The role of TLR4 in pathophysiology of antiphospholipid syndrome-associated thrombosis and pregnancy morbidity

Management of Postpartum Extensive Venous Thrombosis after Second Pregnancy

Background: Pregnancy induces a physiological prothrombotic state. The highest risk period for venous thromboembolism and pulmonary embolism in pregnant women is during the postpartum period. Materials and Methods: We present the case of a young woman who gave birth 2 weeks before admission and was transferred to our clinic for edema. She had an increased temperature in her right limb, and a venous Doppler of the limb confirmed thrombosis of the right femoral vein. From the paraclinical examination, we obtained a CBC with leukocytosis, neutrophilia, and thrombocytosis, and a positive D-dimer test. Thrombophilic tests were negative for AT III, lupus anticoagulant negative, and protein S and C, but were positive for heterozygous PAI-1, heterozygous MTHFR A1298C, and EPCR with A1/A2 alleles. After 2 days of UFH with therapeutic APTT, the patient had pain in her left thigh. We performed a venous Doppler, which revealed bilateral femoral and iliac venous thrombosis. During the computed tomography examination, we assessed the venous thrombosis extension on the inferior cava, common iliac, and bilateral common femoral veins. Thrombolysis was initiated with 100 mg of Alteplase given at a rate of 2 mg/h; however, this did not lead to a considerable reduction in the thrombus. Additionally, the treatment with UFH was continued under therapeutic APTT. After 7 days of UFH and triple antibiotic therapy for genital sepsis, the patient had a favorable evolution with remission of venous thrombosis. Results: Alteplase is a thrombolytic agent that is created with recombinant DNA technology, and it was successfully used to treat thrombosis that occurred in the postpartum period. Conclusions: Thrombophilias are associated with a high VTE risk but also with adverse pregnancy outcomes, including recurrent miscarriages and gestational vascular complications. In addition, the postpartum period is associated with a higher VTE risk. A thrombophilic status with heterozygous PAI-1, heterozygous MTHFR A1298C, and EPCR with A1/A2 positive alleles is associated with a high risk of thrombosis and cardiovascular events. Thrombolysis can be successfully used postpartum to treat VTEs. Thrombolysis can be used successfully in VTE developed in the postpartum period.

Hematological manifestations of antiphospholipid syndrome: Going beyond thrombosis

Thrombotic complications are a hallmark of antiphospholipid syndrome (APS). These vascular - arterial, venous, and/or small vessel - complications are well described and known to hematologists and healthcare providers caring for patients with this disease. In this review, we shed light on other hematological manifestations of the disease, including bleeding, thrombocytopenia, autoimmune hemolytic anemia, and thrombotic microangiopathy syndromes. While these manifestations are not bona fide clinical criteria for the diagnosis of APS, they frequently interact and contribute to the complexity of clinical management of APS.

Periodontal disease in pregnancy and adverse pregnancy outcomes: Progress in related mechanisms and management strategies

Periodontal disease is an inflammatory and destructive disease of tissues supporting the tooth. A large number of studies have confirmed that periodontal pathogens and their metabolites can lead to adverse pregnancy outcomes in direct or indirect ways. Adverse pregnancy outcomes, such as preterm birth, low birth weight, and pre-eclampsia, have a serious impact on human reproductive health. In recent years, although the level of global medical technology has gradually improved, the incidence of adverse pregnancy outcomes has not declined and is still a global public health problem. The purpose of this review is to summarize the current data on periodontal disease in pregnancy and adverse pregnancy outcomes, including the association between periodontal disease and adverse pregnancy outcomes, the pathogenic mechanism related to this association, the efficacy of different nutrition supplements for both periodontal disease and adverse pregnancy outcomes and the effect of providing periodontal treatment on the occurrence of adverse pregnancy outcomes, to provide guidance for the prevention and treatment of adverse pregnancy outcomes in clinical practice.

TFPI and FXIII negatively and S100A8/A9 and Cystatin C positively correlate with D-dimer in COVID-19

D-dimer is an established biomarker of thromboembolism and severity in COVID-19. We and others have recently reported the dysregulation of tissue factor pathway inhibitor (TFPI), FXIII, fibrinolytic pathway, inflammatory markers, and tissue injury markers, particularly in severe COVID-19. However, association of these markers with thromboembolism in COVID-19 remains elusive. The correlation analyses between these markers in patients with moderate (non-ICU) and severe COVID-19 (ICU) were performed to delineate the potential pathomechanisms and impact of thromboembolism. We observe a negative correlation of plasma TFPI (r² = 0.148, P = 0.035), FXIII (r² = 0.242, P = 0.006), and plasminogen (r² = 0.27, P = 0.003) with D-dimer, a biomarker of thromboembolism, levels in these patients. Further analysis revealed a strong positive correlation between fibrinolytic markers tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) (r² = 0.584, P < 0.0001). Interestingly, a significant positive correlation of PAI-1, but not tPA, was observed with platelets and endothelial cells dysfunction markers P-selectin (r² = 0.184, P = 0.01) and soluble CD40 ligand (sCD40 L) (r² = 0.163, P = 0.02). Moreover, calprotectin (S100A8/A9) and cystatin C (CST3), previously linked with thromboembolism, exhibited positive correlations with each other (r² = 0.339, P = 0.0007) and with the level of D-dimer independently in COVID-19. Finally, the tissue injury marker myoglobin demonstrated a strong positive correlation with D-dimer (r² = 0.408, P = 0.0001). Taken together, inverse correlations of TFPI and FXIII with D-dimer suggest the TF pathway activation and aberrant fibrin polymerization in COVID-19 patients. The elevated level of PAI-1 is potentially contributed by activated platelets and endothelial cells. S100A8/A9 may also play roles in impaired fibrinolysis and thromboembolism, in part, through regulating the CST3. These findings strengthen the understanding of thromboembolism and tissue injury and may help in better management of thromboembolic complications in COVID-19 patients.

