SARS-CoV-2-derived peptides define heterologous and COVID-19-induced T cell recognition.

T cell immunity is central for the control of viral infections. To characterize T cell immunity, but also for the development of vaccines, identification of exact viral T cell epitopes is fundamental. Here we identify and characterize multiple dominant and subdominant SARS-CoV-2 HLA class I and HLA-DR peptides as potential T cell epitopes in COVID-19 convalescent and unexposed individuals. SARS-CoV-2-specific peptides enabled detection of post-infectious T cell immunity, even in seronegative convalescent individuals. Cross-reactive SARS-CoV-2 peptides revealed pre-existing T cell responses in 81% of unexposed individuals and validated similarity with common cold coronaviruses, providing a functional basis for heterologous immunity in SARS-CoV-2 infection. Diversity of SARS-CoV-2 T cell responses was associated with mild symptoms of COVID-19, providing evidence that immunity requires recognition of multiple epitopes. Together, the proposed SARS-CoV-2 T cell epitopes enable identification of heterologous and post-infectious T cell immunity and facilitate development of diagnostic, preventive and therapeutic measures for COVID-19.

Sema7A is crucial for resolution of severe inflammation.

Endogenous mediators regulating acute inflammatory responses in both the induction and resolution phases of inflammatory processes are pivotal in host defense and tissue homeostasis. Recent studies have identified neuronal guidance proteins characterized in axonal development that display immunomodulatory functions. Here, we identify the neuroimmune guidance cue Semaphorin 7A (Sema7A), which appears to link macrophage (MΦ) metabolic remodeling to inflammation resolution. Sema7A orchestrated MΦ chemotaxis and chemokinesis, activated MΦ differentiation and polarization toward the proresolving M2 phenotype, and promoted leukocyte clearance. Peritoneal MΦSema7A-/- displayed metabolic reprogramming, characterized by reductions in fatty acid oxidation and oxidative phosphorylation, increases in glycolysis and the pentose phosphate pathway, and truncation of the tricarboxylic acid cycle, which resulted in increased levels of the intermediates succinate and fumarate. The low accumulation of citrate in MΦSema7A-/- correlated with the decreased synthesis of prostaglandins, leading to a reduced impact on lipid-mediator class switching and the generation of specialized pro resolving lipid mediators. Signaling network analysis indicated that Sema7A induced the metabolic reprogramming of MΦ by activating the mTOR- and AKT2-signaling pathways. Administration of Sema7ASL4cd orchestrated the resolution response to tissue homeostasis by shortening the resolution interval, promoting tissue protection in murine peritonitis, and enhancing survival in polymicrobial sepsis.

Hepatic inflammation elicits production of proinflammatory netrin-1 through exclusive activation of translation.

BACKGROUND AND AIMS: Netrin-1 displays protumoral properties, though the pathological contexts and processes involved in its induction remain understudied. The liver is a major model of inflammation-associated cancer development, leading to HCC. APPROACH AND RESULTS: A panel of cell biology and biochemistry approaches (reverse transcription quantitative polymerase chain reaction, reporter assays, run-on, polysome fractionation, cross linking immunoprecipitation, filter binding assay, subcellular fractionation, western blotting, immunoprecipitation, stable isotope labeling by amino acids in cell culture) on in vitro-grown primary hepatocytes, human liver cell lines, mouse samples and clinical samples was used. We identify netrin-1 as a hepatic inflammation-inducible factor and decipher its mode of activation through an exhaustive eliminative approach. We show that netrin-1 up-regulation relies on a hitherto unknown mode of induction, namely its exclusive translational activation. This process includes the transfer of NTN1 (netrin-1) mRNA to the endoplasmic reticulum and the direct interaction between the Staufen-1 protein and this transcript as well as netrin-1 mobilization from its cell-bound form. Finally, we explore the impact of a phase 2 clinical trial-tested humanized anti-netrin-1 antibody (NP137) in two distinct, toll-like receptor (TLR) 2/TLR3/TLR6-dependent, hepatic inflammatory mouse settings. We observe a clear anti-inflammatory activity indicating the proinflammatory impact of netrin-1 on several chemokines and Ly6C+ macrophages. CONCLUSIONS: These results identify netrin-1 as an inflammation-inducible factor in the liver through an atypical mechanism as well as its contribution to hepatic inflammation.

