The complement system: its importance in the host response to viral infection.

The course of an intranasal infection of Sendai virus in CBA and DBA mice was investigated in animals decomplemented with purified cobra venom factor. The mice were decomplemented either immediately before inoculation or at 4 days postinfection. Depletion of complement after the infection had been established had no apparent effect on the course of the viral infection in the two strains of mice. In contrast, both strains of mice were protected completely from the lethal effects of an infectious dose of 1 LD50 of virus when the serum C3 levels were depressed by more than 80% during the early stages of infection. The symptoms of morbidity were less pronounced in these animals and there was a delay in the production of hemagglutination-inhibiting antibody. There was no apparent effect on the growth of the virus in lung tissue. The results suggest that the complement system plays a significant pathogenic role during the course of Sendai virus infections in CBA and DBA mice.

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The Role of the Complement System in the Pathogenesis of SARS-CoV-2 Viral Infection in Mental Illness

Psychiatry ◽

10.30629/2618-6667-2021-19-4-76-89 ◽

2021 ◽

Vol 19 (4) ◽

pp. 76-89

Author(s):

E. G. Cheremnykh ◽

P. A. Ivanov ◽

M. I. Factor ◽

A. N. Pozdnyacova ◽

Y. E. Shilov ◽

...

Keyword(s):

Mental Illness ◽

Viral Infection ◽

Complement System ◽

Critical Factor ◽

Underlying Disease ◽

Scientific Data ◽

Mental Illnesses ◽

Sterile Inflammation ◽

The Complement System

Introduction: the complement system can be a critical factor in the outcome of SARS-CoV-2 viral infection. Many mental illnesses are characterized by systemic sterile inflammation, in which the complement system is an obligatory participant. Purpose: to present an analysis of scientific data on the role of the complement system in the pathogenesis of viral diseases and the characteristics of the course of COVID-19 in mental patients. Material and methods: the keywords “complement system” “SARS-CoV-2”, “inhibition of the complement system”, “COVID-19” “mental illness” were used to search scientific articles in the databases MEDLINE, PubMed and other bibliographic sources. Conclusion: patients with mental illness are at risk due to physiological and mental characteristics, and infection with SARS-CoV-2 can provoke a relapse of the underlying disease. Therapeutic inhibition of complement system will help reduce this risk and reduce the likelihood of severe complications from systemic inflammation caused by this infection.

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Protein S and C4b-Binding Protein: Components Involved in the Regulation of the Protein C Anticoagulant System

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646373 ◽

1991 ◽

Vol 66 (01) ◽

pp. 049-061 ◽

Cited By ~ 233

Author(s):

Björn Dahlbäck

Keyword(s):

Vitamin K ◽

Complement System ◽

Protein C ◽

Protein S ◽

High Affinity ◽

Anticoagulant System ◽

Dependent Protein ◽

The Complement System ◽

Β Chain ◽

Dependent Domain

SummaryThe protein C anticoagulant system provides important control of the blood coagulation cascade. The key protein is protein C, a vitamin K-dependent zymogen which is activated to a serine protease by the thrombin-thrombomodulin complex on endothelial cells. Activated protein C functions by degrading the phospholipid-bound coagulation factors Va and VIIIa. Protein S is a cofactor in these reactions. It is a vitamin K-dependent protein with multiple domains. From the N-terminal it contains a vitamin K-dependent domain, a thrombin-sensitive region, four EGF)epidermal growth factor (EGF)-like domains and a C-terminal region homologous to the androgen binding proteins. Three different types of post-translationally modified amino acid residues are found in protein S, 11 γ-carboxy glutamic acid residues in the vitamin K-dependent domain, a β-hydroxylated aspartic acid in the first EGF-like domain and a β-hydroxylated asparagine in each of the other three EGF-like domains. The EGF-like domains contain very high affinity calcium binding sites, and calcium plays a structural and stabilising role. The importance of the anticoagulant properties of protein S is illustrated by the high incidence of thrombo-embolic events in individuals with heterozygous deficiency. Anticoagulation may not be the sole function of protein S, since both in vivo and in vitro, it forms a high affinity non-covalent complex with one of the regulatory proteins in the complement system, the C4b-binding protein (C4BP). The complexed form of protein S has no APC cofactor function. C4BP is a high molecular weight multimeric protein with a unique octopus-like structure. It is composed of seven identical α-chains and one β-chain. The α-and β-chains are linked by disulphide bridges. The cDNA cloning of the β-chain showed the α- and β-chains to be homologous and of common evolutionary origin. Both subunits are composed of multiple 60 amino acid long repeats (short complement or consensus repeats, SCR) and their genes are located in close proximity on chromosome 1, band 1q32. Available experimental data suggest the β-chain to contain the single protein S binding site on C4BP, whereas each of the α-chains contains a binding site for the complement protein, C4b. As C4BP lacking the β-chain is unable to bind protein S, the β-chain is required for protein S binding, but not for the assembly of the α-chains during biosynthesis. Protein S has a high affinity for negatively charged phospholipid membranes, and is instrumental in binding C4BP to negatively charged phospholipid. This constitutes a novel mechanism for control of the complement system on phospholipid surfaces. Recent findings have shown circulating C4BP to be involved in yet another calcium-dependent protein-protein interaction with a protein known as the serum amyloid P-component (SAP). The binding sites on C4BP for protein S and SAP are independent. SAP, which is a normal constituent in plasma and in tissue, is a so-called pentraxin being composed of 5 non-covalently bound 25 kDa subunits. It is homologous to C reactive protein (CRP) but its function is not yet known. The specific high affinity interactions between protein S, C4BP and SAP suggest the regulation of blood coagulation and that of the complement system to be closely linked.

