Effects of Cl2MDP-encapsulating liposomes in a murine model of Pseudomonas aeruginosa-induced sepsis

Depletion of Alveolar Macrophages Does Not Prevent Hantavirus Disease Pathogenesis in Golden Syrian Hamsters

Andes virus (ANDV) is associated with a lethal vascular leak syndrome in humans termed hantavirus pulmonary syndrome (HPS). The mechanism for the massive vascular leakage associated with HPS is poorly understood; however, dysregulation of components of the immune response is often suggested as a possible cause. Alveolar macrophages are found in the alveoli of the lung and represent the first line of defense to many airborne pathogens. To determine whether alveolar macrophages play a role in HPS pathogenesis, alveolar macrophages were depleted in an adult rodent model of HPS that closely resembles human HPS. Syrian hamsters were treated, intratracheally, with clodronate-encapsulated liposomes or control liposomes and were then challenged with ANDV. Treatment with clodronate-encapsulated liposomes resulted in significant reduction in alveolar macrophages, but depletion did not prevent pathogenesis or prolong disease. Depletion also did not significantly reduce the amount of virus in the lung of ANDV-infected hamsters but altered neutrophil recruitment, MIP-1α and MIP-2 chemokine expression, and vascular endothelial growth factor (VEGF) levels in hamster bronchoalveolar lavage (BAL) fluid early after intranasal challenge. These data demonstrate that alveolar macrophages may play a limited protective role early after exposure to aerosolized ANDV but do not directly contribute to hantavirus disease pathogenesis in the hamster model of HPS.

IMPORTANCE

Hantaviruses continue to cause disease worldwide for which there are no FDA-licensed vaccines, effective postexposure prophylactics, or therapeutics. Much of this can be attributed to a poor understanding of the mechanism of hantavirus disease pathogenesis. Hantavirus disease has long been considered an immune-mediated disease; however, by directly manipulating the Syrian hamster model, we continue to eliminate individual immune cell types. As the most numerous immune cells present in the respiratory tract, alveolar macrophages are poised to defend against hantavirus infection, but those antiviral responses may also contribute to hantavirus disease. Here, we demonstrate that, like in our prior T and B cell studies, alveolar macrophages neither prevent hantavirus infection nor cause hantavirus disease. While these studies reflect pathogenesis in the hamster model, they should help us rule out specific cell types and prompt us to consider other potential mechanisms of disease in an effort to improve the outcome of human HPS.

Therapeutic interventions in sepsis: current and anticipated pharmacological agents

Sepsis is a clinical syndrome characterized by a multisystem response to a pathogenic assault due to underlying infection that involves a combination of interconnected biochemical, cellular and organ-organ interactive networks. After the withdrawal of recombinant human-activated protein C (rAPC), researchers and physicians have continued to search for new therapeutic approaches and targets against sepsis, effective in both hypo- and hyperinflammatory states. Currently, statins are being evaluated as a viable option in clinical trials. Many agents that have shown favourable results in experimental sepsis are not clinically effective or have not been clinically evaluated. Apart from developing new therapeutic molecules, there is great scope for for developing a variety of drug delivery strategies, such as nanoparticulate carriers and phospholipid-based systems. These nanoparticulate carriers neutralize intracorporeal LPS as well as deliver therapeutic agents to targeted tissues and subcellular locations. Here, we review and critically discuss the present status and new experimental and clinical approaches for therapeutic intervention in sepsis.