A targetable pathway in neutrophils mitigates both arterial and venous thrombosis

Arterial and venous thrombosis constitutes a major source of morbidity and mortality worldwide. Long considered as distinct entities, accumulating evidence indicates that arterial and venous thrombosis can occur in the same populations, suggesting that common mechanisms are likely operative. Although hyperactivation of the immune system is a common forerunner to the genesis of thrombotic events in both vascular systems, the key molecular control points remain poorly understood. Consequently, antithrombotic therapies targeting the immune system for therapeutics gain are lacking. Here, we show that neutrophils are key effectors of both arterial and venous thrombosis and can be targeted through immunoregulatory nanoparticles. Using antiphospholipid antibody syndrome (APS) as a model for arterial and venous thrombosis, we identified the transcription factor Krüppel-like factor 2 (KLF2) as a key regulator of neutrophil activation. Upon activation through genetic loss of KLF2 or administration of antiphospholipid antibodies, neutrophils clustered P-selectin glycoprotein ligand 1 (PSGL-1) by cortical actin remodeling, thereby increasing adhesion potential at sites of thrombosis. Targeting clustered PSGL-1 using nanoparticles attenuated neutrophil-mediated thrombosis in APS and KLF2 knockout models, illustrating the importance and feasibility of targeting activated neutrophils to prevent pathological thrombosis. Together, our results demonstrate a role for activated neutrophils in both arterial and venous thrombosis and identify key molecular events that serve as potential targets for therapeutics against diverse causes of immunothrombosis.

Lipocalin-2, S100A8/A9, and cystatin C: Potential predictive biomarkers of cardiovascular complications in COVID-19

Severe coronavirus (SARS-COV-2) infection often leads to systemic inflammation accompanied by cardiovascular complications including venous thromboembolism (VTE). However, it is largely undefined if inflammatory markers such as lipocalin-2 (LNC2), calprotectin (S100A8/A9), and cystatin C (CST3), previously linked with VTE, play roles in cardiovascular complications and advancement of COVID-19 severity. To investigate the same, hospitalized moderate and severe (presented pneumonia and required intensive care) COVID-19 patients were recruited. The levels of plasma LNC2, S100A8/A9, CST3, myoglobin, and cardiac Troponin I (cTnI) were assessed through enzyme-linked immunosorbent assay (ELISA). The investigation revealed a significantly upregulated level of plasma LNC2 at the moderate stage of SARS-CoV-2 infection. In contrast, the levels of S100A8/A9 and CST3 in moderate patients were comparable to healthy controls; however, a profound induction was observed only in severe COVID-19 patients. The tissue injury marker myoglobin was unchanged in moderate patients; however, a significantly elevated level was observed in the critically ill COVID-19 patients. In contrast, cTnI level was unchanged both in moderate and severe patients. Analysis revealed a positive correlation between the levels of S100A8/A9 and CST3 with myoglobin in COVID-19. In silico analysis predicted interactions of S100A8/A9 with toll-like receptor 4 (TLR-4), MyD88 LY96, and LCN2 with several other inflammatory mediators including MMP2, MMP9, TIMP1, and interleukins (IL-6, IL-17A, and IL-10). In summary, early induction of LCN2 likely plays a role in advancing the COVID-19 severity. A positive correlation of S100A8/A9 and CST3 with myoglobin suggests that these proteins may serve as predictive biomarkers for thromboembolism and tissue injury in COVID-19.

FcRn augments induction of tissue factor activity by IgG-containing immune complexes

Thromboembolism complicates disorders caused by immunoglobulin G (IgG)-containing immune complexes (ICs), but the underlying mechanisms are incompletely understood. Prior evidence indicates that induction of tissue factor (TF) on monocytes, a pivotal step in the initiation, localization, and propagation of coagulation by ICs, is mediated through Fcγ receptor IIa (FcγRIIa); however, the involvement of other receptors has not been investigated in detail. The neonatal Fc receptor (FcRn) that mediates IgG and albumin recycling also participates in cellular responses to IgG-containing ICs. Here we asked whether FcRn is also involved in the induction of TF-dependent factor Xa (FXa) activity by IgG-containing ICs by THP-1 monocytic cells and human monocytes. Induction of FXa activity by ICs containing IgG antibodies to platelet factor 4 (PF4) involved in heparin-induced thrombocytopenia (HIT), β-2-glycoprotein-1 implicated in antiphospholipid syndrome, or red blood cells coated with anti-(α)-Rh(D) antibodies that mediate hemolysis in vivo was inhibited by a humanized monoclonal antibody (mAb) that blocks IgG binding to human FcRn. IgG-containing ICs that bind to FcγR and FcRn induced FXa activity, whereas IgG-containing ICs with an Fc engineered to be unable to engage FcRn did not. Infusion of an α-FcRn mAb prevented fibrin deposition after microvascular injury in a murine model of HIT in which human FcγRIIa was expressed as a transgene. These data implicate FcRn in TF-dependent FXa activity induced by soluble and cell-associated IgG-containing ICs. Antibodies to FcRn, now in clinical trials in warm autoimmune hemolytic anemia to lower IgG antibodies and IgG containing ICs may also reduce the risk of venous thromboembolism.

