Genomic view of the evolution of the complement system

The Complement System as a Part of Immunometabolic Post-Exercise Response in Adipose and Muscle Tissue

The precise molecular processes underlying the complement's activation, which follows exposure to physical stress still remain to be fully elucidated. However, some possible mechanisms could play a role in initiating changes in the complement's activity, which are observed post-exposure to physical stress stimuli. These are mainly based on metabolic shifts that occur in the microenvironment of muscle tissue while performing its function with increased intensity, as well as the adipose tissue's role in sterile inflammation and adipokine secretion. This review aims to discuss the current opinions on the possible link between the complement activation and diet, age, sex, and health disorders with a particular emphasis on endocrinopathies and, furthermore, the type of physical activity and overall physical fitness. It has been indicated that regular physical activity incorporated into therapeutic strategies potentially improves the management of particular diseases, such as, e.g., autoimmune conditions. Moreover, it represents a favorable influence on immunoaging processes. A better understanding of the complement system's interaction with physical activity will support established clinical therapies targeting complement components.

Effects of Aeromonas infection on the immune system, physical barriers and microflora structure in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is an intensively cultured and economically important herbivorous fish species in China, but its culture is often impacted by Aeromonas pathogens such as Aeromonas hydrophila and Aeromonas veronii. In this study, healthy grass carp were separately infected with A. hydrophila or A. veronii for 12, 24, 48 or 72 h. The results showed that the mRNA expression levels of intestinal inflammatory factors (tnf-α, il-1β and il-8), complement factors (c3 and c4), antimicrobial peptides (hepcidin, nk-lysin and β-defensin-1), immunoglobulins (igm and igt), and immune pathway-related signaling molecules (tlr1, tlr2, tlr4, myd88, irak4, irak1, traf6, nf-κb p65 and ap-1) were differentially upregulated in response to A. hydrophila and A. veronii challenge. Additionally, the expression levels of the intestinal pro-apoptotic genes tnfr1, tnfr2, tradd, caspase-8, caspase-3 and bax were significantly increased, whereas the expression of the inhibitory factor bcl-2 was significantly downregulated, indicating that Aeromonas infection significantly induced apoptosis in the intestine of grass carp. Moreover, the expression of intestinal tight junction proteins (occludin, zo-1, claudin b and claudin c) was significantly decreased after infection with Aeromonas. Histopathological analysis indicated the Aeromonas challenge caused severe damage to the intestinal villi with adhesions and detachment of intestinal villi accompanied by severe inflammatory cell infiltration at 12 h and 72 h. The 16S rRNA sequencing results showed that Aeromonas infection significantly altered the structure of the intestinal microflora of the grass carp at the phylum (Proteobacteria, Fusobacteria, Bacteroidetes and Firmicutes) and genus (Proteus, Cetobacterium, Bacteroides, and Aeromonas) levels. Take together, the findings of this study revealed that Aeromonas infection induces an intestinal immune response, triggers cell apoptosis, destroys physical barriers and alters microflora structure in the intestine of juvenile grass carp; the results will help to reveal the pathogenesis of intestinal bacterial diseases in grass carp.

The Establishment of Complement System Is from Gene Duplication and Domain Shuffling

The mammalian complement system constitutes a highly sophisticated body defense machinery. The evolutionary origin of the complement system can be traced to Coelenterata as the presence of the central component C3 and two activation proteases BF and MASP. In the present study, the main complement components were screened and analyzed from the genomes of different species in metazoan subphyla/phyla. C1q with classical domains can be traced to Annelida, and ficolin and MBL to Urochordata. C1r and C1s are only found in Chondrichthyes and even higher species, and MASP is traced to Coelenterata. In the evolutionary tree, C1r from Vertebrates is close to MASP1/2/3 from Deuterostomia and Coelenterata, and C1s from Vertebrates is close to MASP-like protease (MASPL) from Arthropoda, Mollusca, and Annelida. C2, BF, and DF can be traced to Mollusca, Coelenterata, and Porifera, respectively. There are no clear C2 and BF branches in the evolutionary tree. C3 can be traced to Coelenterata, and C4 and C5 are only in Chondrichthyes and even higher species. There are three clear C3, C4, and C5 branches in the evolutionary tree. C6-like (C6L) and C8 can be traced to Urochordata, and C7-like (C7L) can be traced to Cephalochordara. C6L, C7L, and C8 from Urochordata and Cephalochordara provide the structural conditions for the formation of Vertebrate MAC components. The findings unveil the evolutionary principles of the complement system and provide insight into its sophistication.

Thrombotic Microangiopathies and the Kidney

Thrombotic microangiopathy (TMA) is a pathological lesion that occurs due to endothelial injury. It can be seen in a heterogenous group of disorders, typically characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end-organ ischemia. TMA can also be renal limited with no systemic manifestations. There are multiple etiologies of a TMA with complement activation being a core underlying mechanism, although the nature and extent of complement involvement can vary. A further complicated factor is the cross talk between complement, neutrophils, and coagulation pathways in the pathophysiology of TMAs. Therefore, a thorough and systematic clinical history and laboratory evaluation are critical to establish the cause and pathophysiology of a TMA. Furthermore, TMAs are associated with significant morbidity and mortality, and timely diagnosis is key for appropriate management and to prevent end-stage kidney disease and other associated complications. In this review, we focus on the pathology, mechanisms, diagnostic work up and treatment of TMAs associated with various etiologies. We also define the complement evaluations that should be conducted in these patients and further highlight the currently approved complement therapies as well as others in the pipeline.

Beneficial versus Detrimental Effects of Complement-Microglial Interactions in Alzheimer's Disease

Research indicates that brain-region-specific synapse loss and dysfunction are early hallmarks and stronger neurobiological correlates of cognitive decline in Alzheimer's disease (AD) than amyloid plaque and neurofibrillary tangle counts or neuronal loss. Even though the precise mechanisms underlying increased synaptic pruning in AD are still unknown, it has been confirmed that dysregulation of the balance between complement activation and inhibition is a crucial driver of its pathology. The complement includes three distinct activation mechanisms, with the activation products C3a and C5a, potent inflammatory effectors, and a membrane attack complex (MAC) leading to cell lysis. Besides pro-inflammatory cytokines, the dysregulated complement proteins released by activated microglia bind to amyloid β at the synaptic regions and cause the microglia to engulf the synapses. Additionally, research indicating that microglia-removed synapses are not always degenerating and that suppression of synaptic engulfment can repair cognitive deficits points to an essential opportunity for intervention that can prevent the loss of intact synapses. In this study, we focus on the latest research on the role and mechanisms of complement-mediated microglial synaptic pruning at different stages of AD to find the right targets that could interfere with complement dysregulation and be relevant for therapeutic intervention at the early stages of the disease.

Emerging role of complement in COVID-19 and other respiratory virus diseases

The complement system, a key component of innate immunity, provides the first line of defense against bacterial infection; however, the COVID-19 pandemic has revealed that it may also engender severe complications in the context of viral respiratory disease. Here, we review the mechanisms of complement activation and regulation and explore their roles in both protecting against infection and exacerbating disease. We discuss emerging evidence related to complement-targeted therapeutics in COVID-19 and compare the role of the complement in other respiratory viral diseases like influenza and respiratory syncytial virus. We review recent mechanistic studies and animal models that can be used for further investigation. Novel knockout studies are proposed to better understand the nuances of the activation of the complement system in respiratory viral diseases.

