TREM-1 deficiency can attenuate disease severity without affecting pathogen clearance

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune reactions. While TREM-1-amplified responses likely aid an improved detection and elimination of pathogens, excessive production of cytokines and oxygen radicals can also severely harm the host. Studies addressing the pathogenic role of TREM-1 during endotoxin-induced shock or microbial sepsis have so far mostly relied on the administration of TREM-1 fusion proteins or peptides representing part of the extracellular domain of TREM-1. However, binding of these agents to the yet unidentified TREM-1 ligand could also impact signaling through alternative receptors. More importantly, controversial results have been obtained regarding the requirement of TREM-1 for microbial control. To unambiguously investigate the role of TREM-1 in homeostasis and disease, we have generated mice deficient in Trem1. Trem1(-/-) mice are viable, fertile and show no altered hematopoietic compartment. In CD4(+) T cell- and dextran sodium sulfate-induced models of colitis, Trem1(-/-) mice displayed significantly attenuated disease that was associated with reduced inflammatory infiltrates and diminished expression of pro-inflammatory cytokines. Trem1(-/-) mice also exhibited reduced neutrophilic infiltration and decreased lesion size upon infection with Leishmania major. Furthermore, reduced morbidity was observed for influenza virus-infected Trem1(-/-) mice. Importantly, while immune-associated pathologies were significantly reduced, Trem1(-/-) mice were equally capable of controlling infections with L. major, influenza virus, but also Legionella pneumophila as Trem1(+/+) controls. Our results not only demonstrate an unanticipated pathogenic impact of TREM-1 during a viral and parasitic infection, but also indicate that therapeutic blocking of TREM-1 in distinct inflammatory disorders holds considerable promise by blunting excessive inflammation while preserving the capacity for microbial control.

A Dose-Response Strategy Reveals Differences between Normal-Weight and Obese Men in Their Metabolic and Inflammatory Responses to a High-Fat Meal.

A dose-response strategy may not only allow investigation of the impact of foods and nutrients on human health but may also reveal differences in the response of individuals to food ingestion based on their metabolic health status. In a randomized crossover study, we challenged 19 normal-weight (BMI: 20-25 kg/m(2)) and 18 obese (BMI: >30 kg/m(2)) men with 500, 1000, and 1500 kcal of a high-fat (HF) meal (60.5% energy from fat). Blood was taken at baseline and up to 6 h postprandially and analyzed for a range of metabolic, inflammatory, and hormonal variables, including plasma glucose, lipids, and C-reactive protein and serum insulin, glucagon-like peptide-1, interleukin-6 (IL-6), and endotoxin. Insulin was the only variable that could differentiate the postprandial response of normal-weight and obese participants at each of the 3 caloric doses. A significant response of the inflammatory marker IL-6 was only observed in the obese group after ingestion of the HF meal containing 1500 kcal [net incremental AUC (net iAUC) = 22.9 ± 6.8 pg/mL × 6 h, P = 0.002]. Furthermore, the net iAUC for triglycerides significantly increased from the 1000 to the 1500 kcal meal in the obese group (5.0 ± 0.5 mmol/L × 6 h vs. 6.0 ± 0.5 mmol/L × 6 h, P = 0.015) but not in the normal-weight group (4.3 ± 0.5 mmol/L × 6 h vs. 4.8 ± 0.5 mmol/L × 6 h, P = 0.31). We propose that caloric dose-response studies may contribute to a better understanding of the metabolic impact of food on the human organism. This study was registered at clinicaltrials.gov as NCT01446068.

