Soluble triggering receptor expressed on myeloid cells (sTREM-1): a new mediator involved in the pathogenesis of peptic ulcer disease

Mechanisms of Resistance to Immunotherapy in Hepatocellular Carcinoma

Systemic treatment for advanced hepatocellular carcinoma (HCC) has been revolutionized over the last few years following the approval of immune checkpoint inhibitors (ICI). Despite the promising survival extension seen with ICI combination regimens, responses are not universally seen and the optimal partner for programmed cell death 1 pathway inhibitors remains to be identified. Even fewer encouraging results have been demonstrated with ICI used for monotherapy. Several mechanisms of resistance have been described so far, involving characteristics of cancer cells (intrinsic mechanisms) and of the surrounding tumor microenvironment (extrinsic mechanisms). Factors related to therapy may also contribute to the development of resistance. Increasing research efforts are being dedicated to the discovery of novel approaches and targets to overcome resistance, some of which may be introduced into clinic in the future. Herein we describe a selection of resistance mechanisms that have been involved in impairing response to ICI and propose potential therapeutic approaches to overcome resistance.

The role of the triggering receptor expressed on myeloid cells-1 (TREM-1) in non-bacterial infections

The triggering receptor expressed on myeloid cells 1 (TREM-1) is a receptor of the innate immune system, expressed mostly by myeloid cells and primarily associated with pro- inflammatory responses. Although the exact nature of its ligands has not yet been fully elucidated, many microorganisms or danger signals have been proposed as inducers of its activation or the secretion of sTREM-1, the soluble form with putative anti-inflammatory effects. In the course of the 20 years since its first description, several studies have investigated the involvement of TREM-1 in bacterial infections. However, the number of studies describing the role of TREM-1 in fungal, viral and parasite-associated infections has only increased in the last few years, showing a diverse contribution of the receptor in these scenarios, with beneficial or detrimental activities depending on the context. Therefore, this review aims to discuss how TREM-1 may influence viral, fungal and parasitic infection outcomes, highlighting its potential as a therapeutic target and biomarker for diagnosis and prognosis of non-bacterial infectious diseases.

TREM Receptors Connecting Bowel Inflammation to Neurodegenerative Disorders

Alterations in Triggering Receptors Expressed on Myeloid cells (TREM-1/2) are bound to a variety of infectious, sterile inflammatory, and degenerative conditions, ranging from inflammatory bowel disease (IBD) to neurodegenerative disorders. TREMs are emerging as key players in pivotal mechanisms often concurring in IBD and neurodegeneration, namely microbiota dysbiosis, leaky gut, and inflammation. In conditions of dysbiosis, compounds released by intestinal bacteria activate TREMs on macrophages, leading to an exuberant pro-inflammatory reaction up to damage in the gut barrier. In turn, TREM-positive activated macrophages along with inflammatory mediators may reach the brain through the blood, glymphatic system, circumventricular organs, or the vagus nerve via the microbiota-gut-brain axis. This leads to a systemic inflammatory response which, in turn, impairs the blood-brain barrier, while promoting further TREM-dependent neuroinflammation and, ultimately, neural injury. Nonetheless, controversial results still exist on the role of TREM-2 compared with TREM-1, depending on disease specificity, stage, and degree of inflammation. Therefore, the present review aimed to provide an update on the role of TREMs in the pathophysiology of IBD and neurodegeneration. The evidence here discussed the highlights of the potential role of TREMs, especially TREM-1, in bridging inflammatory processes in intestinal and neurodegenerative disorders.

Blockade of TREM-1 prevents vitreoretinal neovascularization in mice with oxygen-induced retinopathy

In pathological retinal neovascularization (RNV) disorders, the retina is infiltrated by activated leukocytes and macrophages. Triggering receptor expressed on myeloid cells 1 (TREM-1), an inflammation amplifier, activates monocytes and macrophages and plays an important role in cancer, autoimmune and other inflammation-associated disorders. Hypoxia-inducible TREM-1 is involved in cancer angiogenesis but its role in RNV remains unclear. Here, to close this gap, we evaluated the role of TREM-1 in RNV using a mouse model of oxygen-induced retinopathy (OIR). We found that hypoxia induced overexpression of TREM-1 in the OIR retinas compared to that of the room air group. TREM-1 was observed specifically in areas of pathological RNV, largely colocalizing with macrophage colony-stimulating factor (M-CSF) and CD45- and Iba-1-positive cells. TREM-1 blockade using systemically administered first-in-class ligand-independent TREM-1 inhibitory peptides rationally designed using the signaling chain homooligomerization (SCHOOL) strategy significantly (up to 95%) reduced vitreoretinal neovascularization. The peptides were well-tolerated when formulated into lipopeptide complexes for peptide half-life extension and targeted delivery. TREM-1 inhibition substantially downregulated retinal protein levels of TREM-1 and M-CSF suggesting that TREM-1-dependent suppression of pathological angiogenesis involves M-CSF. Targeting TREM-1 using TREM-1-specific SCHOOL peptide inhibitors represents a novel strategy to treat retinal diseases that are accompanied by neovascularization including retinopathy of prematurity.

Triggering Receptor Expressed on Myeloid Cells-1 Signaling: Protective and Pathogenic Roles on Streptococcal Toxic-Shock-Like Syndrome Caused by Streptococcus suis

Streptococcus suis infections can cause septic shock, which is referred to as streptococcal toxic-shock-like syndrome (STSLS). The disease is characterized by a severe inflammatory response, multiple organ failure, and high mortality. However, no superantigen that is responsible for toxic shock syndrome was detected in S. suis, indicating that the mechanism underlying STSLS is different and remains to be elucidated. Triggering receptor expressed on myeloid cells-1 (TREM-1), belonging to the Ig superfamily, is an activating receptor expressed on myeloid cells, and has been recognized as a critical immunomodulator in several inflammatory diseases of both infectious and non-infectious etiologies. In this review, we discuss the current understanding of the immunoregulatory functions of TREM-1 on acute infectious diseases and then highlight the crucial roles of TREM-1 on the development of STSLS.

