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.

Louis Pasteur: Between Myth and Reality.

Louis Pasteur is the most internationally known French scientist. He discovered molecular chirality, and he contributed to the understanding of the process of fermentation, helping brewers and winemakers to improve their beverages. He proposed a process, known as pasteurization, for the sterilization of wines. He established the germ theory of infectious diseases that allowed Joseph Lister to develop his antiseptic practice in surgery. He solved the problem of silkworm disease, although he had refuted the idea of Antoine Béchamp, who first considered it was a microbial infection. He created four vaccines (fowl cholera, anthrax, pig erysipelas, and rabies) in the paths of his precursors, Henri Toussaint (anthrax vaccine) and Pierre Victor Galtier (rabies vaccine). He generalized the word "vaccination" coined by Richard Dunning, Edward Jenner's friend. Robert Koch, his most famous opponent, pointed out the great ambiguity of Pasteur's approach to preparing his vaccines. Analysis of his laboratory notebooks has allowed historians to discern the differences between the legend built by his hagiographers and reality. In this review, we revisit his career, his undeniable achievements, and tell the truth about a hero who made every effort to build his own fame.

Once upon a time, inflammation.

Inflammation has accompanied humans since their first ancestors appeared on Earth. Aulus Cornelius Celsus (25 BC-50 AD), a Roman encyclopedist, offered a still valid statement about inflammation: "Notae vero inflammationis sunt quatuor: rubor et tumor cum calore and dolore", defining the four cardinal signs of inflammation as redness and swelling with heat and pain. While inflammation has long been considered as a morbid phenomenon, John Hunter (18th century) and Elie Metchnikoff (19th century) understood that it was a natural and beneficial event that aims to address a sterile or an infectious insult. Many other famous scientists and some forgotten ones have identified the different cellular and molecular players, and deciphered the different mechanisms of inflammation. This review pays tribute to some of the giants who made major contributions, from Hippocrates to the late 19th and first half of the 20th century. We particularly address the discoveries related to phagocytes, diapedesis, chemotactism, and fever. We also mention the findings of the various inflammatory mediators and the different approaches designed to treat inflammatory disorders.

COVID-19 and earlier pandemics, sepsis, and vaccines: A historical perspective.

Humanity has regularly faced the threat of epidemics and pandemics over the course of history. Successful attempts to protect populations were initially made with the development of new vaccines, such as those against plague and cholera, under the leadership of the bacteriologist Waldemar Haffkine. Vaccines have led to a complete eradication of smallpox and bovine plague and a major reduction in other infectious diseases including diphtheria, typhoid fever, poliomyelitis, and Haemophilus influenzae type B meningitis. While a few coronaviruses have been identified that seasonally infect humans causing mild symptoms, the emergence of a new zoonotic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly triggered the ongoing coronavirus disease 2019 (COVID-19) as a global pandemic responsible for widespread mortality. The severe phenotypes of COVID-19 resemble a previous infectious threat that was initially designated as hospital fever and puerperal fever, presently known as sepsis. A SARS-CoV-2 infection has frequently been considered as a form of viral sepsis (owing to common features with bacterial sepsis) but is also associated with an array of specific and unique symptoms. Rapid progress in anti-SARS-CoV-2 vaccine development, in particular, the design of efficient messenger RNA (mRNA) and recombinant adenovirus vaccines, is crucial for curbing the pandemic.

Once upon a time, inflammation

Inflammation has accompanied humans since their first ancestors appeared on Earth. Aulus Cornelius Celsus (25 BC-50 AD), a Roman encyclopedist, offered a still valid statement about inflammation: "Notae vero inflammationis sunt quatuor: rubor et tumor cum calore and dolore", defining the four cardinal signs of inflammation as redness and swelling with heat and pain. While inflammation has long been considered as a morbid phenomenon, John Hunter (18th century) and Elie Metchnikoff (19th century) understood that it was a natural and beneficial event that aims to address a sterile or an infectious insult. Many other famous scientists and some forgotten ones have identified the different cellular and molecular players, and deciphered the different mechanisms of inflammation. This review pays tribute to some of the giants who made major contributions, from Hippocrates to the late 19th and first half of the 20th century. We particularly address the discoveries related to phagocytes, diapedesis, chemotactism, and fever. We also mention the findings of the various inflammatory mediators and the different approaches designed to treat inflammatory disorders.(AU)

H3K4me1 Supports Memory-like NK Cells Induced by Systemic Inflammation.

