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Amyotrophic lateral sclerosis (ALS) is a heterogenous neurodegenerative disorder that affects motor neurons and voluntary muscle control1. ALS heterogeneity includes the age of manifestation, the rate of progression and the anatomical sites of symptom onset. Disease-causing mutations in specific genes have been identified and define different subtypes of ALS1. Although several ALS-associated genes have been shown to affect immune functions2, whether specific immune features account for ALS heterogeneity is poorly understood. Amyotrophic lateral sclerosis-4 (ALS4) is characterized by juvenile onset and slow progression3. Patients with ALS4 show motor difficulties by the time that they are in their thirties, and most of them require devices to assist with walking by their fifties. ALS4 is caused by mutations in the senataxin gene (SETX). Here, using Setx knock-in mice that carry the ALS4-causative L389S mutation, we describe an immunological signature that consists of clonally expanded, terminally differentiated effector memory (TEMRA) CD8 T cells in the central nervous system and the blood of knock-in mice. Increased frequencies of antigen-specific CD8 T cells in knock-in mice mirror the progression of motor neuron disease and correlate with anti-glioma immunity. Furthermore, bone marrow transplantation experiments indicate that the immune system has a key role in ALS4 neurodegeneration. In patients with ALS4, clonally expanded TEMRA CD8 T cells circulate in the peripheral blood. Our results provide evidence of an antigen-specific CD8 T cell response in ALS4, which could be used to unravel disease mechanisms and as a potential biomarker of disease state.

Amyotrophic Lateral Sclerosis (ALS) is a heterogeneous neurodegenerative disorder that affects motor neurons in the brain and spinal cord, causing progressive loss of voluntary muscle control1,2. ALS heterogeneity includes the age of manifestation, the rate of progression, and the anatomical sites of symptom onset. In addition, disease-causing mutations in specific genes have been identified and are used to catalog different subtypes of ALS3. Interestingly, several ALS-associated genes have been shown to affect immune functions, and a variety of aberrant inflammatory events have been reported in patients and mouse models4-11, suggesting that specific immune features can also account for ALS heterogeneity. ALS4 is characterized by juvenile-onset and slow progression12. After experiencing mild symptoms during their childhood, ALS4 patients show motor difficulties by their 30s, and most of them require walkers or wheelchairs by their 50s. ALS4 is caused by dominant mutations in the gene SETX. Using Setx knock-in (KI) mice carrying the ALS4 causative L389S mutation, we discovered an immunological signature consisting of clonally activated CD8 T cells specifically in the central nervous system and blood of KI animals. Expansion of antigen-specific CD8 T cells mirrors disease progression. Bone marrow transplantation experiments indicate an essential role of the immune system in ALS4 neurodegeneration. Furthermore, we found that clonally expanded CD8 T cells circulate in the peripheral blood of ALS4 patients. Our results provide evidence of an antigen-specific CD8 T cell response linked to ALS4, and can serve not only to unravel specific disease mechanisms, but as a potential biomarker of disease activity.

The ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is currently affecting millions of lives worldwide. Large retrospective studies indicate that an elevated level of inflammatory cytokines and pro-inflammatory factors are associated with both increased disease severity and mortality. Here, using multidimensional epigenetic, transcriptional, in vitro, and in vivo analyses, we report that topoisomerase 1 (TOP1) inhibition suppresses lethal inflammation induced by SARS-CoV-2. Therapeutic treatment with two doses of topotecan (TPT), an FDA-approved TOP1 inhibitor, suppresses infection-induced inflammation in hamsters. TPT treatment as late as 4 days post-infection reduces morbidity and rescues mortality in a transgenic mouse model. These results support the potential of TOP1 inhibition as an effective host-directed therapy against severe SARS-CoV-2 infection. TPT and its derivatives are inexpensive clinical-grade inhibitors available in most countries. Clinical trials are needed to evaluate the efficacy of repurposing TOP1 inhibitors for severe coronavirus disease 2019 (COVID-19) in humans., Graphical abstract, Inhibition of topoisomerase 1 through the FDA-approved molecule topotecan suppresses SARS-CoV-2-infection-associated lethal inflammation in hamster and mouse models without compromising antiviral immune responses.

