Evaluation of the diagnostic potential of antibodies to beta2-glycoprotein 1 domain 1 in Chinese patients with antiphospholipid syndrome

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 Antibodies in Critically Ill Patients With COVID-19

OBJECTIVE

Coagulopathy is one of the characteristics observed in critically ill patients with coronavirus disease 2019 (COVID-19). Antiphospholipid antibodies (aPLs) contribute to coagulopathy, though their role in COVID-19 remains unclear. This study was undertaken to determine the prevalence and characteristics of aPLs in patients with COVID-19.

METHODS

Sera collected from 66 COVID-19 patients who were critically ill and 13 COVID-19 patients who were not critically ill were tested by chemiluminescence immunoassay for anticardiolipin antibodies (aCLs), anti-β₂ -glycoprotein I (anti-β₂ GPI) (IgG, IgM, and IgA), and IgG anti-β₂ GPI-domain 1 (anti-β₂ GPI-D1) and IgM and IgG anti-phosphatidylserine/prothrombin (anti-PS/PT) antibodies were detected in the serum by enzyme-linked immunosorbent assay.

RESULTS

Of the 66 COVID-19 patients in critical condition, aPLs were detected in 31 (47% ). Antiphospholipid antibodies were not present among COVID-19 patients who were not in critical condition. The IgA anti-β₂ GPI antibody was the most commonly observed aPL in patients with COVID-19 and was present in 28.8% (19 of 66) of the critically ill patients, followed by IgA aCLs (17 of 66, or 25.8%) and IgG anti-β₂ GPI (12 of 66, or 18.2%). For multiple aPLs, IgA anti-β₂ GPI + IgA aCLs was the most common antibody profile observed (15 of 66, or 22.7%), followed by IgA anti-β₂ GPI + IgA aCL + IgG anti-β₂ GPI (10 of 66, or 15.2%). Antiphospholipid antibodies emerge ~35-39 days after disease onset. A dynamic analysis of aPLs revealed 4 patterns based on the persistence or transient appearance of the aPLs. Patients with multiple aPLs had a significantly higher incidence of cerebral infarction compared to patients who were negative for aPLs (P = 0.023).

CONCLUSION

Antiphospholipid antibodies were common in critically ill patients with COVID-19. Repeated testing demonstrating medium to high titers of aPLs and the number of aPL types a patient is positive for may help in identifying patients who are at risk of developing cerebral infarction. Antiphospholipid antibodies may be transient and disappear within a few weeks, but in genetically predisposed patients, COVID-19 may trigger the development of an autoimmune condition similar to the antiphospholipid syndrome (APS), referred to as "COVID-19-induced APS-like syndrome." Long-term follow-up of COVID-19 patients who are positive for aPLs would be of great importance in understanding the pathogenesis of this novel coronavirus.

16th International Congress on Antiphospholipid Antibodies Task Force Report on Obstetric Antiphospholipid Syndrome

Obstetric antiphospholipid syndrome (APS) remains a clinical challenge for practitioners, with several controversial points that have not been answered so far. This Obstetric APS Task Force met on the 16th International Congress on Antiphospholipid Antibodies in Manchester, England, to discuss about treatment, diagnostic and clinical aspects of the disease. This report will address evidence-based medicine related to obstetric APS, including limitations on our current management, the relationship between antibodies against domain 1 of β2GPI and obstetric morbidity, hydroxychloroquine use in patients with obstetric APS and factors associated with thrombosis after obstetric APS. Finally, future directions for better understanding this complex condition are also reported by the Task Force coordinators.

Global antiphospholipid syndrome score and anti-ß2-glycoprotein I domain I for thrombotic risk stratification in antiphospholipid syndrome: A four-year prospective study

Objective

This study aimed to assess prospectively the role of anti-ß2-glycoprotein I domain I antibody (aß2GPI-DI) and the Global Antiphospholipid Syndrome Score (GAPSS) in identifying antiphospholipid syndrome (APS) patients at higher risk of a new event.