Comparison of gastric juice soluble triggering receptor expressed on myeloid cells and C-reactive protein for detection of Helicobacter pylori infection

Background and aim

Triggering receptor expressed on myeloid cells (TREM-1) is a receptor on phagocytes that is triggered by infectious agents. The soluble form of it (sTREM-1) can be elevated in gastric juice by Helicobacter pylori (H. pylori) infection of gastric mucosa. The aim of this study was to compare the diagnostic values of sTREM-1 and C-reactive protein (CRP) for detection of H. pylori infection in gastric mucosa.

Methods

In this diagnostic accuracy study on cases who underwent endoscopy from March 2015 to July 2016 in Shahid Beheshti Hospital, Kashan, Iran, gastric juice sTREM-1 and CRP concentrations were measured by enzyme-linked immunosorbent assays (ELISA) and their diagnostic values were compared to detect H. pylori infection. Gold standard test was histopathology. Data were entered into SPSS software version 16. Statistical analysis was made by Kolmogorov-Smirnov, Chi-square, Independent-samples t-test, Kruskal-Wallis, Mann-Whitney U, Pearson product-moment correlation, Receiver operating characteristic curve (ROC), Brier score, Nagelkerke R square and scaled reliability test.

Results

Of a total of 160 cases, 81 (50.6%) were H. pylori-positive based on pathology. The level of sTREM-1 in H. pylori-positive patients was significantly higher than H. pylori-negative patients (p=0.000), but no significant difference between CRP concentrations was shown between groups (p=0.7). Sensitivity, specificity, positive likelihood ratio, negative likelihood ratio and accuracy of sTREM-1 were 82%, 75%, 3.3, 0.25, 78% and for CRP were 62%, 40%, 1.02, 0.98, 51% respectively for diagnosis of H. pylori infection. True positive and negative rates were 66 (81.5%) and 59 (74.7%) for sTREM-1 and 50 (61.7%) and 31 (39.2%) for CRP. The levels of sTREM-1 and CRP were not significantly different between endoscopic finding groups (p=0.97, p=0.2 respectively).

Conclusion

Despite CRP, sTREM-1 was a relatively acceptable indicator of H. pylori infection of gastric mucosa.

sTREM-1 in patients with chronic kidney disease on hemodialysis

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily. TREM-1 has been implicated as an amplifier of inflammation. Soluble TREM-1 (sTREM-1) was investigated in different clinical conditions, but not in hemodialysis (HD) patients. We aimed to investigate sTREM-1 as a marker of inflammation in HD patients. We investigated 40 CKD patients undergoing chronic HD treatment and 15 controls. Routine laboratory investigations in addition to CRP measured by immunoturbidimetry, TNF- α, and sTREM-1 measured by ELISA were assayed in post-hemodialysis patients' blood samples and in controls' blood samples. CRP, TNF-α, and sTREM-1 levels were significantly higher in HD patients than in controls (p < 0.001 for all). sTREM-1 was positively correlated with CRP and TNF-α (r = +0.50, p < 0.001 and r = +0.53, p < 0.001 respectively). It was negatively correlated with hemoglobin concentration (r = -0.69, p < 0.001). Hemoglobin concentration was the significant predictor of sTREM-1 level (p < 0.001). In conclusion, sTREM-1 level is significantly increased in HD patients as are other pro-inflammatory markers.

Tumor necrosis factor-α regulates triggering receptor expressed on myeloid cells-1-dependent matrix metalloproteinases in the carotid plaques of symptomatic patients with carotid stenosis

OBJECTIVE

To determine the relationship between increased triggering receptor expressed on myeloid cells (TREM)-1 and plaque stability in atherosclerotic carotid stenosis.

METHODS

The mRNA transcripts and protein for TREM-1, MMP-1, MMP-9, collagen type I (COL1A1) and collagen type III (COL3A1) were analyzed by qPCR and immunofluorescence in both tissues and VSMCs isolated from atherosclerotic carotid plaques of symptomatic and asymptomatic patients with carotid stenosis.

RESULTS

The TREM-1, MMP-1 and MMP-9 mRNA transcripts were significantly increased (TREM-1, p < 0.01; MMP-1, p < 0.01 and MMP-9, p < 0.001) while COL1A1 and COL3A1 mRNA transcripts were decreased (p < 0.001) in VSMCs isolated from carotid plaques of symptomatic (S) than asymptomatic (AS) patients. Stimulation of cells with TNF-α further increased the mRNA transcripts of TREM-1, MMPs, COL1A1 and COL3A1. Modulation of TREM-1 by treatment with TREM-1 decoy receptor rTREM-1/Fc, and either TREM-1 antibodies or TREM-1 siRNA attenuated the TNF-α-induced expression of MMP-1 and MMP-9 (p < 0.01) and COL1A1 and COL3A1 (p < 0.01) in S compared to AS VSMCs isolated from carotid plaques. Inhibition of NF-kB (BAY 11-7085), JNK (SP600125) and PI3K (LY294002) signaling pathways decreased the expression of TREM-1 (p < 0.01), MMP-1 (p < 0.001) and MMP-9 (p < 0.01) in TNF-α-treated VSMCs isolated from S carotid plaques compared to AS patients.

CONCLUSION

Increased expression of TREM-1 in S compared to AS patients involving MMP-1 and MMP-9 suggest a potential role of TREM-1 in plaque destabilization. Selective blockade of TREM-1 may contribute to the development of new therapies and promising targets for stabilizing vulnerable atherosclerotic plaques.