SUMMARYThe ongoing pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is currently affecting millions of lives worldwide. Large retrospective studies indicate that an elevated level of inflammatory cytokines and pro-inflammatory factors are associated with both increased disease severity and mortality. Here, using multidimensional epigenetic, transcriptional, in vitro and in vivo analyses, we report that Topoisomerase 1 (Top1) inhibition suppresses lethal inflammation induced by SARS-CoV-2. Therapeutic treatment with two doses of Topotecan (TPT), a FDA-approved Top1 inhibitor, suppresses infection-induced inflammation in hamsters. TPT treatment as late as four days post-infection reduces morbidity and rescues mortality in a transgenic mouse model. These results support the potential of Top1 inhibition as an effective host-directed therapy against severe SARS-CoV-2 infection. TPT and its derivatives are inexpensive clinical-grade inhibitors available in most countries. Clinical trials are needed to evaluate the efficacy of repurposing Top1 inhibitors for COVID-19 in humans.

RNA viruses are a major human health threat. The life cycles of many highly pathogenic RNA viruses like influenza A virus (IAV) and Lassa virus depends on host mRNA, as viral polymerases cleave 5’-m7G-capped host transcripts to primeviral mRNA synthesis (‘cap-snatching’). We hypothesized that start codons within cap-snatched host transcripts could generate chimeric human-viral mRNAs with coding potential. We report the existence of this mechanism of gene origination, that we named ‘start-snatching’. Depending on the reading frame, start-snatching allows the translation of host and viral “untranslated regions” (UTRs) to create Nterminallyextended viral proteins or entirely novel polypeptides by geneticoverprinting. We show that both types of chimeric proteins are made in IAVinfectedcells, generate T cell responses and contribute to virulence. Our resultsindicate that during infection with IAV, and likely a multitude of other human-,animal- and plant-viruses, a host-dependent mechanism allows the genesis ofhybrid genes.

A method using multilayer perceptrons for analysing diffusion profiles and sketching the temperature history of geological samples is explored. Users of this method can intuitively test and compare results thinking in terms of analytical solutions of the diffusion equation whilst the bulk of the work is made computationally. Being neither completely analytical nor numerical, the method is a hybrid and represents an ideal man-machine interaction. The approach presented in this paper should be preferred when the retrieval of the diffusion coefficients from concentration profiles using dimensionless parameters is not possible and/or there is more than one unknown parameter in the analytical solution of the diffusion equation. Its versatility is a key factor for extending the potential of Dodson’s formulation. The case of a species produced by a radiogenic source and diffusing in a cooling system is therefore discussed. Both the classical change of variable for diffusion coefficients depending on time and an alternative approach decomposing the overall effect of diffusion into a sum of effects due to smaller events could be used to tackle this problem. As multilayer perceptrons can approximate any function, none of the assumptions originally stated by Dodson are necessary.

Motor neuron disorders (MND) cause disability and death globally. Despite an increasing knowledge of the genetic defects of MND, a clear understanding of the mechanisms of disease initiation and progression is lacking. Recent advance in the field has highlighted that several genes linked to MND are essential for maintaining immune homeostasis, suggesting that dysfunctions in the immune system could influence the development of the disease or aggravate its pathology. Amyotrophic Lateral Sclerosis 4 (ALS4) is a rare, juvenile form of MND. It is caused by mutations in the gene SENATAXIN (SETX), which encodes for a nuclear helicase ubiquitously expressed. Our group identified SETX as a transcriptional regulator of inflammatory responses. Since SETX is involved in both MND and the control of the immune response, we hypothesized that underlying defects in the immune system could be associated to ALS4 progression. We took advantage of the Setx-L389S+/− knock-in (KI) mouse carrying the most common causative variant of ALS4 in humans. Surprisingly, we found that SetxL389S needs to be expressed in both neuronal and immune cells to trigger disease. In parallel, we discovered a pathologic signature consisting of high frequencies of activated CD8 T cells in the central nervous system (CNS) and blood of KI animals. Further analyses showed clonal expansion of aberrant activated CD8 T cells. Dysfunctions in the CD8 T cell compartment have been confirmed in the peripheral blood of ALS4 patients, as compared to age-matched controls. Collectively, our results suggest that ALS4 is characterized by aberrant CD8 T cell responses of possible autoimmune origin. Our findings have the potential to pave the way for immune-based diagnosis and therapy for patients.