OxLDL/β2GPI/anti‑β2GPI Ab complex induces inflammatory activation via the TLR4/NF‑κB pathway in HUVECs

Patients with antiphospholipid syndrome have been identified to have higher incidence rates of atherosclerosis (AS) due to the elevated levels of anti-β2-glycoprotein I (β2GPI) antibody (Ab). Our previous studies revealed that the anti-β2GPI Ab formed a stable oxidized low-density lipoprotein (oxLDL)/β2GPI/anti-β2GPI Ab complex, which accelerated AS development by promoting the accumulation of lipids in macrophages and vascular smooth muscle cell. However, the effects of the complex on endothelial cells, which drive the initiation and development of AS, remain unknown. Thus, the present study aimed to determine the proinflammatory roles of the oxLDL/β2GPI/anti-β2GPI Ab complex in human umbilical vein endothelial cells (HUVECs) in an attempt to determine the underlying mechanism. Reverse transcription-quantitative PCR, enzymy-linked immunosorbent assay, western blotting and immunofluorescence staining were performed to detect the expressions of inflammation related factors and adhesion molecules. Monocyte-binding assay was used to investigate the effects of oxLDL/β2GPI/anti-β2GPI Ab complex on monocyte adhesion to endothelial cells. The results demonstrated that the oxLDL/β2GPI/anti-β2GPI Ab complex upregulated the expression of Toll-like receptor (TLR)4 and the levels of NF-κB phosphorylation in HUVECs, and subsequently enhanced the expression levels of inflammatory cytokines, including TNF-α, IL-1β and IL-6, as well as those of adhesion molecules, such as intercellular adhesion molecule 1 and vascular adhesion molecule 1. In addition, the complex facilitated the recruitment of monocytes by promoting the secretion of monocyte chemotactic protein 1 in HUVECs. Notably, the described effects of the oxLDL/β2GPI/anti-β2GPI Ab complex in HUVECs were abolished by either TLR4 or NF-κB blockade. In conclusion, these findings suggested that the oxLDL/β2GPI/anti-β2GPI Ab complex may induce a hyper-inflammatory state in endothelial cells by promoting the secretion of proinflammatory cytokines and monocyte recruitment, which was discovered to be largely dependent on the TLR4/NK-κB signaling pathway.

The Role of TLR-4 and Galectin-3 Interaction in Acute Pancreatitis

Toll-like receptor-4 (TLR-4) is a member of evolutionarily conserved type I transmembrane proteins that can initiate sterile inflammatory cascade in the pancreas. Expression of TLR-4 is up-regulated in pancreatic tissue, as well as, on peripheral blood innate immune cells in human and experimental models of acute pancreatitis. TLR-4 plays important pro-inflammatory roles during development of acute pancreatitis: it recognize alarmins released from injured acinar cells and promotes activation and infiltration of innate immune cells after the premature and intraacinar activation of tripsinogen. Galectin-3 is β-galactoside-binding lectin that plays pro-inflammatory roles in a variety autoimmune diseases, acute bacterial infections and during tumorigenesis. It is reported that Galectin-3 is alarmin in experimental models of neuroinflammation and binds to TLR-4 promoting the pro-inflammatory phenotype of microglia. Also, in experimental model of acute pancreatitis Galectin-3 is colocalized with TLR-4 on innate inflammatory cells resulted in enhanced production of inflammatory cytokines, TNF-α and IL-1β, increased infiltration of pro-inflammatory N1 neutrophils, macrophages and dendritic cells and increased damage of pancreatic tissue. This review paper discusses the role of TLR-4/Gal-3 axis in the pathogenesis of acute pancreatitis.

miR-146a-5p improves the decidual cytokine microenvironment by regulating the toll-like receptor signaling pathway in unexplained spontaneous abortion

Spontaneous abortion (SA) is a common pregnancy failure, but the cause of numerous cases remains unexplained. Decidual immune cells (DICs)-mediated cytokine microenvironment is involved in pregnancy and regulated by many microRNAs, but whether microRNA-146a-5p (miR-146a) regulate the decidual cytokine microenvironment and the potential mechanisms in unexplained SA pathogenesis have rarely been reported. In this study, the levels of cytokines and miR-146a in healthy and unexplained SA deciduae were first investigated, and the correlation between them was analyzed. Then, the effect of miR-146a inhibitor on cytokines was assessed in healthy deciduae-derived DICs. Third, the downstream targets and related molecular mechanisms of miR-146a were analyzed by bioinformatics, and the levels of the predicted targets in deciduae were assessed, followed by the correlation analysis between the levels of miR-146a and the targets. Finally, the effect of miR-146a on the predicted targets and inflammatory cytokines was validated in unexplained SA deciduae-derived DICs. As a result, decreased miR-146a correlated with the cytokine disorder in unexplained SA deciduae, and inhibition of miR-146a promoted pro-inflammatory response in healthy deciduae-derived DICs. One hundred four target genes and related molecular mechanisms of miR-146a were predicted, among which the toll-like receptor (TLR) pathway might be associated with the decidual cytokine regulation. Upregulation of miR-146a inhibited the expression of the predicted molecules enriched in the TLR pathway and improved the cytokine disorder in unexplained SA deciduae-derived DICs. Collectively, miR-146a improves the decidual cytokine microenvironment by regulating the TLR pathway in unexplained SA, providing novel potential targets for further therapeutic research.

