Chemerin regulates formation and function of brown adipose tissue: Ablation results in increased insulin resistance with high fat challenge and aging.

Apart from its role in inflammation and immunity, chemerin is also involved in white adipocyte biology. To study the role of chemerin in adipocyte metabolism, we examined the function of chemerin in brown adipose tissue. Brown and white adipocyte precursors were differentiated into adipocytes in the presence of Chemerin siRNA. Chemerin-deficient (Chem-/- ) mice were compared to wild-type mice when fed a high-fat diet. Chemerin is expressed during brown adipocyte differentiation and knock down of chemerin mRNA results in decreased brown adipocyte differentiation with reduced fatty acid uptake in brown adipocytes. Chem-/- mice are leaner than wild-type mice but gain more weight when challenged with high-fat diet feeding, resulting in a larger increase in fat deposition. Chem-/- mice develop insulin resistance when on a high-fat diet or due to age. Brown adipose depots in Chem-/- mice weigh more than in wild-type mice, but with decreased mitochondrial content and function. Compared to wild-type mice, male Chem-/- mice have decreased oxygen consumption, CO2 production, energy expenditure, and a lower respiratory exchange ratio. Additionally, body temperature of Chem-/- mice is lower than that of wild-type mice. These results revealed that chemerin is expressed during brown adipocyte differentiation and has a pivotal role in energy metabolism through brown adipose tissue thermogenesis.

Prochemerin cleavage by factor XIa links coagulation and inflammation.

Chemerin is a chemoattractant and adipokine that circulates in blood as inactive prochemerin (chem163S). Chem163S is activated by a series of C-terminal proteolytic cleavages resulting in diverse chemerin forms with different levels of activity. We screened a panel of proteases in the coagulation, fibrinolytic, and inflammatory cascades to identify those that process prochemerin in plasma. Factor XIa (FXIa) cleaved chem163S, generating a novel chemerin form, chem162R, as an intermediate product, and chem158K, as the final product. Processing at Arg162 was not required for cleavage at Lys158 or regulation of chemerin bioactivity. Contact phase activation of human platelet-poor plasma by kaolin led to cleavage of chem163S, which was undetectable in FXI-depleted plasma and markedly enhanced in platelet-rich plasma (PRP). Contact phase activation by polyphosphate in PRP resulted in 75% cleavage of chem163S. This cleavage was partially inhibited by hirudin, which blocks thrombin activation of FXI. After activation of plasma, levels of the most potent form of chemerin, chem157S, as well as inactive chem155A, increased. Plasma levels of chem163S in FXI-deficient patients were significantly higher compared with a matched control group (91 ± 10 ng/mL vs 58 ± 3 ng/mL, n = 8; P < .01) and inversely correlated with the plasma FXI levels. Thus FXIa, generated on contact phase activation, cleaves chem163S to generate chem158K, which can be further processed to the most active chemerin form, providing a molecular link between coagulation and inflammation.

Activated TAFI Promotes the Development of Chronic Thromboembolic Pulmonary Hypertension: A Possible Novel Therapeutic Target.

RATIONALE: Pulmonary hypertension is a fatal disease; however, its pathogenesis still remains to be elucidated. Thrombin-activatable fibrinolysis inhibitor (TAFI) is synthesized by the liver and inhibits fibrinolysis. Plasma TAFI levels are significantly increased in chronic thromboembolic pulmonary hypertension (CTEPH) patients. OBJECTIVE: To determine the role of activated TAFI (TAFIa) in the development of CTEPH. METHODS AND RESULTS: Immunostaining showed that TAFI and its binding partner thrombomodulin (TM) were highly expressed in the pulmonary arteries (PAs) and thrombus in patients with CTEPH. Moreover, plasma levels of TAFIa were increased 10-fold in CTEPH patients compared with controls. In mice, chronic hypoxia caused a 25-fold increase in plasma levels of TAFIa with increased plasma levels of thrombin and TM, which led to thrombus formation in PA, vascular remodeling, and pulmonary hypertension. Consistently, plasma clot lysis time was positively correlated with plasma TAFIa levels in mice. Additionally, overexpression of TAFIa caused organized thrombus with multiple obstruction of PA flow and reduced survival rate under hypoxia in mice. Bone marrow transplantation showed that circulating plasma TAFI from the liver, not in the bone marrow, was activated locally in PA endothelial cells through interactions with thrombin and TM. Mechanistic experiments demonstrated that TAFIa increased PA endothelial permeability, smooth muscle cell proliferation, and monocyte/macrophage activation. Importantly, TAFIa inhibitor and peroxisome proliferator-activated receptor-α agonists significantly reduced TAFIa and ameliorated animal models of pulmonary hypertension in mice and rats. CONCLUSIONS: These results indicate that TAFIa could be a novel biomarker and realistic therapeutic target of CTEPH.

