The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field.

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

Divergent effects of tumor necrosis factor (TNF) in sepsis: a meta-analysis of experimental studies.

INTRODUCTION: Experimental studies in animals have yielded conflicting results on the role of Tumor Necrosis Factor (TNF) in sepsis and endotoxemia, with some reporting adaptive and others inappropriate effects. A meta-analysis of the available literature was performed to determine the factors explaining this discrepancy. METHODS: The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The protocol was registered with PROSPERO (CRD42020167384) prior to data collection. PubMed and Embase were the databases queried. Risk of bias was evaluated using the SYRCLE Risk of Bias Tool. All animal studies investigating sepsis-related mortality and modified TNF signaling were considered eligible. The exclusion criteria were: lack of mortality data, 7-day mortality rates below 10% in both wild type and TNF-altered pathway animals, and absence of an English abstract. To determine the role of TNF according to the experimental protocol, three approaches were used: first an approach based on the statistical significance of each experiment, then the pooled mortality was calculated, and finally the weighted risk ratio for mortality was assessed. RESULTS: A total of 175 studies were included in the analysis, comprising a total of 760 experiments and involving 19,899 animals. The main species used were mice (77%) and rats (21%). The most common method of TNF pathway modulation was TNF pathway inactivation that was primarily associated with an inappropriate secretion of TNF. At the opposite, TNF injection was associated with an adaptive role of TNF. Lipopolysaccharide (LPS) injection was the most used stimulus to establish an infectious model (42%) and was strongly associated with an inappropriate role of TNF. Conversely, live bacterial models, especially the cecal ligation and puncture (CLP) model, pneumonia, meningitis, and gastrointestinal infection, were associated with an adaptive role. This was particularly evident for Listeria monocytogenes, Streptococcus pneumoniae. CONCLUSION: The role of TNF during infection varies depending on the experimental model used. Models that mimic clinical conditions, based on virulent bacteria that cause high mortality even at low inocula, demonstrated an adaptive role of TNF. Conversely, models based on LPS or low-pathogenic live bacteria, administered at doses well above physiological thresholds and combined with early antibiotic therapy, were associated with an inappropriate role.

From septicemia to sepsis 3.0-from Ignaz Semmelweis to Louis Pasteur.

Sepsis remains a contemporary threat, and its frequency remains high amongst an aging population. Its definition has been regularly revisited, but the impact of the translational research studying it remains very modest compared to the results seen after the introduction of hygiene and the use of antibiotics. In the past, the main forms of sepsis were hospital gangrene (also known as nosocomial fever or putrid fever) that affected the wounded, and puerperal fever that affected women shortly after delivery. In 1858, Armand Trousseau stated that these two pathologies were identical. Lucrezia Borgia, who died in 1519, is undoubtedly the most famous woman to die from puerperal fever. The notion of sepsis as a real epidemic was deplored. For decades doctors remained deaf to the recommendations of their clairvoyant colleagues who advocated for the use of hygienic measures. It was as early as 1795 that Alexander Gordon (UK) and later in 1843, Oliver Holmes (USA), called for the use of hygienic practices. In 1847, Ignaz Semmelweis, a Hungarian physician, provided an irrefutable demonstration of the importance of hygiene in the prevention of contamination by the hands of the practitioners. But Ignaz Semmelweis' life was a tragedy, his fight against the medical nomenklatura was a tragedy, and his death was a tragedy! Nowadays, Ignaz Semmelweis is receiving the honor that he deserves, but never received during his life. Carl Mayrhofer, Victor Feltz, and Léon Coze were the first to associate the presence of bacteria with sepsis. These observations were confirmed by Louis Pasteur who, thanks to his prestige, had a great influence on how to undertake measures to prevent infections. He inspired Joseph Lister who reduced mortality associated with surgery, particularly amputation, by utilizing antiseptic methods.

Duclaux, Chamberland, Roux, Grancher, and Metchnikoff: the five musketeers of Louis Pasteur.

