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Essentially all Staphylococcus aureus (S. aureus) bacteria that gain access to the circulation are plucked out of the bloodstream by the intravascular macrophages of the liver - the Kupffer cells. It is also thought that these bacteria are disseminated via the bloodstream to other organs. Our data show that S. aureus inside Kupffer cells grew and escaped across the mesothelium into the peritoneal cavity and immediately infected GATA-binding factor 6-positive (GATA6+) peritoneal cavity macrophages. These macrophages provided a haven for S. aureus, thereby delaying the neutrophilic response in the peritoneum by 48 hours and allowing dissemination to various peritoneal and retroperitoneal organs including the kidneys. In mice deficient in GATA6+ peritoneal macrophages, neutrophils infiltrated more robustly and reduced S. aureus dissemination. Antibiotics administered i.v. did not prevent dissemination into the peritoneum or to the kidneys, whereas peritoneal administration of vancomycin (particularly liposomal vancomycin with optimized intracellular penetrance capacity) reduced kidney infection and mortality, even when administered 24 hours after infection. These data indicate that GATA6+ macrophages within the peritoneal cavity are a conduit of dissemination for i.v. S. aureus, and changing the route of antibiotic delivery could provide a more effective treatment for patients with peritonitis-associated bacterial sepsis.

All bacterial infections occur within a polymicrobial environment, from which a pathogen population emerges to establish disease within a host. Emphasis has been placed on prevention of pathogen dominance by competing microflora acting as probiotics 1 . Here we show that the virulence of the human pathogen Staphylococcus aureus is augmented by native, polymicrobial, commensal skin flora and individual species acting as 'proinfectious agents'. The outcome is pathogen proliferation, but not commensal. Pathogenesis augmentation can be mediated by particulate cell wall peptidoglycan, reducing the S. aureus infectious dose by over 1,000-fold. This phenomenon occurs using a range of S. aureus strains and infection models and is not mediated by established receptor-mediated pathways including Nod1, Nod2, Myd88 and the NLPR3 inflammasome. During mouse sepsis, augmentation depends on liver-resident macrophages (Kupffer cells) that capture and internalize both the pathogen and the proinfectious agent, leading to reduced production of reactive oxygen species, pathogen survival and subsequent multiple liver abscess formation. The augmented infection model more closely resembles the natural situation and establishes the role of resident environmental microflora in the initiation of disease by an invading pathogen. As the human microflora is ubiquitous 2 , its role in increasing susceptibility to infection by S. aureus highlights potential strategies for disease prevention.

