Endogenous protein C has a protective role during Gram-negative pneumosepsis (melioidosis)

Selective inhibition of activated protein C anticoagulant activity protects against hemophilic arthropathy in mice

Recurrent spontaneous or trauma-related bleeding into joints in hemophilia leads to hemophilic arthropathy (HA), a debilitating joint disease. Treatment of HA consists of preventing joint bleeding by clotting factor replacement, and in extreme cases, orthopedic surgery. We recently showed that administration of endothelial cell protein C receptor (EPCR) blocking monoclonal antibodies (mAb) markedly reduced the severity of HA in factor VIII (FVIII)-/- mice. EPCR blocking inhibits activated protein C (APC) generation and EPCR-dependent APC signaling. The present study was aimed to define the role of inhibition of APC anticoagulant activity, APC signaling, or both in suppressing HA. FVIII-/- mice were treated with a single dose of isotype control mAb, MPC1609 mAb, that inhibits anticoagulant, and signaling properties of APC, or MAPC1591 mAb that only blocks the anticoagulant activity of APC. Joint bleeding was induced by needle puncture injury. HA was evaluated by monitoring joint bleeding, change in joint diameter, and histopathological analysis of joint tissue sections for synovial hypertrophy, macrophage infiltration, neoangiogenesis, cartilage degeneration, and chondrocyte apoptosis. No significant differences were observed between MPC1609 and MAPC1591 in inhibiting APC anticoagulant activity in vitro and equally effective in correcting acute bleeding induced by the saphenous vein incision in FVIII-/- mice. Administration of MAPC1591, and not MPC1609, markedly reduced the severity of HA. MAPC1591 inhibited joint bleed-induced inflammatory cytokine interleukin-6 expression and vascular leakage in joints, whereas MPC1609 had no significant effect. Our data show that an mAb that selectively inhibits APC's anticoagulant activity without compromising its cytoprotective signaling offers a therapeutic potential alternative to treat HA.

Thrombocytopenia Impairs Host Defense Against Burkholderia pseudomallei (Melioidosis)

Background

Infection with the gram-negative bacillus Burkholderia pseudomallei (melioidosis) is an important cause of pneumosepsis in Southeast Asia and has a mortality of up to 40%. We aimed to assess the role of platelets in the host response against B. pseudomallei infection.

Methods

Association between platelet counts and mortality was determined in 1160 patients with culture-proven melioidosis. Mice treated with (low- or high-dose) platelet-depleting antibody were inoculated intranasally with B. pseudomallei and killed. Additional studies using functional glycoprotein Ibα-deficient mice were conducted.

Results

Thrombocytopenia was present in 31% of patients at admission and predicted mortality in melioidosis patients even after adjustment for confounders. In our murine-melioidosis model, platelet counts decreased, and mice treated with a platelet-depleting antibody showed enhanced mortality and higher bacterial loads compared to mice with normal platelet counts. Low platelet counts had a modest impact on early-pulmonary neutrophil influx. Reminiscent of their role in hemostasis, platelet depletion impaired vascular integrity, resulting in early lung bleeding. Glycoprotein Ibα-deficient mice had reduced platelet counts during B. pseudomallei infection together with an impaired local host defense in the lung.

Conclusions

Thrombocytopenia predicts mortality in melioidosis patients and, during experimental melioidosis, platelets play a protective role in both innate immunity and vascular integrity.

Role of Toll-Like Receptor 5 (TLR5) in Experimental Melioidosis

The Gram-negative intracellular pathogen Burkholderia pseudomallei is the causative agent of melioidosis, an important cause of sepsis in Southeast Asia. Recognition of pathogen-associated molecular patterns by Toll-like receptors (TLRs) is essential for an appropriate immune response during pathogen invasion. In patients with melioidosis, TLR5 is the most abundantly expressed TLR, and a hypofunctional TLR5 variant has been associated with improved survival. Here, we studied the functional role of TLR5 and its ligand flagellin in experimental melioidosis. First, we observed differential TLR5 expression in the pulmonary and hepatic compartments upon infection with B. pseudomallei Next, we found that B. pseudomallei-challenged TLR5-deficient (Tlr5^-/- ) mice were more susceptible to infection than wild-type (WT) mice, as demonstrated by higher systemic bacterial loads, increased organ injury, and impaired survival. Lung bacterial loads were not different between the two groups. The phenotype was flagellin independent; no difference in in vivo virulence was observed for the flagellin-lacking mutant MM36 compared to the wild-type B. pseudomallei strain 1026b. Tlr5^-/- mice showed a similar impaired antibacterial defense when infected with MM36 or 1026b. Ex vivo experiments showed that TLR5-deficient macrophages display markedly impaired phagocytosis of B. pseudomallei In conclusion, these data suggest that TLR5 deficiency has a detrimental flagellin-independent effect on the host response against pulmonary B. pseudomallei infection.

