Colonization of dermal arterioles by Neisseria meningitidis provides a safe haven from neutrophils

Protein C in adult patients with sepsis: from pathophysiology to monitoring and supplementation

Protein C (PC) plays a crucial role in modulating inflammation and coagulation in sepsis. Its anticoagulant and cytoprotective properties are critical in mitigating sepsis-induced coagulopathy, which is associated with high mortality rates. In sepsis, low levels of PC are associated with an elevated risk of multiple organ dysfunction and increased mortality. Routine monitoring of PC levels is not widely implemented but appears relevant in selected populations, such as patients with purpura fulminans, sepsis-induced coagulopathy (SIC), disseminated intravascular coagulopathy (DIC) or hyperinflammatory septic shock phenotypes. Treatment with PC has been limited to PC concentrate approved for paediatric use in congenital PC deficiencies and purpura fulminans, while the efficacy of PC supplementation in sepsis remains a subject of debate. Considering the physiological significance of PC and its role in sepsis pathophysiology, additional studies are necessary to fully elucidate its therapeutic efficacy in specific clinical settings.

Myocarditis and neutrophil-mediated vascular leakage but not cytokine storm associated with fatal murine leptospirosis

BACKGROUND

Leptospirosis is a globally neglected re-emerging zoonosis affecting all mammals, albeit with variable outcomes. Humans are susceptible to leptospirosis; infection with Leptospira interrogans species can cause severe disease in humans, with multi-organ failure, mainly affecting kidney, lung and liver function, leading to death in 10% of cases. Mice and rats are more resistant to acute disease and can carry leptospires asymptomatically in the kidneys and act as reservoirs, shedding leptospires into the environment. The incidence of leptospirosis is higher in tropical countries, and countries with poor sanitation, where heavy rainfall and flooding favour infection. Diagnosis of leptospirosis is difficult because of the many different serovars and the variety of clinical symptoms that can be confused with viral infections. The physiopathology is poorly understood, and leptospirosis is often regarded as an inflammatory disease, like sepsis.

METHODS

To investigate the causes of death in lethal leptospirosis, we compared intraperitoneal infection of male and female C57BL6/J mice with 108Leptospira of two strains of pathogenic L. interrogans. One strain, L. interrogans Manilae L495, killed the mice 4 days after infection, whereas the other strain, L. interrogans Icterohaemorrhagiae Verdun, did not induce any major symptoms in the mice. On day 3 post infection, the mice were humanely euthanised and blood and organs were collected. Bacterial load, biochemical parameters, cytokine production and leucocyte population were assessed by qPCR, ELISA, cytometry and immunohistochemistry.

FINDINGS

Neither lung, liver, pancreas or kidney damage nor massive necroptosis or cytokine storm could explain the lethality. Although we did not find pro-inflammatory cytokines, we did find elevated levels of the anti-inflammatory cytokine IL-10 and the chemokine RANTES in the serum and organs of Leptospira-infected mice. In contrast, severe leptospirosis was associated with neutrophilia and vascular permeability, unexpectedly due to neutrophils and not only due to Leptospira infection. Strikingly, the main cause of death was myocarditis, an overlooked complication of human leptospirosis.

INTERPRETATION

Despite clinical similarities between bacterial sepsis and leptospirosis, striking differences were observed, in particular a lack of cytokine storm in acute leptospirosis. The fact that IL-10 was increased in infected mice may explain the lack of pro-inflammatory cytokines, emphasising the covert nature of Leptospira infections. Neutrophilia is a hallmark of human leptospirosis. Our findings confirm the ineffective control of infection by neutrophils and highlight their deleterious role in vascular permeability, previously only attributed to the ability of leptospires to damage and cross endothelial junctions. Finally, the identification of death due to myocarditis rather than kidney, liver or liver failure may reflect an overlooked but common symptom associated with poor prognosis in human leptospirosis. These features of neutrophilia and myocarditis are also seen in patients, making this mouse model a paradigm for better understanding human leptospirosis and designing new therapeutic strategies.