Pulmonary macrophage subpopulations in the induction and resolution of acute lung injury

Macrophages are key orchestrators of the inflammatory and repair responses in the lung, and the diversity of their function is indicated by their polarized states and distinct subpopulations and localization in the lung. Here, we characterized the pulmonary macrophage populations in the interstitial and alveolar compartments during the induction and resolution of acute lung injury induced by Pseudomonas aeruginosa infection. We identified macrophage subpopulations and polarity according to FACS analysis of cell surface protein markers, combined with cell sorting for gene expression using real-time PCR. With these techniques, we validated a novel, alternatively activated (M2) marker (transferrin receptor), and we described three interstitial and alveolar macrophage subpopulations in the lung whose distribution and functional state evolved from the induction to resolution phases of lung injury. Together, these findings indicate the presence and evolution of distinct macrophage subsets in the lung that serve specific niches in regulating the inflammatory response and its resolution. Alterations in the balance and function of these subpopulations could lead to nonresolving acute lung injury.

Depletion of phagocytes in the reticuloendothelial system causes increased inflammation and mortality in rabbits with Pseudomonas aeruginosa pneumonia

Phagocytes of the reticuloendothelial system are important in clearing systemic infection; however, the role of the reticuloendothelial system in the response to localized infection is not well-documented. The major goals of this study were to investigate the roles of phagocytes in the reticuloendothelial system in terms of bacterial clearance and inflammatory modulation in sepsis caused by Pseudomonas pneumonia. Macrophages in liver and spleen were depleted by administering liposome encapsulated dichloromethylene diphosphonate (clodronate) intravenously 36 h before the instillation of Pseudomonas aeruginosa into the lungs of anesthetized rabbits. Blood samples were analyzed for bacteria and cytokine concentrations. Lung injury was assessed by the bidirectional flux of albumin and by wet-to-dry weight ratios. Blood pressure and cardiac outputs decreased more rapidly and bacteremia occurred earlier in the clodronate-treated rabbits compared with the nondepleted rabbits. Plasma TNF-alpha (1.08 +/- 0.54 vs. 0.08 +/- 0.02 ng/ml) and IL-8 (6.8 +/- 1.5 vs. 0.0 +/- 0.0 ng/ml) were higher in the depleted rabbits. The concentration of IL-10 in liver of the macrophage-depleted rabbits was significantly lower than in normal rabbits at 5 h. Treatment of macrophage-depleted rabbits with intravenous IL-10 reduced plasma proinflammatory cytokine concentrations and reduced the decline in blood pressure and cardiac output. These results show that macrophages in the reticuloendothelial system have critical roles in controlling systemic bacteremia and reducing systemic inflammation, thereby limiting the systemic effects of a severe pulmonary bacterial infection.

CD40 and CD80/86 act synergistically to regulate inflammation and mortality in polymicrobial sepsis

RATIONALE

Costimulatory molecules, including the CD40-CD154 and CD80/86-CD28 dyads, play a prominent role in regulating inflammation in the adaptive immune response. Studies from our group and others suggest a potentially important role for these costimulatory cascades in innate immunity as well.

OBJECTIVES

To determine the role of CD80/86 alone and in combination with CD40 in lethal polymicrobial sepsis in mice and humans.

METHODS

The murine cecal ligation and puncture (CLP) model was used to determine the role of CD80/86 alone and in combination with CD40 using wild-type mice, CD80/86(-/-) mice, and novel CD40/80/86(-/-) mice. Expression of cell-bound and soluble costimulatory molecules was assessed in humans via ELISA and flow cytometry.

MEASUREMENTS AND MAIN RESULTS

Lethal CLP was associated with up-regulation of CD40 and CD80/86 and their respective ligands CD28 and CD154 on innate effector cells. Blockade or deletion of CD80/86 attenuated mortality and inflammatory cytokine production during CLP. CD40/80/86(-/-) mice exhibited further reductions in mortality, lung injury, and inflammatory cytokine production compared with CD80/86(-/-) mice. Finally, humans with sepsis had increased monocyte expression of CD40 and CD80 compared with healthy control subjects; with higher levels in subjects requiring vasopressor support. Levels of soluble CD28 and CD154 were significantly higher in patients who died compared with those who lived.