Identification of a Novel Splice Variant Isoform of TREM-1 in Human Neutrophil Granules

Triggering receptor expressed on myeloid cells-1 (TREM-1) is critical for inflammatory signal amplification. Humans have two forms of TREM-1: a membrane receptor, associated with the adaptor DAP12, and a soluble receptor detected at times of infection. The membrane receptor isoform acts synergistically with the TLR pathway to promote cytokine secretion and neutrophil migration, whereas the soluble receptor functions as a counterregulatory molecule. In multiple models of sepsis, exogenous administration of soluble forms of TREM-1 attenuates inflammation and markedly improves survival. Despite intense interest in soluble TREM-1, both as a clinical predictor of survival and as a therapeutic tool, the origin of native soluble TREM-1 remains controversial. Using human neutrophils, we identified a 15-kDa TREM-1 isoform in primary (azurophilic) and secondary (specific) granules. Mass spectrometric analysis, ELISA, and immunoblot confirm that the 15-kDa protein is a novel splice variant form of TREM-1 (TREM-1sv). Neutrophil stimulation with Pseudomonas aeruginosa, LPS, or PAM(3)Cys4 resulted in degranulation and release of TREM-1sv. The addition of exogenous TREM-1sv inhibited TREM-1 receptor-mediated proinflammatory cytokine production. Thus, these data reveal that TREM-1 isoforms simultaneously activate and inhibit inflammation via the canonical membrane TREM-1 molecule and this newly discovered granular isoform, TREM-1sv.

Correlation between soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) expression and endoscopic activity in inflammatory bowel diseases

BACKGROUND

Recently, a triggering receptor expressed on myeloid cells-1 was shown to be upregulated in the intestines of patients with inflammatory bowel diseases.

AIMS

To investigate the relationship between serum soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) level and endoscopic activity in patients with inflammatory bowel diseases.

METHODS

A total of 85 patients with ulcerative colitis and 34 patients with Crohn's disease were prospectively enrolled. Endoscopic disease activity was determined using the Mayo score and the Simplified Endoscopic Activity Score for Crohn's disease.

RESULTS

In ulcerative colitis, sTREM-1 level was correlated more strongly with the endoscopic activity (r=0.498) than the C-reactive protein level (r=0.386) or erythrocyte sedimentation rate (r=0.272), although not superior to the partial Mayo score (r=0.611). Moreover, only sTREM-1 was correlated significantly with the endoscopic activity irrespective of the disease extent. In Crohn's disease, the Simplified Endoscopic Activity Score for Crohn's disease was correlated with both the C-reactive protein level (r=0.585) and erythrocyte sedimentation rate (r=0.474), but not with sTREM-1 level (r=0.097).

CONCLUSIONS

In ulcerative colitis, sTREM-1 level was correlated most closely with the endoscopic disease activity among serum biomarkers, but was not superior to the clinical activity index. Our results suggest that sTREM-1 level may represent a complementary marker for the assessment of endoscopic activity in ulcerative colitis, but not in Crohn's disease.

Levels of plasma-soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) are correlated with disease activity in rheumatoid arthritis

OBJECTIVE

To determine whether levels of plasma-soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) are elevated in patients with rheumatoid arthritis (RA) and whether levels are correlated with disease activity and other variables.

METHODS

Our study included 71 patients with RA and 50 age- and sex-matched healthy controls. Clinical characteristics and laboratory measures, including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and 28-joint Disease Activity Score (DAS28) were assessed. Plasma levels of sTREM-1 and tumor necrosis factor-α (TNF-α) were measured by ELISA.

RESULTS

Patients with RA had significantly higher plasma sTREM-1 levels than healthy controls (170.10 ± 84.71 pg/ml vs 97.41 ± 40.64 pg/ml; p < 0.001). In patients with RA, plasma sTREM-1 levels were found to be correlated with DAS28, ESR, CRP, white blood cell counts, neutrophil counts, and plasma TNF-α levels (r = 0.329, p = 0.005; r = 0.241, p = 0.043; r = 0.314, p < 0.001; r = 0.261, p = 0.028; r = 0.278, p = 0.019; and r = 0.313, p = 0.009, respectively). Plasma sTREM-1 levels in patients with active disease status (DAS28 > 3.2) were significantly higher than in those with low disease status (DAS28 ≤ 3.2; 208.89 ± 100.14 pg/ml vs 150.29 ± 68.70 pg/ml; p = 0.005).

CONCLUSION

Patients with RA had higher plasma sTREM-1 levels than healthy controls, and plasma sTREM-1 levels were correlated with disease activity measures, suggesting that plasma sTREM-1 could play a role in the inflammatory process associated with TNF-α, and that it may be a useful disease activity marker in RA.

Serum sTREM-1 as a surrogate marker of treatment outcome in patients with peptic ulcer disease

OBJECTIVE

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is elevated in the gastric juice and in cultures of gastric mucosa of patients with peptic ulcer disease (PUD). Its application as a surrogate marker for the treatment of PUD was assessed.

METHODS

From 138 eligible patients, 96 were enrolled; 50 with duodenal ulcer, 29 with gastric ulcer and 17 with chronic gastritis. Patients were endoscoped twice; once before treatment and once after treatment. Biopsy specimens were collected for histopathologic estimation of gastritis. Blood was sampled prior to each endoscopy. Serum was collected and sTREM-1 was measured by an enzyme immunoabsorbent assay ( http://www.clinicaltrials.gov identifier NCT00534443).

RESULTS

At the end of treatment sTREM-1 was either: (a) below the limit of detection (this occurred in 62 patients and it was accompanied by lacks signs of residual disease in 58 patients, 93.5%); or (b) above the limit of detection (this occurred in 17 patients and it was accompanied by residual disease in 14 patients, 82.3%) (p < 0.0001). Odds ratio for complete healing of peptic ulcer with sTREM-1 below detection limit was 5.30 (95% CI: 1.89-14.83, p < 0.001) compared to serum sTREM-1 above the limit of detection.

CONCLUSIONS

Serum sTREM-1 below detection limit may effectively distinguish patients who successfully completed therapy for PUD from those with residual disease and apply as a surrogate marker.

