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Perspective
Coagulation and innate immune responses: can we view them separately?
*Mieke Delvaeye1 and *Edward M. Conway1,2
1Vesalius
Research Center (VRC), University of Leuven (KUL), Leuven, Belgium; and 2Centre for Blood Research, Faculty of Medicine, University of
British Columbia, Vancouver, BC
The horseshoe crab is often referred to as
a “living fossil,” representative of the
oldest classes of arthropods, almost identical to species in existence more than
500 million years ago. Comparative analyses of the defense mechanisms used by
the horseshoe crab that allowed it to
survive mostly unchanged throughout the
millennia reveal a common ancestry of
the coagulation and innate immune sys-
tems that are totally integrated—indeed,
almost inseparable. In human biology, we
traditionally view the hemostatic pathways and those regulating innate immune
responses to infections and tissue damage as entirely separate entities. But are
they? The last couple of decades have
revealed a remarkable degree of interplay
between these systems, and the linking
cellular and molecular mechanisms are
rapidly being delineated. In this review,
we present some of the major points of
intersection between coagulation and innate immunity. We attempt to highlight
the potential impact of these findings by
identifying recently established paradigms that will hopefully result in the
emergence of new strategies to treat a
range of inflammatory and hemostatic
disorders. (Blood. 2009;114:2367-2374)
Introduction
The most menacing challenge to survival that is faced by organisms
throughout the animal kingdom is invasion by infections and
foreign antigens—events that are frequently accompanied by
trauma or a wound. Organisms have thus necessarily developed a
variety of effective means to restrict and to fight infections, to
contain wounds by limiting bleeding with clot formation, and to
rapidly initiate healing. The coexistence of thrombosis with
inflammatory responses supports the notion that common molecular mechanisms regulate these complex biologic systems. The last
couple of decades have seen major progress in identifying cellular
and molecular links between these systems.
In this review, we consider some of the key pathways involved
in hemostasis, innate immunity, and inflammation, and provide
recent data that demonstrate how they are integrated. The interactions are multiple and complex, and present new challenges to
identify those that are clinically relevant, with the promise of
discovering novel and more effective therapies for a range of
diseases.
Coagulation
The coagulation system is characterized by the sequential, rapid,
and highly localized activation of a series of serine proteases,
culminating in the generation of thrombin, with subsequent conversion of fibrinogen into a fibrin clot. Tissue factor (TF) is the key
initiator of coagulation (reviewed in Mackman1), and is expressed
primarily by subendothelial mural cells and adventitial fibroblasts
in and around the vessel wall. Somewhat controversial, it may also
be expressed at low levels by monocytes and neutrophils, and
found circulating in microparticles and in a soluble form.2 With
vascular endothelial cell damage, TF is exposed to the circulation,
and complexes with factor VII/VIIa, initiating activation of factors
IX and X. Factor Xa converts prothrombin to thrombin in sufficient
quantities to activate factors V and VIII. Factors VIIIa and Va are,
respectively, cofactors for factor IXa–mediated activation of factor
X and factor Xa–mediated conversion of prothrombin to thrombin.
The resultant thrombin-induced transformation of fibrinogen into a
fibrin clot is solidified by factor XIa, whereas factor XIIIa is
required for cross-linking the fibrin. A hemostatic plug develops as
activated platelets adhere to and aggregate on TF-presenting cells,
further promoting coagulation and thrombus formation.
Thrombin generation is tightly regulated to ensure that clot
formation is not excessive and that it remains highly localized.
Three major natural anticoagulant mechanisms have been delineated: TFPI, heparin-antithrombin (AT), and the protein C (PC)–
thrombomodulin system (reviewed in Crawley and Lane,3 Rau et
al,4 and Van de Wouwer et al5). These biochemical pathways are
physiologically relevant, since their disruption often predisposes to
hypercoagulable disorders. Modulation of the extent of clot
formation, and restoration of vascular integrity with healing, is
further mediated by the fibrinolytic system (supplemental Table 1
provides a list of abbreviations and is available on the Blood
website; see the Supplemental Materials link at the top of the online
article).
Innate immunity
As with the coagulation system, the innate immune response to
damaged host cells and invading pathogens is immediate and local,
thereby limiting damage and promoting healing (reviewed in
Mogensen6). This is accomplished by rapid recognition of potential
injurious agents, and the simultaneous recruitment of cellular,
molecular, and chemical mechanisms for their effective deactivation, destruction, and/or removal.
The innate cellular response is mediated primarily by phagocytic macrophages and antigen-presenting cells, which relies upon
Submitted May 19, 2009; accepted June 23, 2009. Prepublished online as
Blood First Edition paper, July 7, 2009; DOI 10.1182/blood-2009-05-199208.
The online version of this article contains a data supplement.
*M.D. and E.M.C. contributed equally in preparing and writing this review.
© 2009 by The American Society of Hematology
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
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2368
DELVAEYE and CONWAY
the recognition of conserved structures on pathogens, pathogenassociated molecular patterns (PAMPs), through pathogen recognition receptors (PRRs). PAMPs include for example, LPS, lipoproteins, peptidoglycans, heat shock proteins, and oligosaccharides.
Several families of PRRs exist that may be cell associated (eg,
Toll-like receptors [TLRs], complement receptors) or soluble (eg,
complement components). TLRs are the best characterized and are
expressed on immune cells, including endothelial cells and platelets (reviewed in Beutler7). PRRs also recognize host cell–derived
factors as “danger signals” (alarmins) that are generated during
infection, inflammation, or stress.8 Together, PAMPs and alarmins
are referred to as danger-associated molecular patterns (DAMPs).
Their engagement with PRRs induces the release of proinflammatory and antimicrobial cytokines, and chemokines and upregulation of leukocyte adhesion molecules. The host responds
either with resolution of the insult before host cellular damage or at
the other extreme, with the emergence of an inflammatory illness.
The innate immune system also uses complement to aid in the
efficient disposal of DAMPs. The complement system comprises
more than 30 soluble and membrane-bound proteins.9 Its activation
is achieved via 3 main cascade-like pathways: classical (CP), lectin
(LP), and alternative (AP). The CP is initiated via antigen-antibody
interactions. Activation of the LP starts with recognition of
carbohydrates on the surface of microbes and antigens by circulating mannose-binding lectin, followed by activation of mannosebinding lectin–associated serine proteases (MASP1, MASP2,
MASP3). The AP is constitutively active, amplified by the presence
of almost any foreign substance. A fourth pathway has been
described in which thrombin cleaves and activates C5 to the
anaphylatoxin, C5a.10 Except for the latter, all pathways converge
with activation of C3, and generation of anaphylatoxins and
opsonins (C3a, C5a) and a lytic membrane attack complex (C5b-9),
all designed to recruit activated leukocytes and to destroy the
invader. Similar to coagulation, to prevent host cell damage,11 the
complement system is tightly controlled by membrane-anchored
and fluid-phase regulators. Notably, unregulated activation of
complement is a common cause of atypical hemolytic-uremic
syndrome, a thrombotic microangiopathy.
