Prothrombotic autoantibodies in serum from patients hospitalized with COVID-19.

Patients with COVID-19 are at high risk for thrombotic arterial and venous occlusions. Lung histopathology often reveals fibrin-based blockages in the small blood vessels of patients who succumb to the disease. Antiphospholipid syndrome is an acquired and potentially life-threatening thrombophilia in which patients develop pathogenic autoantibodies targeting phospholipids and phospholipid-binding proteins (aPL antibodies). Case series have recently detected aPL antibodies in patients with COVID-19. Here, we measured eight types of aPL antibodies in serum samples from 172 patients hospitalized with COVID-19. These aPL antibodies included anticardiolipin IgG, IgM, and IgA; anti-ß2 glycoprotein I IgG, IgM, and IgA; and anti-phosphatidylserine/prothrombin (aPS/PT) IgG and IgM. We detected aPS/PT IgG in 24% of serum samples, anticardiolipin IgM in 23% of samples, and aPS/PT IgM in 18% of samples. Antiphospholipid autoantibodies were present in 52% of serum samples using the manufacturer's threshold and in 30% using a more stringent cutoff (≥40 ELISA-specific units). Higher titers of aPL antibodies were associated with neutrophil hyperactivity, including the release of neutrophil extracellular traps (NETs), higher platelet counts, more severe respiratory disease, and lower clinical estimated glomerular filtration rate. Similar to IgG from patients with antiphospholipid syndrome, IgG fractions isolated from patients with COVID-19 promoted NET release from neutrophils isolated from healthy individuals. Furthermore, injection of IgG purified from COVID-19 patient serum into mice accelerated venous thrombosis in two mouse models. These findings suggest that half of patients hospitalized with COVID-19 become at least transiently positive for aPL antibodies and that these autoantibodies are potentially pathogenic.

Anti-ß2GPI antibodies enhance atherosclerosis in ApoE-deficient mice.

Accelerated atherosclerosis often occurs in patients with antiphospholipid syndrome (APS), and auto-antibodies to ß2 glycoprotein I (anti-ß2GPI) are confirmed as pathogenic antibodies to APS. Our previous studies have demonstrated that the conversion of mouse peritoneal macrophages into foam cells could be enhanced by co-existence of ß2GPI and anti-ß2GPI IgG, but this phenomenon has not been explored in vivo. Here, we present a mouse model to observe the effect of anti-ß2GPI IgG in the development of atherosclerosis. Male ApoE-deficient mice were intraperitoneally injected with anti-ß2GPI IgG (100 µg/mouse) and homologous control IgG (100 µg/mouse) every week for 16 weeks. Plasma lipid composition, magnetic resonance imaging (MRI) and histological staining were used to evaluate vascular inflammation, lumen stenosis and plaque stability. The results showed that the levels of total cholesterol, triglycerol and low-density lipoprotein-cholesterol in plasma were not changed in all mice fed with high-fat diet, but the level of high-density lipoprotein-cholesterol was lower and the atherosclerosis index was significantly increased in HD + anti-ß2GPI group than in other high-fat diet groups. In addition, compared with NR IgG-treated mice, anti-ß2GPI IgG-treated mice showed more lipid deposition in the carotid artery, markedly narrowed arteriolar lumen as well as higher MMP-9 expression, more macrophages and fewer collagen fibers in the aortic arch root. Furthermore, the aortic mRNA levels of TNF-α, IL-1ß, and MCP-1 were significantly increased in anti-ß2GPI IgG-treated mice. Together, these data indicate that anti-ß2GPI IgG increases vascular inflammation, aggravates atherosclerosis and promotes the formation of vulnerable plaque in ApoE-deficient mice.

Recurrent miscarriage: causes, evaluation and management.

Recurrent miscarriage is frustrating for the physician and a heartbreaking experience for the patient. Approximately 5% of couples trying to conceive have two consecutive miscarriages. Despite a thorough study of patients, the aetiology of this common obstetric complication is unknown in 50% of cases. Known causes include abnormal chromosomes, endocrinological disorders and uterine abnormalities. Although antiphospholipid antibodies have been demonstrated in miscarriages, the role played by alloimmune mechanisms remains unclear. New immunological approaches such as natural killer cells, regulatory T cells, tumour necrosis factor α, cell-derived microparticles, leptin, certain glycoproteins and cytokines should be considered. The management of thyroid diseases and immunological disorders is continuously evolving. Several genetic diagnostic procedures such as parental karyotyping and preimplantation genetic screening should probably not be used routinely. Antiphopholipid syndrome and some recurrent miscarriage-related endocrinological disorders can be effectively treated. Finally, new therapeutic approaches and the pleiotropic effects of old ones have led to improved fetal-maternal outcomes.

