitory checkpoints like PD-1/PD-L1. High plasma levels of several inflammatory cytokines and chemokines, including GM-CSF, IL-18, CCL2, CXCL10, and osteopontin, finally confirm the importance of monocytes in COVID-19 immunopathogenesis.

MAVS Deficiency Is Associated With a Reduced T Cell Response Upon Secondary RSV Infection in Mice

Infections with respiratory syncytial virus (RSV) occurs repeatedly throughout life because sustained, protective memory responses fail to develop. Why this occurs is not known. During RSV infection the recognition of the virus via the cytosolic RIG-I like receptors and signaling via the adaptor protein MAVS is crucial for mounting an innate immune response. However, if this signaling pathway is important for T cell responses during primary infection and during re-infection is not fully elucidated. We describe a second peak of pro-inflammatory mediators during the primary immune response to RSV that coincides with the arrival of T cells into the lung. This second peak of cytokines/chemokines is regulated differently than the early peak and is largely independent of signaling via MAVS. This was concurrent with Mavs^−/− mice mounting a strong T cell response to primary RSV infection, with robust IFN-γ; and Granzyme B production. However, after RSV re-infection, Mavs^−/− mice showed fewer CD4⁺ and CD8⁺ short term memory T cells and their capacity to produce IFN-γ; and Granzyme B, was decreased. In sum, cytosolic recognition of RSV is important not only for initiating innate anti-viral responses but also for generating or maintaining efficient, short term T cell memory responses.

Lactococcus lactis subsp. Cremoris C60 restores T Cell Population in Small Intestinal Lamina Propria in Aged Interleukin-18 Deficient Mice

Lactic acid bacteria (LAB), a major commensal bacterium in the small intestine, are well known beneficial bacteria which promote establishment of gut-centric immunity, such as anti-inflammation and anti-infection. In this report, we show that a LAB strain Lactococcus lactis subsp. Cremoris C60 possess an ability to activate antigen presenting cells, such as dendritic cells (DCs), and intestinal T cells which possibly support to maintain healthy intestinal immunological environment in aging process. We found that CD4+ T cells in the small intestine are dramatically decreased in aged Interleukin-18 knock out (IL-18KO) mice, associated with the impairment of IFN-γ production in the CD4+ T cells, especially in small intestinal lamina propria (LP). Surprisingly, heat killed-C60 (HK-C60) diet completely recovered the CD4+ T cells population and activity in SI-LP and over activated the population in Peyer's patches (PPs) of IL-18KO mice. The HK-C60 diet was effective approach not only to restore the number of cells, but also to recover IFN-γ production in the CD4+ T cell population in the small intestine of IL-18-deficient mice. As a possible cause in the age-associated impairment of CD4+ T cells activity in IL-18KO mice, we found that the immunological activity was downregulated in the IL-18-deficient DCs. The cytokines production and cellular activation markers expression were downregulated in the IL-18-deficient bone marrow derived dendritic cells (BMDCs) at the basal level, however, both activities were highly upregulated in HK-C60 stimulation as compared to those of WT cells. Antigen uptake was also attenuated in the IL-18-deficient BMDCs, and it was significantly enhanced in the cells as compared to WT cells in HK-60 stimulation. An in vitro antigen presentation assay showed that IFN-γ production in the CD4+ T cells was significantly enhanced in the culture of IL-18-deficient BMDCs compared with WT cells in the presence of HK-C60. Thus, we conclude that HK-C60 diet possesses an ability to restore T cells impairment in the small intestine of IL-18-deficient environment. In addition, the positive effect is based on the immunological modification of DCs function which directory influences into the promotion of effector CD4+ T cells generation in the small intestine.

A gammaherpesvirus licenses CD8 T cells to protect the host from pneumovirus-induced immunopathologies

Human respiratory syncytial virus (RSV) is a pneumovirus that causes severe infections in infants worldwide. Despite intensive research, safe and effective vaccines against RSV have remained elusive. The main reason is that RSV infection of children previously immunized with formalin-inactivated-RSV vaccines has been associated with exacerbated pathology, a phenomenon called RSV vaccine-enhanced respiratory disease. In parallel, despite the high RSV prevalence, only a minor proportion of children develop severe diseases. Interestingly, variation in the immune responses against RSV or following RSV vaccination could be linked with differences of exposure to microbes during childhood. Gammaherpesviruses (γHVs), such as the Epstein-Barr virus, are persistent viruses that deeply influence the immune system of their host and could therefore affect the development of pneumovirus-induced immunopathologies for the long term. Here, we showed that a previous ɣHV infection protects against both pneumovirus vaccine-enhanced disease and pneumovirus primary infection and that CD8 T cells are essential for this protection. These observations shed a new light on the understanding of pneumovirus-induced diseases and open new perspectives for the development of vaccine strategies.

Treatment of mice with S4B6 IL-2 complex prevents lethal toxoplasmosis via IL-12- and IL-18-dependent interferon-gamma production by non-CD4 immune cells

Toxoplasmic encephalitis is an AIDS-defining condition. The decline of IFN-γ-producing CD4⁺ T cells in AIDS is a major contributing factor in reactivation of quiescent Toxoplasma gondii to an actively replicating stage of infection. Hence, it is important to characterize CD4-independent mechanisms that constrain acute T. gondii infection. We investigated the in vivo regulation of IFN-γ production by CD8⁺ T cells, DN T cells and NK cells in response to acute T. gondii infection. Our data show that processing of IFN-γ by these non-CD4 cells is dependent on both IL-12 and IL-18 and the secretion of bioactive IL-18 in response to T. gondii requires the sensing of viable parasites by multiple redundant inflammasome sensors in multiple hematopoietic cell types. Importantly, our results show that expansion of CD8⁺ T cells, DN T cells and NK cell by S4B6 IL-2 complex pre-treatment increases survival rates of mice infected with T. gondii and this is dependent on IL-12, IL-18 and IFN-γ. Increased survival is accompanied by reduced pathology but is independent of expansion of T_Reg cells or parasite burden. This provides evidence for a protective role of IL2C-mediated expansion of non-CD4 cells and may represent a promising lead to adjunct therapy for acute toxoplasmosis.