The Institut Pasteur was created, thanks to worldwide generosity with the aim to welcome and treat rabies patients, to provide a place for scientific research and to offer new teaching programs in microbiology. Louis Pasteur invited his main collaborators, who had accompanied him during his previous investigations at École Normale Supérieure, to join him in his new institute. They contributed to the principle discoveries of Pasteur, such as the fight against spontaneous generation, the identification of the ferments of putrefaction, the fight against the silk worm disease, the research on wine and beer, and the set-up of the first vaccines against avian cholera, anthrax, swine erysipelas, and rabies. There were two scientists, Émile Duclaux and Charles Chamberland, and two medical doctors, Émile Roux, and Joseph Grancher. In addition, two Russian scientists were invited to join the Institute and to head a research laboratory, Élie Metchnikoff and Nikolaï Gamaleïa; the later will finally never join the institute.

A Novel Polyaminocarboxylate Compound To Treat Murine Pulmonary Aspergillosis by Interfering with Zinc Metabolism.

Aspergillus fumigatus can cause pulmonary aspergillosis in immunocompromised patients and is associated with a high mortality rate due to a lack of reliable treatment options. This opportunistic pathogen requires zinc in order to grow and cause disease. Novel compounds that interfere with fungal zinc metabolism may therefore be of therapeutic interest. We screened chemical libraries containing 59,223 small molecules using a resazurin assay that compared their effects on an A. fumigatus wild-type strain grown under zinc-limiting conditions and on a zinc transporter knockout strain grown under zinc-replete conditions to identify compounds affecting zinc metabolism. After a first screen, 116 molecules were selected whose inhibitory effects on fungal growth were further tested by using luminescence assays and hyphal length measurements to confirm their activity, as well as by toxicity assays on HeLa cells and mice. Six compounds were selected following a rescreening, of which two were pyrazolones, two were porphyrins, and two were polyaminocarboxylates. All three groups showed good in vitro activity, but only one of the polyaminocarboxylates was able to significantly improve the survival of immunosuppressed mice suffering from pulmonary aspergillosis. This two-tier screening approach led us to the identification of a novel small molecule with in vivo fungicidal effects and low murine toxicity that may lead to the development of new treatment options for fungal infections by administration of this compound either as a monotherapy or as part of a combination therapy.

Minimum Quality Threshold in Pre-Clinical Sepsis Studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.

PURPOSE: Pre-clinical animal studies precede the majority of clinical trials. While the clinical sepsis definitions and recommended treatments are regularly updated, a systematic review of pre-clinical models of sepsis has not been done and clear modeling guidelines are lacking. To address this deficit, a Wiggers-Bernard Conference on pre-clinical sepsis modeling was held in Vienna in May, 2017. The conference goal was to identify limitations of pre-clinical sepsis models and to propose a set of guidelines, defined as the "Minimum Quality Threshold in Pre-Clinical Sepsis Studies" (MQTiPSS), to enhance translational value of these models. METHODS: 31 experts from 13 countries participated and were divided into 6 thematic Working Groups (WG): (1) Study Design, (2) Humane modeling, (3) Infection types, (4) Organ failure/dysfunction, (5) Fluid resuscitation and (6) Antimicrobial therapy endpoints. As basis for the MQTiPSS discussions, the participants conducted a literature review of the 260 most highly cited scientific articles on sepsis models (2002-2013). RESULTS: Overall, the participants reached consensus on 29 points; 20 at "recommendation" (R) and 9 at "consideration" (C) strength. This Executive Summary provides a synopsis of the MQTiPSS consensus (Tables 1, 2 and 3). CONCLUSIONS: We believe that these recommendations and considerations will serve to bring a level of standardization to pre-clinical models of sepsis and ultimately improve translation of pre-clinical findings. These guideline points are proposed as "best practices" that should be implemented for animal sepsis models. In order to encourage its wide dissemination, this article is freely accessible in Shock, Infection and Intensive Care Medicine Experimental.

Correction to: Minimum Quality Threshold in Pre-Clinical Sepsis Studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.

The original version of this article unfortunately contained mistakes.

Local Microenvironment Controls the Compartmentalization of NK Cell Responses during Systemic Inflammation in Mice.