MicroRNA-16 directly binds to DEC2 and inactivates the TLR4 signaling pathway to inhibit lupus nephritis-induced kidney tissue hyperplasia and mesangial cell proliferation

Lupus nephritis (LN) is the most serious manifestation of systemic lupus erythematosus (SLE) and a major risk of mortality. This research focused on the function of microRNA-16 (miR-16) in LN development. Fcgamma receptor II-b-deficient (Fcgr2b^-/-) mice with the natural potential to develop SLE- and LN-like diseases were used. Gain- and loss-of-function studies were performed to explore the function of miR-16 in pathological symptoms in mouse kidney tissues and the proliferation of mesangial cells (SV40 MES-13). The putative downstream molecules of miR-16 were explored. Consequently, poor expression of miR-16 was found in kidney tissues. Upregulation of miR-16 inhibited tissue hyperplasia, inflammatory infiltration, glomerular injury and fibrosis but increased cell apoptosis in mouse kidney tissues, and it inhibited proliferation but promoted apoptosis of MES-13 cells as well. miR-16 directly bound to DEC2 and inactivated the TLR4 signaling. DEC2 blocked the protective roles of miR-16 in MES-13 cells. The enhanced proliferation in MES-13 cells following miR-16 inhibition was reversed by chloroquine phosphate, a TLR4 antagonist. To sum up, miR-16 was evidenced to have a potent protective capacity in LN through relieving the LN symptoms in kidney tissues and reducing proliferation of mesangial cells, during which DEC2 silencing and TLR4 signaling deficit were involved.

Saturation of acyl chains converts cardiolipin from an antagonist to an activator of Toll-like receptor-4

Cardiolipins (CLs) are tetra-acylated diphosphatidylglycerols found in bacteria, yeast, plants, and animals. In healthy mammals, CLs are unsaturated, whereas saturated CLs are found in blood cells from Barth syndrome patients and in some Gram-positive bacteria. Here, we show that unsaturated but not saturated CLs block LPS-induced NF-κB activation, TNF-α and IP-10 secretion in human and murine macrophages, as well as LPS-induced TNF-α and IL-1β release in human blood mononuclear cells. Using HEK293 cells transfected with Toll-like receptor 4 (TLR4) and its co-receptor Myeloid Differentiation 2 (MD2), we demonstrate that unsaturated CLs compete with LPS for binding TLR4/MD2 preventing its activation, whereas saturated CLs are TLR4/MD2 agonists. As a consequence, saturated CLs induce a pro-inflammatory response in macrophages characterized by TNF-α and IP-10 secretion, and activate the alternative NLRP3 inflammasome pathway in human blood-derived monocytes. Thus, we identify that double bonds discriminate between anti- and pro-inflammatory properties of tetra-acylated molecules, providing a rationale for the development of TLR4 activators and inhibitors for use as vaccine adjuvants or in the treatment of TLR4-related diseases.

Altered Th17/Treg Ratio in Peripheral Blood of Systemic Lupus Erythematosus but Not Primary Antiphospholipid Syndrome

Introduction: The role of the immune response in the pathogenesis of antiphospholipid syndrome (APS) remains elusive. It is possible that differences in the frequencies of Th17 cells and/or defects in the immunoregulatory mechanisms are involved in the pathogenesis of APS. Our aim was to determine the peripheral blood Th cells phenotype and the circulating cytokine profile in patients with primary APS (pAPS) and compare it with systemic lupus erythemathosus (SLE) as disease control group.

Methods: The frequencies of circulating regulatory T cells (Tregs) were determined in PBMCs from 36 patients with pAPS by flow cytometry. As control groups we included 21 age- and gender-matched healthy controls (HC) and 11 patients with SLE. The suppressive capacity of Tregs was evaluated in vitro by coculture assay. On the other hand, intracellular cytokine production was assessed in Th1, Th2, and Th17 cells and circulating IL-6, IL-10, and IL-35 were measured by Cytometric Bead Array and ELISA. The quantification of Th master gene expression levels was performed by real time quantitative PCR.

Results: pAPS patients and SLE patients did not show differences in the percentage or number of Tregs compared to HC. The suppressive capacity of Tregs was also similar in the three study group. Instead, we found higher FoxP3·mRNA expression levels in pAPS patients and HC than SLE patients. Regarding the Th17 response, patients with pAPS and HC showed a significantly lower frequency of circulating Th17 cells than SLE. However, no differences were observed in the Th1 response between patients and controls. Thus, increased Th17/Th1 and Th17/Treg ratios were found in SLE patients but not in pAPS patients. pAPS and SLE patients had higher serum IL-6 levels than HC but there was not difference between both disease groups. Besides, a significant increase in the immunosuppressive cytokine levels was observed only in pAPS as compared to HC.

Conclusions: Our data demonstrate an increased inflammatory profile of peripheral blood CD4⁺ T cells from SLE as compared with pAPS mostly due to an increased Th17 response. In conclusion, there seems not to be a direct pathogenic role for Th cells in pAPS but in SLE.

