scholarly journals SARS-CoV-2 Antibodies Mediate Complement and Cellular Driven Inflammation

2021 ◽  
Vol 12 ◽  
Author(s):  
Ida Jarlhelt ◽  
Sif Kaas Nielsen ◽  
Camilla Xenia Holtermann Jahn ◽  
Cecilie Bo Hansen ◽  
Laura Pérez-Alós ◽  
...  
Keyword(s):  
Antibody Response ◽  
Disease Severity ◽  
Complement Activation ◽  
Negative Consequences ◽  
Complement Pathway ◽  
Fc Gamma Receptor ◽  
Specific Antibodies ◽  
Classical Complement Pathway ◽  
Gamma Receptor ◽  
Classical Complement

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to constitute a serious public health threat worldwide. Protective antibody-mediated viral neutralization in response to SARS-CoV-2 infection has been firmly characterized. Where the effects of the antibody response are generally considered to be beneficial, an important biological question regarding potential negative outcomes of a SARS-CoV-2 antibody response has yet to be answered. We determined the distribution of IgG subclasses and complement activation levels in plasma from convalescent individuals using in-house developed ELISAs. The IgG response towards SARS-CoV-2 receptor-binding domain (RBD) after natural infection appeared to be mainly driven by IgG1 and IgG3 subclasses, which are the main ligands for C1q mediated classical complement pathway activation. The deposition of the complement components C4b, C3bc, and TCC as a consequence of SARS-CoV-2 specific antibodies were depending primarily on the SARS-CoV-2 RBD and significantly correlated with both IgG levels and disease severity, indicating that individuals with high levels of IgG and/or severe disease, might have a more prominent complement activation during viral infection. Finally, freshly isolated monocytes and a monocyte cell line (THP-1) were used to address the cellular mediated inflammatory response as a consequence of Fc-gamma receptor engagement by SARS-CoV-2 specific antibodies. Monocytic Fc gamma receptor charging resulted in a significant rise in the secretion of the pro-inflammatory cytokine TNF-α. Our results indicate that SARS-CoV-2 antibodies might drive significant inflammatory responses through the classical complement pathway and via cellular immune-complex activation that could have negative consequences during COVID-19 disease. We found that increased classical complement activation was highly associated to COVID-19 disease severity. The combination of antibody-mediated complement activation and subsequent cellular priming could constitute a significant risk of exacerbating COVID-19 severity.

scholarly journals Continual Low-Level Activation of the Classical Complement Pathway

2001 ◽  
Vol 194 (6) ◽  
pp. 747-756 ◽  
Author(s):  
Anthony P. Manderson ◽  
Matthew C. Pickering ◽  
Marina Botto ◽  
Mark J. Walport ◽  
Christopher R. Parish
Keyword(s):  
Complement Activation ◽  
Alternative Pathway ◽  
Blood Stasis ◽  
Classical Pathway ◽  
Complement Pathway ◽  
Complement Components ◽  
Classical Complement Pathway ◽  
Alternative Complement ◽  
Classical Complement

There is evidence that the classical complement pathway may be activated via a “C1-tickover” mechanism, analogous to the C3-tickover of the alternative pathway. We have quantitated and characterized this pathway of complement activation. Analysis of freshly collected mouse and human plasma revealed that spontaneous C3 activation rapidly occurred with the generation of C3 fragments in the plasma. By the use of complement- and Ig-deficient mice it was found that C1q, C4, C2, and plasma Ig were all required for this spontaneous C3 activation, with the alternative complement pathway further amplifying C3 fragment generation. Study of plasma from a human with C1q deficiency before and after therapeutic C1q infusion confirmed the existence of a similar pathway for complement activation in humans. Elevated levels of plasma C3 were detected in mice deficient in complement components required for activation of either the classical or alternative complement pathways, supporting the hypothesis that there is continuous complement activation and C3 consumption through both these pathways in vivo. Blood stasis was found to stimulate C3 activation by classical pathway tick-over. This antigen-independent mechanism for classical pathway activation may augment activation of the complement system at sites of inflammation and infarction.