Network-based Transcriptome-wide Expression Study for Postmenopausal Osteoporosis

PURPOSE

Menopause is a crucial physiological transition during a woman's life, and it occurs with growing risks of health issues like osteoporosis. To identify postmenopausal osteoporosis-related genes, we performed transcriptome-wide expression analyses for human peripheral blood monocytes (PBMs) using Affymetrix 1.0 ST arrays in 40 Caucasian postmenopausal women with discordant bone mineral density (BMD) levels.

METHODS

We performed multiscale embedded gene coexpression network analysis (MEGENA) to study functionally orchestrating clusters of differentially expressed genes in the form of functional networks. Gene sets net correlations analysis (GSNCA) was applied to assess how the coexpression structure of a predefined gene set differs in high and low BMD groups. Bayesian network (BN) analysis was used to identify important regulation patterns between potential risk genes for osteoporosis. A small interfering ribonucleic acid (siRNA)-based gene silencing in vitro experiment was performed to validate the findings from BN analysis.

RESULT

MEGENA showed that the "T cell receptor signaling pathway" and the "osteoclast differentiation pathway" were significantly enriched in the identified compact network, which is significantly correlated with BMD variation. GSNCA revealed that the coexpression structure of the "Signaling by TGF-beta receptor complex pathway" is significantly different between the 2 BMD discordant groups; the hub genes in the postmenopausal low and high BMD group are FURIN and SMAD3 respectively. With siRNA in vitro experiments, we confirmed the regulation relationship of TGFBR2-SMAD7 and TGFBR1-SMURF2.

MAIN CONCLUSION

The present study suggests that biological signals involved in monocyte recruitment, monocyte/macrophage lineage development, osteoclast formation, and osteoclast differentiation might function together in PBMs that contribute to the pathogenesis of postmenopausal osteoporosis.

Microbiota stimulation generates LCMV-specific memory CD8+ T cells in SPF mice and determines their TCR repertoire during LCMV infection

Both mouse and human harbour memory phenotype CD8⁺ T cells specific for antigens in hosts that have not been previously exposed to these antigens. The origin and the nature of the stimuli responsible for generation of CD44^hi CD8⁺ T cells in specific pathogen-free (SPF) mice remain controversial. It is known that microbiota plays a crucial role in the prevention and resolution of systemic infections by influencing myelopoiesis, regulating dendritic cells, inflammasome activation and promoting the production of type I and II interferons. By contrast, here we suggest that microbiota has a direct effect on generation of memory phenotype CD44^hiGP33⁺CD8⁺ T cells. In SPF mice, it generates a novel GP33⁺CD44^hiCD8⁺ T cell sub-population associating the properties of innate and genuine memory cells. These cells are highly enriched in the bone marrow, proliferate rapidly and express immediate effector functions. They dominate the response to LCMV and express particular TCRβ chains. The sequence of these selected TCRβ chains overlaps with that of GP33⁺CD8⁺ T cells directly selected by microbiota in the gut epithelium of SPF mice, demonstrating a common selection mechanism in gut and peripheral CD8⁺ T cell pool. Therefore microbiota has a direct role in priming T cell immunity in SPF mice and in the selection of TCRβ repertoires during systemic infection. We identify a mechanism that primes T cell immunity in SPF mice and may have a major role in colonization resistance and protection from infection.

Natural products that target macrophages in treating non-alcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is the progressive subtype of non-alcoholic fatty liver disease and potentiates risks for both hepatic and metabolic diseases. Although the pathophysiology of NASH is not completely understood, recent studies have revealed that macrophage activation is a major contributing factor for the disease progression. Macrophages integrate the immune response and metabolic process and have become promising targets for NASH therapy. Natural products are potential candidates for NASH treatment and have multifactorial underlying mechanisms. Macrophage involvement in the development of steatosis and inflammation in NASH has been widely investigated. In this review, we assess the evidence for natural products or their active ingredients in the modulation of macrophage activation, recruitment, and polarization, as well as the metabolic status of macrophages. Our work may highlight the possible natural products that target macrophages as potential treatment options for NASH.

Relationship between T cells and microbiota in health and disease

In the past decades, the fields of microbiology and immunology have largely advanced by using germ-free animals and next-generation sequencing. Many studies revealed the relationship among gut microbiota, activation of immune system, and various diseases. Especially, some gut commensals can generate their antigen-specific T cells. It is becoming clear that commensal bacteria have important roles in various autoimmune and inflammatory diseases, such as autism, rheumatoid arthritis (RA), and inflammatory bowel diseases (IBD). Recently, it was reported that commensals contribute to the cancer immune therapy. However, how commensal-specific T cells contribute to the disease development and cancer treatment are not fully understood yet. In this chapter, we will summarize the decade history of the studies associated with commensal-induced T cells and commensal-causing diseases.

Structure and function of the immune system in the spleen

The spleen is the largest secondary lymphoid organ in the body and, as such, hosts a wide range of immunologic functions alongside its roles in hematopoiesis and red blood cell clearance. The physical organization of the spleen allows it to filter blood of pathogens and abnormal cells and facilitate low-probability interactions between antigen-presenting cells (APCs) and cognate lymphocytes. APCs specific to the spleen regulate the T and B cell response to these antigenic targets in the blood. This review will focus on cell types, cell organization, and immunologic functions specific to the spleen and how these affect initiation of adaptive immunity to systemic blood-borne antigens. Potential differences in structure and function between mouse and human spleen will also be discussed.

