The production of neutrophil extracellular traps (NETs) is a process that enables neutrophils to help catch and kill bacteria. However, increasing evidence suggests that this process might also occur ...in noninfectious, sterile inflammation. In this Review, we describe the role of NETosis in autoimmunity, coagulation, acute injuries and cancer, and discuss NETs as potential therapeutic targets. Furthermore, we consider whether extracellular DNA is always detrimental in sterile inflammation and whether the source is always NETs.
Autoimmune diseases, such as psoriasis and arthritis, show a patchy distribution of inflammation despite systemic dysregulation of adaptive immunity. Thus, additional tissue-derived signals, such as ...danger-associated molecular patterns (DAMPs), are indispensable for manifestation of local inflammation. S100A8/S100A9 complexes are the most abundant DAMPs in many autoimmune diseases. However, regulatory mechanisms locally restricting DAMP activities are barely understood. We now unravel for the first time, to our knowledge, a mechanism of autoinhibition in mice and humans restricting S100-DAMP activity to local sites of inflammation. Combining protease degradation, pull-down assays, mass spectrometry, and targeted mutations, we identified specific peptide sequences within the second calcium-binding EF-hands triggering TLR4/MD2-dependent inflammation. These binding sites are free when S100A8/S100A9 heterodimers are released at sites of inflammation. Subsequently, S100A8/S100A9 activities are locally restricted by calcium-induced (S100A8/S100A9)2 tetramer formation hiding the TLR4/MD2-binding site within the tetramer interphase, thus preventing undesirable systemic effects. Loss of this autoinhibitory mechanism in vivo results in TNF-α-driven fatal inflammation, as shown by lack of tetramer formation in crossing S100A9-/- mice with 2 independent TNF-α-transgene mouse strains. Since S100A8/S100A9 is the most abundant DAMP in many inflammatory diseases, specifically blocking the TLR4-binding site of active S100 dimers may represent a promising approach for local suppression of inflammatory diseases, avoiding systemic side effects.
Macrophages play an important role in structural cardiac remodeling and the transition to heart failure following myocardial infarction (MI). Previous research has focused on the impact of ...blood-derived monocytes on cardiac repair. Here we examined the contribution of resident cavity macrophages located in the pericardial space adjacent to the site of injury. We found that disruption of the pericardial cavity accelerated maladaptive post-MI cardiac remodeling. Gata6+ macrophages in mouse pericardial fluid contributed to the reparative immune response. Following experimental MI, these macrophages invaded the epicardium and lost Gata6 expression but continued to perform anti-fibrotic functions. Loss of this specialized macrophage population enhanced interstitial fibrosis after ischemic injury. Gata6+ macrophages were present in human pericardial fluid, supporting the notion that this reparative function is relevant in human disease. Our findings uncover an immune cardioprotective role for the pericardial tissue compartment and argue for the reevaluation of surgical procedures that remove the pericardium.
Display omitted
•Pericardial cavity in mouse and human serves as a reservoir for GPCMs•GPCMs are transcriptionally distinct from neighboring cardiac macrophages•GPCMs relocate rapidly to the ischemic heart and undergo phenotypic alterations•Absence of GPCMs in Lyz2cre;Gata6fl/fl mice promotes post-injury cardiac fibrosis
Deniset et al. describe the pericardial cavity as an important source of resident macrophages that migrate into the heart following ischemic injury and prevent detrimental repair caused by excessive fibrosis.
Antimicrobial resistance (AMR) has emerged as a significant global healthcare problem. Antibiotic use has accelerated the physiologic process of AMR, particularly in Gram-negative pathogens. Urinary ...tract infections (UTIs) are predominantly of a Gram-negative nature. Uropathogens are evolutionarily highly adapted and selected strains with specific virulence factors, suggesting common mechanisms in how bacterial cells acquire virulence and AMR factors. The simultaneous increase in resistance and virulence is a complex and context-dependent phenomenon. Among known AMR mechanisms, the plenitude of different β-lactamases is especially prominent. The risk for AMR in UTIs varies in different patient populations. A history of antibiotic consumption and the physiology of urinary flow are major factors that shape AMR prevalence. The urinary tract is in close crosstalk with the microbiome of other compartments, including the gut and genital tracts. In addition, pharmacokinetic properties and the physiochemical composition of urinary compartments can contribute to the emergence of AMR. Alternatives to antibiotic treatment and a broader approach to address bacterial infections are needed. Among the various alternatives studied, antimicrobial peptides and bacteriophage treatment appear to be highly promising approaches. We herein summarize the present knowledge of clinical and microbiological AMR in UTIs and discuss innovative approaches, namely new risk prediction tools and the use of non-antibiotic approaches to defend against uropathogenic microbes.
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.
Display omitted
•S. aureus AT intoxication leads to platelet aggregates that are deposited in the liver•Infection induces beneficial platelet responses followed by damaging AT-induced thrombosis•Antibody-mediated neutralization of AT prevents microvascular dysfunction and thrombosis
Staphylococcal sepsis often results in thrombocytopenia and multi-organ dysfunction. Using intravital imaging, Surewaard et al. discovered that α-toxin (AT) directly targets platelets, resulting in detrimental aggregation in the circulation. Neutralizing AT during staphylococcal sepsis does not interfere with beneficial platelet responses, while preventing microvascular dysfunction and thrombosis.
