scholarly journals Structure and activation of C1, the complex initiating the classical pathway of the complement cascade

2017 ◽  
Vol 114 (5) ◽  
pp. 986-991 ◽  
Author(s):  
Simon A. Mortensen ◽  
Bjoern Sander ◽  
Rasmus K. Jensen ◽  
Jan Skov Pedersen ◽  
Monika M. Golas ◽  
...  
Keyword(s):  
Serine Protease ◽  
Innate Immune System ◽  
Innate Immune ◽  
Lectin Pathway ◽  
Classical Pathway ◽  
Structural Studies ◽  
Proteolytic Activation ◽  
Molecular Patterns ◽  
The Complement System ◽  
Recognition Molecule

The complement system is an important antimicrobial and inflammation-generating component of the innate immune system. The classical pathway of complement is activated upon binding of the 774-kDa C1 complex, consisting of the recognition molecule C1q and the tetrameric protease complex C1r2s2, to a variety of activators presenting specific molecular patterns such as IgG- and IgM-containing immune complexes. A canonical model entails a C1r2s2with its serine protease domains tightly packed together in the center of C1 and an intricate intramolecular reaction mechanism for activation of C1r and C1s, induced upon C1 binding to the activator. Here, we show that the serine protease domains of C1r and C1s are located at the periphery of the C1r2s2tetramer both when alone or within the nonactivated C1 complex. Our structural studies indicate that the C1 complex adopts a conformation incompatible with intramolecular activation of C1, suggesting instead that intermolecular proteolytic activation between neighboring C1 complexes bound to a complement activating surface occurs. Our results rationalize how a multitude of structurally unrelated molecular patterns can activate C1 and suggests a conserved mechanism for complement activation through the classical and the related lectin pathway.

scholarly journals Systemic complement activation is associated with respiratory failure in COVID-19 hospitalized patients

2020 ◽  
Vol 117 (40) ◽  
pp. 25018-25025 ◽  
Author(s):  
Jan C. Holter ◽  
Soeren E. Pischke ◽  
Eline de Boer ◽  
Andreas Lind ◽  
Synne Jenum ◽  
...  
Keyword(s):  
Viral Load ◽  
Respiratory Failure ◽  
Complement Activation ◽  
Blood Donors ◽  
Innate Immune ◽  
Lectin Pathway ◽  
Complement Inhibitors ◽  
Activation Products ◽  
The Complement System ◽  
Recognition Molecule

Respiratory failure in the acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is hypothesized to be driven by an overreacting innate immune response, where the complement system is a key player. In this prospective cohort study of 39 hospitalized coronavirus disease COVID-19 patients, we describe systemic complement activation and its association with development of respiratory failure. Clinical data and biological samples were obtained at admission, days 3 to 5, and days 7 to 10. Respiratory failure was defined as PO2/FiO2 ratio of ≤40 kPa. Complement activation products covering the classical/lectin (C4d), alternative (C3bBbP) and common pathway (C3bc, C5a, and sC5b-9), the lectin pathway recognition molecule MBL, and antibody serology were analyzed by enzyme-immunoassays; viral load by PCR. Controls comprised healthy blood donors. Consistently increased systemic complement activation was observed in the majority of COVID-19 patients during hospital stay. At admission, sC5b-9 and C4d were significantly higher in patients with than without respiratory failure (P = 0.008 and P = 0.034). Logistic regression showed increasing odds of respiratory failure with sC5b-9 (odds ratio 31.9, 95% CI 1.4 to 746, P = 0.03) and need for oxygen therapy with C4d (11.7, 1.1 to 130, P = 0.045). Admission sC5b-9 and C4d correlated significantly to ferritin (r = 0.64, P < 0.001; r = 0.69, P < 0.001). C4d, sC5b-9, and C5a correlated with antiviral antibodies, but not with viral load. Systemic complement activation is associated with respiratory failure in COVID-19 patients and provides a rationale for investigating complement inhibitors in future clinical trials.

scholarly journals Insidious pathogen-mimicking properties of nanoparticles in triggering the lectin pathway of the complement system

