A systematic review of the association between anti-β-2 glycoprotein I antibodies and APS manifestations

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.

Evaluation of Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) affects approximately 5% of couples. Although RPL definitions vary across professional societies, an evaluation after a second clinically recognized first-trimester pregnancy loss is recommended. Good quality evidence links parental chromosomal rearrangements, uterine anomalies, and antiphospholipid syndrome (APS) to RPL. In contrast, the relationship between RPL and other endocrine, hematologic, and immunologic disorders or environmental exposures is less clear. Anticoagulant therapy and low-dose aspirin are recommended for patients with RPL who have also been diagnosed with APS. Vaginal progesterone supplementation may be considered in patients experiencing vaginal bleeding during the first trimester. Surgical correction may be considered for patients with RPL in whom a uterine anomaly is identified. Evaluation and management of additional comorbidities should be guided by the patient's history rather than solely based on the diagnosis of RPL, with the goal of improving overall health to reduce complications in the event of pregnancy. Most people with RPL, including those without identifiable risk factors, are expected to achieve a live birth within 5 years from the initial evaluation. Nevertheless, clinicians should be sensitive to the psychological needs of individuals with this condition and provide compassionate and supportive care across all stages.

How I diagnose and treat antiphospholipid syndrome in pregnancy

ABSTRACT

Antiphospholipid syndrome (APS) is a rare autoimmune disease characterized by arterial, venous, or microvascular thrombosis, pregnancy morbidities, or nonthrombotic manifestations in patients with persistently positive antiphospholipid antibodies. These antibodies bind cellular phospholipids and phospholipid-protein complexes resulting in cellular activation and inflammation that lead to the clinical features of APS. Our evolving understanding of APS has resulted in more specific classification criteria. Patients meeting these criteria should be treated during pregnancy according to current guidelines. Yet, despite treatment, those positive for lupus anticoagulant have at least a 30% likelihood of adverse pregnancy outcomes. Patients with recurrent early miscarriage or fetal death in the absence of preeclampsia or placental insufficiency may not meet current classification criteria for APS. Patients with only low titer anticardiolipin or anti-β(2)-glycoprotein I antibodies or immunoglobulin M isotype antibodies will not meet current classification criteria. In such cases, clinicians should implement management plans that balance potential risks and benefits, some of which involve emotional concerns surrounding the patient's reproductive future. Finally, APS may present in pregnancy or postpartum as a thrombotic microangiopathy, a life-threatening condition that may initially mimic preeclampsia with severe features but requires a very different treatment approach.

SAMD1 attenuates antiphospholipid syndrome-induced pregnancy complications

OBJECTIVE

This study was intended to investigate the effect of SAMD1 on antiphospholipid syndrome (APS)-induced pregnancy complications in mice.

METHODS

The mRNA and protein expression of SAMD1 in APS patients and healthy controls was detected by qRT-PCR and western blot. Anti-B2 GPI and ACA levels were tested by ELISA, MMP-9, iNOS, ICAM-1 and MCP-1 mRNA and protein levels determined by qRT-PCR and western blot, cellular senescence detected by β-galactosidase staining, cell proliferation ability detected by CCK-8 assay, cell viability detected by trypan blue staining, cell mobility detected by Transwell, and cell angiogenesis ability detected by matrigel tube formation assay. An APS pregnant mouse model was constructed, and the embryo absorption rate was calculated.

RESULTS

SAMD1 expression was low in serum of APS patients, which was correlated with the history of thrombosis and the number of adverse pregnancies. Anti-B2 GPI and ACA levels were increased in APS. The expressions of MMP-9, iNOS, ICAM-1, and MCP-1 were also significantly upregulated in HUVECs treated with APS serum. APS promoted HUVEC senescence and inhibited cell proliferation, migration and angiogenesis. Overexpression of SAMD1 reversed the above results. Experiments on the APS pregnant mouse model confirmed that overexpression of SAMD1 reduced the rate of fetal loss.

CONCLUSION

SAMD1 may reduce APS-induced embryo loss by regulating cellular senescence, proliferation, migration, and angiogenesis.

