Terminal Complement Complex C5b-9 Research Articles

#2866 The CompAct-HD trial reports a persistent inflammatory profile in patients undergoing haemodialysis, acutely exacerbated with each treatment

Abstract Background and Aims Inflammation induced by haemodialysis (HD) treatment has been recognised for several decades. Despite significant advances in technology, there is evidence that incompatibility between the dialyser, a foreign surface, and the patients’ blood, results in activation of the immune system. With each session, blood-membrane interaction leads to a repetitive activation of the innate complement system and a subsequent inflammatory response. It is now widely acknowledged that the consequences of long-term inflammation include fibrosis and accelerated cardiovascular disease, a common cause of mortality in patients with renal failure. The aim of the CompAct-HD trial is to characterize complement activation and biomarker response to blood-membrane-circuit interaction during HD. Method For a single session, six timed intradialytic blood samples were collected from HD patients during standard treatment with ultrapure water and high flux “biocompatible” membranes. Complement activity potential was determined from timepoint 1 and inflammatory biomarkers from timepoints 2 to 6. Single time point samples were also collected from 7 healthy donors. Highly multiplexed assays enabled to determine 30 biomarkers of inflammation, including cytokines, chemokines, growth factors and complement proteins, from a single blood sample. Data analysis was performed using Microsoft® Excel Version 16.80 and GraphPad Prism 10.1.0. Results 354 patients were recruited from 8 dialysis units across Greater Manchester, UK. An interim analysis was performed on 150 HD patients receiving standard care as well as 7 healthy donors. Dialysis appears to generate an acute inflammatory response, that is, within 15 minutes of commencing treatment which does not appear to resolve by the end of the session. This heightened inflammatory state was observed in HD patients in comparison to healthy donors (Fig. 1) with most pronounced changes seen in cytokines IL-1β, IL-10, IL-12p40 and TNF-α during dialysis. Established markers such as IL-6 also showed a 6-fold increase at the 75th percentile. Similarly, an exaggerated intradialytic response was observed in complement proteins, including the terminal complement complex (TCC) C5b-9 and anaphylatoxin C5a with spikes of up to 7-fold and 10-fold respectively (Fig. 2). A session of HD was shown to cause a relative increase in complement proteins and inflammatory biomarkers. The magnitude of response seen in patients was variable (Fig. 3) with the greatest rise seen in the top quartile (above the Q3 boundary). Conclusion Our findings evidence a sharp inflammatory response to modern day HD treatment across a large cohort of dialysis patients. When compared to healthy donors, we observed heightened levels of inflammation in dialysis patients that is further exacerbated with each treatment session. This study shows that HD has a significant role to play in the chronic inflammatory state of patients with end stage renal failure. Furthermore, here we describe potential targets, in both cytokine and complement proteins, which could be the key to downregulation of inflammation. Using targeted therapeutics, we have an opportunity to deliver a more biocompatible treatment, improving patient outcomes.

Forensic significance of intracardiac expressions of Nrf2 in acute myocardial ischemia

When exposed to oxidative and electrophilic stress, a protective antioxidant response is initiated by nuclear factor erythroid 2-related factor 2 (Nrf2). However, the extent of its importance in the forensic diagnosis of acute ischemic heart diseases (AIHD), such as myocardial infarction (MI), remains uncertain. On the other hand, immunohistochemical analyses of fibronectin (FN) and the terminal complement complex (C5b-9) prove valuable in identifying myocardial ischemia that precedes necrosis during the postmortem diagnosis of sudden cardiac death (SCD). In this study, we investigated the immunohistochemical levels of Nrf2, FN, and C5b-9 in human cardiac samples to explore their forensic relevance for the identification of acute cardiac ischemia. Heart samples were obtained from 25 AIHD cases and 39 non-AIHD cases as controls. Nrf2 was localized in the nuclei of cardiomyocytes, while FN and C5b-9 were detected in the myocardial cytoplasm. The number of intranuclear Nrf2 positive signals in cardiomyocytes increased in AIHD cases compared to control cases. Additionally, the grading of positive portions of cardiac FN and C5b-9 in the myocardium was also significantly enhanced in AIHD, compared to controls. Collectively, these results indicate that the immunohistochemical investigation of Nrf2 combined with FN, and/or C5b-9 holds the potential for identifying early-stage myocardial ischemic lesions in cases of SCD.

Femoral nailing associated with bone marrow emboli in pigs induced a specific increase in blood IL-6 and broad inflammatory responses in the heart and lungs.