α2-Macroglobulin Is a Significant In Vivo Inhibitor of Activated Protein C and Low APC:α2M Levels Are Associated with Venous Thromboembolism

BACKGROUND

Activated protein C (APC) is a major regulator of thrombin formation. Two major plasma inhibitors form complexes with APC, protein C inhibitor (PCI) and α₁-antitrypsin (α₁AT), and these complexes have been quantified by specific enzyme-linked immunosorbent assays (ELISAs). Also, complexes of APC with α₂-macroglobulin (α₂M) have been observed by immunoblotting. Here, we report an ELISA for APC:α₂M complexes in plasma.

METHODS

Plasma samples were pre-treated with dithiothreitol and then with iodoacetamide. The detection range of the newly developed APC:α₂M assay was 0.031 to 8.0 ng/mL of complexed APC. Following infusions of APC in humans and baboons, complexes of APC with α₂M, PCI and α₁AT were quantified. These complexes as well as circulating APC were also measured in 121 patients with a history of venous thromboembolism (VTE) and 119 matched controls.

RESULTS

In all the in vivo experiments, α₂M was a significant APC inhibitor. The VTE case-control study showed that VTE patients had significantly lower APC:α₂M and APC levels than the controls (p < 0.001). Individuals in the lowest quartile of APC:α₂M or the lowest quartile of APC had approximately four times more VTE risk than those in the highest quartile of APC:α₂M or of APC. The risk increased for individuals with low levels of both parameters.

CONCLUSION

The APC:α₂M assay reported here may be useful to help monitor the in vivo fate of APC in plasma. In addition, our results show that a low APC:α₂M level is associated with increased VTE risk.

PAR1 biased signaling is required for activated protein C in vivo benefits in sepsis and stroke

Activated protein C (APC) cleaves protease-activated receptor 1 (PAR1) in vitro at R46 to initiate beneficial cell signaling; however, thrombin and APC can cleave at R41. To elucidate PAR1-dependent aspects of the pharmacologic in vivo mechanisms of APC, we generated C57BL/6 mouse strains carrying QQ41 or QQ46 point mutations in PAR1 (F2r gene). Using these strains, we determined whether or not recombinant murine signaling-selective APC mutants would reduce septic death or provide neuroprotection against ischemic stroke when mice carried PAR1-homozygous mutations that prevent cleavage at either R41 or R46. Intercrossing PAR1+/R46Q mice generated expected numbers of PAR1+/+, PAR1+/R46Q, and R46Q/R46Q offspring whereas intercrossing PAR1+/R41Q mice gave decreased R41Q/R41Q homozygotes (resembling intercrossing PAR1+/PAR1-knockout mice). QQ41-PAR1 and QQ46-PAR1 brain endothelial cells showed the predicted retention or loss of cellular responses to thrombin receptor-activating peptide, thrombin, or APC for each PAR1 mutation. In sepsis studies, exogenous APC reduced mortality from 50% to 10% in Escherichia coli-induced pneumonia for wild-type (Wt) PAR1 and QQ41-PAR1 mice (P < .01) but had no benefit for QQ46-PAR1 mice. In transient distal middle cerebral artery occlusion stroke studies, exogenous APC significantly reduced infarct size, edema, and neuronal apoptosis for Wt mice and QQ41-PAR1 mice but had no detectable benefits for mice carrying QQ46-PAR1. In functional studies of forelimb-asymmetry and foot-fault tests at 24 hours after stroke induction, signaling-selective APC was beneficial for Wt and QQ41-PAR1 mice but not QQ46-PAR1 mice. These results support the concept that APC-induced, PAR1-dependent biased signaling following R46 cleavage is central to the in vivo benefits of APC.

