Excessive Subchorionic Fibrinoid Deposition as a Component of Massive Perivillous Fibrin Deposition: A Case With Maternal Immune Thrombocytopenia

Maternal floor infarction (MFI) and massive perivillous fibrin deposition (MPFD) are overlapping placental disorders of unknown etiology, associated with adverse obstetric outcome, and a significant risk of recurrence. We describe a 31-year-old mother with asymptomatic thrombocytopenia throughout pregnancy and a positive lupus anticoagulant. She delivered a normal female neonate at term, whose weight was small for gestational age, with a placenta weighing less than the 10th percentile. Placental examination showed MPFD together with excessive subchorionic fibrinoid deposition. The placenta showed diffuse C4d deposition and an immune-mediated reaction was postulated for the pathogenesis of the placental changes. We suggest that excessive subchorionic fibrinoid deposition may be part of the morphologic spectrum of MFI/MPFD.

Blocking of inflammatory heparan sulfate domains by specific antibodies is not protective in experimental glomerulonephritis

Glomerulonephritis is an acquired serious glomerular disease, which involves the interplay of many factors such as cytokines, chemokines, inflammatory cells, and heparan sulfate (HS). We previously showed that blocking of inflammatory heparan sulfate domains on cultured glomerular endothelium by specific anti-HS single chain antibodies reduced polymorphonuclear cell (PMN) adhesion and chemokine binding. We hypothesized that injection of anti-HS antibodies in PMN-driven experimental glomerulonephritis should reduce glomerular influx of PMNs and thereby lead to a better renal outcome. In contrast to our hypothesis, co-injection of anti-HS antibodies did not alter the final outcome of anti-glomerular basement membrane (anti-GBM)-induced glomerulonephritis. Glomerular PMN influx, normally peaking 2 hours after induction of glomerulonephritis with anti-GBM IgG was not reduced by co-injection of anti-HS antibodies. Four days after induction of glomerulonephritis, albuminuria, renal function, glomerular hyalinosis and fibrin deposition were similar in mice treated and not treated with anti-HS antibodies. Interestingly, we observed transient effects in mice co-injected with anti-HS antibodies compared to mice that did not receive anti-HS antibodies: (i) a decreased renal function 2 hours and 1 day after induction of glomerulonephritis; (ii) an increased albuminuria after 2 hours and 1 day; (iii) an increased glomerular fibrin deposition after 1 day; (iv) a reduced glomerular macrophage influx after 1 day; (v) a sustained glomerular presence of PMNs at day 1 and 4, accompanied by an increased renal expression of IL-6, CXCL1, ICAM-1, L-selectin, CD11b and NF-κB. The mechanism underlying these observations induced by anti-HS antibodies remains unclear, but may be explained by a temporarily altered glycocalyx and/or altered function of PMNs due to the binding of anti-HS antibodies. Nevertheless, the evaluated anti-HS antibodies do not show therapeutic potential in anti-GBM-induced glomerulonephritis. Future research should evaluate other strategies to target HS domains involved in inflammatory processes during glomerulonephritis.

The Deleterious Effects of Impaired Fibrinolysis on Skeletal Development Are Dependent on Fibrin(ogen), but Independent of Interlukin-6

Chronic diseases in growing children, such as autoimmune disorders, obesity, and cancer, are hallmarked by musculoskeletal growth disturbances and osteoporosis. Many of the skeletal changes in these children are thought to be secondary to chronic inflammation. Recent studies have likewise suggested that changes in coagulation and fibrinolysis may contribute to musculoskeletal growth disturbances. In prior work, we demonstrated that mice deficient in plasminogen, the principal protease of degrading and clearing fibrin matrices, suffer from inflammation-driven systemic osteoporosis and that elimination of fibrinogen resulted in normalization of IL-6 levels and complete rescue of the skeletal phenotype. Given the intimate link between coagulation, fibrinolysis, and inflammation, here we determined if persistent fibrin deposition, elevated IL-6, or both contribute to early skeletal aging and physeal disruption in chronic inflammatory conditions. Skeletal growth as well as bone quality, physeal development, and vascularity were analyzed in C57BL6/J mice with plasminogen deficiency with and without deficiencies of either fibrinogen or IL-6. Elimination of fibrinogen, but not IL-6, rescued the skeletal phenotype and growth disturbances in this model of chronic disease. Furthermore, the skeletal phenotypes directly correlated with both systemic and local vascular changes in the skeletal environment. In conclusion, these results suggest that fibrinolysis through plasmin is essential for skeletal growth and maintenance, and is multifactorial by limiting inflammation and preserving vasculature.