Microbial infections often precede the onset of autoimmunity. How infections trigger autoimmunity remains poorly understood. We investigated the possibility that infection might create conditions that allow the stimulatory presentation of self peptides themselves and that this might suffice to elicit autoreactive T cell responses that lead to autoimmunity. Self-reactive CD4(+) T cells are major drivers of autoimmune disease, but their activation is normally prevented through regulatory mechanisms that limit the immunostimulatory presentation of self antigens. Here we found that the apoptosis of infected host cells enabled the presentation of self antigens by major histocompatibility complex class II molecules in an inflammatory context. This was sufficient for the generation of an autoreactive TH17 subset of helper T cells, prominently associated with autoimmune disease. Once induced, the self-reactive TH17 cells promoted auto-inflammation and autoantibody generation. Our findings have implications for how infections precipitate autoimmunity.

Endogenous retroviruses (ERVs) occupy extensive regions of the human genome. Although many of these retroviral elements have lost their ability to replicate, those whose insertion took place more recently, such as the HML-2 group of HERV-K elements, still retain intact open reading frames and the capacity to produce certain viral RNA and/or proteins. Transcription of these ERVs is, however, tightly regulated by dedicated epigenetic control mechanisms. Nonetheless, it has been reported that some pathological states, such as viral infections and certain cancers, coincide with ERV expression, suggesting that transcriptional reawakening is possible. HML-2 elements are reportedly induced during HIV-1 infection, but the conserved nature of these elements has, until recently, rendered their expression profiling problematic. Here, we provide comprehensive HERV-K HML-2 expression profiles specific for productively HIV-1-infected primary human CD4 + T cells. We combined enrichment of HIV-1 infected cells using a reporter virus expressing a surface reporter for gentle and efficient purification with long-read single-molecule real-time sequencing. We show that three HML-2 proviruses—6q25.1, 8q24.3, and 19q13.42—are upregulated on average between 3- and 5-fold in HIV-1-infected CD4 + T cells. One provirus, HML-2 12q24.33, in contrast, was repressed in the presence of active HIV replication. In conclusion, this report identifies the HERV-K HML-2 loci whose expression profiles differ upon HIV-1 infection in primary human CD4 + T cells. These data will help pave the way for further studies on the influence of endogenous retroviruses on HIV-1 replication. IMPORTANCE Endogenous retroviruses inhabit big portions of our genome. Moreover, although they are mainly inert, some of the evolutionarily younger members maintain the ability to express both RNA and proteins. We have developed an approach using long-read single-molecule real-time (SMRT) sequencing that produces long reads that allow us to obtain detailed and accurate HERV-K HML-2 expression profiles. We applied this approach to study HERV-K expression in the presence or absence of productive HIV-1 infection of primary human CD4 + T cells. In addition to using SMRT sequencing, our strategy also includes the magnetic selection of the infected cells so that levels of background expression due to uninfected cells are kept at a minimum. The results presented here provide a blueprint for in-depth studies of the interactions of the authentic upregulated HERV-K HML-2 elements and HIV-1.

A novel method using neural networks to analyse diffusion profiles is presented. Multilayer perceptrons are used to approximate the analytical solution of the diffusion equation and find within it any unknown parameter that best fits a given data set. An example based on published data of diffusion of helium is examined to illustrate the main steps of the method. The exercise shows that it is possible to refine the value of diffusion coefficients up to two orders of magnitude in terms of precision. A particular feature of the method is that calibration curves can be taken into account when choosing the best setup of a network, which allows minimization of instrument specific error. A general version of the method giving the opportunity to define a local diffusion coefficient is also discussed, which could be considered for cases where the analytical solution of the diffusion equation cannot be identified a priori or does not exist.

