Ficolins: complement-activating lectins involved in innate immunity

O26 Polysaccharides as Key Players in Enteropathogenic E. coli Immune Evasion and Vaccine Development

Enteropathogenic Escherichia coli (EPEC) produce a capsule of polysaccharides identical to those composing the O-antigen polysaccharide of its LPS (lipopolysaccharide) molecules. In light of this, the impact of O26 polysaccharides on the immune evasion mechanisms of capsulated O26 EPEC compared to non-capsulated enterohemorrhagic Escherichia coli (EHEC) was investigated. Our findings reveal that there was no significant difference between the levels in EPEC and EHEC of rhamnose (2.8:2.5), a molecule considered to be a PAMP (Pathogen Associated Molecular Patterns). However, the levels of glucose (10:1.69), heptose (3.6:0.89) and N-acetylglucosamine (4.5:2.10), were significantly higher in EPEC than EHEC, respectively. It was also observed that the presence of a capsule in EPEC inhibited the deposition of C3b on the bacterial surface and protected the pathogen against lysis by the complement system. In addition, the presence of a capsule also protected EPEC against phagocytosis by macrophages. However, the immune evasion provided by the capsule was overcome in the presence of anti-O26 polysaccharide antibodies, and additionally, these antibodies were able to inhibit O26 EPEC adhesion to human epithelial cells. Finally, the results indicate that O26 polysaccharides can generate an effective humoral immune response, making them promising antigens for the development of a vaccine against capsulated O26 E. coli.

Increased expression of ficolin-1 is associated with airway obstruction in asthma

BACKGROUND

The activated complement cascade is involved in asthmatic airway inflammation. Ficolins are essential for innate immunity and can activate the complement lectin pathway. Despite this, the significance of ficolins in asthma has yet to be determined. This study aimed to explore the presence of ficolins in individuals with asthma and to determine the relationship between ficolins and clinical characteristics.

METHODS

For the study, 68 asthmatic patients and 30 healthy control subjects were recruited. Enzyme-linked immunosorbent assay was used to determine plasma ficolin-1, ficolin-2, and ficolin-3 concentrations both before and after inhaled corticosteroid (ICS) therapy. Further, the associations of plasma ficolin-1 level with pulmonary function and asthma control questionnaire (ACQ) score were examined in the asthma patients.

RESULTS

Patients with asthma exhibited significantly elevated plasma ficolin-1 levels (median, 493.9 ng/mL; IQR, 330.2-717.8 ng/mL) in comparison to healthy controls (median, 330.6 ng/mL; IQR, 233.8-371.1 ng/mL). After ICS treatment, plasma ficolin-1 (median, 518.1 ng/mL; IQR, 330.2-727.0 ng/mL) in asthmatic patients was significantly reduced (median, 374.7 ng/mL; IQR, 254.8-562.5 ng/mL). Additionally, ficolin-1 expressions in plasma were significantly correlated with pulmonary function parameters and ACQ score in asthmatic patients. Asthma patients with higher plasma ficolin-1 levels demonstrated poorer lung function than those with lower plasma ficolin-1 levels.

CONCLUSIONS

The results revealed that asthmatic patients had higher plasma ficolin-1 concentrations, which decreased after ICS treatment and were linked to their lung function, implying a potential involvement of ficolin-1 in asthma pathogenesis.

Effect of Polymorphisms in the FCN1, FCN2, and FCN3 Genes on the Susceptibility to Develop Rheumatoid Arthritis: A Systematic Review

Genetic association studies in rheumatoid arthritis conducted in various populations have yielded heterogeneous results. The present systematic review was conducted to synthesize the results of the studies in order to establish the impact of polymorphisms in the ficolin-coding genes FCN1, FCN2, and FCN3 on the susceptibility to develop rheumatoid arthritis. A systematic literature review was performed using the following keywords "gene (FCN1/FCN2/FCN3)", "Polymorphism/Genetic Variant", and "rheumatoid arthritis" in different databases until January 2022. Authors assessed articles by title/abstract and then assessed by full text for data extraction. The risk of bias was assessed using the Newcastle-Ottawa scale. Data synthesis was performed qualitatively and quantitatively. A total of 1519 articles were eligible for inclusion in this review, 3 were identified as relevant for the quantitative synthesis with 670 patients and 1019 controls. For the FCN1 gene, an association was found in the dominant and recessive genetic models of the variants rs2989727 (genotype TT = OR: 0.577, 95% CI: 0.430-0.769) and rs1071583 (genotype GG = OR: 1.537, 95% CI: 1.153-2.049, p = 0.0032) with the development of rheumatoid arthritis as a protective or susceptibility factor. FCN2 and FCN3 genes did not show association with disease development. The FCN1 gene variants rs2989727 and rs1071583 are associated with the risk of developing rheumatoid arthritis in populations from Brazil and Belgium, but not in FCN2 and FCN3 gene variants.

A pattern recognition receptor ficolin from Portunus trituberculatus (Ptficolin) regulating immune defense and hemolymph coagulation

Ficolins, belonging to the fibrinogen-related protein superfamily, are important pattern recognition receptors in innate immunity. Here, a ficolin gene Ptficolin was characterized from the swimming crab Portunus trituberculatus. The completed cDNA sequence of Ptficolin encoded a signal peptide, a coiled-coil region and a fibrinogen-like domain but without the typical collagen region of vertebrate ficolins. Ptficolin showed higher expression in stomach and hepatopancreas, and presented a time-dependent response after pathogen challenge and injury stimulation. The recombinant Ptficolin (rPtficolin) could bind to various PAMPs and microorganisms, and agglutinate microorganisms and rabbit erythrocytes in a Ca²⁺-dependent manner, with strong binding ability to N-acetyl sugars. Meanwhile, rPtficolin promoted the hemocyte phagocytosis and clearance activity of Vibrio, while Ptficolin knockdown impaired the bacterial phagocytosis and clearance ability, suggesting the opsonin activity of Ptficolin. Knockdown of Ptficolin could downregulate the transcription of most complement-like genes and AMPs, but enhance the expression of most proPO system-related genes and key genes of Toll, IMD and JNK pathways. Moreover, knockdown of Ptficolin led to the increased hemolymph clotting time and the decreased expression of clotting-related genes. Our results indicate that Ptficolin could recognize and eliminate invading pathogens, and might be a prominent component in hemolymph coagulation of crab.