Background: Severe complicated intra-abdominal sepsis (SCIAS) has an increasing incidence with mortality rates over 80% in some settings. Mortality typically results from disruption of the gastrointestinal tract, progressive and self-perpetuating bio-mediator generation, systemic inflammation, and multiple organ failure. Principles of treatment include early antibiotic administration and operative source control. A further therapeutic option may be open abdomen (OA) management with active negative peritoneal pressure therapy (ANPPT) to remove inflammatory ascites and ameliorate the systemic damage from SCIAS. Although there is now a biologic rationale for such an intervention as well as non-standardized and erratic clinical utilization, this remains a novel therapy with potential side effects and clinical equipoise., Methods: The Closed Or Open after Laparotomy (COOL) study will constitute a prospective randomized controlled trial that will randomly allocate eligible surgical patients intra-operatively to either formal closure of the fascia or use of the OA with application of an ANPTT dressing. Patients will be eligible if they have free uncontained intra-peritoneal contamination and physiologic derangements exemplified by septic shock OR a Predisposition-Infection-Response-Organ Dysfunction Score ≥ 3 or a World-Society-of-Emergency-Surgery-Sepsis-Severity-Score ≥ 8. The primary outcome will be 90-day survival. Secondary outcomes will be logistical, physiologic, safety, bio-mediators, microbiological, quality of life, and health-care costs. Secondary outcomes will include days free of ICU, ventilation, renal replacement therapy, and hospital at 30 days from the index laparotomy. Physiologic secondary outcomes will include changes in intensive care unit illness severity scores after laparotomy. Bio-mediator outcomes for participating centers will involve measurement of interleukin (IL)-6 and IL-10, procalcitonin, activated protein C (APC), high-mobility group box protein-1, complement factors, and mitochondrial DNA. Economic outcomes will comprise standard costing for utilization of health-care resources., Discussion: Although facial closure after SCIAS is considered the current standard of care, many reports are suggesting that OA management may improve outcomes in these patients. This trial will be powered to demonstrate a mortality difference in this highly lethal and morbid condition to ensure critically ill patients are receiving the best care possible and not being harmed by inappropriate therapies based on opinion only., Trial Registration: ClinicalTrials.gov, NCT03163095., Competing Interests: The COOL trial has been ethically approved at the lead and pilot center by the Conjoint Health Research Ethics Board (CHREB) of the University of Calgary (REB16-1588). The study has also been registered with the National Institutes of Health (ClinicalTrials.gov, identifier: NCT03163095).Andrew W. Kirkpatrick serves in the Canadian Forces Medical Services and has consulted for the Innovative Trauma Care and Acelity Corporations. Jessica L. McKee declares that she has consulted for Innovative Trauma Care, Aceso, and the Acelity Corporations. Osvaldo Chiara reported having consulted for the Acelity Corporation. Jose J. Diaz reported having consulted for the Acelity Corporation. Michael Sugrue reported having consulted for the Smith and Nephew Corporation. Ernest E. Moore reported Research support and intellectual property related to the Haemonetics, TEM Systems, Pryor Corporations, and being a Cofounder of Thrombo Therapeutics Inc. The remaining authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Background: Severe complicated intra-abdominal sepsis (SCIAS) is a worldwide challenge with increasing incidence. Open abdomen management with enhanced clearance of fluid and biomediators from the peritoneum is a potential therapy requiring prospective evaluation. Given the complexity of powering multi-center trials, it is essential to recruit an inception cohort sick enough to benefit from the intervention; otherwise, no effect of a potentially beneficial therapy may be apparent. An evaluation of abilities of recognized predictive systems to recognize SCIAS patients was conducted using an existing intra-abdominal sepsis (IAS) database., Methods: All consecutive adult patients with a diffuse secondary peritonitis between 2012 and 2013 were collected from a quaternary care hospital in Finland, excluding appendicitis/cholecystitis. From this retrospectively collected database, a target population (93) of those with either ICU admission or mortality were selected. The performance metrics of the Third Consensus Definitions for Sepsis and Septic Shock based on both SOFA and quick SOFA, the World Society of Emergency Surgery Sepsis Severity Score (WSESSSS), the APACHE II score, Manheim Peritonitis Index (MPI), and the Calgary Predisposition, Infection, Response, and Organ dysfunction (CPIRO) score were all tested for their discriminant ability to identify this subgroup with SCIAS and to predict mortality., Results: Predictive systems with an area under-the-receiving-operating characteristic (AUC) curve > 0.8 included SOFA, Sepsis-3 definitions, APACHE II, WSESSSS, and CPIRO scores with the overall best for CPIRO. The highest identification rates were SOFA score ≥ 2 (78.4%), followed by the WSESSSS score ≥ 8 (73.1%), SOFA ≥ 3 (75.2%), and APACHE II ≥ 14 (68.8%) identification. Combining the Sepsis-3 septic-shock definition and WSESSS ≥ 8 increased detection to 80%. Including CPIRO score ≥ 3 increased this to 82.8% (Sensitivity-SN; 83% Specificity-SP; 74%. Comparatively, SOFA ≥ 4 and WSESSSS ≥ 8 with or without septic-shock had 83.9% detection (SN; 84%, SP; 75%, 25% mortality)., Conclusions: No one scoring system behaves perfectly, and all are largely dominated by organ dysfunction. Utilizing combinations of SOFA, CPIRO, and WSESSSS scores in addition to the Sepsis-3 septic shock definition appears to offer the widest "inclusion-criteria" to recognize patients with a high chance of mortality and ICU admission., Trial Registration: https://clinicaltrials.gov/ct2/show/NCT03163095; Registered on May 22, 2017., Competing Interests: A retrospectively collected database of SCIAS cases was created at a quaternary care hospital in Helsinki, Finland. This database enrolled all consecutive adult patients with a diffuse secondary peritonitis between 2012 and 2013, although cases of appendicitis or cholecystitis were excluded. The institutional human research review committee approved the study design, and as it was an observational retrospective cohort study, neither informed consent nor ethics committee’s approval was required.Not Applicable.Jessica L McKee declares that she has consulted for Innovative Trauma Care, Aceso, and the Acelity Corporations. Osvaldo Chiara reported having consulted for the Acelity Corporation. Jose J. Diaz reported having consulted for the Acelity Corporation. Michael Sugrue reported having consulted for the Smith and Nephew Corporation. Ernest E. Moore reported Research support and Intellectual property related to the Haemonetics, TEM Systems, Pryor Corporations, and being a Cofounder of Thrombo Therapeutics Inc. Andrew W Kirkpatrick serves in the Canadian Forces Medical Services and has consulted for the Innovative Trauma Care and Acelity Corporations. All other authors declared that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