Cutting Edge: Antitumor Immunity by Pathogen-Specific CD8 T Cells in the Absence of Cognate Antigen Recognition

Cancer prognosis often correlates with the number of tumor-infiltrating CD8 T cells, but many of these cells recognize pathogens that commonly infect humans. The contribution of pathogen-specific "bystander" CD8 T cells to antitumor immunity remains largely unknown. Inflammatory cytokines are sufficient for memory CD8 T cell activation and gain of effector functions, indicating tumor-derived inflammation could facilitate pathogen-specific CD8 T cells to participate in tumor control. In this study, we show in contrast to tumor-specific CD8 T cells that pathogen-specific primary memory CD8 T cells inside tumor were not able to exert their effector functions and influence tumor progression. However, infection-induced memory CD8 T cells with defined history of repeated Ag encounters (i.e., quaternary memory) showed increased sensitivity to tumor-derived inflammation that resulted in activation, gain of effector functions, and better control of tumor growth. Thus, memory CD8 T cells with heightened ability to recognize environmental inflammatory stimuli can contribute to antitumor immunity in the absence of cognate Ag recognition.

Infection History Determines Susceptibility to Unrelated Diseases

Epidemiological data suggest that previous infections can alter an individual's susceptibility to unrelated diseases. Nevertheless, the underlying mechanisms are not completely understood. Substantial research efforts have expanded the classical concept of immune memory to also include long-lasting changes in innate immunity and antigen-independent reactivation of adaptive immunity. Collectively, these processes provide possible explanations on how acute infections might induce long-term changes that also affect immunity to unrelated diseases. Here, we review lasting changes the immune compartment undergoes upon infection and how infection experience alters the responsiveness of immune cells towards universal signals. This heightened state of alert enhances the ability of the immune system to combat even unrelated infections but may also increase susceptibility to autoimmunity. At the same time, infection-induced changes in the regulatory compartment may dampen subsequent immune responses and promote pathogen persistence. The concepts presented here outline how infection-induced changes in the immune system may affect human health.

The activation of bystander CD8+ T cells and their roles in viral infection

During viral infections, significant numbers of T cells are activated in a T cell receptor-independent and cytokine-dependent manner, a phenomenon referred to as "bystander activation." Cytokines, including type I interferons, interleukin-18, and interleukin-15, are the most important factors that induce bystander activation of T cells, each of which plays a somewhat different role. Bystander T cells lack specificity for the pathogen, but can nevertheless impact the course of the immune response to the infection. For example, bystander-activated CD8⁺ T cells can participate in protective immunity by secreting cytokines, such as interferon-γ. They also mediate host injury by exerting cytotoxicity that is facilitated by natural killer cell-activating receptors, such as NKG2D, and cytolytic molecules, such as granzyme B. Interestingly, it has been recently reported that there is a strong association between the cytolytic function of bystander-activated CD8⁺ T cells and host tissue injury in patients with acute hepatitis A virus infection. The current review addresses the induction of bystander CD8⁺ T cells, their effector functions, and their potential roles in immunity to infection, immunopathology, and autoimmunity.

Control of memory CD8+ T cell longevity and effector functions by IL-15

IL-15 is a member of the common gamma chain family of cytokines and plays important roles in regulating several aspects of innate and adaptive immunity. Besides its established role in controlling homeostatic proliferation and survival of memory CD8⁺ T cells and natural killer cells, recent findings demonstrate that inflammatory IL-15 can also stimulate a variety of effector functions, such as enhanced cytotoxicity, entry into the cell cycle, and trafficking into non-lymphoid tissues. Here, we discuss how IL-15 is critical in regulating many functions of memory CD8⁺ T cells and how these processes act collectively to ensure optimal protective cellular immunity against re-infections.

CD4+ T cell help creates memory CD8+ T cells with innate and help-independent recall capacities

CD4⁺ T cell help is required for the generation of CD8⁺ cytotoxic T lymphocyte (CTL) memory. Here, we use genome-wide analyses to show how CD4⁺ T cell help delivered during priming promotes memory differentiation of CTLs. Help signals enhance IL-15-dependent maintenance of central memory T (T_CM) cells. More importantly, help signals regulate the size and function of the effector memory T (T_EM) cell pool. Helped T_EM cells produce Granzyme B and IFNγ upon antigen-independent, innate-like recall by IL-12 and IL-18. In addition, helped memory CTLs express the effector program characteristic of helped primary CTLs upon recall with MHC class I-restricted antigens, likely due to epigenetic imprinting and sustained mRNA expression of effector genes. Our data thus indicate that during priming, CD4⁺ T cell help optimizes CTL memory by creating T_EM cells with innate and help-independent antigen-specific recall capacities.

Monocytes affect bone mineral density in pre- and postmenopausal women through ribonucleoprotein complex biogenesis by integrative bioinformatics analysis

Osteoporosis is one of the most common metabolic bone disease among pre- and postmenopausal women. As the precursors of osteoclast cells, circulating monocytes play important role in bone destruction and remodeling. The aim of study is to identify potential key genes and pathways correlated with the pathogenesis of osteoporosis. Then we construct novel estimation model closely linked to the bone mineral density (BMD) with key genes. Weighted gene co-expression network analysis (WGCNA) were conducted by collecting gene data set with 80 samples from gene expression omnibus (GEO) database. Besides, hub genes were identified by series of bioinformatics and machine learning algorithms containing protein-protein interaction (PPI) network, receiver operating characteristic curve and Pearson correlation. The direction of correlation coefficient were performed to screen for gene signatures with high BMD and low BMD. A novel BMD score system was put forward based on gene set variation analysis and logistic regression, which was validated by independent data sets. We identified six modules correlated with BMD. Finally 100 genes were identified as the high bone mineral density signatures while 130 genes were identified as low BMD signatures. Besides, we identified the significant pathway in monocytes: ribonucleoprotein complex biogenesis. What's more, our score validated it successfully.