Bone marrow embolization may complicate orthopedic surgery, potentially causing fat embolism syndrome. The inflammatory potential of bone marrow emboli is unclear. We aimed to investigate the inflammatory response to femoral intramedullary nailing, specifically the systemic inflammatory effects in plasma, and local tissue responses. Additionally, the plasma response was compared to that following intravenous injection of autologous bone marrow. Twelve pigs underwent femoral nailing (previously shown to have fat emboli in lung and heart), four received intravenous bone marrow, and four served as sham controls. Blood samples were collected hourly and tissue samples postmortem. Additionally, we incubated bone marrow and blood, separately and in combination, from six pigs in vitro. Complement activation was detected by C3a and the terminal C5b-9 complement complex (TCC), and the cytokines TNF, IL-1β, IL-6 and IL-10 as well as the thrombin-antithrombin complexes (TAT) were all measured using enzyme-immunoassays. After nailing, plasma IL-6 rose 21-fold, compared to a 4-fold rise in sham (p=0.0004). No plasma differences in the rest of the inflammatory markers were noted across groups. However, nailing yielded 2-3-times higher C3a, TCC, TNF, IL-1β and IL-10 in lung tissue compared to sham (p<0.0001-0.03). Similarly, heart tissue exhibited 2-times higher TCC and IL-1β compared to sham (p<0.0001-0.03). Intravenous bone marrow yielded 8-times higher TAT than sham at 30 minutes (p<0.0001). In vitro, incubation of bone marrow for four hours resulted in 95-times higher IL-6 compared to whole blood (p=0.03). A selective increase in plasma IL-6 was observed following femoral nailing, whereas lung and heart tissues revealed a broad local inflammatory response not reflected systemically. In vitro experiments may imply bone marrow to be the primary IL-6 source.

Ocrelizumab and ofatumumab, but not rituximab, trigger complement induction in vitro

The clinical and adverse effects of the therapeutic monoclonal antibodies (mAb) ocrelizumab, ofatumumab and rituximab in multiple sclerosis (MS) are presently subject to extensive study. While the two former are approved for MS, the older and less costly rituximab is used off label, and adverse effect profiles are important in their evaluation. The three mAbs all induce B cell depletion, with complement-dependent cytotoxicity (CDC) as one of several mechanisms of action. Complement activation is also postulated to underlie adverse reactions related to infusion/injection. Such administration-related reactions are associated with all three mAbs, but comparisons have so far been indirect, resting on incidence reports from separate clinical trials. The objective of this study was to perform head-to-head comparison of complement activation by ofatumumab, ocrelizumab and rituximab. In vitro experiments were performed in whole blood from healthy donors. The complement-activating potential of the three mAbs was analyzed after 30 min of exposure to 0.3 mg/mL or 0.9 mg/mL of each drug, and compared with those of the well-known TNF inhibitory mAbs adalimumab and infliximab, the latter with recognized potential for infusion reactions. Ofatumumab, ocrelizumab, and infliximab, but not rituximab and adalimumab, triggered statistically significant complement activation measured as increased levels of terminal C5b-9 complement complex (TCC), a sensitive marker of such activation. While results demand careful interpretation, they provide an indication of distinct complement-inducing potential among anti-CD20 mAbs currently used to treat MS.

Plasma Inflammatory Biomarkers Are Associated With Poststroke Cognitive Impairment: The Nor-COAST Study.

Inflammation is proposed to be involved in the pathogenesis of poststroke cognitive impairment. The aim of this study was to investigate associations between concentrations of systemic inflammatory biomarkers after ischemic stroke and poststroke cognitive impairment. The Nor-COAST study (Norwegian Cognitive Impairment After Stroke) is a prospective observational multicenter cohort study, including patients hospitalized with acute stroke between 2015 and 2017. Inflammatory biomarkers, including the TCC (terminal C5b-9 complement complex) and 20 cytokines, were analyzed in plasma, collected at baseline, 3-, and 18 months poststroke, using ELISA and a multiplex assay. Global cognitive outcome was assessed with the Montreal Cognitive Assessment (MoCA) scale. We investigated the associations between plasma inflammatory biomarkers at baseline and MoCA score at 3-, 18-, and 36-month follow-ups; the associations between inflammatory biomarkers at 3 months and MoCA score at 18- and 36-month follow-ups; and the association between these biomarkers at 18 months and MoCA score at 36-month follow-up. We used mixed linear regression adjusted for age and sex. We included 455 survivors of ischemic stroke. Higher concentrations of 7 baseline biomarkers were significantly associated with lower MoCA score at 36 months; TCC, IL (interleukin)-6, and MIP (macrophage inflammatory protein)-1α were associated with MoCA at 3, 18, and 36 months (P<0.01). No biomarker at 3 months was significantly associated with MoCA score at either 18 or 36 months, whereas higher concentrations of 3 biomarkers at 18 months were associated with lower MoCA score at 36 months (P<0.01). TCC at baseline and IL-6 and MIP-1α measured both at baseline and 18 months were particularly strongly associated with MoCA (P<0.01). Higher concentrations of plasma inflammatory biomarkers were associated with lower MoCA scores up to 36 months poststroke. This was most pronounced for inflammatory biomarkers measured in the acute phase following stroke. URL: https://www. gov; Unique identifier: NCT02650531.