Evolutionary perspectives
The notion that coagulation and innate immunity are coregulated
and intertwined is clearly evident from comparative studies.
Invertebrates and vertebrates share several major biologic host
defense systems (reviewed in Iwanaga and Lee12). These include
TLR-mediated antimicrobial production, coagulation, reactive oxygen species production, phagocytosis, and complement activation.
The horseshoe crab, a “living fossil” representative of the oldest
classes of arthropods, has an open circulatory system. It lacks an
adaptive immune system, but has effective innate defense mechanisms to restrict invasion of common pathogens and to promote
rapid healing. Ninety-nine percent of its circulating cells are
hematocytes that express PRRs that bind to invading pathogens
(reviewed in Iwanaga13). This causes the cells to degranulate,
leading to formation of a localized matrix (clot) that restricts the
loss of hemolymph, and simultaneously traps bacteria, preventing
invasion of infection into the hemocoel. This coordinated response
is possible due to the contents of hematocyte secretory granules,
which include clotting factors, clottable coagulogen, antimicrobial
factors, lectins that recognize carbohydrates on pathogens, and
defensins. Released coagulation factors C and G are serine protease
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
zymogens with opsonic properties and structural motifs similar to
those in human complement and coagulation factors.14 Upon
release, these are activated and induce a cascade that transforms
coagulogen to coagulin. The activation peptide fragments, the
coagulin itself, and other hematocyte-derived proteins have bacterial agglutinating and microbicidal activities. Finally, analogous to
factor XIIIa in humans, a transglutaminase cross-links the coagulin, improving the seal and promoting wound healing.
The implication from most studies is that the vertebrate blood
clotting system is evolutionarily a by-product of the innate immune
system (reviewed in Krem and Di Cera15), the blood clotting serine
proteases having diverged from those comprising the complement
system. Differences gradually emerged, evident by the acquisition
of unique protein structures, such as kringle domains and gla
domains, as the increasingly complex vertebrate systems required
more specialized mechanisms to defend against a range of infections and injuries. However, links between the systems remain, and
the value of this combinatorial approach is highlighted in the
horseshoe crab, which has allowed it to survive for more than
500 million years.
Initiation: common steps via TF
Initiation of the host response to injury and/or pathogen invasion,
with simultaneous induction of procoagulant and proinflammatory
activities, is centered around TF (Figure 1). Bacterial components
activate TLRs on monocytes, inducing the release of proinflammatory cytokines and up-regulation of leukocyte adhesion molecules,
while also increasing the expression of TF.16 Many other DAMPs
have similar effects, often synergizing to simultaneously promote
coagulation and inflammation by up-regulating TF expression and
inducing cytokine release from monocytes, neutrophils, and endothelial cells. Whatever the initiating event, a positive feedback loop
ensues, whereby the inflammatory system sustains TF expression
through the action of cytokines, chemokines, and activated complement components, enhanced by interactions with activated granulocytes and platelets.17
Although there is a lack of a clear view of the cellular and tissue
source(s) of TF in the setting of infections and inflammation,
loss-of-function and blocking studies in animal models confirm the
pivotal role of TF in modulating inflammation and coagulation, and
mediating their cross-talk. Mice with genetically reduced levels of
TF exhibit less coagulation, inflammation, end-organ damage, and
mortality in response to endotoxin.18 Interestingly, the cytoplasmic
domain of TF regulates its endotoxin-TLR–mediated expression,
and lack of this structure in a murine model of endotoxemia
transiently increases hemostatic system activity and significantly
dampens the inflammatory response.19 Because TF is the centerpiece for initiation and propagation of coagulation and inflammation, elucidating its cellular sites of expression, and the mechanisms by which it is regulated, is key for the development of
TF-targeted therapies.
The main inhibitor of TF-initiated coagulation is TFPI. With
inflammation-induced TLR-dependent activation of neutrophils,
TFPI is degraded and/or suppressed, leaving TF available to further
promote coagulation and inflammation. These imbalances are
associated with a poor outcome in patients with sepsis and acute
respiratory distress syndrome, and further demonstrate the interplay between innate immunity and coagulation. Although exogenous administration of TFPI has provided protection in animal
models of sepsis, a survival benefit has not been shown in humans
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BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
COAGULATION AND INNATE IMMUNITY
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Figure 1. Interplay between coagulation and innate immune pathways in response to DAMPs. Danger-associated molecular patterns (DAMPs) from invading pathogens
or damaged host cells are recognized by pathogen recognition receptors (PRRs) on antigen-presenting cells (APCs), neutrophils (PMNs), monocytes, macrophages
(mono/macro), endothelial cells (ECs), and platelets (plts). This results in tissue factor (TF) exposure, sustained by cytokines and chemokines with proinflammatory and
opsonic properties, and associated with increased expression of leukocyte adhesion molecules (LAMs). In parallel, DAMP-induced complement activation via 1 or more
pathways (CP, classical; AP, alternative; LP, lectin) leads to generation of potent active complement factors, C3a and C5a, and the membrane attack complex, C5b-9. MASP2
directly converts prothrombin to thrombin. C5a feeds back to promote expression of more TF. TF-VIIa initiates activation of coagulation, leading to transformation of factor X to
Xa with cofactor VIIIa, and prothrombin to thrombin (IIa) with cofactor Va. C5b-9 lyses pathogens, but also supports generation of IIa. Fibrin monomers are formed by thrombin
cleavage of fibrinogen, itself considered a DAMP, with release of fibrinopeptide A (FPA), which is also chemotactic and activates leukocytes. Factor XIIIa, generated by both IIa
and MASP1, cross-links fibrin monomers and suppresses cytokine release and leukocyte adhesion. Fibrinolysis is facilitated by urokinase (uPA) to generate fibrin degradation
products (FDPs), both of which have antimicrobial activity. Both IIa and Xa can activate PARs and usually promote inflammation, although the response varies according to the
nature of the stimulus and likely many factors. Several natural mechanisms modulate and localize the response to injury and pathogen invasion. Thus, TFPI suppresses TF
activity, but is itself down-regulated by inflammatory cytokines. AT interferes with proinflammatory/procoagulant factors Xa and IIa, and depresses PRR-mediated activation of
monocytes and cytokine release. APC interferes with TF release and generation of Xa and IIa, and via EPCR and PAR signaling, suppresses cytokine release, provides
cytoprotection, and promotes EC integrity. Protein S (PS) enhances the anticoagulant activity of APC, and aided by C4BP, promotes phagocytosis of apoptotic cells.
Thrombomodulin (TM) is a critical cofactor for thrombin-mediated activation of PC and, by binding to thrombin, neutralizes its proinflammatory and procoagulant activities (not
shown). TM also suppresses leukocyte adhesion and activation, interferes with complement activation, and supports thrombin-mediated generation of TAFIa, the latter which
inactivates C3a and C5a. TLR-mediated activation of platelets induces binding to neutrophils with formation of neutrophil extracellular traps (NETs) that trap and kill bacteria.