DOCK2 Sets the Threshold for Entry into the Virtual Memory CD8+ T Cell Compartment by Negatively Regulating Tonic TCR Triggering

The control of cytoskeletal dynamics by dedicator of cytokinesis 2 (DOCK2), a hematopoietic cell-specific actin effector protein, has been implicated in TCR signaling and T cell migration. Biallelic mutations in Dock2 have been identified in patients with a recessive form of combined immunodeficiency with defects in T, B, and NK cell activation. Surprisingly, we show in this study that certain immune functions of CD8⁺ T cells are enhanced in the absence of DOCK2. Dock2-deficient mice have a pronounced expansion of their memory T cell compartment. Bone marrow chimera and adoptive transfer studies indicate that these memory T cells develop in a cell-intrinsic manner following thymic egress. Transcriptional profiling, TCR repertoire analyses, and cell surface marker expression indicate that Dock2-deficient naive CD8⁺ T cells directly convert into virtual memory cells without clonal effector T cell expansion. This direct conversion to memory is associated with a selective increase in TCR sensitivity to self-peptide MHC in vivo and an enhanced response to weak agonist peptides ex vivo. In contrast, the response to strong agonist peptides remains unaltered in Dock2-deficient T cells. Collectively, these findings suggest that the regulation of the actin dynamics by DOCK2 enhances the threshold for entry into the virtual memory compartment by negatively regulating tonic TCR triggering in response to weak agonists.

A Batf3/Nlrp3/IL-18 Axis Promotes Natural Killer Cell IL-10 Production during Listeria monocytogenes Infection

The bacterial pathogen Listeria monocytogenes (Lm) capitalizes on natural killer (NK) cell production of regulatory interleukin (IL)-10 to establish severe systemic infections. Here, we identify regulators of this IL-10 secretion. We show that IL-18 signals to NK cells license their ability to produce IL-10. IL-18 acts independent of IL-12 and STAT4, which co-stimulate IFNγ secretion. Dendritic cell (DC) expression of Nlrp3 is required for IL-18 release in response to the Lm p60 virulence protein. Therefore, mice lacking Nlrp3, Il18, or Il18R fail to accumulate serum IL-10 and are highly resistant to systemic Lm infection. We further show that cells expressing or dependent on Batf3 are required for IL-18-inducing IL-10 production observed in infected mice. These findings explain how Il18 and Batf3 promote susceptibility to bacterial infection and demonstrate the ability of Lm to exploit NLRP3 for the promotion of regulatory NK cell activity.

CXCR3 enables recruitment and site-specific bystander activation of memory CD8+ T cells

Bystander activation of memory T cells occurs in the absence of cognate antigen during infections that elicit strong systemic inflammatory responses, which subsequently affect host immune responses. Here we report that memory T cell bystander activation is not limited to induction by systemic inflammation. We initially observe potential T cell bystander activation in a cohort of human vaccine recipients. Using a mouse model system, we then find that memory CD8⁺ T cells are specifically recruited to sites with activated antigen-presenting cells (APCs) in a CXCR3-dependent manner. In addition, CXCR3 is also necessary for T cell clustering around APCs and T cell bystander activation, which temporospatially overlaps with the subsequent antigen-specific T cell response. Our data thus suggest that bystander activation is part of the initial localized immune response, and is mediated by a site-specific recruitment process of memory T cells.

Pregnancy-Induced Alterations in NK Cell Phenotype and Function

Pregnant women are particularly susceptible to complications of influenza A virus infection, which may result from pregnancy-induced changes in the function of immune cells, including natural killer (NK) cells. To better understand NK cell function during pregnancy, we assessed the ability of the two main subsets of NK cells, CD56^dim, and CD56^bright NK cells, to respond to influenza-virus infected cells and tumor cells. During pregnancy, CD56^dim and CD56^bright NK cells displayed enhanced functional responses to both infected and tumor cells, with increased expression of degranulation markers and elevated frequency of NK cells producing IFN-γ. To better understand the mechanisms driving this enhanced function, we profiled CD56^dim and CD56^bright NK cells from pregnant and non-pregnant women using mass cytometry. NK cells from pregnant women displayed significantly increased expression of several functional and activation markers such as CD38 on both subsets and NKp46 on CD56^dim NK cells. NK cells also displayed diminished expression of the chemokine receptor CXCR3 during pregnancy. Overall, these data demonstrate that functional and phenotypic shifts occur in NK cells during pregnancy that can influence the magnitude of the immune response to both infections and tumors.

IFNγ: signalling, epigenetics and roles in immunity, metabolism, disease and cancer immunotherapy

IFNγ is a cytokine with important roles in tissue homeostasis, immune and inflammatory responses and tumour immunosurveillance. Signalling by the IFNγ receptor activates the Janus kinase (JAK)-signal transducer and activator of transcription 1 (STAT1) pathway to induce the expression of classical interferon-stimulated genes that have key immune effector functions. This Review focuses on recent advances in our understanding of the transcriptional, chromatin-based and metabolic mechanisms that underlie IFNγ-mediated polarization of macrophages to an 'M1-like' state, which is characterized by increased pro-inflammatory activity and macrophage resistance to tolerogenic and anti-inflammatory factors. In addition, I describe the newly discovered effects of IFNγ on other leukocytes, vascular cells, adipose tissue cells, neurons and tumour cells that have important implications for autoimmunity, metabolic diseases, atherosclerosis, neurological diseases and immune checkpoint blockade cancer therapy.