A multi-isotope approach has been used in the Marano lagoon (NE Italy) and parts of its catchment area to identify causes of increased View the MathML source pollution. The hydrogeochemical features of different water types and potential sources of View the MathML source were characterized using the isotopic composition of View the MathML source (d15N, d18O, and ?17O) and other source-related species such as B (d11B), water (d2H and d18O) and View the MathML source (d34S and d18O). Water samples from the lagoon, its tributary rivers, the groundwater up-welling line, groundwater, sewer pipes, and open sea water have been collected at quarterly intervals in the years 2009–2010. The results indicate that the View the MathML source load in the lagoon was not only derived from agricultural activities but also from other sources such as urban waste water, in situ nitrification and atmospheric deposition. The d34S signature in the lagoon clearly denotes the largely prevailing origin of aqueous View the MathML source from seawater, and practically points to the absence of any appreciable redox process involving S species in the lagoon. It also supports the existence of a connection between the lagoon and the nearby Tagliamento river.

Due to increased pollution by nitrate from intensive agricultural and other anthropogenic activities the Marano lagoon (northeast Italy) and part of its catchment area have been investigated, applying a combined approach of hydrochemical and isotopic techniques. Thus, to identify and characterize the potential multiple-sources of nitrate pollution the isotopic compositions of nitrate (δ 15 N, δ 18 O, and Δ 17 O), boron (δ 11 B), water (δ 2 H and δ 18 O), and sulphate (δ 34 S and δ 18 O), as well as the chemical composition of different water types have been determined. In the monitoring program water samples from the lagoon, its tributary rivers, the groundwater upwelling line, groundwater, sewage, and open sea on a quarterly interval from 2009 to 2010 have been collected and analyzed. Coupling isotopic and hydrochemical results indicate that the nitrate load in the lagoon was not only derived from agriculture activities but also from other sources such as urban wastewaters, in situ nitrification, and atmospheric deposition. However, none of the samples showed the isotopic characteristics of synthetic fertilizers.

Unwinding DNA and unleasing inflammation Fighting infections often comes with collateral damage, which sometimes can be deadly. For instance, in septic shock, the overwhelming release of inflammatory mediators drives multi-organ failure. Rialdi et al. now report a potential new therapeutic target for controlling excessive inflammation: the DNA unwinding enzyme topoisomerase I (Top1) (see the Perspective by Pope and Medzhitov). Upon infection, Top1 specifically localizes to the promoters of pathogen-induced genes and promotes their transcription by helping to recruit RNA polymerase II. Pharmacological inhibition of Top1 in a therapeutic setting increased survival in several mouse models of severe microbially induced inflammation. Science , this issue p. 10.1126/science.aad7993 ; see also p. 1058

International audience; Memory CD8(+) T lymphocytes are critical effector cells of the adaptive immune system mediating long-lived pathogen-specific protective immunity. Three signals - antigen, costimulation and inflammation - orchestrate optimal CD8(+) T-cell priming and differentiation into effector and memory cells and shape T-cell functional fate and ability to protect against challenge infections. While among the conventional spleen DCs (cDCs), the CD8α(+) but not the CD8α(-) cDCs most efficiently mediate CD8(+) T-cell priming, it is unclear which subset, irrespective of their capacity to process MHC class I-associated antigens, is most efficient at inducing naïve CD8(+) T-cell differentiation into pathogen-specific protective memory cells in vivo. Moreover, the origin of the required signals is still unclear. Using mice infected with the intracellular bacterium Listeria monocytogenes, we show that splenic CD8α(+) cDCs become endowed with all functional features to optimally prime protective memory CD8(+) T cells in vivo within only a few hours post-immunization. Such programming requires both cytosolic signals resulting from bacterial invasion of the host cells and extracellular inflammatory mediators. Thus, these data designate these cells as the best candidates to facilitate the development of cell-based vaccine therapy.

