INTRAPULMONARY TREATMENT WITH A NOVEL TLR4 AGONIST CONFERS PROTECTION AGAINST KLEBSIELLA PNEUMONIA

Role of endosomal toll-like receptors in immune sensing of Klebsiella pneumoniae

Klebsiella pneumoniae is the causative agent of a wide range of antibiotic-resistant infections, including nosocomial pneumonia and neonatal sepsis. We investigate here the mechanisms underlying innate immune recognition of this pathogen by focusing on the role of endosomal Toll-like receptors (TLRs), which sense prokaryotic nucleic acids, in comparison with TLR4, which recognizes the cell-wall lipopolysaccharide component. Lack of functional endosomal TLRs made mice more susceptible to pulmonary infection by K. pneumoniae, in association with reduced production of proinflammatory and chemotactic cytokines and reduced neutrophil recruitment to the lung. This phenotype was as severe as that of TLR4-deficient mice and only moderately milder than that of mice lacking the TLR adaptor MyD88. Notably, macrophages lacking at the same time TLR7, 9 and 13 were more defective than those lacking only TLR9 in their ability to produce proinflammatory cytokines, suggesting a role for the RNA sensing TLR7 and 13 receptors in K. pneumoniae recognition. Collectively, our results unveil the presence of an integrated system of DNA and RNA sensing TLRs that cooperates with TLR4 in immune detection and clearance of K. pneumoniae. These data may be useful to devise alternative therapeutic approaches aimed at stimulating responses against antibiotic-resistant K. pneumoniae strains.

Saponin TQL1055 adjuvant-containing vaccine confers protection upon Mycobacterium tuberculosis challenge in mice

Tuberculosis (TB), caused by the intracellular pathogen Mycobacterium tuberculosis (Mtb), affects the lungs of infected individuals (pulmonary TB) but can also affect other sites (extrapulmonary TB). The only licensed vaccine Mycobacterium bovis bacillus Calmette-Guerin (BCG) protects infants and young children but exhibits variable efficacy in protecting against adult pulmonary TB. Poor compliance and prolonged treatment regimens associated with the use of chemotherapy has contributed to the development of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb. Thus, there is an urgent need for the design of more effective vaccines against TB. The development of safe and novel adjuvants for human use is critical. In this study, we demonstrate that saponin-based TQL1055 adjuvant when formulated with a TLR4 agonist (PHAD) and Mtb specific immunodominant antigens (ESAT-6 and Ag85B) and delivered intramuscularly in mice, the SA-TB vaccine induced potent lung immune responses. Additionally, the SA-TB vaccine conferred significant protection against Mtb infection, comparable with levels induced by BCG. These findings support the development of a SA-TB vaccine comprising TQL1055, as a novel, safe and effective TB vaccine for potential use in humans.

GENETIC ABLATION OF THE C-TYPE LECTIN RECEPTOR CLEC2D INCREASES PERITONITIS MORTALITY, INFLAMMATION, AND PHYSIOLOGY WITHOUT DIMINISHING ORGAN INJURY

ABSTRACT

Background: Sepsis accounts for substantial morbidity and mortality motivating investigators to continue the search for pathways and molecules driving the pathogenesis of the disease. The current study examined if the novel C-type lectin receptor (CLR), Clec2d, plays a significant role in the pathogenesis of sepsis. Methods: Clec2d knockout (KO) mice were fully backcrossed onto the C57/BL6 background. Acute endotoxemia was induced with an intraperitoneal injection of lipopolysaccharide (LPS). Sepsis was induced in two different models, cecal ligation and puncture (CLP) and Pseudomonas aeruginosa pneumonia. Both models were treated with antibiotics and fluid resuscitation. In the sepsis models, physiologic and hematologic measurements were measured at 24 h by collecting a small sample of peripheral blood. Mortality was followed for 14 days. Results : A total of 197 mice were studied, 58 wild type (WT) and 54 knock-out (KO) in the LPS model; 27 wild type and 21 KO mice in the CLP model; and 22 WT and 15 KO mice in the pneumonia model. Clec2d KO mice had greater mortality in the LPS and CLP studies but not the pneumonia model. There were significant differences in multiple parameters determined 24 h post sepsis between mice who subsequently died and those lived. Consistent with previous reports in the CLP model, higher concentrations of IL-6, increased numbers of peripheral blood lymphocytes and greater renal injury were found in the dying mice. In contrast, in the pneumonia model, IL-6 was higher in the surviving mice; however, the IL-6 levels in the pneumonia model (0.6 ± 0.3 ng/mL mean ± SEM) were less than 2% of the IL-6 levels of mice that died in the CLP model (41 ± 9 ng/mL, mean ± SEM). There were no differences in the lymphocyte count or renal injury between living and dying mice in the pneumonia model. In both sepsis models, dying mice had lower heart rates, respiratory rates, and body temperatures. These values were also lower in the KO mice compared to the WT in CLP, but the breath rate and body temperature were increased in the KO pneumonia mice. Conclusion: The C-type lectin receptor Clec2d plays a complicated role in the pathogenesis of sepsis, which varies with source of infection as demonstrated in the models used to study the disease. These data highlight the heterogeneity of the responses to sepsis and provide further evidence that a single common pathway driving sepsis organ injury and death likely does not exist.