Natural killer (NK) cells are unique players in innate immunity and, as such, an attractive target for immunotherapy. NK cells display immune memory properties in certain models, but the long-term status of NK cells following systemic inflammation is unknown. Here we show that following LPS-induced endotoxemia in mice, NK cells acquire cell-intrinsic memory-like properties, showing increased production of IFNγ upon specific secondary stimulation. The NK cell memory response is detectable for at least 9 weeks and contributes to protection from E. coli infection upon adoptive transfer. Importantly, we reveal a mechanism essential for NK cell memory, whereby an H3K4me1-marked latent enhancer is uncovered at the ifng locus. Chemical inhibition of histone methyltransferase activity erases the enhancer and abolishes NK cell memory. Thus, NK cell memory develops after endotoxemia in a histone methylation-dependent manner, ensuring a heightened response to secondary stimulation.

Current gaps in sepsis immunology: new opportunities for translational research.

Increasing evidence supports a central role of the immune system in sepsis, but the current view of how sepsis affects immunity, and vice versa, is still rudimentary. The European Group on Immunology of Sepsis has identified major gaps that should be addressed with high priority, such as understanding how immunological alterations predispose to sepsis, key aspects of the immunopathological events during sepsis, and the long-term consequences of sepsis on patient's immunity. We discuss major unmet topics in those three categories, including the role of key immune cells, the cause of lymphopenia, organ-specific immunology, the dynamics of sepsis-associated immunological alterations, the role of the microbiome, the standardisation of immunological tests, the development of better animal models, and the opportunities offered by immunotherapy. Addressing these gaps should help us to better understand sepsis physiopathology, offering translational opportunities to improve its prevention, diagnosis, and care.

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.

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.

Immunosuppression is Inappropriately Qualifying the Immune Status of Septic and SIRS Patients.

Immunosuppression is the most commonly used concept to qualify the immune status of patients with either sterile systemic inflammatory response syndrome (SIRS) or sepsis. In this review we attempt to demonstrate that the concept of immunosuppression is an oversimplification of the complex anti-inflammatory response that occurs in patients dealing with a severe sterile or infectious insult. Particularly, the immune status of leukocytes varies greatly depending on the compartment from where they are derived from. Furthermore, although certain functions of immune cells present in the blood stream or in the hematopoietic organs can be significantly diminished, other functions are either unchanged or even enhanced. This juxtaposition illustrates that there is no global defect. The mechanisms called reprogramming or trained innate immunity are probably aimed at preventing a generalized deleterious inflammatory reaction, and work to maintain the defense mechanisms at their due levels.

Gastro-protective, therapeutic and anti-inflammatory activities of Pistacia lentiscus L. fatty oil against ethanol-induced gastric ulcers in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Pistacia lentiscus L. (Anacardiaceae) (PL) is a flowering plant that grows in the Mediterranean area. It is traditionally used in the treatment of various skin, respiratory and gastrointestinal disorders AIM OF THE STUDY: In the present study, we investigated the anti-ulcerogenic activity of Pistacia lentiscus fatty oil (PLFO) on ethanol-induced gastric ulcers in Wistar rats MATERIAL AND METHODS: PLFO was orally administered to two experimental groups of rats before or after ethanol induction of gastric ulcer. The lesions of the gastric mucosa were evaluated by macroscopic and histopathological examination. In addition, the amount of nitric oxide (NO) and pro-inflammatory cytokines [tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6)] in the supernatant from cultures of gastric mucosa explants were assessed. Finally, the mucus production and iNOS (inducible NO synthase) expression were determined by histochemical and immunohistochemical analysis, respectively RESULT: Our results indicated that the PLFO pretreatment or PLFO treatment significantly reduced ulcerated and hemorrhagic areas. Additionally, pretreatment or treatment with PLFO after ethanol-induced ulceration significantly reduced the plasma concentration of NO. Furthermore, a significant decrease of NO, IL-6 and TNF-α levels was observed in explant culture supernatants. iNOS expression was also reduced in the gastric mucosa. In contrast, mucus production by goblet cells was enhanced. Interestingly, histological analysis of the gastric mucosa has indicated that PLFO- pretreated and treated groups displayed normal histology CONCLUSION: Our results demonstrate that PLFO display significant prophylactic and therapeutic effects against gastric ulcers. Importantly, the mechanism underlying PLFO activities might implicate inhibition of inflammatory responses during gastric ulcer.

Historical links between toxinology and immunology.