Targeting activated protein C to treat hemophilia

PURPOSE OF REVIEW

Hemophilia is a debilitating disease, marked by frequent, painful bleeding events, joint deterioration and early death. All current treatments consist of i.v. infusions of replacement factor or other procoagulant factors, and are incompletely effective, due in part to the short half-lives of the proteins. An alternative approach is to rebalance hemostasis by inhibiting natural anticoagulant mechanisms. In this article, we explain why activated protein C (APC) is an appropriate and safe target for the treatment of hemophilia.

RECENT FINDINGS

A serpin (serine protease inhibitor) was engineered to specifically inhibit APC and was found to rescue hemostasis in a hemophilia mouse model, even after a severe tail clip injury. However, APC is also anti-inflammatory and has cytoprotective activities, raising safety concerns over the use of an APC inhibitor to treat hemophilia. We summarize the molecular basis of the anticoagulant and signaling activities of APC to assess the potential impact of targeting APC.

SUMMARY

We conclude that the signaling and anticoagulant functions of APC are in spatially and kinetically distinct compartments, and that it is possible to specifically inhibit the anticoagulant activity of APC. Targeting APC with a serpin is remarkably effective and may be safe for long-term prophylactic use in the treatment of hemophilia.

Impact of thrombosis on pulmonary endothelial injury and repair following sepsis

The prevailing morbidity and mortality in sepsis are largely due to multiple organ dysfunction (MOD), most commonly lung injury, as well as renal and cardiac dysfunction. Despite recent advances in defining many aspects of the pathogenesis of sepsis-related MOD, including acute respiratory distress syndrome (ARDS), there are currently no effective pharmacological or cell-based treatments for the disease. Human and animal studies have shown that pulmonary thrombosis is common in sepsis-induced ARDS, and preclinical studies have shown that anticoagulation may improve outcome following sepsis challenge. The potential beneficial effect of anticoagulation on outcome is unconvincing in clinical studies, however, and these discrepancies may arise from the multiple and sometimes opposing actions of thrombosis on the pulmonary endothelium following sepsis. It has been suggested, for example, that mild pulmonary thrombosis prevents escape of bacterial infection into the circulation, while severe thrombosis causes hypoxia and results in pulmonary endothelial damage. Evidence from both human and animal studies has demonstrated the key role of microvascular leakage in determining the outcome of sepsis. In this review, we describe thrombosis-dependent mechanisms that regulate pulmonary endothelial injury and repair following sepsis, including activation of the coagulation cascade by tissue factor and stimulation of vascular repair by hypoxia-inducible factors. Targeting such mechanisms through anticoagulant, anti-inflammatory, and reparative methods may represent a novel approach for the treatment of septic patients.

Activated protein C protects against renal ischaemia/reperfusion injury, independent of its anticoagulant properties

Acute renal failure, a serious condition characterised by a drastic decline in renal function, often follows ischaemia/reperfusion (I/R) episodes. I/R is characterised by necrosis, inflammation and activation of coagulation, in concert causing renal tissue damage. In this context, activated protein C (APC) might be of importance in the pathogenesis of renal I/R. APC is a serine protease which has anticoagulant but also several anti-inflammatory and cytoprotective effects such as protection of endothelial barrier function. It was our objective to study the role of cytoprotective and anticoagulant functions of APC during renal I/R. C57BL/6j mice subjected to renal I/R were treated with intraperitoneally injected exogenous human APC, or two mutant forms of APC (200 µg/kg) which specifically lack anticoagulant or signalling properties. In a different experiment mice received specific monoclonal antibodies (20 mg/kg) that block the cytoprotective and/or anticoagulant properties of endogenous APC. Treatment with APC reduced tubular injury and enhanced renal function without altering the inflammatory response and did reduce renal fibrin deposition. Administration of APC mutant lacking anticoagulant properties reduced renal damage and enhanced renal function. Blocking the anticoagulant and cytoprotective functions of endogenous APC resulted in elevated tubular damage and reduced tubular cell proliferation, however, without influencing renal function or the inflammatory response. Furthermore, blocking both the anticoagulant and cytoprotective effects of APC resulted in dramatic renal interstitial haemorrhage, indicative of impaired vascular integrity. Blocking only the anticoagulant function of APC did not result in interstitial bleeding. In conclusion, the renoprotective effect of APC during I/R is independent of its anticoagulant properties.