2015 ◽  
Vol 7 (3) ◽  
Author(s):  
S. Moein Moghimi ◽  
Peter P. Wibroe ◽  
Linping Wu ◽  
Z. Shadi Farhangrazi
Keyword(s):  
Immune System ◽  
Complement System ◽  
Innate Immune System ◽  
Innate Immune ◽  
Engineered Nanoparticles ◽  
Lectin Pathway ◽  
Structural Motifs ◽  
Polymeric Surface ◽  
The Complement System ◽  
Independent Reaction

AbstractThe lectin pathway of the complement system is an integral component of the innate immune system recognizing pathogens through patterns of sugar moieties displayed on their surfaces and neutralizing them through an antibody-independent reaction cascade. Many engineered nanoparticles incite complement through the lectin pathway, but these nanoparticles inherently do not express surface-exposed sugars. However, the projected polymeric surface architecture of nanoparticles may transiently resemble structural motifs of peptidoglycan constituents of pathogens and trigger the lectin pathway. We discuss these issues in relation to nanomedicine design and immune safety.

scholarly journals NOD-Like Receptors: Guards of Cellular Homeostasis Perturbation during Infection

2021 ◽  
Vol 22 (13) ◽  
pp. 6714
Author(s):  
Gang Pei ◽  
Anca Dorhoi
Keyword(s):  
Immune System ◽  
Innate Immune System ◽  
Current Knowledge ◽  
Protein Translation ◽  
Innate Immune ◽  
Cellular Homeostasis ◽  
Translation Block ◽  
Cytoskeleton Disruption ◽  
Molecular Patterns ◽  
Fine Tune

The innate immune system relies on families of pattern recognition receptors (PRRs) that detect distinct conserved molecular motifs from microbes to initiate antimicrobial responses. Activation of PRRs triggers a series of signaling cascades, leading to the release of pro-inflammatory cytokines, chemokines and antimicrobials, thereby contributing to the early host defense against microbes and regulating adaptive immunity. Additionally, PRRs can detect perturbation of cellular homeostasis caused by pathogens and fine-tune the immune responses. Among PRRs, nucleotide binding oligomerization domain (NOD)-like receptors (NLRs) have attracted particular interest in the context of cellular stress-induced inflammation during infection. Recently, mechanistic insights into the monitoring of cellular homeostasis perturbation by NLRs have been provided. We summarize the current knowledge about the disruption of cellular homeostasis by pathogens and focus on NLRs as innate immune sensors for its detection. We highlight the mechanisms employed by various pathogens to elicit cytoskeleton disruption, organelle stress as well as protein translation block, point out exemplary NLRs that guard cellular homeostasis during infection and introduce the concept of stress-associated molecular patterns (SAMPs). We postulate that integration of information about microbial patterns, danger signals, and SAMPs enables the innate immune system with adequate plasticity and precision in elaborating responses to microbes of variable virulence.

Das Komplementsystem

2012 ◽  
Vol 32 (04) ◽  
pp. 276-285 ◽  
Author(s):  
V. Frauenknecht ◽  
V. Schroeder
Keyword(s):  
Coronary Artery Disease ◽  
Complement System ◽  
Innate Immune System ◽  
Innate Immune ◽  
The Other ◽  
Atherosclerotic Plaques ◽  
Inflammatory Processes ◽  
Artery Disease ◽  
The Complement System ◽  
Novel Therapeutic

SummaryAtherosclerotic diseases such as coronary artery disease and ischaemic stroke are caused by chronic inflammation in arterial vessel walls. The complement system is part of the innate immune system. It is involved in many processes contributing to onset and development of atherosclerotic plaques up to the final stage of acute thrombotic events. This is due to its prominent role in inflammatory processes. In addition, there is increasing evidence that interactions between complement and coagulation provide a link between inflammation and thrombosis. On the other hand, the complement system also has an atheroprotective function through the clearance of apoptotic material.The knowledge of these complex mechanisms will become increasingly important, also for clinicians, since it may lead to novel therapeutic and diagnostic options. Therapies targeting the complement system have the potential to reduce tissue damage caused by acute ischaemic events. Whether early anti-inflammatory and anti-complement therapy may be able to prevent atherosclerosis, remains a hot topic for research.

scholarly journals Orally administered β-glucan improves the hemolytic activity of the complement system in horses