Systemic inflammatory response syndrome is a whole-body reaction to a triggering insult that often results in life-threatening illness. Contributing to the development of this inflammatory cascade are numerous cellular partners, among which NK cells were shown to play a key role. Accumulating evidence points to organ-specific properties of systemic inflammation and NK cells. However, little is known about compartment-specific activation of NK cells during systemic inflammatory response syndrome or the relative contribution of NK cell-intrinsic properties and microenvironmental cues. In this study, we undertook a sequential characterization of NK responses in the spleen, lungs, bone marrow, peritoneum, and blood using a mouse model of endotoxemia. We report that, despite similar systemic dynamics of NK cell responses, expression of activation markers (CD69 and CD25) and effector molecules (IFN-γ, granzyme B, and IL-10) display organ-specific thresholds of maximum activation. Using adoptive transfers of spleen and lung NK cells, we found that these cells have the capacity to quickly adapt to a new environment and adjust their response levels to that of resident NK cells. This functional adaptation occurs without significant alterations in phenotype and independently of subpopulation-specific trafficking. Thus, using a dynamic in vivo-transfer system, to our knowledge our study is the first to report the compartmentalization of NK cells responses during systemic inflammation and to show that NK cell-intrinsic properties and microenvironmental cues are involved in this process, in a sequential manner.

Administration of Zinc Chelators Improves Survival of Mice Infected with Aspergillus fumigatus both in Monotherapy and in Combination with Caspofungin.

Aspergillus fumigatus can infect immunocompromised patients, leading to high mortality rates due to the lack of reliable treatment options. This pathogen requires uptake of zinc from host tissues in order to successfully grow and cause virulence. Reducing the availability of that micronutrient could help treat A. fumigatus infections. In this study, we examined the in vitro effects of seven chelators using a bioluminescent strain of A. fumigatus 1,10-Phenanthroline and N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine (TPEN) proved to be the chelators most effective at inhibiting fungal growth. Intraperitoneal administration of either phenanthroline or TPEN resulted in a significant improvement in survival and decrease of weight loss and fungal burden for immunosuppressed mice intranasally infected with A. fumigatus In vitro both chelators had an indifferent effect when employed in combination with caspofungin. The use of TPEN in combination with caspofungin also significantly increased survival compared to that when using these drugs individually. Our results suggest that zinc chelation may be a valid strategy for dealing with A. fumigatus infections and that both phenanthroline and TPEN could potentially be used either independently or in combination with caspofungin, indicating that their use in combination with other antifungal treatments might also be applicable.

Intravenous Immunoglobulin with Enhanced Polyspecificity Improves Survival in Experimental Sepsis and Aseptic Systemic Inflammatory Response Syndromes.

Sepsis is a major cause for death worldwide. Numerous interventional trials with agents neutralizing single proinflammatory mediators have failed to improve survival in sepsis and aseptic systemic inflammatory response syndromes. This failure could be explained by the widespread gene expression dysregulation known as "genomic storm" in these patients. A multifunctional polyspecific therapeutic agent might be needed to thwart the effects of this storm. Licensed pooled intravenous immunoglobulin preparations seemed to be a promising candidate, but they have also failed in their present form to prevent sepsis-related death. We report here the protective effect of a single dose of intravenous immunoglobulin preparations with additionally enhanced polyspecificity in three models of sepsis and aseptic systemic inflammation. The modification of the pooled immunoglobulin G molecules by exposure to ferrous ions resulted in their newly acquired ability to bind some proinflammatory molecules, complement components and endogenous "danger" signals. The improved survival in endotoxemia was associated with serum levels of proinflammatory cytokines, diminished complement consumption and normalization of the coagulation time. We suggest that intravenous immunoglobulin preparations with additionally enhanced polyspecificity have a clinical potential in sepsis and related systemic inflammatory syndromes.

CD24-triggered caspase-dependent apoptosis via mitochondrial membrane depolarization and reactive oxygen species production of human neutrophils is impaired in sepsis.

