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Severe inflammatory complications are a potential consequence in patients with predetermined conditions of infections, pulmonary diseases, or cardiovascular disorders. Notably, the amplitude of the inflammatory response towards these complications can dictate the disease progression and outcome. During the recent years, evidence from basic research as well as from clinical studies has identified self-extracellular nucleic acids as important players in the crosstalk between immunity and cardiovascular diseases. These stress- or injury-induced endogenous polymeric macromolecules not only serve as "alarmins" or "Danger-associated molecular patterns" (DAMPs), but their functional repertoire goes far beyond such activities in innate immunity. In fact, (patho-) physiological functions of self-extracellular DNA and RNA are associated and in many cases causally related to arterial and venous thrombosis, atherosclerosis, ischemia-reperfusion injury or tumour progression. Yet, the underlying molecular mechanisms are far from being completely understood. Interestingly enough, however, novel antagonistic approaches in vitro and in vivo, particularly using natural endonucleases or synthetic nucleic acid binding polymers, appear to be promising and safe therapeutic options for future studies. The aim of this review article is to provide an overview of the current state of (patho-) physiological functions of self-extracellular nucleic acids with special emphasis on their role as beneficial / alerting or adverse / damaging factors in connection with immune responses, inflammation, thrombosis, and cardiovascular diseases.

Activation of thrombin is a critical determinant in many physiological and pathological processes including haemostasis and inflammation. Under physiological conditions many of these functions are involved in wound healing or eradication of an invading pathogen. However, when activated systemically, thrombin can contribute to severe and life-threatening conditions by causing complications such as multiple multi-organ failure and disseminated intravascular coagulation. In the present study we investigated how the activity of thrombin is modulated when it is bound to the surface of Streptococcus pyogenes. Our data show that S. pyogenes bacteria become covered with a proteinaceous layer when incubated with human plasma, and that thrombin is a constituent of this layer. Though the coagulation factor is found attached to the bacteria with a functional active site, thrombin has lost its capacity to interact with its natural substrates and inhibitors. Thus, the interaction of bacteria with human plasma renders thrombin completely inoperable at the streptococcal surface. This could represent a host defense mechanism to avoid systemic activation of coagulation which could be otherwise induced when bacteria enter the circulation and cause systemic infection.

Coagulation factor XIII (FXIII), a plasma transglutaminase, is best known as the final enzyme in the coagulation cascade, where it is responsible for cross-linking of fibrin. However, a growing body of evidence has demonstrated that FXIII targets a wide range of additional substrates that have important roles in health and disease. These include antifibrinolytic proteins, with cross-linking of α2-antiplasmin to fibrin, and potentially fibrinogen, being the principal mechanism(s) whereby plasmin-mediated clot degradation is minimised. FXIII also acts on endothelial cell VEGFR-2 and αvβ3 integrin, which ultimately leads to downregulation of the antiangiogenic protein thrombospondin-1, promoting angiogenesis and neovascularisation. Under infectious disease conditions, FXIII cross-links bacterial surface proteins to fibrinogen, resulting in immobilisation and killing, while during wound healing, FXIII induces cross-linking of the provisional matrix. The latter process has been shown to influence the interaction of leukocytes with the provisional extracellular matrix and promote wound healing. Through these actions, there are good rationales for evaluating the therapeutic potential of FXIII in diseases in which tissue repair is dysregulated or perturbed, including systemic sclerosis (scleroderma), invasive bacterial infections, and tissue repair, for instance healing of venous leg ulcers or myocardial injuries. Adequate levels of FXIII are also required in patients undergoing surgery to prevent or treat perioperative bleeding, and its augmentation in patients with/at risk for perioperative bleeding may also have potential clinical benefit. While there are preclinical and/or clinical data to support the use of FXIII in a range of settings, further clinical evaluation in these underexplored applications is warranted.

Activated platelets and neutrophils exacerbate atherosclerosis. Platelets release the chemokines CXCL4, CXCL4L1 and CCL5, whereas myeloperoxidase (MPO) and azurocidin are neutrophil-derived. We investigated whether plasma levels of these platelet and neutrophil mediators are affected by the acute coronary syndrome (ACS), its medical treatment, concomitant clinical or laboratory parameters, and predictive for the progression of coronary artery disease (CAD). In an observational study, the association of various factors with plasma concentrations of platelet chemokines and neutrophil mediators in 204 patients, either upon admission with ACS and 6 hours later or without ACS or CAD, was determined by multiple linear regression. Mediator release was further analysed after activation of blood with ACS-associated triggers such as plaque material. CXCL4, CXCL4L1, CCL5, MPO and azurocidin levels were elevated in ACS. CXCL4 and CCL5 but not CXCL4L1 or MPO were associated with platelet counts and CRP. CXCL4 (in association with heparin treatment) and MPO declined over 6 hours during ACS. Elevated CCL5 was associated with a progression of CAD. Incubating blood with plaque material, PAR1 and PAR4 activation induced a marked release of CXCL4 and CCL5, whereas CXCL4L1 and MPO were hardly or not altered. Platelet chemokines and neutrophil products are concomitantly elevated in ACS and differentially modulated by heparin treatment. CCL5 levels during ACS predict a progression of preexisting CAD. Platelet-derived products appear to dominate the inflammatory response during ACS, adding to the emerging evidence that ACS per se may promote vascular inflammation.