Complement Suppresses the Initial Type 1 Interferon Response to Ocular Herpes Simplex Virus Type 1 Infection in Mice

The complement system (CS) contributes to the initial containment of viral and bacterial pathogens and clearance of dying cells in circulation. We previously reported mice deficient in complement component 3 (C3KO mice) were more sensitive than wild-type (WT) mice to ocular HSV-1 infection, as measured by a reduction in cumulative survival and elevated viral titers in the nervous system but not the cornea between days three and seven post infection (pi). The present study was undertaken to determine if complement deficiency impacted virus replication and associated changes in inflammation at earlier time points in the cornea. C3KO mice were found to possess significantly (p < 0.05) less infectious virus in the cornea at 24 h pi that corresponded with a decrease in HSV-1 lytic gene expression at 12 and 24 h pi compared to WT animals. Flow cytometry acquisition found no differences in the myeloid cell populations residing in the cornea including total macrophage and neutrophil populations at 24 h pi with minimal infiltrating cell populations detected at the 12 h pi time point. Analysis of cytokine and chemokine content in the cornea measured at 12 and 24 h pi revealed that only CCL3 (MIP-1α) was found to be different between WT and C3KO mice with >2-fold increased levels (p < 0.05, ANOVA and Tukey's post hoc t-test) in the cornea of WT mice at 12 h pi. C3KO mouse resistance to HSV-1 infection at the early time points correlated with a significant increase in type I interferon (IFN) gene expression including IFN-α1 and IFN-β and downstream effector genes including tetherin and RNase L (p < 0.05, Mann-Whitney rank order test). These results suggest early activation of the CS interferes with the induction of the type I IFN response and leads to a transient increase in virus replication following corneal HSV-1 infection.

The Importance of Complement-Mediated Immune Signaling in Alzheimer's Disease Pathogenesis

As an essential component of our innate immune system, the complement system is responsible for our defense against pathogens. The complement cascade has complex roles in the central nervous system (CNS), most of what we know about it stems from its role in brain development. However, in recent years, numerous reports have implicated the classical complement cascade in both brain development and decline. More specifically, complement dysfunction has been implicated in neurodegenerative disorders, such as Alzheimer's disease (AD), which is the most common form of dementia. Synapse loss is one of the main pathological hallmarks of AD and correlates with memory impairment. Throughout the course of AD progression, synapses are tagged with complement proteins and are consequently removed by microglia that express complement receptors. Notably, astrocytes are also capable of secreting signals that induce the expression of complement proteins in the CNS. Both astrocytes and microglia are implicated in neuroinflammation, another hallmark of AD pathogenesis. In this review, we provide an overview of previously known and newly established roles for the complement cascade in the CNS and we explore how complement interactions with microglia, astrocytes, and other risk factors such as TREM2 and ApoE4 modulate the processes of neurodegeneration in both amyloid and tau models of AD.

Functional Analysis of a Novel Complement C5a Receptor 1-Blocking Monoclonal Antibody

INTRODUCTION

The complement system anaphylatoxin C5a is a critical player in inflammation. By binding to complement C5a receptor 1 (C5aR1/CD88), C5a regulates many cellular functions, mainly as a potent pro-inflammatory inducer. We describe the generation and selection of a potent antagonistic C5aR1 mouse monoclonal antibody (mAb).

METHODS

Initial C5aR1 hybridoma clone selection was performed with a cell-binding study in human whole blood. In-house C5aR1 mAb assessment for C5aR1 inhibition was done via the iLite® C5a assay. C5aR1 mAb specificity was investigated on C5aR1his- and C5aR2his-expressing Flp-In™-CHO cells. Physiological C5aR1 inhibition was assessed via a C5a-driven calcium flux assay and stimulation assay based on isolated polymorphonuclear leukocytes (PMNs) and a whole blood model stimulated with Escherichia coli.

RESULTS

The supernatant of hybridoma clones targeting the N-terminal section of C5aR1 displayed efficient binding to C5aR1 in whole blood, which was confirmed for purified mAbs. The C5aR1 mAb 18-41-6 was selected following the assay of in-house C5aR1 mAbs via the iLite® C5a assay. The mAb 18-41-6 was specific for C5aR1. Full-size and/or F(ab')2 preparations of mAb 18-41-6 were found to efficiently abrogate C5a-induced calcium flux in neutrophils and to significantly reduce the upregulation of the activation markers CD11b (neutrophils, monocytes) and CD66b (neutrophils).

CONCLUSION

Our results demonstrate that mAb 18-41-6 is a valuable tool for investigating the C5a-C5aR1 axis and a potential therapeutic candidate for inflammatory disease treatment.

Full-length transcriptome analysis provides new insights into the diversity of immune-related genes in the threatened freshwater shellfish Solenaia oleivora

Solenaia oleivora, a valuable and rare bivalve endemic to China, is becoming a threatened freshwater sepcies. However, the lack of research on its genome and immune system will hinder advances in its conservation and artificial breeding. In this study, we obtained the full-length transcriptome of S. oleivora using PacBio sequencing. A total of 21,415 transcripts with an average length of 1,726 bp were generated. Among these transcripts, 12,084 had coding sequences (CDS), of which 8,639 were annotated in 6 databases. The structure analysis identified 625 transcript factors (TFs), 8,005 long non-coding RNAs (lncRNAs), and 5,288 simple sequences repeat (SSRs). Meanwhile, massive immune genes were identified from the transcriptome of S. oleivora. In terms of non-self-identification, 97 transcripts of pattern recognition receptors (PRRs) were discovered, including peptidoglycan recognition proteins (PGRPs), gram-negative bacteria binding proteins (GNBPs), toll-like receptors (TLRs), scavenger receptors (SRs), galectins (GALs), C-type lectins (CLTs), and fibrinogen-related protein (FREPs). For pathogen elimination, 7 transcripts related to antimicrobial peptides, lysozymes, and lysosomal enzymes were identified. Moreover, 33 complement-associated transcripts were found. This study enriched the genome resources of S. oleivora and provided new insights for the study of the immune system of S. oleivora.

Complement component C1q is an immunological rheostat that regulates Fc:Fc[Formula: see text]R interactions

Though binding sites for the complement factor C1q and the canonical fragment crystallizable (Fc) gamma receptors (Fc[Formula: see text]Rs) on immunoglobulin G (IgG) molecules overlap, how C1q decoration of immune complexes (ICs) influences their ability to engage Fc[Formula: see text]Rs remains unknown. In this report, we use recombinant human Fc multimers as stable IC mimics to show that C1q engagement of ICs directly and transiently inhibits their interactions with Fc[Formula: see text]RIII (CD16) on human natural killer (NK) cells. This inhibition occurs by C1q engagement alone as well as in concert with other serum factors. Furthermore, the inhibition of Fc[Formula: see text]RIII engagement mediated by avid binding of C1q to ICs is directly associated with IC size and dependent on the concentrations of both C1q and Fc multimers present. Functionally, C1q-mediated Fc blockade limits the ability of NK cells to induce the upregulation of the cosignaling molecule, 4-1BB (CD137), and to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Although C1q is traditionally viewed as a soluble effector molecule, we demonstrate that C1q may also take on the role of an "immunologic rheostat," buffering Fc[Formula: see text]R-mediated activation of immune cells by circulating ICs. These data define a novel role for C1q as a regulator of immune homeostasis and add to our growing understanding that complement factors mediate pleiotropic effects.

C9 regulates the complement-mediated cell lysis in association with CD59 to resist bacterial infection in a primary animal

Complement component 9 (C9), as an essential component of terminal membrane attack complex of complement system, plays an important role in innate immune defense. However, the function and regulatory mechanism of C9 in the antimicrobial immune response of teleost fish remain unclear. In this study, the open reading frame of Nile tilapia (Oreochromis niloticus) C9 (OnC9) gene was amplified. The mRNA and protein expression of OnC9 were significantly changed upon infection with Streptococcus agalactiae and Aeromonas hydrophila in vivo and in vitro. Upon bacterial challenge, the OnC9 knockdown could lead to rapid proliferation of the pathogenic bacteria, ultimately resulting in tilapia death. However, the phenotype was rescued by re-injection of OnC9, which restored the healthy status of the knockdown tilapia. Further, the OnC9 was an essential component in complement-mediated cell lysis and associated with OnCD59 to regulate the efficiency of lysis. Overall, this study indicates that OnC9 is involved in host defense against bacterial infection, and provides a valuable reference for further exploration of the molecular regulatory mechanism of C9 in innate immune defense in a primary animal.