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.
Leukocytes are among the most mobile and versatile cells that have many essential functions in homeostasis and survival. Especially cells from the innate immune system, i.e., neutrophils and ...macrophages, play an important role as rapid first responders against invading microorganisms. With the advent of novel imaging techniques, new ways of visualizing innate immune cells have become available in recent years, thereby enabling more and more detailed discoveries about their nature, function and interaction partners. Besides intravital spinning-disc and 2-photon microscopy, clearing and 3D-imaging techniques provide new insights into the mechanism of innate immune cell behavior in their natural environment. This mini review focuses on the contributions of novel-imaging techniques to provide insight into the functions of neutrophils and macrophages under homeostasis and in infections. Imaging setups for different organs like the liver, kidney, heart, lung, and the peritoneal cavity are discussed as well as the current limitations of these imaging techniques.
Display omitted
Familial Mediterranean fever (FMF), caused by mutations in the pyrin-encoding MEFV gene, is characterized by uncontrolled caspase-1 activation and IL-1β secretion. A similar mechanism ...drives inflammation in cryopyrin-associated periodic fever syndrome (CAPS) caused by mutations in NLRP3. CAPS and FMF, however, result in largely different clinical manifestations, pointing to additional, autoinflammatory pathways involved in FMF. Another hallmark of FMF is extraordinarily high expression of S100A8 and S100A9. These alarmins are ligands of Toll-like receptor 4 and amplifiers of inflammation. However, the relevance of this inflammatory pathway for the pathogenesis of FMF is unknown.
This study investigated whether mutations in pyrin result in specific secretion of S100A8/A9 alarmins through gasdermin D pores’ amplifying FMF pathology.
S100A8/A9 levels in FMF patients were quantified by enzyme-linked immunosorbent assay. In vitro models with knockout cell lines and specific protein inhibitors were used to unravel the S100A8/A9 secretion mechanism. The impact of S100A8/A9 to the pathophysiology of FMF was analyzed with FMF (MEFVV726A/V726A) and S100A9−/− mouse models. Pyrin-S100A8/A9 interaction was investigated by coimmunoprecipitation, immunofluorescence, and enzyme-linked immunosorbent assay studies.
The S100A8/A9 complexes directly interacted with pyrin. Knocking out pyrin, caspase-1, or gasdermin D inhibited the secretion of these S100 alarmins. Inflammatory S100A8/A9 dimers were inactivated by tetramer formation. Blocking this inactivation by targeted S100A9 deletion in a murine FMF model demonstrated the relevance of this novel autoinflammatory pathway in FMF.
This is the first proof that members of the S100 alarmin family are released in a pyrin/caspase-1/gasdermin D–dependent pathway and directly drive autoinflammation in vivo.
Despite extensive molecular characterization, human glioblastoma remains a fatal disease with survival rates measured in months. Little improvement is seen with standard surgery, radiotherapy and ...chemotherapy. Clinical progress is hampered by the inability to detect and target glioblastoma disease reservoirs based on a diffuse invasive pattern and the presence of molecular and phenotypic heterogeneity. The goal of this study was to target the invasive and stem-like glioblastoma cells that evade first-line treatments using agents capable of delivering imaging enhancers or biotherapeutic cargo. To accomplish this, a combinatorial phage display library was biopanned against glioblastoma cell model systems that accurately recapitulate the intra- and inter-tumor heterogeneity and infiltrative nature of the disease. Candidate peptides were screened for specificity and ability to target glioblastoma cells in vivo. Cargo-conjugated peptides delivered contrast-enhancing agents to highly infiltrative tumor populations in intracranial xenograft models without the obvious need for blood brain barrier disruption. Simultaneous use of five independent targeting peptides provided greater coverage of this complex tumor and selected peptides have the capacity to deliver a therapeutic cargo (oncolytic virus VSVΔM51) to the tumor cells in vivo. Herein, we have identified a series of peptides with utility as an innovative platform to assist in targeting glioblastoma for the purpose of diagnostic or prognostic imaging, image-guided surgery, and/or improved delivery of therapeutic agents to glioblastoma cells implicated in disease relapse.
Macrophages play an important role in structural cardiac remodeling and
the transition to heart failure following myocardial infarction (MI). Previous
research has focused on the impact of ...blood-derived monocytes on cardiac repair.
Here we examined the contribution of resident cavity macrophages located in the
pericardial space adjacent to the site of injury. We found that disruption of
the pericardial cavity accelerated maladaptive post-MI cardiac remodeling.
Gata6+ macrophages in mouse pericardial fluid contributed to the reparative
immune response. Following experimental MI, these macrophages invaded the
epicardium, lost Gata6 expression, but continued to perform anti-fibrotic
functions. Loss of this specialized macrophage population enhanced interstitial
fibrosis after ischemic injury. Gata6+ macrophages were present in human
pericardial fluid, supporting the notion that this reparative function is
relevant in human disease. Our findings uncover an immune cardioprotective role
for the pericardial tissue compartment and argue for the reevaluation of
surgical procedures that remove the pericardium.
Deniset et al. describe the pericardial cavity as an important source of
resident macrophages that migrate into the heart following ischemic injury and
prevent detrimental repair caused by excessive fibrosis.
PDF