Antiphospholipid antibodies induce translocation of TLR7 and TLR8 to the endosome in human monocytes and plasmacytoid dendritic cells.

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by thromboembolic events and/or fetal loss in the presence of antiphospholipid antibodies (aPLs). The mechanisms underlying the pathogenicity of aPLs are still poorly understood. Here we show that 3 human monoclonal aPLs as well as IgG fractions from patients with the APS increase mRNA expression of the intracellular toll-like receptor (TLR) 7 in plasmacytoid dendritic cells and TLR8 in monocytes. Simultaneously they induce the translocation of TLR7 or TLR8 from the endoplasmic reticulum to the endosome. These effects depend on the uptake of aPLs into the endosome, subsequent activation of endosomal NADPH oxidase, and generation of superoxide. As a consequence cells are dramatically sensitized to ligands for TLR7 and TLR8. This observation delineates a novel signal transduction pathway in innate immunity originating from the endosome. Because the overexpression of TLR7 can also be detected in plasmacytoid dendritic cells from patients with the APS ex vivo, our results provide an explanation for proinflammatory and procoagulant effects of aPLs. Because inappropriate expression of TLR7 has been implicated in the development of systemic autoimmunity, these findings may also be relevant for the understanding of autoimmunity.

A unique preliminary study on placental apoptosis in mice with passive immunization of anti-phosphatidylethanolamine antibodies and anti-factor XII antibodies.

PROBLEM: Antiphospholipid antibodies have been investigated both in humans and in animal models. In contrast, there are fewer reports describing anti-phosphatidylethanolamine (aPE) antibodies in humans, and there are no reports of animal studies with aPE till date. Clinically, FXII deficiency or anti-FXII antibodies are sometimes associated with aPE in patients with recurrent pregnancy loss. Therefore, we asked whether aPE and/or anti-FXII in mice could cause fetal resorption, placental thrombosis and apoptosis. Moreover, antibodies to respective target antigens (LDC27 or IPP30) could cause pregnancy failure as well. METHODS OF STUDY: Animal models were used to carry out these objectives. All the animals were immunized with different antibodies by passive immunization. Placental samples were used for various observations. RESULTS AND CONCLUSIONS: Mice with passive immunization of aPE (or anti-LDC27) and aFXII (or anti-IPP30) produced a slight increase in fetal resorption, but markedly induced thrombosis and hemorrhage in the placenta associated with lower platelet counts and increased placental apoptosis. In addition, fewer mitotic cells, less trophoblast giant cell invasion, and more shrunken cells in the deciduas were seen. Our study supports the pathogenic role of aPE and aFXII in pregnancy complications and also suggests a beneficial role of LDC27 and IPP30 antigens on pregnancy failures.

Classical complement activation as a footprint for murine and human antiphospholipid antibody-induced fetal loss.

Recurrent miscarriage, fetal growth restriction and intrauterine fetal death are frequently occurring complications of pregnancy in patients with systemic lupus erythaematosus (SLE) and antiphospholipid syndrome (APS). Murine models show that complement activation plays a pivotal role in antiphospholipid antibody-mediated pregnancy morbidity, but the exact pathways of complement activation and their potential role in human pregnancy are insufficiently understood. We hypothesized that the classical pathway would play a major role in inducing fetal loss. Pregnant C57BL/6 mice and mice deficient in C1q and factor D were injected with antiphospholipid antibodies or normal human IgG. Mouse placentas were subsequently stained with an anti-C4 antibody and anti-normal human IgG to determine the presence of classical complement activation and IgG binding. Findings in mice were validated in 88 human placentae from 83 women (SLE and APS cases versus controls), which were immunohistochemically stained for C4d, C1q, properdin and MBL. Staining patterns were compared to pregnancy outcome. In murine placentae of mice pretreated with antiphospholipid antibodies, increased C4 deposition was observed, which was associated with adverse fetal outcome but not with IgG binding. In humans, diffuse C4d staining at the feto-maternal interface was present almost exclusively in patients with SLE and/or APS (p < 0.001) and was related to intrauterine fetal death (p = 0.03). Our data show that presence of C4d in murine and human placentae is strongly related to adverse fetal outcome in the setting of SLE and APS. The excessive deposition of C4d supports the concept of severe autoantibody-mediated injury at the fetal-maternal interface. We suggest C4d as a potential biomarker of autoantibody-mediated fetal loss in SLE and APS.