2021 ◽  
Vol 14 (4) ◽  
pp. 835-840
Author(s):  
Taline Scalco Picetti ◽  
Lucas de Figueiredo Soveral ◽  
Rovian Miotto ◽  
Luana Marina Scheer Erpen ◽  
Yasmin Kreutz ◽  
...  
Keyword(s):  
Hemolytic Activity ◽  
Innate Immune ◽  
Stressful Events ◽  
The Other ◽  
Control Group ◽  
Classical Pathway ◽  
Immune Parameters ◽  
Thoroughbred Horses ◽  
Hematological Analysis ◽  
The Complement System

Background and Aim: Immune-modulating molecules mainly act on innate immune cells, which are central to early defense against invading pathogens and contribute to developing adaptive immunity. Yeast-extracted β-glucan, a model immune-modulating molecule, is widely used in several animal species; however, its effect on horse immune parameters has not been thoroughly investigated yet. This study aimed to evaluate the effects of orally administered β-glucan on selected innate immune parameters in horses. Materials and Methods: Eighteen thoroughbred horses were assigned equally into three groups as follows: One control group (no β-glucan) and two β-glucan experimental groups (one received 125 mg and the other 2 g of β-glucan per day for 28 days). Blood samples were collected before and at the end of the experiment for hematological analysis, whole blood phagocytosis, respiratory burst assays, and to assess the serum lysozyme and complement hemolytic activities. Results: At the end of the experiment, significant decreases (p<0.05) in monocyte numbers were observed in the control horses (258.8±45.9 vs. 115.3±41.5) and in those fed 125 mg/day of β-glucan (208.8±72.3 vs. 99.2±60.7), whereas a significant increase in numbers was noted in the horses that were fed 2 g/day of β-glucan (303.5±45.8 vs. 429.8±86.0; p<0.05). The natural hemolytic activity of the complement was higher only in horses fed 2 g/day of β-glucan (p=0.018) compared to the other groups. The hemolytic activity in the classical pathway was higher in those fed 125 mg/day (p=0.0035) and 2 g/day of β-glucan (p=0.0001). Conclusion: β-glucan improves important innate immune parameters and might be fed to horses before stressful events.

scholarly journals Therapeutic Interventions into Innate Immune Diseases by Means of Aptamers

Pharmaceutics ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 955
Author(s):  
Farzana Yasmeen ◽  
Hana Seo ◽  
Nasir Javaid ◽  
Moon Suk Kim ◽  
Sangdun Choi
Keyword(s):  
Pattern Recognition ◽  
Immune System ◽  
Crucial Role ◽  
Innate Immune System ◽  
Innate Immune ◽  
Therapeutic Interventions ◽  
Immune System Diseases ◽  
Target Molecules ◽  
Molecular Patterns ◽  
Recognition Receptor

The immune system plays a crucial role in the body’s defense system against various pathogens, such as bacteria, viruses, and parasites, as well as recognizes non-self- and self-molecules. The innate immune system is composed of special receptors known as pattern recognition receptors, which play a crucial role in the identification of pathogen-associated molecular patterns from diverse microorganisms. Any disequilibrium in the activation of a particular pattern recognition receptor leads to various inflammatory, autoimmune, or immunodeficiency diseases. Aptamers are short single-stranded deoxyribonucleic acid or ribonucleic acid molecules, also termed “chemical antibodies,” which have tremendous specificity and affinity for their target molecules. Their features, such as stability, low immunogenicity, ease of manufacturing, and facile screening against a target, make them preferable as therapeutics. Immune-system–targeting aptamers have a great potential as a targeted therapeutic strategy against immune diseases. This review summarizes components of the innate immune system, aptamer production, pharmacokinetic characteristics of aptamers, and aptamers related to innate-immune-system diseases.

scholarly journals Case Report: Innate Immune System Challenge Unleashes Paraneoplastic Neurological Autoimmunity

2020 ◽  
Vol 11 ◽  
Author(s):  
Mingqin Zhu ◽  
Yuetao Ma ◽  
Anastasia Zekeridou ◽  
Vanda A. Lennon
Keyword(s):  
Immune System ◽  
Innate Immune System ◽  
Protein Complexes ◽  
Innate Immune ◽  
Neurological Symptoms ◽  
Autoimmune Response ◽  
Tnf Α ◽  
Bladder Instillation ◽  
Molecular Patterns ◽  
Symptoms And Signs