Research on bacterial toxins is closely linked to the birth of immunology. Our understanding of the interaction of bacterial protein toxins with immune cells has helped to decipher immunopathology, develop preventive and curative treatments for infections, and propose anti-cancer immunotherapies. The link started when Behring and Kitasato demonstrated that serotherapy was effective against 'the strangling angel', namely diphtheria, and its dreadful toxin discovered by Roux and Yersin. The antitoxin treatment helped to save thousands of children. Glenny demonstrated the efficacy of the secondary immune response compared to the primary one. Ramon described anatoxins that allowed the elaboration of effective vaccines and discovered the use of adjuvant to boost the antibody response. Similar approaches were later made for the tetanus toxin. Studying antitoxin antibodies Ehrlich demonstrated, for the first time, the transfer of immunity from mother to newborns. In 1989 Marrack and Kappler coined the concept of 'superantigens' to characterize protein toxins that induce T-lymphocyte proliferation, and cytokine release by both T-lymphocytes and antigen presenting cells. More recently, immunotoxins have been designed to kill cancer cells targeted by either specific antibodies or cytokines. Finally, the action of IgE antibodies against toxins may explain their persistence through evolution despite their side effect in allergy.

Specific features of human monocytes activation by monophosphoryl lipid A.

We deciphered the mechanisms of production of pro- and anti-inflammatory cytokines by adherent human blood mononuclear cells (PBMC) activated by lipopolysaccharide (LPS) or monophosphoryl lipid A (MPLA). Both LPS and MPLA induced tumor necrosis factor (TNF) production proved to be dependent on the production of interleukin-1ß (IL-1ß). Of note, MPLA induced IL-1ß release in human adherent PBMCs whereas MPLA was previously reported to not induce this cytokine in murine cells. Both LPS and MPLA stimulatory effects were inhibited by Toll-like receptor-4 (TLR4) antagonists. Only monocytes activation by LPS was dependent on CD14. Other differences were noticed between LPS and MPLA. Among the different donors, a strong correlation existed in terms of the levels of TNF induced by different LPSs. In contrast, there was no correlation between the TNF productions induced by LPS and those induced by MPLA. However, there was a strong correlation when IL-6 production was analyzed. Blocking actin polymerization and internalization of the agonists inhibited MPLA induced TNF production while the effect on LPS induced TNF production depended on the donors (i.e. high TNF producers versus low TNF producers). Finally, conventional LPS, tolerized adherent PBMCs to TLR2 agonists, while MPLA primed cells to further challenge with TLR2 agonists.

Compartment diversity in innate immune reprogramming.

Pathogens or endogenous molecules can reprogram innate immunity. This process can take the form of priming or tolerance depending on the activating signal, and favors enhanced resistance to infection and other insults, by modulating inflammation. Similarly to their organ-specific properties, reprogramming of macrophages and NK cells, is also compartmentalized.

Exotoxins and endotoxins: Inducers of inflammatory cytokines.

Endotoxins and exotoxins are among the most potent bacterial inducers of cytokines. During infectious processes, the production of inflammatory cytokines including tumor necrosis factor (TNF), interleukin-1ß (IL-1ß), gamma interferon (IFNγ) and chemokines orchestrates the anti-infectious innate immune response. However, an overzealous production, leading up to a cytokine storm, can be deleterious and contributes to mortality consecutive to sepsis or toxic shock syndrome. Endotoxins of Gram-negative bacteria (lipopolysaccharide, LPS) are particularly inflammatory because they generate auto-amplificatory loops after activation of monocytes/macrophages. LPS and numerous pore-forming exotoxins also activate the inflammasome, the molecular platform that allows the release of mature IL-1ß and IL-18. Among exotoxins, some behave as superantigens, and as such activate the release of cytokines by T-lymphocytes. In most cases, pre-exposure to exotoxins enhances the cytokine production induced by LPS and its lethality, whereas pre-exposure to endotoxin usually results in tolerance. In this review we recall the various steps, which, from the very early discovery of pyrogenicity induced by bacterial products, ended to the discovery of the endogenous pyrogen. Furthermore, we compare the specific characteristics of endotoxins and exotoxins in their capacity to induce inflammatory cytokines.

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.

Cathepsin B-Deficient Mice Resolve Leishmania major Inflammation Faster in a T Cell-Dependent Manner.