Methods

Thrombotic APS patients were followed from May 2013 to July 2017. At baseline, we measured lupus anticoagulant, IgG/IgM anticardiolipin, anti-ß2-glycoprotein I, antiphosphatidylserine-prothrombin (aPS/PT) and IgG aß2GPI-DI, and calculated GAPSS for each patient.

Results

A total of 44 patients (age 43 ± 10 years, 89% female, 73% primary APS) were followed for 39 months (range 9–46 months). Four new thromboses occurred, two of them after vitamin K antagonist interruption. Recurrent patients presented higher GAPSS (median 20) and were triple and aß2GPI-DI positive; non-recurrent patients had lower GAPSS (median 10.5, range 0–20) and lower ratio of triple (33%) and aß2GPI-DI positivities (38%). aß2GPI-DI was associated with higher GAPSS (median 19 vs. 7, p < 0.001; Pearson correlation 0.82, p < 0.001) and had a greater proportion of triple (83% vs. 4%, p < 0.001) and aPS/PT positivity (94% vs. 50%, p = 0.002).

Conclusion

Our data show a significant correlation between a validated risk score such as GAPSS and the novel antiphospholipid antibody aß2GPI-DI. Future studies are needed. However, one could speculate a role of aß2GPI-DI as a risk-stratifying tool for thrombotic events in APS.

Detection of anti-domain I antibodies by chemiluminescence enables the identification of high-risk antiphospholipid syndrome patients: A multicenter multiplatform study

BACKGROUND

Classification of the antiphospholipid syndrome (APS) relies predominantly on detecting antiphospholipid antibodies (aPLs). Antibodies against a domain I (DI) epitope of anti-β2glycoprotein I (β2GPI) proved to be pathogenic, but are not included in the current classification criteria.

OBJECTIVES

Investigate the clinical value of detecting anti-DI IgG in APS.

PATIENTS/METHODS

From eight European centers 1005 patients were enrolled. Anti-cardiolipin (CL) and anti-β2GPI were detected by four commercially available solid phase assays; anti-DI IgG by the QUANTA Flash® β2GPI domain I assay.

RESULTS

Odds ratios (ORs) of anti-DI IgG for thrombosis and pregnancy morbidity proved to be higher than those of the conventional assays. Upon restriction to patients positive for anti-β2GPI IgG, anti-DI IgG positivity still resulted in significant ORs. When anti-DI IgG was added to the criteria aPLs or used as a substitute for anti-β2GPI IgG/anti-CL IgG, ORs for clinical symptoms hardly improved. Upon removing anti-DI positive patients, lupus anticoagulant remained significantly correlated with clinical complications. Anti-DI IgG are mainly present in high-risk triple positive patients, showing higher levels. Combined anti-DI and triple positivity confers a higher risk for clinical symptoms compared to only triple positivity.

CONCLUSIONS

Detection of anti-DI IgG resulted in higher ORs for clinical manifestations than the current APS classification criteria. Regardless of the platform used to detect anti-β2GPI/anti-CL, addition of anti-DI IgG measured by QUANTA Flash® did not improve the clinical associations, possibly due to reduced exposure of the pathogenic epitope of DI. Our results demonstrate that anti-DI IgG potentially helps in identifying high-risk patients.

Characteristics of pregnancy complications and treatment in obstetric antiphospholipid syndrome in China

OBJECTIVES

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by obstetric complications and thrombotic events associated with antiphospholipid antibodies (aPL). We aimed to compare the clinical characteristics and treatment of primary APS (PAPS) and secondary APS (systemic lupus erythematosus-APS, SAPS) patients and investigate risk factors associated with obstetric complications in Shanghai, China.

METHODS

We retrospectively collected and analyzed the data of obstetric APS (OAPS) patients from 2000 to 2017 in the APS-Shanghai (APS-SH) database.