l-ficolin-MASP arm of the complement system in schizophrenia

The abnormal neurodevelopment secondary to in utero adversities, such as hypoxia, malnutrition and maternal infections, underlies schizophrenia (SZ) etiology. As the genes of MBL-associated serine proteases (MASP) of the complement lectin pathway, MASP1 and MASP2, are expressed in the developing cortex and are functionally important for neuronal migration, we hypothesize that the malfunction ofl-ficolin-MASP arm may also be involved in schizophrenia pathophysiology as it was shown for MBL-MASP complexes. We investigated serum l-ficolin and plasma MASP-2 levels, the activity of l-ficolin-bound MASP-2, as well as an array of the complement-related variables in chronic schizophrenic patients in the acute phase of the disease and controls without physical or mental diagnoses. The median concentration of l-ficolin in Armenian controls was 3.66 μg/ml and similar to those reported for other Caucasian populations. SZ-cases had ∼40 % increase in serum l-ficolin (median 5.08 μg/ml; P < 0.0024). In the pooled sample, l-ficolin level was higher in males than in females (P < 0.0031), but this gender dichotomy was not affecting the variable association with schizophrenia (P < 0.016). Remarkably, MASP-2 plasma concentration showed gender-dependent significant variability in the group of patients but not in controls. When adjusted for gender and gender*diagnosis interaction, a significantly high MASP-2 level in female patients versus female controls was observed (median: 362 ng/ml versus 260 ng/ml, respectively; P < 0.0020). A significant increase in l-ficolin-bound MASP-2 activity was also observed in schizophrenia (on the median, cases vs controls: 7.60 vs 6.50 RU; P < 0.021). Correlation analyses of the levels of l-ficolin and MASP-2, l-ficolin-(MASP-2) activity and the demographic data did not show any significant association with the age of individuals, family history, age at onset and duration of the illness, and smoking. Noteworthy, the levels of l-ficolin and MASP-2 in circulation were significantly associated with the type of schizophrenia (paranoid SZ-cases had much higher l-ficolin (P < 0.0035) and lower MASP-2 levels than the other types combined (P < 0.049)). Correlations were also found between: (i) the classical pathway functional activity and l-ficolin level (rs = 0.19, P < 0.010); (ii) the alternative pathway functional activity and MASP-2 level (rs = 0.26, P < 0.00035); (iii) the activity of l-ficolin-bound MASP2 and the downstream C2 component haemolytic activity (rs = -0.19, P < 0.017); and (iv) l-ficolin and the upstream C-reactive protein (CRP) serum concentrations (r = 0.28, P < 0.018). Overall, the results showed l-ficolin-related lectin pathway alterations in schizophrenia pathophysiology. It is likely that in addition to the MBL-MASP component over-activity reported previously, the alterations of the lectin pathway in schizophrenia also involve variations of l-ficolin-(MASP-2) on protein concentration and activity levels.

Gene polymorphisms within regions of complement component C1q in HIV associated preeclampsia

OBJECTIVE

This study investigates the association of C1q gene (rs292001 and rs294183) polymorphisms in HIV infected and uninfected preeclamptic women of African ancestry.

MATERIALS AND METHODS

The study population consisted of 325 pregnant women of African ancestry grouped into 145 normotensive pregnant women (72 HIV uninfected normotensive, 73 HIV infected normotensive) and 180 preeclamptic pregnant women (103 HIV uninfected preeclamptics, 77 HIV infected preeclamptics). Preeclamptic pregnant women were further sub-grouped into 79 early-onset preeclampsia (EOPE) (40 HIV uninfected EOPE, 39 HIV infected EOPE) and 101 late-onset preeclampsia (LOPE) (63 HIV uninfected LOPE, 38 HIV infected LOPE). Genotyping of complement C1q gene polymorphisms (rs292001 and rs294183) was detected using a TaqMan® SNP Genotyping assay from purified DNA.

RESULTS

No significant differences in allelic and genotype frequencies of rs292001 and rs294183 between preeclamptic and normotensive women were observed. Likewise, there were no significant differences in allelic and genotype frequencies between HIV infected normotensive vs HIV infected preeclampsia and HIV uninfected normotensive vs HIV uninfected preeclampsia for both SNPs. However, the odds ratio of preeclamptic women having the GA genotype was 1:2.

CONCLUSION

We demonstrate that SNPs of the C1q gene (rs292001 and rs294183) are not associated with the pathogenesis of PE development in women of African ancestry. The role ofC1qrs292001 heterozygous GA is highlighted (with and without HIV infection) may affect susceptibility to PE development. Notably, this dysregulation may affect C1q translation and protein output thus influencing the downstream role of the complement system and functional immunology in HIV infection comorbid with PE.

Review of the unique and dominant lectin pathway of complement activation in agnathans

As the most primitive vertebrates, lampreys are significant in understanding the early origin and evolution of the vertebrate innate and adaptive immune systems. The complement system is a biological response system with complex and precise regulatory mechanisms and plays an important role in innate and adaptive immunity. It consists of more than 30 distinct components, including intrinsic components, regulatory factors, and complement receptors. Complement system is the humoral backbone of the innate immune defense and complement-like factors have also been found in cyclostomes. Our knowledge as such in lamprey has dramatically increased in the recent years. The searching for complement components in the reissner lamprey Lethenteron reissneri genome database, together with published data, has unveiled the existence of all the orthologues of mammalian complement components identified thus far, including the complement regulatory proteins and complement receptors, in lamprey. This review, summarizes the key themes and recent updates on the complement system of agnathans and discusses the individual complement components of lampreys, and critically compare their functions to that of mammalian complement components. Interestingly, the adaptive immune system of agnathans differs from that of gnathostomes. Lamprey complement components also display some distinctive features, such as lampreys are characterized by the variable lymphocyte receptors (VLRs)-based alternative adaptive immunity. This review may serve as important literature for deducing the evolution of the immune system from invertebrates to vertebrates.

Complement-related proteins in crustacean immunity

As an important part of innate immune system, complement system is widely involved in defense response and immune regulation, and plays an important biological role. The complement system has been deeply studied. More than 30 complement-related molecules and three major complement-activation pathways have been identified in vertebrates. Crustacean animals do not have complement system. There are only some complement-related proteins in crustaceans which are important for host defense. In this review, we summarize the current knowledge about complement-related proteins in crustaceans, and their functions in crustacean immunity. We also make a comparation of the crustacean pro-phenoloxidase activating system and the mammalian complement system. This review provides a better understanding of the evolution and function of complement-related proteins in crustaceans.

The primitive complement system in molluscs

The complement system is an important immune defense mechanism that plays essential roles in both innate and adaptive immunity of vertebrates. Since complement components are identified in deuterostome and even primitive protostome species, the origin and evolution of complement system in invertebrates have been of great interest. Recently, research on the complement system in mollusc immunity has been increasing due to their importance in worldwide aquaculture, and their phylogenetic position. Complement components including C3, C1q domain containing protein (C1qDCP), C-type lectin (CTL), ficolin-like, mannose-binding lectin (MBL)-associated serine proteases like (MASPL), and factor B have been identified, suggesting the existence of complement system in molluscs. The lectin pathway has been outlined in molluscs, which is initiated by CTL with CCP domain and MASPL protein to generate C3 cleavage fragments. The molluscan C1qDCP exhibits the capability to bind human IgG, indicating the existence of possible C1qDCP-mediated activation pathway in molluscs. The activation of C3 regulates the expressions of immune effectors (cytokines and antibacterial peptides), mediates the haemocyte phagocytosis, and inhibits the bacterial growth. Some MACPF domain containing proteins may replace the missing terminal pathway in molluscs. This article provides a review of complement system in molluscs, including its components, activation mechanisms and functions in the immune response of molluscs.

The localization of Toll and Imd pathway and complement system components and their response to Vibrio infection in the nemertean Lineus ruber

BACKGROUND

Innate immunity is the first line of defense against pathogens. In animals, the Toll pathway, the Imd pathway, the complement system, and lectins are well-known mechanisms involved in innate immunity. Although these pathways and systems are well understood in vertebrates and arthropods, they are understudied in other invertebrates.

RESULTS

To shed light on immunity in the nemertean Lineus ruber, we performed a transcriptomic survey and identified the main components of the Toll pathway (e.g., myD88, dorsal/dif/NFκB-p65), the Imd pathway (e.g., imd, relish/NFκB-p105/100), the complement system (e.g., C3, cfb), and some lectins (FreD-Cs and C-lectins). In situ hybridization showed that TLRβ1, TLRβ2, and imd are expressed in the nervous system; the complement gene C3-1 is expressed in the gut; and the lectins are expressed in the nervous system, the blood, and the gut. To reveal their potential role in defense mechanisms, we performed immune challenge experiments, in which Lineus ruber specimens were exposed to the gram-negative bacteria Vibrio diazotrophicus. Our results show the upregulation of specific components of the Toll pathway (TLRα3, TLRβ1, and TLRβ2), the complement system (C3-1), and lectins (c-lectin2 and fred-c5).