Membrane oxygenator longevity was higher in argatroban-treated patients undergoing vvECMO.

BACKGROUND: In severe acute respiratory distress syndrome (ARDS), venovenous extracorporeal membrane oxygenation (vvECMO) can be a lifesaver. However, anticoagulation therapy is mandatory because the nonendothelial extracorporeal surface increases the risk of thromboembolic problems. Heparin is still the most common anticoagulant, but argatroban could be an alternative. This work investigates whether argatroban offers a therapeutic advantage over heparin during vvECMO. METHODS: We performed a retrospective cohort study of patients who underwent vvECMO for severe ARDS and received heparin or argatroban as anticoagulation therapy. Demographic variables, intensive care unit (ICU) treatment and outcome parameters were evaluated. The primary outcome parameter was the operating time of the membrane oxygenator normalized to the duration of vvECMO treatment. Secondary outcome parameters were transfusion requirements normalized to the duration of vvECMO therapy. RESULTS: Fifty seven patients from January 2019 to February 2021 underwent vvECMO and were included in this study. Thirty three patients received heparin and 24 patients argatroban as anticoagulatory therapy. The groups did not differ in demographics, ICU scoring systems, or comorbidities. Platelet counts and partial prothrombin time did not differ between the two groups during the first 6 days of vvECMO. The argatroban group had lower requirements for red blood cells, platelets and fresh frozen plasma. The mean runtime of the individual membrane oxygenator increased from 12.3 days (heparin group) to 16.6 days in the argatroban group. CONCLUSIONS: Our findings suggest that argatroban can be considered as anticoagulant during vvECMO.

Early vvECMO implantation may be associated with lower mortality in ARDS.

BACKGROUND: Venovenous extracorporeal membrane oxygenation (vvECMO) is used to treat hypoxia in patients with severe acute respiratory distress syndrome (ARDS). Nevertheless, uncertainty exists regarding the optimal timing of initiation of vvECMO therapy. We aimed to investigate the association between number of days of invasive mechanical ventilation (IMV) prior to vvECMO implantation and mortality. METHODS: In this retrospective observational study, we included patients treated at an academic intensive care unit with vvECMO for severe ARDS. The primary outcome was all-cause 28-day mortality. We conducted a multivariate logistic regression analysis to estimate the association between number of days of IMV prior to vvECMO implantation and mortality after adjustment for confounders. RESULTS: Out of 274 patients who underwent ECMO for severe ARDS, 158 patients (median age: 58 years) with relevant data were included in the analysis. The mean duration of IMV prior to vvECMO was significantly shorter in survivors than in nonsurvivors [survivors median: 1; interquartile range: 1-3; non-survivors median 4; interquartile range: 1-5.75; p = 0.0001). Logistic regression showed an association between the duration of ventilation prior to vvECMO and patient mortality. The odds ratio for the all-cause 28-day mortality and in-hospital mortality was significantly reduced in patients who received vvECMO within the first 5 days of IMV. CONCLUSIONS: Early vvECMO implantation may be associated with lower mortality in ARDS.

Inhaled prostacyclin therapy in the acute respiratory distress syndrome: a randomized controlled multicenter trial.