Targeting thromboinflammation in COVID-19 - A narrative review of the potential of C1 inhibitor to prevent disease progression

Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 is associated with a clinical spectrum ranging from asymptomatic carriers to critically ill patients with complications including thromboembolic events, myocardial injury, multisystemic inflammatory syndromes and death. Since the beginning of the pandemic several therapeutic options emerged, with a multitude of randomized trials, changing the medical landscape of COVID-19. The effect of various monoclonal antibodies, antiviral, anti-inflammatory and anticoagulation drugs have been studied, and to some extent, implemented into clinical practice. In addition, a multitude of trials improved the understanding of the disease and emerging evidence points towards a significant role of the complement system, kallikrein-kinin, and contact activation system as drivers of disease in severe COVID-19. Despite their involvement in COVID-19, treatments targeting these plasmatic cascades have neither been systematically studied nor introduced into clinical practice, and randomized studies with regards to these treatments are scarce. Given the multiple-action, multiple-target nature of C1 inhibitor (C1-INH), the natural inhibitor of these cascades, this drug may be an interesting candidate to prevent disease progression and combat thromboinflammation in COVID-19. This narrative review will discuss the current evidence with regards to the involvement of these plasmatic cascades as well as endothelial cells in COVID-19. Furthermore, we summarize the evidence of C1-INH in COVID-19 and potential benefits and pitfalls of C1-INH treatment in COVID-19.

First Insights into the Repertoire of Secretory Lectins in Rotifers

Due to their high biodiversity and adaptation to a mutable and challenging environment, aquatic lophotrochozoan animals are regarded as a virtually unlimited source of bioactive molecules. Among these, lectins, i.e., proteins with remarkable carbohydrate-recognition properties involved in immunity, reproduction, self/nonself recognition and several other biological processes, are particularly attractive targets for biotechnological research. To date, lectin research in the Lophotrochozoa has been restricted to the most widespread phyla, which are the usual targets of comparative immunology studies, such as Mollusca and Annelida. Here we provide the first overview of the repertoire of the secretory lectin-like molecules encoded by the genomes of six target rotifer species: Brachionus calyciflorus, Brachionus plicatilis, Proales similis (class Monogononta), Adineta ricciae, Didymodactylos carnosus and Rotaria sordida (class Bdelloidea). Overall, while rotifer secretory lectins display a high molecular diversity and belong to nine different structural classes, their total number is significantly lower than for other groups of lophotrochozoans, with no evidence of lineage-specific expansion events. Considering the high evolutionary divergence between rotifers and the other major sister phyla, their widespread distribution in aquatic environments and the ease of their collection and rearing in laboratory conditions, these organisms may represent interesting targets for glycobiological studies, which may allow the identification of novel carbohydrate-binding proteins with peculiar biological properties.

Selective covalent capture of collagen triple helices with a minimal protecting group strategy

A minimal protecting group strategy is developed to allow selective covalent capture of collagen-like triple helices. This allows stabilization of this critical fold while preserving charge–pair interactions critical for biological applications.

Two fibrinogen-related proteins (FREPs) in the razor clam (Sinonovacula constricta) with a broad recognition spectrum and bacteria agglutination activity

Fibrinogen-related proteins (FREPs) that contain only the fibrinogen-related domain are likely involved in pathogen recognition. In this study, we identified two FREPs from the razor clam (Sinonovacula constricta), called ScFREP-1 and ScFREP-2, and investigated their roles in the immune response. Both ScFREP-1 and ScFREP-2 contained a fibrinogen-related domain at the C-terminal. ScFREP-1 and ScFREP-2 mRNAs were detected in all adult clam tissues tested, with the highest expression levels in the gill and mantle, respectively. Their expression levels were significantly upregulated after microbe infection. Recombinant ScFREPs could bind Gram-positive and Gram-negative bacteria as well as some pathogen-associated molecular patterns (PAMPs), and they could agglutinate those bacteria. These results showed that ScFREPs functioned as potential pattern recognition receptors to mediate immune response by recognizing PAMPs and agglutinating invasive microbes.

Innate immune responses against viral pathogens in Macrobrachium

Some members of genus Macrobrachium are important economically prawns and valuable objects for studying the innate immune defense mechanism of crustaceans. Studies have focused on immune responses against bacterial and fungal infections and have expanded to include antiviral immunity over the past two decades. Similar to all living organisms, prawns are exposed to viruses, including white spot syndrome virus, Macrobrachium rosenbergii nodavirus, and Decapod iridescent virus 1 and develop effective defense mechanisms. Here, we review current understanding of the antiviral host defense in two species of Macrobrachium. The main antiviral defense of Macrobrachium is the activation of intracellular signaling cascades, leading to the activation of cellular responses (apoptosis) and humoral responses (immune-related signaling pathways, antimicrobial and antiviral peptides, lectins, and prophenoloxidase-activating system).

Tick Immune System: What Is Known, the Interconnections, the Gaps, and the Challenges

Ticks are ectoparasitic arthropods that necessarily feed on the blood of their vertebrate hosts. The success of blood acquisition depends on the pharmacological properties of tick saliva, which is injected into the host during tick feeding. Saliva is also used as a vehicle by several types of pathogens to be transmitted to the host, making ticks versatile vectors of several diseases for humans and other animals. When a tick feeds on an infected host, the pathogen reaches the gut of the tick and must migrate to its salivary glands via hemolymph to be successfully transmitted to a subsequent host during the next stage of feeding. In addition, some pathogens can colonize the ovaries of the tick and be transovarially transmitted to progeny. The tick immune system, as well as the immune system of other invertebrates, is more rudimentary than the immune system of vertebrates, presenting only innate immune responses. Although simpler, the large number of tick species evidences the efficiency of their immune system. The factors of their immune system act in each tick organ that interacts with pathogens; therefore, these factors are potential targets for the development of new strategies for the control of ticks and tick-borne diseases. The objective of this review is to present the prevailing knowledge on the tick immune system and to discuss the challenges of studying tick immunity, especially regarding the gaps and interconnections. To this end, we use a comparative approach of the tick immune system with the immune system of other invertebrates, focusing on various components of humoral and cellular immunity, such as signaling pathways, antimicrobial peptides, redox metabolism, complement-like molecules and regulated cell death. In addition, the role of tick microbiota in vector competence is also discussed.

Human Lectins, Their Carbohydrate Affinities and Where to Find Them

Lectins are a class of proteins responsible for several biological roles such as cell-cell interactions, signaling pathways, and several innate immune responses against pathogens. Since lectins are able to bind to carbohydrates, they can be a viable target for targeted drug delivery systems. In fact, several lectins were approved by Food and Drug Administration for that purpose. Information about specific carbohydrate recognition by lectin receptors was gathered herein, plus the specific organs where those lectins can be found within the human body.