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Stimulated Glanzmann’s Thrombasthenia Platelets Produce Microvesicles

Thrombosis and Haemostasis ◽

10.1055/s-0038-1649978 ◽

1995 ◽

Vol 74 (06) ◽

pp. 1533-1540 ◽

Cited By ~ 23

Author(s):

Pål André Holme ◽

Nils Olav Solum ◽

Frank Brosstad ◽

Nils Egberg ◽

Tomas L Lindahl

Keyword(s):

Complement System ◽

Shape Change ◽

Annexin V ◽

Platelet Surface ◽

Glanzmann’S Thrombasthenia ◽

Large Numbers ◽

Glanzmann's Thrombasthenia ◽

Series Of Experiments ◽

The Complement System ◽

Number Of Particles

SummaryThe mechanism of formation of platelet-derived microvesicles remains controversial.The aim of the present work was to study the formation of microvesicles in view of a possible involvement of the GPIIb-IIIa complex, and of exposure of negatively charged phospholipids as procoagulant material on the platelet surface. This was studied in blood from three Glanzmann’s thrombasthenia patients lacking GPIIb-IIIa and healthy blood donors. MAb FN52 against CD9 which activates the complement system and produces microvesicles due to a membrane permeabilization, ADP (9.37 μM), and the thrombin receptor agonist peptide SFLLRN (100 μM) that activates platelets via G-proteins were used as inducers. In a series of experiments platelets were also preincubated with PGE1 (20 μM). The number of liberated microvesicles, as per cent of the total number of particles (including platelets), was measured using flow cytometry with FITC conjugated antibodies against GPIIIa or GPIb. Activation of GPIIb-IIIa was detected as binding of PAC-1, and exposure of aminophospholipids as binding of annexin V. With normal donors, activation of the complement system induced a reversible PAC-1 binding during shape change. A massive binding of annexin V was seen during shape change as an irreversible process, as well as formation of large numbers of microvesicles (60.6 ±2.7%) which continued after reversal of the PAC-1 binding. Preincubation with PGE1 did not prevent binding of annexin V, nor formation of microvesicles (49.5 ± 2.7%), but abolished shape change and PAC-1 binding after complement activation. Thrombasthenic platelets behaved like normal platelets after activation of complement except for lack of PAC-1 binding (also with regard to the effect of PGE1 and microvesicle formation). Stimulation of normal platelets with 100 μM SFLLRN gave 16.3 ± 1.2% microvesicles, and strong PAC-1 and annexin V binding. After preincubation with PGE1 neither PAC-1 nor annexin V binding, nor any significant amount of microvesicles could be detected. SFLLRN activation of the thrombasthenic platelets produced a small but significant number of microvesicles (6.4 ± 0.8%). Incubation of thrombasthenic platelets with SFLLRN after preincubation with PGE1, gave results identical to those of normal platelets. ADP activation of normal platelets gave PAC-1 binding, but no significant annexin V labelling, nor production of microvesicles. Thus, different inducers of the shedding of microvesicles seem to act by different mechanisms. For all inducers there was a strong correlation between the exposure of procoagulant surface and formation of microvesicles, suggesting that the mechanism of microvesicle formation is linked to the exposure of aminophospholipids. The results also show that the GPIIb-IIIa complex is not required for formation of microvesicles after activation of the complement system, but seems to be of importance, but not absolutely required, after stimulation with SFLLRN.

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