Black arrows represent long-established coagulation and innate immune/complement pathways. Green arrows indicate increase in response; red lines indicate suppression.
with sepsis.20 Further studies are necessary to clarify the mechanisms underlying its failure in that setting, and how it might be used
more successfully.
Thrombin, factor Xa, and the
protease-activated receptors
In addition to thrombin playing a key role in coagulation,
thrombin’s proinflammatory properties are well documented.
Thrombin induces the release of a host of proinflammatory
cytokines from endothelial cells, mural cells, epithelial cells,
adipocytes, and immune cells.21-23 It is chemotactic for monocytes
and neutrophils, induces expression of adhesion molecules, and
promotes release of growth factors and chemokines from platelets.
Thrombin directly activates both C3 and C5,10,24 and modulates
innate immune responses by altering cytokine secretion and
receptor expression by antigen-presenting cells.25 Thrombin at low
concentrations may enhance endothelial barrier function, but at
higher doses, it increases endothelial permeability, the latter being a
feature of inflammation.26
In a similar manner to thrombin, factor Xa exhibits a wide range
of proinflammatory properties (reviewed in Krupiczojc et al27).
Moreover, generation of factor Xa may be facilitated by pathogens,
such as viruses28 or immune cells, without requiring TF. For
example, neutrophil-derived cathepsin G, and some microbial
proteinases directly cleave and activate factor X. Factor Xa
inhibitors have thus been used to treat local inflammatory disorders
caused by those specific bacteria.29 This underscores the importance of delineating the mechanisms by which specific microbes
invade and spread by modulating the coagulation and immune
systems.
Most of the aforementioned noncoagulation-related cellular
activities of thrombin and factor Xa are mediated by the proteaseactivated receptors (PARs). The PARs, of which there are 4 (PAR1,
2, 3, 4), are G-coupled 7-pass transmembrane proteins that play a
key role in linking coagulation and inflammation (reviewed in
Shpacovitch et al30). Analogous to PRRs, which are the sentinels of
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DELVAEYE and CONWAY
innate immunity, PARs are sensors for extracellular proteases.
PARs are expressed by a variety of cells, including leukocytes,
platelets, and endothelial cells. PAR signaling is critical for
thrombin-mediated platelet activation, and is thus a key player in
hemostasis. However, several proteases, involved in both coagulation and inflammation, regulate PAR signaling, implicating these in
a spectrum of biologic systems. Thus, PAR1 is activated by
thrombin, factor Xa, APC, trypsin, granzyme A, gingipains-R, and
matrix metalloprotease-131; PAR2, by factor Xa, factor VIIa-TF,
and neutrophil proteinase 3 (PR3); and PAR4, by trypsin, cathepsin
G, gingipains-R, and relatively high concentrations of thrombin.
Activation of PAR2 by factor Xa or VIIa-TF mediates house dust
mite allergen responses, and promotes the expression of defensins,
proinflammatory cytokines, and chemokines. PAR2 physically
interacts with TLR4 in activating NFkB by sharing utilization of
intracellular adaptor proteins, and thereby modulates the inflammatory response.32 PAR2 also cooperates with PAR1, but increases
endothelial barrier protective properties of factor Xa.26 All may be
variably cleaved and inactivated by a variety of inflammatory
proteases, including cathepsin G, plasmin, elastase, PR3, and
trypsin.30
The in vivo role of the PARs, particularly PAR1 in sepsis, is
currently an active area of research, rife with controversy. There are
opposing views as to whether PAR1 deficiency confers a survival
advantage in endotoxemia, although inconsistencies may be partly
ascribed to differences in endotoxin (LPS) dose.33,34 Studies by
Kuliopulos and coworkers suggest that during progression of
sepsis, PAR1 switches from being a vascular-disruptive receptor to
a vascular-protective receptor and that the beneficial effects of
PAR1 require transactivation of PAR2 (Kaneider et al35). The
protective effects of APC in LPS-induced endotoxemia—believed
to be mediated via PAR1–sphingosine-1-phosphate pathways36—
were evident only after endotoxin exposure. In contrast, others
have observed a beneficial effect of APC (below) even when
administered concurrently with endotoxin.37 The complexity is
enhanced by the observation that PAR1 signaling may be antiinflammatory in endothelial cells and proinflammatory in dendritic
cells.34 These examples highlight the fact that PAR signaling
pathways are important in coagulation and innate immune responses, coregulated, and interdependent. The differential, temporally distinct, and dose-dependent responses of the PARs to a wide
range of proteases, and their complex interactions with an array of
intracellular signaling pathways, reveal both the challenges and the
potential benefits of targeting these for therapeutic purposes.38
Antithrombin
AT plays a key role in protecting against thrombosis, neutralizing
thrombin, and factors IXa, Xa, XIa, and XIIa.4 During sepsis,
decreased hepatic synthesis, more rapid clearance, and neutrophil
elastase degradation cause AT levels to decrease, contributing to a
hypercoagulable state. In vitro, AT interferes with endothelial cell
and monocyte release of cytokines, and the expression of TF and
leukocyte adhesion molecules, and indirectly interferes with platelet aggregation.39 The protective properties of exogenous AT were
observed in several bacterial sepsis and acute lung injury studies in
animals. Unfortunately, phase 3 studies failed to show that AT
could reduce mortality rates in patients with severe sepsis.20
Nonetheless, in concert with other factors or in other diseases, it is
likely that AT does have physiologic importance in modulating the
inflammatory response.
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
The protein C–thrombomodulin mechanism
The protein C (PC) pathway decidedly provides strong evidence of
the interplay between coagulation and inflammation/innate immunity, and underlines the impact of delineating these interactions for
the development of novel therapies (reviewed in Jackson and
Xue40). The major components—activated PC (APC), endothelial
PC receptor (EPCR), protein S (PS), and thrombomodulin (TM)—
each are critically involved in regulating coagulation, inflammation, and the innate immune response.
PC is a circulating zymogen that is activated by thrombin when
complexed with the endothelial protein TM. The resultant APC
inactivates factors Va and VIIIa, enhanced by the cofactor protein S
(PS), and suppresses further thrombin generation (reviewed in Van
de Wouwer et al5). Thrombotic disorders are associated with
defects in PC and PS, and resistance of factor Va to APC. APC has
several means by which it dampens inflammation. It inhibits
expression of TF and the release of proinflammatory cytokines by
monocytes, blocks expression of leukocyte adhesion molecules,
inhibits neutrophil chemotaxis, and is cytoprotective. APC also is
endothelial-barrier protective, an effect that is believed to be
mediated via EPCR-PAR1 signaling that induces release of
sphingosine-1-phosphate.41 Indeed, many of the protective effects
of APC are mediated by binding to EPCR, which positions it for
activation of PAR1, although other receptors, such as ApoER2,
likely also contribute.42 When dissociated from EPCR, APC binds
to PS on activated platelets and endothelial cells where it interferes
with coagulation. When bound to EPCR, APC transmits its
anti-inflammatory and vasculoprotective signals. Thus, EPCR is a
molecular switch for APC in determining whether the latter will
function as an anticoagulant or an anti-inflammatory molecule.
