Requirement of activation of complement C3 and C5 for antiphospholipid antibody-mediated thrombophilia

Lipid-binding antiphospholipid antibodies: significance for pathophysiology and diagnosis of the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of pathogenic antiphospholipid antibodies (aPL). Since approximately 30 years ago, lipid-binding aPL, which do not require a protein cofactor, have been regarded as irrelevant for APS pathogenesis even though anticardiolipin are a diagnostic criterion of APS. In this review, we will summarize the available evidence from in vitro studies, animal models, and epidemiologic studies, which suggest that this concept is no longer tenable. Accordingly, we will only briefly touch on the role of other aPL in APS. This topic has been amply reviewed in detail elsewhere. We will discuss the consequences for laboratory diagnostics and future research required to resolve open questions related to the pathogenic role of different aPL specificities.

Rethinking antiphospholipid syndrome to guide future management and research

Antiphospholipid syndrome (APS) consists of thrombotic, non-thrombotic and obstetric clinical manifestations developing in individuals with persistent antiphospholipid antibodies (aPL). Although researchers have made progress in characterizing different clinical phenotypes of aPL-positive people, the current approach to clinical management is still mostly based on a 'one size fits all' strategy, which is derived from the results of a limited number of prospective, controlled studies. With the 2023 publication of the ACR-EULAR APS classification criteria, it is now possible to rethink APS, to lay the groundwork for subphenotyping through novel pathophysiology-informed approaches, and to set a future APS research agenda guided by unmet needs in clinical management.

Antiphospholipid syndrome pathogenesis in 2023: an update of new mechanisms or just a reconsideration of the old ones?

Antibodies against phospholipid (aPL)-binding proteins, in particular, beta 2 glycoprotein I (β2GPI), are diagnostic/classification and pathogenic antibodies in antiphospholipid syndrome (APS). β2GPI-aPL recognize their target on endothelium and trigger a pro-thrombotic phenotype which is amplified by circulating monocytes, platelets and neutrophils. Complement activation is required as supported by the lack of aPL-mediated effects in animal models when the complement cascade is blocked. The final result is a localized clot. A strong generalized inflammatory response is associated with catastrophic APS, the clinical variant characterized by systemic thrombotic microangiopathy. A two-hit hypothesis was suggested to explain why persistent aPL are associated with acute events only when a second hit allows antibody/complement binding by modulating β2GPI tissue presentation. β2GPI/β2GPI-aPL are also responsible for obstetric APS, being the molecule physiologically present in placental/decidual tissues. Additional mechanisms mediated by aPL with different characteristics have been reported, but their diagnostic/prognostic value is still a matter of research.

What we know and what we don't know about catastrophic antiphospholipid syndrome

Catastrophic antiphospholipid syndrome (CAPS) is a severe condition with high mortality. Since its description in 1992, an important effort has been made to improve and disseminate knowledge on CAPS. Most of our current knowledge comes from the studies performed using the CAPS Registry, a database created in 2000 to gather as many cases as possible in order to better define this disease. It has demonstrated that this condition has multiple faces and is often triggered by a precipitating factor that leads to a thrombotic microangiopathy and cytokine storm involving almost any organ of the body. Analysis of the CAPS Registry has also shown that patients receiving anticoagulation, glucocorticoids and plasma exchange and/or IVIG have a better prognosis. However, there are still many unresolved questions. In this review we summarize what is known and what is still a matter of research in this condition.

Complement biomarkers in the antiphospholipid syndrome - Approaches to quantification and implications for clinical management

Complement is a major driver of antiphospholipid syndrome (APS) and a promising therapeutic target in refractory and catastrophic APS. Complement testing in APS is largely limited to research settings, and reliable, rapid-turnaround biomarkers are needed to predict those at risk for adverse clinical outcomes and most likely to benefit from complement inhibition. We review complement biomarkers and their association with thrombosis and obstetric outcomes, including: (i) complement proteins and activation fragments in the fluid phase; (ii) assays that evaluate complement on cell membranes (e.g. in vivo cell-bound complement fragments, hemolytic assays, and ex vivo 'functional' cell-based assays, and (iii) sequencing of complement genes. Current studies highlight the inconsistencies in testing both between studies and various aPL/APS subgroups, suggesting that either cell-based testing or multiplex panels employing a combination of biomarkers simultaneously may be most clinically relevant. Standardization of complement assays is needed to ensure reproducibility and establish clinically relevant applications.

Association between ovarian reserve and spontaneous miscarriage and their shared genetic architecture

STUDY QUESTION

Can potential mechanisms involved in the likely concurrence of diminished ovarian reserve (DOR) and miscarriage be identified using genetic data?

SUMMARY ANSWER

Concurrence between ovarian reserve and spontaneous miscarriage was observed, and may be attributed to shared genetic risk loci enriched in antigen processing and presentation and autoimmune disease pathways.

WHAT IS KNOWN ALREADY

Previous studies have shown that lower serum anti-Müllerian hormone (AMH) levels are associated with increased risk of embryo aneuploidy and spontaneous miscarriage, although findings have not been consistent across all studies. A recent meta-analysis suggested that the association between DOR and miscarriage may not be causal, but rather a result of shared underlying causes such as clinical conditions or past exposure. Motivated by this hypothesis, we conducted the present analysis to explore the concurrence between DOR and miscarriage, and to investigate potential mechanisms using genetic data.

STUDY DESIGN, SIZE, DURATION

Three data sources were used in the study: the clinical IVF data were retrospectively collected from an academically affiliated Reproductive Medicine Center (17 786 cycles included); the epidemiological data from the UK Biobank (UKB), which is a large-scale, population-based, prospective cohort study (35 316 white women included), were analyzed; and individual-level genotype data from the UKB were extracted for further analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

There were three modules of analysis. First, clinical IVF data were used to test the association between ovarian reserve biomarkers and the subsequent early spontaneous miscarriage risk. Second, the UKB data were used to test the association of spontaneous miscarriage history and early menopause. Third, individual-level genotype data from the UKB were analyzed to identify specific pleiotropic genes which affect the development of miscarriage and menopause.

MAIN RESULTS AND THE ROLE OF CHANCE

In the analysis of clinical IVF data, the risk of early spontaneous miscarriage was 1.57 times higher in the group with AMH < 1.1 ng/ml group (P < 0.001), 1.62 times for antral follicular count <5 (P < 0.001), and 1.39 times for FSH ≥10 mIU/ml (P < 0.001) in comparison with normal ovarian reserve groups. In the analysis of UKB data, participants with a history of three or more miscarriages had a one-third higher risk of experiencing early menopause (odds ratio: 1.30, 95% CI 1.13-1.49, P < 0.001), compared with participants without spontaneous miscarriage history. We identified 158 shared genetic risk loci that affect both miscarriage and menopause, which enrichment analysis showed were involved in antigen processing and presentation and autoimmune disease pathways.