Hyperactivity induced by antiphospholipid syndrome serum.

Antiphospholipid syndrome (APS) is a multisystem disorder characterized by arterial and venous thrombosis, pregnancy morbidity, and neuropsychiatric manifestations. Antiphospholipid IgG injected intracerebroventricularly (i.c.v.) cause behavioral hyperactivity in mice. In the present study we investigated the effects of APS whole-serum i.c.v. administration in female Balb/C mice. Control mice were injected with serum derived from healthy subjects or saline solution. Behavior was assessed by the staircase apparatus which combines locomotor (stair-climbing) exploratory activities and rearing as a measure of anxiety. Mice injected with serum from APS patients or serum from normal subjects showed a trend to an increase in the number of stairs climbed in the APS group. The results suggest a differential effect of specific IgG and other serum components in the CNS manifestations of APS.

Pravastatin prevents miscarriages in antiphospholipid antibody-treated mice.

Miscarriages in patients with antiphospholipid (aPL) antibodies have been attributed to thrombosis of placental vessels. However, we have shown that inflammation plays a crucial role in fetal injury. We identified tissue factor (TF), the major cellular activator of the coagulation cascade, as a key mediator in inflammation and fetal injury in aPL antibody-treated mice. We found that TF in maternal neutrophils was associated with fetal injury. TF expression in neutrophils contributes to the respiratory burst and subsequent trophoblast oxidative injury and pregnancy loss induced by aPL antibodies. We also analysed how TF contributes to neutrophil activation and trophoblast injury in this model. We showed that neutrophils from aPL antibody-treated mice express protease activated receptor 2 (PAR-2) and that stimulation of this receptor leads to neutrophil activation, trophoblast injury and fetal death. Mice deficient in PAR-2 and treated with aPL antibodies exhibited reduced neutrophil activation and normal pregnancies, indicating that PAR-2 plays an important role in the pathogenesis of aPL antibody-induced fetal injury. In addition, we demonstrated that the statins simvastatin and pravastatin downregulate TF and PAR-2 expression in neutrophils and thus prevent pregnancy loss. In summary, this study shows that TF signaling through PAR-2 mediates neutrophil activation and fetal death in antiphospholipid syndrome, and that statins may be an appropriate treatment for women with aPL antibody-induced pregnancy complications.

Anti-phospholipid antibodies restore mesenteric ischemia/reperfusion-induced injury in complement receptor 2/complement receptor 1-deficient mice.

Complement receptor 2-deficient (Cr2(-/-)) mice are resistant to mesenteric ischemia/reperfusion (I/R) injury because they lack a component of the natural Ab repertoire. Neither the nature of the Abs that are involved in I/R injury nor the composition of the target Ag, to which recognition is lacking in Cr2(-/-) mice, is known. Because anti-phospholipid Abs have been shown to mediate fetal growth retardation and loss when injected into pregnant mice, we performed experiments to determine whether anti-phospholipid Abs can also reconstitute I/R injury and, therefore, represent members of the injury-inducing repertoire that is missing in Cr2(-/-) mice. We demonstrate that both murine and human monoclonal and polyclonal Abs against negatively charged phospholipids can reconstitute mesenteric I/R-induced intestinal and lung tissue damage in Cr2(-/-) mice. In addition, Abs against beta2 glycoprotein I restore local and remote tissue damage in the Cr2(-/-) mice. Unlike Cr2(-/-) mice, reconstitution of I/R tissue damage in the injury-resistant Rag-1(-/-) mouse required the infusion of both anti-beta2-glycoprotein I and anti-phospholipid Ab. We conclude that anti-phospholipid Abs can bind to tissues subjected to I/R insult and mediate tissue damage.

Fluvastatin inhibits up-regulation of tissue factor expression by antiphospholipid antibodies on endothelial cells.