RESULTS

One hundred eighty OAPS patients with a total of 450 pregnancies were included in this study. Two hundred twenty-one (49.11%) pregnancies resulted in miscarriage, and 161 (35.77%) pregnancies resulted in intrauterine death. In our cohort, when women were treated, 57 out of 66 pregnancies resulted in live births (86%). Of the 9 treated patients who failed to have live births, 3 had intrauterine deaths, 3 had fetal growth restriction, 2 had pneumorrhagia of the newborn, and 1 had a miscarriage. OAPS patients were divided into two groups: PAPS and SAPS. More SAPS patients than PAPS patients used glucocorticoids (GCs) and hydroxychloroquine (both p < 0.001). However, there was no significant difference in the GC dosage between SAPS and PAPS patients (p = 0.188). Lupus anticoagulant (LAC) and IgG aβ2GPI were risk factors for miscarriage (odds ratio (OR) = 2.398, 95% confidence interval (CI) = 1.276-4.505, p = 0.002; OR = 2.907, 95% CI = 1.558-5.405, p = 0.001, respectively) and intrauterine death (OR = 2.439, 95% CI = 1.299-4.580, p = 0.006; OR = 2.060, 95% CI = 1.089-3.897, p = 0.026, respectively).

CONCLUSIONS

The live birth rate of OAPS patients in Shanghai was 86%. Even if OAPS patients were treated, pregnancy complications could occur, and these patients might need further second-line treatment. Key Points • This is the first study to report data on Chinese OAPS patients. The live birth rate was 86%. • Lupus anticoagulant and IgG aβ2GPI were risk factors for miscarriage and intrauterine death in our cohort. • Despite active treatment, 9 patients had obstetric complications. Therefore, further second-line treatment is still needed.

Oral administration of Domain-I of beta-2glycoprotein-I induces immunological tolerance in experimental murine antiphospholipid syndrome

It is well established that the humoral immunity in antiphospholipid syndrome (APS) is presented by circulating pathogenic anti-β2GPI autoantibodies targeting mainly domain I of the β2GPI protein, playing a major role in the disease pathogenesis. Previously, we have demonstrated that treatment of experimental APS mice with tolerogenic dendritic cells loaded with domain-I was more efficient in tolerance induction than with the whole molecule or domain-V. In the current study we had orally administered a domain-I derivative of the β2GPI molecule, as a new therapeutic approach to induce oral tolerance in this mouse model of APS. BALB/c mice immunized with β2GPI, were fed with either domain-I, domain-V derivative or the complete β2GPI protein. β2GPI immunized mice developed experimental APS which were fed with domain-I significantly had decreased fetal loss (p < 0.004), a lower size of thrombi (p < 0.001) and lower circulating anti-β2GPI Abs in comparison to mice fed with domain-V or PBS (p < 0.002). Likewise, Domain-I fed mice had a lowered inflammatory response, exhibited by decreased expression of inflammatory cytokines (IFNγ, IL-6, IL-17) and elevated production of IL-10 anti-inflammatory cytokine by splenocytes. Moreover, the anti-inflammatory response in the domain-I fed APS mice was associated with increased circulating miRNA variations (155, 146, 182, 98) by RT-PCR, which are associated with immunomodulation of the immune network. We propose that oral tolerance with domain-I can be a novel therapy for patients with APS.

Antiphospholipid Antibodies to Domain I of Beta-2-Glycoprotein I Show Different Subclass Predominance in Comparison to Antibodies to Whole Beta-2-glycoprotein I