Escherichia coli-induced inflammatory responses are temperature-dependent in human whole blood ex vivo

Systemic inflammatory conditions are often associated with hypothermia or hyperthermia. Therapeutic hypothermia is used in post-cardiac arrest and some other acute diseases. There is a need for more knowledge concerning the effect of various temperatures on the acute inflammatory response. The complement system plays a crucial role in initiating the inflammatory response. We hypothesized that temperatures above and below the physiologic 37 °C affect complement activation and cytokine production ex vivo. Lepirudin-anticoagulated human whole blood from 10 healthy donors was incubated in the presence or absence of Escherichia coli at different temperatures (4 °C, 12 °C, 20 °C, 33 °C, 37 °C, 39 °C, and 41 °C). Complement activation was assessed by the terminal C5b-9 complement complex (TCC) and the alternative convertase C3bBbP using ELISA. Cytokines were measured using a 27-plex assay. Granulocyte and monocyte activation was evaluated by CD11b surface expression using flow cytometry. A consistent increase in complement activation was observed with rising temperature, reaching a maximum at 41 °C, both in the absence (C3bBbP p < 0.05) and presence (C3bBbP p < 0.05 and TCC p < 0.05) of E. coli. Temperature alone did not affect cytokine production, whereas incubation with E. coli significantly increased cytokine levels of IL-1β, IL-2, IL-6, IL-8, IFN-γ, and TNF at temperatures > 20 °C. Maximum increase occurred at 39 °C. However, a consistent decrease was observed at 41 °C, significant for IL-1β (p = 0.003). Granulocyte CD11b displayed the same temperature-dependent pattern as cytokines, with a corresponding increase in endothelial cell apoptosis and necrosis. Thus, blood temperature differentially determines the degree of complement activation and cytokine release.

Complement, but Not Platelets, Plays a Pivotal Role in the Outcome of Mucormycosis In Vivo

Mucormycetes, a heterogeneous group of fungi, induce a life-threatening disease called mucormycosis. Immune deficiencies represent a major risk factor; hence, we wanted to illuminate the role of complement and platelets in the defense against mucormycetes. Rhizopus arrhizus (Ra), Rhizopus microsporus (Rm), Lichtheimia ramosa (Lr), Lichtheimia corymbifera (Lc), Rhizomucor pusillus (Rmp), and Mucor circinelloides (Mc) spores were opsonized with human and mouse serum, and C1q, C3c, and terminal complement complex (C5b-9) deposition was measured. Additionally, thrombocytopenic, C3-deficient, or C6-deficient mice were intravenously infected with selected isolates. Survival and immunological parameters were monitored, and fungal burden was determined and compared to that of immunocompetent and neutropenic mice. In vitro experiments showed significant differences in complement deposition between mucormycetes. Mc isolates bound up to threefold more human C5b-9 than other mucormycetes. Lr, Lc, and Mc bound high levels of murine C3c, whereas human C3c deposition was reduced on Mc compared to Lr and Lc. Murine C3c deposition negatively correlated with virulence. Complement deficiencies and neutropenia, but not thrombocytopenia, were shown to be a risk factor for a lethal outcome. Complement deposition varies between mucormycetes. Additionally, we demonstrated that complement and neutrophilic granulocytes, but not platelets, play an important role in a murine model of disseminated mucormycosis.