BACKGROUND: Acute respiratory distress syndrome (ARDS) results in significant hypoxia, and ARDS is the central pathology of COVID-19. Inhaled prostacyclin has been proposed as a therapy for ARDS, but data regarding its role in this syndrome are unavailable. Therefore, we investigated whether inhaled prostacyclin would affect the oxygenation and survival of patients suffering from ARDS. METHODS: We performed a prospective randomized controlled single-blind multicenter trial across Germany. The trial was conducted from March 2019 with final follow-up on 12th of August 2021. Patients with moderate to severe ARDS were included and randomized to receive either inhaled prostacyclin (3 times/day for 5 days) or sodium chloride (Placebo). The primary outcome was the oxygenation index in the intervention and control groups on Day 5 of therapy. Secondary outcomes were mortality, secondary organ failure, disease severity and adverse events. RESULTS: Of 707 patients approached 150 patients were randomized to receive inhaled prostacyclin (n = 73) or sodium chloride (n = 77). Data from 144 patients were analyzed. The baseline PaO2/FiO2 ratio did not differ between groups. The primary analysis of the study was negative, and prostacyclin improved oxygenation by 20 mmHg more than Placebo (p = 0.17). Secondary analysis showed that the oxygenation was significantly improved in patients with ARDS who were COVID-19-positive (34 mmHg, p = 0.04). Mortality did not differ between groups. Secondary organ failure and adverse events were similar in the intervention and control groups. CONCLUSIONS: The primary result of our study was negative. Our data suggest that inhaled prostacyclin might be beneficial treatment in patients with COVID-19 induced ARDS. TRIAL REGISTRATION: The study was approved by the Institutional Review Board of the Research Ethics Committee of the University of Tübingen (899/2018AMG1) and the corresponding ethical review boards of all participating centers. The trial was also approved by the Federal Institute for Drugs and Medical Devices (BfArM, EudraCT No. 2016003168-37) and registered at clinicaltrials.gov (NCT03111212) on April 6th 2017.

COVID-19 does not influence functional status after ARDS therapy.

RATIONALE: Health-related quality of life after surviving acute respiratory distress syndrome has come into focus in recent years, especially during the coronavirus disease 2019 pandemic. OBJECTIVES: A total of 144 patients with acute respiratory distress syndrome caused by COVID-19 or of other origin were recruited in a randomized multicenter trial. METHODS: Clinical data during intensive care treatment and data up to 180 days after study inclusion were collected. Changes in the Sequential Organ Failure Assessment score were used to quantify disease severity. Disability was assessed using the Barthel index on days 1, 28, 90, and 180. MEASUREMENTS: Mortality rate and morbidity after 180 days were compared between patients with and without COVID-19. Independent risk factors associated with high disability were identified using a binary logistic regression. MAIN RESULTS: The SOFA score at day 5 was an independent risk factor for high disability in both groups, and score dynamic within the first 5 days significantly impacted disability in the non-COVID group. Mortality after 180 days and impairment measured by the Barthel index did not differ between patients with and without COVID-19. CONCLUSIONS: Resolution of organ dysfunction within the first 5 days significantly impacts long-term morbidity. Acute respiratory distress syndrome caused by COVID-19 was not associated with increased mortality or morbidity.

Hypoxia-Inducible Factor 1 Alpha-Mediated RelB/APOBEC3B Down-regulation Allows Hepatitis B Virus Persistence.

BACKGROUND AND AIMS: Therapeutic strategies against HBV focus, among others, on the activation of the immune system to enable the infected host to eliminate HBV. Hypoxia-inducible factor 1 alpha (HIF1α) stabilization has been associated with impaired immune responses. HBV pathogenesis triggers chronic hepatitis-related scaring, leading inter alia to modulation of liver oxygenation and transient immune activation, both factors playing a role in HIF1α stabilization. APPROACH AND RESULTS: We addressed whether HIF1α interferes with immune-mediated induction of the cytidine deaminase, apolipoprotein B mRNA editing enzyme catalytic subunit 3B (APOBEC3B; A3B), and subsequent covalently closed circular DNA (cccDNA) decay. Liver biopsies of chronic HBV (CHB) patients were analyzed by immunohistochemistry and in situ hybridization. The effect of HIF1α induction/stabilization on differentiated HepaRG or mice ± HBV ± LTßR-agonist (BS1) was assessed in vitro and in vivo. Induction of A3B and subsequent effects were analyzed by RT-qPCR, immunoblotting, chromatin immunoprecipitation, immunocytochemistry, and mass spectrometry. Analyzing CHB highlighted that areas with high HIF1α levels and low A3B expression correlated with high HBcAg, potentially representing a reservoir for HBV survival in immune-active patients. In vitro, HIF1α stabilization strongly impaired A3B expression and anti-HBV effect. Interestingly, HIF1α knockdown was sufficient to rescue the inhibition of A3B up-regulation and -mediated antiviral effects, whereas HIF2α knockdown had no effect. HIF1α stabilization decreased the level of v-rel reticuloendotheliosis viral oncogene homolog B protein, but not its mRNA, which was confirmed in vivo. Noteworthy, this function of HIF1α was independent of its partner, aryl hydrocarbon receptor nuclear translocator. CONCLUSIONS: In conclusion, inhibiting HIF1α expression or stabilization represents an anti-HBV strategy in the context of immune-mediated A3B induction. High HIF1α, mediated by hypoxia or inflammation, offers a reservoir for HBV survival in vivo and should be considered as a restricting factor in the development of immune therapies.