EPCR itself is down-regulated during inflammation by activated
neutrophil PR3-mediated proteolytic degradation,43 again demonstrating bidirectional pathways between coagulation and
inflammation.
APC has entered the clinic, not primarily as an anticoagulant,
but rather to treat patients with severe sepsis where it provides
protection against multiorgan failure.44 Indeed, APC appears to
have a broad range of activities against alarmin-mediated organ
damage, as it has been shown recently in animal models to suppress
hypoxia-induced brain injury, renal ischemia, acute lung injury, and
arthritis.40 Nonetheless, there is considerable controversy as to
whether the beneficial effects of APC, particularly in the setting of
sepsis, are due to its anti-inflammatory or its anticoagulant
properties.45 Moreover, its efficacy in treating severe sepsis in
pediatric populations, or in patients with severe sepsis and a low
risk of death or single organ failure, has not been demonstrated,46
raising questions as to the mechanisms underlying its apparent
restricted utility. The design of mutant forms of APC that dissociate
its anticoagulant and immune-modulating effects, coupled with
greater mechanistic insights into the relevant intracellular signaling
pathways, will hopefully help to clarify some of these issues, and
lead to the development of safer therapies for both hemostatic and
immune disorders.47
A cofactor for the anticoagulant function of APC, deficiency of
PS is associated with a thrombotic diathesis. PS provides a direct
connection between coagulation and innate immunity. Approximately 60% of PS circulates in complex with the complement
component, C4b-binding protein (C4bBP), a cofactor that negatively regulates complement activation. When bound to the C4bBP␤
form, PS loses its anticoagulation cofactor function. In the early
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BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
stages of inflammation, free PS also binds to apoptotic cells
providing a platform for a PS-C4bBP complex that promotes
phagocytosis of apoptotic cells. Interestingly, autoantibodyinduced PS deficiency has been observed in postinfectious purpura
fulminans,48 as well as in patients with systemic lupus erythematosis with excess inflammation.49
TM is expressed by endothelial cells throughout the vasculature
and plays a key role in simultaneously regulating coagulation and
innate immunity. During sepsis or inflammation, TM levels are
down-regulated by cytokines and C5a, and are rendered anticoagulantly inactive by the products of activated neutrophils that oxidize
and degrade the protein. This decreases the generation of the
anticoagulant/anti-inflammatory/cytoprotective APC. Mutations in
mice that diminish the expression and anticoagulant function of
TM result in both a hypercoagulable state and a poor immune
response to endotoxemia.50 Mice lacking the N-terminal lectin-like
domain of TM, which does not regulate coagulation, exhibit
increased sensitivity to tissue damage in models of arthritis, acute
lung injury, sepsis, and ischemia-reperfusion injury, with higher
levels of inflammatory cytokines, increased neutrophil tissue
infiltration, and activation of complement.51 The lectin-like domain
interferes with leukocyte adhesion to endothelial cells, promotes
endothelial cell survival, and suppresses complement activation. It
binds to and agglutinates bacteria, promotes their phagocytosis,52
and interferes with DAMP-PRR interactions.53
TM additionally regulates innate immune responses by acting
as a cofactor for thrombin-mediated generation of the plasma
carboxypeptidase, TAFIa, which inactivates C3a and C5a.54 Finally, TM is expressed by monocytes and dendritic cells, and may
therefore play a role in the pathogenesis of atopy and asthma.55 In
preclinical models, recombinant forms of TM confer protection
against inflammation, ischemia-reperfusion injury, and endotoxemia.51,53,56-58 Sepsis-associated disseminated intravascular coagulation in patients responded beneficially to treatment with recombinant soluble TM, effects that may be attributed to its combined
effects on inflammation and coagulation.59
In view of the wide spectrum of activities of APC, TM, EPCR,
and PS, characterization of the structure-function correlates of each
molecule, their complex interactions with components of the
immune system, and the signaling mechanisms by which they are
regulated are crucial for the development of therapies with greater
specificity and safety.
Fibrin/ogen and plasmin/ogen
Critical for generation of fibrin clots, fibrinogen also plays a role in
innate immunity and may be viewed as a DAMP, as it stimulates
monocyte secretion of several cytokines after engagement with
TLR4.60 Fibrin/ogen interacts directly with integrins on monocytes,
macrophages, neutrophils, and dendritic cells, thereby promoting
diverse proinflammatory responses. Mice deficient in fibrinogen, or
expressing mutant forms, exhibit a dampened inflammatory response in different mouse models (reviewed in Adams et al61).
Fibrin/ogen activation peptides are chemotactic for phagocytic
leukocytes and promote adhesion of immune cells.62,63 The observation that MASP2 converts prothrombin to thrombin on the surface
of bacteria is proposed to be a host immune response to locally
generate immunoreactive, protective fibrin/ogen peptides.64 The
potential value of targeting these pathways in disease requires
further study in vivo.
COAGULATION AND INNATE IMMUNITY
2371
Cross-linking fibrin requires factor XIIIa, generated by thrombin activation of factor XIII, but notably also activated by
MASP1.65 Factor XIIIa also plays a role in innate immune
responses, although the pathways are not fully delineated. It
increases endothelial barrier function, but also enhances leukocyte
adhesion and migration. Factor XIII is also activated intracellularly
in monocytes, where it enhances their phagocytic properties by
altering the cytoskeleton.66 Elastases from activated neutrophils
degrade factor XIIIa, thereby interfering with its functions in
coagulation and inflammation. In vivo studies using a rat sepsis
model support its protective properties in that administration of
factor XIII improves capillary perfusion and reduces leukocyte
adhesion and cytokine release.67
The fibrinolytic system modulates the immune system, is
itself regulated by inflammatory mediators, and is also recruited
by invading pathogens, often at the expense of the host. Indeed,
the finding that several bacteria activate plasminogen (eg,
Staphylococcus aureus, Streptococcus, Yersinia pestis) to help
invade and/or propagate in the host (reviewed in Degen et al68)
may lead to the design of specific strategies to disarm these
harmful organisms.
The 2 major activators of fibrinolysis are urokinase plasminogen activator (uPA), and tissue-type plasminogen activator (tPA).
uPA and its GPI-linked receptor uPAR are expressed by several
blood-borne cells and are up-regulated during infections. uPA
promotes activation of neutrophils, induces discharge of proinflammatory mediators from monocytes,69 and has direct cytolytic
effects on some bacteria. uPAR facilitates leukocyte adhesion and
migration via uPA-dependent and -independent pathways, and
activated neutrophils release a chemotactically active form of
soluble uPAR, thereby amplifying the inflammatory response.
Deficiency of either uPAR or uPA in mice results in reduced
leukocyte recruitment and a dampened inflammatory response in
models of pneumonia and arthritis, respectively.70
tPA also displays properties that extend beyond its wellrecognized role in cleaving plasminogen to plasmin. This is most
evident in the brain, where active tPA is found in parenchymal cells
and interacts with the N-methyl-D-aspartate receptor, low-density
lipoprotein receptor-related protein, and annexin-II receptor, inducing mostly proinflammatory and neurotoxic effects. Increased tPA
activity levels have been linked to neural damage associated with
prion disease. Yet, tPA is also believed to be important for normal
learning and synaptic plasticity, and low levels have been found in
models of neuroinflammation and neurodegeneration (reviewed in
Yepes et al71), underscoring the need for a critical balance to avoid
disease.