CONCLUSIONS

These data demonstrate a central role for CD40 and CD80/86 in the innate immune response and suggest that combined inhibition of CD40 and CD80/86 may improve mortality in sepsis. Expression of costimulatory molecules may serve as biomarkers for outcome in septic patients.

Contribution of alveolar macrophages to the response of the TIMP-3 null lung during a septic insult

Mice deficient in tissue inhibitor of metalloproteinase-3 (TIMP-3) develop an emphysema-like phenotype involving increased pulmonary compliance, tissue degradation, and matrix metalloproteinase (MMP) activity. After a septic insult, they develop a further increase in compliance that is thought to be a result of heightened metalloproteinase activity produced by the alveolar macrophage, potentially modeling an emphysemic exacerbation. Therefore, we hypothesized that TIMP-3 null mice lacking alveolar macrophages would not be susceptible to the altered lung function associated with a septic insult. TIMP-3 null and wild-type (WT) mice were depleted of alveolar macrophages before the induction of a septic insult and assessed for alteration in lung mechanics, alveolar structure, metalloproteinase levels, and inflammation. The results showed that TIMP-3 null mice lacking alveolar macrophages were protected from sepsis-induced alterations in lung mechanics, particularly pulmonary compliance, a finding that was supported by changes in alveolar structure. Additionally, changes in lung mechanics involved primarily peripheral tissue vs. central airways as determined using the flexiVent system. From investigation into possible molecules that could cause these alterations, it was found that although several proteases and inflammatory mediators were increased during the septic response, only MMP-7 was attenuated after macrophage depletion. In conclusion, the alveolar macrophage is essential for the TIMP-3 null sepsis-induced compliance alterations. This response may be mediated in part by MMP-7 activity but occurs independently of inflammatory cytokine and/or chemokine concentrations.

Defect in early lung defence against Pseudomonas aeruginosa in DBA/2 mice is associated with acute inflammatory lung injury and reduced bactericidal activity in naive macrophages

Pseudomonas aeruginosa is an opportunistic pathogen that causes serious respiratory disease in the immune-compromised host. Using an aerosol infection model, 11 inbred mouse strains (129/Sv, A/J, BALB/c, C3H/HeN, C57BL/6, DBA/2, FVB, B10.D2/oSnJ, B10.D2/nSnJ, AKR/J and SWR/J) were tested for increased susceptibility to P. aeruginosa lung colonization. DBA/2 was the only mouse strain that had increased bacterial counts in the lung within 6 h post-infection. This deficiency incited a marked inflammatory response with reduced bacterial lung clearance and a mortality rate of 96.7 %. DBA/2 mice displayed progressive deterioration of lung pathology with extensive alveolar exudate and oedema formation at 48-72 h post-infection. The neutrophil-specific myeloperoxidase activity remained elevated throughout infection, suggesting that the increased leukocyte infiltration into alveoli caused acute inflammatory lung injury. DBA/2 mice lack the haemolytic complement; however, three additional mouse strains (AKR/J, SWR/J and A/J) with the same defect effectively cleared the infection, indicating that other host factors are involved in defence. Bone marrow-derived macrophages of DBA/2 showed an initial increase in phagocytosis, while their bactericidal activity was reduced compared to that of C57BL/6 macrophages. Comparison of pulmonary cytokine profiles of DBA/2 versus C57BL/6 or C3H/HeN indicated that DBA/2 had similar increases in tumour necrosis factor (TNF)-alpha, KC and interleukin (IL)-1a as C3H/HeN, but showed specific induction of IL-17, monocyte chemotactic protein (MCP)-1 and vascular endothelial growth factor (VEGF). Together, DBA/2 mice have a defect in the initial lung defence against P. aeruginosa colonization, which causes the host to produce a greater, but damaging, inflammatory response. Such a response may originate from the reduced antimicrobial activity of DBA/2 macrophages.