Inhibition of Δ24-dehydrocholesterol reductase activates pro-resolving lipid mediator biosynthesis and inflammation resolution.

Targeting metabolism through bioactive key metabolites is an upcoming future therapeutic strategy. We questioned how modifying intracellular lipid metabolism could be a possible means for alleviating inflammation. Using a recently developed chemical probe (SH42), we inhibited distal cholesterol biosynthesis through selective inhibition of Δ24-dehydrocholesterol reductase (DHCR24). Inhibition of DHCR24 led to an antiinflammatory/proresolving phenotype in a murine peritonitis model. Subsequently, we investigated several omics layers in order to link our phenotypic observations with key metabolic alterations. Lipidomic analysis revealed a significant increase in endogenous polyunsaturated fatty acid (PUFA) biosynthesis. These data integrated with gene expression analysis, revealing increased expression of the desaturase Fads6 and the key proresolving enzyme Alox-12/15 Protein array analysis, as well as immune cell phenotype and functional analysis, substantiated these results confirming the antiinflammatory/proresolving phenotype. Ultimately, lipid mediator (LM) analysis revealed the increased production of bioactive lipids, channeling the observed metabolic alterations into a key class of metabolites known for their capacity to change the inflammatory phenotype.

Neuronal guidance proteins in cardiovascular inflammation.

Cardiovascular pathologies are often induced by inflammation. The associated changes in the inflammatory response influence vascular endothelial biology; they complicate the extent of ischaemia and reperfusion injury, direct the migration of immune competent cells and activate platelets. The initiation and progression of inflammation is regulated by the classical paradigm through the system of cytokines and chemokines. Therapeutic approaches have previously used this knowledge to control the extent of cardiovascular changes with varying degrees of success. Neuronal guidance proteins (NGPs) have emerged in recent years and have been shown to be significantly involved in the control of tissue inflammation and the mechanisms of immune cell activation. Therefore, proteins of this class might be used in the future as targets to control the extent of inflammation in the cardiovascular system. In this review, we describe the role of NGPs during cardiovascular inflammation and highlight potential therapeutic options that could be explored in the future.

Hypoxia-inducible factor-dependent induction of netrin-1 dampens inflammation caused by hypoxia.

The neuronal guidance molecule netrin-1 is linked to the coordination of inflammatory responses. Given that mucosal surfaces are particularly prone to hypoxia-elicited inflammation, we sought to determine the function of netrin-1 in hypoxia-induced inflammation. We detected hypoxia-inducible factor 1alpha (HIF-1alpha)-dependent induction of expression of the gene encoding netrin-1 (Ntn1) in hypoxic epithelia. Neutrophil transepithelial migration studies showed that by engaging A2B adenosine receptor (A2BAR) on neutrophils, netrin-1 attenuated neutrophil transmigration. Exogenous netrin-1 suppressed hypoxia-elicited inflammation in wild-type but not in A2BAR-deficient mice, and inflammatory hypoxia was enhanced in Ntn1(+/-) mice relative to that in Ntn1(+/+) mice. Our studies demonstrate that HIF-1alpha-dependent induction of netrin-1 attenuates hypoxia-elicited inflammation at mucosal surfaces.