Apoptosis is the most common pathway of neutrophil death under both physiological and inflammatory conditions. In this study, we describe an apoptotic pathway in human neutrophils that is triggered via the surface molecule CD24. In normal neutrophils, CD24 ligation induces death through depolarization of the mitochondrial membrane in a manner dependent on caspase-3 and caspase-9 and reactive oxygen species. Proinflammatory cytokines such as TNF-α, IFN-γ, and GM-CSF upregulated the expression of CD24 in vitro, favoring the emergence of a new CD16(high)/CD24(high) subset of cultured neutrophils. We observed that CD24 expression (at both mRNA and protein levels) was significantly downregulated in neutrophils from sepsis patients but not from patients with systemic inflammatory response syndrome. This downregulation was reproduced by incubation of neutrophils from healthy controls with corticosteroids or with plasma collected from sepsis patients, but not with IL-10 or TGF-ß. Decreased CD24 expression observed on sepsis neutrophils was associated with lack of functionality of the molecule, because cross-ligation of CD24 failed to trigger apoptosis in neutrophils from sepsis patients. Our results suggest a novel aspect of CD24-mediated immunoregulation and represent, to our knowledge, the first report showing the role of CD24 in the delayed/defective cell death in sepsis.

Low titers of serum antibodies inhibiting hemagglutination predict fatal fulminant influenza A(H1N1) 2009 infection.

RATIONALE: The biology of fatal pandemic influenza infection remains undefined. OBJECTIVES: To characterize the virologic and immune parameters associated with severity or death in patients who required mechanical ventilation for A(H1N1) 2009 pneumonia of various degrees of severity during the two waves of the 2009-2011 pandemic in Paris, France. METHODS: This multicenter study included 34 unvaccinated patients with very severe or fatal confirmed influenza A(H1N1) infections. It analyzed plasma A(H1N1) 2009 reverse-transcriptase polymerase chain reaction, hemagglutinin 222G viral mutation, and humoral and cellular immune responses to the virus, assessed in hemagglutination inhibition (HI), microneutralization, ELISA, lymphoproliferative, ELISpot IFN-γ, and cytokine and chemokine assays. MEASUREMENTS AND MAIN RESULTS: The patients' median age was 35 years. Influenza A(H1N1) 2009 viremia was detected in 4 of 34 cases, and a 222G hemagglutinin mutation in 7 of 17 cases, all of them with sequential organ failure assessment greater than or equal to 8. HI antibodies were detectable in 19 of 26 survivors and undetectable in all six fatal fulminant cases. ELISA and microneutralization titers were concordant. B-cell immunophenotyping and plasma levels of immunoglobulin classes did not differ between patients who survived and died. After immune complex dissociation, influenza ELISA serology became strongly positive in the bronchoalveolar lavage of the two fatal cases tested. H1N1-specific T-cell responses in lymphoproliferative and IFN-γ assays were detectable in survivors' peripheral blood, and lymphoproliferative assays were negative in the three fatal cases tested. Plasma levels of IL-6 and IL-10 were high in fatal cases and correlated with severity. Finally, a negative HI serology 4 days after the onset of influenza symptoms predicted death from fulminant influenza (P = 0.04). CONCLUSIONS: Early negative A(H1N1) 2009 HI serology can predict death from influenza. This negative serology in fatal cases in young adults reflects the trapping of anti-H1N1 antibodies in immune complexes in the lungs, associated with poor specific helper T-cell response. Clinical trial registered with www.clinicaltrials.gov (NCT 01089400).

Interferon-γ and granulocyte/monocyte colony-stimulating factor production by natural killer cells involves different signaling pathways and the adaptor stimulator of interferon genes (STING).