LIMITATIONS, REASONS FOR CAUTION

The analyses of the UKB data were restricted to participants of European ancestry, as 94.6% of the cohort were of white ethnicity. Further studies are needed in non-white populations. Additionally, maternal age at the time of spontaneous miscarriage was not available in the UKB cohort, therefore we adjusted for age at baseline assessment in the models instead. It is known that miscarriage rate in IVF is higher compared to natural conception, highlighting a need for caution when generalizing our findings from the IVF cohort to the general population.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings have implications for IVF clinicians in terms of patient counseling on the prognosis of IVF treatment, as well as for genetic counseling regarding miscarriage. Our results highlight the importance of further research on the shared genetic architecture and common pathophysiological basis of DOR and miscarriage, which may lead to new therapeutic opportunities.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Hunan Youth Science and Technology Innovation Talent Project (2020RC3060), the International Postdoctoral Exchange Fellowship Program (Talent-Introduction Program, YJ20220220), the fellowship of China Postdoctoral Science Foundation (2022M723564), and the Natural Science Foundation of Hunan Province, China (2023JJ41016). This work has been accepted for poster presentation at the 39th Annual Meeting of ESHRE, Copenhagen, Denmark, 25-28 June 2023 (Poster number: P-477). The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Antiphospholipid syndrome nephropathy: Current knowledge and unanswered questions

The definition of acute and chronic antiphospholipid syndrome (APS) nephropathy was recently updated using a multiphase methodology in the context of the development of the new APS classification criteria. Currently, there is no consensus for the treatment of APS nephropathy, which mainly relies on the general recommendations for the management of APS. Based on evidence from experimental studies and a few clinical studies and case series, targeted treatments such as B-cell depletion, anti-B-cell activating factor antibody, complement inhibition, mammalian target of rapamycin inhibition, and neutrophil extracellular traps or interferon targeting may show promise for the treatment of microvascular manifestations in APS, including APS nephropathy. Validation of the new APS nephropathy definition and/or efforts for improvement in proposed terminology, along with the assessment of the safety and efficacy of potential targeted treatments in randomized controlled trials, are major future research directions. In this review, we summarize the current knowledge of APS nephropathy and discuss unanswered questions.

The role of C5a receptors in autoimmunity

The complement system is an essential component of the innate immune response and plays a vital role in host defense and inflammation. Dysregulation of the complement system, particularly involving the anaphylatoxin C5a and its receptors (C5aR1 and C5aR2), has been linked to several autoimmune diseases, indicating the potential for targeted therapies. C5aR1 and C5aR2 are seven-transmembrane receptors with distinct signaling mechanisms that play both partially overlapping and opposing roles in immunity. Both receptors are expressed on a broad spectrum of immune and non-immune cells and are involved in cellular functions and physiological processes during homeostasis and inflammation. Dysregulated C5a-mediated inflammation contributes to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, epidermolysis bullosa acquisita, antiphospholipid syndrome, and others. Therefore, targeting C5a or its receptors may yield therapeutic innovations in these autoimmune diseases by reducing the recruitment and activation of immune cells that lead to tissue inflammation and injury, thereby exacerbating the autoimmune response. Clinical trials focused on the inhibition of C5 cleavage or the C5a/C5aR1-axis using small molecules or monoclonal antibodies hold promise for bringing novel treatments for autoimmune diseases into practice. However, given the heterogeneous nature of (systemic) autoimmune diseases, there are still several challenges, such as patient selection, optimal dosing, and treatment duration, that require further investigation and development to realize the full therapeutic potential of C5a receptor inhibition, ideally in the context of a personalized medicine approach. Here, we aim to provide a brief overview of the current knowledge on the function of C5a receptors, the involvement of C5a receptors in autoimmune disorders, the molecular mechanisms underlying C5a receptor-mediated autoimmunity, and the potential for targeted therapies to modulate their activity.

Complement therapeutics are coming of age in rheumatology

The complement system was described over 100 years ago, and it is well established that activation of this pathway accompanies the great majority of autoimmune and inflammatory diseases. In addition, over three decades of work in murine models of human disease have nearly universally demonstrated that complement activation is upstream of tissue injury and the engagement of pro-inflammatory mechanisms such as the elaboration of cytokines and chemokines, as well as myeloid cell recruitment and activation. With that background, and taking advantage of advances in the development of biologic and small-molecule therapeutics, the creation and clinical evaluation of complement therapeutics is now rapidly expanding. This article reviews the current state of the complement therapeutics field, with a focus on their use in diseases cared for or consulted upon by rheumatologists. Included is an overview of the activation mechanisms and components of the system, in addition to the mechanisms by which the complement system interacts with other immune system constituents. The various therapeutic approaches to modulating the system in rheumatic and autoimmune diseases are reviewed. To understand how best to clinically assess the complement system, methods of its evaluation are described. Finally, next-generation therapeutic and diagnostic advances that can be envisioned for the future are discussed.

An update on the biologics for the treatment of antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by thrombosis and pregnancy morbidity with the persistent presence of antiphospholipid antibodies (aPLs). Although anticoagulation is the primary treatment for APS, it fails in approximately 20-30% of obstetric APS cases and more than 30% of thrombotic APS cases. Therefore, there is a need for new, targeted treatments beyond anticoagulants. Biologics, such as rituximab and eculizumab, have been recommended for refractory catastrophic APS. This review focuses on the recent advancements in the pathogenesis of APS and explores the potential of targeted treatments, including eculizumab, rituximab, belimumab, daratumumab, obinutuzumab, and anti-TNF-α antibodies, for APS management.

Antiphospholipid syndrome: advances in diagnosis, pathogenesis, and management

Antiphospholipid syndrome (APS) is a thrombo-inflammatory disease propelled by circulating autoantibodies that recognize cell surface phospholipids and phospholipid binding proteins. The result is an increased risk of thrombotic events, pregnancy morbidity, and various other autoimmune and inflammatory complications. Although antiphospholipid syndrome was first recognized in patients with lupus, the stand alone presentation of antiphospholipid syndrome is at least equally common. Overall, the diagnosis appears to affect at least one in 2000 people. Studies of antiphospholipid syndrome pathogenesis have long focused on logical candidates such as coagulation factors, endothelial cells, and platelets. Recent work has shed light on additional potential therapeutic targets within the innate immune system, including the complement system and neutrophil extracellular traps. Vitamin K antagonists remain the mainstay of treatment for most patients with thrombotic antiphospholipid syndrome and, based on current data, appear superior to the more targeted direct oral anticoagulants. The potential role of immunomodulatory treatments in antiphospholipid syndrome management is receiving increased attention. As for many systemic autoimmune diseases, the most important future direction is to more precisely identify mechanistic drivers of disease heterogeneity in pursuit of unlocking personalized and proactive treatments for patients.

Advances in the Pathophysiology of Thrombosis in Antiphospholipid Syndrome: Molecular Mechanisms and Signaling through Lipid Rafts

The pathological features of antiphospholipid syndrome (APS) are related to the activity of circulating antiphospholipid antibodies (aPLs) associated with vascular thrombosis and obstetric complications. Indeed, aPLs are not only disease markers, but also play a determining pathogenetic role in APS and exert their effects through the activation of cells and coagulation factors and inflammatory mediators for the materialization of the thromboinflammatory pathogenetic mechanism. Cellular activation in APS necessarily involves the interaction of aPLs with target receptors on the cell membrane, capable of triggering the signal transduction pathway(s). This interaction occurs at specific microdomains of the cell plasma membrane called lipid rafts. In this review, we focus on the key role of lipid rafts as signaling platforms in the pathogenesis of APS, and propose this pathogenetic step as a strategic target of new therapies in order to improve classical anti-thrombotic approaches with "new" immunomodulatory drugs.