Polyfunctional tumor-reactive T cells are effectively expanded from non-small cell lung cancers, and correlate with an immune-engaged T cell profile

Non-small cell lung cancer (NSCLC) is the second most prevalent type of cancer. With the current treatment regimens, the mortality rate remains high. Therefore, better therapeutic approaches are necessary. NSCLCs generally possess many genetic mutations and are well infiltrated by T cells (TIL), making TIL therapy an attractive option. Here we show that T cells from treatment naive, stage I-IVa NSCLC tumors can effectively be isolated and expanded, with similar efficiency as from normal lung tissue. Importantly, 76% (13/17) of tested TIL products isolated from NSCLC lesions exhibited clear reactivity against primary tumor digests, with 0.5%-30% of T cells producing the inflammatory cytokine Interferon (IFN)-γ. Both CD4⁺ and CD8⁺ T cells displayed tumor reactivity. The cytokine production correlated well with CD137 and CD40L expression. Furthermore, almost half (7/17) of the TIL products contained polyfunctional T cells that produced Tumor Necrosis Factor (TNF)-α and/or IL-2 in addition to IFN-γ, a hallmark of effective immune responses. Tumor-reactivity in the TIL products correlated with high percentages of CD103⁺CD69⁺CD8⁺ T cell infiltrates in the tumor lesions, with PD-1^hiCD4⁺ T cells, and with FoxP3⁺CD25⁺CD4⁺ regulatory T cell infiltrates, suggesting that the composition of T cell infiltrates may predict the level of tumor reactivity. In conclusion, the effective generation of tumor-reactive and polyfunctional TIL products implies that TIL therapy will be a successful treatment regimen for NSCLC patients.

Spatial and temporal coordination of antiviral responses by group 1 ILCs

Group 1 innate lymphocytes consist of a phenotypically, spatially, and functionally heterogeneous population of NK cells and ILC1s that are engaged during pathogen invasion. We are only beginning to understand the context-dependent roles that different subsets of group 1 innate lymphocytes play during homeostatic perturbations. With a focus on viral infection, this review highlights the organization and regulation of spatially and temporally distinct waves of NK cell and ILC1 responses that collectively serve to achieve optimal viral control.

Interferon regulatory factor 3 plays a role in macrophage responses to interferon-γ

IFN-γ produced during viral infections activates the IFN-γ receptor (IFNGR) complex for STAT1 transcriptional activity leading to expression of Interferon Regulatory Factors (IRF). Simultaneous activation of TBK/IKKε via TLR3 during viral infections activates the transcription factor IRF3. Together these transcription factors contributes to expression of intracellular proteins (e.g. ISG49, ISG54) and secreted proteins (e.g. IFN-β, IP-10, IL-15) that are essential to innate antiviral immunity. Here we examined the role of IRF3 in expression of innate anti-viral proteins produced in response to IFN-γ plus TLR3 agonist. Wild-type (WT) and IRF3KO RAW264.7 cells, each with ISG54-promoter-luciferase reporter vectors, were stimulated with IFN-γ, poly I:C, or both together. ISG54 promoter activity was significantly reduced in IRF3KO RAW264.7 cells responding to IFN-γ, poly I:C, or IFN-γ plus poly I:C, compared with WT RAW264.7 cells. These data were confirmed with western blot and qRT-PCR. Primary macrophages and dendritic cells (DCs) from IRF3KO mice also showed decreased ISG54 in response to IFN-γ, poly I:C, or IFN-γ plus poly I:C compared with those from WT mice. Moreover, pharmacological inhibition of TBK/IKKε significantly reduced ISG54 promoter activity in response to IFN-γ, poly I:C, or IFN-γ plus poly I:C. Similarly, expression of ISG49 and IL-15, but not IP-10, was impaired in IRF3KO RAW264.7 cells responding to IFN-γ or poly I:C, which also had impaired STAT1 phosphorylation and IRF1 expression. These data show that IRF3 contributes to IFN-γ/IFNGR signaling for expression of innate anti-viral proteins in macrophages.

Innate and Adaptive Immune Responses during Listeria monocytogenes Infection

It could be argued that we understand the immune response to infection with Listeria monocytogenes better than the immunity elicited by any other bacteria. L. monocytogenes are Gram-positive bacteria that are genetically tractable and easy to cultivate in vitro, and the mouse model of intravenous (i.v.) inoculation is highly reproducible. For these reasons, immunologists frequently use the mouse model of systemic listeriosis to dissect the mechanisms used by mammalian hosts to recognize and respond to infection. This article provides an overview of what we have learned over the past few decades and is divided into three sections: "Innate Immunity" describes how the host initially detects the presence of L. monocytogenes and characterizes the soluble and cellular responses that occur during the first few days postinfection; "Adaptive Immunity" discusses the exquisitely specific T cell response that mediates complete clearance of infection and immunological memory; "Use of Attenuated Listeria as a Vaccine Vector" highlights the ways that investigators have exploited our extensive knowledge of anti-Listeria immunity to develop cancer therapeutics.

Staphylococcus aureus and Host Immunity in Recurrent Furunculosis

Staphylococcus aureus is one of the severest and most persistent bacterial pathogens. The most frequent S. aureus infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis. S. aureus produces a great variety of cellular and extracellular factors responsible for its invasiveness and ability to cause pathological lesions. Their expression depends on the growth phase, environmental factors, and location of the infection. Susceptibility to staphylococcal infections is rooted in multiple mechanisms of host immune responses and reactions to bacterial colonization. Immunological and inflammatory processes of chronic furunculosis are based on the pathogenicity of S. aureus as well as innate and acquired immunity. In-depth knowledge about them may help to discover the whole pathomechanism of the disease and to develop effective therapeutic options. In this review, we focus on the S. aureus-host immune interactions in the pathogenesis of recurrent furunculosis according to the most recent experimental and clinical findings.