Plasmin, like thrombin, has multiple substrates, and thus a wide
spectrum of biologic effects beyond clot lysis, some of which are
mediated via activation of PAR1. The zymogen for plasmin,
plasminogen, binds directly to the extracellular matrix, positioning
plasmin to readily degrade extracellular matrix proteins and
activate matrix metalloproteases, thereby facilitating leukocyte
activation and migration. It is therefore not surprising that plasminogen deficiency in mice is characterized by resistance to inflammatory stimuli, with diminished macrophage migration across extracellular matrix.72
The overwhelming evidence of interplay between innate immune defense mechanisms and essentially all components of the
coagulation/fibrinolytic system compels us to view these as entirely
integrated.
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DELVAEYE and CONWAY
Platelets
Platelets are well recognized for their vital role in maintaining
hemostasis and promoting thrombus growth. They are also critical
players in immune surveillance, a key cellular interface between
coagulation and inflammation. In response to injury and infection,
platelets are rapidly activated and localize to sites of injury and
infection, releasing prothrombotic, proinflammatory, and antimicrobial mediators and bidirectionally interacting with other innate
immune cells (reviewed in Weyrich and Zimmerman73 and Ma and
Kubes74).
Platelets are activated by a range of agonists, PAMPS, and
alarmins, and release factors that target cells of the coagulation,
innate, and adaptive immune systems. Indeed, the list of inflammatory and immune-modulating factors that are secreted by activated
platelets is long, underscoring the vital role of the platelet in
hemostasis and immunity. This includes, among others, chemokines, histamine, serotonin, PDGF, TGF␤, IL-1␤, HMGB1, ADP,
and RANTES, as well as peptides with direct microbicidal
properties.75 For example, the chemokine platelet factor 4 binds to
receptors on neutrophils, triggering their adhesion to immobilized
platelets and enhancing phagocytosis of invading pathogens.
Platelets also display chemokine receptors on their surface, which
allows for simultaneous amplification of the platelet release
response, promoting inflammation and thrombosis.
CD40 ligand (CD40L) is a transmembrane glycoprotein member of the tumor necrosis factor superfamily, expressed by endothelial cells, monocytes, T cells, and most prominently by platelets.
Upon activation, CD40L is translocated to the platelet surface
within seconds, where it remains cell associated, or is cleaved to
yield soluble CD40L. Membrane-bound and soluble forms exert
diverse proinflammatory and prothrombotic effects by binding
mainly to CD40 on the surface of vascular wall and circulating
cells (reviewed in Rizvi et al76). For example, CD40L-CD40
interactions trigger endothelial cells to acquire a prothrombotic
phenotype, with enhanced expression of adhesion molecules and
the release of IL-8, MCP-1, matrix metalloproteases, and reactive
oxygen species. Interactions of platelets with neutrophils and
monocytes may also be mediated by CD40L-CD40 binding,
promoting leukocyte activation, migration, extravasation, and
propagation of the inflammatory reaction. Soluble CD40L also
binds to platelet integrin glycoprotein IIb/IIIa, amplifying platelet
activation in an autocrine fashion. Moreover, via expression of
CD40L, T cells directly contact and activate platelets, inducing
platelet release of RANTES, which further promotes T-cell recruitment.77 CD40L-CD40 signaling has additional well-established
roles in adaptive immunity, being required for immunoglobulin
class switching. Dysregulation of CD40L-CD40 signaling pathways has been implicated in contributing to the development of
autoimmune, inflammatory and thrombotic diseases, and efforts are
under way to further unravel the molecular mechanisms, to identify
potential therapeutic targets, and to assess the role of CD40L as a
biologic marker of disease.76
As with other immune cells, platelets express several PRRs,
including TLRs and complement receptors.78 They store complement regulatory and activating factors,79 and provide a surface for
generation of C3a and the C5b-9 complex. C3a may activate other
platelets, and C5b-9 can catalyze prothrombin conversion to
thrombin.80 It is likely that platelets and procoagulant plateletderived microparticles focus complement and TF to sites of injury,
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
recruiting immune cells to that region, for a rapid and highly
localized inflammatory and procoagulant response.81
TLR2 expression on platelets can be activated by bacteria,
which promotes platelet adhesion/aggregation with release of
reactive oxygen species and expression of P-selectin.82 P-selectin
has several procoagulant and proinflammatory properties. It induces monocyte release of TF-containing microparticles. It acts as
a receptor for C3b,79 further targeting complement activation to
sites of thrombosis and inflammation. Platelet-associated P-selectin
binds to the receptor PSGL-1 on leukocytes, promoting their
adhesion to endothelial cells and aggregation of platelets on
leukocytes. Soluble P-selectin, in murine ischemia-reperfusion
injury models, reduces complement activation, and protects against
organ damage.83 Inhibition of either P-selectin or PSGL-1 dampens
fibrin deposition and reduces leukocyte adhesion (reviewed in
Polgar et al84).
TLR4 activation on platelets also induces platelet binding to
adherent neutrophils, followed by robust neutrophil activation and
the formation of so-called neutrophil extracellular traps,85,86 weblike DNA structures that trap bacteria and yeast, killing them via
release of neutrophil constituents. These fascinating findings,
which provide novel insights into the pathogenesis of acute
respiratory distress syndrome, emphasize the role of platelets—
traditionally viewed as “cells for hemostasis”—in enhancing the
first-line innate immune defense by neutrophils.
As the complex interplay between hemostasis and the innate
immune system as modulated by platelets is further elucidated, it
will impact on our understanding of often serious diseases, raising
the hopes for the development of better therapies. Identifying
which molecular mechanism(s) is more or less important during the
course of a range of diseases will continue to be a challenge,
requiring excellent preclinical models, and carefully designed
clinical trials.
The antiphospholipid syndrome
The interplay between innate immunity and coagulation is evident
in many disease states. The antiphospholipid (aPL) syndrome
(APS) represents one example of a serious disorder, in which recent
elegant studies have provided important new insights into its
pathogenesis that will impact on therapeutic strategies. APS is
characterized by the presence of aPL antibodies in patients with
associated arterial and/or venous thromboses and/or recurrent fetal
loss. One recently proposed paradigm to explain aPL-dependent
fetal loss suggests that the aPL antibody activates complement on
trophoblasts, leading to generation of C5a, which binds to C5aR on
neutrophils. The C5a-activated neutrophils up-regulate TF expression, which itself potentiates inflammation in the decidua with
release of reactive oxygen species, trophoblast injury, and ultimately fetal loss.87 Autoantibodies to EPCR, known to be expressed on the trophoblast surface,88 have also been identified as a
risk factor for APS-associated fetal loss.89 Although not demonstrated, it is possible that these autoantibodies not only interfere
with generation of APC, but also enhance complement activation
on the trophoblast surface. Further studies are necessary to
determine how these findings relate to aPL-associated vascular
thrombosis, as well as the relevance to human disease.