Machine learning identifies ICU outcome predictors in a multicenter COVID-19 cohort.

BACKGROUND: Intensive Care Resources are heavily utilized during the COVID-19 pandemic. However, risk stratification and prediction of SARS-CoV-2 patient clinical outcomes upon ICU admission remain inadequate. This study aimed to develop a machine learning model, based on retrospective & prospective clinical data, to stratify patient risk and predict ICU survival and outcomes. METHODS: A Germany-wide electronic registry was established to pseudonymously collect admission, therapeutic and discharge information of SARS-CoV-2 ICU patients retrospectively and prospectively. Machine learning approaches were evaluated for the accuracy and interpretability of predictions. The Explainable Boosting Machine approach was selected as the most suitable method. Individual, non-linear shape functions for predictive parameters and parameter interactions are reported. RESULTS: 1039 patients were included in the Explainable Boosting Machine model, 596 patients retrospectively collected, and 443 patients prospectively collected. The model for prediction of general ICU outcome was shown to be more reliable to predict "survival". Age, inflammatory and thrombotic activity, and severity of ARDS at ICU admission were shown to be predictive of ICU survival. Patients' age, pulmonary dysfunction and transfer from an external institution were predictors for ECMO therapy. The interaction of patient age with D-dimer levels on admission and creatinine levels with SOFA score without GCS were predictors for renal replacement therapy. CONCLUSIONS: Using Explainable Boosting Machine analysis, we confirmed and weighed previously reported and identified novel predictors for outcome in critically ill COVID-19 patients. Using this strategy, predictive modeling of COVID-19 ICU patient outcomes can be performed overcoming the limitations of linear regression models. Trial registration "ClinicalTrials" (clinicaltrials.gov) under NCT04455451.

Mesenchymal Stem Cell Therapy for Severe COVID-19 ARDS.

BACKGROUND: The COVID-19 pandemic reached Germany in spring 2020. No proven treatment for SARS-CoV-2 was available at that time, especially for severe COVID-19-induced ARDS. We determined whether the infusion of mesenchymal stromal cells (MSCs) would help to improve pulmonary function and overall outcome in patients with severe COVID-19 ARDS. We offered MSC infusion as an extended indication to all critically ill COVID-19 patients with a Horovitz index <100. We treated 5 out of 23 patients with severe COVID-19 ARDS with an infusion of MSCs. One million MSCs/kg body weight was infused over 30 minutes, and the process was repeated in 3 patients twice and in 2 patients 3 times. RESULT: Four out of 5 MSC-treated patients compared to 50% of control patients (9 out of 18) received ECMO support (80%). The MSC group showed a higher Murray score on admission than control patients, reflecting more severe pulmonary compromise (3.5 ± 0.2 versus 2.8 ± 0.3). MSC infusion was safe and well tolerated. The MSC group had a significantly higher Horovitz score on discharge than the control group. Compared to controls, patients with MSC treatment showed a significantly lower Murray score upon discharge than controls. In the MSC group, 4 out of 5 patients (80%) survived to discharge and exhibited good pulmonary function, whereas only 8 out of 18 patients (45%) in the control group survived to discharge. CONCLUSION: MSC infusion is a safe treatment for COVID-19 ARDS that improves pulmonary function and overall outcome in this patient population.

Immunomodulatory Functions of Neuronal Guidance Proteins.

Neuronal guidance proteins (NGPs) were originally identified for their role during the embryonic development of the nervous system. Recent years have seen the discovery of NGP functions during immune responses. In this context, NGPs were demonstrated to control leukocyte migration and the release of cytokines during conditions of acute inflammation, such as lung injury or sepsis. However, NGPs also display potent actions in the resolution of inflammation, chronic inflammatory conditions, the development of atherosclerosis, and during ischemia followed by reperfusion. Here, we provide an overview of the current state of knowledge about the role of NGPs in the immune system and describe their immunomodulatory function.

Targeting CD39 Toward Activated Platelets Reduces Systemic Inflammation and Improves Survival in Sepsis: A Preclinical Pilot Study.