CONCLUSIONS

Therefore, similarly to what occurs in other invertebrates, our study shows that components of the Toll pathway, the complement system, and lectins are involved in the immune response in the nemertean Lineus ruber. The presence of these pathways and systems in Lineus ruber, but also in other spiralians; in ecdysozoans; and in deuterostomes suggests that these pathways and systems were involved in the immune response in the stem species of Bilateria.

Alternative pathway activation: Ever ancient and ever new

Primitive underpinnings of the alternative pathway (AP), namely, a C3-like protein, likely arose more than a billion years ago. The development of an AP amplification loop, while greatly enhancing speed and potency, also presents a double-edged sword. Although critical to combat an infectious disease, it is also potentially destructive, particularly in a chronic disease process involving vital organs where scarring and reduction of regulatory function can occur. Furthermore, new knowledge is pointing to genetic factors involved in an increasing number of complement-related diseases such as age-related macular degeneration. However, even a normal functioning repertoire of complement components can drive cellular damage as a result of low-level complement activation over time. Thus, the modern human AP now faces a new challenge: cumulatively-driven tissue damage from chronic inflammatory processes that mediate cellular injury. The impact of ongoing low-level AP-enhanced complement activation in disease processes is just beginning to be appreciated and studied. However, the sheer numbers of individuals affected by chronic diseases emphasize the need for novel therapeutic agents capable of modulating the AP. The more we learn about this ancient system, the greater is the likelihood of developing fresh perspectives that could contribute to improved human health.

Insights into the Antibacterial Properties of Complement Peptides C3a, C4a, and C5a across Vertebrates

Complement peptides C3a, C4a, and C5a are important components of innate immunity in vertebrates. Although they diverged from a common ancestor, only C3a and C4a can act as antibacterial peptides in Homo sapiens, suggesting that C5a has evolved into a purely chemotactic molecule; however, the antibacterial properties of C3a, C4a, and C5a across vertebrates still require elucidation. In this article, we show that, unlike those in H. sapiens, Mus musculus C3a, C4a, and C5a all possess antibacterial activities, implying that the antibacterial properties of C3a, C4a, and C5a have evolved divergently in vertebrates. The extremely different net charge, a key factor determining the antibacterial activities of cationic antimicrobial peptides, of vertebrate C3a, C4a, and C5a supports this speculation. Moreover, the antibacterial activity of overlapping peptides covering vertebrate C3a, C4a, and C5a further strongly supports the speculation, because their activity is positively correlated with the net charge of source molecules. Notably, the structures of C3a, C4a, and C5a are conserved in vertebrates, and the inactive overlapping peptides can become antibacterial peptides if mutated to possess enough net positive charges, indicating that net charge is the only factor determining the antibacterial properties of vertebrate C3a, C4a, and C5a. More importantly, many vertebrate C3a-, C4a-, and C5a-derived peptides possess high antibacterial activities yet exhibit no hemolytic activities, suggesting the application potential in anti-infective therapy. Taken together, our findings reveal that vertebrate C3a, C4a, and C5a are all sources of antibacterial peptides that will facilitate the design of excellent peptide antibiotics.

Birth and death in terminal complement pathway

The cytolytic activity of the membrane attack complex (MAC) is pivotal in the complement-mediated elimination of pathogens. Terminal complement pathway (TCP) genes encode the proteins that form the MAC. Although the TCP genes are well conserved within most vertebrate species, the early evolution of the TCP genes is poorly understood. Based on the comparative genomic analysis of the early evolutionary history of the TCP homologs, we evaluated four possible scenarios that could have given rise to the vertebrate TCP. Currently available genomic data support a scheme of complex sequential protein domain gains that may be responsible for the birth of the vertebrate C6 gene. The subsequent duplication and divergence of this vertebrate C6 gene formed the C7, C8α, C8β, and C9 genes. Compared to the widespread conservation of TCP components within vertebrates, we discovered that C9 has disintegrated in the genomes of galliform birds. Publicly available genome and transcriptome sequencing datasets of chicken from Illumina short read, PacBio long read, and Optical mapping technologies support the validity of the genome assembly at the C9 locus. In this study, we have generated a > 120X coverage whole-genome Chromium 10x linked-read sequencing dataset for the chicken and used it to verify the loss of the C9 gene in the chicken. We find multiple CR1 (chicken repeat 1) element insertions within and near the remnant exons of C9 in several galliform bird genomes. The reconstructed chronology of events shows that the CR1 insertions occurred after C9 gene loss in an early galliform ancestor. Loss of C9 in galliform birds, in contrast to conservation in other vertebrates, may have implications for host-pathogen interactions. Our study of C6 gene birth in an early vertebrate ancestor and C9 gene death in galliform birds provides insights into the evolution of the TCP.

Innate Immunity: A Balance between Disease and Adaption to Stress

Since first being documented in ancient times, the relation of inflammation with injury and disease has evolved in complexity and causality. Early observations supported a cause (injury) and effect (inflammation) relationship, but the number of pathologies linked to chronic inflammation suggests that inflammation itself acts as a potent promoter of injury and disease. Additionally, results from studies over the last 25 years point to chronic inflammation and innate immune signaling as a critical link between stress (exogenous and endogenous) and adaptation. This brief review looks to highlight the role of the innate immune response in disease pathology, and recent findings indicating the innate immune response to chronic stresses as an influence in driving adaptation.

Synergy of protease-binding sites within the ecotin homodimer is crucial for inhibition of MASP enzymes and for blocking lectin pathway activation

Ecotin is a homodimeric serine protease inhibitor produced by many commensal and pathogenic microbes. It functions as a virulence factor, enabling survival of various pathogens in the blood. The ecotin dimer binds two protease molecules, and each ecotin protomer has two protease-binding sites: site1 occupies the substrate-binding groove, whereas site2 engages a distinct secondary region. Owing to the twofold rotational symmetry within the ecotin dimer, sites 1 and 2 of a protomer bind to different protease molecules within the tetrameric complex. Escherichia coli ecotin inhibits trypsin-like, chymotrypsin-like, and elastase-like enzymes, including pancreatic proteases, leukocyte elastase, key enzymes of blood coagulation, the contact and complement systems, and other antimicrobial cascades. Here, we show that mannan-binding lectin-associated serine protease-1 (MASP-1) and MASP-2, essential activators of the complement lectin pathway, and MASP-3, an essential alternative pathway activator, are all inhibited by ecotin. We decipher in detail how the preorganization of site1 and site2 within the ecotin dimer contributes to the inhibition of each MASP enzyme. In addition, using mutated and monomeric ecotin variants, we show that site1, site2, and dimerization contribute to inhibition in a surprisingly target-dependent manner. We present the first ecotin:MASP-1 and ecotin:MASP-2 crystal structures, which provide additional insights and permit structural interpretation of the observed functional results. Importantly, we reveal that monomerization completely disables the MASP-2-inhibitory, MASP-3-inhibitory, and lectin pathway-inhibitory capacity of ecotin. These findings provide new opportunities to combat dangerous multidrug-resistant pathogens through development of compounds capable of blocking ecotin dimer formation.

Domain-Dependent Evolution Explains Functional Homology of Protostome and Deuterostome Complement C3-Like Proteins

Complement proteins emerged early in evolution but outside the vertebrate clade they are poorly characterized. An evolutionary model of C3 family members revealed that in contrast to vertebrates the evolutionary trajectory of C3-like genes in cnidarian, protostomes and invertebrate deuterostomes was highly divergent due to independent lineage and species-specific duplications. The deduced C3-like and vertebrate C3, C4 and C5 proteins had low sequence conservation, but extraordinarily high structural conservation and 2-chain and 3-chain protein isoforms repeatedly emerged. Functional characterization of three C3-like isoforms in a bivalve representative revealed that in common with vertebrates complement proteins they were cleaved into two subunits, b and a, and the latter regulated inflammation-related genes, chemotaxis and phagocytosis. Changes within the thioester bond cleavage sites and the a-subunit protein (ANATO domain) explained the functional differentiation of bivalve C3-like. The emergence of domain-related functions early during evolution explains the overlapping functions of bivalve C3-like and vertebrate C3, C4 and C5, despite low sequence conservation and indicates that evolutionary pressure acted to conserve protein domain organization rather than the primary sequence.