The cryptococcal enzyme inositol phosphosphingolipid-phospholipase C confers resistance to the antifungal effects of macrophages and promotes fungal dissemination to the central nervous system

In recent years, sphingolipids have emerged as critical molecules in the regulation of microbial pathogenesis. In fungi, the synthesis of complex sphingolipids is important for the regulation of pathogenicity, but the role of sphingolipid degradation in fungal virulence is not known. Here, we isolated and characterized the inositol phosphosphingolipid-phospholipase C1 (ISC1) gene from the fungal pathogen Cryptococcus neoformans and showed that it encodes an enzyme that metabolizes fungal inositol sphingolipids. Isc1 protects C. neoformans from acidic, oxidative, and nitrosative stresses, which are encountered by the fungus in the phagolysosomes of activated macrophages, through a Pma1-dependent mechanism(s). In an immunocompetent mouse model, the C. neoformans Deltaisc1 mutant strain is almost exclusively found extracellularly and in a hyperencapsulated form, and its dissemination to the brain is remarkably reduced compared to that of control strains. Interestingly, the dissemination of the C. neoformans Deltaisc1 strain to the brain is promptly restored in these mice when alveolar macrophages are pharmacologically depleted or when infecting an immunodeficient mouse in which macrophages are not efficiently activated. These studies suggest that Isc1 plays a key role in protecting C. neoformans from the intracellular environment of macrophages, whose activation is important for preventing fungal dissemination of the Deltaisc1 strain to the central nervous system and the development of meningoencephalitis.

Similarity of gene expression patterns in human alveolar macrophages in response to Pseudomonas aeruginosa and Burkholderia cepacia

To determine if differences in the severity of pulmonary infection in cystic fibrosis seen with late isolates of Pseudomonas aeruginosa and Burkholderia cepacia are associated with differences in the initial response of alveolar macrophages (AM) to these pathogens, we assessed gene expression changes in human AM in response to infection with a laboratory strain, early and late clinical isolates of P. aeruginosa, and B. cepacia. Analysis of gene expression changes at the RNA level using oligonucleotide microarrays, following exposure to laboratory P. aeruginosa strain PAK, showed significant (P < 0.01) >2.5-fold upregulation of 42 genes and >2.5-fold downregulation of 45 genes. The majority of the changes in gene expression involved genes as part of inflammatory pathways and signaling systems. Interestingly, similar responses were observed following exposure of AM to early and late clinical isolates of P. aeruginosa, as well as with B. cepacia, suggesting that the more severe clinical outcome of infections with late clinical isolates of P. aeruginosa or with B. cepacia cannot be explained by differences in the early interactions of these organisms with the human AM, as reflected by the similarity of gene expression changes in response to exposure of AM to these pathogens.

Pathogen-host interactions in Pseudomonas aeruginosa pneumonia

Pseudomonas aeruginosa is an important pathogen causing a wide range of acute and chronic infections. P. aeruginosa rarely causes infection in the normal host, but is an efficient opportunistic pathogen causing serious infections in patients who are mechanically ventilated, individuals who are immunocompromised, and patients with malignancies or HIV infection. Among these risk groups, the most vulnerable hosts are neutropenic and patients who are mechanically ventilated. In addition, P. aeruginosa is the most prevalent chronic infection contributing to the pathogenesis of cystic fibrosis. Because of the ubiquitous nature of P. aeruginosa and its ability to develop resistance to antibiotics, it continues to be problematic from a treatment perspective. The pathogenicity of P. aeruginosa is largely caused by multiple bacterial virulence factors and genetic flexibility enabling it to survive in varied environments. Lung injury associated with P. aeruginosa infection results from both the direct destructive effects of the organism on the lung parenchyma and exuberant host immune responses. This article focuses on the major bacterial virulence factors and important aspects of the host immunity that are involved in the pathogenesis of serious P. aeruginosa infection. In addition to antibiotic therapy, strategies directed toward enhancing host defense and/or limiting excessive inflammation could be important to improve outcome in P. aeruginosa lung infections.