Antiphospholipid antibodies (aPL), the serological hallmark of antiphospholipid syndrome (APS), are a heterogeneous group of autoantibodies raised against circulating blood proteins. Of these proteins, the phospholipid-binding b2-glycoprotein I (β2GPI) is considered to be the main autoantigen in APS. Indeed, IgG antibodies targeting b2GPI (ab2GPI) directly cause both thrombosis and pregnancy morbidity in several mouse models. While antibodies raised against all five domains of b2GPI have been reported, a subgroup of IgG ab2GPI raised against the first domain (DI) of b2GPI (aDI), strongly correlate with thrombotic APS, and drive thrombosis and pregnancy loss in vivo. Few studies have focused on determining the type of IgG subclass(es) for aPL. The subclass of an antibody is important as this dictates the potential activity of an antibody; for example, IgG1 and IgG3 can fix complement better and are able to cross the placenta compared to IgG2 and IgG4. It is unknown what subclass IgG aDI are, and whether they are the same as ab2GPI. To determine IgG subclass distribution for ab2GPI and aDI, we purified total IgG from the serum of 19 APS patients with known ab2GPI and aDI activity. Using subclass-specific conjugated antibodies, we modified our established in-house ab2GPI and aDI ELISAs to individually measure IgG1, IgG2, IgG3, and IgG4. We found that while IgG1, IgG2, and IgG3 ab2GPI levels were similar, a marked difference was seen in IgG subclass aDI levels. Specifically, significantly higher levels of IgG3 aDI were detected compared to IgG1, IgG2, or IgG4 (p < 0.05 for all comparisons). Correlation analysis of subclass-specific ab2GPI vs. aDI demonstrated that IgG3 showed the weakest correlation (r = 0.45, p = 0.0023) compared to IgG1 (r = 0.61, p = 0.0001) and IgG2 (r = 0.81, p = 0.0001). Importantly, total subclass levels in IgG purified from APS and healthy serum (n = 10 HC n = 12 APS) did not differ, suggesting that the increased IgG3 aDI signal seen in APS-derived IgG is antigen-specific. To conclude, our data suggests that aDI show a different IgG subclass distribution to ab2GPI. Our results highlight the importance of aDI testing for patient stratification and may point toward differential underlying aPL-driven pathogenic processes that may be subclass restricted.

Antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of antiphospholipid antibodies, such as lupus anticoagulant, anticardiolipin antibodies and anti-β2-glycoprotein 1 antibodies. APS can present with a variety of clinical phenotypes, including thrombosis in the veins, arteries and microvasculature as well as obstetrical complications. The pathophysiological hallmark is thrombosis, but other factors such as complement activation might be important. Prevention of thrombotic manifestations associated with APS includes lifestyle changes and, in individuals at high risk, low-dose aspirin. Prevention and treatment of thrombotic events are dependent mainly on the use of vitamin K antagonists. Immunosuppression and anticomplement therapy have been used anecdotally but have not been adequately tested. Pregnancy morbidity includes unexplained recurrent early miscarriage, fetal death and late obstetrical manifestation such as pre-eclampsia, premature birth or fetal growth restriction associated with placental insufficiency. Current treatment to prevent obstetrical morbidity is based on low-dose aspirin and/or low-molecular-weight heparin and has improved pregnancy outcomes to achieve successful live birth in >70% of pregnancies. Although hydroxychloroquine and pravastatin might further improve pregnancy outcomes, prospective clinical trials are required to confirm these findings.

Coexistence of anti-β2-glycoprotein I domain I and anti-phosphatidylserine/prothrombin antibodies suggests strong thrombotic risk

BACKGROUND

Highly specific assays for measuring antiphospholipid antibodies (aPLs) are required for accurate assessment of thrombotic risk. aPLs against β2-glycoprotein I domain I (anti-β2GPIdI) and against prothrombin complexed with phosphatidylserine (anti-PS/PT) have been recently identified as being associated with a hypercoagulable state. This study evaluated the synergism between anti-β2GPIdI and anti-PS/PT for predicting thrombotic events.

METHODS

A total of 180 patients with clinical suspicion of hypercoagulability were evaluated. The plasma levels of lupus anticoagulant (LA) and antibodies against anticardiolipin (anti-CL) (IgG and IgM), β2GPI (IgG and IgM), PS/PT (IgG and IgM), and β2GPI dI (IgG) were measured.