Whole blood transcriptome identifies interferon-regulated genes as key drivers in thrombotic primary antiphospholipid syndrome

OBJECTIVE

Pathogenesis of antiphospholipid syndrome (APS) isn't fully elucidated. We aimed to identify gene signatures characterizing thrombotic primary APS (thrPAPS) and subgroups at high risk for worse outcomes.

METHODS

We performed whole blood next-generation RNA-sequencing in 62 patients with thrPAPS and 29 age-/sex-matched healthy controls (HCs), followed by differential gene expression analysis (DGEA) and enrichment analysis. We trained models on transcriptomics data using machine learning.

RESULTS

DGEA of 12.306 genes revealed 34 deregulated genes in thrPAPS versus HCs; 33 were upregulated by at least 2-fold, and 14/33 were type I and II interferon-regulated genes (IRGs) as determined by interferome database. Machine learning applied to deregulated genes returned 79% accuracy to discriminate thrPAPS from HCs, which increased to 82% when only the most informative IRGs were analyzed. Comparison of thrPAPS subgroups versus HCs showed an increased presence of IRGs among upregulated genes in venous thrombosis (21/23, 91%), triple-antiphospholipid antibody (aPL) positive (30/50, 60%), and recurrent thrombosis (19/42, 45%) subgroups. Enrichment analysis of upregulated genes in triple-aPL positive patients revealed terms related to 'type I interferon signaling pathway' and 'innate immune response'. DGEA among thrPAPS subgroups revealed upregulated genes, including IRGs, in patients with venous versus arterial thrombosis (n = 11, 9 IRGs), triple-aPL versus non-triple aPL (n = 10, 9 IRGs), and recurrent versus non-recurrent thrombosis (n = 10, 3 IRGs).

CONCLUSION

Upregulated IRGs may better discriminate thrPAPS from HCs than all deregulated genes in peripheral blood. Taken together with DGEA data, IRGs are highly expressed in thrPAPS and high-risk subgroups of triple-aPL and recurrent thrombosis, with potential treatment implications.

Contributions of animal models to mechanistic understandings of antibody-dependent disease and roles of the amplification loop

The complement system plays an important pathophysiologic role in human diseases associated with immune or ischemic insults. In addition to understanding the effector mechanisms that are important for the biological effects of the system, substantial efforts have gone into understanding which specific complement activation pathways generate these potent effects. These approaches include the use of gene-targeted mice and specific pathway inhibitors, as well as the integration of human disease genetic and biomarker studies. In some disease states, it is quite clear that the alternate pathway plays a unique role in the initiation of the complement system. However, although initially a widely unexpected finding, it has now been shown in many tissue-based disease models and in initial human studies that engagement of the amplification loop is also essential for tissue injury when the classical and/or lectin pathways initiate pathway activation through pathogenic autoantibodies. This review provides evidence for such a conclusion through animal models, focusing on pathogenic antibody passive transfer models but also other relevant experimental systems. These data, along with initial biomarkers and clinical trial outcomes in human diseases that are associated with pathogenic autoantibodies, suggest that targeting the alternative pathway amplification loop may have near-universal therapeutic utility for tissue-based diseases.

C3-dependent effector functions of complement

C3 is the central effector molecule of the complement system, mediating its multiple functions through different binding sites and their corresponding receptors. We will introduce the C3 forms (native C3, C3 [H₂ O], and intracellular C3), the C3 fragments C3a, C3b, iC3b, and C3dg/C3d, and the C3 expression sites. To highlight the important role that C3 plays in human biological processes, we will give an overview of the diseases linked to C3 deficiency and to uncontrolled C3 activation. Next, we will present a structural description of C3 activation and of the C3 fragments generated by complement regulation. We will proceed by describing the C3a interaction with the anaphylatoxin receptor, followed by the interactions of opsonins (C3b, iC3b, and C3dg/C3d) with complement receptors, divided into two groups: receptors bearing complement regulatory functions and the effector receptors without complement regulatory activity. We outline the molecular architecture of the receptors, their binding sites on the C3 activation fragments, the cells expressing them, the diversity of their functions, and recent advances. With this review, we aim to give an up-to-date analysis of the processes triggered by C3 activation fragments on different cell types in health and disease contexts.

Soluble LILRA3 is aberrantly expressed in antiphospholipid syndrome (APS) and is a potential marker of thrombotic APS

OBJECTIVE

Leucocyte immunoglobulin-like receptor A3 (LILRA3) belongs to a family of leucocyte receptors. Our previous study reported LILRA3 transcripts were markedly upregulated in neutrophils from patients with APS. We undertook this study to investigate clinical implications of LILRA3 in APS and its potential role in APS-associated thrombosis.

METHODS

Two independent cohorts were studied. The first consisted of 294 APS patients, 48 asymptomatic aPL carriers and 150 healthy controls (HCs) from Peking University People's Hospital. The second included 99 APS patients, 25 aPL carriers and 40 HCs from United States APS centres. Serum or plasma concentrations of LILRA3 and MPO-DNA complexes were measured. Additionally, 35 patients with thrombotic APS (tAPS) were evaluated to determine potential effects of immunosuppressive therapy on serum concentrations of LILRA3 and MPO-DNA complexes.

RESULTS

Both positivity and serum concentration of LILRA3 were significantly increased in APS patients, especially in those with tAPS. LILRA3-positive tAPS patients displayed more severe thrombotic manifestations. Serum LILRA3 was positively correlated with MPO-DNA complexes in LILRA3-positive tAPS. After immunosuppressive treatment, LILRA3 and MPO-DNA complexes were consistently decreased in tAPS patients. Key findings from the Peking cohort were confirmed in the United States cohort.

CONCLUSION

Our study provides first evidence that LILRA3 is aberrantly expressed in APS, especially in patients with tAPS. Serum LILRA3 correlated with MPO-DNA complexes, and the two indices were consistently decreased in tAPS patients after treatment. LILRA3 may play a role in thrombosis of APS and may serve as a biomarker and/or therapeutic target in tAPS.

Emerging Therapies in Antiphospholipid Syndrome

The antiphospholipid syndrome (APS) is the most common cause of acquired immune-mediated thrombophilia. This syndrome is broadly defined by the presence of arterial or venous thrombosis, or pregnancy morbidity, in the presence of high levels of antiphospholipid antibodies. Despite recognition of this disorder more than 50 years ago, a fundamental unifying pathogenesis has not been determined. Due to this, mechanism-based therapies for APS are not available, and current management following thrombotic events suggests anticoagulation of indeterminate duration, or for obstetric complications, heparin/low molecular weight heparin and aspirin. However, APS is an autoimmune disorder, and several approaches focused on modulating the immune response or its effectors have been employed. Those which have been most extensively studied include hydroxychloroquine, rituximab and eculizumab, an inhibitor of complement C5. In this report, we review in depth, and critique, key clinical studies of these agents. Since all of these studies are small, our conclusions are qualified. However, it appears that hydroxychloroquine may enhance the anticoagulant efficacy of vitamin K antagonists in APS patients, and that rituximab may ameliorate some of the "non-criteria" manifestations of APS. The catastrophic antiphospholipid syndrome (CAPS) is associated with diffuse thrombosis, multi-organ dysfunction, and ∼30% mortality. A high incidence of complement regulatory gene mutations, and compelling data concerning the efficacy of eculizumab in CAPS, suggests an important role for complement in this disorder. However, additional work is needed to clarify the role of complement in non-catastrophic APS, though emerging data suggests that complement inhibition may be effective in preventing thrombosis in these patients as well.