BACKGROUND: Mechanisms of thrombosis induced by antiphospholipid (aPL) antibodies include up-regulation of tissue factor (TF) expression on endothelial cells (ECs). Statins have been shown to reduce levels of TF induced by tumor necrosis factor (TNF-alpha) and lipopolysaccharide (LPS) on ECs. In a recent study, fluvastatin inhibited thrombogenic and proinflammatory properties of aPL antibodies in in vivo models. The aim of this study was to determine whether fluvastatin has an effect on aPL-induced expression of TF on ECs. METHODS: IgGs were purified from four patients with APS (IgG-APS) and from control sera (IgG-NHS). Cultured human umbilical vein endothelial cells (HUVEC) were treated with IgG-APS or IgG-NHS or with medium alone or with phorbol myristate acetate (PMA), as a positive control. In some experiments, cells were pretreated with fluvastatin (2.5, 5 or 10 micro m) with and without mevalonate (100 micro m). TF expression on HUVECs was measured by ELISA. RESULTS: PMA and the four IgG-APS preparations increased the expression of TF on EC significantly (4.9-, 2.4-, 4.2-, 3.5- and 3.1-fold, respectively), in a dose-dependent fashion. Fluvastatin (10 micro m) inhibited the effects of PMA and the four IgG-APS on TF expression by 70, 47, 65, 22 and 68%, respectively, and this effect was dose-dependent. Mevalonate (100 micro m) completely abrogated the inhibitory effects of fluvastatin on TF expression induced by aPL. CONCLUSION: Because of the suggested pathogenic role of aPL on induction of TF on ECs, our data provide a rationale for using statins as a therapeutic tool in treatment of thrombosis in APS.

Thrombogenicity of beta 2-glycoprotein I-dependent antiphospholipid antibodies in a photochemically induced thrombosis model in the hamster.

We previously showed that beta(2)-glycoprotein I (beta(2)GPI)-dependent lupus anticoagulants (LAs) form bivalent antigen-antibody complexes with high affinity for phospholipids; these complexes are responsible for their in vitro anticoagulant effect. We now studied the role of these bivalent complexes in arterial thrombosis in the hamster. Three monoclonal antibodies (mAbs) raised against human beta(2)GPI were selected on the basis of their cross-reactivity with hamster beta(2)GPI. Two of these, one with LA activity, 5H2, and one with only anticardiolipin properties, 11E8, were infused at 0 to 10 mg/kg prior to photochemically induced vessel damage. 5H2 promoted thrombus formation dose dependently, raising the thrombus size from 6.0 arbitrary units (AU) in controls (n = 9) to 65.0 AU in the high-dose group (10 mg/kg, n = 6, P =.007). The LA(-) mAb 11E8 and mAb 27A8, reactive with human beta(2)GPI exclusively, did not significantly promote thrombus formation. In a second set of experiments, intact mAb 5H2 was compared to its fragments. Intact mAb 5H2 at 3.3 mg/kg and the equimolar dose of F(ab')(2) fragments (2.2 mg/kg) promoted thrombus formation equally well (55.8 AU, n = 8 and 62.5 AU, n = 7, respectively); mAb 5H2-derived Fab' fragments were inactive. Immunohistochemical analysis showed platelet-rich thrombi, with 5H2 or its F(ab')(2) fragments mainly bound to individual platelets. Our results indicate that bivalent immune complex formation plays an important role in the genesis of arterial thrombosis by certain antiphospholipid antibodies. Cellular activation via the Fc portion of these immune complexes, however, is not essential, because F(ab')(2) fragments of 5H2 still promote thrombus formation.

GDKV-induced antiphospholipid antibodies enhance thrombosis and activate endothelial cells in vivo and in vitro.

Antiphospholipid (aPL) Abs are associated with thrombosis, pregnancy loss, and thrombocytopenia in patients with systemic lupus erythematosus or primary antiphospholipid syndrome (APS). beta2-Glycoprotein I (beta2GPI), a phospholipid-binding serum protein, is involved in aPL binding to phospholipids. aPL can be generated in mice by immunization with beta2GPI, and these Abs are thrombogenic and cause pregnancy loss in mice. The objective of this study is to determine whether aPL induced by immunization with the phospholipid-binding site of beta2GPI are thrombogenic and whether they activate endothelial cells (EC) in vivo and in vitro. Murine monoclonal aPL were generated from spleen cells of a mouse immunized with GDKV, a synthetic 15-aa peptide spanning Gly274-Cys288 in the fifth domain of human beta2GPI, which represents the phospholipid-binding site of beta2GPI. The Abs generated had aPL and anti-beta2GPI activities. The effect of these Abs on thrombus formation and on EC activation in vivo was determined using a mouse model of thrombosis and microcirculation that enables examination of the adhesion of leukocyte to EC as an indication of EC activation as well as adhesion molecule expression using in vitro ELISA analysis. Mice injected with this monoclonal aPL showed a significant increase in leukocyte sticking and also produced larger thrombi that persisted longer. Exposure to GDKV-induced aPL for 4 h significantly increased surface Ag expression of E-selectin, ICAM-1, and VCAM-1. These data indicate that aPL induced by immunization with the phospholipid binding site of beta2GPI are thrombogenic and activate endothelial cells.