Cytokine induction in human mononuclear cells stimulated by IgG-coated culture surfaces and by IgG for infusion

The effect of IgG on cytokine production by human mononuclear cells (MNC) was studied. Tumor necrosis factor-alpha (TNF) was determined both by bioassay and by immunoassay. Interleukin-1 (IL1) was measured by a thymocyte costimulator assay, which was shown to be completely inhibitable by polyclonal anti-IL1. Precautions were taken to avoid inadvertent exposure of the studied cells to endotoxin. In a first model, TNF and IL1 production by adherent MNC in IgG-coated cluster plates were determined. IgG induced a strong TNF response, usually leveling off after 6 hr, and was comparable in kinetics and magnitude with an LPS-induced response. The thymocyte co-stimulatory activity response was relatively weak and peaked at 6 hr. In contrast, LPS-induced co-stimulatory activity production steadily increased over 24 hr. In a second model, MNC in suspension cultures containing autologous serum were exposed to IgG for intravenous use (IgG-IV). Cells exposed to IgG-IV produced higher amounts of cytokines than control counterparts and were primed for enhanced production of cytokines upon a second, unrelated stimulus. This implies that the effect of IgG-IV on suspended MNC resembles that of surface-adsorbed IgG and raises the possibility that cytokine release is an integral part of the mechanism of action of infused IgG. Evidence is presented suggesting that both surface IgG and IgG-IV act directly on monocytes, in a Fc-dependent manner.

Fibrinogen association with human monocytes: evidence for constitutive expression of fibrinogen receptors and for involvement of Mac-1 (CD18, CR3) in the binding

Radiolabeled fibrinogen (Fg) specifically binds to mononuclear leukocytes (MNL) and to purified monocytes, but not to nylon-nonadherent lymphocytes. The association is rapid, Ca++-dependent and reversible. MNL containing Fg-binding monocytes had not been exposed to endotoxin (less than 4 pg/mL) during the isolation and the binding test, and Fg binding was not altered by preincubation of MNL with lipopolysaccharide. The binding of Fg was inhibited by anti-Mac-1 antibodies (OKM1). Antibodies to surface-bound Fg were able to induce luminol-dependent chemiluminescence, indicating that Fg binding sites have receptor function. Emission of a signal depended on MNL exposure to Fg, on specific, divalent antibodies, but not on the antibody Fc portion. These data show that human monocytes constitutively express specific Fg receptors and suggest that Mac-1, a member of the integrin superfamily, is involved in Fg recognition.

[Adsorption therapy in sepsis.]

BACKGROUND The activation of multiple pro- and anti-inflammatory mediators is a key feature in the pathophysiology of sepsis. Many of these mediators may directly contribute to organ dysfunction and determine disease severity. So far our ability to modulate these upregulated mediator pathways is very limited. Therefore the adsorption of such mediators via an extracorporeal circuit may be a beneficial intervention during sepsis. OBJECTIVES Recent technical innovations have made this intervention feasible. Both systems for exclusive mediator adsorption and for adsorption beside a conventional renal replacement therapy are now available. Some of the membranes can adsorb a broad range of mediators by rather unspecific binding, whereas others specifically adsorb endotoxin or mediators. DISCUSSION Whilst biochemical efficacy could be demonstrated by some of the systems, controlled and randomized studies demonstrating improved clinical endpoints are still lacking. Therefore the use of such therapies outside clinical studies cannot yet be recommended.

Phospholipid oxidation generates potent anti-inflammatory lipid mediators that mimic structurally related pro-resolving eicosanoids by activating Nrf2.

Exposure of biological membranes to reactive oxygen species creates a complex mixture of distinct oxidized phospholipid (OxPL) species, which contribute to the development of chronic inflammatory diseases and metabolic disorders. While the ability of OxPL to modulate biological processes is increasingly recognized, the nature of the biologically active OxPL species and the molecular mechanisms underlying their signaling remain largely unknown. We have employed a combination of mass spectrometry, synthetic chemistry, and immunobiology approaches to characterize the OxPL generated from the abundant phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC) and investigated their bioactivities and signaling pathways in vitro and in vivo. Our study defines epoxycyclopentenones as potent anti-inflammatory lipid mediators that mimic the signaling of endogenous, pro-resolving prostanoids by activating the transcription factor nuclear factor E2-related factor 2 (Nrf2). Using a library of OxPL variants, we identified a synthetic OxPL derivative, which alleviated endotoxin-induced lung injury and inhibited development of pro-inflammatory T helper (Th) 1 cells. These findings provide a molecular basis for the negative regulation of inflammation by lipid peroxidation products and propose a novel class of highly bioactive compounds for the treatment of inflammatory diseases.