Paraneoplastic autoimmune neurological disorders reflect tumor-initiated immune responses against onconeural antigens. Symptoms and signs can affect the central and/or peripheral nervous systems, neuromuscular junction or muscle, and typically evolve subacutely before an underlying neoplasm is discovered. We describe four patients whose neurological symptoms were precipitated by potent innate immune system challenges: bladder instillation of BCG, tick bite and an “alternative cancer therapy” with bacterial extracts and TNF-α. We hypothesize that a tumor-initiated autoimmune response (evidenced by autoantibody profiles), pre-dating the immune system challenge, was unmasked or amplified in these patients by cytokines released systemically from innate immune cells activated by microbial pathogen-associated molecular patterns (PAMPs). The resultant upregulation of cognate onconeural peptides as MHC1 protein complexes on neural cell surfaces would render those cells susceptible to killing by CD8+ T cells, thus precipitating the patient's neurological symptoms.

Bacterial cell wall macroamphiphiles: Pathogen-/microbe-associated molecular patterns detected by mammalian innate immune system

Biochimie ◽  
2013 ◽  
Vol 95 (1) ◽  
pp. 33-42 ◽  
Author(s):  
Aurélie Ray ◽  
Marlène Cot ◽  
Germain Puzo ◽  
Martine Gilleron ◽  
Jérôme Nigou
Keyword(s):  
Cell Wall ◽  
Immune System ◽  
Bacterial Cell ◽  
Innate Immune System ◽  
Bacterial Cell Wall ◽  
Innate Immune ◽  
Molecular Patterns

Role of Toll-like receptors in liver health and disease

2011 ◽  
Vol 121 (10) ◽  
pp. 415-426 ◽  
Author(s):  
Ruth Broering ◽  
Mengji Lu ◽  
Joerg F. Schlaak
Keyword(s):  
Immune System ◽  
Liver Disease ◽  
Innate Immune System ◽  
Innate Immune ◽  
Toll Like Receptors ◽  
Evolutionarily Conserved ◽  
Liver Health ◽  
Health And Disease ◽  
Molecular Patterns

TLRs (Toll-like receptors), as evolutionarily conserved germline-encoded pattern recognition receptors, have a crucial role in early host defence by recognizing so-called PAMPs (pathogen-associated molecular patterns) and may serve as an important link between innate and adaptive immunity. In the liver, TLRs play an important role in the wound healing and regeneration processes, but they are also involved in the pathogenesis and progression of various inflammatory liver diseases, including autoimmune liver disease, alcoholic liver disease, non-alcoholic steatohepatitis, fibrogenesis, and chronic HBV (hepatitis B virus) and HCV (hepatitis C virus) infection. Hepatitis viruses have developed different evading strategies to subvert the innate immune system. Thus recent studies have suggested that TLR-based therapies may represent a promising approach in the treatment in viral hepatitis. The present review focuses on the role of the local innate immune system, and TLRs in particular, in the liver.

scholarly journals Toll-like receptors and hypertension

2014 ◽  
Vol 307 (5) ◽  
pp. R501-R504 ◽  
Author(s):  
Madhu V. Singh ◽  
François M. Abboud
Keyword(s):  
Immune System ◽  
Innate Immune System ◽  
Expression Patterns ◽  
Adaptor Proteins ◽  
Nuclear Factor Κb ◽  
Innate Immune ◽  
Toll Like Receptors ◽  
Cardiovascular Damage ◽  
Inflammatory Processes ◽  
Molecular Patterns

Hypertension and associated inflammatory processes that accelerate cardiovascular damage are regulated by the innate immune system. Toll-like receptors (TLR) are major components of the innate immune system that recognize endogenous damage-associated molecular patterns to activate prominent inflammatory signaling including activation of nuclear factor-κB (NF-κB). However, the role of TLR in the etiology of hypertension is not well understood. TLR signaling is dependent on adaptor proteins that, along with the TLR expression patterns, confer specificity of the inflammatory response and its pathological targets. Here we review the conceptual framework of how TLR and their adaptor proteins may differentially affect hypertension and cardiac hypertrophy by different stimuli.

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