Síndrome de sneddon, anticardiolipinas y embarazo: presentación de un caso / Sneddon's syndrome, anticardiolipins and pregnancy: case report

Se presenta un caso de livedo reticularis y enfermedad cerebro vascular (síndrome de Sneddon) quien posee historia de pérdida fetales recurrentes y anticuerposs anticardiolipinas positivos. Fue admitida en nuestra institución en dos ocasiones: en la primera cursaba con embarazo de edad de gestión incerta (el cual concluyó en aborto espontanéo) además de accidente cerebro vascular isquémico, recibiendo tratamiento con heparina y warfarina, con buena recuperación neurológica. En la segunda hospitalización a pesar de recibir terapia anticoagulante presentó huevo muerto retenido, realizándose legrado uterino y a los dos meses de su egreso tuvo nuevo accidente cerebro vascular isquémico, por lo que se asoció prednisona al tratamiento, resultando negarivos los anticuerpos anticardiolipinas a los 10 días de iniciada la terapia inmunosupresora. LLamamos la atención, sobre la amplia discusión del significado fisiopatológico de los anticuerpos anticardiolipinas y la diversidad de opiniones respecto al tratamiento para disminuir la morbimortalidad de este gran complejo sindromático

The pathogenic role of anti-phosphatidylserine antibodies: active immunization with the antibodies leads to the induction of antiphospholipid syndrome.

Primary antiphospholipid syndrome (pAPS) can be experimentally induced in mice by immunization with anti-cardiolipin (aCL) antibodies (Abs). Recently, we have pointed to the pathogenic role of antiphosphatidylserine (aPS) Abs by inducing an experimental model of pAPS in naive mice following passive transfer of human aPS to the tail vein of ICR mice. The aim of the present study was to induce experimental pAPS in mice following active immunization with aPS. Mice were immunized with IgG and IgM aPS, purified from two patients with pAPS. The sera of the mice were examined for the presence of different antiphospholipid Abs, and the beta 2 GPI dependency of aPS, using an enzyme-linked immunosorbent assay (ELISA). Inhibition ELISA studies, with silica beads coated with phospholipids, were used to detect cross-reactivity of aPS or aCL to other phospholipids. The mice were also tested for the presence of thrombocytopenia, prolonged activated partial thromboplastin time (APTT), and the percentage of fetal resorptions. The purified IgG aPS but not IgM aPS had a strong lupus anticoagulant activity. Both IgG and IgM aPS were beta 2 GPI dependent and did not bind PS in the absence of the glycoprotein. The mice immunized with IgG aPS, but not IgM aPS, developed high titers of mouse aPS. The mice generated polyspecific Abs, cross-reacting with aCL and aPS, as well as individual aPS or aCL Abs. Only the mice immunized with IgG aPS developed clinical parameters of pAPS: prolonged APTT, thrombocytopenia, and an increased fetal resorption rate. In conclusion, active immunization with IgG, but not IgM, aPS induces experimental pAPS in naive mice, thus pointing to the participation of aPS in the idiotypic network.

Anticuerpos anticardiolipina en pacientes con anemía drepanocítica / Anticardiolipin antibodies in patients eith sickle

Se presenta un trabajo prospectivo, caso-control con relación 2:1, para medir los niveles de anticuerpos anticardiolipina del tipo IgM e IgG, en pacientes drepanocíticos del Hospital General del Oeste y que no tuviesen evidencias de infección, drogas o patologías protombóticas. Se estudiaron 20 pacientes de los cuales 7 eran heterocigotos y 11 homocigotos, siendo estos últimos quienes presentaron las crisis dolorosas. Los niveles de IgM no se elevaron, mientras que los niveles de IgG, presentaron una diferencia estadísticamente significativa al compararse con el grupo control (p<0,05). Durante las crisis todos los pacientes recibieron tratamiento convencional remitiendo las mismas. Se concluye que los niveles de IgG, se corresponden con los episodios de crisis dolorosa, por lo que se propone su uso experimental en el diagnóstico, tratamiento y seguimiento para determinar su rol definitivo en esta enfermedad