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Melioidosis is caused by the soil saprophyte Burkholderia pseudomallei and is endemic in Southeast Asia. The pathogenesis of melioidosis is still largely unknown, although gamma interferon (IFN-γ) seems to play an obligatory role in host defense. Previously, we have shown that IFN-γ production in melioidosis is controlled in part by interleukin-18 (IL-18). The aim of the present study was to determine the role of IL-18 in the immune response to B. pseudomallei . For this the following investigations were performed. (i) Plasma IL-18 and blood monocyte IL-18 mRNA levels were elevated in 34 patients with culture-proven melioidosis compared to the levels in 32 local healthy controls; in addition, IL-18 binding protein levels were markedly elevated in patients, strongly correlating with mortality. (ii) IL-18 gene-deficient (IL-18 knockout [KO]) mice showed accelerated mortality after intranasal infection with a lethal dose of B. pseudomallei , which was accompanied by enhanced bacterial growth in their lungs, livers, spleens, kidneys, and blood at 24 and 48 h postinfection, compared to wild-type mice. In addition, IL-18 KO mice displayed evidence of enhanced hepatocellular injury and renal insufficiency. Together, these data indicate that the enhanced production of IL-18 in melioidosis is an essential part of a protective immune response to this severe infection.

Contains fulltext : 48033.pdf (Publisher’s version ) (Closed access) For quantitative assessment of polymorphonuclear granulocyte (PMN)-mediated pseudohyphal damage, an improved tetrazolium (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide; XTT) dye assay was developed. The modified assay proved to be a reliable indicator of viable pseudohyphal inoculum sizes. In addition, the influence of various endogenous pro-inflammatory cytokines on the capacity of PMN to damage Candida albicans pseudohyphae was investigated. PMN obtained from mice in which the genes encoding for tumor necrosis factor-alpha/lymphotoxin-alpha (TNF/LT), interferon-gamma (IFNgamma), interleukin (IL)-1alpha, or IL-1beta were disrupted, showed a significantly reduced pseudohyphal damage capacity in comparison with control PMN. The reduction amounted 25% for TNF-/- LT-/-, 11% for IFNgamma-/-, 21% for IL-1alpha-/-, and 34% for IL-1alpha-/-beta-/- PMN. In contrast, deficiency of IL-12 or IL-18 did not result in a diminished capacity to damage pseudohyphae and the capacity of PMN to damage Candida pseudohyphae was even slightly increased by 10% in IL-18-/- mice. These data suggest that endogenous pro-inflammatory cytokines are able to modulate antihyphal activity of PMN, the main effector cells against disseminated candidiasis by virtue of their capacity to kill both Candida blastoconidia and pseudohyphae.

TLRs are important for the recognition of conserved motifs expressed by invading bacteria. TLR4 is the signaling receptor for LPS, the major proinflammatory component of the Gram-negative cell wall, whereas CD14 serves as the ligand-binding part of the LPS receptor complex. Triggering of TLR4 results in the activation of two distinct intracellular pathways, one that relies on the common TLR adaptor MyD88 and one that is mediated by Toll/IL-1R domain-containing adaptor-inducing IFN-β (TRIF). Nontypeable Haemophilus influenzae (NTHi) is a common Gram-negative respiratory pathogen that expresses both TLR4 (LPS and lipooligosaccharide) and TLR2 (lipoproteins) ligands. To determine the roles of CD14, TLR4, and TLR2 during NTHi pneumonia, the following studies were performed: 1) Alveolar macrophages from CD14 and TLR4 knockout (KO) mice were virtually unresponsive to NTHi in vitro, whereas TLR2 KO macrophages displayed a reduced NTHi responsiveness. 2) After intranasal infection with NTHi, CD14 and TLR4 KO mice showed an attenuated early inflammatory response in their lungs, which was associated with a strongly reduced clearance of NTHi from the respiratory tract; in contrast, in TLR2 KO mice, lung inflammation was unchanged, and the number of NTHi CFU was only modestly increased at the end of the 10-day observation period. 3) MyD88 KO, but not TRIF mutant mice showed an increased bacterial load in their lungs upon infection with NTHi. These data suggest that the MyD88-dependent pathway of TLR4 is important for an effective innate immune response to respiratory tract infection caused by NTHi.

The dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) homolog, SIGN-related 1 (SIGNR1) is a pathogen receptor expressed by splenic marginal zone and peritoneal macrophages, and is essential for clearance of Streptococcus pneumoniae by phagocytosis after intraperitoneal infection. Here, we identified an important in vivo function for SIGNR1 in S. pneumonia infection induced via its natural entrance route. Upon intranasal infection with S. pneumoniae, SIGNR1-deficient mice did not clear bacteria from lung and blood, and displayed severely enhanced inflammatory parameters compared to the wild-type mice. However, SIGNR1 is not expressed by alveolar macrophages, suggesting that another mechanism than a decrease in phagocytosis is responsible for this difference. Natural anti-phosphorylcholine IgM produced by marginal zone B cells is essential for protection against infection with S. pneumoniae. Strikingly, during infection, SIGNR1-deficient mice failed to produce a rapid anti-phosphorylcholine IgM response. Marginal zone macrophages have been suggested to capture antigens for presentation to marginal zone B cells. We demonstrate that marginal zone macrophages from SIGNR1-deficient mice in contrast to wild-type mice are not able to capture pneumococci from blood, suggesting that SIGNR1 on marginal zone macrophages captures S. pneumoniae for antigen presentation to and activation of marginal zone B cells, resulting in an anti-phosphorylcholine IgM response.

Thrombomodulin (TM) plays an essential role in the generation of activated protein C (APC), a mediator with both anticoagulant and anti-inflammatory properties, and is preferentially expressed in lungs. To investigate the role of TM in the coagulant and inflammatory response in the lung during tuberculosis, mice with a mutation in the TM gene (Thbd), which results in a minimal capacity for APC generation (TMpro/pro mice), were intranasally infected with live virulent Mycobacterium tuberculosis. Whereas pulmonary tuberculosis was not associated with activation of coagulation in either wild-type or TMpro/pro mice, 5 weeks after infection TMpro/pro mice displayed an uncontrolled inflammatory response in their lungs, as reflected by higher lung weights, a diminished ability to form well-shaped granulomas, elevated levels of proinflammatory cytokines, and concurrently reduced concentrations of anti-inflammatory cytokines. During a 36-week follow-up after infection with a lower dose of M tuberculosis, 35% of TMpro/pro mice died from week 28 onward versus none of the wild-type mice, and the surviving TMpro/pro mice displayed increased lung inflammation accompanied by higher mycobacterial loads in liver and spleen. These data suggest that a TM mutation that impairs APC generation results in uncontrolled lung inflammation during tuberculosis.

The development of active tuberculosis after infection with Mycobacterium tuberculosis is almost invariably caused by a persistent or transient state of relative immunodeficiency. Leptin, the product of the obese (ob) gene, is a pleiotropic protein produced mainly by adipocytes and is down-regulated during malnutrition and starvation, conditions closely connected with active tuberculosis. To investigate the role of leptin in tuberculosis, we intranasally infected wild-type (Wt) and leptin-deficient ob/ob mice with live virulent M. tuberculosis. Ob/ob mice displayed higher mycobacterial loads in the lungs after 5 and 10 weeks of infection, although the difference with Wt mice remained 1 log of M. tuberculosis colony forming unit. Nevertheless, ob/ob mice were less able to form well-shaped granuloma and lung lymphocyte numbers were reduced compared with Wt mice early during infection. In addition, ob/ob mice had a reduced capacity to produce the protective cytokine IFN gamma at the site of the infection early during infection and upon antigen-specific recall stimulation, and showed reduced delayed-type hypersensitivity reaction to intra-dermal tuberculin purified protein derivative. Leptin replacement restored the reduced IFN gamma response observed in ob/ob mice. Mortality did not differ between ob/ob and Wt mice. These data suggest that leptin plays a role in the early immune response to pulmonary tuberculosis