Sweet turning bitter: Carbohydrate sensing of complement in host defence and disease

The complement system plays a major role in threat recognition and in orchestrating responses to microbial intruders and accumulating debris. This immune surveillance is largely driven by lectins that sense carbohydrate signatures on foreign, diseased and healthy host cells and act as complement activators, regulators or receptors to shape appropriate immune responses. While carbohydrate sensing protects our bodies, misguided or impaired recognition can contribute to disease. Moreover, pathogenic microbes have evolved to evade complement by mimicking host signatures. While complement is recognized as a disease factor, we only slowly start to appreciate the role of carbohydrate interactions in the underlying processes. A better understanding of complement's sweet side will contribute to a better description of disease mechanisms and enhanced diagnostic and therapeutic options. This review introduces the key components in complement-mediated carbohydrate sensing, discusses their role in health and disease, and touches on the potential effects of carbohydrate-related disease intervention. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

A fibrinogen-related protein (Mnfico3) acts as a novel pattern recognition receptor in Macrobrachium nipponense

Fibrinogen-related proteins (FREPs) are widely found in both vertebrates as well as invertebrates, and they play a crucial role in host immunity. In this study, we isolated a novel ficolin gene (Mnfico3) from the oriental river prawn Macrobrachium nipponense. The complete cDNA sequence of Mnfico3 was 1133 bp long, containing an open reading frame of 765 bp coding for Mnfico3, a protein consisting of 254 amino acids. The Mnfico3 protein contained a putative N-terminal signal peptide and a fibrinogen-related protein domain present at the C-terminal. Phylogenetic analysis indicated that Mnfico3 had a closer evolutionary relationship with vertebrate ficolins than with its invertebrate homologues. Tissue distribution analysis indicated that Mnfico3 was predominantly expressed in muscle, in which its transcription was increased following bacterial challenge by Aeromonas veronii. Function analysis using recombinant protein revealed that rMnFico3 had broad-spectrum binding capacity to a variety of microorganisms and pathogen-associated molecular pattern (PAMP) ligands. Furthermore, rMnFico3 exhibited Ca2+-dependent agglutinating activity against microbes in vitro, and ability to attach to the hemocyte surface which promoted phagocytosis and subsequent clearance of invasive bacteria in vivo. Silencing rMnFico3 in prawn through RNAi did not alter the expression of antimicrobial peptide genes (ALF and Crustin). These results manifested that MnFico3 functioned as a potential pattern recognition receptor (PPR) to mediate cellular immune response by recognizing PAMPs, agglutinating invasive microbes, and promoting phagocytosis of hemocytes.

Molecular characterization and expression analysis of fibrinogen related protein (FREP) genes of Manila clam (Ruditapes philippinarum) after lipopolysaccharides challenge

Ruditapes philippinarum has high economic value and is distributed all over the world. Fibrinogen associated protein (FREP) is a type of pattern recognition receptor, participates in the innate immune response to eliminate pathogens after the invasion of pathogenic microorganisms. In this study, three FREP genes (FREP-1, FREP-2, and FREP-3) were identified and characterized from R. philippinarum. The protein sequence of FREPs were highly conserved with those homologous in vertebrates, and FBG domain possessed significantly high structural conservation in polypeptide binding site and Ca²⁺ binding site. The tissues expression analysis of FREPs in three shell color strains and two population of R. philippinarum were examined, with the highest expression level in gill and hepatopancreas. Besides, FREP genes were demonstrated to be induced by lipopolysaccharides injection, the significantly changes were observed after LPS injected. Our results suggest the involvement of FREPs in response to LPS injection, and it might exert a significant function on the innate immune defense of the Manila clam.

Toxoplasma gondii Recruits Factor H and C4b-Binding Protein to Mediate Resistance to Serum Killing and Promote Parasite Persistence in vivo

Regulating complement is an important step in the establishment of infection by microbial pathogens. Toxoplasma gondii actively resists complement-mediated killing in non-immune human serum (NHS) by inactivating C3b, however the precise molecular basis is unknown. Here, a flow cytometry-based C3b binding assay demonstrated that Type II strains had significantly higher levels of surface-bound C3b than Type I strains. However, both strains efficiently inactivated C3b and were equally resistant to serum killing, suggesting that resistance is not strain-dependent. Toxoplasma activated both the lectin (LP) and alternative (AP) pathways, and the deposition of C3b was both strain and lectin-dependent. A flow cytometry-based lectin binding assay identified strain-specific differences in the level and heterogeneity of surface glycans detected. Specifically, increased lectin-binding by Type II strains correlated with higher levels of the LP recognition receptor mannose binding lectin (MBL). Western blot analyses demonstrated that Toxoplasma recruits both classical pathway (CP) and LP regulator C4b-binding proteins (C4BP) and AP regulator Factor H (FH) to the parasite surface to inactivate bound C3b-iC3b and C3dg and limit formation of the C5b-9 attack complex. Blocking FH and C4BP contributed to increased C5b-9 formation in vitro. However, parasite susceptibility in vitro was only impacted when FH was blocked, indicating that down regulation of the alternative pathway by FH may be more critical for parasite resistance. Infection of C3 deficient mice led to uncontrolled parasite growth, acute mortality, and reduced antibody production, indicating that both the presence of C3, and the ability of the parasite to inactivate C3, was protective. Taken together, our results establish that Toxoplasma regulation of the complement system renders mice resistant to acute infection by limiting parasite proliferation in vivo, but susceptible to chronic infection, with all mice developing transmissible cysts to maintain its life cycle.

Evaluation of Ficolin-3 as a Potential Prognostic Serum Biomarker in Chinese Patients with Esophageal Cancer

Aims: Ficolin-3 is a circulating pattern recognition molecule of the lectin pathway, which participates in the host immune responses to cancer. Our study aimed to evaluate the prognostic efficacy of ficolin-3 in patients with esophageal cancer (EC). Methods: A total of 233 patients with EC were recruited for this study during a period from March 2013 to March 2016. Clinical information and pretherapeutic tumor specimens from all of the patients were analyzed. Serum ficolin-3 levels were determined by enzyme-linked immunosorbent assay. Patients were then assigned into quartiles according to their serum ficolin-3 levels. The Cox proportional hazards model was utilized to explore the correlation between ficolin-3 levels with overall survival (OS) and disease-specific survival (DSS). Results: The serum ficolin-3 level in the esophageal squamous cell carcinoma (ESCC) group was significantly higher than in the esophageal adenocarcinoma (EAC) group (19.59 ± 4.35 ng/mL vs. 18.39 ± 5.42 ng/mL, p < 0.01). There were great differences in prevalence of ESCC, tumor length, involvement of adventitia, and lymph node status among patients in different ficolin-3 groups (all p < 0.01). Both univariate analyses and further multivariate analyses revealed the close association between ficolin-3 levels and EAC (For OS and DSS, all p < 0.05). Out of 233 patients, survival information was available for 220, including 100 (45.45%) females and 120 (54.54%) males. When dividing the ficolin-3 levels into quartiles, patients with higher serum ficolin-3 levels showed a trend toward longer OS and DSS no matter whether they were diagnosed as ESCC or EAC (HR 0.21-0.55, all p < 0.05). Conclusions: Serum ficolin-3 levels were identified as an independent prognostic biomarker for DSS and OS in Chinese patients with EC, especially EAC.