Expression of a soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) correlates with clinical disease activity in intestinal Behcet's disease

BACKGROUND

No serological marker currently exists to assess disease activity in patients with intestinal Behcet's disease (BD). We conducted this study to determine if the expression level of serum soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) can be used as a biological marker to assess disease activity in intestinal BD.

METHODS

A total of 88 patients with intestinal BD were enrolled prospectively. We assessed their clinical disease activities using the disease activity index for intestinal BD (DAIBD). At the time that the DAIBD was assessed, serum erythrocyte sedimentation rate (ESR) as well as levels of TREM-1, C-reactive protein (CRP), and tumor necrosis factor-α (TNF-α) were measured.

RESULTS

The mean ESR and mean levels of sTREM-1, CRP, and TNF-α in patients with intestinal BD were significantly higher than those in healthy controls. Levels of sTREM-1 were the most highly correlated with disease activity (r = 0.762 for the DAIBD score), followed by CRP levels (r = 0.383 for the DAIBD score) and ESR (r = 0.236 for the DAIBD score). However, serum levels of TNF-α level were not correlated with disease activity (r = -0.017 for the DAIBD score).

CONCLUSIONS

Serum sTREM-1 levels were more highly correlated with disease activity than were CRP levels or ESR in patients with intestinal BD, suggesting that serum sTREM-1 level could be a potential marker for the assessment of disease activity of intestinal BD.

Relationships between genetic polymorphisms of triggering receptor expressed on myeloid cells-1 and inflammatory bowel diseases in the Korean population

AIMS

Triggering receptor expressed on myeloid cells-1 (TREM-1) has been shown to play a crucial role in the propagation of inflammatory responses. Recent studies have reported that TREM-1 expression is up-regulated in patients with inflammatory bowel disease (IBD). Therefore, we investigated the associations between TREM-1 genetic polymorphisms and IBD development and its phenotypes in the Korean population.

MAIN METHODS

Three TREM-1 single nucleotide polymorphisms (SNPs, rs2234237, rs3789205, and rs9471535) were genotyped by Taqman technology on 202 Crohn's disease (CD), 265 ulcerative colitis (UC), 138 with intestinal Behcet's disease (BD), and 234 healthy controls and the relationships between these SNPs and IBD development and phenotypes were evaluated.

KEY FINDINGS

We found that TREM-1 SNPs are significantly associated with the development of intestinal Behcet's disease (rs9471535: odds ratio [OR]=1.637, P=0.025; rs3789205: OR=1.668, P=0.019; rs2234237: OR=1.691, P=0.016), and in particular with skin involvement (rs9471535: OR=2.723, P=0.009; rs3789205: OR=2.477, P=0.017; rs2234237: OR=2.278, P=0.030) and the risk of azathioprine use (rs9471535: OR=2.722, P=0.021; rs3789205: OR=2.493, P=0.032; rs2234237: OR=2.638, P=0.026). However, TREM-1 SNPs were not significantly associated with the development of Crohn's disease or ulcerative colitis.

SIGNIFICANCE

The results of our study suggest that TREM-1 SNPs may play a significant role in the development of intestinal Behcet's disease and may have modest effects on disease severity.

TNF-alpha promotes LPA1- and LPA3-mediated recruitment of leukocytes in vivo through CXCR2 ligand chemokines

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid present in low concentrations in serum and biological fluids but in high concentrations at sites of inflammation. LPA evokes a variety of cellular responses via binding to and activation of its specific G protein-coupled receptors (GPCR), namely LPA(1-6). Even though LPA is a chemoattractant for inflammatory cells in vitro, such a role for LPA in vivo remains largely unexplored. In the present study, we used the murine air pouch model to study LPA-mediated leukocyte recruitment in vivo using selective LPA receptor agonist/antagonist and LPA(3)-deficient mice. We report that 1) LPA injection into the air pouch induced leukocyte recruitment and that both LPA(1) and LPA(3) were involved in this process; 2) LPA stimulated the release of the pro-inflammatory chemokines keratinocyte-derived chemokine (KC) and interferon-inducible protein-10 (IP-10) in the air pouch; 3) tumor necrosis factor-α (TNF-α) injected into the air pouch prior to LPA strongly potentiated LPA-mediated secretion of cytokines/chemokines, including KC, IL-6, and IP-10, which preceded the enhanced leukocyte influx; and 4) blocking CXCR2 significantly reduced leukocyte infiltration. We suggest that LPA, via LPA(1) and LPA(3) receptors, may play a significant role in inducing and/or sustaining the massive infiltration of leukocytes during inflammation.

Serum soluble triggering receptor expressed on myeloid cells-1 in acute respiratory distress syndrome: a prospective observational cohort study

Background/Purpose

Serum soluble triggering receptor expressed on myeloid cells-1 (sTREM-1), a detector of acute inflammatory response to microbial products and a good marker for diagnosing sepsis and pneumonia, has not yet been described as a predictor for infection or a prognostic factor in patients with acute respiratory distress syndrome (ARDS).

Methods

This prospective observational cohort study enrolled 63 ventilated adult patients with ARDS; 50 as septic and 13 as non-septic, and followed them for 28 days in intensive care units at a university hospital in Taiwan. Serial serum sTREM-1 levels and cytokines, such as interleukin (IL)-1, IL-8, and tumor necrosis factor-α, on days 1, 3, 5, 7 and 14 were measured by an enzyme-linked immunosorbent assay. The association between biomarkers and clinical infectious diagnosis/outcome in ARDS was explored.

Results

Serum sTREM-1 and cytokine levels could not differentiate septic from non-septic ARDS. Serum log sTREM-1 and inflammatory cytokine levels were correlated positively (r = 0.325 for IL-1β; r = 0.247 for IL-8; r = 0.480 for tumor necrosis factor-α). As prognostic factors, higher serum sTREM-1 level on day 1 and increasing levels over time, especially in the first 5 days, were independent predictors of mortality on day 28, using a multivariate Cox regression model. Serum sTREM-1 levels remained stable or even increased in the non-surviving patients, but decreased in the survivors.