Involvement of ILR4α and TLR4 in miscarriages

BACKGROUND

The purpose of this study was to analyze the involvement of signaling via Interleukin-4-Receptor α (IL4Rα) and Toll like receptor (TLR) 4 at the fetomaternal interface in the process of early pregnancy.

PATIENTS AND METHODS

Placenta specimens of 46 patients in early pregnancy were analyzed (normal pregnancy (n = 15), spontaneous (n = 15) and habitual abortion (n = 16)). TLR4 and IL4Rα were analyzed by immunohistochemistry, immunofluorescence and real time PCR. Statistical analysis was carried out using SPSS 23 and Microsoft Excel.

RESULTS

IL4Rα could be detected in trophoblast cells of all groups. It was significantly downregulated in the syncytiotrophoblast of spontaneous and recurrent abortions (p = 0.001), and in decidual tissue of spontaneous abortions (p = 0.001). Expression of TLR4 was decreased in the intermediate villous trophoblast (IVT) and decidua of spontaneous abortions (p = 0.04 & 0.003, respectively). On mRNA level expression of IL4Rα and TLR4 was significantly decreased in the group of recurrent miscarriages (IL4Rα p = 0.002, TLR4 p = 0.004).

CONCLUSION

This study contributes new findings to the understanding of the complex molecular interplay at the fetomaternal interface in normal pregnancy and miscarriages. For the first time signaling via IL4Rα being involved at the very beginning of the generation of new life could demonstrated. Moreover, new evidence was provided regarding TLR4 playing a pivotal role in early pregnancy.

Anti-β2 -glycoprotein I antibody with DNA binding activity enters living monocytes via cell surface DNA and induces tissue factor expression

Autoantibodies characteristic for anti‐phospholipid syndrome (APS) and systemic lupus erythematosus (SLE) are anti‐β₂‐glycoprotein I (β₂GPI) antibodies and anti‐DNA antibodies, respectively, and almost half of APS cases occur in SLE. Anti‐β₂GPI antibodies are recognized to play a pivotal role in inducing a prothrombotic state, but the precise mechanism has not been fully elucidated. In a widely accepted view, binding of anti‐β₂GPI antibodies to cell surface β₂GPI in monocytes and endothelial cells triggers the Toll‐like receptor 4‐myeloid differentiation primary response 88 (TLR)‐4‐MyD88) signaling pathway which leads to activation of p38 mitogen‐activated protein kinase (MAPK), mitogen‐activated protein kinase kinase 1/extracellular signal‐regulated kinases (MEK‐1/ERK) and/or nuclear factor kappa B (NF‐κB) and expression of tissue factor (TF). However, resting cells do not express substantial amounts of TLR‐4. Previously, we generated a mouse monoclonal anti‐β₂GPI antibody WB‐6 and showed that it induced a prothrombotic state – including TF expression on circulating monocytes – in normal mice. In the current study, we aimed to clarify the mechanism of interaction between WB‐6 and resting monocytes, and found that WB‐6 exhibits binding activity to DNA and enters living monocytes or a monocytic cell line and, to a lesser extent, vascular endothelial cells. Treatment of the cells with DNase I reduced the internalization, suggesting the involvement of cell surface DNA in this phenomenon. Monocytes harboring internalized WB‐6 expressed TF and tumor necrosis factor (TNF)‐α which, in turn, stimulated endothelial cells to express intercellular adhesion molecule 1 (ICAM‐I) and vascular cell adhesion molecule 1 (VCAM‐I). These results suggest the possibility that a subset of anti‐β₂GPI antibodies with dual reactivity to DNA possesses ability to stimulate DNA sensors in the cytoplasm, in addition to the cell surface receptor‐mediated pathways, leading to produce proinflammatory and prothrombotic states.

Anticardiolipin (aCL) in sera from periodontitis subjects activate Toll-like receptor 4 (TLR4)

Anticardiolipin antibodies (aCL) have been reported to be present in 15–20% of sera from subjects with periodontitis at concentrations exceeding those found in 95% of the healthy adult population. These antibodies, albeit at concentrations exceeding those generally found in periodontitis subjects, are typically present in patients with the antiphospholipid syndrome (APS), an autoimmune disease characterized by thrombosis and recurrent pregnancy loss. aCL from APS patients are proinflammatory and can activate trophoblasts, macrophages, and platelets via cell-surface interactions with their target antigen beta-2-glycoprotein-I (β2GPI). β2GPI is an anionic phospholipid-binding serum protein that can associate with toll-like receptors (TLR’s) on the cell-surface, leading to cell activation following interaction with autoimmune aCL. We examined an expanded series of 629 sera from clinically characterized subjects for aCL content, and observed that 14–19% of these sera contained elevated (>95^th %-tile) levels of aCL. We purified IgG from 16 subjects with elevated or normal levels of aCL and examined their ability to activate TLR2- or TLR4-transfected human embryonic kidney (HEK) cells, and observed that IgG from periodontitis patients with elevated aCL activated HEK-TLR4 cells, but not HEK-TLR2 cells. Prior removal of aCL by immunoabsorption significantly reduced the ability of IgG preparations from these sera to activate TLR4. Further experiments using a human first trimester trophoblastic cell line (HTR8 sv/neo) revealed that aCL from periodontitis patients stimulated IL-8 production, which was profoundly decreased if aCL was removed by immunoabsorption or if HTR8 sv/neo were pretreated with blocking anti-TLR4 antibodies. Thus, it appears that aCL from periodontitis patients can be proinflammatory, activating cells via TLR4. Since these antibodies are likely produced via molecular mimicry due to similarities between oral bacterial antigens and β2GPI, the data indicate that circulating serum aCL may induce or influence inflammatory responses at sites distant from the oral cavity.