During the systemic inflammatory response of severe sepsis, neutrophils accumulate in the liver microcirculation, but their functional significance is largely unknown. We show that neutrophils migrate to liver sinusoids during endotoxemia and sepsis where they exert protective effects by releasing neutrophil extracellular traps (NETs), which are DNA-based structures that capture and eliminate microbes. NETs released into the vasculature ensnare bacteria from the bloodstream and prevent dissemination. NET production requires platelet-neutrophil interactions and can be inhibited by platelet depletion or disruption of integrin-mediated platelet-neutrophil binding. During sepsis, NET release increases bacterial trapping by 4-fold (beyond the basal level provided by resident intravascular macrophages). Blocking NET formation reduces the capture of circulating bacteria during sepsis, resulting in increased dissemination to distant organs. Thus, NETs ensnare circulating bacteria and provide intravascular immunity that protects against bacterial dissemination during septic infections., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Neutrophils are circulating leukocytes with great cytotoxic potential, responsible for the first combat against invading pathogens. Their accumulation in tissues must be highly controlled so that the number of neutrophils delivered to the affected site is sufficient to control infection with minimum injury to the surrounding healthy tissue. In sepsis, neutrophil migration is dysregulated - resulting in insufficient delivery of neutrophils to the infectious site and massive neutrophil accumulation in uninfected organs. This dysregulation has the potential to cause inappropriate tissue injury that may explain the multiple organ dysfunction observed in severe sepsis. A better understanding of the mechanisms that contribute to this process is fundamental to design therapeutic strategies to circumvent tissue injury and organ dysfunction in sepsis., (© 2011 BioMed Central Ltd)

It has been known for many years that neutrophils and platelets participate in the pathogenesis of severe sepsis, but the inter-relationship between these players is completely unknown. We report several cellular events that led to enhanced trapping of bacteria in blood vessels: platelet TLR4 detected TLR4 ligands in blood and induced platelet binding to adherent neutrophils. This led to robust neutrophil activation and formation of neutrophil extracellular traps (NETs). Plasma from severely septic humans also induced TLR4-dependent platelet-neutrophil interactions, leading to the production of NETs. The NETs retained their integrity under flow conditions and ensnared bacteria within the vasculature. The entire event occurred primarily in the liver sinusoids and pulmonary capillaries, where NETs have the greatest capacity for bacterial trapping. We propose that platelet TLR4 is a threshold switch for this new bacterial trapping mechanism in severe sepsis.

Bloodstream infection is a hallmark of sepsis, a medically emergent condition requiring rapid treatment. However, upregulation of host defense proteins through toll-like receptors and NFκB requires hours after endotoxin detection. Using confocal pulmonary intravital microscopy, we identified that the lung provides a TLR4-Myd88-and abl tyrosine kinase-dependent niche for immediate CD11b-dependent neutrophil responses to endotoxin and Gram-negative bloodstream pathogens. In an in vivo model of bacteremia, neutrophils crawled to and rapidly phagocytosed Escherichia coli sequestered to the lung endothelium. Therefore, the lung capillaries provide a vascular defensive niche whereby endothelium and neutrophils cooperate for immediate detection and capture of disseminating pathogens.

Summary: Coronavirus disease 2019 (COVID‐19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and has resulted in more than 6 million deaths worldwide. COVID‐19 is a respiratory disease characterized by pulmonary dysfunction leading to acute respiratory distress syndrome (ARDs), as well as disseminated coagulation, and multi‐organ dysfunction. Neutrophils and neutrophil extracellular traps (NETs) have been implicated in the pathogenesis of COVID‐19. In this review, we highlight key gaps in knowledge, discuss the heterogeneity of neutrophils during the evolution of the disease, how they can contribute to COVID‐19 pathogenesis, and potential therapeutic strategies that target neutrophil‐mediated inflammatory responses. [ABSTRACT FROM AUTHOR]