Central memory CD8+ T cells become CD69+ tissue-residents during viral skin infection independent of CD62L-mediated lymph node surveillance

Memory CD8+ T cells in the circulation rapidly infiltrate non-lymphoid tissues following infection and provide protective immunity in an antigen-specific manner. However, the subsequent fate of memory CD8+ T cells after entering non-lymphoid tissues such as the skin during a secondary infection is largely unknown. Furthermore, because expression of CD62L is often used to identify the central memory (TCM) CD8+ T cell subset, uncoupling the physical requirement for CD62L-mediated lymph node homing versus other functional attributes of TCM CD8+ T cells remains unresolved. Here, we show that in contrast to naïve CD8+ T cells, memory CD8+ T cells traffic into the skin independent of CD62L-mediated lymph node re-activation and provide robust protective immunity against Vaccinia virus (VacV) infection. TCM, but not effector memory (TEM), CD8+ T cells differentiated into functional CD69+/CD103- tissue residents following viral clearance, which was also dependent on local recognition of antigen in the skin microenvironment. Finally, we found that memory CD8+ T cells expressed granzyme B after trafficking into the skin and utilized cytolysis to provide protective immunity against VacV infection. Collectively, these findings demonstrate that TCM CD8+ T cells become cytolytic following rapid infiltration of the skin to protect against viral infection and subsequently differentiate into functional CD69+ tissue-residents.

Infection-Induced Resistance to Experimental Cerebral Malaria Is Dependent Upon Secreted Antibody-Mediated Inhibition of Pathogenic CD8+ T Cell Responses

Cerebral malaria (CM) is one of the most severe complications of Plasmodium falciparum infection. There is evidence that repeated parasite exposure promotes resistance against CM. However, the immunological basis of this infection-induced resistance remains poorly understood. Here, utilizing the Plasmodium berghei ANKA (PbA) model of experimental cerebral malaria (ECM), we show that three rounds of infection and drug-cure protects against the development of ECM during a subsequent fourth (4X) infection. Exposure-induced resistance was associated with specific suppression of CD8+ T cell activation and CTL-related pathways, which corresponded with the development of heterogeneous atypical B cell populations as well as the gradual infection-induced generation and maintenance of high levels of anti-parasite IgG. Mechanistically, transfer of high-titer anti-parasite IgG did not protect 1X infected mice against ECM and depletion of atypical and regulatory B cells during 4X infection failed to abrogate infection-induced resistance to ECM. However, IgMi mice that were unable to produce secreted antibody, or undergo class switching, during the repeated rounds of infection failed to develop resistance against ECM. The failure of infection-induced protection in IgMi mice was associated with impaired development of atypical B cell populations and the inability to suppress pathogenic CD8+ T cell responses. Our results, therefore, suggest the importance of anti-parasite antibody responses, gradually acquired, and maintained through repeated Plasmodium infections, for modulating the B cell compartment and eventually suppressing memory CD8+ T cell reactivation to establish infection-induced resistance to ECM.

Interleukin-18 in Health and Disease

Interleukin (IL)-18 was originally discovered as a factor that enhanced IFN-γ production from anti-CD3-stimulated Th1 cells, especially in the presence of IL-12. Upon stimulation with Ag plus IL-12, naïve T cells develop into IL-18 receptor (IL-18R) expressing Th1 cells, which increase IFN-γ production in response to IL-18 stimulation. Therefore, IL-12 is a commitment factor that induces the development of Th1 cells. In contrast, IL-18 is a proinflammatory cytokine that facilitates type 1 responses. However, IL-18 without IL-12 but with IL-2, stimulates NK cells, CD4⁺ NKT cells, and established Th1 cells, to produce IL-3, IL-9, and IL-13. Furthermore, together with IL-3, IL-18 stimulates mast cells and basophils to produce IL-4, IL-13, and chemical mediators such as histamine. Therefore, IL-18 is a cytokine that stimulates various cell types and has pleiotropic functions. IL-18 is a member of the IL-1 family of cytokines. IL-18 demonstrates a unique function by binding to a specific receptor expressed on various types of cells. In this review article, we will focus on the unique features of IL-18 in health and disease in experimental animals and humans.

Cytokine-Mediated Regulation of CD8 T-Cell Responses During Acute and Chronic Viral Infection

The common γ-chain cytokines, interleukin (IL)-2, IL-7, and IL-15, regulate critical aspects of antiviral CD8 T-cell responses. During acute infections, IL-2 controls expansion and differentiation of antiviral CD8 T cells, whereas IL-7 and IL-15 are key cytokines to maintain memory CD8 T cells long term in an antigen-independent manner. On the other hand, during chronic infections, in which T-cell exhaustion is established, precise roles of these cytokines in regulation of antiviral CD8 T-cell responses are not well defined. Nonetheless, administration of IL-2, IL-7, or IL-15 can increase function of exhausted CD8 T cells, and thus can be an attractive therapeutic approach. A new subset of stem-cell-like CD8 T cells, which provides a proliferative burst after programmed cell death (PD)-1 therapy, has been recently described during chronic viral infection. Further understanding of cytokine-mediated regulation of this CD8 T-cell subset will improve cytokine therapies to treat chronic infections and cancer in combination with immune checkpoint inhibitors.

IL-15 is a component of the inflammatory milieu in the tumor microenvironment promoting antitumor responses

Previous studies have provided evidence that IL-15 expression within human tumors is crucial for optimal antitumor responses; however, the regulation of IL-15 within the tumor microenvironment (TME) is unclear. We report herein, in analyses of mice implanted with various tumor cell lines, soluble IL-15/IL-15Rα complexes (sIL-15 complexes) are abundant in the interstitial fluid of tumors with expression preceding the infiltration of tumor-infiltrating lymphocytes. Moreover, IL-15 as well as type I IFN, which regulates IL-15, was required for establishing normal numbers of CD8 T cells and natural killer cells in tumors. Depending on tumor type, both the tumor and the stroma are sources of sIL-15 complexes. In analyses of IL-15 reporter mice, most myeloid cells in the TME express IL-15 with CD11b⁺Ly6C^hi cells being the most abundant, indicating there is a large source of IL-15 protein in tumors that lies sequestered within the tumor stroma. Despite the abundance of IL-15-expressing cells, the relative levels of sIL-15 complexes are low in advanced tumors but can be up-regulated by local stimulator of IFN genes (STING) activation. Furthermore, while treatment of tumors with STING agonists leads to tumor regression, optimal STING-mediated immunity and regression of distant secondary tumors required IL-15 expression. Overall, our study reveals the dynamic regulation of IL-15 in the TME and its importance in antitumor immunity. These findings provide insight into an unappreciated attribute of the tumor landscape that contributes to antitumor immunity, which can be manipulated therapeutically to enhance antitumor responses.