Triggering Receptor Expressed on Myeloid Cells (TREM)-2 Impairs Host Defense in Experimental Melioidosis

Background

Triggering receptor expressed on myeloid cells (TREM) -1 and TREM-2 are key regulators of the inflammatory response that are involved in the clearance of invading pathogens. Melioidosis, caused by the "Tier 1" biothreat agent Burkholderia pseudomallei, is a common form of community-acquired sepsis in Southeast-Asia. TREM-1 has been suggested as a biomarker for sepsis and melioidosis. We aimed to characterize the expression and function of TREM-1 and TREM-2 in melioidosis.

Methodology/Principal Findings

Wild-type, TREM-1/3 (Trem-1/3^-/-) and TREM-2 (Trem-2^-/-) deficient mice were intranasally infected with live B. pseudomallei and killed after 24, and/or 72 h for the harvesting of lungs, liver, spleen, and blood. Additionally, survival studies were performed. Cellular functions were further analyzed by stimulation and/or infection of isolated cells. TREM-1 and TREM-2 expression was increased both in the lung and liver of B. pseudomallei-infected mice. Strikingly, Trem-2^-/-, but not Trem-1/3^-/-, mice displayed a markedly improved host defense as reflected by a strong survival advantage together with decreased bacterial loads, less inflammation and reduced organ injury. Cellular responsiveness of TREM-2, but not TREM-1, deficient blood and bone-marrow derived macrophages (BMDM) was diminished upon exposure to B. pseudomallei. Phagocytosis and intracellular killing of B. pseudomallei by BMDM and alveolar macrophages were TREM-1 and TREM-2-independent.

Conclusions/Significance

We found that TREM-2, and to a lesser extent TREM-1, plays a remarkable detrimental role in the host defense against a clinically relevant Gram-negative pathogen in mice: TREM-2 deficiency restricts the inflammatory response, thereby decreasing organ damage and mortality.

Triggering receptor expressed on myeloid cells (TREM)-1 and -2 are receptors on immune cells that act as mediators of the innate immune response. It is thought that TREM-1 amplifies the immune response, while TREM-2 acts as a negative regulator. Previously, we found that TREM-1 is upregulated in melioidosis patients. In contrast, nothing is known on TREM-2 expression and its role in melioidosis. In this study we examined the expression and functional role of both TREM-1 and -2 in a murine melioidosis model. We found that TREM-1 and-2 expression was upregulated during melioidosis. Using our experimental melioidosis model, we observed that Trem-2^-/- mice were protected against B.pseudomallei-induced lethality. Trem-2^-/- mice demonstrated reduced bacterial loads, inflammation and organ damage compared to wild-type mice in experimental melioidosis. Despite reduced bacterial dissemination of B.pseudomallei to distant organs in Trem-1/3^-/ mice^-, no differences in survival were found between Trem-1/3^-/- and wild-type mice during melioidosis. Lastly, we investigated cellular functions of TREM-1 and TREM-2 and found that TREM-2 deficiency led to decreased cellular responsiveness to B. pseudomallei infection. In conclusion, we found that TREM-2 plays an important role during experimental murine melioidosis. TREM-2-deficiency reduces inflammation and organ damage, thereby improving survival.

Diabetes-independent increase of factor VII-activating protease activation in patients with Gram-negative sepsis (melioidosis)

BACKGROUND

The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. Nucleosomes are markers of cell death, and extracellular cell-free DNA has been suggested to play an important role in inflammation and has been demonstrated to correlate with severity and outcome in sepsis patients.

OBJECTIVE

To investigate FSAP activation in patients suffering from Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia. As diabetes mellitus (DM) is the most important risk factor for both melioidosis and sepsis, we were also able to examine the role of DM in FSAP activation in this cohort of patients.

METHODS

In a prospective observational study, complexes of FSAP with α2 -antiplasmin (AP) were assayed in 44 patients with melioidosis, 34 of whom were classified as diabetic. Eighty-two healthy subjects served as controls (52 with DM and 30 without).

RESULTS

FSAP-AP complex levels were markedly elevated in patients as compared with controls. The FSAP level increased by 16.82 AU mL(-1) in patients with melioidosis after adjustment for the effect of DM in the regression model. As expected, FSAP activation was correlated with nucleosome release (slope = 0.74). No difference in FSAP activation on admission was seen between survivors and non-survivors, but the extent of FSAP activation correlated with stage of the disease; repeated testing during convalescence showed a return towards normal values (day 0 vs. day 28, 4.16 AU mL(-1) , 95% confidence interval [CI] 1.42-12.22).