Patterns of expression of factor VIII and von Willebrand factor by endothelial cell subsets in vivo.

UNLABELLED: Circulating factor VIII (FVIII) is derived from liver and from extrahepatic sources probably of endothelial origin, but the vascular sites of FVIII production remain unclear. Among organs profiled, only liver and lymph nodes (LNs) show abundant expression of F8 messenger RNA (mRNA). Transcriptomic profiling of subsets of stromal cells, including endothelial cells (ECs) from mouse LNs and other tissues, showed that F8 mRNA is expressed by lymphatic ECs (LECs) but not by capillary ECs (capECs), fibroblastic reticular cells, or hematopoietic cells. Among blood ECs profiled, F8 expression was seen only in fenestrated ECs (liver sinusoidal and renal glomerular ECs) and some high endothelial venules. In contrast, von Willebrand factor mRNA was expressed in capECs but not in LECs; it was coexpressed with F8 mRNA in postcapillary high endothelial venules. Purified LECs and liver sinusoidal ECs but not capECs from LNs secrete active FVIII in culture, and human and mouse lymph contained substantial FVIII: C activity. Our results revealed localized vascular expression of FVIII and von Willebrand factor and identified LECs as a major cellular source of FVIII in extrahepatic tissues.

Discovery of selective urokinase plasminogen activator (uPA) inhibitors as a potential treatment for multiple sclerosis.

We report here the design and synthesis of a novel series of benzylamines that are potent and selective inhibitors of uPA with promising oral availability in rat. Further evaluation of one representative (ZK824859) of the new structural class showed that this compound lowered clinical scores when dosed in either acute or chronic mouse EAE models, suggesting that uPA inhibitors of this type could be useful for the treatment of multiple sclerosis.

Targeting complement component 5a promotes vascular integrity and limits airway remodeling.

Increased microvascular dilatation and permeability is observed during allograft rejection. Because vascular integrity is an important indicator of transplant health, we have sought to limit injury to blood vessels by blocking complement activation. Although complement component 3 (C3) inhibition is known to be vasculoprotective in transplantation studies, we recently demonstrated the paradoxical finding that, early in rejection, C3(-/-) transplant recipients actually exhibit worse microvascular injury than controls. In the genetic absence of C3, thrombin-mediated complement component 5 (C5) convertase activity leads to the generation of C5a (anaphylatoxin), a promoter of vasodilatation and permeability. In the current study, we demonstrated that microvessel thrombin deposition is significantly increased in C3(-/-) recipients during acute rejection. Thrombin colocalization with microvessels is closely associated with remarkably elevated plasma levels of C5a, vasodilatation, and increased vascular permeability. Administration of NOX-D19, a specific C5a inhibitor, to C3(-/-) recipients of airway transplants significantly improved tissue oxygenation, limited microvascular leakiness, and prevented airway ischemia, even in the absence of conventional T-cell-directed immunosuppression. As C3 inhibitors enter the clinics, the simultaneous targeting of this thrombin-mediated complement activation pathway and/or C5a itself may confer significant clinical benefit.

Thrombin cleavage of osteopontin disrupts a pro-chemotactic sequence for dendritic cells, which is compensated by the release of its pro-chemotactic C-terminal fragment.