Dendritic cells (DCs) have the striking ability to cross-present exogenous antigens in association with major histocompatibility complex (MHC) class I to CD8(+) T cells. However, the intracellular pathways underlying cross-presentation remain ill defined. Current models involve cytosolic proteolysis of antigens by the proteasome and peptide import into endoplasmic reticulum (ER) or phagosomal lumen by the transporters associated with antigen processing (TAP1 and TAP2). Here, we show that DCs expressed an ER-resident 47 kDa immune-related GTPase, Igtp (Irgm3). Igtp resides on ER and lipid body (LB) membranes where it binds the LB coat component ADFP. Inactivation of genes encoding for either Igtp or ADFP led to defects in LB formation in DCs and severely impaired cross-presentation of phagocytosed antigens to CD8(+) T cells but not antigen presentation to CD4(+) T cells. We thus define a new role for LB organelles in regulating cross-presentation of exogenous antigens to CD8(+) T lymphocytes in DCs.

The nuclear RNA exosome is an essential multi-subunit complex that controls RNA homeostasis. Congenital mutations in RNA exosome genes are associated with neurodegenerative diseases. Little is known about the role of the RNA exosome in the cellular response to pathogens. Here, using NGS and human and mouse genetics, we show that influenza A virus (IAV) ribogenesis and growth are suppressed by impaired RNA exosome activity. Mechanistically, the nuclear RNA exosome coordinates the initial steps of viral transcription with RNAPII at host promoters. The viral polymerase complex co-opts the nuclear RNA exosome complex and cellular RNAs en route to 3' end degradation. Exosome deficiency uncouples chromatin targeting of the viral polymerase complex and the formation of cellular:viral RNA hybrids, which are essential RNA intermediates that license transcription of antisense genomic viral RNAs. Our results suggest that evolutionary arms races have shaped the cellular RNA quality control machinery.

Apoptosis is a programmed form of cell death whereby characteristic internal cellular dismantling is accompanied by the preservation of plasma membrane integrity. Maintaining this order during apoptosis prevents the release of cellular contents and ensures a noninflammatory death. Here, we consider examples of apoptosis in different contexts and discuss how the same form of cell death could have different immunological consequences. Multiple parameters such as cell death as a result of microbial infection, the nature of the inflammatory microenvironment, the type of responding phagocytic cells and the genetic background of the host organism all differentially influence the immunological consequences of apoptosis.

Viruses are obligate parasites and thus require the machinery of the host cell to replicate. Inhibition of host factors co-opted during active infection is a strategy hosts use to suppress viral replication and a potential pan-antiviral therapy. To define the cellular proteins and processes required for a virus during infection is thus crucial to understanding the mechanisms of virally induced disease. In this report, we generated fully infectious tagged influenza viruses and used infection-based proteomics to identify pivotal arms of cellular signaling required for influenza virus growth and infectivity. Using mathematical modeling and genetic and pharmacologic approaches, we revealed that modulation of Sec61-mediated cotranslational translocation selectively impaired glycoprotein proteostasis of influenza as well as HIV and dengue viruses and led to inhibition of viral growth and infectivity. Thus, by studying virus-human protein-protein interactions in the context of active replication, we have identified targetable host factors for broad-spectrum antiviral therapies. Viruses are obligate parasites dependent on the host cell machinery. Using infection-based proteomics, biochemistry, and mathematical modeling, Marazzi and colleagues reveal that targeting host factors controlling essential cellular functions can provide broad-spectrum antiviral effects. Loss-of-function and chemical inhibition of one such factor, Sec61, inhibited influenza, HIV, and dengue virus replication. Fil: Heaton, Nicholas S.. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Moshkina, Natasha. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Fenouil, Romain. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Gardner, Thomas J.. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Aguirre, Sebastian. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Shah, Priya S.. University of California; Estados Unidos Fil: Zhao, Nan. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Manganaro, Lara. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Hultquist, Judd F.. University of California; Estados Unidos Fil: Noel, Justine. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Sachs, David H.. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Hamilton, Jennifer. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Leon, Paul E.. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Chawdury, Amit. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Tripathi, Shashank. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Melegari, Camilla. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Campisi, Laura. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Hai, Rong. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Metreveli, Giorgi. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Gamarnik, Andrea Vanesa. Fundación Instituto Leloir; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina Fil: García Sastre, Adolfo. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Greenbaum, Benjamin. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Simon, Viviana. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Fernandez Sesma, Ana. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Krogan, Nevan J.. University of California; Estados Unidos Fil: Mulder, Lubbertus C.F.. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: van Bakel, Harm. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Tortorella, Domenico. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Taunton, Jack. University of California; Estados Unidos Fil: Palese, Peter. Icahn School Of Medicine At Mount Sinai; Estados Unidos Fil: Marazzi, Ivan. Icahn School Of Medicine At Mount Sinai; Estados Unidos

