Pathogenic mechanisms of antiphospholipid syndrome: a new autoimmune disease

Thrombotic microangiopathy due to primary antiphospholipid syndrome: successful treatment with eculizumab

Antiphospholipid syndrome nephropathy includes a variety of histological lesions, including thrombotic microangiopathy, which is not included among the diagnostic criteria of antiphospholipid syndrome. Whereas in secondary antiphospholipid syndrome, e.g. to systemic lupus erythematosus, there is emerging evidence of a benefit from complement blockade with eculizumab, optimal treatment of primary antiphospholipid syndrome-associated thrombotic microangiopathy is currently unknown. We report the case of a 36-year-old male patient with primary antiphospholipid syndrome-associated thrombotic microangiopathy, presenting with a clinical picture of atypical hemolytic-uremic syndrome with frequent relapses, treated with eculizumab (four 900 mg weekly doses followed by 1200 mg fortnightly infusions) leading to resolution of hemolysis, long-term remission and partial kidney function recovery (peak serum creatinine 3.8 mg/dL, decreased and stabilized around 2.5 mg/dL) over a follow up period of over 2 years.

Evaluation of patients with antiphospholipid syndrome subsequently COVID-19 vaccinations: A retrospective cohort study

The aim of this study is to evaluate development of side effects, thrombotic or obstetric complications in our antiphospholipid syndrome (APS) patient group, after vaccination against coronavirus disease 2019 (COVID-19). A cohort was formed from patients who have previously been followed up with a diagnosis of APS. The patients of the cohort were evaluated retrospectively to find out if they were vaccinated with CoronaVac and/or BNT162b2 vaccines which are being used in our country. To evaluate the side effects seen after the vaccination, the information was collected by the patients in their outpatient appointments or making a phone call. Thirty-five APS patients who had received at least 1 dose of any of the COVID-19 vaccines were included in the study. Median (min-max) number of vaccine doses per patient was 2 (1-3). Eleven patients had a booster dose after primary vaccination. Twenty patients were ever vaccinated with BNT162b2 and 18 with CoronaVac. Among BNT162b2 recipients, 9 (45.0%) and among CoronaVac recipients 15 (42.9%) reported an adverse event after a vaccine administration. The most common adverse events were myalgia and malaise after any dose of both vaccines. No vaccine-related new thrombotic events or APS flares were observed. Our results were comparable with those reported in the literature. Comprehensive large-scale studies are needed for more accurate results on the evaluation of side effects after COVID-19 vaccination in APS patients.

Antiphospholipid antibodies and risk of post-COVID-19 vaccination thrombophilia: The straw that breaks the camel's back?

Antiphospholipid antibodies (aPLs), present in 1–5 % of healthy individuals, are associated with the risk of antiphospholipid syndrome (APS), which is the most common form of acquired thrombophilia. APLs may appear following infections or vaccinations and have been reported in patients with COronaVIrus Disease-2019 (COVID-19). However, their association with COVID-19 vaccination is unclear. Notably, a few cases of thrombocytopenia and thrombotic events resembling APS have been reported to develop in recipients of either adenoviral vector- or mRNA-based COVID-19 vaccines.

The aim of this review is therefore to speculate on the plausible role of aPLs in the pathogenesis of these rare adverse events.

Adenoviral vector-based vaccines can bind platelets and induce their destruction in the reticuloendothelial organs. Liposomal mRNA-based vaccines may instead favour activation of coagulation factors and confer a pro-thrombotic phenotype to endothelial cells and platelets. Furthermore, both formulations may trigger a type I interferon response associated with the generation of aPLs. In turn, aPLs may lead to aberrant activation of the immune response with participation of innate immune cells, cytokines and the complement cascade. NETosis, monocyte recruitment and cytokine release may further support endothelial dysfunction and promote platelet aggregation. These considerations suggest that aPLs may represent a risk factor for thrombotic events following COVID-19 vaccination, and deserve further investigations.