Circulating immune-complexes of IgG/IgM bound to B2-glycoprotein-I associated with complement consumption and thrombocytopenia in antiphospholipid syndrome

Background

Antiphospholipid syndrome (APS) is a multisystemic autoimmune disorder characterized by thrombotic events and/or gestational morbidity in patients with antiphospholipid antibodies (aPL). In a previous single center study, APS-related clinical manifestations that were not included in the classification criteria (livedo reticularis, thrombocytopenia, leukopenia) were associated with the presence of circulating immune-complexes (CIC) formed by beta-2-glycoprotein-I (B2GP1) and anti-B2GP1 antibodies (B2-CIC). We have performed a multicenter study on APS features associated with the presence of B2-CIC.

Methods

A multicenter, cross-sectional and observational study was conducted on 303 patients recruited from six European hospitals who fulfilled APS classification criteria: 165 patients had primary APS and 138 APS associated with other systemic autoimmune diseases (mainly systemic lupus erythematosus, N=112). Prevalence of B2-CIC (IgG/IgM isotypes) and its association with clinical manifestations and biomarkers related to the disease activity were evaluated.

Results

B2-CIC prevalence in APS patients was 39.3%. B2-CIC-positive patients with thrombotic APS presented a higher incidence of thrombocytopenia (OR: 2.32, p=0.007), heart valve thickening and dysfunction (OR: 9.06, p=0.015) and triple aPL positivity (OR: 1.83, p=0.027), as well as lower levels of C3, C4 and platelets (p-values: <0.001, <0.001 and 0.001) compared to B2-CIC-negative patients. B2-CIC of IgM isotype were significantly more prevalent in gestational than thrombotic APS.

Conclusions

Patients with thrombotic events and positive for B2-CIC had lower platelet count and complement levels than those who were negative, suggesting a greater degree of platelet activation.

Impact of Neutrophil Extracellular Traps on Thrombosis Formation: New Findings and Future Perspective

Thrombotic diseases seriously endanger human health, neutrophils and neutrophil extracellular traps (NETs) play an important role in abnormal thrombus formation. NETs are extracellular structures released by neutrophils upon stimulation by pathogens. NETs include neutrophil elastase (NE), myeloperoxidase (MPO), cathepsin G and other active substances. The network structure provided by NETs can prevent the spread of pathogens and effectively kill and eliminate pathogens. However, the components of NETs can also abnormally activate the coagulation pathway and participate in the formation of pathological thrombi. This review aims to summarize the mechanisms of NETs formation in detail; the research progress of NETs in venous thrombosis, arterial thrombosis, acquired disease-associated thrombosis, sepsis coagulation disorder; as well as the strategies to target NETs in thrombosis prevention and treatment.

Complement Mediated Endothelial Damage in Thrombotic Microangiopathies

Thrombotic microangiopathies (TMA) constitute a group of different disorders that have a common underlying mechanism: the endothelial damage. These disorders may exhibit different mechanisms of endothelial injury depending on the pathological trigger. However, over the last decades, the potential role of the complement system (CS) has gained prominence in their pathogenesis. This is partly due to the great efficacy of complement-inhibitors in atypical hemolytic syndrome (aHUS), a TMA form where the primary defect is an alternative complement pathway dysregulation over endothelial cells (genetic and/or adquired). Complement involvement has also been demonstrated in other forms of TMA, such as thrombotic thrombocytopenic purpura (TTP) and in Shiga toxin-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS), as well as in secondary TMAs, in which complement activation occurs in the context of other diseases. However, at present, there is scarce evidence about the efficacy of complement-targeted therapies in these entities. The relationship between complement dysregulation and endothelial damage as the main causes of TMA will be reviewed here. Moreover, the different clinical trials evaluating the use of complement-inhibitors for the treatment of patients suffering from different TMA-associated disorders are summarized, as a clear example of the entry into a new era of personalized medicine in its management.

Immunological parameters of recurrent miscarriages among women in Thi-Qar province

Recurrent miscarriage (RM) is defined as the loss of pregnancy three or more consecutive times in the first and second trimester, which in some cases occurs due to immune abnormalities. This study aimed to assess some immunological parameters in women with recurrent miscarriages, including the level of antiphospholipid antibody (APA), anticardiolipin (ACA), antinuclear antibody (ANA), complement C3 and C4, and interleukine-3 (IL-3). We included 100 patients together with 100 healthy women as a control. ELIZA was used to measure some types of autoantibodies. APA and ACA significantly increased (P≤0.05) in patients compared to control. In addition, 29% of the patients were positive for antinuclear antibodies (ANA), while the control subjects had negative results for these autoantibodies. Regarding the complement, the serum levels of C3 and C4 were significantly elevated in the serum level of patients when compared to the control group, but in treated patients (heparin and low-dose aspirin), the levels of the complement (C3 and C4) showed a significant decrease in patients compared to total controls. Cytokine level (IL-3) significantly decreased in untreated patients 302.78 pg/ml compared to treated patients (741.57 pg/ml). Antiphospholipid antibodies are more prevalent among women with recurrent miscarriages and are also believed to be the result of abnormal autoimmune activation.

The complement system and autoimmune diseases

The complement system plays a key role in the pathogenesis of autoimmune diseases, which usually injures the kidney. More and more studies have shown the pathogenic role and indicated that abnormal activation of the complement system was highly involved in the outbreak of autoimmune diseases. This review mainly introduced recent studies of complement system activation contributing to the pathogenesis of autoimmune diseases, including systemic lupus erythematosus, antiphospholipid syndrome, antineutrophil cytoplasmic antibody‐associated vasculitides, and so on. Understanding the pathogenic roles of complement activation in various autoimmune diseases will identify potential novel therapeutic targets on complement systems.

The complement system is important in the pathogenesis of a group of autoimmune diseases.

Targeting the complement system might provide us with novel target therapies in autoimmune diseases.

Cardiovascular disease risk in antiphospholipid syndrome: Thrombo-inflammation and atherothrombosis

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of antiphospholipid antibodies (aPL) (lupus anticoagulant, anticardiolipin antibodies and anti-beta2glycoprotein I (anti-β2GPI) antibodies) and a plethora of macro- and micro-vascular manifestations, affecting predominantly young adults. Cardiovascular events are the leading causes of morbidity and mortality in APS. APL-mediated thrombo-inflammation and atherothrombosis are emerging pathogenetic mechanisms of cardiovascular disease (CVD) in APS, involving endothelial cell and monocyte activation, cytokines and adhesion molecules expression, complement and neutrophils activation, neutrophil extracellular traps formation, platelet cell activation and aggregation, and subsequent thrombin generation, in parallel with an oxidized low-density lipoprotein (oxLDL)-β2GPI complex induced macrophage differentiation to foam cells. High risk aPL profile, especially the presence of lupus anticoagulant and triple aPL positivity (all three aPL subtypes), co-existence with Systemic Lupus Erythematosus (SLE), as well as traditional risk factors such as smoking, hypertension, hyperlipemia and obesity are associated with both subclinical atherosclerosis and cardiovascular events in APS. Increased awareness of CVD risk by the physicians and patients, regular assessment and strict control of traditional risk factors, and lifestyle modifications are recommended. Use of low-dose aspirin should be considered for cardiovascular prevention in asymptomatic aPL carriers or SLE patients with high-risk aPL profile. The role of older agents such as hydroxychloroquine and statins or new potential targeted treatments against immuno- and athero-thrombosis has been demonstrated by experimental and some clinical studies and needs to be further evaluated by randomized controlled studies. This review summarizes the available evidence about the pathogenetic mechanisms and prevalence of cardiovascular events and subclinical atherosclerosis, the interrelationship between traditional and disease-related CVD risk factors, and the cardiovascular risk assessment and management in APS.