Conclusion

Serum sTREM-1 level might not be a reliable marker for infection in ARDS patients. However, as an inflammatory marker, initial serum sTREM-1 level and its trend over time, especially in the first 5 days, could be predictive of short-term mortality. A progressive decline in serum sTREM-1 levels during follow-up indicates a favorable outcome, whereas persistently elevated sTREM-1 indicates a poor prognosis and should lead to a re-evaluation of therapy.

Diagnostic value of triggering receptor expressed on myeloid cells-1 and C-reactive protein for patients with lung infiltrates: an observational study

Background

Differential diagnosis of patients with lung infiltrates remains a challenge. Triggering receptor expressed on myeloid cells (TREM)-1 is a neutrophil and monocyte receptor up-regulated during infection. The aim of this study was to evaluate the diagnostic accuracy of TREM-1 and of C-reactive protein (CRP) from patients with lung infiltrates to discern community acquired lung infections.

Methods

68 patients admitted to a medical ward with acute respiratory illness were enrolled in the study. Neutrophil and monocyte TREM-1 expression were measured by flow cytometry, sTREM-1 by an enzyme immunoassay and C-reactive protein by nephelometry. Clinical pulmonary infection score was recorded.

Results

34 patients were diagnosed with bacterial community acquired pneumonia (group A) and 34 with non-bacterial pulmonary disease (group B). Median serum TREM-1 concentration was 102.09 pg/ml in group A and lower than 15.10 pg/ml (p < 0.0001) in group B. Mean±SE neutrophil TREM-1 expression was 4.67 ± 0.53 MFI in group A and 2.64 ± 0.25 MFI (p = 0.001) in group B. Monocyte TREM-1 expression was 4.2 ± 0.42 MFI in group A and 2.64 ± 0.35 MFI (p = 0.007) in group B and mean±SE CRP was 18.03 ± 2 mg/ml in group A and 7.1 ± 1.54 mg/ml (p < 0.001) in group B. A cut-off of 19.53 pg/ml of sTREM-1 with sensitivity 82.6% and specificity 63% to discriminate between infectious and non-infectious pulmonary infiltrates was found. sTREM-1 at admission greater than 180 pg/ml was accompanied with unfavourable outcome.

Conclusion

TREM-1 myeloid expression and sTREM-1 are reliable markers of bacterial infection among patients with pulmonary infiltrates; sTREM-1 is a predictor of final outcome.

Amniotic fluid sTREM-1 in normal pregnancy, spontaneous parturition at term and preterm, and intra-amniotic infection/inflammation

OBJECTIVE

Intra-amniotic infection/inflammation (IAI) is one of the most important mechanisms of disease in preterm birth. Triggering receptor expressed on myeloid cells (TREM)- 1 is a transmembrane glycoprotein expressed by neutrophils, macrophages and mature monocytes. TREM-1 is upregulated in biological fluids and tissues infected by Gram (+) and Gram (-) bacteria and fungi, amplifies the production of pro-inflammatory cytokines and chemokines, and its soluble form (sTREM-1) is released in the presence of infection. The aim of this study was to determine the effect of gestational age, parturition (term and preterm) and IAI in the amniotic fluid (AF) concentrations of sTREM-1.

STUDY DESIGN

This cross-sectional study included 434 patients in the following groups: (1) mid-trimester of pregnancy (14-18 weeks, n = 38); (2) normal pregnant women at term with (n = 39) and without (n = 39) labor; (3) patients with spontaneous preterm labor (PTL) and intact membranes classified into: (a) PTL who delivered at term (n = 99); (b) PTL who delivered preterm (<37 weeks gestation) without IAI (n = 80); and (c) PTL with IAI (n = 59); and (4) women with preterm prelabor rupture of membranes (PROM) with (n = 40) and without (n = 40) IAI. The AF concentration of sTREM-1 was determined by enzyme-linked immunoassay. Non-parametric statistics were used for analyses.

RESULTS

(1) sTREM-1 was detected in all the AF samples; (2) the median AF sTREM-1 concentration at term was higher than in the mid-trimester (4277.6 pg/ml vs. 1140.4 pg/ml; p < 0.001); (3) among patients with PTL, the median AF sTREM-1 concentration was higher in patients with IAI than in those without IAI (6154.4 pg/ml vs. 3282.8 pg/ml; p < 0.001) and those with PTL who delivered at term (6154.4 pg/ml vs. 2794 pg/ml; p < 0.001); (4) patients with preterm PROM with IAI had a higher median AF sTREM-1 concentration than those without IAI (7893.1 pg/ml vs. 3386.6 pg/ml; p < 0.001); (5) no differences were observed in the median AF sTREM-1 concentration between patients with spontaneous labor at term and those at term not in labor (4712.4 pg/ml vs. 4277.6 pg/ml; respectively p = 0.4); and 6) an AF sTREM-1 concentration >or=6416 pg/ml (derived from a ROC curve) had a sensitivity of 72% and a specificity of 89% for the diagnosis of intra-amniotic infection.

CONCLUSIONS

sTREM-1 is a physiologic constituent of the AF, and its concentration: (1) is significantly elevated in the presence of IAI; (2) increases with advancing gestation; and (3) does not change in the presence of spontaneous labor at term. We propose that sTREM-1 play a role in the innate immune response against intra-amniotic infection.

Soluble triggering receptor expressed on myeloid cells 1 and the diagnosis of sepsis

PURPOSE

Early diagnosis and assessment of the systemic inflammatory response to infection are difficult with usual markers (fever, leukocytosis, C-reactive protein [CRP]). Triggering receptor expressed on myeloid cells-1 (TREM-1) expression on phagocytes is up-regulated by microbial products. We studied the ability of soluble TREM-1 (sTREM-1) to identify patients with sepsis.

