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Mechanism of aPL-induced TF increase and fetal death. APL antibodies are preferentially targeted to the placenta where they activate complement leading to the generation of potent anaphylatoxin C5a. C5a attracts and activates neutrophils. As a result of C5a-C5aR interaction, neutrophils express TF. TF on neutrophils contribute to oxidative burst and subsequent trophoblast injury and ultimately fetal death.
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Fetal loss in patients with antiphospholipid (aPL) antibodies has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically activation of complement with generation of the anaphylotoxin C5a, is an essential trigger of fetal injury. In this study, we analyzed the role of the procoagulant molecule tissue...
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... this study, we demonstrate that TF expression on neutrophils is an important effector molecule in fetal injury induced by aPL antibodies. We found that binding of C5a to its receptor induces TF expression in neutrophils. Importantly, TF contributes to the oxidative burst and thus enhances decidual damage that leads to pregnancy loss in APS. Mice that received aPL-IgG showed increased TF expression throughout the decidual tissue and on embryonic debris. This higher TF expression was not associated with either fibrin deposition or thrombi formation in deciduas from aPL-treated mice. We have previously shown that anticoagulants, such as hirudin or fondaparinux, do not prevent pregnancy loss in our mouse APS model, suggesting that thrombosis is not the cause of fetal death in this model. 32 These data, together with theobservation that there is no increase in fibrin deposition or detectable thrombi in deciduas from aPL-treated mice, support the idea that TF promotes fetal loss not by inducing thrombus formation but by enhancing inflammation. Our results are consistent with previous reports that demonstrate TF enhances inflammation in a model of crescentic glomerulonephritis in a fibrin-independent manner. 17 In addition, the death of embryos lacking the anticoagulant protein thrombomodulin is associated with increased TF expression without fibrin deposition or thrombosis. The death of the embryos appears to be due to growth arrest of trophoblast cells. 33 These studies indicate that TF increases inflammation in different models. We demonstrated that blockade of TF or reducing TF expression has protective effect in aPL-induced pregnancy loss. Reduced levels of TF not only rescue pregnancies in aPL-treated mice but also diminish inflammation. Less decidual inflammation (fewer neutrophils and less C3 deposition) and increased embryo survival are observed in aPL-treated low TF–expressing mice and mice that were treated with aPL plus anti-TF Ab. These observations suggest that TF is a proinflammatory molecule in aPL-induced pregnancy loss. Blockade of TF has been shown to limit inflammation and tissue injury in other in vivo studies. Anti-TF antibody attenuated septic shock, 34 and antisense TF mRNA suppressed leukocyte adhesion and coagulation-dependent inflammation in renal and hepatic ischemia reperfusion injury. 35 Furthermore, low TF mice are protected from endotoxemia and renal failure and neutrophil accumulation and show lower levels of chemokines after ischemia reperfusion. 36,37 We previously demonstrated that complement activation is an essential intermediate in aPL-induced pregnancy loss. 19,20 Here, we found that aPL-induced TF expression depends on complement activation. Antibodies that bind to trophoblasts but do not activate the complement system (FD1) neither induce TF increase nor induce fetal damage, suggesting that direct binding of aPL is not enough to modulate TF expression and cause fetal demise. Only aPL antibodies that cause complement activation (FB1) induce TF expression and fetal death. Moreover, complement inhibition with Crry-Ig prevented aPL-induced TF increase and fetal injury in this model. We identified the complement components that are required to induce TF expression. Poor pregnancy and increased decidual TF expression were observed in C3aR- and C6-deficient mice, indicating that neither C3a nor the MAC is required for fetal damage. On the other hand, C5aR-deficient mice were protected from pregnancy loss and no increased TF expression was observed in the deciduas of these mice, indicating that the proinflammatory sequelae of C5a-C5aR is critical for TF expression and fetal death induced by aPL antibodies. C5a is an anaphylotoxin that recruits and activates neutrophils. We have previously shown that neutrophils are required for aPL-induced pregnancy loss. In mice depleted of neutrophils, administration of aPL did not cause fetal loss. Similarly, induction of TF expression was prevented by neutrophil depletion. These data indicate that induction of TF expression is downstream of complement activation and neutrophil recruitment. We demonstrated by flow cytometry that neutrophils from aPL-treated mice express TF and that this process is dependent on C5a-C5aR interaction. These results are consistent with the reported studies by Ritis et al, who recently demonstrated by in vitro experiments that aPL-induced complement activation and downstream signaling via C5a receptors in human neutrophils lead to the induction of TF expression in neutrophils. 