Elevated levels of C3 , C4 , and CH50 of the complement system in ICU and non‐ICU patients with COVID ‐19

Purpose

SARS‐CoV‐2 infection has spread in each corner of the world. Many health systems have dealt with it intensively. The complement system is an instrumental component in the inflammatory immune response and plays a role in the activation of blood coagulation. Our understanding of the pathophysiology of SARS‐CoV‐2 is still limited but is constantly expanding. This study aimed to determine changes in the complement system in intensive care unit (ICU) and non‐ICU patients with COVID‐19.

Methods

In a cross‐sectional study, plasma levels of C3, C4, and CH50 were determined in two groups of ICU and non‐ICU patients with COVID‐19 to understand the potential effects of SARS‐CoV‐2 on the innate immune system. The assays of C3 and C4 were conducted using turbidimetry method. The CH50 test was conducted using the functional method.

Results

The present study revealed that the C3, C4, and CH50 plasma levels were 142.48 ± 30.38 mg/dL, 32.58 ± 8.78 mg/dL, and 61.74 ± 19.54%, respectively. These results indicate high levels of complement components C3 and C4 and complement function (CH50) in patients with COVID‐19 than normal ranges. Plasma levels of C3, C4, and CH50 were higher in ICU patients than in non‐ICU COVID‐19 groups.

Conclusion

These results indicate that the innate immune system was activated in both ICU and non‐ICU patients in response to SARS‐CoV‐2 infection. Further studies with a larger number of COVID‐19 patients and additional testing of complement components (C3a and C5a) may reveal the role of COVID‐19 infection in the activation of the complement system.

Mechanisms of immunothrombosis and vasculopathy in antiphospholipid syndrome

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.

Pathogenesis, Diagnosis and Management of Obstetric Antiphospholipid Syndrome: A Comprehensive Review

Antiphospholipid syndrome is an autoimmune disorder characterized by vascular thrombosis and/or pregnancy morbidity associated with persistent antiphospholipid antibody positivity. Cases fulfilling the Sydney criteria for obstetric morbidity with no previous thrombosis are known as obstetric antiphospholipid syndrome (OAPS). OAPS is the most identified cause of recurrent pregnancy loss and late-pregnancy morbidity related to placental injury. Cases with incomplete clinical or laboratory data are classified as obstetric morbidity APS (OMAPS) and non-criteria OAPS (NC-OAPS), respectively. Inflammatory and thrombotic mechanisms are involved in the pathophysiology of OAPS. Trophoblasts, endothelium, platelets and innate immune cells are key cellular players. Complement activation plays a crucial pathogenic role. Secondary placental thrombosis appears by clot formation in response to tissue factor activation. New risk assessment tools could improve the prediction of obstetric complication recurrences or thromboses. The standard-of-care treatment consists of low-dose aspirin and prophylactic low molecular weight heparin. In refractory cases, the addition of hydroxychloroquine, low-dose prednisone or IVIG improve pregnancy outcomes. Statins and eculizumab are currently being tested for treating selected OAPS women. Finally, we revisited recent insights and concerns about the pathophysiology, diagnosis and management of OAPS.

Eculizumab for Refractory Thrombosis in Antiphospholipid Syndrome

Recurrent thrombosis can present in antiphospholipid syndrome despite anticoagulation, antiplatelet, and immunosuppressive therapies.

Complement inhibition may be a therapeutic option for recurrent thrombosis associated with antiphospholipid syndrome.

Antiphospholipid syndrome (APS) is characterized by arterial and/or venous thrombosis with antiphospholipid antibodies. Dysregulation of the complement pathway has been implicated in APS pathophysiology. We report the successful use of eculizumab, an anti-C5 monoclonal antibody, in controlling and preventing recurrent thrombosis in a refractory case of APS. An 18-year-old female was diagnosed with APS after developing extensive, unprovoked deep vein thrombosis (DVT) of axillary, inferior vena cava, and brachiocephalic veins. Thrombophilia evaluation revealed triple-positive lupus anticoagulant, β-2 glycoprotein IgM, IgA, and anticardiolipin antibodies (each >40 U/mL) with persistently positive titers after 12 weeks. She was refractory to multiple anticoagulants alone (enoxaparin, fondaparinux, apixaban, rivaroxaban, and warfarin) with antiplatelet (aspirin and clopidogrel) and adjunctive therapies (hydroxychloroquine, immunosuppression with steroids and rituximab, and plasmapheresis). Despite these, she continued to develop recurrent thrombosis and additionally developed hepatic infarction and pulmonary embolism with failure to decrease titers after 6 weeks of plasma exchange. Following this event, eculizumab (600 mg weekly × 4 weeks followed by 900 mg every 2 weeks) was initiated in combination with fondaparinux, aspirin, clopidogrel, and hydroxychloroquine. She has remained on this regimen without recurrence of thrombosis. Our case suggests that eculizumab may have a role as a therapeutic option in refractory thrombosis in APS.

Neuropsychiatric Manifestations of Antiphospholipid Syndrome—A Narrative Review

Antiphospholipid syndrome (APS) is a common autoimmune pro-thrombotic condition characterised by thrombosis and pregnancy morbidity. There are a broad range of neuropsychiatric manifestations associated with APS, from focal symptoms to more global dysfunction. Patients commonly present with transient ischaemic attacks and ischaemic strokes, with identifiable lesions on brain imaging. However, the underlying pathogenesis remains uncertain in other manifestations, such as cognitive dysfunction, seizures, headache and chorea. The aim is to provide a comprehensive review of the various neuropsychiatric manifestations associated with APS. A detailed literature search was applied to PubMed, including citations from 1983 to December 2021.

The digestive system involvement of antiphospholipid syndrome: pathophysiology, clinical characteristics, and treatment strategies

Antiphospholipid syndrome (APS) is an autoimmune disease mainly characterised by vascular thrombosis and pregnancy morbidity. APS has broad spectrum of clinical manifestations. The digestive system involvement of antiphospholipid syndrome is a critical but under-recognised condition. Digestive system involvement may be the result of direct (autoimmune-mediated) or indirect (thrombotic) mechanisms. Liver is the most commonly involved organ, followed by intestines, oesophagus, stomach, pancreas and spleen. This review describes possible digestive system manifestations in APS patients, and illustrates the epidemiology and possible pathophysiology of APS. The role of different treatment strategies in the management of digestive system manifestations of APS were also discussed.Key messagesAntiphospholipid syndrome is a multi-organ, multi-system disease and its clinical manifestation spectrum is gradually expanding. Since the first diagnosis of APS, the clinical manifestations of digestive system have been reported successively. This narrative review describes the major digestive system manifestations of APS and illustrates the epidemiology, pathophysiology and the role of therapeutic strategies of these patients.