Genetic composition and major histocompatibility complex polymorphisms unequivocally predispose to autoimmune disease, but environmental factors also play a critical role in precipitating disease in susceptible individuals. Notorious among these has been microbial infection. Older studies describing associations between microbial infection and autoimmune disease are now followed by new studies demonstrating correlations between susceptibility to autoimmune disease and commensal colonization of the intestinal tract. T helper 17 (T(H)17) cells have gained a prominent role in autoimmune disease, and notably, their development within the intestine has been linked to colonization with specific commensal bacteria. Here, we consider current views on how microbes, T(H)17 cells, and autoimmunity are connected. We speculate on how the intricate relationships among commensal, pathogen, and the host might ultimately determine susceptibility to autoimmune disease.

International audience; CX(3)CR1 expression is associated with the commitment of CSF-1R(+) myeloid precursors to the macrophage/dendritic cell (DC) lineage. However, the relationship of the CSF-1R(+) CX(3)CR1(+) macrophage/DC precursor (MDP) with other DC precursors and the role of CX(3)CR1 in macrophage and DC development remain unclear. We show that MDPs give rise to conventional DCs (cDCs), plasmacytoid DCs (PDCs), and monocytes, including Gr1(+) inflammatory monocytes that differentiate into TipDCs during infection. CX(3)CR1 deficiency selectively impairs the recruitment of blood Gr1(+) monocytes in the spleen after transfer and during acute Listeria monocytogenes infection but does not affect the development of monocytes, cDCs, and PDCs.

Imaging techniques have been revolutionized by advancements in both microscope instrumentation and data collection processing software. Immunologists and microbiologists now have access to a large panel of powerful technologies that are characterized by different spatial and time resolutions. In this review, we discuss recent studies in which emerging imaging technologies have been used to decipher the complexity of the interactions between pathogens and their mammalian hosts. By focusing on two very different pathogens, Plasmodium and Salmonella, we emphasize the critical role of imaging studies in the understanding of the host's immune system response to a pathogen.

Cytolysis, interferon γ and tumor necrosis factor (TNF) α secretion are major effector mechanisms of memory CD8+ T cells that are believed to be required for immunological protection in vivo. By using mutants of the intracellular bacterium Listeria monocytogenes, we found that none of these effector activities is sufficient to protect against secondary infection with wild-type (WT) bacteria. We demonstrated that CCL3 derived from reactivated memory CD8+ T cells is required for efficient killing of WT bacteria. CCL3 induces a rapid TNF-α secretion by innate inflammatory mononuclear phagocytic cells (MPCs), which further promotes the production of radical oxygen intermediates (ROIs) by both MPCs and neutrophils. ROI generation is the final bactericidal mechanism involved in L. monocytogenes clearance. These results therefore uncover two levels of regulation of the antibacterial secondary protective response: (a) an antigen-dependent phase in which memory CD8+ T cells are reactivated and control the activation of the innate immune system, and (b) an antigen-independent phase in which the MPCs coordinate innate immunity and promote the bactericidal effector activities. In this context, CCL3-secreting memory CD8+ T cells are able to mediate “bystander” killing of an unrelated pathogen upon antigen-specific reactivation, a mechanism that may be important for the design of therapeutic vaccines.