The Effect of High-Intensity Interval Training on Physical Parameters, Metabolomic Indexes and Serum Ficolin-3 Levels in Patients with Prediabetes and Type 2 Diabetes

BACKGROUND

Exercise benefits people with abnormal glucose metabolism, and serum ficolin-3 levels have been reported to be associated with diabetes. However, no relevant study has discussed the relationship between high-intensity interval training (HIIT) and ficolin-3 in a Chinese population.

OBJECTIVE

To compare the effect of HIIT and moderate-intensity continuous training (MICT) on blood pressure, glucose control, the lipid profile and the serum ficolin-3 level in patients with prediabetes and type 2 diabetes (T2D).

METHODS

We recruited 145 patients with prediabetes and 196 T2D patients from March to June 2018. All participants were randomly grouped into HIIT and MICT groups. HIIT consisted of progressing to twelve 1-min bouts at 90% maximal aerobic capacity (1 min recovery), and MICT consisted of progressing to 20 min at 65% maximal aerobic capacity. ˙VO₂peak, body composition, blood pressure, glucose, the lipid profile and the serum ficolin-3 level were measured before and after three weeks of training.

RESULTS

After 3 weeks of training, participants in both the HIIT and MICT groups had significantly lower SBP, BMI, waist circumference, % body fat, and serum levels of FPG, TC, TGs, UA and ficolin-3, as well as increased vital capacity and VOmax. Additionally, the patients in the HIIT group still had significantly lower levels of 2hPG and LDL-C, regardless of prediabetes or diabetes status. After comparing the differences in the variation in parameters between the HIIT and MICT groups, we found that HIIT could help patients with prediabetes or diabetes acquire better effects of treatment in regard to anthropometry, blood pressure, glucose control, UA and ficolin-3 levels than MICT. Finally, the patients in the HIIT group had a lower rate of loss to follow-up and a higher rate of session attendance.

CONCLUSIONS

Both HIIT and MICT were beneficial exercise strategies for health in patients with prediabetes or T2D. However, HIIT is a more time-efficient strategy and could lower the serum level of ficolin-3 in patients after 3 weeks of training.

Overview of the role of kinetoplastid surface carbohydrates in infection and host cell invasion: prospects for therapeutic intervention

Kinetoplastid parasites are responsible for serious diseases in humans and livestock such as Chagas disease and sleeping sickness (caused by Trypanosoma cruzi and Trypanosoma brucei, respectively), and the different forms of cutaneous, mucocutaneous and visceral leishmaniasis (produced by Leishmania spp). The limited number of antiparasitic drugs available together with the emergence of resistance underscores the need for new therapeutic agents with novel mechanisms of action. The use of agents binding to surface glycans has been recently suggested as a new approach to antitrypanosomal design and a series of peptidic and non-peptidic carbohydrate-binding agents have been identified as antiparasitics showing efficacy in animal models of sleeping sickness. Here we provide an overview of the nature of surface glycans in three kinetoplastid parasites, T. cruzi, T. brucei and Leishmania. Their role in virulence and host cell invasion is highlighted with the aim of identifying specific glycan-lectin interactions and carbohydrate functions that may be the target of novel carbohydrate-binding agents with therapeutic applications.

Decreased Ficolin-3-mediated Complement Lectin Pathway Activation and Alternative Pathway Amplification During Bacterial Infections in Patients With Type 2 Diabetes Mellitus

Bacterial infections are frequent and severe in patients with diabetes mellitus. Whether diabetes per se induces functional alterations in the complement system hampering activation during infection is unknown. We investigated key elements of the complement system during bacterial infections in patients with type 2 diabetes mellitus (T2DM) and compared them to non-diabetic (ND) individuals. Using a prospective design, we included 197 T2DM, and 196 ND subjects, all with clinical diagnosis of acute community-acquired bacterial infections. Functional activities of the ficolin-3-mediated lectin (F3-LP), mannose binding lectin-mediated lectin- (MBL-LP), classical (CP), and alternative pathways (AP), as well as concentrations of complement activation products C4d and sC5b-9 were determined. Functional in vitro activities of F3-LP and AP were significantly higher in T2DM than in ND subjects, (median 64% vs. 45%, p = 0.0354 and 75 vs. 28%, p = 0.0013, respectively), indicating a decreased in vivo activation and lack of consumption of F3-LP and AP in T2DM patients, whereas no difference in functional capacities of CP and MBL-LP were observed between T2DM and ND subjects. Diminished F3-LP and AP activation was most pronounced in diabetic patients with urinary tract infections with positive microbiological culture results for Escherichia coli bacteria. In the T2DM group 3-months mortality significantly associated with diminished F3-LP and AP, but not with CP activation. Concentrations of C4d and sC5b-9 were significantly lower in the T2DM than in ND patients. In conclusion, we found impaired F3-LP activation and lack of AP amplification during bacterial infections in patients with type 2 diabetes, compared to non-diabetic subjects, suggesting a diminished complement mediated protection to bacterial infections in T2DM.

Influenza virus N-linked glycosylation and innate immunity

Influenza viruses cause seasonal epidemics and sporadic pandemics in humans. The virus’s ability to change its antigenic nature through mutation and recombination, and the difficulty in developing highly effective universal vaccines against it, make it a serious global public health challenge. Influenza virus’s surface glycoproteins, hemagglutinin and neuraminidase, are all modified by the host cell’s N-linked glycosylation pathways. Host innate immune responses are the first line of defense against infection, and glycosylation of these major antigens plays an important role in the generation of host innate responses toward the virus. Here, we review the principal findings in the analytical techniques used to study influenza N-linked glycosylation, the evolutionary dynamics of N-linked glycosylation in seasonal versus pandemic and zoonotic strains, its role in host innate immune responses, and the prospects for lectin-based therapies. As the efficiency of innate immune responses is a critical determinant of disease severity and adaptive immunity, the study of influenza glycobiology is of clinical as well as research interest.

Deep sequencing analysis of toad Rhinella schneideri skin glands and partial biochemical characterization of its cutaneous secretion

Background

Animal poisons and venoms are sources of biomolecules naturally selected. Rhinella schneideri toads are widespread in the whole Brazilian territory and they have poison glands and mucous gland. Recently, protein from toads’ secretion has gaining attention. Frog skin is widely known to present great number of host defense peptides and we hypothesize toads present them as well. In this study, we used a RNA-seq analysis from R. schneideri skin and biochemical tests with the gland secretion to unravel its protein molecules.