Thrombin cleavage alters the function of osteopontin (OPN) by exposing an integrin binding site and releasing a chemotactic C-terminal fragment. Here, we examined thrombin cleavage of OPN in the context of dendritic cell (DC) migration to define its functional domains. Full-length OPN (OPN-FL), thrombin-cleaved N-terminal fragment (OPN-R), thrombin- and carboxypeptidase B2-double-cleaved N-terminal fragment (OPN-L), and C-terminal fragment (OPN-CTF) did not have intrinsic chemotactic activity, but all potentiated CCL21-induced DC migration. OPN-FL possessed the highest potency, whereas OPNRAA-FL had substantially less activity, indicating the importance of RGD. We identified a conserved (168)RSKSKKFRR(176) sequence on OPN-FL that spans the thrombin cleavage site, and it demonstrated potent pro-chemotactic effects on CCL21-induced DC migration. OPN-FLR168A had reduced activity, and the double mutant OPNRAA-FLR168A had even lower activity, indicating that these functional domains accounted for most of the pro-chemotactic activity of OPN-FL. OPN-CTF also possessed substantial pro-chemotactic activity, which was fully expressed upon thrombin cleavage and its release from the intact protein, because OPN-CTF was substantially more active than OPNRAA-FLR168A containing the OPN-CTF sequence within the intact protein. OPN-R and OPN-L possessed similar potency, indicating that the newly exposed C-terminal SVVYGLR sequence in OPN-R was not involved in the pro-chemotactic effect. OPN-FL and OPN-CTF did not directly bind to the CD44 standard form or CD44v6. In conclusion, thrombin cleavage of OPN disrupts a pro-chemotactic sequence in intact OPN, and its loss of pro-chemotactic activity is compensated by the release of OPN-CTF, which assumes a new conformation and possesses substantial activity in enhancing chemokine-induced migration of DCs.

Thrombin-cleaved fragments of osteopontin are overexpressed in malignant glial tumors and provide a molecular niche with survival advantage.

Osteopontin (OPN), which is highly expressed in malignant glioblastoma (GBM), possesses inflammatory activity modulated by proteolytic cleavage by thrombin and plasma carboxypeptidase B2 (CPB2) at a highly conserved cleavage site. Full-length OPN (OPN-FL) was elevated in cerebrospinal fluid (CSF) samples from all cancer patients compared with noncancer patients. However, thrombin-cleaved OPN (OPN-R) and thrombin/CPB2-double-cleaved OPN (OPN-L) levels were markedly increased in GBM and non-GBM gliomas compared with systemic cancer and noncancer patients. Cleaved OPN constituted ∼23 and ∼31% of the total OPN in the GBM and non-GBM CSF samples, respectively. OPN-R was also elevated in GBM tissues. Thrombin-antithrombin levels were highly correlated with cleaved OPN, but not OPN-FL, suggesting that the cleaved OPN fragments resulted from increased thrombin and CPB2 in this extracellular compartment. Levels of VEGF and CCL4 were increased in CSF of GBM and correlated with the levels of cleaved OPN. GBM cell lines were more adherent to OPN-R and OPN-L than OPN-FL. Adhesion to OPN altered gene expression, in particular genes involved with cellular processes, cell cycle regulation, death, and inflammation. OPN and its cleaved forms promoted motility of U-87 MG cells and conferred resistance to apoptosis. Although functional mutation of the RGD motif in OPN largely abolished these functions, OPN(RAA)-R regained significant cell binding and signaling function, suggesting that the SVVYGLR motif in OPN-R may substitute for the RGD motif if the latter becomes inaccessible. OPN cleavage contributes to GBM development by allowing more cells to bind in niches where they acquire anti-apoptotic properties.

Thrombomodulin modulates dendritic cells via both antagonism of high mobility group protein B1 and an independent mechanism.