COVID-19 Associated Atypical Hemolytic Uremic Syndrome

Introduction: Atypical hemolytic uremic syndrome (atypical HUS) is a complement-mediated thrombotic microangiopathy (TMA) that affects multiple organs including the kidneys. We present a case of 37-year-old male with recent COVID-19 infection who presented with epistaxis. His blood work was consistent with TMA and acute kidney injury (AKI). Hemodialysis and plasmapheresis (PLEX) were initiated for presumed thrombotic thrombocytopenic purpura (TTP) but after excluding ADAMTS-13 deficiency, eculizumab was started for possible atypical HUS. Renal biopsy and genetic testing ultimately confirmed diagnosis of atypical HUS. Case presentation: A 37-year-old male with past medical history of recent COVID infection presented to the emergency room with complaint of epistaxis. Physical exam showed mild epistaxis from right naris and bilateral leg swelling. Initial laboratory findings were hemoglobin (Hb) 5 g/dL, platelets 70 B/L, Lactate dehydrogenase (LDH) 581 IU/L, haptoglobin < 10 mg/dL, creatinine (Cr) 36.80 mg/dL, blood urea nitrogen (BUN) 232 mg/dL, potassium (K) 6.6 mmol/L, calcium (Ca) 6 mg/dL and normal prothrombin time (PT) and partial thromboplastin time (PTT). Complement C3 levels were low but normal C4 levels. Peripheral blood smear showed schistocytes confirming TMA. He was started on both PLEX and hemodialysis (HD) along with prednisone 80 mg daily. PLEX was stopped on day 4 after normal ADAMTS-13 levels resulted, helping rule out TTP. Based on history and laboratory findings, diagnosis of atypical HUS was favored and eculizumab was started. He received meningococcal vaccine and prophylactic penicillin while on eculizumab. Hemodialysis was continued with eventual improvement of his labs to Hb 7, platelets 119, LDH 339, haptoglobin < 10, Cr 9.07, BUN 85, K 5.8, and Ca 8.0. He was discharged on bimonthly dose of eculizumab and hemodialysis three times a week. Two months later, his labs were Hb 10.4, platelets 184, LDH 490, haptoglobin < 10, Cr 11.60, BUN 82, K 5.2, and Ca 9.2. PT and PTT remained normal. Given persistence of laboratory findings, renal biopsy and genetic testing for complement proteins was done. Kidney biopsy showed diffuse global renal microangiopathy with negative C3. Genetic testing showed a heterozygous C3 variant, homozygous deletion of CFHR1-CFHR4, negative factor H autoantibodies (FHAA), and single nucleotide variant in C5 gene. Discussion: Atypical HUS is a disease characterized by the triad of microangiopathic hemolytic anemia, thrombocytopenia, and AKI. The complement system is a part of the immune system that enhances the ability of phagocytic cells to clear microbes and damaged cells. Atypical HUS is caused by dysregulation of the alternative complement pathway that leads to microvascular thrombosis. Various mutations in complement and its regulatory proteins have been discovered in atypical HUS patients. Heterozygous C3 variants result in persistently low C3 levels and cause severe disease. Most individuals with a homozygous deletion of CFHR1 and/or CFHR3, CFHR4 genes have a pathogenic role in the development of the anti-factor H autoantibodies. These autoantibodies interfere with the binding of CFH to the C3 convertase and are associated with defective CFH-dependent cell protection. Some case reports of COVID-19 patients showed that complement activation was significantly stronger in lung alveolar septa, hyaline membranes, and in alveolar lumina via the lectin and alternative complement pathways. Treatment of atypical HUS is symptomatic but in severe disease eculizumab or ravulizumab have roles by binding to the complement protein C5, inhibiting its cleavage to C5a and C5b, and preventing formation of terminal complement complex C5b-9. Patients on these therapies are at risk of meningococcal disease, thus it is recommended to get meningococcal vaccines and prophylactic penicillin for the duration of therapy. Our patient had homozygous deletion of CFHR1-CFHR4 genes with no factor H autoantibodies. However, he did have C3 variant with gain of function mutation which caused overt activation of alternative pathway as indicated by his low C3 levels with normal C4 levels. He responded partially to eculizumab and discussion on possible kidney transplant has been started.

Pitfalls in complement analysis: A systematic literature review of assessing complement activation

The complement system is an essential component of our innate defense and plays a vital role in the pathogenesis of many diseases. Assessment of complement activation is critical in monitoring both disease progression and response to therapy. Complement analysis requires accurate and standardized sampling and assay procedures, which has proven to be challenging. We performed a systematic analysis of the current methods used to assess complement components and reviewed whether the identified studies performed their complement measurements according to the recommended practice regarding pre-analytical sample handling and assay technique. Results are supplemented with own data regarding the assessment of key complement biomarkers to illustrate the importance of accurate sampling and measuring of complement components. A literature search using the Pubmed/MEDLINE database was performed focusing on studies measuring the key complement components C3, C5 and/or their split products and/or the soluble variant of the terminal C5b-9 complement complex (sTCC) in human blood samples that were published between February 2017 and February 2022. The identified studies were reviewed whether they had used the correct sample type and techniques for their analyses. A total of 92 out of 376 studies were selected for full-text analysis. Forty-five studies (49%) were identified as using the correct sample type and techniques for their complement analyses, while 25 studies (27%) did not use the correct sample type or technique. For 22 studies (24%), it was not specified which sample type was used. A substantial part of the reviewed studies did not use the appropriate sample type for assessing complement activation or did not mention which sample type was used. This deviation from the standardized procedure can lead to misinterpretation of complement biomarker levels and hampers proper comparison of complement measurements between studies. Therefore, this study underlines the necessity of general guidelines for accurate and standardized complement analysis.

Terminal complement complex C5b-9 and C5b assay in sera of COVID-19 patients with different disease severities

Terminal complement complex C5b-9 and C5b assay in sera of COVID-19 patients with different disease severities

Soluble concentrations of the terminal complement complex C5b-9 correlate with end-organ injury in preeclampsia.