Overall, the observations in this one example of a difficult to
manage, clinical disorder demonstrate the importance of viewing
all thrombotic and inflammatory diseases in the context of both
From www.bloodjournal.org by guest on April 28, 2017. For personal use only.
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
coagulation and inflammation, the end point of which may impact
on therapy selection.
COAGULATION AND INNATE IMMUNITY
2373
grated will provide new directions for the development of many
more effective treatment strategies.
Acknowledgments
Conclusion
We have focused on only a few of the many biochemical and
cellular pathways that link hemostasis and the innate immune
system. Many others exist. For example, we have not explored the
role of the endothelial cell, which maintains hemostatic balance by
variably expressing anticoagulant and procoagulant molecules, yet
is also an active immune cell, expressing PRRs, mediating
leukocyte trafficking, and regulating complement activation. Several shared cell surface and intracellular signaling pathways have
not been mentioned. Despite major advances in our understanding
of the numerous interactions between the systems, patients continue to lack therapies for serious illnesses in which thrombosis and
inflammation coexist. Characterization of APC as more than an
anticoagulant molecule, and its introduction into the clinic to treat
patients with serious sepsis, is only a first step. Viewing the
coagulation and innate immune system pathways as wholly inte-
We thank Dr Marc Hoylaerts for providing valuable suggestions to
improve the quality of this paper.
M.D. was supported in part by the Association for International
Cancer Research (AICR).
Authorship
Contribution: M.D. and E.M.C. equally researched and wrote this
review.
Conflict-of-interest disclosure: E.M.C. holds a patent for use of
the lectin-like domain of thrombomodulin as an anti-inflammatory
agent. M.D. declares no competing financial interests.
Correspondence: Edward M. Conway, Centre for Blood Research, University of British Columbia, Life Sciences Centre, No.
4303, 2350 Health Sciences Mall, Vancouver BC V6T 1Z3,
Canada; e-mail: [email protected].
References
1. Mackman N. The role of tissue factor and factor
VIIa in hemostasis. Anesth Analg. 2009;108(5):
1447-1452.
2. Butenas S, Orfeo T, Mann KG. Tissue factor activity and function in blood coagulation. Thromb
Res. 2008;122(suppl 1):S42-S46.
3. Crawley JT, Lane DA. The haemostatic role of
tissue factor pathway inhibitor. Arterioscler
Thromb Vasc Biol. 2008;28(2):233-242.
4. Rau JC, Beaulieu LM, Huntington JA, Church FC.
Serpins in thrombosis, hemostasis and fibrinolysis. J Thromb Haemost. 2007;5(suppl 1):102-115.
agulation. Trends Biochem Sci. 2002;27(2):6774.
16. Opal SM, Esmon CT. Bench-to-bedside review:
functional relationships between coagulation and
the innate immune response and their respective
roles in the pathogenesis of sepsis. Crit Care.
2003;7(1):23-38.
17. Busso N, Chobaz-Peclat V, Hamilton J, Spee P,
Wagtmann N, So A. Essential role of platelet activation via protease activated receptor 4 in tissue
factor-initiated inflammation. Arthritis Res Ther.
2008;10(2):R42. http://arthritis-research.com/
content/10/2/R42. Accessed June 2009.
26.
27.
28.
5. Van de Wouwer M, Collen D, Conway EM.
Thrombomodulin-Protein C-EPCR System: integrated to regulate coagulation and inflammation.
Arterioscler Thromb Vasc Biol. 2004;24(8):13741383.
18. Pawlinski R, Pedersen B, Schabbauer G, et al.
Role of tissue factor and protease-activated receptors in a mouse model of endotoxemia. Blood.
2004;103(4):1342-1347.
6. Mogensen TH. Pathogen recognition and inflammatory signaling in innate immune defenses. Clin
Microbiol Rev. 2009;22(2):240-273.
19. Sharma L, Melis E, Hickey MJ, et al. The cytoplasmic domain of tissue factor contributes to leukocyte recruitment and death in endotoxemia.
Am J Pathol. 2004;165(1):331-340.
30.
20. Abraham E, Reinhart K, Opal S, et al. Efficacy
and safety of tifacogin (recombinant tissue factor
pathway inhibitor) in severe sepsis: a randomized
controlled trial. JAMA. 2003;290(2):238-247.
31.
7. Beutler BA. TLRs and innate immunity. Blood.
2009;113(7):1399-1407.
8. Bianchi ME. DAMPs, PAMPs and alarmins: all we
need to know about danger. J Leukoc Biol. 2007;
81(1):1-5.
9. Sjöberg AP, Trouw LA, Blom AM. Complement
activation and inhibition: a delicate balance.
Trends Immunol. 2009;30(2):83-90.
10. Huber-Lang M, Sarma JV, Zetoune FS, et al.
Generation of C5a in the absence of C3: a new
complement activation pathway. Nat Med. 2006;
12(6):682-687.
11. Noris M, Remuzzi G. Hemolytic uremic syndrome. J Am Soc Nephrol. 2005;16(4):10351050.
12. Iwanaga S, Lee BL. Recent advances in the innate immunity of invertebrate animals. J Biochem
Mol Biol. 2005;38(2):128-150.
13. Iwanaga S. The molecular basis of innate immunity in the horseshoe crab. Curr Opin Immunol.
2002;14(1):87-95.
14. Zhu Y, Thangamani S, Ho B, Ding JL. The ancient
origin of the complement system. EMBO J. 2005;
24(2):382-394.
15. Krem MM, Di Cera E. Evolution of enzyme cascades from embryonic development to blood co-
21. Drake WT, Lopes NN, Fenton JW II, Issekutz AC.
Thrombin enhancement of interleukin-1 and tumor necrosis factor-alpha induced polymorphonuclear leukocyte migration. Lab Invest. 1992;
67(5):617-627.
22. Fujita T, Yamabe H, Shimada M, et al. Thrombin
enhances the production of monocyte chemoattractant protein-1 and macrophage inflammatory
protein-2 in cultured rat glomerular epithelial
cells. Nephrol Dial Transplant. 2008;23(11):34123417.
23. Wadgaonkar R, Somnay K, Garcia JG. Thrombin
induced secretion of macrophage migration inhibitory factor (MIF) and its effect on nuclear signaling in endothelium. J Cell Biochem. 2008;
105(5):1279-1288.
24. Clark A, Weymann A, Hartman E, et al. Evidence
for non-traditional activation of complement factor
C3 during murine liver regeneration. Mol Immunol. 2008;45(11):3125-3132.
25. Naldini A, Aarden L, Pucci A, Bernini C, Carraro F.
Inhibition of interleukin-12 expression by alphathrombin in human peripheral blood mononuclear
29.
32.
33.
34.
35.
36.
cells: a potential mechanism for modulating Th1/
Th2 responses. Br J Pharmacol. 2003;140(5):
980-986.