Successful Treatment of Catastrophic Antiphospholipid Syndrome Using Rituximab: Case Report and Review of the Literature

BACKGROUND

Kidney involvement is a frequent complication of systemic lupus erythematosus (SLE) and kidney biopsy is essential in differentiating lupus nephritis (LN) from thrombotic microangiopathy (TMA) secondary to antiphospholipid autoantibodies (aPL). Association between antiphospholipid syndrome (APS) and acquired hemophilia due to inhibitors was very rarely described in SLE patients.

CASE PRESENTATION

We present the case of a 61-year-old male diagnosed with SLE who acquired deficiency of clotting factor VIII due to circulating inhibitors, admitted for acute kidney injury (AKI), microangiopathic hemolytic anemia, thrombocytopenia, and diplopia. Kidney biopsy showed TMA due to APS, but no signs of LN. Head computed tomography identified low dense areas in the white matter, suggesting small blood vessels' involvement. A diagnosis of probable catastrophic antiphospholipid syndrome (CAPS) was established and treatment with low molecular weight heparin, intravenous methylprednisolone, plasmapheresis, and rituximab was initiated, followed by resolution of AKI, diplopia, and TMA with complete depletion of CD19+B-lymphocytes (CD19+B-Ly) after one month. We further review the current knowledge regarding pathogenesis and management of CAPS in SLE patients.

CONCLUSIONS

Targeted therapy was possible after kidney biopsy, improving renal and general prognosis. CD19+B-Ly repopulation preceded biological relapse, so monitoring of CD19+B-Ly may serve as a tool to predict relapses and guide rituximab therapy.

B cell-derived anti-beta 2 glycoprotein I antibody contributes to hyperhomocysteinaemia-aggravated abdominal aortic aneurysm

AIMS

Overactivated B cells secrete pathological antibodies, which in turn accelerate the formation of abdominal aortic aneurysms (AAAs). Hyperhomocysteinaemia (HHcy) aggravates AAA in mice; however, the underlying mechanisms remain largely elusive. In this study, we further investigated whether homocysteine (Hcy)-activated B cells produce antigen-specific antibodies that ultimately contribute to AAA formation.

METHODS AND RESULTS

ELISA assays showed that HHcy induced the secretion of anti-beta 2 glycoprotein I (anti-β2GPI) antibody from B cells both in vitro and in vivo. Mechanistically, Hcy increased the accumulation of various lipid metabolites in B cells tested by liquid chromatography-tandem mass spectrometry, which contributed to elevated anti-β2GPI IgG secretion. By using the toll-like receptor 4 (TLR4)-specific inhibitor TAK-242 or TLR4-deficient macrophages, we found that culture supernatants from Hcy-activated B cells and HHcy plasma IgG polarized inflammatory macrophages in a TLR4-dependent manner. In addition, HHcy markedly increased the incidence of elastase- and CaPO4-induced AAA in male BALB/c mice, which was prevented in μMT mice. To further determine the importance of IgG in HHcy-aggravated AAA formation, we purified plasma IgG from HHcy or control mice and then transferred the IgG into μMT mice, which were subsequently subjected to elastase- or CaPO4-induced AAA. Compared with μMT mice that received plasma IgG from control mice, μMT mice that received HHcy plasma IgG developed significantly exacerbated elastase- or CaPO4-induced AAA accompanied by increased elastin degradation, MMP2/9 expression, and anti-β2GPI IgG deposition in vascular lesions, as shown by immunofluorescence histochemical staining.

CONCLUSION

Our findings reveal a novel mechanism by which Hcy-induced B cell-derived pathogenic anti-β2GPI IgG might, at least in part, contribute to HHcy-aggravated chronic vascular inflammation and AAA formation.

Complement and the prothrombotic state

In 2007 and 2009 the regulatory approval of the first-in-class complement inhibitor Eculizumab has revolutionized the clinical management of two rare, life-threatening clinical conditions: paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). While being completely distinct diseases affecting blood cells and the glomerulus, PNH and aHUS remarkably share several features in their etiology and clinical presentation. An imbalance between complement activation and regulation at host surfaces underlies both diseases precipitating in severe thrombotic events that are largely resistant to anti-coagulant and/or anti-platelet therapies. Inhibition of the common terminal complement pathway by Eculizumab prevents the frequently occurring thrombotic events responsible for the high mortality and morbidity observed in patients not treated with anti-complement therapy. While many in vitro and ex vivo studies elaborate numerous different molecular interactions between complement activation products and hemostasis, this review focuses on the clinical evidence that links these two fields in humans. Several non-infectious conditions with known complement involvement are scrutinized for common patterns concerning a prothrombotic statues and the occurrence of certain complement activation levels. Next to PNH and aHUS, germline encoded CD59 or CD55 deficiency (the latter causing the disease Complement Hyperactivation, Angiopathic thrombosis, and Protein-Losing Enteropathy; CHAPLE), autoimmune hemolytic anemia (AIHA), (catastrophic) anti-phospholipid syndrome (APS, CAPS) and C3 glomerulopathy are considered. Parallels and distinct features among these conditions are discussed against the background of thrombosis, complement activation, and potential complement diagnostic and therapeutic avenues.

Low Preconception Complement Levels Are Associated with Adverse Pregnancy Outcomes in a Multicenter Study of 260 Pregnancies in 197 Women with Antiphospholipid Syndrome or Carriers of Antiphospholipid Antibodies

Antiphospholipid antibodies (aPL) can induce fetal loss in experimental animal models. Human studies did find hypocomplementemia associated with pregnancy complications in patients with antiphospholipid syndrome (APS), but these results are not unanimously confirmed. To investigate if the detection of low C3/C4 could be considered a risk factor for adverse pregnancy outcomes (APO) in APS and aPL carriers' pregnancies we performed a multicenter study including 503 pregnancies from 11 Italian and 1 Russian centers. Data in women with APS and asymptomatic carriers with persistently positive aPL and preconception complement levels were available for 260 pregnancies. In pregnancies with low preconception C3/C4, a significantly higher prevalence of pregnancy losses was observed (p = 0.008). A subgroup analysis focusing on triple aPL-positive patients found that preconception low C3 and/or C4 levels were associated with an increased rate of pregnancy loss (p = 0.05). Our findings confirm that decreased complement levels before pregnancy are associated with increased risk of APO. This has been seen only in women with triple aPL positivity, indeed single or double positivity does not show this trend. Complement levels are cheap and easy to be measured therefore they could represent a useful aid to identify patients at increased risk of pregnancy loss.

Ischemic Stroke: An Underestimated Complication of COVID-19

The coronavirus disease 2019 (COVID-19) has spread rapidly as a pandemic around the world. In addition to severe acute respiratory syndrome, more and more studies have focused on the complication of COVID-19, especially ischemic stroke. Here, we propose several pathophysiological processes and possible mechanisms underlying ischemic stroke after COVID-19 for early prevention and better treatment of COVID-19-related stroke.