The EPICC Family of Anti-Inflammatory Peptides: Next Generation Peptides, Additional Mechanisms of Action, and In Vivo and Ex Vivo Efficacy

The EPICC peptides are a family of peptides that have been developed from the sequence of the capsid protein of human astrovirus type 1 and previously shown to inhibit the classical and lectin pathways of complement. The EPICC peptides have been further optimized to increase aqueous solubility and identify additional mechanisms of action. Our laboratory has developed the lead EPICC molecule, PA-dPEG24 (also known as RLS-0071), which is composed of a 15 amino acid peptide with a C-terminal monodisperse 24-mer PEGylated moiety. RLS-0071 has been demonstrated to possess other mechanisms of action in addition to complement blockade that include the inhibition of neutrophil-driven myeloperoxidase (MPO) activity, inhibition of neutrophil extracellular trap (NET) formation as well as intrinsic antioxidant activity mediated by vicinal cysteine residues contained within the peptide sequence. RLS-0071 has been tested in various ex vivo and in vivo systems and has shown promise for the treatment of both immune-mediated hematological diseases where alterations in the classical complement pathway plays an important pathogenic role as well as in models of tissue-based diseases such as acute lung injury and hypoxic ischemic encephalopathy driven by both complement and neutrophil-mediated pathways (i.e., MPO activity and NET formation). Next generation EPICC peptides containing a sarcosine residue substitution in various positions within the peptide sequence possess aqueous solubility in the absence of PEGylation and demonstrate enhanced complement and neutrophil inhibitory activity compared to RLS-0071. This review details the development of the EPICC peptides, elucidation of their dual-acting complement and neutrophil inhibitory activities and efficacy in ex vivo systems using human clinical specimens and in vivo efficacy in animal disease models.

How COVID-19 and other pathological conditions and medical treatments activate our intravascular innate immune system

COVID-19 has been shown to have a multifaceted impact on the immune system. In a recently published article in Front Immunol, we show that the intravascular innate immune system (IIIS) is strongly activated in severe COVID-19 with ARDS and appears to be one of the causes leading to severe COVID-19. In this article, we describe the IIIS and its physiological function, but also the strong pro-inflammatory effects that are observed in COVID-19 and in various other pathological conditions and treatments such as during ischemia reperfusion injury and in treatments where biomaterials come in direct contact with blood in, e.g., extracorporeal and intravasal treatments. In the present article, we describe how the IIIS, a complex network of plasma proteins and blood cells, constitute the acute innate immune response of the blood and discuss the effects that the IIIS induces in pathological disorders and treatments in modern medicine.

C4d Deposition after Allogeneic Renal Transplantation in Rats Is Involved in Initial Apoptotic Cell Clearance

In the context of transplantation, complement activation is associated with poor prognosis and outcome. While complement activation in antibody-mediated rejection is well-known, less is known about complement activation in acute T cell-mediated rejection (TCMR). There is increasing evidence that complement contributes to the clearance of apoptotic debris and tissue repair. In this regard, we have analysed published human kidney biopsy transcriptome data clearly showing upregulated expression of complement factors in TCMR. To clarify whether and how the complement system is activated early during acute TCMR, experimental syngeneic and allogeneic renal transplantations were performed. Using an allogeneic rat renal transplant model, we also observed upregulation of complement factors in TCMR in contrast to healthy kidneys and isograft controls. While staining for C4d was positive, staining with a C3d antibody showed no C3d deposition. FACS analysis of blood showed the absence of alloantibodies that could have explained the C4d deposition. Gene expression pathway analysis showed upregulation of pro-apoptotic factors in TCMR, and apoptotic endothelial cells were detected by ultrastructural analysis. Monocytes/macrophages were found to bind to and phagocytise these apoptotic cells. Therefore, we conclude that early C4d deposition in TCMR may be relevant to the clearance of apoptotic cells.

The conservation and diversity of ascidian cells and molecules involved in the inflammatory reaction: The Ciona robusta model

Ascidians are marine invertebrate chordates belonging to the earliest branch (Tunicata) in the chordate phylum, therefore, they are of interest for studying the evolution of immune systems. Due to the known genome, the non-colonial Ciona robusta, previously considered to be C. intestinalis type A, is a model species for the study of inflammatory response. The internal defense of ascidians mainly relies on hemocytes circulating in the hemolymph and pharynx. Hemocytes can be in vivo challenged by LPS injection and various granulocyte and vacuolated cell populations differentiated to produce and release inflammatory factors. Molecular biology and gene expression studies revealed complex defense mechanisms involving different inflammatory hemocytes. Furthermore, cloning procedures allowed sequence analyses and molecular studies disclose immune-related gene families including TOLL-like receptors, galectins, C-type lectins, collectins, interlectins, pentraxine-like, peroxinectins, complement factors-like, TNFα-like, IL-17-like, TGF-like, MIF-like. These genes are promptly upregulated by the inflammatory stimulus and show a time course of transcription similar to each other. Domains sequence similarity and phylogenetic relationships with the vertebrate counterparts are shedding some light on immune-related gene evolution. Selective bioassays as well as bioinformatic approaches have allowed the characterization of antimicrobial peptides and the identification of post transcriptional molecular mechanisms able of influencing dynamics of gene regulation are described. In synthesis, the purpose of this article is to further explore the topic of hemocyte and molecules related to internal defence of ascidians involved in the inflammatory reaction, as well as to discuss current and future study options through a detailed literature review.

The Chicken Embryo Model: A Novel and Relevant Model for Immune-Based Studies

Dysregulation of the immune system is associated with many pathologies, including cardiovascular diseases, diabetes, and cancer. To date, the most commonly used models in biomedical research are rodents, and despite the various advantages they offer, their use also raises numerous drawbacks. Recently, another in vivo model, the chicken embryo and its chorioallantoic membrane, has re-emerged for various applications. This model has many benefits compared to other classical models, as it is cost-effective, time-efficient, and easier to use. In this review, we explain how the chicken embryo can be used as a model for immune-based studies, as it gradually develops an embryonic immune system, yet which is functionally similar to humans'. We mainly aim to describe the avian immune system, highlighting the differences and similarities with the human immune system, including the repertoire of lymphoid tissues, immune cells, and other key features. We also describe the general in ovo immune ontogeny. In conclusion, we expect that this review will help future studies better tailor their use of the chicken embryo model for testing specific experimental hypotheses or performing preclinical testing.

Chemosensory Exploitation and Predator-Prey Arms Races

Thousands of armed predatory species, distributed widely across the metazoan tree-of-life, consume only hard-shell or exoskeleton-bearing organisms (called “durophagy”). Prey armor clearly has evolved in response to selection by predators, but there is little evidence of the contrary, counter-adaptation by predators. Evolved consumer responses to prey, in general, might be more readily expressed in ways other than morphological traits, including via sensory cues. Here, we explored the chemosensory basis for durophagy in a model predator-prey system, and identified intimate associations between durophagous predators and their shelled prey. Barnacles (Balanus glandula and Semibalanus cariosus) bear hard shells and secrete, respectively, a 199 or 201 kDa glycoprotein ortholog (named “MULTIFUNCin”), with expression limited to the body armor (epidermis, cuticle, and live shell). To test for effects of MULTIFUNCin on predators, we constructed faux prey to mimic meaningful physical and chemical characteristics of live barnacles. In separate experiments, each consumer species was presented MULTIFUNCin, purified from either B. glandula or S. cariosus, at a typical armor concentration. All six predatory species (sea star, Pisaster ochraceus; whelks, Acanthinucella spirata, Nucella emarginata, N. ostrina, N. canaliculata, and N. lamellosa) attacked and ate MULTIFUNCin-infused faux prey significantly more than controls. Akin to barnacles, secretion of glycoprotein-rich extracellular matrices is common among armored prey species—from marine sponges to terrestrial vertebrates. Our results, therefore, suggest that chemosensory exploitation of glycoproteins could be widespread, with notable consequences for life on land and in the sea.