CONCLUSION

Patients with Gram-negative sepsis caused by B. pseudomallei have abundant FSAP activation, which significantly correlates with stage of disease. The presence of DM, however, does not influence the extent of FSAP activation.

Overexpression of activated protein C hampers bacterial dissemination during pneumococcal pneumonia

Background

During pneumonia, inflammation and coagulation are activated as part of anti-bacterial host defense. Activated protein C (APC) has anticoagulant and anti-inflammatory properties and until recently was a registered drug for the treatment of severe sepsis. Streptococcus (S.) pneumoniae is the most common causative pathogen in community-acquired pneumonia.

Methods

We aimed to investigate the effect of high APC levels during experimental pneumococcal pneumonia. Wild type (WT) and APC overexpressing (APC^high)-mice were intranasally infected with S. pneumoniae and sacrificed after 6, 24 or 48 hours, or followed in a survival study.

Results

In comparison to WT mice, APC^high-mice showed decreased bacterial dissemination to liver and spleen, while no differences in bacterial loads were detected at the primary site of infection. Although no differences in the extent of lung histopathology were seen, APC^high-mice showed a significantly decreased recruitment of neutrophils into lung tissue and bronchoalveolar lavage fluid. Activation of coagulation was not altered in APC^high-mice. No differences in survival were observed between WT and APC^high-mice (P =0.06).

Conclusion

APC overexpression improves host defense during experimental pneumococcal pneumonia. This knowledge may add to a better understanding of the regulation of the inflammatory and procoagulant responses during severe Gram-positive pneumonia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0559-3) contains supplementary material, which is available to authorized users.

Neutrophil extracellular traps in the host defense against sepsis induced by Burkholderia pseudomallei (melioidosis)

Background

Neutrophil extracellular traps (NETs) are a central player in the host response to bacteria: neutrophils release extracellular DNA (nucleosomes) and neutrophil elastase to entrap and kill bacteria. We studied the role of NETs in Burkholderia pseudomallei infection (melioidosis), an important cause of Gram-negative sepsis in Southeast Asia.

Methods

In a prospective observational study, circulating nucleosomes and neutrophil elastase were assayed in 44 patients with Gram-negative sepsis caused by B. pseudomallei (melioidosis) and 82 controls. Functional assays included human neutrophil stimulation and killing assays and a murine model of B. pseudomallei infection in which NET function was compromised using DNase. Specified pathogen-free 8- to 12-week-old C57BL/6 mice were sacrificed post-infection to assess bacterial loads, inflammation, and pathology.

Results

Nucleosome and neutrophil elastase levels were markedly elevated in patients compared to controls. NETs killed B. pseudomallei effectively, and neutrophils stimulated with B. pseudomallei showed increased elastase and DNA release in a time- and dose-dependent matter. In mice, NET disruption with intravenous DNase administration resulted in decreased nucleosome levels. Although DNase treatment of mice resulted in diminished liver inflammation, no differences were observed in bacterial dissemination or systemic inflammation.

Conclusion

B. pseudomallei is a potent inducer of NETosis which was reflected by greatly increased levels of NET-related components in melioidosis patients. Although NETs exhibited antibacterial activity against B. pseudomallei, NET formation did not protect against bacterial dissemination and inflammation during B. pseudomallei-induced sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-014-0021-2) contains supplementary material, which is available to authorized users.

Pneumonia, thrombosis and vascular disease

SUMMARY

An enhanced risk of cardiovascular mortality has been observed after pneumonia. Epidemiological studies have shown that respiratory tract infections are associated with an increased risk of thrombotic-related vascular disease such as myocardial infarction, ischemic stroke and venous thrombosis. Myocardial infarction and stroke have been detected essentially in the early phase of the disease (i.e. within 48 h from hospital admission), with an incidence ranging from as low as 1% to as high as 11%. Age, previous cardiovascular events and high pneumonia severity index were independent predictors of myocardial infarction; clinical predictors of stroke were not identified. Deep venous thrombosis and pulmonary embolism may also occur after pneumonia but incidence and clinical predictors must be defined. The biological plausibility of such an association may be deduced by experimental and clinical studies, showing that lung infection is complicated by platelet aggregation and clotting system activation, as documented by up-regulation of tissue factor and down-regulation of activated protein C. The effect of antithrombotic drugs has been examined in experimental and clinical studies but results are still inconclusive.