Effects of Toll-like receptor 4 on β2-glycoprotein I-induced splenic T cell subsets differentiation

Our previous study demonstrated that beta 2-glycoprotein I (β2GPI) stimulation promotes bone marrow derived dendritic cells (BMDCs) maturation and T cell proliferation in a Toll-like receptor 4 (TLR4) dependent manner. However, β2GPI induced T cell differentiation and the role of TLR4 in this process have rarely been reported. In the present study, we focused on the differentiation of splenic T cells in β2GPI immunized Balb/c, C3H/HeN and C3H/HeJ mice. According to our results, Th2 dominated differentiation was observed in β2GPI immunized Balb/c and C3H/HeN mice than in those treated with normal saline (NS), namely the up-regulated levels of Th2 markers GATA3 and IL-4 (p < 0.05). Meanwhile, reduced Th1 markers T-bet and IFN-γ, and Treg marker Foxp3 were observed in β2GPI immunized mice (p < 0.05). C3H/HeJ mice have the same gene background with C3H/HeN mice except a functional mutant in TLR4 gene. However, the described Th2 differentiation was not detected in these TLR4 deficient mice, indicating the importance of TLR4 in immune response against β2GPI. In addition, we found that β2GPI-induced Th2 differentiation could be strengthened by cytokines secreted by dendritic cells (DCs) and DCs-T cells interaction. However, DCs-T cells contact was indispensable during this process because of its unique role in suppressing Th1 function. Furthermore, this Th2 biased differentiation pattern was more noticeable in mice received 4 times β2GPI immunization than those received 2 times, suggesting the amplifying effects of anti-β2GPI Ab on β2GPI induced Th2 response. These findings may partly explain the immune imbalance in APS patient through the view angle of T cell differentiation and anti-β2GPI antibody production.

Estradiol Suppresses TLR4-triggered Apoptosis of Decidual Stromal Cells and Drives an Anti-inflammatory TH2 Shift by Activating SGK1

A pro-inflammatory cytokine profile at the feto-maternal interface may predispose immune maladaptation notably in early miscarriages. We investigated the involvement of estradiol (E2)-activated serum-glucocorticoid regulated kinase 1 (SGK1) in preserving the tolerogenic and pro-survival intrauterine microenvironment beneficial to gestation maintenance. Decidual SGK1 was down-regulated in early miscarriage, consistent with the lower serum E2 concentration seen in pregnancy loss. Lipopolysaccharide (LPS)/Toll-like receptors 4 (TLR4) signaling induced apoptosis and the pro-inflammatory T helper type (TH) 1 response of decidual stromal cells (DSCs) were associated with miscarriage. SGK1 activation was suppressed by LPS/TLR4 signaling and would be rescued by E2 administration via the PI3K signaling pathway in DSCs. SGK1 activation attenuated TLR4-mediated cell apoptosis, while promoting cell viability of DSCs by up-regulating the pro-survival genes BCL2 and XIAP, and enhancing the phosphorylation of FOXO1. Furthermore, E2-induced SGK1 activation reduced the secretion of pro-inflammatory TH1 cytokines, and promoted the generation of TH2 cytokines and elevated IRF4 mRNA and protein levels in LPS-incubated DSCs. Pharmacologic inhibition of SGK1 or suppression by small interfering (si) RNA increased the phosphorylation and nuclear translocation of NF-κB to reverse the pro-TH2 and anti-inflammatory effects of E2 pretreatment, leading to compromised pregnancy. These findings suggest that the E2-mediated SGK1 activation suppressed LPS-mediated apoptosis and promoted the anti-inflammatory TH2 responses in DSCs, ultimately contributing to a successful pregnancy.

New Insights in the Pathophysiology of Antiphospholipid Syndrome

The antiphospholipid syndrome (APS) is an autoimmune disorder characterized by an elevated risk for arterial and venous thrombosis and pregnancy-related morbidity. Since the discovery of the disease in 1980s, numerous studies in cell culture systems, in animal models, and in patient populations have been reported, leading to a deeper understanding of the pathogenesis of APS. These studies have determined that circulating autoantibodies, collectively called antiphospholipid antibodies (aPL), the majority of which recognize cell surface proteins attached to the plasma membrane phospholipids, play a causal role in the development of the disease. The binding of aPL to the cell surface antigens triggers interaction of the complex with transmembrane receptors to initiate intracellular signaling in critical cell types, including platelets, monocytes, endothelial cells, and trophoblasts. Subsequent alteration of various cell functions results in inflammation, thrombus formation, and pregnancy complications. Apolipoprotein E receptor 2 (apoER2), a lipoprotein receptor family member, has been implicated as a mediator for aPL actions in platelets and endothelial cells. Nitric oxide (NO) is a signaling molecule known to exert potent antithrombotic, anti-inflammatory, and anti-atherogenic effects. NO insufficiency and oxidative stress have been linked to APS pathogenesis. This review will focus on the recent findings on how apoER2 and dysregulation of NO production contribute to aPL-mediated pathologies in APS.