MATERIALS AND METHODS

Plasma samples were obtained on intensive care unit admission from patients with systemic inflammatory response syndrome for sTREM-1 measurement.

RESULTS

Soluble TREM-1, CRP concentrations and erythrocyte sedimentation rate (ESR) were higher in the sepsis group (n = 52) than in the non-infectious systemic inflammatory response syndrome group (n = 43; P = .00, .02, and .001, respectively). Soluble TREM-1, CRP concentrations, white blood cell count and ESR were higher in the sepsis group than in the non SIRS group (n = 37; P = .04, .00, .01, and .00, respectively). In a receiver-operating characteristic curve analysis, ESR, CRP and sTREM-1 had an area under the curve larger than 0.65 (P = .00), in distinguishing between septic and non-infectious SIRS patients. CRP, ESR, sTREM-1 had a sensitivity of 60%, 70% and 70% and a specificity of 60%, 69% and, 60% respectively in diagnosing infection in SIRS.

CONCLUSION

C-reactive protein and ESR performed better than sTREM-1 and white blood cell count in diagnosing infection.

TREM-1 expression is increased in the synovium of rheumatoid arthritis patients and induces the expression of pro-inflammatory cytokines

OBJECTIVES

To investigate the expression and function of triggering receptor expressed on myeloid cells-1 (TREM-1) in the synovium of human RA patients as well as the level of soluble TREM-1 in the plasma of RA patients.

METHODS

Twenty-four RA synovial samples were analysed by gene expression oligonucleotide microarrays. Expression levels of TREM-1 mRNA in murine CIA paws were determined by quantitative PCR (qPCR). TREM-1 protein expression was detected by immunohistochemistry in five RA synovial samples and two OA synovial samples. TREM-1-positive cells from five RA synovial tissues were analysed by FACS staining to determine the cell type. Activation of TREM-1 was tested in five RA synovial samples. Soluble TREM-1 was measured in serum from 32 RA patients.

RESULTS

The expression of TREM-1 mRNA was found to increase 6.5-fold in RA synovial samples, whereas it was increased 132-fold in CIA paws. Increased numbers of TREM-1-positive cells were seen in RA synovium sections and these cells co-expressed CD14. Using a TREM-1-activating cross-linking antibody in RA synovial cultures, multiple pro-inflammatory cytokines were induced. The average amount of soluble TREM-1 in plasma from RA patients was found to be higher than that in plasma from healthy volunteers.

CONCLUSIONS

These findings suggest that the presence of high levels of functionally active TREM-1 in RA synovium may contribute to the development or maintenance of RA, or both. Inhibiting TREM-1 activity may, therefore, have a therapeutic effect on RA. High levels of soluble TREM-1 in the plasma of RA patients compared with healthy volunteers may indicate disease activity.

Correlation of serum-soluble triggering receptor expressed on myeloid cells-1 with clinical disease activity in inflammatory bowel disease

Although triggering receptor expressed on myeloid cells-1 (TREM-1) has recently been shown to be upregulated in the intestines of patients with inflammatory bowel disease (IBD), it remains unclear whether serum-soluble TREM-1 (sTREM-1) level reflects disease activity in patients with IBD. This study aimed to evaluate the correlation of sTREM-1 level with disease activity in IBD. We prospectively enrolled consecutive patients with IBD and assessed their clinical disease activity using the guidelines of the American College of Gastroenterology. At the time that disease activity was assessed, sTREM-1 level (using an enzyme-linked immunosorbent assay method) and other laboratory findings including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were also measured. A total of 31 patients with ulcerative colitis (UC) and 22 with Crohn's disease (CD) were enrolled. The mean sTREM-1 level in patients with either UC (60.4 +/- 41.8 pg/ml) or CD (66.5 +/- 42.4 pg/ml) was significantly higher than in healthy controls (0.6 +/- 1.4 pg/ml) (P = 0.003 and P = 0.002, respectively). In patients with UC, sTREM-1 level was more highly correlated with disease activity (r = 0.849) than was ESR (r = 0.619) or CRP level (r = 0.546). Moreover, sTREM-1 level correlated well with disease activity irrespective of disease extent. In patients with CD, sTREM-1 level was lower in those with remission compared with those without (46.8 +/- 35.3 pg/ml versus 77.8 +/- 43.1 pg/ml), but this trend did not reach statistical significance (P = 0.100). The results of our study suggest that sTREM-1 could be a potential marker for disease activity in IBD patients, especially those with UC.

TREM and TREM-like receptors in inflammation and disease

Since the discovery of triggering receptor expressed on myeloid cells (TREM)-1 in 2000, evidence documenting the profound ability of the TREM and TREM-like receptors to regulate inflammation has rapidly accumulated. Monocytes, macrophages, myeloid dendritic cells, plasmacytoid dendritic cells, neutrophils, microglia, osteoclasts, and platelets all express at least one member of the TREM family, underscoring the importance of these proteins in the regulation of innate resistance. Recent work on the TREM family includes: characterization of a new receptor expressed on plasmacytoid dendritic cells; definition of a key role for TREM in inflammatory bowel disease and multiple sclerosis; an expanded list of diseases associated with the release of soluble forms of TREM proteins; and identification of the first well characterized TREM ligand: B7-H3, a ligand for TREM-like Transcript (TLT)-2. Moreover, analysis of TREM signaling has now identified key regulatory components and defined pathways that may be responsible for the complex functional interactions between the TREM and toll-like receptors. In addition, there is expanding evidence of a role for TREM in the regulation of integrin function via Plexin-A1. Together these new findings define the TREM and TREM-like receptors as pluripotent modifiers of disease through the integration of inflammatory signals with those associated with leukocyte adhesion.