741 A complex clinical mosaic of severe autoimmune calcific constrictive pericarditis with striking haemodynamic response to immunosuppressive therapy

Autoimmune constrictive pericarditis constitutes a conundrum to modern cardiology with much uncertainty surrounding both pathophysiology and optimal treatment strategies. We hereby describe the case of a 35-year-old woman of Nigerian origin with severe right heart failure secondary to calcific constrictive pericarditis. Her past medical history included coagulation factor XI deficiency, leukopenia, 2nd trimester miscarriage and premature labour due to placenta previa with fibrin deposition. Further investigations revealed atrial fibrillation, severe biatrial enlargement, moderate tricuspid and mitral regurgitation, pericardial thickening, post-capillary pulmonary hypertension and right ventricular dip-and-plateau pattern, compatible with severe constrictive pericarditis. Extensive screening for infectious and autoimmune causes only revealed borderline positive ANA (1:80). Thereafter, the patient underwent complete surgical pericardiectomy with pericardial biopsies revealing fibrous thickening, diffuse calcification and lymphocyte/macrophage infiltrates, in the absence of giant multinucleated cells or granulomas. The patient was later discharged but soon experienced relapse of exertional dyspnoea presenting with right-sided haemo-pneumothorax (requiring pleural drainage), diffuse alveolar haemorrhage, large right-sided basal and infrascissural pleural effusion, and ascites. She was treated with high dose iv furosemide, oral ibuprofen and colchicine, suspension of rate control medications, achieving initial reduction in pulmonary oedema and ascites, relapsing however after attempts to switch to oral diuretic therapy. Due to the finding of persistent lymphopenia, further immunological tests were conducted, revealing raised IgG1 levels as well as altered peripheral lymphocyte populations (raised CD4+/CD8+ ratio and CD8+ central memory, reduced CD8 effector memory). This finding in conjunction with the history of factor XI deficiency, 2nd trimester miscarriage and placental fibrin deposition as well as the observation of painful cutaneous nodules at sites of venepuncture, suggestive of Koebner’s phenomenon, veered the diagnostic focus to a potential autoimmune aetiology and in particular to systemic lupus erythematosus (>10 ACR-EULAR score points with case reports describing all the above as potential disease manifestations). Furthermore, revision of thoracic CT scans, demonstrated bilateral migratory peribronchovascular nodules with ground-glass halo. CT- guided biopsies thereof were performed revealing focal alveolar damage with capillaritis and alveolar haemorrhage, further corroborating the clinical suspicion of autoimmune disease and justifying the introduction of high-dose oral corticosteroid therapy. In liaison with our tertiary rheumatology centre, the patient was later switched to mycophenolate with gradual weaning from corticosteroid. Concurrent cardiological follow-up revealed persistence of good haemodynamic status (NYHA class II, absence of pulmonary oedema and ascites) with oral diuretic therapy, regression of cutaneous symptoms and echocardiography demonstrating consistent reduction in both mitral and tricuspid regurgitation. This constitutes to our knowledge the first report of autoimmune calcific constrictive pericarditis with significant haemodynamic response to immunosuppressive therapy. Despite the relative rarity of this disease entity, early recognition and instatement of immunosuppressive treatment may prove fundamental to halt and potentially reverse the haemodynamic progression of this highly morbid condition.

SARS-CoV-2 Infection in Pregnancy: Clinical Signs, Placental Pathology, and Neonatal Outcome—Implications for Clinical Care

Introduction: The current COVID-19 pandemic has been associated with high rates of mortality and significant morbidity. Both the risk of infection for pregnant women and the risk of vertical transmission have been evaluated, and the presence of the SARS-CoV-2 virus has been demonstrated both in the placenta and in the amniochorionic membranes. However, the actual effects of this pathogen on pregnancy and on placental morphology are still unclear.Objective: To describe histopathologic findings in the placentas of women with SARS-CoV-2 infection during pregnancy and their correlation with clinical signs and perinatal outcome.Methods: Placental tissues from pregnant women with SARS-CoV-2 infection delivering between March 2020 and February 2021 were analyzed.Results: One hundred six placentas from women with SARS-CoV-2 infection during pregnancy who delivered in Fondazione Policlinico A. Gemelli were examined. Most of them were asymptomatic. All neonates had available test results for SARS-CoV-2 and only one resulted positive. Placental tissues mainly showed signs of maternal vascular malperfusion and of placenta injury in terms of syncytial node increase (96.2%), villar agglutination (77.3%), neointimal hyperplasia (76.4%), excessive fibrin deposition (43.3%), and chorangiosis (35.8%). No significant differences in the frequency of the histopathological lesions were observed according to maternal symptoms.Conclusion: Looking to placental tissues from SARS-CoV-2 positive women at the screening performed close to delivery, placental injuries could be detected without any correlation with fetal and neonatal outcomes. We hypothesize that short latency between SARS-CoV-2 infection and delivery is the main reason for these observations.