BACKGROUND: Thrombomodulin treatment modulates the properties of dendritic cells (DCs) converting them from immunogenic to tolerogenic and inducing its own expression on DCs. Thrombomodulin binds to the inflammatory mediator, high mobility group protein B1 (HMGB1), antagonizing signalling through its receptor, receptor for advanced glycation end products (RAGE). METHODS: To test if soluble thrombomodulin could antagonize HMGB1 signaling via RAGE on DCs. DCs were prepared from mouse bone marrow cells or human monocytes. In some experiments dendritic cells were sorted into thrombomodulin+ and thrombomodulin- populations. Expression of surface maturation markers was determined by flow cytometry following treatment with thrombomodulin in the presence or absence of HMGB1. RESULTS: Thrombomodulin+ dendritic cells secrete less HMGB1 into the medium. HMGB1 reduces the effects of thrombomodulin on expression of DC maturation markers. Treatment with thrombomodulin reduces the expression of maturation markers such as CD80 and CD86 and increases the expression of thrombomodulin on the DC surface. Treatment of DCs with neutralizing anti-HMGB1 antibody acted synergistically with thrombomodulin in increasing thrombomodulin expression on DCs. Treatment with thrombomodulin can still reduce the expression of surface markers on DCs derived from mice that are deficient in RAGE showing that thrombomodulin can affect DCs by an alternative mechanism. CONCLUSIONS: The results of this study show that thrombomodulin modulates DCs both by antagonizing the interaction of HMGB1 with RAGE and by an independent mechanism.

Chemerin Levels in Individuals with Type 2 Diabetes and a Normal Weight versus Individuals with Type 2 Diabetes and Obesity: An Observational, Cross-Sectional Study.

Chemerin acts as both a chemotactic agent and an adipokine that undergoes proteolytic cleavage, converting inactive precursors into their active forms before being subsequently inactivated. Elevated chemerin levels are linked to obesity and type 2 diabetes mellitus (T2D). This study aimed to elucidate the effects of T2D and obesity on chemerin levels by comparing plasma samples from individuals with a normal weight and T2D (BMI < 25; NWD group n = 22) with those from individuals who are overweight or obese and have T2D (BMI ≥ 25; OWD group n = 39). The total chemerin levels were similar in the NWD and OWD groups, suggesting that T2D may equalize the chemerin levels irrespective of obesity status. The cleavage of chemerin has been previously linked to myocardial infarction and stroke in NWD, with potential implications for inflammation and mortality. OWD plasma exhibited lower levels of cleaved chemerin than the NWD group, suggesting less inflammation in the OWD group. Here, we showed that the interaction between obesity and T2D leads to an equalization in the total chemerin levels. The cleaved chemerin levels and the associated inflammatory state, however, differ significantly, underscoring the complex relationship between chemerin, T2D, and obesity.

Chemerin in Participants with or without Insulin Resistance and Diabetes.

Chemerin is a chemokine/adipokine, regulating inflammation, adipogenesis and energy metabolism whose activity depends on successive proteolytic cleavages at its C-terminus. Chemerin levels and processing are correlated with insulin resistance. We hypothesized that chemerin processing would be higher in individuals with type 2 diabetes (T2D) and in those who are insulin resistant (IR). This hypothesis was tested by characterizing different chemerin forms by specific ELISA in the plasma of 18 participants with T2D and 116 without T2D who also had their insulin resistance measured by steady-state plasma glucose (SSPG) concentration during an insulin suppression test. This approach enabled us to analyze the association of chemerin levels with a direct measure of insulin resistance (SSPG concentration). Participants were divided into groups based on their degree of insulin resistance using SSPG concentration tertiles: insulin sensitive (IS, SSPG ≤ 91 mg/dL), intermediate IR (IM, SSPG 92-199 mg/dL), and IR (SSPG ≥ 200 mg/dL). Levels of different chemerin forms were highest in patients with T2D, second highest in individuals without T2D who were IR, and lowest in persons without T2D who were IM or IS. In the whole group, chemerin levels positively correlated with both degree of insulin resistance (SSPG concentration) and adiposity (BMI). Participants with T2D and those without T2D who were IR had the most proteolytic processing of chemerin, resulting in higher levels of both cleaved and degraded chemerin. This suggests that increased inflammation in individuals who have T2D or are IR causes more chemerin processing.