Methods

Total RNA from the toad skin was extracted using TRizol reagent, sequenced in duplicate using Illumina Hiseq2500 in paired end analysis. The raw reads were trimmed and de novo assembled using Trinity. The resulting sequences were submitted to functional annotation against non-redundant NCBI database and Database of Anuran Defense Peptide. Furthermore, we performed caseinolytic activity test to assess the presence of serine and metalloproteases in skin secretion and it was fractionated by fast liquid protein chromatography using a reverse-phase column. The fractions were partially sequenced by Edman’s degradation.

Results

We were able to identify several classes of antimicrobial peptides, such as buforins, peroniins and brevinins, as well as PLA₂, lectins and galectins, combining protein sequencing and RNA-seq analysis for the first time. In addition, we could isolate a PLA₂ from the skin secretion and infer the presence of serine proteases in cutaneous secretion.

Conclusions

We identified novel toxins and proteins from R. schneideri mucous glands. Besides, this is a pioneer study that presented the in depth characterization of protein molecules richness from this toad secretion. The results obtained herein showed evidence of novel AMP and enzymes that need to be further explored.

Electronic supplementary material

The online version of this article (10.1186/s40409-018-0173-8) contains supplementary material, which is available to authorized users.

A bite so sweet: the glycobiology interface of tick-host-pathogen interactions

Vector-borne diseases constitute 17% of all infectious diseases in the world; among the blood-feeding arthropods, ticks transmit the highest number of pathogens. Understanding the interactions between the tick vector, the mammalian host and the pathogens circulating between them is the basis for the successful development of vaccines against ticks or the tick-transmitted pathogens as well as for the development of specific treatments against tick-borne infections. A lot of effort has been put into transcriptomic and proteomic analyses; however, the protein-carbohydrate interactions and the overall glycobiology of ticks and tick-borne pathogens has not been given the importance or priority deserved. Novel (bio)analytical techniques and their availability have immensely increased the possibilities in glycobiology research and thus novel information in the glycobiology of ticks and tick-borne pathogens is being generated at a faster pace each year. This review brings a comprehensive summary of the knowledge on both the glycosylated proteins and the glycan-binding proteins of the ticks as well as the tick-transmitted pathogens, with emphasis on the interactions allowing the infection of both the ticks and the hosts by various bacteria and tick-borne encephalitis virus.

Identification of genetic variation in equine collagenous lectins using targeted resequencing

Collagenous lectins are a family of soluble pattern recognition receptors that play an important role in innate immune resistance to infectious disease. Through recognition of carbohydrate motifs on the surface of pathogens, some collagenous lectins can activate the lectin pathway of complement, providing an effective means of host defense. Genetic polymorphisms in collagenous lectins have been shown in several species to predispose animals to a variety of infectious diseases. Infectious diseases are an important cause of morbidity in horses, however little is known regarding the role of equine collagenous lectins. Using a high-throughput, targeted re-sequencing approach, the relationship between genetic variation in equine collagenous lectin genes and susceptibility to disease was investigated. DNA was isolated from tissues obtained from horses submitted for post-mortem examination. Animals were divided into two populations, those with infectious or autoinflammatory diseases (n = 37) and those without (n = 52), and then subdivided by dominant pathological process for a total of 21 pools, each containing 4-5 horses. DNA was extracted from each horse and pooled in equimolar amounts, and the exons, introns, upstream (approximately 50 kb) and downstream (approximately 3 kb) regulatory regions for the 11 equine collagenous lectin genes and related MASP genes were targeted for re-sequencing. A custom target capture kit was used to prepare a sequencing library, which was sequenced on an Illumina MiSeq. After implementing quality control filters, 4559 variants were identified. Of these, 92 were present in the coding regions (43 missense, 1 nonsense, and 48 synonymous), 1414 in introns, 3029 in the upstream region, and 240 in the downstream region. In silico analysis of the missense short nucleotide variants identified 12 mutations with potential to disrupt collagenous lectin protein structure or function, 280 mutations located within predicted transcription factor binding sites, and 95 mutations located within predicted microRNA binding elements. Analysis of allelic association identified 113 mutations that segregated between the infectious/autoinflammatory and non-infectious populations. The variants discovered in this experiment represent potential genetic contributors to disease susceptibility of horses, and will serve as candidates for further population-level genotyping. This study contributes to the growing body of evidence that pooled, high-throughput sequencing is a viable strategy for cost-effective variant discovery.

Genetic and molecular basis of the immune system in the brachiopod Lingula anatina

The extension of comparative immunology to non-model systems, such as mollusks and annelids, has revealed an unexpected diversity in the complement of immune receptors and effectors among evolutionary lineages. However, several lophotrochozoan phyla remain unexplored mainly due to the lack of genomic resources. The increasing accessibility of high-throughput sequencing technologies offers unique opportunities for extending genome-wide studies to non-model systems. As a result, the genome-based study of the immune system in brachiopods allows a better understanding of the alternative survival strategies developed by these immunologically neglected phyla. Here we present a detailed overview of the molecular components of the immune system identified in the genome of the brachiopod Lingula anatina. Our findings reveal conserved intracellular signaling pathways as well as unique strategies for pathogen detection and killing in brachiopods.

Fundamental aspects of arm repair phase in two echinoderm models

Regeneration is a post-embryonic developmental process that ensures complete morphological and functional restoration of lost body parts. The repair phase is a key step for the effectiveness of the subsequent regenerative process: in vertebrates, efficient re-epithelialisation, rapid inflammatory/immune response and post-injury tissue remodelling are fundamental aspects for the success of this phase, their impairment leading to an inhibition or total prevention of regeneration. Among deuterostomes, echinoderms display a unique combination of striking regenerative abilities and diversity of useful experimental models, although still largely unexplored. Therefore, the brittle star Amphiura filiformis and the starfish Echinaster sepositus were here used to comparatively investigate the main repair phase events after injury as well as the presence and expression of immune system and extracellular matrix (i.e. collagen) molecules using both microscopy and molecular tools. Our results showed that emergency reaction and re-epithelialisation are similar in both echinoderm models, being faster and more effective than in mammals. Moreover, in comparison to the latter, both echinoderms showed delayed and less abundant collagen deposition at the wound site (absence of fibrosis). The gene expression patterns of molecules related to the immune response, such as Ese-fib-like (starfishes) and Afi-ficolin (brittle stars), were described for the first time during echinoderm regeneration providing promising starting points to investigate the immune system role in these regeneration models. Overall, the similarities in repair events and timing within the echinoderms and the differences with what has been reported in mammals suggest that effective repair processes in echinoderms play an important role for their subsequent ability to regenerate. Targeted molecular and functional analyses will shed light on the evolution of these abilities in the deuterostomian lineage.