The coagulation system in melioidosis: from pathogenesis to new treatment strategies

Melioidosis, caused by the Gram-negative bacterium Burkholderia pseudomallei, is a dreadful disease common in South-East Asia and Northern Australia and is characterized by chronic suppurative lesions and pneumonia. Melioidosis may evolve into severe sepsis with multi-organ failure with high mortalities, despite proper antibiotic therapy. Besides activation of a strong pro-inflammatory host response, the coagulation system plays an important role during melioidosis, which is thought to be host-protective. In particular, a procoagulant state together with downregulation of anticoagulant pathways and activation of fibrinolysis are present, all closely interrelated with parameters of inflammation. This review presents an overview of recent studies in which the role of coagulation, anti-coagulation and fibrinolysis during melioidosis was investigated both in patients and in experimental settings.

A thrombomodulin mutation that impairs active protein C generation is detrimental in severe pneumonia-derived gram-negative sepsis (melioidosis)

Background

During severe (pneumo)sepsis inflammatory and coagulation pathways become activated as part of the host immune response. Thrombomodulin (TM) is involved in a range of host defense mechanisms during infection and plays a pivotal role in activation of protein C (PC) into active protein C (APC). APC has both anticoagulant and anti-inflammatory properties. In this study we investigated the effects of impaired TM-mediated APC generation during melioidosis, a common form of community-acquired Gram-negative (pneumo)sepsis in South-East Asia caused by Burkholderia (B.) pseudomallei.

Methodology/Principal Findings

(WT) mice and mice with an impaired capacity to activate protein C due to a point mutation in their Thbd gene (TM^pro/pro mice) were intranasally infected with B. pseudomallei and sacrificed after 24, 48 or 72 hours for analyses. Additionally, survival studies were performed. When compared to WT mice, TM^pro/pro mice displayed a worse survival upon infection with B. pseudomallei, accompanied by increased coagulation activation, enhanced lung neutrophil influx and bronchoalveolar inflammation at late time points, together with increased hepatocellular injury. The TM^pro/pro mutation had limited if any impact on bacterial growth and dissemination.

Conclusion/Significance

TM-mediated protein C activation contributes to protective immunity after infection with B. pseudomallei. These results add to a better understanding of the regulation of the inflammatory and procoagulant response during severe Gram-negative (pneumo)sepsis.

Pneumonia and sepsis are conditions in which a procoagulant state is observed, with activation of coagulation and downregulation of anticoagulant pathways, both closely interrelated with inflammation. The protein C (PC) system is an important anticoagulant pathway implicated in the pathogenesis of sepsis. After binding to thrombomodulin (TM), PC is converted into active protein C (APC), mediated via high-affinity binding of thrombin to thrombomodulin (TM) and further augmented via association of the endothelial protein C receptor (EPCR) to the TM-thrombin complex. We studied the role of TM-associated PC-activation during the host response during pneumonia-derived sepsis caused by Burkholderia (B.) pseudomallei, the causative agent of melioidosis, a common form of community-acquired Gram-negative (pneumo)sepsis in South-East Asia and a serious potential bioterrorism threat agent. Mice with an impaired capacity to activate protein C displayed a worse survival upon infection with B. pseudomallei, accompanied by increased coagulation activation, enhanced lung neutrophil influx and bronchoalveolar inflammation at late time points, together with increased hepatocellular injury. These data further expand the knowledge about the role of the protein C system during melioidosis and may be of value in the development of therapeutic strategies against this dangerous pathogen.

The coagulation system and its function in early immune defense

Blood coagulation has a Janus-faced role in infectious diseases. When systemically activated, it can cause serious complications associated with high morbidity and mortality. However, coagulation is also part of the innate immune system and its local activation has been found to play an important role in the early host response to infection. Though the latter aspect has been less investigated, phylogenetic studies have shown that many factors involved in coagulation have ancestral origins which are often combined with anti-microbial features. This review gives a general overview about the most recent advances in this area of research also referred to as immunothrombosis.