Complement, inflammation and thrombosis

A mutual relationship exists between immune activation and mechanisms of thrombus formation. In particular, elements of the innate immune response such as the complement system can modulate platelet activation and subsequently thrombus formation. Several components of the complement system including C3 or the membrane attack complex have been reported to be associated with platelets and become functionally active in the micromilieu of platelet activation. The exact mechanisms how this interplay is regulated and its consequences for tissue inflammation, damage or recovery remain to be defined. This review addresses the current state of knowledge on this topic and puts it into context with diseases featuring both thrombosis and complement activation. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

New insights into the pathogenic mechanisms and treatment of arterial thrombosis in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic disorder clinically characterized by widespread thrombosis and obstetric complications associated with the persistent presence of antiphospholipid antibodies (aPLs). The persistent presence of aPLs represents a thrombotic risk in APS, which can be stratified according to the aPL profile. Thrombosis occurs in both arteries and veins. Notably, arterial thromboses have a higher recurrence compared with venous thromboses and a tendency for recurrence in the same vascular (arterial) site. Secondary prevention of arterial thrombosis requires more intensive treatment than prevention of venous thrombosis. Data from randomized clinical trials indicated that factor Xa inhibitors should not be recommended for APS. Recurrent thromboses in patients with APS treated with factor Xa inhibitors were mainly arterial, with a high rate of stroke. Dual antiplatelet therapy may have some benefit for preventing the recurrence of arterial thrombosis in patients with APS. This review article describes pathogenic mechanisms, clinical features, risk assessment, and management of arterial thrombosis in patients with APS. Particularly, we discuss how secondary prophylaxis may be a useful approach to reduce the occurrence of arterial thrombosis.

The interaction between the complement system and hemostatic factors

PURPOSE OF REVIEW

To discuss the crosstalk between the complement system and hemostatic factors (coagulation cascade, platelet, endothelium, and Von Willebrand Factor), and the consequences of this interaction under physiologic and pathologic conditions.

RECENT FINDINGS

The complement and coagulation systems are comprised of serine proteases and are genetically related. In addition to the common ancestral genes, the complement system and hemostasis interact directly, through protein-protein interactions, and indirectly, on the surface of platelets and endothelial cells. The close interaction between the complement system and hemostatic factors is manifested both in physiologic and pathologic conditions, such as in the inflammatory response to thrombosis, thrombosis at the inflamed area, and thrombotic complications of complement disorders.

SUMMARY

The interaction between the complement system and hemostasis is vital for homeostasis and the protective response of the host to tissue injury, but also results in the pathogenesis of several thrombotic and inflammatory disorders.

B cells in primary antiphospholipid syndrome: Review and remaining challenges

It is now widely accepted that antiphospholipid antibodies (aPL) have direct pathogenic effects and that B cells, notably through aPL production, play a key role in the development of antiphospholipid syndrome (APS). Recent findings strengthened the implication of B cells with the description of specific B cell phenotype abnormalities and inborn errors of immunity involving B cell signaling in APS patients. In addition, it has been shown in preclinical models that cross-reactivity between APS autoantigens and mimotopes expressed by human gut commensals can lead to B cell tolerance breakdown and are sufficient for APS development. However, B cell targeting therapies are surprisingly not as effective as expected in APS compared to other autoimmune diseases. Elucidation of the B cell tolerance breakdown mechanisms in APS patients may help to develop and guide the use of novel therapeutic agents that target B cells or specific immune pathway.

Understanding the Pathophysiology of Thrombotic APS through Animal Models

Antiphospholipid syndrome (APS) is a leading acquired cause of thrombotic events, with a notable tendency to promote thrombosis in vascular beds of all sizes, including both arterial and venous circuits. While pathogenic antiphospholipid antibodies circulate at relatively stable levels in blood, thrombosis tends to manifest as discrete and acute events, suggesting the requirement for a “second hit.” While this two-hit model is generally accepted, much remains to be learned about exactly how antiphospholipid antibodies predispose to thrombosis in vivo and exactly how this predisposition interacts with the second hit. To this end, investigators have turned to animal models. Numerous approaches for modeling APS in animals have been described to date, each with potential advantages and disadvantages. This review will attempt to describe the most common APS models employed so far while discussing some pros and cons of each. Mechanisms of thrombotic APS that have thus far been explored in animal models will also be briefly addressed.

Systemic lupus erythematosus multiorgan flare with quiescent serologic markers

Systemic lupus erythematosus (SLE) can affect almost every organ with differing degrees of severity. Typically, SLE activity is associated with hypocomplimentaemia and elevated double-stranded DNA (dsDNA) levels. We describe a case of a severe multiorgan lupus flare including lupus cerebritis, autoimmune haemolytic anaemia, lupus nephritis and lupus myopericarditis with normal complement and dsDNA levels. This highlights the importance of understanding the heterogeneous nature of SLE flares.

Antiphospholipid syndrome: Complement activation, complement gene mutations, and therapeutic implications

Antiphospholipid syndrome (APS) is an acquired thromboinflammatory disorder characterized by the presence of antiphospholipid antibodies as well as an increased frequency of venous or arterial thrombosis and/or obstetrical morbidity. The spectrum of disease varies from asymptomatic to a severe form characterized by widespread thrombosis and multiorgan failure, termed catastrophic APS (CAPS). CAPS affects only about ∼1% of APS patients, often presents as a thrombotic microangiopathy and has a fulminant course with >40% mortality, despite the best available therapy. Animal models have implicated complement in the pathophysiology of thrombosis in APS, with more recent data from human studies confirming the interaction between the coagulation and complement pathways. Activation of the complement cascade via antiphospholipid antibodies can cause cellular injury and promote coagulation via multiple mechanisms. Finally, analogous to classic complement-mediated diseases such as atypical hemolytic uremic syndrome, a subset of patients with APS may be at increased risk for development of CAPS because of the presence of germline variants in genes crucial for complement regulation. Together, these data make complement inhibition an attractive and potentially lifesaving therapy to mitigate morbidity and mortality in severe thrombotic APS and CAPS.

Neuropathological spectrum in systemic lupus erythematosus: A single institute autopsy experience

AIM

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease characterized by circulating autoantibodies and immune complexes involving virtually every organ of the body. However, with respect to central nervous system (CNS), the mechanism of injury is still debated as complement mediated or thrombo-ischemic in nature. We studied the spectrum of neuropathological changes in twelve autopsy cases of SLE and evaluated the role of immune-complexes and complement activation in contributing to the thrombo-ischemic injury and correlated these features with clinical profile.

METHODS

Autopsy records of all cases of SLE over a period of 20 years (2000-2019) were reviewed. Clinical history including neuropsychiatric symptoms and detailed histopathological analysis was performed. Direct immunofluorescence for IgM, IgG, IgA, C1q, C3, C4d, Kappa, Lambda and immunohistochemistry for C5b-9 was performed on lesional areas in paraffin embedded brain sections. Control tissue from brain was taken from two patients who died of sudden cardiac event.

RESULTS

Our cohort comprised of 12 cases with age range from 12 to 40 years and all were female patients. Microinfarction and vasculopathy seen in eight cases were the commonest findings. Four cases with microinfarcts had non-bacterial thrombotic endocarditis in heart. Microthrombi adjacent to microinfarcts were seen in 4 cases. Variable deposition of immunoglobulins (predominantly IgG) and complements (C1q, C3, C4d) was evident in cortical arterioles (2 cases) and small capillaries (1 case). Neurological symptoms were seen in four cases, of which, three had associated invasive fungal infection with secondary vasculitis. Active lupus vasculitis was identified in a single case. C5b-9 immunoexpression was not detected in any of the cases.

CONCLUSIONS

Our study adds observational data to the existing literature that the predominant neuropathological features of SLE are related to thrombo-ischemic injury and small vasculopathic changes. Only in a minor subset (25%), it is mediated by immune-complexes and complements. Immune-complex deposition on immunofluorescence in cortical vessels (cerebral lupus vasculopathy) is a novel finding which has not been reported earlier.