Brain Expression of CPB2 and Effects of Cpb2 Deficiency in Mouse Models of Behavior.

BACKGROUND: Procarboxypeptidase B2 (proCPB2 or TAFI) is a zymogen that after activation cleaves C-terminal basic residues from peptides or proteins with many identified targets. A splice variant of CPB2 has been found in the brain lacking essential residues for its carboxypeptidase function. The aim was to determine CPB2 expression in the brain and effects of CPB2 deficiency (Cpb2 -/-) on behavior. MATERIALS AND METHODS: Behavioral effects were tested by comparing Cpb2 -/- mice in short-term (open field and elevated zero maze tests) and long-term (Phenotyper) observations with wild-type (WT) controls. RESULTS: Long-term observation compared day 1 (acclimatizing to novel environment) to day 4 (fully acclimatized) with the inactive (day) and active (night) periods analyzed separately. Brain expression of CPB2 mRNA and protein was interrogated in publicly available databases. Long-term observation demonstrated differences between WT and Cpb2 -/- mice in several parameters. For example, Cpb2 -/- mice moved more frequently on both days 1 and 4, especially in the normally inactive periods. Cpb2 -/- mice spent more time on the shelter and less time in it. Differences were more pronounced on day 4 after the mice had fully acclimatized. In short-term observations, no differences were observed between Cpb2 -/- mice and WT mice. Brain expression of CBP2 was not detectable in the human protein atlas. Databases of single-cell RNAseq did not show expression of CPB2 mRNA in either human or mouse brain. CONCLUSION: Continuous observation of home-cage behavior suggests that Cpb2 -/- mice are more active than WT mice, show different day-night activity levels, and might have a different way of processing information.

Thrombin-activatable fibrinolysis inhibitor protects against acute lung injury by inhibiting the complement system.

Acute lung injury (ALI) is a devastating disease with an overall mortality rate of 30 to 40%. The coagulation/fibrinolysis system is implicated in the pathogenesis of ALI. Thrombin-activatable fibronolysis inhibitor (TAFI) is an important component of the fibrinolysis system. Recent studies have shown that the active form of TAFI can also regulate inflammatory responses by its ability to inhibit complement C3a, C5a, and osteopontin. We hypothesized that TAFI might have a protective role in ALI. To demonstrate this hypothesis, the development of ALI was compared between wild-type (WT) and TAFI-deficient mice. ALI was induced by intratracheal instillation of LPS. Control mice were treated with saline. Animals were killed 24 hours after LPS. The number of inflammatory cells and the concentration of total protein and inflammatory cytokines were significantly increased in bronchoalveolar lavage fluid from LPS-treated, TAFI-deficient mice compared with their WT counterparts. Significantly higher concentrations of C5a were found in bronchoalveolar lavage fluid and plasma in LPS-treated TAFI knockout mice compared with WT mice. Pretreatment with inhaled C5a receptor antagonist blocked the detrimental effects of TAFI deficiency to levels found in WT mice. Our results show that TAFI protects against ALI, at least in part, by inhibiting the complement system.

Thrombin Cleavage of Osteopontin and the Host Anti-Tumor Immune Response.

Osteopontin (OPN) is a multi-functional protein that is involved in various cellular processes such as cell adhesion, migration, and signaling. There is a single conserved thrombin cleavage site in OPN that, when cleaved, yields two fragments with different properties from full-length OPN. In cancer, OPN has tumor-promoting activity and plays a role in tumor growth and metastasis. High levels of OPN expression in cancer cells and tumor tissue are found in various types of cancer, including breast, lung, prostate, ovarian, colorectal, and pancreatic cancer, and are associated with poor prognosis and decreased survival rates. OPN promotes tumor progression and invasion by stimulating cell proliferation and angiogenesis and also facilitates the metastasis of cancer cells to other parts of the body by promoting cell adhesion and migration. Furthermore, OPN contributes to immune evasion by inhibiting the activity of immune cells. Thrombin cleavage of OPN initiates OPN's tumor-promoting activity, and thrombin cleavage fragments of OPN down-regulate the host immune anti-tumor response.