T Cells in Adipose Tissue in Aging

Similar to obesity, aging is associated with visceral adiposity and insulin resistance. Inflammation in adipose tissue, mainly evidenced by increased accumulation and proinflammatory polarization of T cells and macrophages, has been well-documented in obesity and may contribute to the associated metabolic dysfunctions including insulin resistance. Studies show that increased inflammation, including inflammation in adipose tissue, also occurs in aging, so-called "inflamm-aging." Aging-associated inflammation in adipose tissue has some similarities but also differences compared to obesity-related inflammation. In particular, conventional T cells are elevated in adipose tissue in both obesity and aging and have been implicated in metabolic functions in obesity. However, the changes and also possibly functions of regulatory T cells (Treg) in adipose tissue are different in aging and obesity. In this review, we will summarize recent advances in research on the changes of these immune cells in adipose tissue with aging and obesity and discuss their possible contributions to metabolism and the potential of these immune cells as novel therapeutic targets for prevention and treatment of metabolic diseases associated with aging or obesity.

Bystander T Cells: A Balancing Act of Friends and Foes

T cell responses are essential for appropriate protection against pathogens. T cell immunity is achieved through the ability to discriminate between foreign and self-molecules, and this relies heavily on stringent T cell receptor (TCR) specificity. Recently, bystander activated T lymphocytes, that are specific for unrelated epitopes during an antigen-specific response, have been implicated in diverse diseases. Numerous infection models have challenged the classic dogma of T cell activation as being solely dependent on TCR and major histocompatibility complex (MHC) interactions, indicating an unappreciated role for pathogen-associated receptors on T cells. We discuss here the specific roles of bystander activated T cells in pathogenesis, shedding light on the ability of these cells to modulate disease severity independently from TCR recognition.

Critical role of post-transcriptional regulation for IFN-γ in tumor-infiltrating T cells

Protective T cell responses against tumors require the production of Interferon gamma (IFN-γ). However, tumor-infiltrating T cells (TILs) gradually lose their capacity to produce IFN-γ and therefore fail to clear malignant cells. Dissecting the underlying mechanisms that block cytokine production is thus key for improving T cell products. Here we show that although TILs express substantial levels of Ifng mRNA, post-transcriptional mechanisms impede the production of IFN-γ protein due to loss of mRNA stability. CD28 triggering, but not PD1 blocking antibodies, effectively restores the stability of Ifng mRNA. Intriguingly, TILs devoid of AU-rich elements within the 3'untranslated region maintain stabilized Ifng mRNA and produce more IFN-γ protein than wild-type TILs. This sustained IFN-γ production translates into effective suppression of tumor outgrowth, which is almost exclusively mediated by direct effects on the tumor cells. We therefore conclude that post-transcriptional mechanisms could be modulated to potentiate effective T cell therapies in cancer.

Is There Natural Killer Cell Memory and Can It Be Harnessed by Vaccination? Can Natural Killer and CD8 T Cells Switch Jobs?

Natural killer (NK) cells are components of innate immunity mediating defense at early times after viral infections. Their cytokine production and cell-mediated cytotoxicity functions overlap those of CD8 T cells elicited later during primary adaptive immune responses, but the populations are distinguished by their basal states and activating receptors as well as the kinetics of their responses. Demonstration of long-lived NK cells has led to speculation on the potential for inducing these to contribute to immunological memory. Conversely, activated CD8 T cells can acquire responses to innate cytokines and, as a result, have the potential to contribute to innate immunity. These observations beg the question: what is required to be a player in innate and adaptive immunity?

Local Adjuvant Treatment with Low-Dose CpG-B Offers Durable Protection against Disease Recurrence in Clinical Stage I-II Melanoma: Data from Two Randomized Phase II Trials

Purpose: Although risk of recurrence after surgical removal of clinical stage I-II melanoma is considerable, there is no adjuvant therapy with proven efficacy. Here, we provide clinical evidence that a local conditioning regimen, aimed at immunologic arming of the tumor-draining lymph nodes, may provide durable protection against disease recurrence (median follow-up, 88.8 months).Experimental Design: In two randomized phase II trials, patients, diagnosed with stage I-II melanoma after excision of the primary tumor, received local injections at the primary tumor excision site within 7 days preceding re-excision and sentinel lymph node (SLN) biopsy of either a saline placebo (n = 22) or low-dose CpG type B (CpG-B) with (n = 9) or without (n = 21) low-dose GM-CSF.Results: CpG-B treatment was shown to be safe, to boost locoregional and systemic immunity, to be associated with lower rates of tumor-involved SLN (10% vs. 36% in controls, P = 0.04), and, at a median follow-up of 88.8 months, to profoundly improve recurrence-free survival (P = 0.008), even for patients with histologically confirmed (i.e., pathologic) stage I-II disease (P = 0.02).Conclusions: Potentially offering durable protection, local low-dose CpG-B administration in early-stage melanoma provides an adjuvant treatment option for a large group of patients currently going untreated despite being at considerable risk for disease recurrence. Once validated in a larger randomized phase III trial, this nontoxic immunopotentiating regimen may prove clinically transformative. Clin Cancer Res; 23(19); 5679-86. ©2017 AACR.