The Role of TLR4 on B Cell Activation and Anti-2GPI Antibody Production in the Antiphospholipid Syndrome

High titer of anti-β₂-glycoprotein I antibodies (anti-β₂GPI Ab) plays a pathogenic role in antiphospholipid syndrome (APS). Numerous studies have focused on the pathological mechanism in APS; however, little attention is paid to the immune mechanism of production of anti-β₂GPI antibodies in APS. Our previous study demonstrated that Toll-like receptor 4 (TLR4) plays a vital role in the maturation of bone marrow-derived dendritic cells (BMDCs) from the mice immunized with human β₂-glycoprotein I (β₂GPI). TLR4 is required for the activation of B cells and the production of autoantibody in mice treated with β₂GPI. However, TLR4 provides a third signal for B cell activation and then promotes B cells better receiving signals from both B cell antigen receptor (BCR) and CD40, thus promoting B cell activation, surface molecules expression, anti-β₂GPI Ab production, and cytokines secretion and making B cell functioning like an antigen presenting cell (APC). At the same time, TLR4 also promotes B cells producing antibodies by upregulating the expression of B-cell activating factor (BAFF). In this paper, we aim to review the functions of TLR4 in B cell immune response and antibody production in autoimmune disease APS and try to find a new way for the prevention and treatment of APS.

The Effects of NF-κB and c-Jun/AP-1 on the Expression of Prothrombotic and Proinflammatory Molecules Induced by Anti-β2GPI in Mouse

Our previous data demonstrated that nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) are involved in the process of anti-β₂GPI/β₂GPI-induced tissue factor (TF) expression in monocytes. However, the role of NF-κB and AP-1 in pathogenic mechanisms of antiphospholipid syndrome (APS) in vivo has been rarely studied. This study aimed to investigate whether NF-κB and c-Jun/AP-1 are involved in anti-β₂GPI-induced expression of prothrombotic and proinflammatory molecules in mouse. IgG-APS or anti-β₂GPI antibodies were injected into BALB/c mice in the presence or absence of PDTC (a specific inhibitor of NF-κB) and Curcumin (a potent inhibitor of AP-1) treatment. Our data showed that both IgG-APS and anti-β₂GPI could induce the activation of NF-κB and c-Jun/AP-1 in mouse peritoneal macrophages. The anti-β₂GPI-induced TF activity in homogenates of carotid arteries and peritoneal macrophages from mice could significantly decrease after PDTC and/or Curcumin treatment, in which PDTC showed the strongest inhibitory effect, but combination of two inhibitors had no synergistic effect. Furthermore, anti-β₂GPI-induced expression of TF, VCAM-1, ICAM-1 and E-selectin in the aorta and expression of TF, IL-1β, IL-6 and TNF-α in peritoneal macrophages of mice were also significantly attenuated by PDTC and/or Curcumin treatment. These results indicate that both NF-κB and c-Jun/AP-1 are involved in regulating anti-β₂GPI-induced expression of prothrombotic and proinflammatory molecules in vivo. Inhibition of NF-κB and c-Jun/AP-1 pathways may be beneficial for the prevention and treatment of thrombosis and inflammation in patients with APS.

TLR4 is involved in the pathogenic effects observed in a murine model of antiphospholipid syndrome

Antiphospholipid (aPL)/anti-β2-glycoprotein I (β2GPI) antibodies are considered to play a pivotal pathogenic role in antiphospholipid syndrome (APS) by inducing an intracellular signaling and procoagulant/proinflammatory phenotype that leads to thrombosis. There is increasing evidence that Toll-like receptor 4 (TLR4) could serve as an important molecule for anti-β2GPI recognition on target cells. However, few studies have focused on the effects of TLR4 in in vivo models. Here, we investigated the role of TLR4 in the pathogenic effects of aPL/anti-β2GPI more precisely using TLR4-intact (C3H/HeN) and TLR4-defective (C3H/HeJ) mice. C3H/HeN and C3H/HeJ mice were injected with either IgG isolated from patient with APS (IgG-APS) or epitope-specific anti-β2GPI purified from β2GPI peptide-immunized rabbits. We found that, following anti-β2GPI injections and vascular injury, thrombus formation in both the carotid artery and femoral vein was markedly reduced in C3H/HeJ mice when compared with C3H/HeN mice. IgG-APS or anti-β2GPI-induced carotid artery and peritoneal macrophage tissue factor activity/expression was significantly lesser in C3H/HeJ than in C3H/HeN mice. Furthermore, the IgG-APS or anti-β2GPI induced expression of VCAM-1, ICAM-1, and E-selectin in the aorta and of IL-1β, IL-6, and TNF-α in peritoneal macrophages of C3H/HeJ mice was also significantly reduced compared to C3H/HeN mice. Together, these data suggest that TLR4 is involved in the pathogenic effects of aPL/anti-β2GPI antibodies in vivo.