Feistritzer C, Riewald M. Endothelial barrier protection by activated protein C through PAR1-dependent sphingosine 1-phosphate receptor-1
crossactivation. Blood. 2005;105(8):3178-3184.
Krupiczojc MA, Scotton CJ, Chambers RC. Coagulation signalling following tissue injury: focus
on the role of factor Xa. Int J Biochem Cell Biol.
2008;40(6-7):1228-1237.
Sutherland MR, Friedman HM, Pryzdial EL. Herpes simplex virus type 1-encoded glycoprotein C
enhances coagulation factor VIIa activity on the
virus. Thromb Haemost. 2004;92(5):947-955.
Matsushita K, Imamura T, Tomikawa M,
Tancharoen S, Tatsuyama S, Maruyama I. DX9065a inhibits proinflammatory events induced by
gingipains and factor Xa. J Periodontal Res.
2006;41(2):148-156.
Shpacovitch V, Feld M, Hollenberg MD, Luger TA,
Steinhoff M. Role of protease-activated receptors
in inflammatory responses, innate and adaptive
immunity. J Leukoc Biol. 2008;83(6):1309-1322.
Trivedi V, Boire A, Tchernychev B, et al. Platelet
matrix metalloprotease-1 mediates thrombogenesis by activating PAR1 at a cryptic ligand site.
Cell. 2009;137(2):332-343.
Rallabhandi P, Nhu QM, Toshchakov VY, et al.
Analysis of proteinase-activated receptor 2 and
TLR4 signal transduction: a novel paradigm for
receptor cooperativity. J Biol Chem. 2008;
283(36):24314-24325.
Camerer E, Cornelissen I, Kataoka H, Duong DN,
Zheng YW, Coughlin SR. Roles of protease-activated receptors in a mouse model of endotoxemia. Blood. 2006;107(10):3912-3921.
Niessen F, Schaffner F, Furlan-Freguia C, et al.
Dendritic cell PAR1-S1P3 signalling couples coagulation and inflammation. Nature.
2008;452(7187):654-658.
Kaneider NC, Leger AJ, Agarwal A, et al. ‘Role
reversal’ for the receptor PAR1 in sepsis-induced
vascular damage. Nat Immunol. 2007;8(12):
1303-1312.
Niessen F, Furlan-Freguia C, Fernandez JA, et al.
Endogenous EPCR/aPC-PAR1 signaling prevents inflammation-induced vascular leakage and
lethality. Blood. 2009;113(12):2859-2866.
From www.bloodjournal.org by guest on April 28, 2017. For personal use only.
2374
DELVAEYE and CONWAY
37. Kerschen EJ, Fernandez JA, Cooley BC, et al.
Endotoxemia and sepsis mortality reduction by
non-anticoagulant activated protein C. J Exp
Med. 2007;204(10):2439-2448.
38. Kahn ML. Counteracting clotting in sepsis. Nat
Med. 2008;14(9):918-919.
39. Wiedermann C, Romisch J. The antiinflammatory actions of antithrombin–a review.
Acta Med Austriaca. 2002;29(3):89-92.
40. Jackson CJ, Xue M. Activated protein C: an anticoagulant that does more than stop clots. Int
J Biochem Cell Biol. 2008;40(12):2692-2697.
41. Riewald M, Petrovan RJ, Donner A, Ruf W. Activated protein C signals through the thrombin receptor PAR1 in endothelial cells. J Endotoxin
Res. 2003;9(5):317-321.
42. Yang XV, Banerjee Y, Fernandez JA, et al. Activated protein C ligation of ApoER2 (LRP8)
causes Dab1-dependent signaling in U937 cells.
Proc Natl Acad Sci U S A. 2009;106(1):274-279.
43. Villegas-Mendez A, Montes R, Ambrose LR,
Warrens AN, Laffan M, Lane DA. Proteolysis of
the endothelial cell protein C receptor by neutrophil proteinase 3. J Thromb Haemost. 2007;5(5):
980-988.
44. Bernard GR. Drotrecogin alfa (activated) (recombinant human activated protein C) for the treatment of severe sepsis. Crit Care Med. 2003;
31(3):S85-S93.
45. Levi M. Activated protein C in sepsis: a critical
review. Curr Opin Hematol. 2008;15(5):481-486.
46. Nadel S, Goldstein B, Williams MD, et al. Drotrecogin alfa (activated) in children with severe
sepsis: a multicentre phase III randomised controlled trial. Lancet. 2007;369(9564):836-843.
47. Mosnier LO, Zlokovic BV, Griffin JH. The cytoprotective protein C pathway. Blood. 2007;109(8):
3161-3172.
48. Regnault V, Boehlen F, Ozsahin H, et al. Antiprotein S antibodies following a varicella infection: detection, characterization and influence on
thrombin generation. J Thromb Haemost. 2005;
3(6):1243-1249.
49. Rezende SM, Simmonds RE, Lane DA. Coagulation, inflammation, and apoptosis: different roles
for protein S and the protein S-C4b binding protein complex. Blood. 2004;103(4):1192-1201.
50. Weiler H, Lindner V, Kerlin B, et al. Characterization of a mouse model for thrombomodulin deficiency. Arterioscler Thromb Vasc Biol. 2001;
21(19):1531-1537.
51. Van de Wouwer M, Plaisance S, DeVries A, et al.
The lectin-like domain of thrombomodulin interferes with complement activation and protects
against arthritis. J Thromb Haemost. 2006;4(8):
1813-1824.
52. Shi CS, Shi GY, Hsiao SM, et al. Lectin-like domain of thrombomodulin binds to its specific ligand Lewis Y antigen and neutralizes lipopolysaccharide-induced inflammatory response.
Blood. 2008;112(90):3661-3670.
53. Abeyama K, Stern DM, Ito Y, et al. The N-terminal
domain of thrombomodulin sequesters high-mobility group-B1 protein, a novel antiinflammatory
mechanism. J Clin Invest. 2005;115(5):12671274.
54. Myles T, Nishimura T, Yun TH, et al. Thrombin
activatable fibrinolysis inhibitor: a potential regulator of vascular inflammation. J Biol Chem. 2003;
278(51):51059-51067.
55. Yerkovich ST, Roponen M, Smith ME, et al.
Allergen-enhanced thrombomodulin (blood den-
BLOOD, 17 SEPTEMBER 2009 䡠 VOLUME 114, NUMBER 12
dritic cell antigen 3, CD141) expression on dendritic cells is associated with a TH2-skewed immune response. J Allergy Clin Immunol. 2009;
123(1):209-216.
56. Ikeguchi H, Maruyama S, Morita Y, et al. Effects
of human soluble thrombomodulin on experimental glomerulonephritis. Kidney Int. 2002;61(2):
490-501.
57. Geudens N, Van de Wouwer M, Banaudenaerde
B, et al. The lectin-like domain of thrombomodulin
protects against ischemia-reperfusion lung injury.
Eur Resp Journal. 2008;32(4):862-870.