6 We have shown that neutrophils play a key role in aPL antibody–induced fetal loss. In contrast, monocytes do not contribute to fetal loss. Experiments performed using low TF females mated with wild-type males and TF floxed/floxed /LysMCre mice allowed us to distinguish the role of trophoblasts TF from that of myeloid cells TF. The protection from aPL-induced pregnancy loss observed in both of these mice emphasizes the crucial role of TF in maternal neutrophils. Experiments performed using TF floxed/floxed /LysM-Cre mice that do not express TF on neutrophils confirmed that the neutrophil is the pathologic site of TF expression in aPL-induced fetal injury. TF floxed/floxed / LysM-Cre mice were protected from aPL-induced fetal damage. Normal pregnancies and diminished decidual TF expression and inflammation were observed in aPL-treated TF floxed/floxed / LysM-Cre mice, suggesting that TF expression on neutrophils modulates the ability of neutrophils to induce tissue damage. Importantly, we demonstrate that TF expression on neutrophils contributes to the production of ROSs, potent effector molecules of inflammatory fetal injury. We showed that TF expression on neutrophils is required for oxidative burst induced in response to aPL antibodies. This is consistent with the enhanced oxidative stress found in deciduas from aPL-treated mice. In aPL-treated mice, increased superoxide production in decidual tissue and fetal demise were observed. TF floxed/floxed /LysM-Cre mice that do not express TF on neutrophils in response to aPL did not show oxidative stress in deciduas and pregnancies were protected. In addition, low TF mice treated with aPL did not show signs of oxidative stress in the deciduas and embryo survival. Enhancement of ROS production by TF was also found in human macrophages in vitro and in vivo in rabbit peritoneal macrophages. 38 It has been described that binding of TF to factor VIIa results in proinflamma- tory changes in human macrophages in vitro and that anti-TF antibodies attenuated ROS production in rabbit peritoneal macrophages in vivo. 39 Binding of FVIIa to TF enhances LPS induction of proinflammatory genes expression in monocyte-derived macrophages. 39 This amplification loop of leukocyte activation and recruitment may also account for the proinflammatory effects of TF observed in aPL-induced fetal injury. In addition, TF has been shown to enhance cell survival of baby hamster kidney cells. 40 Another study showed that C5a delayed neutrophil apoptosis and enhanced organ injury in a rat model of sepsis. 41 This is another possible mechanism by which aPL-induced TF expression in neutrophils may enhance neutrophil survival and exacerbate fetal injury. Collectively, our study demonstrates that TF expression on neutrophils is essential in the pathogenesis of aPL-induced fetal loss and reveals a functional linkage among C5a, neutrophil activation, and fetal injury. We propose that complement activation is initiated by aPL-IgG binding to trophoblasts and leads to generation of the anaphylatoxin C5a, which attracts and activates neutrophils through C5aR (Figure 7). The engagement of the neutrophil C5a-C5aR pathway results in neutrophil TF expression. TF expression enhances neutrophil oxidative burst leading to decidual injury and fetal death. Although we have used a mouse model, we believe that the finding that neutrophil TF is an important effector in aPL-induced inflammation may allow the development of new therapies to abrogate theinflammatory loop caused by TF and improve pregnancy outcomes in patients with ...
Citations
... Mutations in complement-related genes result in abnormal activation of the alternative complement pathway [165]. C5a produced from an abnormally activated alternative complement pathway acts on leukocytes to express tissue factor and induce a coagulation reaction [166], and C5b-9 acts on activated platelets and activated endothelial cells. Phosphatidylserine is exposed on the outside of the cell membrane of endothelial cells, on which the prothrombinase complex is formed, promoting the coagulation reaction and producing large amounts of thrombin [167]. ...