Cellular fibronectin containing extra domain A promotes arterial thrombosis in mice through platelet Toll-like receptor 4

Cellular fibronectin containing extra domain A (Fn-EDA+), which is produced in response to tissue injury in several disease states, has prothrombotic activity and is known to interact with Toll-like-receptor 4 (TLR4). The underlying mechanism and cell types involved in mediating the prothrombotic effect of Fn-EDA+ still remain unknown. Using intravital microscopy, we evaluated susceptibility to carotid artery thrombosis after FeCl3-induced injury in mice expressing Fn lacking EDA (Fn-EDA(-/-) mice) or Fn containing EDA (Fn-EDA(+/+) mice). Fn-EDA(-/-) mice exhibited prolonged times to first thrombus formation and complete occlusion and a significant decrease in the rate of thrombus growth (P < .05 vs Fn-EDA(+/+) mice). Genetic deletion of TLR4 reversed the accelerated thrombosis in Fn-EDA(+/+) mice (P < .05) but had no effect in Fn-EDA(-/-) mice. Bone marrow transplantation experiments revealed that TLR4 expressed on hematopoietic cells contributes to accelerated thrombosis in Fn-EDA(+/+) mice. In vitro studies showed that cellular Fn-EDA+ interacts with platelet TLR4 and promotes agonist-induced platelet aggregation. Finally, Fn-EDA(+/+) mice specifically lacking platelet TLR4 exhibited prolonged times to first thrombus formation and complete occlusion (P < .05 vs Fn-EDA(+/+) mice containing platelet TLR4). We conclude that platelet TLR4 contributes to the prothrombotic effect of cellular Fn-EDA+, suggesting another link between thrombosis and innate immunity.

Role of Toll-like receptors 2 and 4 in mediating endothelial dysfunction and arterial remodeling in primary arterial antiphospholipid syndrome

OBJECTIVE

To assess the role of Toll-like receptors (TLRs) in antiphospholipid antibody (aPL)-mediated vascular abnormalities in patients with primary arterial antiphospholipid syndrome (APS).

METHODS

Forty-eight subjects participated in the study. Arterial function and structure and TLR pathway activation were determined in patients with primary arterial APS and matched controls. The pathogenic effects of aPL isolated from patients were assessed in wild-type (WT) and TLR-knockout mice.

RESULTS

APS patients had endothelial dysfunction, arterial stiffening, and hypertrophy, as evidenced by decreased brachial artery endothelium-dependent flow-mediated dilation (FMD) and increased aortic pulse wave velocity and carotid intima-media thickness (IMT), as compared with controls. Plasma samples from APS patients revealed decreased nitric oxide (NO) availability and a pro-oxidative, proinflammatory, and prothrombotic state illustrated by a decrease in nitrite and an increase in lipid peroxidation, tumor necrosis factor α levels, and tissue factor (TF) levels. Furthermore, TLR pathway activation was found in APS patients with increased TLR-2 and TLR-4 messenger RNA expression and increased protein levels of the activated TLR transduction protein interleukin-1 receptor-associated kinase 1 in peripheral blood mononuclear cells. Moreover, agonist-stimulated cell-surface expression of TLR-2 and TLR-4 in circulating monocytes was higher in APS patients than in controls. These changes were positively associated with IMT and negatively associated with FMD. Finally, aPL injection decreased mesenteric endothelium-dependent relaxation and increased TF expression in WT mice but not in TLR-2- or TLR-4-knockout mice.

CONCLUSION

This translational study supports the notion that TLR-2 and TLR-4 play a role in mediating vascular abnormalities in patients with primary arterial APS. TLRs thus constitute a promising pharmacologic target for preventing cardiovascular complications in APS.

The

The addition of the word “catastrophic” to the term antiphospholipid syndrome (APS) was proposed 20 years ago by Ronald Asherson when he published an editorial in The Journal of Rheumatology describing a group of patients who develop multiple thrombosis in a short period of time and with a much worse prognosis than that attributed to patients with classic APS [1]. Since then, many cases have been published reporting patients with this devastating variant of the APS.

Tolerogenic dendritic cells specific for β2-glycoprotein-I Domain-I, attenuate experimental antiphospholipid syndrome

Tolerogenic dendritic cells (tDCs) have the potential to control the outcome of autoimmunity by modulating the immune response. The aim of this study was to uncover the tolerance efficacy attributed to beta-2-glycoprotein-I (β2GPI) tDCs or β2GPI domain-I (D-I) and domain-V (D-V)-tDCs in mice with antiphospholipid syndrome (APS). tDCs were pulsed with β2GPI or D-I or D-V derivatives. Our results revealed that β2GPI related tDCs phenotype includes CD80(high), CD86(high) CD40(high) MHC class II(high). The miRNA profiling encompass miRNA 23b(high), miRNA 142-3p(low) and miRNA 221(low). In addition the β2GPI related tDCs showed reduced secretion of IL-1β, IL-12 and IL-23. D-I tDCs treatment was more efficient than β2GPI tDCs in inducing of tolerance in APS mice, manifested by lowered titers of anti- β2GPI antibodies (Abs) and reduced percentage of fetal loss. Tolerance induction was accompanied by poor T cell response to β2GPI, high numbers of CD4 + CD25 + FOXP3 + T-regulatory cells (Treg), reduced levels of IFNγ, IL-17 and increased expression of IL-10 and TGFβ. Tolerance was successfully transferred by Treg cells from the tolerized mice to β2GPI immunized mice. We conclude that predominantly D-I-tDCs and β2GPI tDCs have the potential to attenuate experimental APS by induction of Treg cells, reduction of anti- β2GPI Abs titers and increased expression of anti-inflammatory cytokines. We suggest that β2-GPI-D-I-tDCs may offer a novel approach for developing therapy for APS patients.