Weight loss-induced adipose macrophage memory improves local Staphylococcus aureus clearance in male mice

Different stimuli can induce innate immune memory to improve pathogen defense or worsen cardiometabolic disease. However, it is less clear if the same stimuli can induce both the protective and detrimental effects of innate immune memory. We previously showed that weight loss induces innate immune memory in adipose macrophages that correlates with worsened diabetes risk after weight regain. In this study, we investigated the effect of weight loss on macrophage cytokine production and overall survival in a mouse model of infection. Male C57Bl/6J mice were put on high-fat or low-fat diets over 18 weeks to induce weight gain or weight loss. Lean mice served as controls. All mice were then infected IV with 2.5×10^6 CFU Staphylococcus aureus . Tissues were collected from 10 mice/group at day 3 and the remaining animals were followed for survival. Weight gain mice had the highest blood neutrophils and the highest bacterial burden in the kidney. However, there was no significant difference in survival. The weight loss group had the highest plasma TNF-α and a significant reduction in bacterial burden in the adipose tissue that correlated with increased adipose macrophage cytokine production. Thus, weight loss-induced adipose macrophage memory may both improve local S.aureus clearance and worsen diabetes risk upon weight regain. Collectively, these findings support the notion that innate immune memory is an evolutionarily protective mechanism that also contributes to the development of cardiometabolic diseases.

EXTRACELLULAR CIRP INHIBITS NEUTROPHIL APOPTOSIS TO PROMOTE ITS AGING BY UPREGULATING SERPINB2 IN SEPSIS

ABSTRACT

Background: Sepsis reduces neutrophil apoptosis. As the result, neutrophils may become aged, exacerbating inflammation and tissue injury. Extracellular cold-inducible RNA-binding protein (eCIRP) acts as a damage-associated molecular pattern to promote inflammation and tissue injury in sepsis. SerpinB2, a serine protease inhibitor, has been shown to inhibit apoptosis. We hypothesize that eCIRP upregulates SerpinB2 to promote aged neutrophil subset by inhibiting apoptosis in sepsis. Methods: We stimulated bone marrow-derived neutrophils (BMDNs) of wild-type (WT) mice with 1 μg/mL of recombinant mouse CIRP (i.e., eCIRP) and assessed cleaved caspase-3 and SerpinB2 by western blotting. Apoptotic neutrophils were assessed by Annexin V/PI. Bone marrow-derived neutrophils were stimulated with 1 μg/mL eCIRP and treated with or without PAC-1 (caspase-3 activator) and aged neutrophils (CXCR4 hi CD62L lo ) were assessed by flow cytometry. To induce sepsis, we performed cecal ligation and puncture in WT or CIRP -/- mice. We determined the percentage of aged neutrophils and SerpinB2 + neutrophils in blood and spleen by flow cytometry. Results: We found that cleaved caspase-3 levels were increased at 4 h of PBS treatment compared with 0 h but decreased by eCIRP treatment. Extracellular cold-inducible RNA-binding protein reduced apoptotic cells after 20 h of treatment. Extracellular cold-inducible RNA-binding protein also increased the frequencies of aged neutrophils compared with PBS after 20 h, while PAC-1 treatment reduced aging in eCIRP-treated BMDNs. Extracellular cold-inducible RNA-binding protein significantly increased the expression of SerpinB2 at protein levels in BMDNs at 20 h. In WT mice, the frequencies of aged and SerpinB2 + neutrophils in blood and spleen were increased after 20 h of cecal ligation and puncture, while in CIRP -/- mice, aged and SerpinB2 + neutrophils were significantly decreased compared with WT mice. We also found that aged neutrophils expressed significantly higher levels of SerpinB2 compared with non-aged neutrophils. Conclusions: eCIRP inhibits neutrophil apoptosis to increase aged phenotype by increasing SerpinB2 expression in sepsis. Thus, targeting eCIRP could be a new therapeutic strategy to ameliorate inflammation caused by neutrophil aging in sepsis.