Circulating microparticles, lupus anticoagulant and recurrent miscarriages

Pregnancy is a pro-inflammatory/hypercoagulable state. Impairment of trophoblastic invasion and placental microthrombi are involved mechanisms in the pathogenesis of recurrent miscarriages (RM). Although in RM related to antiphospholipid antibodies (aPL) non-thrombotic mechanism seems to play an important role as well, we focused this review on the thrombotic mechanisms of RM related to aPL. Thus, in cases of RM related to aPL, placental injury produces inflammatory changes in endothelial cells. Endothelial dysfunction has been shown by increased plasma levels of ICAM-1/VCAM-1 and E-selectin. In RM associated with aPL, the thrombogenic mechanisms included different pathways: protein C inhibition, annexin-5 displacement, blocking of beta(2)GP1 anticoagulant activity and tissue factor upregulation. A new marker/causative agent of RM by itself or in relation to lupus anticoagulant (LA) has risen: circulating microparticles. Microparticles are a heterogeneous group of small, membrane-coated vesicles with a diameter of 0.1-1 microm. Microparticles are released from the cellular membrane during cell activation/apoptosis. Exposition of phospholipids in the outer membrane leaflet could explain the role of microparticles in the thrombotic events. Microparticles have been associated with RM. Microparticles are increased in women with RM when compared with healthy pregnant women. A relationship between aPL and activated endothelial cells (EC) occurs, as well as between EC and circulating microparticles. Interestingly, microparticles induced coagulation in vitro via tissue factor, especially in plasmas with LA. Finally, the relationship between EC, microparticles, LA and RM is revised.

Pathogenesis of the antiphospholipid syndrome: an additional example of the mosaic of autoimmunity

The antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by an adaptive immune response against self-PL-binding proteins ending in the production of specific autoantibodies. Antiphospholipid antibodies (aPL; and in particular anti-beta2 glycoprotein I antibodies) are formal diagnostic markers and pathogenic antibodies. Although APS may be considered as an autoantibody-mediated disease, there is now evidence that aPL are necessary but not sufficient to trigger some of the clinical manifestations of the syndrome. For example, additional factors, such as mediators of the innate immunity are now recognized to play a key role as second hits able to induce the thrombotic events in the presence of the autoantibodies. The APS scenario is also supplemented by the influence of genetically determined factors. Finally, environmental agents - in particular infectious ones - were reported to act as triggers for the production of autoantibodies cross-reacting with PL-binding proteins as well as inflammatory stimuli that potentiate the aPL thrombogenic effect. Altogether these findings do support the concept of a mosaic of factors that participate to the pathogenesis of the syndrome at different levels.

Complement activation in anti-phospholipid syndrome: A clue for an inflammatory process?

Anti-phospholipid syndrome (APS) is defined by recurrent arterial/venous thrombosis and/or fetal losses in the persistent presence of anti-phospholipid antibodies (aPL). In in vivo experimental models aPL thrombogenic activity is associated with a pro-inflammatory endothelial phenotype (increased adhesion molecule [ADM] expression and leukocyte adhesion) in addition to a pro-coagulant one (tissue factor [TF] expression). This is in line with the in vitro aPL ability to trigger intracellular signalling and to up-regulate ADM, TF and pro-inflammatory cytokine/chemokine expression at the mRNA and protein level in endothelial cells. Comparable effects were also reported in monocytes in vitro. In addition, complement activation is required by aPL to display their thrombogenic activity in in vivo models. Interestingly, complement activation blocking as well as Tumor Necrosis Factor alpha neutralization protect animals from aPL-induced fetal losses. Altogether these findings speak in favour for a role of inflammation in APS in spite of the absence of a clear inflammatory signature in the patients. We could not find any complement (C3c and C4d) deposition in the placentas from 2 late abortions (20 weeks of gestation) in APS women. Further studies are necessary to investigate whether complement activation and inflammatory processes found in animal models are taking place in APS patients.

Thrombus formation induced by antibodies to beta2-glycoprotein I is complement dependent and requires a priming factor

We monitored the number of intravascular platelet-leukocyte aggregates (PLAs) and thrombotic occlusions (TOs) by intravascular microscopy in the mesentery of rats receiving antiphospholipid (aPL) immunoglobulin G (IgG) purified from the sera of patients with antiphospholipid syndrome. aPL IgG had no procoagulant effect, but it caused rapid endothelial deposition of fibrinogen, followed by PLA and TO in rats receiving an intraperitoneal injection of bacterial lipopolysaccharide 3 hours before IgG infusion. Anti-beta2-glycoprotein I-depleted aPL IgG failed to induce PLAs and TOs. C3 and C9 colocalized with aPL IgG on the mesenteric vessels. The number of PLAs and TOs was markedly reduced in C6-deficient rats and in animals treated with anti-C5 miniantibody, suggesting the contribution of the terminal complement (C) complex to the aPL antibody-mediated intravascular thrombosis. In conclusion, our data indicate that antibodies to beta2-glycoprotein I trigger coagulation subsequent to a priming proinflammatory factor and that the terminal C complex is the main mediator of the coagulation process.