Soluble triggering receptor expressed on myeloid cells 1 is released in patients with stable chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is increasingly recognized as a systemic disease that is associated with increased serum levels of markers of systemic inflammation. The triggering receptor expressed on myeloid cells 1 (TREM-1) is a recently identified activating receptor on neutrophils, monocytes, and macrophage subsets. TREM-1 expression is upregulated by microbial products such as the toll-like receptor ligand lipoteichoic acid of Gram-positive or lipopolysaccharides of Gram-negative bacteria. In the present study, sera from 12 COPD patients (GOLD stages I-IV, FEV1 51 +/- 6%) and 10 healthy individuals were retrospectively analyzed for soluble TREM-1 (sTREM-1) using a newly developed ELISA. In healthy subjects, sTREM-1 levels were low (median 0.25 ng/mL, range 0-5.9 ng/mL). In contrast, levels of sTREM-1 in sera of COPD patients were significantly increased (median 11.68 ng/mL, range 6.2-41.9 ng/mL, P<.05). Furthermore, serum levels of sTREM-1 showed a significant negative correlation with lung function impairment. In summary, serum concentrations of sTREM-1 are increased in patients with COPD. Prospective studies are warranted to evaluate the relevance of sTREM-1 as a potential marker of the disease in patients with COPD.

Evidence for the role of gastric mucosa at the secretion of soluble triggering receptor expressed on myeloid cells (strem-1) in peptic ulcer disease

AIM: To investigate the role of gastric mucosa at the secretion of sTREM-1 in peptic ulcer.

METHODS: Seventy two patients were enrolled; 35 with duodenal, 21 with gastric ulcer and 16 with chronic gastritis. Patients were endoscoped and gastric juice was aspirated. Patients with duodenal and gastric ulcer underwent a second endoscopy post-treatment. Biopsies were incubated in the absence/presence of endotoxins or gastric juice. Supernatants were collected and sTREM-1 and TNFα were measured by enzyme immunoabsorbent assays. Scoring of gastritis was performed before and after treatment according to updated Sydney score.

RESULTS: Patients with duodenal and gastric ulcer and those with chronic gastritis had similar scores of gastritis. sTREM-1 was higher in supernatants of tissue samples of H pylori-positive than of H pylori-negative patients with gastric ulcer. Median (± SE) sTREM-1 was found increased in supernatants of patients with gastric ulcer before treatment (203.21 ± 88.91 pg/1000 cells) compared to supernatants either from the same patients post-treatment (8.23 ± 5.79 pg/1000 cells) or from patients with chronic gastritis (6.21 ± 0.71 pg/1000 cells) (P < 0.001 and < 0.001, respectively). Similar differences for sTREM-1 were recorded among LPS-stimulated tissue samples of patients (P = 0.001). Similar differences were not found for TNFα. Positive correlations were found between sTREM-1 of supernatants from patients with both duodenal and gastric ulcer before treatment and the degree of infiltration of neutrophils and monocytes.

CONCLUSION: sTREM-1 secreted by the gastric mucosa is an independent mechanism connected to the pathogenesis of peptic ulcer. sTREM-1 was released at the presence of H pylori from the inflamed gastric mucosa in the field of gastric ulcer.

Metalloproteinases Shed TREM-1 Ectodomain from Lipopolysaccharide-Stimulated Human Monocytes

Triggering receptors expressed on myeloid cell (TREM) proteins are a family of cell surface receptors that participate in diverse cellular processes such as inflammation, coagulation, and bone homeostasis. TREM-1, in particular, is expressed on neutrophils and monocytes and is a potent amplifier of inflammatory responses. LPS and other microbial products induce up-regulation of cell surface-localized TREM-1 and the release of its soluble form, sTREM-1. Two hypotheses have been advanced to explain the origin of sTREM-1: alternative splicing of TREM-1 mRNA and proteolytic cleavage(s) of mature, membrane-anchored TREM-1. In this report, we present conclusive evidence in favor of the proteolytic mechanism of sTREM-1 generation. No alternative splicing forms of TREM-1 were detected in monocytes/macrophages. Besides, metalloproteinase inhibitors increased the stability of TREM-1 at the cell surface while significantly reducing sTREM-1 release in cultures of LPS-challenged human monocytes and neutrophils. We conclude that metalloproteinases are responsible for shedding of the TREM-1 ectodomain through proteolytic cleavage of its long juxtamembrane linker.

Can soluble triggering receptor expressed on myeloid cells (sTREM-1) be considered an anti-inflammatory mediator in the pathogenesis of peptic ulcer disease?

Soluble triggering receptor expressed on myeloid cells (sTREM-1) is a novel mediator involved in the pathogenesis of peptic ulcer disease. To investigate the potential role of sTREM-1 in the anti-inflammatory response in chronic gastritis, sTREM-1 was compared with other anti-inflammatory mediators of gastritis. Forty patients with dyspepsia were enrolled: 20 with peptic ulcer and 20 controls without any macroscopic abnormalities. All patients were examined by endoscopy; gastric juice was aspirated and biopsy specimens were collected from the antrum and corpus of the stomach. sTREM-1, interleukin (IL)-8, and IL-10 were estimated by enzyme immunoassays. Median sTREM-1 in patient controls and in patients with peptic ulcer disease was 3.91 and 44.27 pg/ml, respectively (P=0.006). Respective values of IL-8 were 1856.97 and 2030.66 pg/ml (P=0.023); those of IL-10 were 16.92 and 18.43 pg/ml (NS). The odds ratio for the presence of peptic ulcer in the event of a concentration of sTREM-1 higher than 15 pg/ml was 23.22 (95% CI, 2.58-208.62; P=0.002). A positive correlation was found between the ratios of IL-8/sTREM-1 and IL-8/IL-10 (r (s), + 0.365; P=0.021). In conclusion, sTREM-1 is an independent factor for the generation of peptic ulcer disease and might behave as an anti-inflammatory mediator in chronic gastritis.