Development and preclinical efficacy of novel transforming growth factor-ß1 short interfering RNAs for pulmonary fibrosis.

Idiopathic pulmonary fibrosis is a chronic devastating disease of unknown etiology. No therapy is currently available. A growing body of evidence supports the role of transforming growth factor (TGF)-ß1 as the major player in the pathogenesis of the disease. However, attempts to control its expression and to improve the outcome of pulmonary fibrosis have been disappointing. We tested the hypothesis that TGF-ß1 is the dominant factor in the acute and chronic phases of pulmonary fibrosis and developed short interfering (si)RNAs directed toward molecules implicated in the disease. This study developed novel sequences of siRNAs targeting the TGF-ß1 gene and evaluated their therapeutic efficacy in two models of pulmonary fibrosis: a model induced by bleomycin and a novel model of the disease developed spontaneously in mice overexpressing the full length of human TGF-ß1 in the lungs. Intrapulmonary delivery of aerosolized siRNAs of TGF-ß1 with sequences common to humans and rodents significantly inhibited bleomycin-induced pulmonary fibrosis in the acute and chronic phases of the disease and in a dose-dependent manner. Aerosolized human-specific siRNA also efficiently inhibited pulmonary fibrosis, improved lung function, and prolonged survival in human TGF-ß1 transgenic mice. Mice showed no off-target effects after intratracheal administration of siRNA. These results suggest the applicability of these novel siRNAs as tools for treating pulmonary fibrosis in humans.

Proteolytic cleavage of chemerin protein is necessary for activation to the active form, Chem157S, which functions as a signaling molecule in glioblastoma.

Chemerin is a chemoattractant involved in innate and adaptive immunity as well as an adipokine implicated in adipocyte differentiation. Chemerin circulates as an inactive precursor in blood whose bioactivity is closely regulated through proteolytic processing at its C terminus. We developed methodology for production of different recombinant chemerin isoforms (chem163S, chem157S, and chem155A) which allowed us to obtain large quantities of these proteins with purity of >95%. Chem158K was generated from chem163S by plasmin cleavage. Characterization by mass spectrometry and Edman degradation demonstrated that both the N and C termini were correct for each isoform. Ca(2+) mobilization assays showed that the EC(50) values for chem163S and chem158K were 54.2 ± 19.9 nm and 65.2 ± 13.2 nm, respectively, whereas chem157S had a ∼50-fold higher potency with an EC(50) of 1.2 ± 0.7 nm. Chem155A had no agonist activity and weak antagonist activity, causing a 50% reduction of chem157S activity at a molar ratio of 100:1. Similar results were obtained in a chemotaxis assay. Because chem158K is the dominant form in cerebrospinal fluid from patients with glioblastoma (GBM), we examined the significance of chemerin in GBM biology. In silico analysis showed chemerin mRNA was significantly increased in tissue from grade III and IV gliomas. Furthermore, U-87 MG cells, a human GBM line, express the chemerin receptors, chemokine-like receptor 1 and chemokine receptor-like 2, and chem157S triggered Ca(2+) flux. This study emphasized the necessity of appropriate C-terminal proteolytic processing to generate the likely physiologic form of active chemerin, chem157S, and suggested a possible role in malignant GBM.

Chemerin158K protein is the dominant chemerin isoform in synovial and cerebrospinal fluids but not in plasma.