Antibodies to Domain I β2-Glycoprotein 1 in Patients with Antiphospholipid Syndrome and Systemic Lupus Erythematosus

The role of antiphospholipid antibodies (aPL), which are not included in the Sydney diagnostic criteria, in antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) is poorly understood. The aim of this study was to determine the clinical significance of IgG antibodies for domain 1 of β2-glycoprotein 1 (β2-GP1), IgG anti-β2-GP1DI, in patients with APS with and without SLE. The study included 187 patients with APS with or without SLE, 49 patients formed the comparison group, and 100 apparently healthy individuals formed the control group. IgG/IgM antibodies to cardiolipin (aCL) and IgG/IgM anti-β2-GP1 were determined by enzyme immunoassay (ELISA) in patients with or without APS, and IgG anti-β2-GP1DI was determined by chemiluminescence assay (CLA) in all patients and controls. IgG anti-β2-GP1DI was detected in 37 (71%) of 52 patients with primary APS (PAPS), in 6 (50%) of 12 patients with probable APS, in 42 (71%) of 59 patients with SLE + APS, in 17 (26%) of 64 patients with SLE, in 1 (2%) of the comparison group, and in none of the control group. IgG anti-β2-GP1DI was significantly associated with PAPS and SLE + APS compared with the patients with SLE (p = 0.0002 and 0.0001, respectively). The association of IgG anti-β2-GP1DI with clinical manifestations of APS (thrombosis (p = 0.001) and obstetric pathology (p = 0.04)) was detected. There was a significant association of IgG anti-β2-GP1DI with arterial thrombosis (p = 0.002) and with late gestational obstetric pathology (p = 0.01). High specificity of IgG anti-β2-GP1DI depending on the diagnosis and clinical manifestations of APS despite low sensitivity was noted: specificity was 84% for thrombosis, 94% for obstetric pathology, and 89% for APS. Isolated IgG anti-β2-GP1DI positivity was reported in 2% of 50 aPL-negative patients and was not associated with APS manifestations. The frequency of IgG anti-β2-GP1DI detection was higher in the patients with APS compared to the patients with SLE, comparison group, and control (p < 0.05). Positive IgG anti-β2-GP1DI values were significantly associated with thrombotic complications and with obstetric pathology (p = 0.002 and p = 0.01, respectively). Specificity of IgG anti-β2-GP1DI for APS and its clinical manifestations (thrombosis and obstetric pathology) was higher than sensitivity (89, 94, and 84%, respectively).

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.

Laboratory Testing for Non-criteria Antiphospholipid Antibodies: Antibodies Toward the Domain I of Beta2-Glycoprotein I (aDI)

Anti-β2GPI antibodies (aβ2GPI) are one of the laboratory criteria for antiphospholipid syndrome (APS), along with lupus anticoagulant (LA) and anticardiolipin antibodies (aCL). A subset of the aβ2GPI are the antibodies directed toward the domain I of the β2GPI (aDI). The aDI are regarded as non-criteria aPL and are among the most studied non-criteria aPL. Antibodies directed against a specific epitope in the domain I (G40-R43) of β2GPI were shown to be strongly correlated with thrombotic and obstetric events in APS. Many studies illustrated the pathogenic capacity of these antibodies, although with various results, depending on the assay used. The first studies were performed with an in-house ELISA with high specificity for aDI toward the G40-R43 epitope. More recently, a commercial chemiluminescence immunoassay for aDI IgG became obtainable for diagnostic laboratories. Although the added value of aDI on top of the criteria aPL is not clear, with opposing findings in literature, the assay might help in the diagnosis of APS, identifying the patients at risk since aDI are frequently present with high titers in triple-positive patients (positive for LA, aβ2GPI, and aCL). aDI can be used as a confirmatory test and is useful for proving the specificity of the aβ2GPI antibodies. In this chapter, the procedure for detecting these antibodies is outlined, using an automated chemiluminescence assay which can be used to determine the presence of IgG aDI in human samples. General guidelines that will facilitate optimal performance of the aDI assay are also provided.

Antiphospholipid Antibody Testing for Anti-cardiolipin and Anti-β2 Glycoprotein I Antibodies Using Chemiluminescence-Based Panels

Antiphospholipid (antibody) syndrome (APS) is a prothrombotic condition with increased risk for thrombosis and pregnancy-related morbidity. In addition to clinical criteria related to these risks, APS is characterized by the persistent presence of antiphospholipid antibodies (aPL), as detected in the laboratory using a potentially wide variety of assays. The three APS criteria-related assays are lupus anticoagulant (LA), as detected using clot-based assays, and the solid-phase assays of anti-cardiolipin antibodies (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI), with immunoglobulin subclasses of IgG and/or IgM. These tests may also be used for the diagnosis of systemic lupus erythematosus (SLE). In particular, APS diagnosis/exclusion remains challenging for clinicians and laboratories because of the heterogeneity of clinical presentations in those being evaluated and the technical application and variety of the associated tests used in laboratories. Although LA testing is affected by a wide variety of anticoagulants, which are often given to APS patients to prevent any associated clinical morbidity, detection of solid-phase aPL is not influenced by these anticoagulants, and this thus represents a potential advantage to their application. On the other hand, various technical issues challenge accurate laboratory detection or exclusion of aPL. This report describes protocols for the assessment of solid-phase aPL, specifically aCL and aβ2GPI of IgG and IgM class by means of a chemiluminescence-based assay panel. These protocols reflect tests able to be performed on the AcuStar instrument (Werfen/Instrumentation Laboratory). Certain regional approvals may also allow this testing to be performed on a BIO-FLASH instrument (Werfen/Instrumentation Laboratory).