Activation of the Classical Pathway of Complement by Resting and Shear Stress-Stimulated Human Endothelial Cells.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2664-2664
Author(s):  
Wei Yin ◽  
Babette Weksler ◽  
David Varon ◽  
Naphtali Savion ◽  
Berhane Ghebrehiwet ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Complement Activation ◽  
Binding Domain ◽  
Complement Pathway ◽  
Complement Components ◽  
Classical Complement Pathway ◽  
Pathway Activation ◽  
Static Conditions ◽  
Classical Complement

Abstract Complement activation is associated with a variety of inflammatory conditions including atherosclerosis, but the mechanism of complement activation in these settings is poorly understood. Endothelial cells (EC) play an important role in vascular pathology and express a variety of complement receptors, including gC1qR/p33, recognizing the globular domain of the complement component C1q. In preliminary studies, purified recombinant gC1qR/p33 was found to support C1q-dependent C4 activation in vitro, comprising 19.5% ± 8.3% (mean ± S.D., n=5) of that produced by aggregated IgG. In contrast, a truncated form of gC1qR/p33, lacking the C1q binding domain, failed to support C4 activation. Additional studies were performed with immortalized bone marrow microvascular EC to investigate classical complement pathway activation and deposition. EC were exposed to anticoagulated (0.32 % sodium citrate) human plasma, diluted (1/10) in 0.01 M HEPES buffered modified Tyrode’s solution, pH 7.5, containing 2 mM Mg Cl2 and 1 mM CaCl2, for 60 min, 37°C. A solid phase ELISA approach was used to detect EC-associated C1q and C4 activation (C4d). Statistically significant deposition of C4d (0.72 ± 0.3. OD units (ODU), n=4)(p=0.04) and C1q (0.57 ± 0.19. ODU, n=4) (p=0.002) was observed on EC that had been immobilized on poly-L-lysine coated microtiter wells. Consistent with classical complement pathway activation, C4d deposition remained at baseline (0.23 ± 0.13, ODU, n=4) in the presence of 10 mM EDTA, but C1q deposition was unaffected. Moreover, no significant C1q or C4d deposition occurred when endothelial cells were exposed to C1q depleted serum. Similar studies were performed using EC grown to confluence on Type I collagen to examine the effect of shear stress (12 dynes/cm2 for 1 hour in a cone-and-plate shearing device), simulating flow conditions in coronary arteries, on classical complement pathway activation and deposition. Compared to static conditions, shear stress resulted in an approximately 50% increase in C1q and C4d deposition on EC. This was accompanied by an approximately 2-fold increase in EC binding of a monoclonal antibody, 60.11, recognizing the N-terminal C1q binding domain of gC1qR/p33. Taken together, these data present evidence for a potential paradigm shift, illustrating immune complex independent classical complement pathway activation by gC1qR/p33, and deposition of activated classical complement components on EC. The generation and deposition of active complement components on EC is likely to contribute directly to vascular inflammation and atherosclerotic changes.

scholarly journals Classical Pathway of Complement Activation in ITP: Inhibition By TNT003, a Novel C1s Inhibitor

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1453-1453
Author(s):  
Ellinor I.B. Peerschke ◽  
Sandip Panicker ◽  
Alexa M. Sughroue ◽  
James B. Bussel
Keyword(s):  
Complement Activation ◽  
In Vitro Assay ◽  
Classical Pathway ◽  
Complement Pathway ◽  
Research Support ◽  
Vitro Assay ◽  
Classical Complement Pathway ◽  
Pathway Activation ◽  
Classical Complement