Severe trauma is accompanied by a profound activation of the immune system. Patients with polytrauma develop systemic inflammatory response syndrome (SIRS) and often sepsis, which contributes substantially to high mortality of this condition. On a cellular level, necrosis and loss of plasma membrane integrity lead to the release of endogenous “damage-associated molecular patterns” (DAMPs) as danger signals, which in turn activate innate immune cells. Inflammation that occurs in the absence of invading pathogens has been termed sterile inflammation and trauma with tissue damage represents an acute form of sterile inflammation. Macrophages are a heterogeneous group of phagocytes of the innate immune system and serve as sentinels to detect loss of tissue integrity. Macrophages show a remarkable plasticity and undergo phenotypical changes in response to injury and repair. Under basal conditions, tissue-resident macrophages are distributed in various organ systems and have critical functions in tissue development and the maintenance of homeostasis. Inflammatory conditions, such as major trauma, lead to the rapid recruitment of blood-derived monocytes that mature into macrophages as well as direct recruitment of macrophages from the cavity that surrounds the injured organ. This leads to augmentation of the pool of tissue-resident macrophages. Besides their essential role in sensing tissue damage and initiating inflammation, macrophages contribution critically to tissue repair and wound healing, ultimately allowing full restoration. Dysregulated sterile inflammation and defective healing result in chronic inflammatory disease with persistent tissue damage. In this review, we summarize the cellular and molecular mechanisms that lead to activation of sterile inflammation, recruitment of immune cells and initiation of wound healing. We focus on the pivotal role of macrophages played in this context. [ABSTRACT FROM AUTHOR]

The primary function of platelets is to patrol the vasculature and seal vessel breaches to limit blood loss. However, it is becoming increasingly clear that they also contribute to pathophysiological conditions like thrombosis, atherosclerosis, stroke and infection. Severe sepsis is a devastating disease that claims hundreds of thousands of lives every year in North America and is a major burden to the public health system. Platelet surface receptors like GPIb, αIIbβ3, TLR2 and TLR4 are involved in direct platelet-bacteria interactions. Plasma proteins like fibrinogen and vWF enable indirect interactions. Furthermore, platelet granules contain a plethora of proteins that modulate the immune response as well as microbicidal agents which can directly lyse bacteria. Bacterial toxins are potent platelet activators and can cause intravascular platelet aggregation. Platelets contribute to the antibacterial response of the host involving Kupffer cells, neutrophils and the complement system. In this review we summarize the current knowledge about platelet-bacteria interactions and highlight recent advances in the field. [ABSTRACT FROM AUTHOR]

Here we focus on how neutrophils have a key regulatory role in vascular inflammation. Recent studies using advanced imaging techniques have yielded new insights into the mechanisms by which neutrophils contribute to defense against bacterial infections and also against sterile injury. In these settings, neutrophils are recruited by various mechanisms depending on the situation. We also describe how these processes may be disrupted in systemic infections, with a particular emphasis on mouse models of sepsis. Neutrophils are often immobilized in the lungs and liver during systemic infections, and this immobilization may be a mechanism through which bacteria can evade the innate immune response or allow neutrophils to form neutrophil extracellular traps that trap and kill bacteria in blood. The platelet is also an important player in sepsis, and we describe how it collaborates with neutrophils in the formation of neutrophil extracellular traps. [ABSTRACT FROM AUTHOR]

Lipopolysaccharide (LPS) is thought to be an important molecule in myocardial depression in sepsis. Toll-like receptor 4 (TLR4), the lipopolysaccharide receptor, is known to underlie these responses. Because TLR4 is expressed on both cardiac myocytes and immune cells, it is unclear as to which cell type is responsible for myocyte depression. In this article, we present evidence that the early response is likely related to TLR4 on immune cells and most likely macrophages, whereas the more delayed response may involve various immune cells as well as myocytes. [Copyright &y& Elsevier]

In sepsis, and in models of sepsis including endotoxemia, impaired neutrophil recruitment and chemotaxis have been reported. The inability of the endotoxemic neutrophil to chemotax could be attributed to the fact that intracellular signaling via LPS overrides signals from endogenous chemokines or, alternatively, that sequestration of neutrophils into lungs prevents access to peripheral tissues. Using both in vitro and in vivo chemotaxis assays the authors established that neutrophils from healthy mice chemotaxed in vivo toward MIP-2, whereas endotoxemic neutrophils did not. Since LPS activates leukocytes via the p38 MAPK pathway, SKF86002, a p38 MAPK inhibitor, was given to endotoxemic animals. SKF86002 significantly reversed the LPS-induced impairment in emigration of endotoxic neutrophils in response to MIP-2. Neutrophil chemotaxis in vitro was also impaired by LPS, via a p38 MAPK-dependent pathway, and this impairment could be reversed via p38 MAPK inhibition. Although neutrophil numbers dropped in the circulation and trapped in lungs during endotoxemia, SKF86002 did not reverse these parameters, demonstrating that p38 MAPK inhibition did not release trapped neutrophils from the lungs. In conclusion, the data suggest that the impaired emigration and chemotaxis of neutrophils at peripheral sites during endotoxemia may be partially due to a p38 MAPK-mediated inhibition of neutrophil responses to endogenous chemokines. Microcirculation (2005) 12, 421-432. doi:10.1080/10739680590960368 [ABSTRACT FROM AUTHOR]