58. Sharfuddin AA, Sandoval RM, Berg DT, et al.
Soluble thrombomodulin protects ischemic kidneys. J Am Soc Nephrol. 2009;20(3):524-534.
59. Saito H, Maruyama I, Shimazaki S, et al. Efficacy
and safety of recombinant human soluble thrombomodulin (ART-123) in disseminated intravascular coagulation: results of a phase III, randomized, double-blind clinical trial. J Thromb
Haemost. 2007;5(1):31-41.
72.
73.
74.
75.
76.
77.
60. Smiley ST, King JA, Hancock WW. Fibrinogen
stimulates macrophage chemokine secretion
through toll-like receptor 4. J Immunol. 2001;
167(5):2887-2894.
61. Adams RA, Schachtrup C, Davalos D, Tsigelny I,
Akassoglou K. Fibrinogen signal transduction as
a mediator and therapeutic target in inflammation:
lessons from multiple sclerosis. Curr Med Chem.
2007;14(27):2925-2936.
62. Kay AB, Pepper DS, McKenzie R. The identification of fibrinopeptide B as a chemotactic agent
derived from human fibrinogen. Br J Haematol.
1974;27(4):669-677.
63. Flick MJ, Du X, Witte DP, et al. Leukocyte engagement of fibrin(ogen) via the integrin receptor
alphaMbeta2/Mac-1 is critical for host inflammatory response in vivo. J Clin Invest. 2004;113(11):
1596-1606.
78.
79.
80.
81.
64. Krarup A, Wallis R, Presanis JS, Gal P, Sim RB.
Simultaneous activation of complement and coagulation by MBL-associated serine protease 2.
PLoS ONE. 2007;2:e623. http://www.plosone.org/
article/info%3Adoi%2F10.1371%2Fjournal.pone.
0000623. Accessed June 2009.
82.
65. Hajela K, Kojima M, Ambrus G, et al. The biological functions of MBL-associated serine proteases
(MASPs). Immunobiology. 2002;205(4-5):467475.
83.
66. Sárváry A, Szucs S, Balogh I, et al. Possible role
of factor XIII subunit A in Fcgamma and complement receptor-mediated phagocytosis. Cell Immunol. 2004;228(2):81-90.
67. Birnbaum J, Hein OV, Luhrs C, et al. Effects of
coagulation factor XIII on intestinal functional
capillary density, leukocyte adherence and mesenteric plasma extravasation in experimental endotoxemia. Crit Care. 2006;10(1):R29. http://
ccforum.com/content/10/1/R29. Accessed June
2009.
68. Degen JL, Bugge TH, Goguen JD. Fibrin and fibrinolysis in infection and host defense. J Thromb
Haemost. 2007;5(suppl 1):24-31.
69. Mondino A, Blasi F. uPA and uPAR in fibrinolysis,
immunity and pathology. Trends Immunol. 2004;
25(8):450-455.
70. Rijneveld AW, Levi M, Florquin S, Speelman P,
Carmeliet P, van Der Poll T. Urokinase receptor is
necessary for adequate host defense against
pneumococcal pneumonia. J Immunol. 2002;
168(7):3507-3511.
71. Yepes M, Roussel BD, Ali C, Vivien D. Tissue-
84.
85.
86.
87.
88.
89.
type plasminogen activator in the ischemic brain:
more than a thrombolytic. Trends Neurosci. 2009;
32(1):48-55.
Gong Y, Hart E, Shchurin A, Hoover-Plow J. Inflammatory macrophage migration requires
MMP-9 activation by plasminogen in mice. J Clin
Invest. 2008;118(9):3012-3024.
Weyrich AS, Zimmerman GA. Platelets: signaling
cells in the immune continuum. Trends Immunol.
2004;25(9):489-495.
Ma AC, Kubes P. Platelets, neutrophils, and neutrophil extracellular traps (NETs) in sepsis.
J Thromb Haemost. 2008;6(3):415-420.
von Hundelshausen P, Koenen RR, Weber C.
Platelet-mediated enhancement of leukocyte adhesion. Microcirculation. 2009;16(1):84-96.
Rizvi M, Pathak D, Freedman JE, Chakrabarti S.
CD40-CD40 ligand interactions in oxidative
stress, inflammation and vascular disease.
Trends Mol Med. 2008;14(12):530-538.
Danese S, de la Motte C, Reyes BM, Sans M,
Levine AD, Fiocchi C. Cutting edge: T cells trigger
CD40-dependent platelet activation and granular
RANTES release: a novel pathway for immune
response amplification. J Immunol. 2004;172(4):
2011-2015.
Andonegui G, Kerfoot SM, McNagny K, Ebbert
KV, Patel KD, Kubes P. Platelets express functional Toll-like receptor-4. Blood. 2005;106(7):
2417-2423.
Del Conde I, Cruz MA, Zhang H, Lopez JA,
Afshar-Kharghan V. Platelet activation leads to
activation and propagation of the complement
system. J Exp Med. 2005;201(6):871-879.
Wiedmer T, Esmon CT, Sims PJ. Complement
proteins C5b-9 stimulate procoagulant activity
through platelet prothrombinase. Blood. 1986;
68(4):875-880.
Yin W, Ghebrehiwet B, Peerschke EI. Expression
of complement components and inhibitors on
platelet microparticles. Platelets. 2008;19(3):225233.
Blair P, Rex S, Vitseva O, et al. Stimulation of Tolllike receptor 2 in human platelets induces a
thromboinflammatory response through activation of phosphoinositide 3-kinase. Circ Res. 2009;
104(3):346-354.
Kyriakides C, Woodcock SA, Wang Y, et al.
Soluble P-selectin moderates complementdependent reperfusion injury of ischemic skeletal
muscle. Am J Physiol Cell Physiol. 2000;279(2):
C520-C528.
Polgar J, Matuskova J, Wagner DD. The Pselectin, tissue factor, coagulation triad. J Thromb
Haemost. 2005;3(8):1590-1596.
Clark SR, Ma AC, Tavener SA, et al. Platelet
TLR4 activates neutrophil extracellular traps to
ensnare bacteria in septic blood. Nat Med. 2007;
13(4):463-469.
Brinkmann V, Reichard U, Goosmann C, et al.
Neutrophil extracellular traps kill bacteria. Science. 2004;303(5663):1532-1535.
Girardi G, Berman J, Redecha P, et al. Complement C5a receptors and neutrophils mediate fetal
injury in the antiphospholipid syndrome. J Clin
Invest. 2003;112(11):1644-1654.
Li W, Zheng X, Gu JM, et al. Extra-embryonic expression of EPCR is essential for embryonic viability. Blood. 2005;106(8):2716-2722.
Hurtado V, Montes R, Gris JC, et al. Autoantibodies against EPCR are found in antiphospholipid
syndrome and are a risk factor for fetal death.
Blood. 2004;104(5):1369-1374.
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2009 114: 2367-2374
doi:10.1182/blood-2009-05-199208 originally published
online July 7, 2009
Coagulation and innate immune responses: can we view them
separately?
Mieke Delvaeye and Edward M. Conway
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