A critical role for intracellular TLR9 has been described in recognition and host resistance to Leishmania parasites. As TLR9 requires endolysosomal proteolytic cleavage to achieve signaling functionality, we investigated the contribution of different proteases like asparagine endopeptidase (AEP) or cysteine protease cathepsins B (CatB), L (CatL) and S (CatS) to host resistance during Leishmania major (L. major) infection in C57BL/6 (WT) mice and whether they would impact on TLR9 signaling. Unlike TLR9-/-, which are more susceptible to infection, AEP-/-, CatL-/- and CatS-/- mice are as resistant to L. major infection as WT mice, suggesting that these proteases are not individually involved in TLR9 processing. Interestingly, we observed that CatB-/- mice resolve L. major lesions significantly faster than WT mice, however we did not find evidence for an involvement of CatB on either TLR9-dependent or independent cytokine responses of dendritic cells and macrophages or in the innate immune response to L. major infection. We also found no difference in antigen presenting capacity. We observed a more precocious development of T helper 1 responses accompanied by a faster decline of inflammation, resulting in resolution of footpad inflammation, reduced IFNγ levels and decreased parasite burden. Adoptive transfer experiments into alymphoid RAG2-/-γc-/- mice allowed us to identify CD3+ T cells as responsible for the immune advantage of CatB-/- mice towards L. major. In vitro data confirmed the T cell intrinsic differences between CatB-/- mice and WT. Our study brings forth a yet unappreciated role for CatB in regulating T cell responses during L. major infection.

Infection-Mediated Priming of Phagocytes Protects against Lethal Secondary Aspergillus fumigatus Challenge.

Phagocytes restrict the germination of Aspergillus fumigatus conidia and prevent the establishment of invasive pulmonary aspergillosis in immunecompetent mice. Here we report that immunecompetent mice recovering from a primary A. fumigatus challenge are protected against a secondary lethal challenge. Using RAGγc knock-out mice we show that this protection is independent of T, B and NK cells. In protected mice, lung phagocytes are recruited more rapidly and are more efficient in conidial phagocytosis and killing. Protection was also associated with an enhanced expression of CXCR2 and Dectin-1 on bone marrow phagocytes. We also show that protective lung cytokine and chemokine responses are induced more rapidly and with enhanced dynamics in protected mice. Our findings support the hypothesis that following a first encounter with a non-lethal dose of A. fumigatus conidia, the innate immune system is primed and can mediate protection against a secondary lethal infection.

Comparative Study of Injury Models for Studying Muscle Regeneration in Mice.

BACKGROUND: A longstanding goal in regenerative medicine is to reconstitute functional tissues or organs after injury or disease. Attention has focused on the identification and relative contribution of tissue specific stem cells to the regeneration process. Relatively little is known about how the physiological process is regulated by other tissue constituents. Numerous injury models are used to investigate tissue regeneration, however, these models are often poorly understood. Specifically, for skeletal muscle regeneration several models are reported in the literature, yet the relative impact on muscle physiology and the distinct cells types have not been extensively characterised. METHODS: We have used transgenic Tg:Pax7nGFP and Flk1GFP/+ mouse models to respectively count the number of muscle stem (satellite) cells (SC) and number/shape of vessels by confocal microscopy. We performed histological and immunostainings to assess the differences in the key regeneration steps. Infiltration of immune cells, chemokines and cytokines production was assessed in vivo by Luminex®. RESULTS: We compared the 4 most commonly used injury models i.e. freeze injury (FI), barium chloride (BaCl2), notexin (NTX) and cardiotoxin (CTX). The FI was the most damaging. In this model, up to 96% of the SCs are destroyed with their surrounding environment (basal lamina and vasculature) leaving a "dead zone" devoid of viable cells. The regeneration process itself is fulfilled in all 4 models with virtually no fibrosis 28 days post-injury, except in the FI model. Inflammatory cells return to basal levels in the CTX, BaCl2 but still significantly high 1-month post-injury in the FI and NTX models. Interestingly the number of SC returned to normal only in the FI, 1-month post-injury, with SCs that are still cycling up to 3-months after the induction of the injury in the other models. CONCLUSIONS: Our studies show that the nature of the injury model should be chosen carefully depending on the experimental design and desired outcome. Although in all models the muscle regenerates completely, the trajectories of the regenerative process vary considerably. Furthermore, we show that histological parameters are not wholly sufficient to declare that regeneration is complete as molecular alterations (e.g. cycling SCs, cytokines) could have a major persistent impact.

The fiendish behavior of TNF can be counteracted by microRNA.

Tumor necrosis factor (TNF) is a fascinating anti­tumoral cytokine, which plays a key role in orchestrating the fight of innate immunity against infection. Concomitantly, TNF is a major player of the inflammatory response, as illustrated by successful therapeutic strategies targeting TNF in patho logies such as Crohn's diseases, rheumatoid arthritis or psoriasis. In mice, TNF is able to induce tissue injuries and lethal shock. In this issue of EMBO Molecular Medicine, Puimège et al (2015) elegantly demonstrated that the lethal shock induced by TNF reflects high levels of its receptor TNFRI as seen in sensitive (Mus musculus), vs. resistant (Mus spretus) mice, where TNFR1 expression is low. They reported that this expression is under the control of a microRNA (miR­511), which itself is induced by glucocorticoids.