Platelets play an important role in hemostasis, and a low platelet count usually increases the risk of bleeding. Conditions in which thrombosis occurs despite low platelet counts are referred to as thrombosis with thrombocytopenia syndrome, including heparin-induced thrombocytopenia, vaccine-induced immune thrombotic thrombocytopenia, paroxysmal nocturnal hemoglobinuria, antiphospholipid syndrome, thrombotic microangiopathy (TMA), and disseminated intravascular coagulation. TMA includes thrombotic thrombocytopenic purpura, Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome (HUS), and atypical HUS. Patients with these pathologies present with thrombosis and consumptive thrombocytopenia associated with the activation of platelets and the coagulation system. Treatment varies from disease to disease, and many diseases have direct impacts on mortality and organ prognosis if therapeutic interventions are not promptly implemented. Underlying diseases and the results of physical examinations and general laboratory tests as part of a thorough workup for patients should promptly lead to therapeutic intervention before definitive diagnosis. For some diseases, the diagnosis and initial treatment must proceed in parallel. Utilization of not only laboratory tests but also various scoring systems is important for validating therapeutic interventions based on clinical information.
... A complete blood count, signs and symptoms of bleeding, and a comprehensive metabolic panel that assesses albumin, total bilirubin, serum creatinine, and liver function tests are additional general monitoring markers. 44,[45][46][47][48] ...
... When managing DOAC medication, three categories of drug interactions must be considered: (1) medicines that alter renal clearance, (2) agents that affect hepatic clearance, and (3) agents that concurrently affect hemostasis. 46,47,[48][49][50][51][52][53] ...
Traditionally, heparin was given to patients who needed parenteral anticoagulation, while warfarin was given to patients who needed oral anticoagulation. There has been a push to create newer, more potent anticoagulants because of warfarin's limited therapeutic index and the requirement for regular laboratory monitoring. For the prevention and treatment of thrombosis, anticoagulants continue to be the principal approach. Since direct thrombin inhibitors are usually saved for patients who need intervention or who have complications, unfractionated heparin, low molecular weight heparin, and warfarin have all been thoroughly studied and used. As a result of their improved pharmacodynamic profiles and ease of use, novel oral anticoagulants are predicted to supplant older ones once they emerge from clinical development. Of all the side effects of anticoagulants, bleeding is the most worrying. Anticoagulant pharmacology, dosage, and toxicity are widely used, so clinicians must be well-versed in these areas.
... Thrombotic and non-thrombotic mechanisms acting on both the maternal and fetal side of the placenta can be observed in obAPS (Fig. 1, panel A) [11][12][13][14][15][16][17][18][19][20]. Maternal immune response takes place during a normal pregnancy, but acute inflammation is not physiological; in obAPS, inflammatory events are numerous and occur early in pregnancy, suggesting their driving role in the development of placental insufficiency (Fig. 1, panel B) [19,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. ...
... ApoER2 can interact with b2GPI and serve as a receptor for anti-b2GPI-b2GPI complexes, which in turn are able to activate endothelial cells [35,36]. Innate immunity seems to play a role in the early stages with complement activation [19,[27][28][29][30] and neutrophils recruitment with formation of NETs [38][39][40]. Autophagy induced by the dysfunction of endothelial mitochondria has been suggested as additional mechanism [21]. ...
This review focuses on the management of reproductive issues in women who have antiphospholipid syndrome (APS) or are carriers of antiphospholipid antibodies (aPL). The importance of aPL detection during preconception counselling relies on their pathogenic potential for placental insufficiency and related obstetric complications. The risk of adverse pregnancy outcomes can be minimized by individualized risk stratification and tailored treatment aimed at preventing placental insufficiency. Combination therapy of low-dose acetylsalicylic acid and heparin is the mainstay of prophylaxis during pregnancy; immunomodulation, especially with hydroxychloroquine, should be considered in refractory cases. Supplementary ultrasound surveillance is useful to detect fetal growth restriction and correctly tailor the time of delivery. The individual aPL profile must be considered in the stratification of thrombotic risk, such as during assisted reproduction techniques requiring hormonal ovarian stimulation or during the follow-up after pregnancy in order to prevent the first vascular event.