Abstract Background: Immune thrombocytopenic purpura (ITP) is an autoimmune disorder in which antiplatelet antibodies mediate accelerated platelet clearance from circulation and also inhibit platelet production, resulting in thrombocytopenia. Activation of the classical pathway (CP) of complement is associated with a variety of immune disorders involving the presence of autoantibodies. The role of the complement system in ITP is poorly understood. Methods: Plasma samples (0.32% sodium citrate) from patients with chronic ITP (n=55) were evaluated for their ability to activate the CP of complement. The 55 patients consisted primarily of adult but also of pediatric patients with ITP, undergoing various treatment regimens. The most common included IVIG, rituximab, and especially thrombopoietic agents (eltrombopag, romiplostim). Almost all patients included in the analysis had chronic ITP, defined as ITP lasting > 12 months. The complement activating capacity (CAC) of patient plasma was evaluated with a previously described in vitro assay ( Peerschke et al., Brit J Haematol, 2009) that measures complement activation on immobilized, fixed heterologous platelets using an ELISA approach with monoclonal antibodies to C1q, C4d, iC3b, and C5b-9. CAC represents assay optical density readings normalized to reference normal plasma pool. A CAC of >1.5 was considered indicative of enhanced complement activation, based on reference ranges established for plasma from healthy volunteers. Patient CAC values were correlated with platelet count. The ability of TNT003 to block in vitro complement activation was assessed relative to an isotype matched control. TNT003 is a mouse monoclonal antibody (IgG2a) that targets the CP-serine protease C1s. Results: A statistically significant (p=0.042) inverse correlation was noted between C4d deposition and platelet count in the 55 ITP patient samples tested. Heightened classical complement pathway activation was demonstrated in 7 of 55 patients (~13%) with ITP as evidenced by increased C4d deposition. 6 of the 7 patients with increased C4d deposition had platelet counts <100k/mcL, and 5 patients had platelet counts <50K/mcL. There was a non-significant trend for higher C4d levels on platelets and lower AIPF (absolute immature platelet fraction, equivalent to platelet reticulocytes). TNT003 (100 mcg/ml) inhibited C4 activation by 44 + 43% in ITP plasma in vitro. Inhibition of downstream complement activation, iC3b and C5b-9 deposition, was 72% + 17 % and 82% + 14% (mean + S.D.), respectively. Similar results were obtained using 10 mM EDTA, a known inhibitor of complement activation. Conclusions: The heterogeneity of patient responses to different treatment modalities in ITP support the concept of different immune mechanisms contributing to thrombocytopenia. Our data demonstrate classical complement pathway activation in a subgroup of patients with ITP, and further present the first evidence of CP complement inhibition by a novel C1s inhibitor in this setting. Failure to completely block C4 activation in ITP plasma in vitro by either of TNT003 or EDTA, suggests the presence of preformed, circulating C4d containing complement complexes in patient plasma. The ability of TNT003 to more completely inhibit C3 activation and C5b-9 assembly downstream of C4 in the in vitro assay system is consistent with direct activation and inhibition of complement at the platelet surface. Thus, TNT003 may mitigate enhanced platelet clearance by RES via inhibition of complement mediated platelet opsonization by C3b and platelet lysis by C5b-9. Further studies are required to evaluate the impact of TNT003 on thrombocytopenia in ITP. Disclosures Peerschke: True North Therapeutics: Research Support Other. Panicker:True North Therapeutics: Employment. Bussel:True North Therapeutics: Research Support Other.

Heparin-protamine Complexes and C-reactive Protein Induce Activation of the Classical Complement Pathway: Studies in Patients Undergoing Cardiac Surgery and In Vitro

2000 ◽  
Vol 84 (08) ◽  
pp. 237-243 ◽  
Author(s):  
Henk Velthuis ◽  
Anke Eerenberg-Belmer ◽  
Aria Yazdanbakhsh ◽  
Eddy de Beaumont ◽  
León Eijsman ◽  
...  
Keyword(s):  
Cardiac Surgery ◽  
Complement Activation ◽  
Complement Pathway ◽  
C Reactive Protein ◽  
Postoperative Arrhythmia ◽  
Classical Complement Pathway ◽  
Reactive Protein ◽  
Protamine Administration ◽  
Classical Complement

SummaryThe administration of protamine to patients undergoing cardiopulmonary bypass (CPB) to neutralize heparin and to reduce the risk of bleeding, induces activation of the classical complement pathway mainly by heparin-protamine complexes. We investigated whether C-reactive protein (CRP) contributes to protamine-induced complement activation.In 24 patients during myocardial revascularization, we measured complement, CRP, and complement-CRP complexes, reflecting CRPmediated complement activation in vivo. We also incubated plasma from healthy volunteers and patients with heparin and protamine in vitro to study CRP-mediated complement activation. During CPB, CRP levels remained unchanged while C3 activation products increased. C4 activation occurred after protamine administration. CRP-complement complexes increased at the end of CPB and upon protamine administration. Incubation of plasma with heparin and protamine in vitro generated complement-CRP complexes, which was blocked by phosphorylcholine and stimulated by exogenous CRP. C4d-CRP complex formation after protamine administration correlated clinically with the incidence of postoperative arrhythmia.Protamine administration during cardiac surgery induces complement activation which in part is CRP-dependent, and correlates with postoperative arrhythmia.

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