RESULTS

IgG anti-β2GPIdI and LA were highly associated with thrombosis. Mean values and positivity rates of IgG anti-β2GPI dI and IgG anti-PS/PT were significantly higher in the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+) than in the other groups. Interestingly, the thrombotic risk [odds ratio (OR) 24.400, 95% confidence interval (CI) 1.976-63.273, p<0.001] of the newly defined triple positive group (LA+, IgG anti-CL+, IgG anti-β2GPIdI+; OR 11.182, 95% CI 1.976-63.273, p=0.006) was more than twice that of the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+). Double positivity for IgG anti-PS/PT and IgG anti-β2GPI also indicated significant thrombotic risk (OR 7.467, 95% CI 2.350-23.729, p=0.001). Furthermore, the thrombotic risk associated with double positivity for IgG anti-PS/PT and IgG anti-β2GPIdI was markedly elevated (OR 33.654, 95% CI 6.322-179.141, p<0.001).

CONCLUSIONS

Our data suggest that simultaneous measurement of IgG anti-β2GPIdI and IgG anti-PS/PT may improve clinical decision-making for aPL-positive patients.

Dimerized Domain V of Beta2-Glycoprotein I Is Sufficient to Upregulate Procoagulant Activity in PMA-Treated U937 Monocytes and Require Intact Residues in Two Phospholipid-Binding Loops

Upregulation of the procoagulant activity of monocytes by antibodies to beta2- glycoprotein I (β2GPI) is one of the mechanisms contributing to thrombosis in antiphospholipid syndrome. Current knowledge about receptors responsible for the upregulation of procoagulant activity by β2GPI/anti-β2GPI complexes and their binding sites on β2GPI is far from complete. We quantified the procoagulant activity expressed by phorbol 12-myristate 13-acetate (PMA)- differentiated U937 cells by measuring clotting kinetics in human plasma exposed to stimulated cells. Cells stimulated with anti-β2GPI were compared to cells treated with dimerized domain V of β2GPI (β2GPI-DV) or point mutants of β2GPI-DV. We demonstrated that dimerized β2GPI-DV is sufficient to induce procoagulant activity in monocytes. Using site-directed mutagenesis, we determined that the phospholipid-binding interface on β2GPI is larger than previously thought and includes Lys308 in β2GPI-DV. Intact residues in two phospholipid-binding loops of β2GPI-DV were important for the potentiation of procoagulant activity. We did not detect a correlation between the ability of β2GPI-DV variants to bind ApoER2 and potentiation of the procoagulant activity of cells. The region on β2GPI inducing procoagulant activity in monocytes can now be narrowed down to β2GPI-DV. The ability of β2GPI-DV dimers to come close to cell membrane and attach to it is important for the stimulation of procoagulant activity.

A novel approach for the chromatographic purification and peptide mass fingerprinting of urinary free light chains

We describe a chromatographic approach for the purification of urinary free light chains (FLCs) viz., lambda free light chains (λ-FLCs) and kappa free light chains (κ-FLCs). Isolated urinary FLCs were analyzed by SDS-PAGE, immunoblotting and mass spectrometry (MS). The relative molecular masses of λ-FLC and κ-FLC are 22,933.397 and 23,544.336Da respectively. Moreover, dimer forms of each FLC were also detected in mass spectrum which corresponds to 45,737.747 and 47,348.028Da respectively for λ-FLCs and κ-FLCs. Peptide mass fingerprint analysis of the purified λ-FLCs and κ-FLCs has yielded peptides that partially match with known light chain sequences viz., gi|218783338 and gi|48475432 respectively. The tryptic digestion profile of isolated FLCs infers the exclusive nature of them and they may be additive molecules in the dictionary of urinary proteins. This is the first report of characterization and validation of FLCs from large volume samples by peptide sequencing. This simple and cost-effective approach to purification of FLCs, together with the easy availability of urine samples make the large-scale production of FLCs possible, allowing exploration of various bioclinical as well as biodiagnostic applications.