Translational repression of pre-formed cytokine-encoding mRNA prevents chronic activation of memory T cells

Memory T cells are critical for the immune response to recurring infections. Their instantaneous reactivity to pathogens is empowered by the persistent expression of cytokine-encoding mRNAs. How the translation of proteins from pre-formed cytokine-encoding mRNAs is prevented in the absence of infection has remained unclear. Here we found that protein production in memory T cells was blocked via a 3' untranslated region (3' UTR)-mediated process. Germline deletion of AU-rich elements (AREs) in the Ifng-3' UTR led to chronic cytokine production in memory T cells. This aberrant protein production did not result from increased expression and/or half-life of the mRNA. Instead, AREs blocked the recruitment of cytokine-encoding mRNA to ribosomes; this block depended on the ARE-binding protein ZFP36L2. Thus, AREs mediate repression of translation in mouse and human memory T cells by preventing undesirable protein production from pre-formed cytokine-encoding mRNAs in the absence of infection.

Enzymatic synthesis of core 2 O-glycans governs the tissue-trafficking potential of memory CD8+ T cells

Trafficking of memory CD8⁺ T cells out of the circulation is essential to provide protective immunity against intracellular pathogens in nonlymphoid tissues. However, the molecular mechanisms that dictate the trafficking potential of diverse memory CD8⁺ T cell populations are not completely defined. We show that after infection or inflammatory challenge, central memory (T_CM) CD8⁺ T cells rapidly traffic into nonlymphoid tissues, whereas most effector memory cells remain in the circulation. Furthermore, we demonstrate that cellular migration of memory CD8⁺ T cells into nonlymphoid tissues is driven by interleukin-15 (IL-15)-stimulated enzymatic synthesis of core 2 O-glycans, which generates functional ligands for E- and P-selectins. Given that IL-15-stimulated expression of glycosyltransferase enzymes is largely a feature of T_CM CD8⁺ T cells, this allows T_CM to selectively migrate out of the circulation and into nonlymphoid tissues. Collectively, our data indicate that entry of memory CD8⁺ T cells into inflamed, nonlymphoid tissues is primarily restricted to T_CM cells that have the capacity to synthesize core 2 O-glycans.

A Guide to IL-1 family cytokines in adjuvanticity

Growing awareness of the multiplicity of roles for the IL-1 family in immune regulation has prompted research exploring these cytokines in the context of vaccine-induced immunity. While tightly regulated, cytokines of the IL-1 family are normally released in response to cellular stress and in combination with other danger-/damage-associated molecular patterns (DAMPs), triggering potent local and systemic immune responses. In the context of infection or autoimmunity, engagement of IL-1 family receptors links robust innate responses to adaptive immunity. Clinical and experimental evidence has revealed that many vaccine adjuvants induce the release of one or multiple IL-1 family cytokines. The coordinated release of IL-1 family members in response to adjuvant-induced damage or cell death may be a determining factor in the transition from local inflammation to the induction of an adaptive response. Here, we analyse the effects of IL-1 family cytokines on innate and adaptive immunity with a particular emphasis on activation of antigen-presenting cells and induction of T cell-mediated immunity, and we address in detail the contribution of these cytokines to the modes of action of vaccine adjuvants including those currently approved for human use.

Antigen-Induced but Not Innate Memory CD8 T Cells Express NKG2D and Are Recruited to the Lung Parenchyma upon Viral Infection

The pool of memory-phenotype CD8 T cells is composed of Ag-induced (AI) and cytokine-induced innate (IN) cells. IN cells have been described as having properties similar to those of AI memory cells. However, we found that pathogen-induced AI memory cells can be distinguished in mice from naturally generated IN memory cells by surface expression of NKG2D. Using this marker, we described the increased functionalities of AI and IN memory CD8 T cells compared with naive cells, as shown by comprehensive analysis of cytokine secretion and gene expression. However, AI differed from IN memory CD8 T cells by their capacity to migrate to the lung parenchyma upon inflammation or infection, a process dependent on their expression of ITGA1/CD49a and ITGA4/CD49d integrins.

KLRG1+ Effector CD8+ T Cells Lose KLRG1, Differentiate into All Memory T Cell Lineages, and Convey Enhanced Protective Immunity

Protective immunity against pathogens depends on the efficient generation of functionally diverse effector and memory T lymphocytes. However, whether plasticity during effector-to-memory CD8⁺ T cell differentiation affects memory lineage specification and functional versatility remains unclear. Using genetic fate mapping analysis of highly cytotoxic KLRG1⁺ effector CD8⁺ T cells, we demonstrated that KLRG1⁺ cells receiving intermediate amounts of activating and inflammatory signals downregulated KLRG1 during the contraction phase in a Bach2-dependent manner and differentiated into all memory T cell linages, including CX₃CR1^int peripheral memory cells and tissue-resident memory cells. "ExKLRG1" memory cells retained high cytotoxic and proliferative capacity distinct from other populations, which contributed to effective anti-influenza and anti-tumor immunity. Our work demonstrates that developmental plasticity of KLRG1⁺ effector CD8⁺ T cells is important in promoting functionally versatile memory cells and long-term protective immunity.

Inflammatory monocytes contribute to the persistence of CXCR3hi CX3CR1lo circulating and lung-resident memory CD8+ T cells following respiratory virus infection

Phenotypically diverse memory CD8⁺ T cells are present in the lungs that either re-circulate or reside within the tissue. Understanding the key cellular interactions that regulate the generation and then persistence of these different subsets is of great interest. Recently, DNGR-1⁺ dendritic cell (DC) mediated priming was reported to control the generation of lung-resident but not circulating memory cells following respiratory viral infection. Here, we report an important role for Ly6C⁺ inflammatory monocytes (IMs) in contributing to the persistence of memory CD8⁺ T cells but not their generation. Effector CD8⁺ T cells expanded and contracted normally in the absence of IMs, but the memory compartment declined significantly over time. Quite unexpectedly, this defect was confined to tissue resident and circulating CXCR3^hi CX3CR1^lo memory cells but not CXCR3^hi CX3CR1^int and CXCR3^lo CX3CR1^hi subsets. Thus, two developmentally distinct innate cells orchestrate the generation and persistence of memory T cell subsets following a respiratory virus infection. See also: News and Commentary by Lafouresse & Groom.