[Clinical significance of oxidized low-density lipoprotein antibody in antiphospholipid syndrome]

OBJECTIVE

To investigate the significance and distribution of oxidized low-density lipoprotein antibodies (ox-LDL-Ab) in patients with antiphospholipid syndrome (APS).

METHODS

In this study, 334 patients who were hospitalized in the Department of Rheumatology and Immunology, Peking University People's Hospital were included. There were 162 APS patients, 122 patients with other autoimmune diseases without thrombosis or obstetric disease as disease control and 50 healthy controls. The clinical data and laboratory indicators were retrospectively collected. The ox-LDL-Ab, anticardiolipin (aCL) IgG/IgA/IgM, and anti-β2-glycoprotein Ⅰ (aβ2GPI) IgG/IgA/IgM were detected by enzyme-linked immunosorbent assay (ELISA). The relationship between ox-LDL-Ab and clinical and laboratory parameters were analyzed by SPSS 27.0.

RESULTS

In APS group, 60.5% of patients had thrombosis, 48.1% had pregnancy morbidity, 34.0% had thrombocytopenia. The positive rates of aCL, aβ2GPI and lupus anticoagulant (LAC) were 17.9%, 34.6%, and 46.9%, respectively. The ox-LDL-Ab titers and positive rate in APS group were higher than that in healthy controls [titers: 40.8 (25.4-66.0) U/mL vs. 24.1 (12.3-36.5) U/mL, P=0.001; positive rate: 67.3% vs. 36.0%, P=0.001]. The diffe-rences in titers and positive rate of ox-LDL-Ab between APS patients and disease controls were not statistically significant [titers: 40.8 (25.4-66.0) U/mL vs. 35.9 (24.2-53.1) U/mL, P=0.118; positive rate: 67.3% vs. 61.5%, P=0.318]. The area under curve (AUC) for aβ2GPI, aCL, and ox-LDL-Ab were 0.745 (95%CI: 0.692-0.797), 0.666 (95%CI: 0.608-0.724), 0.609 (95%CI: 0.549-0.669), respectively. The Youden's index was 0.388, 0.269, and 0.132, respectively. The AUC for ox-LDL-Ab in seronegative APS patients was 0.562 (95%CI: 0.480-0.645). The sensitivity and specificity of ox-LDL-Ab in seronegative APS patients were 63.9% and 47.0%, respectively, and the Youden's index was 0.109. The ox-LDL-Ab positive group had higher positive rate of aβ2GPI (42.2% vs. 18.9%, P=0.003) and aCL (22.9% vs. 7.5%, P=0.017) than the ox-LDL-Ab negative group. There was no correlation between ox-LDL-Ab and thrombosis, coronary artery disease, pregnancy morbidity, hyperlipidemia, hypocomplementemia, and LAC positivity.

CONCLUSION

Ox-LDL-Ab was correlated with aCL and aβ2GPI, and no association were observed between ox-LDL-Ab and thrombosis, coronary artery disease, and pregnancy morbidity.

SAMD1 attenuates antiphospholipid syndrome-induced vascular injury and pregnancy complications

OBJECTIVE

This study was intended to investigate the effect of SAMD1 on antiphospholipid syndrome (APS)-induced vascular injury in human umbilical vein endothelial cells (HUVECs) and pregnancy complications in mice.

METHODS

The expression of SAMD1 in APS patients and healthy controls was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Anti-B₂ GPI and anticardiolipin antibody (ACA) levels were tested by enzyme-linked immunosorbent assay, MMP-9, iNOS, ICAM-1, and MCP-1 mRNA and protein levels determined by qRT-PCR and Western blot, cellular senescence detected by β-galactosidase staining, cell proliferation ability detected by CCK-8 assay, cell viability detected by trypan blue staining, cell mobility detected by Transwell, and cell angiogenesis ability detected by matrigel tube formation assay. An APS pregnant mouse model was constructed, and the embryo absorption rate was calculated.

RESULTS

SAMD1 expression was low in serum of APS patients, which was correlated with the history of thrombosis and the number of adverse pregnancies. Anti-B₂ GPI and ACA levels were increased in APS. The expressions of MMP-9, iNOS, ICAM-1, and MCP-1 were also significantly upregulated in HUVECs treated with APS serum. APS promoted HUVEC senescence and inhibited cell proliferation, migration, and angiogenesis. Overexpression of SAMD1 reversed the above results. Experiments on the APS pregnant mouse model confirmed that overexpression of SAMD1 reduced the rate of fetal loss.