We sought to determine if soluble levels of C5b-9, the terminal complement complex, correlate with end-organ injury in preeclampsia. Project COPA (Complement and Preeclampsia in the Americas), a multi-center observational study in Colombia from 2015 to 2016, enrolled hypertensive pregnant women into four groups: chronic hypertension, gestational hypertension, preeclampsia, and preeclampsia with severe features. Trained coordinators collected clinical data, blood and urine. End-organ injury was defined by serum creatinine≥1.0mg/dl, aspartate transaminase≥70U/L, platelet count<150,000/µl, or lactate dehydrogenase≥500 U/L. Data were analyzed by χ2 or Fisher's exact test with significance at P<0.05. C5b-9 concentrations in plasma and urine, using enzyme linked immunosorbent assays. In total, 298 hypertensive participants were enrolled. Plasma and urine C5b-9 levels were measured in all participants and stratified by quartile (Q1-4), from lowest to highest C5b-9 concentration. Participants with low plasma C5b-9 levels (Q1) were more likely to have end-organ injury compared to those with higher levels (Q2-Q4) [platelet count<150,000/μl (20.8% vs. 8.4%, P=0.01); elevated serum creatinine≥1.0mg/dl (14.9% vs. 4.5%, P=0.009)]. In contrast, participants with high urinary C5b-9 levels (Q4) were more likely to have end-organ injury compared to those with lower levels (Q1-Q3) [platelet count<150,000/μl (19.7% vs. 7.4%, P=0.003); elevated serum creatinine≥1.0mg/dl (12.3% vs. 4.4%, P=0.025)]. We identified a pattern of increased urine and low plasma C5b-9 levels in patients with preeclampsia and end-organ injury. Soluble C5b-9 levels may be used to identify complement-mediated end-organ injury in preeclampsia.

Membrane Attack Complex C5b-9 Promotes Renal Tubular Epithelial Cell Pyroptosis in Trichloroethylene-Sensitized Mice.

Trichloroethylene (TCE), a commonly used organic solvent, is known to cause trichloroethylene hypersensitivity syndrome (THS), also called occupational medicamentosa–like dermatitis due to TCE (OMDT) in China. OMDT patients presented with severe inflammatory kidney damage, and we have previously shown that the renal damage is related to the terminal complement complex C5b-9. Here, we sought to determine whether C5b-9 participated in TCE-induced immune kidney injury by promoting pyroptosis, a new form of programed cell death linked to inflammatory response, with underlying molecular mechanisms involving the NLRP3 inflammasome. A BALB/c mouse-based model of OMDT was established by dermal TCE sensitization in the presence or absence of C5b-9 inhibitor (sCD59-Cys, 25μg/mouse) and NLRP3 antagonist (MCC950, 10 mg/kg). Kidney histopathology, renal function, expression of inflammatory mediators and the pyroptosis executive protein gasdermin D (GSDMD), and the activation of pyroptosis canonical NLRP3/caspase-1 pathway were examined in the mouse model. Renal tubular damage was observed in TCE-sensitized mice. GSDMD was mainly expressed on renal tubular epithelial cells (RTECs). The caspase-1–dependent canonical pathway of pyroptosis was activated in TCE-induced renal damage. Pharmacological inhibition of C5b-9 could restrain the caspase-1–dependent canonical pathway and rescued the renal tubular damage. Taken together, our results demonstrated that complement C5b-9 plays a central role in TCE-induced immune kidney damage, and the underlying mechanisms involve NLRP3-mediated pyroptosis.

Candidate Biomarkers for the Detection of Serious Infections in Children: A Prospective Clinical Study.

Serious bacterial infections (SBI) in children are associated with considerable morbidity and mortality, and their early identification remains challenging. The role of laboratory tests in this setting is still debated, and new biomarkers are needed. This prospective, observational, single-center study aims to evaluate the diagnostic role of blood biomarkers in detecting SBI in children presenting with signs of systemic inflammatory response syndrome (SIRS). A panel of biomarkers was performed, including C-reactive protein (CRP), procalcitonin (PCT), white blood cell count (WBC), absolute neutrophil count (ANC), interleukin (IL)-6, IL-8, IL-10, human terminal complement complex (C5b-9), Plasmalemma-Vesicle-associated protein 1 (PV-1), Intercellular Adhesion Molecule-1 (ICAM-1), and Phospholipase A2 (PLA2). Among 103 patients (median age 2.9 years, 60% males), 39 had a diagnosis of SBI (38%). Significant predictors of SBI were CRP (p = 0.001) and ICAM-1 (p = 0.043). WBC (p = 0.035), ANC (p = 0.012) and ANC/WBC ratio (p = 0.015) were also significantly associated with SBI in children without pre-existing neutropenia. ROC curves, however, revealed suboptimal performance for all variables. Nevertheless, a model that combined CRP and ANC/WBC ratio had more in-depth diagnostic accuracy than either of the two variables. Overall, this study confirms the limited usefulness of blood biomarkers for the early diagnosis of SBI. WBC, ANC, ANC/WBC ratio, CRP, and ICAM-1 showed the best, albeit moderate, diagnostic accuracy.