The early second hit in trauma management augments the proinflammatory immune response to multiple injuries

BACKGROUND

Today's management of patients with multiple injuries remains controversial with regard to damage control and the appropriate timing of operative treatment ("second hit"). Among the multitude of physiologic parameters critical to the immune defense and clinical course of recovery, recent research has proven the regulation of distinct pro- and anti-inflammatory mediators to be closely associated with posttraumatic outcome and complications, including systemic inflammatory response syndrome (SIRS) and sepsis. This study sought to investigate the significance of multiple injuries and consecutive operative treatment ("second hit") with regard to the early inflammatory profile and its importance within the host's immune function.

METHODS

Peripheral whole blood was obtained from 32 patients with multiple injuries (injury severity score [ISS] >20) and 14 healthy control subjects on the day of injury (day 0) and 24 hours thereafter (day 1). Trauma patients were divided into two groups (trauma versus trauma + immediate operation ["second hit"]). Whole blood was centrifuged at 400 g at room temperature for subsequent plasma collection and analyses of Interleukin-6 (IL-6), IL-10 and soluble triggering receptor expressed on myeloid cells (sTREM)-1 plasma concentrations by enzyme-linked immunosorbent assay, respectively.

RESULTS

IL-6 plasma levels from second hit trauma patients (n = 18, ISS 35.5 +/- 12.2) significantly exceeded values determined in both trauma patients without a second hit (n = 14, ISS 30.5 +/- 5.3) and healthy control subjects (n = 14) by posttrauma day 1 (p < 0.05). IL-10 plasma concentrations on day 1 were equally and significantly elevated in both trauma patient populations, when compared with control samples (p < 0.05). In contrast, sTREM-1 was exclusively increased in trauma patients with a second hit, suggesting a strong proinflammatory response in patients with multiple injuries challenged with immediate surgical care (p < 0.05).

CONCLUSION

Immediate surgical treatment of patients with multiple injuries augments the proinflammatory immune response in the early phase of recovery as determined by increased IL-6 and sTREM-1 plasma levels. If not required solely for damage control, the early second hit from additional surgical stress might promote posttraumatic complications by surcharging the innate immune response to injury.

TREM-1 ligand expression on platelets enhances neutrophil activation

The triggering receptor expressed on myeloid cells 1 (TREM-1) plays an important role in the innate immune response related to severe infections and sepsis. Modulation of TREM-1-associated activation improves the outcome in rodent models for pneumonia and sepsis. However, the identity and occurrence of the natural TREM-1 ligands are so far unknown, impairing the further understanding of the biology of this receptor. Here, we report the presence of a ligand for TREM-1 on human platelets. Using a recombinant TREM-1 fusion protein, we demonstrate specific binding of TREM-1 to platelets. TREM-1-specific signals are required for the platelet-induced augmentation of polymorphonuclear leukocyte (PMN) effector functions (provoked by LPS). However, TREM-1 interaction with its ligand is not required for platelet/PMN complex formation, which is dependent on integrins and selectins. Taken together, the results indicate that the TREM-1 ligand is expressed by platelets, and the TREM-1/ligand interaction contributes to the amplification of LPS-induced PMN activation. Our results shed new light on our understanding of TREM-1 and its role in the innate inflammatory response in infections and might contribute to the development of future concepts to treat sepsis.

Stress molecules in sepsis and systemic inflammatory response syndrome

During sepsis, microbial derived products ("pathogen-associated molecular patterns", PAMPs) are recognized as exogenous danger signals by specific sensors of the host ("pattern recognitions receptors", PRRs). This interaction leads to the release of numerous stress proteins that are a prerequisite to fight infection, though their overzealous production can contribute to tissue damage, organ dysfunction and eventually death. In critically ill patients, translocation of PAMPs can occur from the gut, and injured tissues and cells release endogenous danger signals called "alarmins" (e.g. High mobility group box-1); that share some properties with PAMPs. Thus, numerous similarities occur during infectious and non-infectious systemic inflammation.

The TREM receptor family and signal integration

TREM proteins are a family of cell surface receptors that participate in diverse cell processes, including inflammation, bone homeostasis, neurological development and coagulation. TREM-1, the first to be identified, acts to amplify inflammation. Other TREM proteins regulate the differentiation and function of macrophages, microglia, dendritic cells, osteoclasts and platelets. Here we discuss the state of the field, putative ligands of TREM proteins and the challenges that remain in understanding TREM biology.

Role of soluble triggering receptor expressed on myeloid cells in inflammatory bowel disease

AIM: To investigate the probable role of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) in the pathogenesis of inflammatory bowel disease (IBD).

METHODS: Fifty-eight patients were enrolled; nineteen healthy volunteers served as controls; 8 patients were diagnosed with Crohn’s disease, and 31 with ulcerative colitis. Clinical and endoscopic activity indexes of patients with Crohn’s disease and ulcerative colitis respectively were estimated. Upon admission blood was sampled; sTREM-1 and TNFα were measured by an immunoassay and malondialdehyde (MDA) by the thiobarbiturate assay, after passage through an HPLC system.

RESULTS: Median ± SE of TNFα of controls, patients with Crohn’s disease and patients with ulcerative colitis were 6.02 ± 3.94, 7.98 ± 5.08 (P = NS vs controls), and 8.45 ± 4.15 ng/L (P = 0.018 vs controls) respectively. Respective values of sTREM-1 were 53.31 ± 32.93, 735.10 ± 197.17 (P = 0.008 vs controls) and 435.82 ± 279.71 ng/L (P = 0.049 vs controls). sTREM-1 was positively correlated with Crohn’s disease activity index and clinical and endoscopic activity indexes of ulcerative colitis (P = 0.002, 0.001 and 0.009, respectively). sTREM-1 of patients with ulcerative colitis was positively correlated with TNFα (P = 0.001).

CONCLUSION: sTREM-1 seems to behave as a novel mediator in IBD in correlation with the degree of the inflammatory reaction of the intestinal mucosa.