Early diagnosis of severe infectious diseases is essential for timely implementation of lifesaving therapies. In a search for novel biomarkers in sepsis diagnosis we focused on polymorphonuclear neutrophils (PMNs). Notably, PMNs have their protein cargo readily stored in granules and following systemic stimulation, an immediate increase of neutrophil-borne proteins can be observed into the circulation of sepsis patients. We applied a combination of mass spectrometry (MS) based approaches, LC-MS/MS and selected reaction monitoring (SRM), to characterise and quantify the neutrophil proteome in healthy or disease conditions. With this approach we identified a neutrophil-derived protein abundance pattern in blood plasma consisting of 20 proteins that can be used as a protein signature for severe infectious diseases. Our results also show that SRM is highly sensitive, specific, and reproducible and, thus, a promising technology to study a complex, dynamic and multifactorial disease such as sepsis.

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.

Fibrinogen is a key player in the blood coagulation system, and is upon activation with thrombin converted into fibrin that subsequently forms a fibrin clot. In the present study, we investigated the role of fibrinogen in the early innate immune response. Here we show that the viability of fibrinogen-binding bacteria is affected in human plasma activated with thrombin. Moreover, we found that the peptide fragment GHR28 released from the β-chain of fibrinogen has antimicrobial activity against bacteria that bind fibrinogen to their surface, whereas non-binding strains are unaffected. Notably, bacterial killing was detected in Group A Streptococcus bacteria entrapped in a fibrin clot, suggesting that fibrinogen and coagulation is involved in the early innate immune system to quickly wall off and neutralise invading pathogens.

Streptococcus pyogenes is the causative agent in a wide range of diseases in humans. Thrombin-activatable fibrinolysis inhibitor (TAFI) binds to collagen-like proteins SclA and SclB at the surface of S. pyogenes. Activation of TAFI at this surface redirects inflammation from a transient to chronic state by modulation of the kallikrein/kinin system. We investigated TAFI binding characteristics to SclA/SclB. Thirty-four overlapping TAFI peptides of ~20 amino acids were generated. Two of these peptides (P18: residues G205-S221, and P19: R214-D232) specifically bound to SclA/SclB with high affinity, and competed in a dose-dependent manner with TAFI binding to SclA/SclB. In another series of experiments, the binding properties of activated TAFI (TAFIa) to SclA/SclB were studied with a quadruple TAFI mutant (TAFI-IIYQ) that after activation is a 70-fold more stable enzyme than wild-type TAFIa. TAFI and TAFI-IIYQ bound to the bacterial proteins with similar affinities. The rate of dissociation was different between the proenzyme (both TAFI and TAFI-IIYQ) and the stable enzyme TAFIa-IIYQ. TAFIa-IIYQ bound to SclA/SclB, but dissociated faster than TAFI-IIYQ. In conclusion, the bacterial proteins SclA and SclB bind to a TAFI fragment encompassing residues G205-D232. Binding of TAFI to the bacteria may allow activation of TAFI, whereafter the enzyme easily dissociates.

Protein C inhibitor (PCI) is a serine protease inhibitor and was originally identified as an inhibitor of activated protein C (APC). However, PCI is not specific for APC and also inhibits several proteases involved in coagulation, fibrinolysis, cancer, wound healing, and fertility. The biological function of PCI is unknown due to broad enzyme specificity, its wide tissue distribution, and the lack of a suitable animal model. This review highlights the specific roles of PCI in the areas of hemostasis and thrombosis and fertilization, and it also describes the latest information on the fascinating participation of the protein in intracellular processes, phospholipid binding, and killing of bacteria., (© Thieme Medical Publishers.)

Hemostasis is a sensitive and tightly regulated process, involving the vascular endothelium and blood cells as well as factors of the coagulation and fibrinolytic cascades. Over the last four decades evidence has accumulated that during infection, inflammatory mediators from the microbe and/or host are capable to modulate the equilibrium between the procoagulant and anticoagulant status of the host. Dependent on the mode of activation, these changes can cause either local or systemic inflammatory reactions that may be beneficial or deleterious to the human host. The present review aims to present the state of the art with respect to the role of the contact system (also known as the intrinsic pathway of coagulation or the kallikrein/kinin system) in innate immunity and systemic inflammatory reactions.

Streptococcus pyogenes is an important Gram-positive pathogen that is strictly limited to infections in humans. Here we report that streptolysin O (SLO), a cytolytic exotoxin secreted by S. pyogenes, activates human polymorphonuclear neutrophils (PMNs) by perforating these cells. This appears to be followed by an influx of Ca(2+) and p38 MAPK activation. As a consequence, PMNs secrete heparin-binding protein, a potent inducer of vascular leakage, and neutrophil-borne proteins, including LL-37, alpha-defensins, and elastase. The results of the present work therefore suggest that the interaction between SLO and PMNs evokes an exaggerated host response which may contribute to the pathogenesis of local and generalized S. pyogenes infections.

Recently it was demonstrated by Gautam, et al. that release of neutrophil-borne heparin-binding protein (HBP), also known as CAP37/azurocidin, induced endothelial hyperpermeability and neutrophil efflux. Here, we show that chronic leg ulcer fluid, in contrast to wound fluid from acute wounds, contains highly increased levels of HBP. Immunohistochemistry demonstrated the presence of HBP in chronic ulcer tissues. Furthermore, secreted products of Pseudomonas aeruginosa were found to induce release of HBP from human neutrophils. Our data suggest a possible link between bacterial presence and HBP-release in chronic ulcers. Thus, targeting HBP offers an interesting option for reduction of endothelial barrier dysfunction in chronic ulcers.