... This is opposed to the direct effects of anaphylatoxins described on leukocytes; for example, C5a was shown to trigger tissue factor expression on neutrophils in models of antiphospholipid syndrome. 7 Furthermore, the authors show quiescent platelets lack C3a and C5a receptors, further arguing against a role for anaphylatoxins in the initiation of platelet activation. ...
... C5a is found to be elevated in serum of patients suffering from inflammatory disorders. It is noteworthy that persistent stimulation of the proinflammatory signaling axes of C5a plays a significant role in the onset and progression of several autoimmune, inflammatory, and neuronal diseases (Fig. 12) like rheumatoid arthritis [135][136][137], respiratory distress syndrome [138], inflammatory bowel disease [139], Crohn's disease [140,141], glomerulonephritis [142,143], Bullous pemphigoid [144,145], ischemia/reperfusion injury [146], chronic obstructive pulmonary disease (COPD) [147], sepsis [148,149], multiple sclerosis [150], asthma [151], allergy [152], atherosclerosis [153,154], xenograft rejection [155,156], hemorrhagic shock [157], and antiphospholipid syndrome [158,159]. ...
The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.
... 10 Complement activation by APLA leads to generation of the anaphylotoxin C5a, which recruits monocytes and neutrophils, activates endothelial cells and induces expression of tissue factor. 11 We report a case of a 32-year-old female diagnosed to have celiac artery and splenic artery thrombosis which developed as a complication of APS. Prompt and timely management with IV anticoagulants, oral warfarin and antiplatelets encouraged successful treatment. ...
Antiphospholipid syndrome (APS) is an autoantibody mediated acquired thrombophilia characterized by recurrent arterial or venous thrombosis and or pregnancy morbidity. We describe a case of 32-year-old female who had a medical history of APLA presented with complaints of abdominal pain for 20 days. On evaluation, CT abdomen contrast revealed celiac and splenic artery thrombosis. She was successfully treated with IV unfractionated heparin, warfarin and antiplatelets.
... Although many studies reported the roles of immune cells in maternal-fetal immunity (15), the contribution of neutrophils is often overlooked. In recent years, the involvement of neutrophils and their subpopulations, especially the LDG, in pregnancy is being discovered, but it is still rarely reported in SA (16)(17)(18). In this study, we first observed that LDG percentage in PBMCs and DICs increases in normal pregnancy, while the loss of this increase is associated with SA. ...
Spontaneous abortion (SA) is a common adverse pregnancy event with unclarified pathogenesis and limited therapeutic efficiency. Although most SA cases with the euploid embryo(s) are associated with immunological factors, the contribution of low-density granulocyte (LDG) in SA pathogenesis is rarely reported. This study aimed to investigate the serial characteristics and possible contribution of LDG and their subpopulations in early pregnancy, especially in early SA. Unpregnant (UP), normally pregnant (NP), and SA women were recruited, and the peripheral blood and endometrium/decidua were collected for LDG isolation and histological observation. The percentage, phenotype, and subpopulations of LDG were analyzed via flow cytometric analysis, and the ability of Nets formation was assessed by immunofluorescent and immunohistochemical assays. As a result, 43 participants were enrolled, including 10 UP, 15 NP, and 18 SA women. Compared with the UP group, the LDG percentage in peripheral blood mononuclear cells (PBMCs) and decidual immune cells (DICs) increased in the NP group, while the loss of this increase was observed in the SA group. Meanwhile, CD16int/− cell percentage in peripheral blood LDG (PB-LDG) increased in the NP and SA groups, and insufficient activation of CD16hi PB-LDG characterized by reduced CD11b expression was discovered in the SA group. Moreover, the LDG percentage in DICs was higher than that in PBMCs, and the decidual LDG (D-LDG) showed a surface marker expression profile that is easier to be activated in the pregnant cohort (NP + SA women). Finally, increased decidual Nets formation was observed in the SA group compared with the NP group, and more Nets formation was detected in D-LDG of NP and SA women following PMA stimulation. Overall, LDG participates in the maintenance of early pregnancy, while dysregulated LDG is responsible for early SA, providing novel potential targets for further exploration of SA pathogenesis and therapeutics.