Abelacimab Reduces Thrombus Propagation in a Baboon Model of Vascular Graft Thrombosis

Background: Factor XI (FXI) inhibition demonstrated strong efficacy in preventing thrombus formation in preclinical and clinical models of arterial and venous thrombosis. However, the effect of FXI inhibition in halting the progression of a formed clot remains largely unknown. Aims: This study aims to test whether abelacimab, a dual-acting FXI and activated FXI (FXIa) monoclonal antibody, is effective in halting clot formation and downstream growth when administered before or during active clot formation in an established baboon femoral arterio-venous (AV) shunt model. Methods: Three baboons had a chronic femoral AV shunt put in place; platelet and fibrin deposition inside and distal to collagen- or collagen + tissue factor (TF)-coated vascular grafts were measured at baseline (control), in a therapeutic setting, where abelacimab (1 mg/kg, intravenously) was administered 30 minutes after thrombus initiation, and in a preventative setting within the first 48 h and 1 week (144 - 216 h) post-administration. Pharmacodynamic effect was measured by activated partial thromboplastin time (aPTT). Results: Consistent with its half-life of 20 to 30 days, single iv administration of abelacimab at a dose of 1 mg/kg resulted in long-lasting (> 4-week) aPTT prolongation (> 2-fold). Administration of abelacimab 30 minutes after initiation of thrombosis using grafts coated either with collagen or with collagen + TF quickly halted downstream propagation of platelet and fibrin deposition compared to control. Further, downstream propagation of platelet and fibrin deposition was markedly reduced when clotting was induced by collagen, or collagen + tissue factor after abelacimab administration. Conclusions: These data suggest that abelacimab, a dual-acting anti-FXI/FXIa monoclonal antibody with a single long-lasting iv injection has the potential to slow down the growth and reduce the size of thrombi when admistered before or after clot induction. Data indicate a potential for therapeutic benefit of targeting FXI both in therapeutic and preventive settings. Sponsored by: Anthos Therapeutics Inc., 55 Cambridge Parkway, Suite 103, Cambridge, MA 02142 Figure 1 Figure 1. Disclosures Wallisch: Aronora Inc,: Current Employment. Khder: Anthos Therapeutics: Consultancy; Novartis: Current equity holder in publicly-traded company, Other: Retiree. Bloomfield: Anthos Therapeutics: Current Employment. Gruber: Aronora Inc.: Current Employment, Current equity holder in publicly-traded company; Oregon Health and Science University: Current Employment.

Enhanced Thrombotic Responses Are Associated With Striatin Deficiency and Aldosterone

Background In addition to its role on blood pressure, aldosterone (ALDO) also affects the hemostatic system leading to increased experimental thrombosis. Striatin is an intermediate in the rapid, nongenomic actions of ALDO. Striatin heterozygote knockout ( Strn +/‐ ) mice have salt sensitivity of blood pressure and mildly chronically increased ALDO levels. In addition, in humans, striatin polymorphic gene variants are associated with increased salt sensitivity of blood pressure. Thus, we hypothesized that striatin deficiency would be associated with an increased prothrombotic response. Methods and Results Strn +/ ‐ mice and wild‐type littermates were maintained on a liberal sodium diet (1.6%). We measured in vivo thrombus formation following laser‐induced injury in cremaster arterioles using intravital microscopy. Mice were randomized to intravenous administration of ALDO or its vehicle. Acutely, ALDO increased thrombotic responses in wild‐type mice ( P <0.01) versus controls within minutes as determined by increased platelet accumulation and fibrin deposition at the site of laser injury. We then compared thrombus formation without ALDO administration in Strn +/‐ and wild‐type mice. Strn +/‐ mice showed highly significant increases in laser‐induced thrombosis ( P <0.001), as shown by increased platelet accumulation and fibrin deposition. Interestingly, the response in the Strn +/‐ mice basally was far greater than the wild‐type mice with ALDO administration, and ALDO administration produced no additional effect on thrombus responses in Strn +/‐ mice. Conclusions These results demonstrate a novel protective role of striatin in experimental thrombosis. Such a protective effect may be reduced in human striatin risk allele carriers, given the similar salt sensitivity of blood pressure in these individuals and Strn +/‐ mice.