Molecular Advances in Preeclampsia and HELLP Syndrome.

Preeclampsia (PE) constitutes one of the principal reasons for maternal and perinatal morbidity and mortality worldwide. The circumstance typically implicates formerly healthful normotensive women, after 20 weeks of gestation, typically withinside the third trimester, without regarded threat elements or past deliveries. PE can be further complicated with hemolysis and thrombocytopenia, leading to the emergence of HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low platelets). Both conditions are classified as hypertensive diseases of pregnancy (HDP), and their pathogenesis has been linked to an excessive maternal inflammatory response, accompanied by enhanced endothelial activation. Several studies have found that in pregnancies affected by PE/HELLP, von Willebrand factor (vWF) antigen levels (vWF:Ag) are significantly elevated, while its cleaving protease (ADAMTS-13, A Disintegrin-like and Metalloprotease with Thrombospondin type 1 motif, member 13) activity is normal to decreased. Furthermore, the higher urine excretion of the terminal complement complex C5b-9, as well as its greater deposition in the placental surface in preeclamptic women, imply that the utero-placental unit’s distinctive deficits are intimately tied to disproportionate complement activation. The goal of this updated evaluation is to provide the most up-to-date molecular advances in the pathophysiology of PE/HELLP syndromes. Recent medical data on vWF:Ag levels in patients with PE, ADAMTS-13, and dysregulation of the complement system, are highlighted and evaluated. Furthermore, we discuss the relationship between those entities and the progression of the disease, as well as their significance in the diagnostic process. Finally, considering the difficulties in analyzing and controlling those symptoms in pregnant women, we can provide a current diagnostic and therapeutic algorithm.

Venous Air Embolism Activates Complement C3 Without Corresponding C5 Activation and Trigger Thromboinflammation in Pigs

IntroductionAir embolism may complicate invasive medical procedures. Bubbles trigger complement C3-mediated cytokine release, coagulation, and platelet activation in vitro in human whole blood. Since these findings have not been verified in vivo, we aimed to examine the effects of air embolism in pigs on thromboinflammation.MethodsForty-five landrace pigs, average 17 kg (range 8.5-30), underwent intravenous air infusion for 300 or 360 minutes (n=29) or served as sham (n=14). Fourteen pigs were excluded due to e.g. infections or persistent foramen ovale. Blood was analyzed for white blood cells (WBC), complement activation (C3a and terminal C5b-9 complement complex [TCC]), cytokines, and hemostatic parameters including thrombin-antithrombin (TAT) using immunoassays and rotational thromboelastometry (ROTEM). Lung tissue was analyzed for complement and cytokines using qPCR and immunoassays. Results are presented as medians with interquartile range.ResultsIn 24 pigs receiving air infusion, WBC increased from 17×109/L (10-24) to 28 (16-42) (p<0.001). C3a increased from 21 ng/mL (15-46) to 67 (39-84) (p<0.001), whereas TCC increased only modestly (p=0.02). TAT increased from 35 µg/mL (28-42) to 51 (38-89) (p=0.002). ROTEM changed during first 120 minutes: Clotting time decreased from 613 seconds (531-677) to 538 (399-620) (p=0.006), clot formation time decreased from 161 seconds (122-195) to 124 (83-162) (p=0.02) and α-angle increased from 62 degrees (57-68) to 68 (62-74) (p=0.02). In lungs from pigs receiving air compared to sham animals, C3a was 34 ng/mL (14-50) versus 4.1 (2.4-5.7) (p<0.001), whereas TCC was 0.3 CAU/mL (0.2-0.3) versus 0.2 (0.1-0.2) (p=0.02). Lung cytokines in pigs receiving air compared to sham animals were: IL-1β 302 pg/mL (190-437) versus 107 (66-120), IL-6 644 pg/mL (358-1094) versus 25 (23-30), IL-8 203 pg/mL (81-377) versus 21 (20-35), and TNF 113 pg/mL (96-147) versus 16 (13-22) (all p<0.001). Cytokine mRNA in lung tissue from pigs receiving air compared to sham animals increased 12-fold for IL-1β, 121-fold for IL-6, and 17-fold for IL-8 (all p<0.001).ConclusionVenous air embolism in pigs activated C3 without a corresponding C5 activation and triggered thromboinflammation, consistent with a C3-dependent mechanism. C3-inhibition might represent a therapeutic approach to attenuate this response.

C5b-9 Membrane Attack Complex Formation andExtracellular Vesicle Shedding in Barrett's Esophagus and Esophageal Adenocarcinoma.