Production and characterization of polyclonal and monoclonal antibodies of lamprey pore-forming protein

In the most primitive jawless vertebrate lamprey, the complement-dependent cytotoxicity regulated by variable lymphocyte receptors (VLRs) plays an important role in the adaptive immunity. Our previous studies have shown that the lamprey pore-forming protein (LPFP) acted as the terminal effector of VLR to lyse and kill the target cells. Here, the recombinant GST-LPFP protein was expressed and purified in prokaryotic expression system, and then used as the immunogen to produce mouse monoclonal antibody and rabbit polyclonal antibody. With these antibodies, we proved that LPFP existed as homodimers in the lamprey serum, and could be recruited to the membrane of target cells after stimulation. In conclusion, the antibodies we produced could specifically recognize the LPFP protein, which could be the useful tools to further study the pore-forming mechanism of LPFP.

Building a better antibody through the Fc: advances and challenges in harnessing antibody Fc effector functions for antiviral protection

Antibodies can provide antiviral protection through neutralization and recruitment of innate effector functions through the Fc domain. While neutralization has long been appreciated for its role in antibody-mediated protection, a growing body of work indicates that the antibody Fc domain also significantly contributes to antiviral protection. Recruitment of innate immune cells such as natural killer cells, neutrophils, monocytes, macrophages, dendritic cells and the complement system by antibodies can lead to direct restriction of viral infection as well as promoting long-term antiviral immunity. Monoclonal antibody therapeutics against viruses are increasingly incorporating Fc-enhancing features to take advantage of the Fc domain, uncovering a surprising breadth of mechanisms through which antibodies can control viral infection. Here, we review the recent advances in our understanding of antibody-mediated innate immune effector functions in protection from viral infection and review the current approaches and challenges to effectively leverage innate immune cells via antibodies.

A novel C-type lectin activates the complement cascade in the primitive oyster Crassostrea gigas

The ancient origin of the lectin pathway of the complement system can be traced back to protochordates (such as amphioxus and tunicates) by the presence of components such as ficolin, glucose-binding lectin, mannose-binding lectin-associated serine protease (MASP), and C3. Evidence for a more primitive origin is offered in the present study on the Pacific oyster Crassostrea gigas. C3 protein in C. gigas (CgC3) was found to be cleaved after stimulation with the bacteria Vibrio splendidus. In addition, we identified a novel C-type lectin (defined as CgCLec) with a complement control protein (CCP) domain, which recognized various pathogen-associated molecular patterns (PAMPs) and bacteria. This protein was involved in the activation of the complement system by binding CgMASPL-1 to promote cleavage of CgC3. The production of cytokines and antibacterial peptides, as well as the phagocytotic ratio of haemocytes in CgCLec-CCP-, CgMASPL-1-, or CgC3-knockdown oysters, decreased significantly after V. splendidus stimulation. Moreover, this activated CgC3 participated in perforation of bacterial envelopes and inhibiting survival of the infecting bacteria. These results collectively suggest that there existed an ancient lectin pathway in molluscs, which was activated by a complement cascade to regulate the production of immune effectors, phagocytosis, and bacterial lysis.

Healing through the lens of immunothrombosis: Biology-inspired, evolution-tailored, and human-engineered biomimetic therapies

Evolution, from invertebrates to mammals, has yielded and shaped immunoclotting as a defense and repair response against trauma and infection. This mosaic of immediate and local wound-sealing and pathogen-killing mechanisms results in survival, restoration of homeostasis, and tissue repair. In mammals, immunoclotting has been complemented with the neuroendocrine system, platelets, and contact system among other embellishments, adding layers of complexity through interconnecting blood-born proteolytic cascades, blood cells, and the neuroendocrine system. In doing so, immunothrombosis endows humans with survival advantages, but entails vulnerabilities in the current unprecedented and increasingly challenging environment. Immunothrombosis and tissue repair appear to go hand in hand with common mechanisms mediating both processes, a fact that is underlined by recent advances that are deciphering the mechanisms of the repair process and of the biochemical pathways that underpins coagulation, hemostasis and thrombosis. This review is intended to frame both the universal aspects of tissue repair and the therapeutic use of autologous fibrin matrix as a biology-as-a-drug approach in the context of the evolutionary changes in coagulation and hemostasis. In addition, we will try to shed some light on the molecular mechanisms underlying the use of the autologous fibrin matrix as a biology-inspired, evolution-tailored, and human-engineered biomimetic therapy.

Measuring Total Classical Pathway and Activities of Individual Components of the Mouse Complement Pathway

The complement system is a central component of innate immunity, responsible for recognition and killing of bacteria by tagging invaders through opsonisation, thereby promoting phagocytosis, and by direct lysis. Complement activity is routinely measured using functional assays that utilise erythrocytes as targets. The classical pathway haemolytic assay (CH50) with antibody sensitised sheep erythrocytes as target is used worldwide in clinical and research laboratories to measure complement activity in human and rodent sera. While there are no particular limitations in the human assay, measuring complement in mouse serum is more difficult and usually requires large amounts of serum, which is challenging to collect in experiments. In particular, it is challenging to measure the activities of individual mouse complement proteins. To overcome this hurdle, we have developed protocols that employ human sera depleted of single complement proteins as the source of the other complement proteins and test mouse serum to restore the relevant component. This simple haemolytic assay is a useful tool for confirming natural or engineered complement deficiencies and complement dysregulation in mouse models.

Hepatitis B Virus-Related Glomerulonephritis with Positive and Negative Serum HBsAg: Different Clinicopathologic Characteristics of Two Clinical Subtypes

INTRODUCTION

The clinicopathologic characteristics of Hepatitis B virus-associated glomerulonephritis (HBV-GN) patients with different serum HBsAg are not well known. This study aims to investigate the characteristics and treatments between HBV-GN patients with positive and negative serum HBsAg.

METHODS

A retrospective review of patients with renal biopsies in Guangdong Provincial People's Hospital from 2005 to 2018 was performed. Clinicopathological data, treatments and remission of proteinuria were collected and compared between HBsAg+ and HBsAg- group.

RESULTS

A total of 101 HBV-GN were recruited. Serum HBsAg+ and HBsAg- patients accounted for 62.4% and 37.6%, respectively. HBsAg+ group had poor kidney and liver functions. Pathological data showed the percentage of membranous nephropathy in HBsAg- group is significantly higher than that of HBsAg+ group (60.3% HBsAg+ vs 89.5% HBsAg-, P<0.05). Chronic renal tubular/interstitial injury was more prevalent in HBsAg+ group (16.9% HBsAg+ vs 2.6% HBsAg-, P<0.05). The deposition sites of immune complexes were significant different between the two groups. In addition, more HBsAg+ patients were given anti-HBV and less were given corticosteroid or immunosuppressants for treatment than that of HBsAg- patients. Percentages of clinical remission were increasing in both HBsAg+ and HBsAg- patients from 1, 3, 6 months to 1 year (18.75%, 45.2%, 67.8%, 82.4% vs 24.4%, 41.2%, 62.8%, 59.3%). The differences of remission betwen two groups were not significant (P>0.05).

CONCLUSION

The clinicopathological characteristics and treatments of HBV-GN with serum HBsAg+ and HBsAg- were distinct, which indicated that the pathogenesis might be different and specific treatments were needed for HBV-GN patients with different serum HBsAg.

Toll-Like Receptors: General Molecular and Structural Biology

Background/Aim

Toll-like receptors (TLRs) are pivotal biomolecules in the immune system. Today, we are all aware of the importance of TLRs in bridging innate and adaptive immune system to each other. The TLRs are activated through binding to damage/danger-associated molecular patterns (DAMPs), microbial/microbe-associated molecular patterns (MAMPs), pathogen-associated molecular patterns (PAMPs), and xenobiotic-associated molecular patterns (XAMPs). The immunogenetic molecules of TLRs have their own functions, structures, coreceptors, and ligands which make them unique. These properties of TLRs give us an opportunity to find out how we can employ this knowledge for ligand-drug discovery strategies to control TLRs functions and contribution, signaling pathways, and indirect activities. Hence, the authors of this paper have a deep observation on the molecular and structural biology of human TLRs (hTLRs).