Chemerin is a chemoattractant involved in immunity that may also function as an adipokine. Chemerin circulates as an inactive precursor (chem163S), and its activation requires proteolytic cleavages at its C terminus, involving proteases involved in coagulation, fibrinolysis, and inflammation. However, the key proteolytic steps in prochemerin activation in vivo remain to be established. Previously, we have shown that C-terminal cleavage of chem163S by plasmin to chem158K, followed by a carboxypeptidase cleavage, leads to the most active isoform, chem157S. To identify and quantify the in vivo chemerin isoforms in biological specimens, we developed specific ELISAs for chem163S, chem158K, and chem157S, using antibodies raised against peptides from the C terminus of the different chemerin isoforms. We found that the mean plasma concentrations of chem163S, chem158K, and chem157S were 40 ± 7.9, 8.1 ± 2.9, and 0.7 ± 0.8 ng/ml, respectively. The total level of cleaved and noncleaved chemerins in cerebrospinal fluids was ∼10% of plasma levels whereas it was elevated ∼2-fold in synovial fluids from patients with arthritis. On the other hand, the fraction of cleaved chemerins was much higher in synovial fluid and cerebrospinal fluid samples than in plasma (∼75%, 50%, and 18% respectively). Chem158K was the dominant chemerin isoform, and it was not generated by ex vivo processing, indicating that cleavage of prochemerin at position Lys-158, whether by plasmin or another serine protease, represents a major step in prochemerin activation in vivo. Our study provides the first direct evidence that chemerin undergoes extensive proteolytic processing in vivo, underlining the importance of measuring individual isoforms.

Role of thrombin-activatable fibrinolysis inhibitor in allergic bronchial asthma.

BACKGROUND: Bronchial asthma is an inflammatory disease of the airways. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase that besides inhibiting fibrinolysis, also regulates inflammatory processes. The only validated substrate known for TAFI is fibrin. In the present study we evaluated the role of TAFI in bronchial asthma by comparing the development of allergic bronchial asthma between wild-type (WT) and TAFI-deficient mice (KO). METHODS: Asthmatic inflammation was induced by sensitization and challenge with ovalbumin in WT (WT/OVA) and TAFI KO (KO/OVA) mice. WT mice (WT/SAL) and TAFI KO (KO/SAL) were used as controls. Cytokines, markers of inflammation, and coagulation were measured in bronchoalveolar lavage fluid (BALF). RESULTS: Airway hyperresponsiveness was worse in KO/OVA mice than in WT/OVA mice or control mice. Markers of lung injury were significantly increased in BALF from KO/OVA mice compared to WT/OVA mice. Airway hyperresponsiveness and the BALF concentrations of IL-5 and osteopontin were significantly increased in KO/OVA mice compared to WT/OVA mice. Treatment of WT/OVA and KO/OVA mice with a C5a receptor antagonist significantly decreased hyperresponsiveness along with the BALF concentrations of total protein and C5a compared to untreated asthmatic mice. CONCLUSION: The results of this study suggest that TAFI plays a protective role in the pathogenesis of allergic inflammation probably by inhibiting the complement system.

Inhibition of allergic bronchial asthma by thrombomodulin is mediated by dendritic cells.

RATIONALE: bronchial asthma is caused by inappropriate acquired immune responses to environmental allergens. It is a major health problem, with a prevalence that is rapidly increasing. Curative therapy is not currently available. OBJECTIVES: to test the hypothesis that thrombomodulin (TM) inhibits allergic bronchial asthma by inducing tolerogenic dendritic cells (DCs). METHODS: the protective effect of TM was evaluated using a murine asthma model. Asthma was induced in mice by exposure to chicken egg ovalbumin, and the effects of inhaled TM or TM-treated DCs were assessed by administering before ovalbumin exposure. MEASUREMENTS AND MAIN RESULTS: treatment with TM protects against bronchial asthma measured as improved lung function and reduced IgE and cells in alveolar lavage fluid by inducing tolerogenic dendritic dells. These are characterized by high expression of surface TM (CD141/TM(+)) and low expression of maturation markers and possess reduced T-cell costimulatory activity. The CD141/TM(+) DCs migrate less toward chemokines, and after TM treatment there are fewer DCs in the draining lymph node and more in the lungs. The TM effect is independent of its role in coagulation. Rather, it is mediated via the TM lectin domain directly interacting with the DCs. CONCLUSIONS: the results of this study show that TM is a modulator of DC immunostimulatory properties and a novel candidate drug for the prevention of bronchial asthma in atopic patients.