Non-mannose-capped lipoarabinomannan induces lung inflammation via toll-like receptor 2.Wieland CW, Knapp S, Florquin S, de Vos AF, Takeda K, Akira S, Golenbock DT, Verbon A, van der Poll T.Laboratory of Experimental Internal Medicine, Department of Pathology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. c.wieland@amc.uva.nlNon-mannose-capped lipoarabinomannan (AraLAM) is part of the cell membrane of atypical mycobacteria. To determine the capacity of AraLAM to induce lung inflammation in vivo and to determine the signaling receptors involved herein, wild-type (WT) mice, lipopolysaccharide binding protein knockout mice, CD14-deficient (CD14 KO) mice, Toll-like receptor (TLR) 4 mutant mice, or TLR2 KO mice were intranasally inoculated with purified AraLAM. AraLAM induced high lung levels of tumor necrosis factor, interleukin-1beta, interleukin-6, and cytokine-induced neutrophil chemoattractant (KC) and an influx of neutrophils into the pulmonary compartment of WT mice. Lipopolysaccharide binding protein knockout, CD14 KO, and TLR4 mutant mice displayed similar inflammatory responses as WT mice, whereas in TLR2 KO mice, AraLAM-induced lung inflammation was strongly diminished. In addition, TLR2 KO mice, but not CD14 KO or TLR4 mutant mice, displayed a delayed clearance of pulmonary infection with the atypical AraLAM expressing Mycobacterium smegmatis. These data indicate that TLR2 is the signaling receptor for purified AraLAM in the lung in vivo and that this receptor contributes to an effective clearance of M. smegmatis from the pulmonary compartment.

Platelet-activating factor (PAF), a glycerophospholipid with proinflammatory properties, exerts its biological effects by interacting with the PAF receptor (PAFR) expressed on many different cell types. The PAFR specifically binds phosphorylcholine, the biologically active component of PAF. However, phosphorylcholine is also a component of the cell wall of nontypeable Haemophilus influenzae (NTHi). In recently published in vitro experiments, the invasion of respiratory epithelial cells by NTHi was mediated by the PAFR. To determine the role of the PAFR in host defense against pneumonia induced by NTHi, PAFR-deficient (PAFR-/-) and normal wild-type mice were intranasally inoculated with NTHi. The absence of a functional PAFR was associated with a normal innate immune response as indicated by similar bacterial counts, myeloperoxidase activity, and inflammation within the pulmonary compartment of PAFR-/- and wild-type mice. These data indicate that the PAFR does not interfere with the clearance of NTHi from the respiratory tract.

In the margin of page 742 of the following article, a red arrow was left from the production process; it has no meaning with respect to the figure or figure legend: Arie J Hoogendijk, Sander H Diks, Maikel P Peppelenbosch, Tom van der Poll, and Catharina W Wieland. Kinase Activity Profiling of Gram-Negative Pneumonia. Mol. Med. 2011;17(7–8):741–7.

Endogenous molecules released during tissue injury can trigger an innate immune response and are termed damage-associated molecular patterns (DAMPs). Uric acid is considered an important DAMP and causes acute lung inflammation when administered locally. The exact role of the innate immune response in ventilator-induced lung injury (VILI) is not yet completely understood. We hypothesized that uric acid is released during VILI and that reduction of uric acid levels attenuates lung injury induced by short-term mechanical ventilation (MV).

Klebsiella species are opportunistic pathogens that can give rise to severe infections including pneumonia and sepsis. Typically, Klebsiella infections are nosocomial and mainly caused by Klebsiella pneumoniae, the medically most important species of the genus.

Summary Burkholderia pseudomallei, which causes melioidosis, a severe, mainly pulmonary disease endemic in South-East Asia, is considered to be the most pathogenic of the Burkholderia genus. B. thailandensis, however, is considered avirulent. We determined differences in patterns of inflammation of B. pseudomallei 1026b (clinical virulent isolate), B. pseudomallei AJ1D8 (an in vitro invasion-deficient mutant generated from strain 1026b by Tn5-OT182 mutagenesis) and B. thailandensis by intranasally inoculating C57BL/6 mice with each strain. Mice infected with B. thailandensis showed a markedly decreased bacterial outgrowth from lungs, spleen and blood 24 h after inoculation, compared with infection with B. pseudomallei and the invasion mutant AJ1D8. Forty-eight hours after inoculation, B. thailandensis was no longer detectable. This was consistent with elevated pulmonary cytokine and chemokine concentrations after infection with B. pseudomallei 1026b and AJ1D8, and the absence of these mediators 48 h, but not 24 h, after inoculation with B. thailandensis. Histological examination, however, did show marked pulmonary inflammation in the mice infected with B. thailandensis, corresponding with substantial granulocyte influx and raised myeloperoxidase levels. Survival experiments showed that infection with 1 × 103 cfu B. thailandensis was not lethal, whereas inoculation with 1 × 106 cfu B. thailandensis was equally lethal as 1 × 103 cfu B. pseudomallei 1026b or AJ1D8. These data show that B. pseudomallei AJ1D8 is just as lethal as wild-type B. pseudomallei in an in vivo mouse model, and B. thailandensis is perhaps more virulent than is often recognized.