Natural killer (NK) cells are important for innate immunity in particular through the production of IFN-γ and GM-CSF. Both cytokines are important in restoration of immune function of tolerized leukocytes under inflammatory events. The expression of TLRs in NK cells has been widely studied by analyzing the mRNA of these receptors, rarely seeking their protein expression. We previously showed that murine spleen NK cells express TLR9 intracellularly and respond to CpG oligodeoxynucleotide (CpG-ODN) by producing IFN-γ and GM-CSF. However, to get such production the presence of accessory cytokines (such as IL-15 and IL-18) was required, whereas CpG-ODN or accessory cytokines alone did not induce IFN-γ or GM-CSF. We show here that TLR9 overlaps with the Golgi apparatus in NK cells. Furthermore, CpG-ODN stimulation in the presence of accessory cytokines induces the phosphorylation of c-Jun, STAT3, and IκBα. IFN-γ and GM-CSF production requires NF-κB and STAT3 activation as well as Erk-dependent mechanisms for IFN-γ and p38 signaling for GM-CSF. Using knock-out-mice, we show that UNC93b1 and IL-12 (produced by NK cells themselves) are also necessary for IFN-γ and GM-CSF production. IFN-γ production was found to be MyD88- and TLR9-dependent, whereas GM-CSF was TLR9-independent but dependent on STING (stimulator of interferon genes), a cytosolic adaptor recently described for DNA sensing. Our study thereby allows us to gain insight into the mechanisms of synergy between accessory cytokines and CpG-ODN in NK cells. It also identifies a new and alternative signaling pathway for CpG-ODN in murine NK cells.

TLR-mediated activation of NK cells and their role in bacterial/viral immune responses in mammals.

Natural killer (NK) cells are important in innate immunity, first described as guardians for the detection and clearance of transformed or virus-infected cells. Later, this cell type was revealed to be also able to recognize and respond to bacteria-infected cells. NK cells possess receptors allowing them to sense and respond to viral and bacterial patterns, including Toll-like receptors (TLRs). Initially described in other innate immune cells, particularly monocytes/macrophages, TLRs have more recently been characterized in NK cells. Controversies remain regarding the TLR expression in NK cells and their responsiveness to agonists, specifically the requirement for the presence of accessory cells, such as dendritic cells, or of accessory cytokines (IL-2, IL-12, IL-15 and IL-18) to respond to TLR agonists. Upon TLR activation, NK cells are an important source of IFN-γ and granulocyte macrophage colony-stimulating factor, cytokines necessary to fight infection but that can also contribute to deleterious inflammation if produced in excessive amounts. Here, we review the current knowledge concerning the expression of TLRs in and on NK cells and the responsiveness to their agonists and review the literature on the role of NK cells in the sensing of bacterial or viral patterns and in combatting infection.

NK cell tolerance to TLR agonists mediated by regulatory T cells after polymicrobial sepsis.

As sensors of infection, innate immune cells are able to recognize pathogen-associated molecular patterns by receptors such as TLRs. NK cells present in many tissues contribute to inflammatory processes, particularly through the production of IFN-γ. They may display a protective role during infection but also a detrimental role during sterile or infectious systemic inflammatory response syndrome. Nevertheless, the exact status of NK cells during bacterial sepsis and their capacity directly to respond to TLR agonists remain unclear. The expression of TLRs in NK cells has been widely studied by analyzing the mRNA of these receptors. The aim of this study was to gain insight into TLR2/TLR4/TLR9 expression on/in murine NK cells at the protein level and determine if their agonists were able to induce cytokine production. We show, by flow cytometry, a strong intracellular expression of TLR2 and a low of TLR4 in freshly isolated murine spleen NK cells, similar to that of TLR9. In vitro, purified NK cells respond to TLR2, TLR4, and TLR9 agonists, in synergy with activating cytokines (IL-2, IL-15, and/or IL-18), and produce proinflammatory cytokines (IFN-γ and GM-CSF). Finally, we explored the possible tolerance of NK cells to TLR agonists after a polymicrobial sepsis (experimental peritonitis). For the first time, to our knowledge, NK cells are shown to become tolerant in terms of proinflammatory cytokines production after sepsis. We show that this tolerance is associated with a reduction of the CD27(+)CD11b(-) subset in the spleen related to the presence of regulatory T cells and mainly mediated by TGF-ß.

Altered immune status of circulating T lymphocytes during sepsis: children also.