CONCLUSION

SAMD1 may reduce APS-induced vascular injury and embryo loss by regulating cellular senescence, proliferation, migration, and angiogenesis.

Determination of Thrombogenicity Levels of Various Antiphospholipid Antibodies by a Modified Thrombin Generation Assay in Patients with Suspected Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is a hypercoagulable state accompanied by the presence of heterogeneous antiphospholipid antibodies (aPL), which nonspecifically affect hemostasis by the presence of lupus anticoagulans (LA), anticardiolipin antibodies (aCL), antibodies against β2-glycoprotein-I (anti-β2GPI), but also non-criteria antibodies such as antibodies against β2-glycoprotein-I domain I (anti-DI), anti-phosphatidylserine/prothrombin (anti-PS/PT), anti-annexin V, and many others. The main target of the antibodies is the activated protein C (APC) system, the elimination of which can manifest itself as a thrombotic complication. The aim of this study was to determine the thrombogenicity of antibodies using a modified protein C-activated thrombin generation assay (TGA) on a group of 175 samples suspected of APS. TGA was measured with/without APC and the ratio of both measurements was evaluated (as for APC resistance), where a cut-off was calculated ≤4.5 (90th percentile) using 21 patients with heterozygous factor V Leiden mutation (FV Leiden heterozygous). Our study demonstrates the well-known fact that multiple positivity of different aPLs is a more severe risk for thrombosis than single positivity. Of the single antibody positivity, LA antibodies are the most serious (p value < 0.01), followed by aCL and their subgroup anti-DI (p value < 0.05). Non-criteria antibodies anti-annexin V and anti-PT/PS has a similar frequency occurrence of thrombogenicity as LA antibodies but without statistical significance or anti-β2GPI1 positivity. The modified TGA test can help us identify patients in all groups who are also at risk for recurrent thrombotic and pregnancy complications; thus, long-term prophylactic treatment is appropriate. For this reason, it is proving increasingly beneficial to include the determination antibodies in combination with modified TGA test.

Solid Phase Assays for Antiphospholipid Antibodies

The diagnosis of antiphospholipid syndrome (APS) relies on the detection of circulating antiphospholipid antibodies (aPL). Currently, lupus anticoagulant (LA), anticardiolipin (aCL), and anti-β2-glycoprotein I antibodies (aβ2GPI) IgG or IgM are the laboratory criteria if persistently present over time. As aCL and aβ2GPI are two out of the three laboratory criteria, the detection of aPL by solid phase assays is an essential step in the diagnosis of APS. Advancement has been made to resolve some of the methodological challenges of aCL and aβ2GPI assays by providing guidelines how to measure aPL, as well as to gain a better understanding of their diagnostic role. However, solid phase assays for aCL and aβ2GPI still show substantive inter-assay differences, resulting in disagreement concerning positive/negative results, but also differences in titer of antibodies. This hampers the semiquantitative classification into low-medium-high positivity. The non-criteria aPL, such as antibodies against the domain one of β2GPI and anti-phosphatidylserine/prothrombin antibodies (aPS/PT) have roles in confirming the risk in APS, and can be useful, especially in patients with incomplete antibody profiles.

Laboratory Diagnosis of Antiphospholipid Syndrome: Insights and Hindrances

Diagnosis of antiphospholipid syndrome (APS) requires the presence of a clinical criterion (thrombosis and/or pregnancy morbidity), combined with persistently circulating antiphospholipid antibodies (aPL). Currently, laboratory criteria aPL consist of lupus anticoagulant (LAC), anticardiolipin antibodies (aCL) IgG/IgM, and anti-β2 glycoprotein I antibodies (aβ2GPI) IgG/IgM. Diagnosis and risk stratification of APS are complex and efforts to standardize and optimize laboratory tests have been ongoing since the initial description of the syndrome. LAC detection is based on functional coagulation assays, while aCL and aβ2GPI are measured with immunological solid-phase assays. LAC assays are especially prone to interference by anticoagulation therapy, but strategies to circumvent this interference are promising. Alternative techniques such as thrombin generation for LAC detection and to estimate LAC pathogenicity have been suggested, but are not applicable yet in routine setting. For aCL and aβ2GPI, a lot of different assays and detection techniques such as enzyme-linked immunosorbent and chemiluminescent assays are available. Furthermore, a lack of universal calibrators or standards results in high variability between the different solid-phase assays. Other non-criteria aPL such as anti-domain I β2 glycoprotein I and antiphosphatidylserine/prothrombin antibodies have been suggested for risk stratification purposes in APS, while their added value to diagnostic criteria seems limited. In this review, we will describe laboratory assays for diagnostic and risk evaluation in APS, integrating applicable guidelines and classification criteria. Current insights and hindrances are addressed with respect to both laboratory and clinical implications.