Host Soluble Mediators: Defying the Immunological Inertness of Aspergillus fumigatus Conidia

Aspergillus fumigatus produce airborne spores (conidia), which are inhaled in abundant quantity. In an immunocompromised population, the host immune system fails to clear the inhaled conidia, which then germinate and invade, leading to pulmonary aspergillosis. In an immunocompetent population, the inhaled conidia are efficiently cleared by the host immune system. Soluble mediators of the innate immunity, that involve the complement system, acute-phase proteins, antimicrobial peptides and cytokines, are often considered to play a complementary role in the defense of the fungal pathogen. In fact, the soluble mediators are essential in achieving an efficient clearance of the dormant conidia, which is the morphotype of the fungus upon inhalation by the host. Importantly, harnessing the host soluble mediators challenges the immunological inertness of the dormant conidia due to the presence of the rodlet and melanin layers. In the review, we summarized the major soluble mediators in the lung that are involved in the recognition of the dormant conidia. This knowledge is essential in the complete understanding of the immune defense against A. fumigatus.

A critical review on serine protease: Key immune manipulator and pathology mediator

Proteolytic activity is fundamental to survival, so it is not surprising that all living organisms have proteases, especially seine protease. This enzyme in its numerous isoforms and homologues, constitutes the quintessential offence and defence factors, in the form of surface proteins, secreted molecules, gut digestive enzymes, venom in specialised glands or plant latex, among other manifestations. Occurring as trypsin, chymotrypsin, elastase, collagenase, thrombin, subtilisin etc., it mediates a diverse array of functions, including pathological roles as inflammatory, coagulatory to haemorrhagic. This review emphasizes that despite the superficial differences in mechanisms, most health issues, be they infectious, allergic, metabolic, or neural have a common conduit. This enzyme, in its various glycosylated forms leads to signal misinterpretations, wreaking havoc. However, organisms are endowed with serine protease inhibitors which might restrain this ubiquitous yet deleterious enzyme. Hence, serine proteases-driven pathogenesis and antagonising role of inhibitors is the focal point of this critical review.

Revisiting venom of the sea anemone Stichodactyla haddoni: Omics techniques reveal the complete toxin arsenal of a well-studied sea anemone genus

More than a century of research on sea anemone venoms has shown that they contain a diversity of biologically active proteins and peptides. However, recent omics studies have revealed that much of the venom proteome remains unexplored. We used, for the first time, a combination of proteomic and transcriptomic techniques to obtain a holistic overview of the venom arsenal of the well-studied sea anemone Stichodactyla haddoni. A purely search-based approach to identify putative toxins in a transcriptome from tentacles regenerating after venom extraction identified 508 unique toxin-like transcripts grouped into 63 families. However, proteomic analysis of venom revealed that 52 of these toxin families are likely false positives. In contrast, the combination of transcriptomic and proteomic data enabled positive identification of 23 families of putative toxins, 12 of which have no homology known proteins or peptides. Our data highlight the importance of using proteomics of milked venom to correctly identify venom proteins/peptides, both known and novel, while minimizing false positive identifications from non-toxin homologues identified in transcriptomes of venom-producing tissues. This work lays the foundation for uncovering the role of individual toxins in sea anemone venom and how they contribute to the envenomation of prey, predators, and competitors.

BIOLOGICAL SIGNIFICANCE

Proteomic analysis of milked venom combined with analysis of a tentacle transcriptome revealed the full extent of the venom arsenal of the sea anemone Stichodactyla haddoni. This combined approach led to the discovery of 12 entirely new families of disulfide-rich peptides and proteins in a genus of anemones that have been studied for over a century.

Innate immune recognition and inflammation in Neisseria meningitidis infection

Neisseria meningitidis (Nme) can cause meningitis and sepsis, diseases which are characterised by an overwhelming inflammatory response. Inflammation is triggered by host pattern recognition receptors (PRRs) which are activated by pathogen-associated molecular patterns (PAMPs). Nme contains multiple PAMPs including lipooligosaccharide, peptidoglycan, proteins and metabolites. Various classes of PRRs including Toll-like receptors, NOD-like receptors, C-type lectins, scavenger receptors, pentraxins and others are expressed by the host to respond to any given microbe. While Toll-like receptors and NOD-like receptors are pivotal in triggering inflammation, other PRRs act as modulators of inflammation or aid in functional antimicrobial responses such as phagocytosis or complement activation. This review aims to give an overview of the various Nme PAMPs reported to date, the PRRs they activate and their implications during the inflammatory response to infection.

Association of a new FCN3 haplotype with high ficolin-3 levels in leprosy

Leprosy is a chronic inflammatory disease caused by Mycobacterium leprae that mainly affects the skin and peripheral nervous system, leading to a high disability rate and social stigma. Previous studies have shown a contribution of genes encoding products of the lectin pathway of complement in the modulation of the susceptibility to leprosy; however, the ficolin-3/FCN3 gene impact on leprosy is currently unknown. The aim of the present study was to investigate if FCN3 polymorphisms (rs532781899: g.1637delC, rs28362807: g.3524_3532insTATTTGGCC and rs4494157: g.4473C>A) and ficolin-3 serum levels play a role in the susceptibility to leprosy. We genotyped up to 190 leprosy patients (being 114 (60%) lepromatous), and up to 245 controls with sequence-specific PCR. We also measured protein levels using ELISA in 61 leprosy and 73 controls. FCN3 polymorphisms were not associated with disease, but ficolin-3 levels were higher in patients with FCN3 *2B1 (CinsA) haplotype (p = 0.032). Median concentration of ficolin-3 was higher in leprosy per se (26034 ng/mL, p = 0.005) and lepromatous patients (28295 ng/mL, p = 0.016) than controls (18231 ng/mL). In addition, high ficolin-3 levels (>33362 ng/mL) were more common in leprosy per se (34.4%) and in lepromatous patients (35.5%) than controls (19.2%; p = 0.045 and p = 0.047, respectively). Our results lead us to suggest that polymorphisms in the FCN3 gene cooperate to increase ficolin-3 concentration and that it might contribute to leprosy susceptibility by favoring M. leprae infection.