Antiphospholipid syndrome: a clinical perspective

Antiphospholipid syndrome (APS) is a thromboinflammatory disease with a variety of clinical phenotypes. Primary thrombosis prophylaxis should take an individualized risk stratification approach. Moderate-intensity vitamin K antagonist such as warfarin remains the primary strategy for secondary thrombosis prophylaxis among APS patients, especially for patients with predominantly venous disease. For now, direct oral anti-coagulants should be avoided in most APS patients, especially those with history of arterial manifestations. Obstetric APS management should be tailored based on an individual patient's antiphospholipid antibody profile, and obstetric and thrombotic history. Pharmacological agents beyond anticoagulants may be considered for the management of microthrombotic and nonthrombotic manifestations of APS, although more data are needed. A relatively recent discovery in the area of APS pathogenesis is the implication of neutrophil extracellular traps in thrombin generation and initiation of inflammatory cascades. APS is a complex thromboinflammatory disease with a broad clinical spectrum. Personalized therapy according to an individual's unique thrombosis and obstetric risk should be advocated.

Thrombotic antiphospholipid syndrome: A practical guide to diagnosis and management

Thrombotic antiphospholipid syndrome (APS) is characterised by venous, arterial and/or small vessel thrombosis in the context of persistently positive antiphospholipid antibodies (aPL). The diagnosis and management of thrombotic APS continues to prove challenging for clinicians. We provide a practical guide to the diagnosis of APS including who to test for aPL and which tests to do. We also consider clinical practice points on the management of venous, arterial and small vessel thrombosis, in the context of first and recurrent thrombotic events. Non-criteria manifestations of APS are reviewed. An approach to recurrent thrombosis and anticoagulant-refractory APS is discussed, with options including increasing the anticoagulation intensity of vitamin K antagonists, switching to low-molecular-weight-heparin, the use of fondaparinux and/or the addition of antiplatelet treatment. Adjunctive options such as vitamin D, hydroxychloroquine and statins are also addressed.

The management of neuropsychiatric lupus in the 21st century: still so many unmet needs?

Neuropsychiatric (NP) events occur in the majority of patients with SLE and predominantly affect the CNS in addition to the peripheral and autonomic systems. Approximately 30% of all NP events are attributable to SLE (NPSLE) and present most frequently around the time of SLE onset. NPSLE is associated with increased morbidity and mortality and the proposed pathogenesis includes both ischaemic and neuroinflammatory mechanisms. Following diagnosis and causal attribution, the treatment of NPSLE is tailored to the type of NP event, the predominant putative pathogenic pathway and the activity and severity of the clinical event. There is a dearth of controlled clinical trials to guide management, but therapeutic options include symptomatic, antithrombotic and immunosuppressive agents that are supported by observational cohort studies. Our objective was to review what is currently known about NPSLE and to identify deficiencies in diagnostic biomarkers, novel therapies and clinical trials for this manifestation of SLE.

Treatment of thrombotic antiphospholipid syndrome in adults and children

PURPOSE OF REVIEW

Antiphospholipid syndrome (APS), more common than once believed, is an autoimmune disease best known for its high risk of incident and recurrent thrombotic events. The approach to treatment potentially differs from treatment of thrombosis in the general population, and this article endeavors to review the latest updates on this topic.

RECENT FINDINGS

The epidemiology of APS is being increasingly elucidated by large population-based studies, with APS perhaps affecting as many as 1 in 2000 individuals. Vitamin K antagonists, aspirin, and heparinoids continue to have obvious roles in the management of patients with APS. There has recently been intensive study of direct oral anticoagulants in APS, with the most recent randomized studies raising concerns about their inferiority to vitamin K antagonists, at least in some subgroups. Other approaches to treating APS beyond anticoagulants and antiaggregants are also receiving increased attention in mechanistic and preclinical studies with an eye toward future roles in patients with refractory and/or microvascular disease. Pediatric APS is identified as an area in desperate need of additional prospective research.

SUMMARY

Progress continues to be made in pursuit of improving the lives of individuals afflicted with APS. The most important future directions would seem to involve leveraging modern molecular technologies in order to improve subphenotyping of antiphospholipid antibody-positive individuals. This will help personalize risk profiles and ideally define the optimal approach to therapy based on future risk, rather than past morbid events.

Complement as a Therapeutic Target in Systemic Autoimmune Diseases

The complement system (CS) includes more than 50 proteins and its main function is to recognize and protect against foreign or damaged molecular components. Other homeostatic functions of CS are the elimination of apoptotic debris, neurological development, and the control of adaptive immune responses. Pathological activation plays prominent roles in the pathogenesis of most autoimmune diseases such as systemic lupus erythematosus, antiphospholipid syndrome, rheumatoid arthritis, dermatomyositis, and ANCA-associated vasculitis. In this review, we will review the main rheumatologic autoimmune processes in which complement plays a pathogenic role and its potential relevance as a therapeutic target.

Recurrent pregnancy loss

Recurrent pregnancy loss is a distressing pregnancy disorder experienced by ~2.5% of women trying to conceive. Recurrent pregnancy loss is defined as the failure of two or more clinically recognized pregnancies before 20-24 weeks of gestation and includes embryonic and fetal losses. The diagnosis of an early pregnancy loss is relatively straightforward, although progress in predicting and preventing recurrent pregnancy loss has been hampered by a lack of standardized definitions, the uncertainties surrounding the pathogenesis and the highly variable clinical presentation. The prognosis for couples with recurrent pregnancy loss is generally good, although the likelihood of a successful pregnancy depends on maternal age and the number of previous losses. Recurrent pregnancy loss can be caused by chromosomal errors, anatomical uterine defects, autoimmune disorders and endometrial dysfunction. Available treatments target the putative risk factors of pregnancy loss, although the effectiveness of many medical interventions is controversial. Regardless of the underlying aetiology, couples require accurate information on their chances of having a baby and appropriate support should be offered to reduce the psychological burden associated with multiple miscarriages. Future research must investigate the pathogenesis of recurrent pregnancy loss and evaluate novel diagnostic tests and treatments in adequately powered clinical trials.

Case of catastrophic antiphospholipid syndrome presenting as neuroretinitis and vaso-occlusive retinopathy

BACKGROUND

Ocular involvement in catastrophic antiphospholipid syndrome (CAPS), a rare, life-threatening form of antiphospholipid syndrome (APS) that results in multiorgan failure and a high mortality rate, has rarely been reported.

CASE PRESENTATION

A 15-year-old girl presented with sudden vision blurring in both eyes. She had marked optic disc swelling and macular exudates in the right eye and intra-arterial white plaques, a few retinal blot hemorrhages, and a white ischemic retina in the left eye. Systemic examination revealed she had acute kidney injury with thrombotic microangiopathy (TMA), multiple cerebral infarcts, valvular dysfunction, and a high titer of triple aPL. Thus, she was diagnosed with CAPS involving the brain, eyes, heart, and kidneys. Plasma exchange and the administration of glucocorticoids, immunoglobulin, warfarin, and rituximab brought a sustained recovery of the TMA, visual symptoms, and echocardiographic findings.

CONCLUSIONS

Ocular involvement of both vaso-occlusive retinopathy, an APS-related thrombotic microangiopathy, and neuroretinitis, a non-thrombotic microangiopathy, can occur as an initial presentation of CAPS.