Methods and Materials

To prepare this paper and fulfill our goals, different search engines (e.g., GOOGLE SCHOLAR), Databases (e.g., MEDLINE), and websites (e.g., SCOPUS) were recruited to search and find effective papers and investigations. To reach this purpose, we tried with papers published in the English language with no limitation in time. The iCite bibliometrics was exploited to check the quality of the collected publications.

Results

Each TLR molecule has its own molecular and structural biology, coreceptor(s), and abilities which make them unique or a complementary portion of the others. These immunogenetic molecules have remarkable roles and are much more important in different sections of immune and nonimmune systems rather than that we understand to date.

Conclusion

TLRs are suitable targets for ligand-drug discovery strategies to establish new therapeutics in the fields of infectious and autoimmune diseases, cancers, and other inflammatory diseases and disorders.

A Fc engineering approach to define functional humoral correlates of immunity against Ebola virus

Protective Ebola virus (EBOV) antibodies have neutralizing activity and induction of antibody constant domain (Fc)-mediated innate immune effector functions. Efforts to enhance Fc effector functionality often focus on maximizing antibody-dependent cellular cytotoxicity, yet distinct combinations of functions could be critical for antibody-mediated protection. As neutralizing antibodies have been cloned from EBOV disease survivors, we sought to identify survivor Fc effector profiles to help guide Fc optimization strategies. Survivors developed a range of functional antibody responses, and we therefore applied a rapid, high-throughput Fc engineering platform to define the most protective profiles. We generated a library of Fc variants with identical antigen-binding fragments (Fabs) from an EBOV neutralizing antibody. Fc variants with antibody-mediated complement deposition and moderate natural killer (NK) cell activity demonstrated complete protective activity in a stringent in vivo mouse model. Our findings highlight the importance of specific effector functions in antibody-mediated protection, and the experimental platform presents a generalizable resource for identifying correlates of immunity to guide therapeutic antibody design.

Tracing and exploring the evolutionary origin and systematic function of fish complement C9

Complement C9, as a member of terminal complement component (TCC) protein, plays important roles in innate immunity. However, some complement components appear to show difference and evolutionary complexity between higher and lower vertebrates. Hence, it is essential to carry on a study of evolutionary origin and systematic function of C9 in fish and non-fish vertebrates. This study aims to explore the complement gene evolution and potential function in fish based on molecular and structural biology. Herein, we found complete divergence of C9 throughout the gene evolution. The optimal codons of C9 sequences tended to be closer to the genomes of lower vertebrates compared to higher vertebrates. Further, conserved amino acids in the C9 TMH1 region were identified, implying their potential functional association with MAC growth and pore formation. Transposons and simple repeats, as gene elements, exhibited a differential distribution in the genomic regions in different animal groups but were sparsely scattered around the sixth exon (TMH1 region). Notably, this demonstrated the regulatory complexity of the C9 gene in higher vertebrates. The negative selection pressures on fish and non-fish groups improved both the sequence conservation and similarity. Through gene/protein regulatory network and pathway analyses, the systematic function of C9 protein was showcased; thus, we could reveal the divergence of the systematic function of C9 across species from different evolutionary positions. In addition, more complicated functions of C9 in higher vertebrates could established by the altered spatial conformation of the protein. Collectively, the present study illustrates the C9 gene evolutionary process and the difference in its systematic function across multiple species. Such advances provide new insights for understanding the evolutionary and potential functions of complement C9.

Drosophila as a Model for Infectious Diseases

The fruit fly, Drosophila melanogaster, has been used to understand fundamental principles of genetics and biology for over a century. Drosophila is now also considered an essential tool to study mechanisms underlying numerous human genetic diseases. In this review, we will discuss how flies can be used to deepen our knowledge of infectious disease mechanisms in vivo. Flies make effective and applicable models for studying host-pathogen interactions thanks to their highly conserved innate immune systems and cellular processes commonly hijacked by pathogens. Drosophila researchers also possess the most powerful, rapid, and versatile tools for genetic manipulation in multicellular organisms. This allows for robust experiments in which specific pathogenic proteins can be expressed either one at a time or in conjunction with each other to dissect the molecular functions of each virulent factor in a cell-type-specific manner. Well documented phenotypes allow large genetic and pharmacological screens to be performed with relative ease using huge collections of mutant and transgenic strains that are publicly available. These factors combine to make Drosophila a powerful tool for dissecting out host-pathogen interactions as well as a tool to better understand how we can treat infectious diseases that pose risks to public health, including COVID-19, caused by SARS-CoV-2.

Investigating an increase in Florida manatee mortalities using a proteomic approach

Two large-scale Florida manatee (Trichechus manatus latirostris) mortality episodes were reported on separate coasts of Florida in 2013. The east coast mortality episode was associated with an unknown etiology in the Indian River Lagoon (IRL). The west coast mortality episode was attributed to a persistent Karenia brevis algal bloom or 'red tide' centered in Southwest Florida. Manatees from the IRL also had signs of cold stress. To investigate these two mortality episodes, two proteomic experiments were performed, using two-dimensional difference in gel electrophoresis (2D-DIGE) and isobaric tags for relative and absolute quantification (iTRAQ) LC-MS/MS. Manatees from the IRL displayed increased levels of several proteins in their serum samples compared to controls, including kininogen-1 isoform 1, alpha-1-microglobulin/bikunen precursor, histidine-rich glycoprotein, properdin, and complement C4-A isoform 1. In the red tide group, the following proteins were increased: ceruloplasmin, pyruvate kinase isozymes M1/M2 isoform 3, angiotensinogen, complement C4-A isoform 1, and complement C3. These proteins are associated with acute-phase response, amyloid formation and accumulation, copper and iron homeostasis, the complement cascade pathway, and other important cellular functions. The increased level of complement C4 protein observed in the red tide group was confirmed through the use of Western Blot.

Quantitative multiplex profiling of the complement system to diagnose complement-mediated diseases

Objectives

Complement deficiencies are difficult to diagnose because of the variability of symptoms and the complexity of the diagnostic process. Here, we applied a novel ‘complementomics’ approach to study the impact of various complement deficiencies on circulating complement levels.

Methods

Using a quantitative multiplex mass spectrometry assay, we analysed 44 peptides to profile 34 complement proteins simultaneously in 40 healthy controls and 83 individuals with a diagnosed deficiency or a potential pathogenic variant in 14 different complement proteins.

Results

Apart from confirming near or total absence of the respective protein in plasma of complement‐deficient patients, this mass spectrometry‐based profiling method led to the identification of additional deficiencies. In many cases, partial depletion of the pathway up‐ and/or downstream of the absent protein was measured. This was especially found in patients deficient for complement inhibitors, such as angioedema patients with a C1‐inhibitor deficiency. The added value of complementomics was shown in three patients with poorly defined complement deficiencies.

Conclusion

Our study shows the potential clinical utility of profiling circulating complement proteins as a comprehensive read‐out of various complement deficiencies. Particularly, our approach provides insight into the intricate interplay between complement proteins due to functional coupling, which contributes to the better understanding of the various disease phenotypes and improvement of care for patients with complement‐mediated diseases.

The immune system of jawless vertebrates: insights into the prototype of the adaptive immune system

Jawless vertebrates diverged from an ancestor of jawed vertebrates approximately 550 million years ago. They mount adaptive immune responses to repetitive antigenic challenges, despite lacking major histocompatibility complex molecules, immunoglobulins, T cell receptors, and recombination-activating genes. Instead of B cell and T cell receptors, agnathan lymphocytes express unique antigen receptors named variable lymphocyte receptors (VLRs), which generate diversity through a gene conversion-like mechanism. Although gnathostome antigen receptors and VLRs are structurally unrelated, jawed and jawless vertebrates share essential features of lymphocyte-based adaptive immunity, including the expression of a single type of receptor on each lymphocyte, clonal expansion of antigen-stimulated lymphocytes, and the dichotomy of cellular and humoral immunity, indicating that the backbone of the adaptive immune system was established in a common ancestor of all vertebrates. Furthermore, recent evidence indicates that, unlike previously thought, agnathans have a unique classical pathway of complement activation where VLRB molecules act as antibodies instead of immunoglobulins. It seems likely that the last common ancestor of all vertebrates had an adaptive immune system resembling that of jawless vertebrates, suggesting that, as opposed to jawed vertebrates, agnathans have retained the prototype of vertebrate adaptive immunity.