OBJECTIVES: Sepsis is associated with a systemic inflammatory reaction, which can result in a life-endangering organ dysfunction. Pro-inflammatory responses during sepsis are characterized by increased activation of leukocytes and platelets, formation of platelet-neutrophil aggregates, and cytokine production. Sequestration of platelet-neutrophil aggregates in the microvasculature contributes to tissue damage during sepsis. At present no effective therapeutic strategy to ameliorate these events is available. In this preclinical pilot study, a novel anti-inflammatory approach was evaluated, which targets nucleoside triphosphate hydrolase activity toward activated platelets via a recombinant fusion protein combining a single-chain antibody against activated glycoprotein IIb/IIIa and the extracellular domain of CD39 (targ-CD39). DESIGN: Experimental animal study and cell culture study. SETTING: University-based experimental laboratory. SUBJECTS: Human dermal microvascular endothelial cells 1, human platelets and neutrophils, and C57BL/6NCrl mice. INTERVENTIONS: Platelet-leukocyte-endothelium interactions were evaluated under inflammatory conditions in vitro and in a murine lipopolysaccharide-induced sepsis model in vivo. The outcome of polymicrobial sepsis was evaluated in a murine cecal ligation and puncture model. To evaluate the anti-inflammatory potential of activated platelet targeted nucleoside triphosphate hydrolase activity, we employed a potato apyrase in vitro and in vivo, as well as targ-CD39 and as a control, nontarg-CD39 in vivo. MEASUREMENTS AND MAIN RESULTS: Under conditions of sepsis, agents with nucleoside triphosphate hydrolase activity decreased platelet-leukocyte-endothelium interaction, transcription of pro-inflammatory cytokines, microvascular platelet-neutrophil aggregate sequestration, activation marker expression on platelets and neutrophils contained in these aggregates, leukocyte extravasation, and organ damage. Targ-CD39 had the strongest effect on these variables and retained hemostasis in contrast to nontarg-CD39 and potato apyrase. Most importantly, targ-CD39 improved survival in the cecal ligation and puncture model to a stronger extent then nontarg-CD39 and potato apyrase. CONCLUSIONS: Targeting nucleoside triphosphate hydrolase activity (CD39) toward activated platelets is a promising new treatment concept to decrease systemic inflammation and mortality of sepsis. This innovative therapeutic approach warrants further development toward clinical application.

The neuroimmune guidance cue netrin-1 controls resolution programs and promotes liver regeneration.

UNLABELLED: Hepatic ischemia/reperfusion (I/R) is a major adverse reaction to liver transplantation, hemorrhagic shock, or resection. Recently, the anti-inflammatory properties of the axonal guidance cue netrin-1 were reported. Here, we demonstrate that netrin-1 also impacts the resolution of inflammation and promotes hepatic repair and regeneration during liver I/R injury. In initial studies, we investigated the induction of netrin-1 and its receptors in murine liver tissues after I/R injury. Hepatic I/R injury was performed in mice with a partial genetic netrin-1 deficiency (Ntn1(+/-) ) or wild-type C57BL/6 treated with exogenous netrin-1 to examine the endogenous and therapeutically administered impact of netrin-1. These investigations were corroborated by studies determining the characteristics of intravascular leukocyte flow, clearance of apoptotic neutrophils (polymorphonuclear cells [PMNs]), production of specialized proresolving lipid mediators (SPMs), generation of specific growth factors contributing to the resolution of inflammation, and liver repair. Hepatic I/R was associated with a significant reduction of netrin-1 transcript and protein in murine liver tissue. Subsequent studies in netrin-1-deficient mice revealed lower efficacies in reducing PMN infiltration, proinflammatory cytokine levels, and hepatic-specific injury enzymes. Conversely, mice treated with exogenous netrin-1 exhibited increased liver protection and repair, reducing neutrophil influx into the injury site, decreasing proinflammatory mediators, increasing efferocytosis of apoptotic PMNs, and stimulating local endogenous biosynthesis of SPMs and the generation of specific growth factors. Finally, genetic studies implicated the A2B adenosine receptor in netrin-1-mediated protection during hepatic I/R injury. CONCLUSION: The present study indicates a previously unrecognized role for netrin-1 in liver protection and its contribution to tissue homeostasis and regeneration.