Altered immune status of blood leukocytes is a general phenomenon observed in adult patients with sepsis or septic shock. This is also the case in children with septic shock for both T helper 1 and T helper 2 lymphocytes, as demonstrated by their reduced ex vivo cytokine production upon activation by phytohemagglutinin.

Is boosting the immune system in sepsis appropriate?

A relative immunosuppression is observed in patients after sepsis, trauma, burns, or any severe insults. It is currently proposed that selected patients will benefit from treatment aimed at boosting their immune systems. However, the host immune response needs to be considered in context with pathogen-type, timing,and mainly tissue specificity. Indeed, the immune status of leukocytes is not universally decreased and their activated status in tissues contributes to organ failure. Accordingly, any new immune-stimulatory therapeutic intervention should take into consideration potentially deleterious effects in some situations.

Compartmentalization of the inflammatory response during bacterial sepsis and severe COVID-19.

Acute infections cause local and systemic disorders which can lead in the most severe forms to multi-organ failure and eventually to death. The host response to infection encompasses a large spectrum of reactions with a concomitant activation of the so-called inflammatory response aimed at fighting the infectious agent and removing damaged tissues or cells, and the anti-inflammatory response aimed at controlling inflammation and initiating the healing process. Fine-tuning at the local and systemic levels is key to preventing local and remote injury due to immune system activation. Thus, during bacterial sepsis and Coronavirus disease 2019 (COVID-19), concomitant systemic and compartmentalized pro-inflammatory and compensatory anti-inflammatory responses are occurring. Immune cells (e.g., macrophages, neutrophils, natural killer cells, and T-lymphocytes), as well as endothelial cells, differ from one compartment to another and contribute to specific organ responses to sterile and microbial insult. Furthermore, tissue-specific microbiota influences the local and systemic response. A better understanding of the tissue-specific immune status, the organ immunity crosstalk, and the role of specific mediators during sepsis and COVID-19 can foster the development of more accurate biomarkers for better diagnosis and prognosis and help to define appropriate host-targeted treatments and vaccines in the context of precision medicine.

Profiling the dysregulated immune response in sepsis: overcoming challenges to achieve the goal of precision medicine.

Sepsis is characterised by a dysregulated host immune response to infection. Despite recognition of its significance, immune status monitoring is not implemented in clinical practice due in part to the current absence of direct therapeutic implications. Technological advances in immunological profiling could enhance our understanding of immune dysregulation and facilitate integration into clinical practice. In this Review, we provide an overview of the current state of immune profiling in sepsis, including its use, current challenges, and opportunities for progress. We highlight the important role of immunological biomarkers in facilitating predictive enrichment in current and future treatment scenarios. We propose that multiple immune and non-immune-related parameters, including clinical and microbiological data, be integrated into diagnostic and predictive combitypes, with the aid of machine learning and artificial intelligence techniques. These combitypes could form the basis of workable algorithms to guide clinical decisions that make precision medicine in sepsis a reality and improve patient outcomes.

Cutting edge: crucial role of IL-1 and IL-23 in the innate IL-17 response of peripheral lymph node NK1.1- invariant NKT cells to bacteria.

We have shown previously that peripheral lymph node-resident retinoic acid receptor-related orphan receptor γt(+) NK1.1(-) invariant NKT (iNKT) cells produce IL-17A independently of IL-6. In this study, we show that the concomitant presence of IL-1 and IL-23 is crucial to induce a rapid and sustained IL-17A/F and IL-22 response by these cells that requires TCR-CD1d interaction and partly relies on IL-23-mediated upregulation of IL-23R and IL-1R1 expression. We further show that IL-1 and IL-23 produced by pathogen-associated molecular pattern-stimulated dendritic cells induce this response from NK1.1(-) iNKT cells in vitro, involving mainly TLR2/4-signaling pathways. Finally, we found that IL-17A production by these cells occurs very early and transiently in vivo in response to heat-killed bacteria. Overall, our study indicates that peripheral lymph node NK1.1(-) iNKT cells could be a source of innate Th17-related cytokines during bacterial infections and supports the hypothesis that they are able to provide an efficient first line of defense against bacterial invasion.