Bioinformatics-based identification of miRNA-, lncRNA-, and mRNA-associated ceRNA networks and potential biomarkers for preeclampsia

This study aimed to identify significantly altered long non-coding RNAs (lncRNAs), microRNAs (miRNAs), mRNAs, pathways in preeclampsia (PE), and to investigate their targeted relationships and biological functions.GSE96985 from Gene Expression Omnibus database was extracted, involving 3 PE and 4 normal tissues. After the differential expression analysis of miRNAs, lncRNAs, and mRNAs using the limma package, protein-protein interaction (PPI) network and module analyses were performed for differentially expressed mRNAs (dif-mRNAs). Combined with the miRanda and miRWalk tools, a regulatory relationship between dif-miRNAs and dif-mRNAs/lncRNAs (dif-mRNAs/dif-lncRNAs) was predicted. Finally, mRNA-miRNA-lncRNA regulatory network construction was performed using Cytoscape software.A total of 511 dif-mRNAs were screened in PE. The top 5 nodes in the PPI networks included up-regulated complement component 3 (C3), C-X-C motif chemokine ligand 8 (CXCL8), and fibronectin 1 (FN1). Three significant network modules were identified for dif-mRNAs. C3 and CXCL8 were identified in module A, and FN1 was identified in module C. A disintegrin and metalloproteinase with thrombospondin motifs 6 (ADAMTS6) was down-regulated by the miR-210-3p. Therefore, lnc-CTD-2383M3.1 functions as a competing endogenous RNA in ADAMTS6 expression regulation by competitively binding to miR-210-3p during the regulation process of PE.C3, CXCL8, FN1, and ADAMTS6 might be involved in the development of PE. The lnc-CTD-2383M3.1-miR-210-3p-ADAMTS6 axis might be a potential regulatory mechanism in PE.

Fish complement C8 evolution, functional network analyses, and the theoretical interaction between C8 alpha chain and CD59

Complement C8, as a main component of the membrane attack complex, has only been identified in vertebrates. C8 comprises three subunits encoded by individual genes: C8a (alpha chain), C8b (beta chain), and C8g (gamma chain). However, in fish, there have been limited studies on the evolutionary history and systematic function of C8. In the present study, phylogenetic analysis indicated the complete divergence of C8 genes in different fish species. Codon usage bias analysis revealed the evolutionary complexity of C8 genes. Selective pressure analysis found that C8 genes have been affected by negative selection during evolution. Sequence alignment identified the sites that are under selective pressure. The systematic functions of C8 were revealed by gene co-expression and protein-protein interaction (PPI) network analyses. Notably, gene ontology enrichment analysis suggested that C8 proteins in zebrafish function mainly in the neuroendocrine system. Protein structural comparisons showed that putative functional residues and domains were conserved between the C8 subunits of human and grass carp. A preliminary study on the theoretical interaction between C8a and CD59 was performed according to the simulated protein stereo structure. The first functionally-related site was absent in the simulated conformation of the grass carp (Ctenopharyngodon idella) C8a-CD59 protein complex. We speculated that Tyr63 is involved in the functional loss of CD59 binding. The docking of CD59 to four potential sites (Met390, Ser391, Leu392, and Val405) in grass carp C8a was analyzed. The results of the present study provide a deeper understanding of the evolution and function of fish complement C8.

Complement System: a Neglected Pathway in Immunotherapy

Approved for the treatment of autoimmune diseases, hematological malignancies, and solid cancers, several monoclonal antibodies (mAb) make use of complement in their mechanism of action. Such an assessment is based on comprehensive investigations that used mouse models, in vitro studies, and analyses from patients at initiation (basal level to highlight deficiencies) and after treatment initiation (mAb impact on complement), which have further provided key insights into the importance of the complement activation and/or complement deficiencies in mAb activity. Accordingly, new approaches can now be developed with the final objective of increasing the clinical efficacy of mAb. These improvements include (i) the concurrent administration of fresh frozen plasma during mAb therapy; (ii) mAb modifications such as immunoglobulin G subclass switching, Fc mutation, or IgG hexamerization to improve the fixation and activation of C1q; (iii) optimization of the target recognition to induce a higher complement-dependent cytotoxicity (CDC) and/or complement-dependant cellular cytotoxicity (CDCC); and (iv) the control of soluble and cellular complement inhibitors.

Cloning, expression profile of the complement component C9 gene and influence of the recombinant C9 protein on peripheral mononuclear leukocytes transcriptome in half-smooth tongue sole (Cynoglossus semilaevis)

The ninth complement component (C9) is a terminal complement component (TCC) that is involved in creating the membrane attack complex (MAC) on the target cell surface. In this study, the CsC9 (C9 of Cynoglossus semilaevis) cDNA sequence was cloned and characterized. The full-length CsC9 cDNA measured 2,150 bp, containing an open reading frame (ORF) of 1,803 bp, a 5'-untranslated region (UTR) of 24 bp and a 3'-UTR of 323 bp. A domain search revealed that the CsC9 protein contains five domains, including two TSP1s, an LDLRA, an EGF, and a MACPF. Quantitative real-time PCR analysis showed that CsC9 at the mRNA level was expressed in all the tested tissues, with the highest expression being observed in the liver. CsC9 expression is significantly upregulated in the tested tissues after challenge with Vibrio anguillarum. To further characterize the role of CsC9, peripheral blood mononuclear cells of C. semilaevis were used for transcriptome analysis after incubation with recombinant CsC9 (rCsC9) protein. A total of 3,775 significant differentially expressed genes (DEGs) were identified between the control and the rCsC9-treated group, including 2,063 upregulated genes and 1,712 downregulated genes. KEGG analyses revealed that the DEGs were enriched in cell adhesion molecules, cytokine-cytokine receptor interactions, T cell receptor signaling pathways, B cell receptor signaling pathways and Toll-like receptor signaling pathways. The results of this study indicate that in addition to participating in MAC formation, CsC9 might play multiple roles in the innate and adaptive immunity of C. semilaevis.

Genomic basis of environmental adaptation in the leathery sea squirt (Styela clava)

Tunicates occupy the evolutionary position at the boundary of invertebrates and vertebrates. It exhibits adaptation to broad environmental conditions and is distributed globally. Despite hundreds of years of embryogenesis studies, the genetic basis of the invasive habits of ascidians remains largely unknown. The leathery sea squirt, Styela clava, is an important invasive species. We used the chromosomal-level genome and transcriptome of S. clava to explore its genomic- and molecular-network-based mechanisms of adaptation to environments. Compared with Ciona intestinalis type A (C. robusta), the size of the S. clava genome was expanded by 2-fold, although the gene number was comparable. An increase in transposon number and variation in dominant types were identified as potential expansion mechanisms. In the S. clava genome, the number of genes encoding the heat-shock protein 70 family and members of the complement system was expanded significantly, and cold-shock protein genes were transferred horizontally into the S. clava genome from bacteria. The expanded gene families potentially play roles in the adaptation of S. clava to its environments. The loss of key genes in the galactan synthesis pathway might explain the distinct tunic structure and hardness compared with the ascidian Ciona species. We demonstrated further that the integrated thyroid hormone pathway participated in the regulation of larval metamorphosis that provides S. clava with two opportunities for adapting to their environment. Thus, our report of the chromosomal-level leathery sea squirt genome provides a comprehensive genomic basis for the understanding of environmental adaptation in tunicates.

The complement system in COVID-19: friend and foe?

Coronavirus disease 2019 (COVID-19), the disease caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has resulted in a global pandemic and a disruptive health crisis. COVID-19-related morbidity and mortality have been attributed to an exaggerated immune response. The role of complement activation and its contribution to illness severity is being increasingly recognized. Here, we summarize current knowledge about the interaction of coronaviruses with the complement system. We posit that (a) coronaviruses activate multiple complement pathways; (b) severe COVID-19 clinical features often resemble complementopathies; (c) the combined effects of complement activation, dysregulated neutrophilia, endothelial injury, and hypercoagulability appear to be intertwined to drive the severe features of COVID-19; (d) a subset of patients with COVID-19 may have a genetic predisposition associated with complement dysregulation; and (e) these observations create a basis for clinical trials of complement inhibitors in life-threatening illness.