Interplay between Myeloid Cells and Humoral Innate Immunity

The innate immune system represents the first line of defense against pathogens and comprises both a cellular and a humoral arm. Fluid-phase pattern recognition molecules (PRMs), which include collectins, ficolins, and pentraxins, are key components of the humoral arm of innate immunity and are expressed by a variety of cells, including myeloid, epithelial, and endothelial cells, mainly in response to infectious and inflammatory conditions. Soluble PRMs share basic multifunctional properties including activation and regulation of the complement cascade, opsonization of pathogens and apoptotic cells, regulation of leukocyte extravasation, and fine-tuning of inflammation. Therefore, soluble PRMs are part of the immune response and retain antibody-like effector functions. Here, we will review the expression and general function of soluble PRMs, focusing our attention on the long pentraxin PTX3.

C1q as an autocrine and paracrine regulator of cellular functions

Most of the complement proteins in circulation are, by and large, synthesized in the liver. However data accumulated over the past several decades provide incontrovertible evidence that some if not most of the individual complement proteins are also synthesized extrahepatically by activated as well as non-activated cells. The question that is finally being addressed by various investigators is: are the locally synthesized proteins solely responsible for the myriad of biological functions in situ without the contribution of systemic complement? The answer is probably "yes". Among the proteins that are synthesized locally, C1q takes center stage for several reasons. First, it is synthesized predominantly by potent antigen presenting cells such as monocytes, macrophages and dendritic cells (DCs), which by itself is a clue that it plays an important role in antigen presentation and/or DC maturation. Second, it is transiently anchored on the cell surface via a transmembrane domain located in its A chain before it is cleaved off and released into the pericellular milieu. The membrane-associated C1q in turn, is able to sense danger patterns via its versatile antigen-capturing globular head domains. More importantly, locally synthesized C1q has been shown to induce a plethora of biological functions through the induction of immunomodulatory molecules by an autocrine- or paracrine- mediated signaling in a manner that mimics those of TNFα. These include recognition of pathogen- and danger- associated molecular patterns, phagocytosis, angiogenesis, apoptosis and induction of cytokines or chemokines that are important in modulating the inflammatory response. The functional convergence between C1q and TNFα in turn is attributed to their shared genetic ancestry. In this paper, we will infer to the aforementioned "local-synthesis-for-local function" paradigm using as an example, the role played by locally synthesized C1q in autoimmunity in general and in systemic lupus erythematosus in particular.

The Lectin Complement Pathway in Patients with Necrotizing Soft Tissue Infection

BACKGROUND

Mannose-binding lectin (MBL) and ficolins are pattern recognition molecules (PRMs) that play an important role during infection through activation of the lectin complement pathway. We assessed whether plasma PRM levels were associated with mortality in patients with necrotizing soft tissue infection (NSTI).

METHODS

We conducted a prospective, observational study over 25 months involving 135 NSTI patients with a maximum follow-up of 2.7 years. Blood samples were taken upon admission. Non-infected patients served as controls.

RESULTS

PRM levels were significantly lower compared with controls. A baseline Ficolin-2 level below the median was associated with mortality at the end of follow-up (p = 0.007). No significant association was found for MBL, Ficolin-1 and Ficolin-3. A Ficolin-2 level below the median had a negative predictive value of 0.94 for 28-day mortality, and a level below the optimal cut-off was independently associated with 28-day mortality when adjusted for age, sex and chronicity [hazard ratio 6.27 (95% confidence interval 2.28-17.21), p < 0.0001], also when Simplified Acute Physiology Score II was included in the analysis [hazard ratio 3.16 (95% confidence interval 1.03-9.73), p = 0.045].

CONCLUSIONS

All PRMs were significantly lower in patients with NSTI than in controls. Only baseline Ficolin-2 was associated with short- and long-term mortality. A high baseline Ficolin-2 level indicated a 94% chance of surviving the first 28 days after admission.

Fluid phase recognition molecules in neutrophil-dependent immune responses

The innate immune system comprises both a cellular and a humoral arm. Neutrophils are key effector cells of the immune and inflammatory responses and have emerged as a major source of humoral pattern recognition molecules (PRMs). These molecules, which include collectins, ficolins, and pentraxins, are specialised in the discrimination of self versus non-self and modified-self and share basic multifunctional properties including recognition and opsonisation of pathogens and apoptotic cells, activation and regulation of the complement cascade and tuning of inflammation. Neutrophils act as a reservoir of ready-made soluble PRMs, such as the long pentraxin PTX3, the peptidoglycan recognition protein PGRP-S, properdin and M-ficolin, which are stored in neutrophil granules and are involved in neutrophil effector functions. In addition, other soluble PRMs, such as members of the collectin family, are not expressed in neutrophils but can modulate neutrophil-dependent immune responses. Therefore, soluble PRMs are an essential part of the innate immune response and retain antibody-like effector functions. Here, we will review the expression and general function of soluble PRMs, focusing our attention on molecules involved in neutrophil effector functions.

Temporal Gene Expression Analysis and RNA Silencing of Single and Multiple Members of Gene Family in the Lone Star Tick Amblyomma americanum

Saliva is an integral factor in the feeding success of veterinary and medically important ticks. Therefore, the characterization of the proteins present in tick saliva is an important area of tick research. Here, we confirmed previously generated sialotranscriptome data using quantitative real-time PCR. The information obtained in this in-depth study of gene expression was used to measure the effects of metalloprotease gene silencing on tick feeding. We analyzed the temporal expression of seven housekeeping genes and 44 differentially expressed salivary molecules selected from a previously published Amblyomma americanum sialotranscriptome. Separate reference genes were selected for the salivary glands and midgut from among the seven housekeeping genes, to normalize the transcriptional expression of differentially expressed genes. The salivary gland reference gene, ubiquitin, was used to normalize the expression of 44 salivary genes. Unsurprisingly, each gene family was expressed throughout the blood meal, but the expression of specific genes differed at each time point. To further clarify the complex nature of the many proteins found in the saliva, we disrupted the translation of several members of the metalloprotease family. Intriguingly, the nucleotide sequence similarity of the reprolysin metalloprotease gene family is so homologous that a single synthesized dsRNA sequence knocked down multiple members of the family. The use of multigene knockdown yielded a more significant picture of the role of metalloproteases in tick feeding success, and changes were observed in the female engorgement weight and larval hatching success. Interestingly, the depletion of metalloprotease transcripts also reduced the total number of bacteria present in the salivary glands. These data provide insight into the expression and functions of tick salivary proteins expressed while feeding on its host.