... The culmination of these (and other related events) is trophoblastic injury and fetal loss. The pathogenicity of C5a, and its potent ability to induce prothrombotic conditions within the deciduas, was confirmed when it was shown that C6 deficient mice had a similar rate of pregnancy loss as wildtype mice, 170 and therefore that the consequences of C5b-9 generation are insignificant in this model. ...
During pregnancy, the maternal host must adapt in order to enable growth of the fetus. These changes affect all organ systems and are designed both to protect the fetus and to minimize risk to the mother. One of the most prominent adaptations involves the immune system. The semi‐allogenic fetoplacental unit has non‐self components and must be protected against attack from the host. This requires both attenuation of adaptive immunity and protection from innate immune defense mechanisms. One of the key innate immune players is complement, and it is important that the fetoplacental unit is not identified as non‐self and subjected to complement attack. Adaptation of the complement response must, however, be managed in such a way that maternal protection against infection is not compromised. As the complement system also plays a significant facilitating role in many of the stages of a normal pregnancy, it is also important that any necessary adaptation to accommodate the semi‐allogenic aspects of the fetoplacental unit does not compromise this. In this review, both the physiological role of the alternative pathway of complement in facilitating a normal pregnancy, and its detrimental participation in pregnancy‐specific disorders, are discussed.
... Antiphospholipid syndrome (APS) is characterised by thrombosis and/or pregnancy morbidity with persistent antiphospholipid antibodies (aPL), and is commonly associated with systemic lupus erythematosus (SLE) [1]. APS is characterised by a prothrombotic and proinflammatory cytokine profile [1], and neutrophil activation and placental inflammation contributing to placental injury and fetal loss [1][2][3]. Platelet activation and platelet-leucocyte aggregates (PLAs) are increased in APS [4], but their contribution to pregnancy complications is unclear. Platelets promote coagulation by providing a catalytic procoagulant surface and amplifying thrombin generation [5,6]. ...
... We show that pregnancy in patients with secondary APS is characterised by platelet and neutrophil activation with increased procoagulant activity, despite standard of care therapy with LMWH and aspirin. Neutrophil activation and neutrophil infiltration of the trophoblast is a hallmark of APS [2,3,8]. We demonstrate that neutrophils in APS are procoagulant, which may contribute to placenta-mediated pregnancy complications. ...
... However, in our study platelet activation was not associated with neutrophil activation in PCs suggesting that neutrophil activation in APS occurs through platelet-independent mechanisms. For example, complement activation generates C5a, which recruits and activates TF expressing neutrophils, which may explain their procoagulant potential [2]. Anticoagulants such as heparin have been shown to increase platelet-monocyte aggregation and neutrophil extracellular traps (NETs) [10,11]. ...
... In the 1990s, prior to the first descriptions of NETs, it was found that mouse monoclonal antibodies against human β 2 GPI activated neutrophils, stimulating degranulation and hydrogen peroxide production [116]. In the early 2000s, an important series of experiments characterized pregnancy models of APS and found that neutrophils and complement were important mediators of fetal injury [117][118][119]. ...
Antiphospholipid syndrome (APS) is an autoimmune thrombophilia propelled by circulating antiphospholipid antibodies that herald vascular thrombosis and obstetrical complications. Antiphospholipid antibodies recognize phospholipids and phospholipid-binding proteins and are not only markers of disease but also key drivers of APS pathophysiology. Thrombotic events in APS can be attributed to various conspirators including activated endothelial cells, platelets, and myeloid-lineage cells, as well as derangements in coagulation and fibrinolytic systems. Furthermore, recent work has especially highlighted the role of neutrophil extracellular traps (NETs) and the complement system in APS thrombosis. Beyond acute thrombosis, patients with APS can also develop an occlusive vasculopathy, a long-term consequence of APS characterized by cell proliferation and infiltration that progressively expands the intima and leads to organ damage. This review will highlight known pathogenic factors in APS and will also briefly discuss similarities between APS and the thrombophilic coagulopathy of COVID-19.