The early complement components have emerged as mediators of pro-oncogenic inflammation, classically inferred to cause terminal complement activation, but there are limited data on the activity of terminal complement in cancer. We previously reported elevated serum and tissue C9, the terminal complement component, in esophageal adenocarcinoma (EAC) compared to the precursor condition Barrett’s Esophagus (BE) and healthy controls. Here, we investigate the level and cellular fates of the terminal complement complex C5b-9, also known as the membrane attack complex. Punctate C5b-9 staining and diffuse C9 staining was detected in BE and EAC by multiplex immunohistofluorescence without corresponding increase of C9 mRNA transcript. Increased C9 and C5b-9 staining were observed in the sequence normal squamous epithelium, BE, low- and high-grade dysplasia, EAC. C5b-9 positive esophageal cells were morphologically intact, indicative of sublytic or complement-evasion mechanisms. To investigate this at a cellular level, we exposed non-dysplastic BE (BAR-T and CP-A), high-grade dysplastic BE (CP-B and CP-D) and EAC (FLO-1 and OE-33) cell lines to the same sublytic dose of immunopurified human C9 (3 µg/ml) in the presence of C9-depleted human serum. Cellular C5b-9 was visualized by immunofluorescence confocal microscopy. Shed C5b-9 in the form of extracellular vesicles (EV) was measured in collected conditioned medium using recently described microfluidic immunoassay with capture by a mixture of three tetraspanin antibodies (CD9/CD63/CD81) and detection by surface-enhanced Raman scattering (SERS) after EV labelling with C5b-9 or C9 antibody conjugated SERS nanotags. Following C9 exposure, all examined cell lines formed C5b-9, internalized C5b-9, and shed C5b-9+ and C9+ EVs, albeit at varying levels despite receiving the same C9 dose. In conclusion, these results confirm increased esophageal C5b-9 formation during EAC development and demonstrate capability and heterogeneity in C5b-9 formation and shedding in BE and EAC cell lines following sublytic C9 exposure. Future work may explore the molecular mechanisms and pathogenic implications of the shed C5b-9+ EV.

Mechanism for the attenuation of neutrophil and complement hyperactivity by MSC exosomes

Complements and neutrophils are two key players of the innate immune system that are widely implicated as drivers of severe COVID-19 pathogenesis, as evident by the direct correlation of respiratory failure and mortality with elevated levels of terminal complement complex C5b-9 and neutrophils. In this study, we identified a feed-forward loop between complements and neutrophils that could amplify and perpetuate the cytokine storm seen in severe SARS-CoV-2–infected patients. We observed for the first time that the terminal complement activation complex C5b-9 directly triggered neutrophil extracellular trap (NET) release and interleukin (IL)-17 production by neutrophils. This is also the first report that the production of NETs and IL-17 induced by C5b-9 assembly on neutrophils could be abrogated by mesenchymal stem cell (MSC) exosomes. Neutralizing anti-CD59 antibodies abolished this abrogation. Based on our findings, we hypothesize that MSC exosomes could alleviate the immune dysregulation in acute respiratory failure, such as that observed in severe COVID-19 patients, by inhibiting complement activation through exosomal CD59, thereby disrupting the feed-forward loop between complements and neutrophils to inhibit the amplification and perpetuation of inflammation during SARS-CoV-2 infection.

The Alternative Complement Pathway Is Activated Without a Corresponding Terminal Pathway Activation in Patients With Heart Failure.

ObjectiveDysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF.MethodsWe analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls.ResultsCompared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years.ConclusionOur findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.

Complement Activation during Vaso-Occlusive Pain Crisis in Pediatric Sickle Cell Disease