FUNDING

The Boneca laboratory was supported by the following programmes: Investissement d'Avenir program, Laboratoire d'Excellence "Integrative Biology of Emerging Infectious Diseases" (ANR-10-LABX-62-IBEID) and by R&D grants from Danone and MEIJI. CW received an ICRAD/ANR grant (S-CR23012-ANR 22 ICRD 0004 01). SP received a scholarship by Université Paris Cité (formerly Université Paris V - Descartes) through Doctoral School BioSPC (ED562, BioSPC). SP has additionally received a scholarship "Fin de Thèse de Science" number FDT202404018322 granted by "Fondation pour la Recherche Médicale (FRM)". The funders had no implication in the design, analysis and reporting of the study.

High-throughput phenotype-to-genotype testing of meningococcal carriage and disease isolates detects genetic determinants of disease-relevant phenotypic traits

Genome-wide association studies (GWAS) with binary or single phenotype data have successfully identified disease-associated genotypes and determinants of antimicrobial resistance. We describe a novel phenotype-to-genotype approach for a major bacterial pathogen that involves simultaneously testing for associations among multiple disease-related phenotypes and linkages between phenotypic variation and genetic determinants. High-throughput assays quantified variation among 163 Neisseria meningitidis serogroup W ST-11 clonal complex isolates for 11 phenotypic traits. A comparison of carriage and two disease subgroups detected significant differences between groups for eight phenotypic traits. Candidate genotypic testing indicated that indels in csw, a capsular biosynthesis gene, were associated with reduced survival in antibody-depleted heat-inactivated serum. GWAS testing detected 341 significant genetic variants (3 single-nucleotide polymorphisms and 338 unitigs) across all traits except serum bactericidal antibody-depleted assays. Growth traits were associated with variants of capsular biosynthesis genes, carbonic anhydrase, and an iron-uptake system while adhesion-linked variation was in pilC2, marR, and mutS. Multiple phase variation states or combinatorial phasotypes were associated with significant differences in multiple phenotypes. Controlling for group effects through regression and recursive random forest approaches detected group-independent effects for nalP with biofilm formation and fetA with a growth trait. Through random forest testing, nine phenotypes were weakly predictive of MenW:cc11 sub-lineage, original or 2013, for disease isolates while three characteristics separated carriage and disease isolates with >80% accuracy. This study demonstrates the power of combining high-throughput phenotypic testing of pathogenically relevant isolate collections with genomics for identifying genetic determinants of specific disease-relevant phenotypes and the pathobiology of microbial pathogens.IMPORTANCENext-generation sequencing technologies have led to the creation of extensive microbial genome sequence databases for several bacterial pathogens. Mining of these databases is now imperative for unlocking the maximum benefits of these resources. We describe a high-throughput methodology for detecting associations between phenotypic variation in multiple disease-relevant traits and a range of genetic determinants for Neisseria meningitidis, a major causative agent of meningitis and septicemia. Phenotypic variation in 11 disease-related traits was determined for 163 isolates of the hypervirulent ST-11 lineage and linked to specific single-nucleotide polymorphisms, short sequence variants, and phase variation states. Application of machine learning algorithms to our data outputs identified combinatorial phenotypic traits and genetic variants predictive of a disease association. This approach overcomes the limitations of generic meta-data, such as disease versus carriage, and provides an avenue to explore the multi-faceted nature of bacterial disease, carriage, and transmissibility traits.

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Implantation of engineered human microvasculature to study human infectious diseases in mouse models

Animal models for studying human pathogens are crucially lacking. We describe the implantation in mice of engineered human mature microvasculature consisting of endothelial and perivascular cells embedded in collagen hydrogel that allows investigation of pathogen interactions with the endothelium, including in vivo functional studies. Using Neisseria meningitidis as a paradigm of human-restricted infection, we demonstrated the strength and opportunities associated with the use of this approach.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.