Inflammation of the intestinal tract remains a very serious concern in the clinical setting. Unfortunately, to date, the mechanisms underlying many inflammatory conditions such as sepsis or inflammatory bowel diseases are poorly understood and our therapeutic interventions are less than ideal. Over the past decade, an abundance of research has been directed toward the role of nitric oxide (NO) in intestinal inflammation. It has become apparent that NO might have a dichotomous role as both a beneficial and detrimental molecule. Nitric oxide is a weak radical produced from L-arginine via the enzyme nitric oxide synthase (NOS). NOS exists in three distinct isoforms; constitutively (cNOS) expressed neuronal NOS (NOS1 or nNOS) and endothelial NOS (NOS3 or eNOS) or an inducible isoform (NOS2 or iNOS) capable of high production output of NO during inflammation. Constitutively expressed NOS has been shown to be critical to normal physiology and inhibition of these enzymes (nNOS or eNOS) caused damage. It has been proposed that the high output production of NO from iNOS causes injury, perhaps through the generation of potent radicals such as peroxynitrite and hence may explain the apparent dichotomous role of NO. However, recent studies have challenged this simple paradigm providing evidence that iNOS may have some protective role in some inflammatory models. Moreover, the importance of peroxynitrite has been questioned. In this review we discuss the role of cNOS and iNOS in intestinal inflammation and provide an overview of peroxynitrite in intestinal inflammation, highlighting some of the controversy that exists. [ABSTRACT FROM AUTHOR]

Summary During sepsis, small blood vessels can become occluded by large platelet aggregates of poorly understood etiology. During Staphylococcal aureus infection, sepsis severity is linked to the bacterial α-toxin (α-hemolysin, AT) through unclear mechanisms. In this study, we visualized intravascular events in the microcirculation and found that intravenous AT injection induces rapid platelet aggregation, forming dynamic micro-thrombi in the microcirculation. These aggregates are retained in the liver sinusoids and kidney glomeruli, causing multi-organ dysfunction. Acute staphylococcal infection results in sequestration of most bacteria by liver macrophages. Platelets are initially recruited to these macrophages and help eradicate S . aureus . However, at later time points, AT causes aberrant and damaging thrombosis throughout the liver. Treatment with an AT neutralizing antibody (MEDI4893 ∗ ) prevents platelet aggregation and subsequent liver damage, without affecting the initial and beneficial platelet recruitment. Thus, AT neutralization may represent a promising approach to combat staphylococcal-induced intravascular coagulation and organ dysfunction. [ABSTRACT FROM AUTHOR]

During Gram-negative sepsis and endotoxemia, CD14 is essential for the recognition of LPS by the TLR4 complex and subsequent generation of systemic inflammation. However, CD14-independent responses to LPS have been reported in vitro and in vivo in selected tissues including the skin. As the liver is a key target organ for neutrophil sequestration and inflammatory pathology during sepsis and endotoxemia, we investigated the role of CD14 in the recruitment of neutrophils into the liver in a mouse model of endotoxemia. Using dynamic in vivo imaging of the liver, we observed that neutrophil recruitment within the sinusoids and post-sinusoidal venules occurred equivalently between LPS-treated wild-type and CD14-knockout mice. Neutrophil recruitment within the liver was completely independent of CD14 regardless of whether it was expressed on cells of hematopoietic or nonhematopoietic origin or in serum as soluble CD14. Whereas CD14 expression was essential for activation of circulating neutrophils and for the development of LPS-induced systemic inflammation (pulmonary neutrophil sequestration, leukopenia, and increased serum proinflammatory cytokine levels), deficiency of CD14 did not limit the adhesion strength of neutrophils in vitro. Furthermore, wild-type and CD14-knockout mice displayed identical deposition of serum-derived hyaluronan-associated protein within liver sinusoids in response to LPS, indicating that the sinusoid-specific CD44/hyaluronan/serum-derived hyaluronan-associated protein-dependent pathway of neutrophil adhesion is activated independently of CD14. Therefore, the liver microcirculation possesses a unique CD14-independent mechanism of LPS detection and activation of neutrophil recruitment. [ABSTRACT FROM AUTHOR]