Background: Sickle cell disease (SCD) affects millions of individuals worldwide with substantial morbidity and mortality. The sickle hemoglobin (HbS) polymerizes upon deoxygenation, causing rigid and adhesive red blood cells (RBCs), triggering vascular occlusion, greatly shortened RBC lifespan, and chronic hemolysis. Amongst acute complications in SCD, vaso-occlusive pain crisis (VOC) is the leading cause of hospitalization, with supportive care being the primary approach to management. We and others have recently demonstrated important contributions of complement to the pathophysiology of SCD. When the complement pathway (CP) is activated during SCD crises, inhibition at C5 using eculizumab, has been successful in treating various acute complications in SCD (Chonat et al, Haematologica). In this study, we prospectively analyzed the extent of CP activation among children with SCD presenting with VOC.Methods: Patients aged 0-21 years old managed at Children's Healthcare of Atlanta with homozygous sickle cell (SS) or S beta zero thalassemia genotypes were enrolled in an IRB-approved research study. Inclusion criteria included those requiring intravenous opioids for VOC, and excluded those with chronic pain, >6 VOC admission in the previous 12 months or on chronic transfusions. Blood samples were collected within 48 hours of VOC presentation, and steady-state levels were obtained at a 4-week clinic follow-up. Data was analyzed using a paired t-test, and receiver operator characteristic (ROC) curves were generated comparing intra-person complement levels during acute VOC versus respective steady-state levels.Results: Sixty-four patients have been enrolled thus far, of which 43 (67%) had steady-state samples collected. The majority of patients (90.5%) have SS genotype with a mean (SD) patient age of 14.15 (4.68) years. Fifty-three (84.1%) patients reported taking hydroxyurea (HU). Fifty-nine (93.7%) patients had at least one VOC admission in the past 12 months, with an average of 2.98 (1.67) VOC admissions. Pain Score reported on 55 patients averaged 4.93 (4.78) on a pain scale of 0 to 10. Mean values during VOC and steady-state of hemoglobin (Hb) were 8.12 and 9.01 g/dL, platelet count 431 and 511, and lactate dehydrogenase (LDH) 549 and 483 U/L, respectively. Seventeen patients had complement work-up performed during acute and steady-state, and 4 of them had additional samples collected during subsequent VOC. Complement protein levels C3, C4, C5, properdin, factor B, and complement regulatory proteins factor H and I were unremarkable during VOC and steady-state. However, complement activation markers, specifically anaphylatoxins C3a, C5a and Bb were significantly elevated during VOC compared to steady-state (see Table 1) suggesting activation of alternative CP during VOC (see Table 1 and Figure 1A-C). Terminal complement complex (C5b9) was not statistically different between VOC and steady-state (Figure 1D, red dotted lines signify normal ranges). Remarkably, patients who re-presented with acute VOC exhibited similar increases in their C3a/C5a (Figure 1E-F), substantiating the increases related to their VOC. Hemoglobin and LDH (Figure 1G-H) were similarly significant, suggestive of intravascular hemolysis. Three (7.1%) patients developed acute chest syndrome, two of whom experienced respiratory failure requiring intensive care management, and all exhibited significant CP activation. The area under the curve (AUC) of the ROC curve was analyzed to determine the ability of complement biomarkers to differentiate VOC from steady-state. Based on the AUC of these biomarkers, complement anaphylatoxins C3a and C5a exhibited the highest AUC of 0.76 and 0.87, respectively.Discussion: To our knowledge, this is the first prospective and comprehensive evaluation of CP in patients with SCD during VOC and steady-states. These preliminary findings suggest CP activation is present in a large proportion of patients during VOC, with increased activation of alternative and common CP, associated with intravascular hemolysis. Minimal increase in C5b9 could be explained by a significant proportion (> 80%) of our patients being on HU therapy, similar to prior data (Roumenina et al, AJH). Specifically, C3a/C5a, along with other biomarkers, could not only predict disease activity in patients during VOC, but provide pharmacological targets in VOC, which need further validation. [Display omitted] DisclosuresStowell: Alexion: Consultancy; Argenx: Speakers Bureau; Grifols: Speakers Bureau. Chonat: Alexion: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Global Blood Therapeutics: Consultancy, Research Funding; Takeda: Consultancy, Research Funding.

Elevated Terminal C5b-9 Complement Complex 10 Weeks Post Kidney Transplantation Was Associated With Reduced Long-Term Patient and Kidney Graft Survival.

BackgroundThe major reason for graft loss is chronic tissue damage, as interstitial fibrosis and tubular atrophy (IF/TA), where complement activation may serve as a mediator. The association of complement activation in a stable phase early after kidney transplantation with long-term outcomes is unexplored.MethodsWe examined plasma terminal C5b-9 complement complex (TCC) 10 weeks posttransplant in 900 patients receiving a kidney between 2007 and 2012. Clinical outcomes were assessed after a median observation time of 9.3 years [interquartile range (IQR) 7.5–10.6].ResultsElevated TCC plasma values (≥0.7 CAU/ml) were present in 138 patients (15.3%) and associated with a lower 10-year patient survival rate (65.7% vs. 75.5%, P < 0.003). Similarly, 10-year graft survival was lower with elevated TCC; 56.9% vs. 67.3% (P < 0.002). Graft survival was also lower when censored for death; 81.5% vs. 87.3% (P = 0.04). In multivariable Cox analyses, impaired patient survival was significantly associated with elevated TCC [hazard ratio (HR) 1.40 (1.02–1.91), P = 0.04] along with male sex, recipient and donor age, smoking, diabetes, and overall survival more than 1 year in renal replacement therapy prior to engraftment. Likewise, elevated TCC was independently associated with graft loss [HR 1.40 (1.06–1.85), P = 0.02] along with the same covariates. Finally, elevated TCC was in addition independently associated with death-censored graft loss [HR 1.69 (1.06–2.71), P = 0.03] as were also HLA-DR mismatches and higher immunological risk.ConclusionsEarly complement activation, assessed by plasma TCC, was associated with impaired long-term patient and graft survival.