Inhibition of Plexin C1 Protects Against Hepatic Ischemia-Reperfusion Injury.

OBJECTIVES: Hepatic ischemia-reperfusion injury is a disease pattern that is associated with an acute inflammatory reaction. It is well known that neutrophils play an essential role in the early phase of hepatic ischemia-reperfusion injury and determine the extent of tissue damage. Hepatic ischemia-reperfusion injury can result in organ failure, which is linked to high mortality. Recent data indicate that the neuronal guidance receptor Plexin C1 is involved in the control of the acute inflammatory response and, as such, modulates the transmigration of neutrophils. Hence, we investigated the functional role of Plexin C1 in a mouse model of early hepatic ischemia-reperfusion injury. DESIGN: Animal study. SETTING: University experimental laboratory. SUBJECTS: Wild-type, PLXNC1 and chimeric mice. INTERVENTIONS: Hepatic ischemia-reperfusion injury or sham operation. MEASUREMENTS AND MAIN RESULTS: We found that the functional inhibition of Plexin C1 in wild-type mice treated with an anti-Plexin C1 antibody and a Semaphorin 7A peptide reduced hepatic ischemia-reperfusion injury, as measured by the levels of lactate dehydrogenase, aspartate, and alanine aminotransferase. This reduction in ischemia-reperfusion injury was accompanied by reduced numbers of neutrophils in ischemic hepatic tissue and reduced serum levels of inflammatory cytokines. Experiments using Plexin C1 receptor-deficient (PLXNC1) mice also demonstrated decreased hepatic ischemia-reperfusion injury. Studies of chimeric mice revealed that the hematopoietic Plexin C1 knockout is crucial for reducing the extent of hepatic ischemia-reperfusion injury. CONCLUSIONS: These results describe a role for Plexin C1 during ischemia-reperfusion injury, highlight the role of hematopoietic Plexin C1 in the development of hepatic ischemia-reperfusion injury, and suggest that Plexin C1 is a potential drug target.

Inhaled carbon monoxide accelerates resolution of inflammation via unique proresolving mediator-heme oxygenase-1 circuits.

Resolution of acute inflammation is an active event accompanied by biosynthesis of specialized proresolving mediators (SPM). We employed a systems approach to determine the impact of CO in resolution active programs during self-limited inflammation in mice. Compared with ambient air, inhaled CO gas (250 ppm) significantly limited PMN infiltration (∼44%, 6 h) into peritoneum and shortened resolution interval from 4 to 2 h. We profiled exudate lipid mediators (LM) via metabololipidomics, CO reduced leukotriene B4 (21 ± 11 versus 59 ± 24 pg/mouse, 6 h), and elevated SPM including resolvin (Rv) D1 (27 ± 4 versus 16 ± 5 pg/mouse) and maresin 1 (26 ± 9 versus 15 ± 3 pg/mouse). With human macrophages, SPM (10 pM-10 nM) elevated heme oxygenase (HO)-1 (∼50%, 8 h). CO also enhanced HO-1 expression and accumulation of RvD1 and RvD5, an action reversed by blockage of a key SPM biosynthesis enzyme 15-lipoxygenase type 1. Compared with normoxia, CO increased ∼30% phagocytosis of opsonized zymosan with human macrophage, which was further enhanced by SPM (∼100%). This CO increased phagocytosis was blocked by 15-lipoxygenase inhibition, and SPM stimulated phagocytosis was diminished by HO-1 inhibition. In murine peritonitis, both pre- and posttreatment with CO inhalation significantly increased macrophages carrying ingested apoptotic PMN in exudates and enhanced PMN apoptosis. Taken together, these results indicate that CO accelerates resolution of acute inflammation, shortens resolution intervals, enhances macrophage efferocytosis, and temporally regulates local levels of lipid mediator/SPM. Moreover, they provide proresolving mechanisms for HO-1/CO, which is part of the SPM-initiated resolution circuit.