Development of porcine ficolin-alpha monoclonal and polyclonal antibodies for determining the binding capacity of multiple GlcNAc-binding proteins to bacterial danger components

Ficolins are a group of oligomeric defense proteins assembled from collagen-like stalks and fibrinogen-like domains that have common biochemical specificity for N-acetyl-d-glucose amine (GlcNAc) and can function as opsonins. In this report, GlcNAc-binding protein (GBP) purified from porcine nonimmune serum was biochemically characterized as ficolin-α. Ficolin-α was used as an immunogen to generate both rabbit polyclonal and murine monoclonal anti-ficolin-α antibodies, which are not yet commercially available. GBPs have been shown to be present in many animals, including humans; however, their functions are largely unknown. GBPs from chicken, dog, horse, bovine, and human sera were isolated using various chromatography methods. Interestingly, anti-ficolin-α antibody showed cross-reaction with those animal sera GBPs. Furthermore, anti-ficolin-α antibody was reactive with the GlcNAc eluate of Escherichia coli O26-bound and Salmonella-bound porcine serum proteins. Functionally, GBPs and bacteria-reactive pig serum proteins were able to bind with pathogen-associated molecular patterns such as lipopolysaccharides and lipoteichoic acids. Our studies demonstrate that ficolin-α specific antibody was reactive with GBPs from many species as well as bacteria-reactive serum proteins. These proteins may play important roles in innate immunity by sensing danger components that can lead to antibacterial activity.

Time-course analysis of C3a and C5a quantifies the coupling between the upper and terminal Complement pathways in vitro

An in vitro zymosan-activation of the Complement system, through the lectin and alternative pathways, was performed in pooled human serum over a 24h time-course. Activation was quantitatively monitored by measuring the concentration of the upper Complement pathway fragment, C3a and the terminal pathway fragment, C5a. Upper Complement showed a maximum activation of 39% and the time-to-maximum activation reduced 8-fold, as a highly non-linear function of the zymosan dose. The C3a:C5a molar ratio rose to a maximum of 1100:1, before terminal pathway activation was initiated; indicating a flux threshold. This threshold appears to be exceeded once more than 31% of C3 molecules are activated. Above this threshold, significant activation of terminal pathway was observed; reducing the molar ratio to 17:1. The C5a/C3a molar ratio was used to determine the terminal pathway activation relative to total Complement activation and ranged from 0.1-0.8%. This depicts upper Complement activation to be 49-fold larger than terminal activation, a figure consistent with the observed density of the membrane attack complex in the membrane of cells. Our results thus indicate that the relative activity of opsonisation is ~50-fold greater than membrane attack complex formation, in vitro, in the pooled serum phenotype. The results suggest a potential clinical application, where an in vitro analysis of a patient on admission, or prior to a surgical procedure, would indicate their upper Complement activation capacity, with activation of C3 measured thereafter, or post-operatively. A patient with an exhausted upper Complement capacity may be vulnerable to infections and complications, such as sepsis.

Association of Ficolin-2 Serum Levels and FCN2 Genetic Variants with Indian Visceral Leishmaniasis

BACKGROUND

Visceral leishmaniasis (VL), one of the neglected tropical diseases, is endemic in the Indian subcontinent. Ficolins are circulating serum proteins of the lectin complement system and involved in innate immunity.

METHODS

We have estimated ficolin-2 serum levels and analyzed the functional variants of the encoding gene FCN2 in 218 cases of VL and in 225 controls from an endemic region of India.

RESULTS

Elevated levels of serum ficolin-2 were observed in VL cases compared to the controls (adjusted P<0.0001). The genetic analysis revealed that the FCN2 structural variant +6359 C>T (p.T236M) was associated with VL (OR=2.2, 95% CI=1.23-7.25, P=0.008) and with high ficolin-2 serum levels. We also found that the FCN2*AAAC haplotype occurred more frequently among healthy controls when compared to cases (OR=0.59, 95%CI=0.37-0.94, P=0.023).

CONCLUSIONS

Our findings indicate that the FCN2 variant +6359C>T is associated with the occurrence of VL and that ficolin-2 serum levels are elevated in Leishmania infections.

Elevated plasma CL-K1 level is associated with a risk of developing disseminated intravascular coagulation (DIC)

Collectin kidney 1 (CL-K1) is a recently identified collectin that is synthesized in most organs and circulates in blood. CL-K1 is an innate immune molecule that may play a significant role in host defense. As some collectins also play a role in coagulation, we hypothesized that an effect of CL-K1 may be apparent in disseminated intravascular coagulation (DIC), a gross derangement of the coagulation system that occurs in the setting of profound activation of the innate immune system. DIC is a grave medical condition with a high incidence of multiple organ failure and high mortality and yet there are no reliable biomarkers or risk factors. In our present study, we measured plasma CL-K1 concentration in a total of 659 specimens, including 549 DIC patients, 82 non-DIC patients and 27 healthy volunteers. The median plasma CL-K1 levels in these cohorts were 424, 238 and 245 ng/ml, respectively, with no significant difference in the latter two groups. The incidence of elevated plasma CL-K1 was significantly higher in the DIC patients compared to the non-DIC patients, resulting in an odds ratio of 1.929 (confidence interval 1.041-3.866). Infection, renal diseases, respiratory diseases, and cardiac diseases were more frequently observed in the DIC group than in the non-DIC group. In the DIC group, vascular diseases were associated with elevated plasma CL-K1 levels while age and acute illness had little effect on plasma CL-K1 levels. Independent of DIC, elevated plasma CL-K1 levels were associated with respiratory disease and coagulation disorders. These results suggest that specific diseases may affect CL-K1 synthesis in an organ dependent manner and that elevated plasma CL-K1 levels are associated with the presence of DIC. Further investigations in cohorts of patients are warranted. We propose that elevated plasma CL-K1 may be a new useful risk factor and possibly biomarker for the prediction of developing DIC.

Targeting mechanisms at sites of complement activation for imaging and therapy

The complement system plays a key role in many acute injury states as well as chronic autoimmune and inflammatory diseases. Localized complement activation and alternative pathway-mediated amplification on diverse target surfaces promote local recruitment of pro-inflammatory cells and elaboration of other mediators. Despite a general understanding of the architecture of the system, though, many of the mechanisms that underlie site-specific complement activation and amplification in vivo are incompletely understood. In addition, there is no capability yet to measure the level of local tissue site-specific complement activation in patients without performing biopsies to detect products using immunohistochemical techniques. Herein is reviewed emerging evidence obtained through clinical research studies of human rheumatoid arthritis along with translational studies of its disease models which demonstrate that several parallel mechanisms are involved in site-specific amplification of activation of the complement system in vivo. Among these processes are de-regulation of the alternative pathway, effector pathway-catalyzed amplification of proximal complement activation, recognition of injury-associated ligands by components of the lectin pathway, and engagement of pathogenic natural antibodies that recognize a limited set of injury-associated neoepitopes. Studies suggest that each of these inter-related processes can play key roles in amplification of complement-dependent injury on self-tissues in vivo. These findings, in addition to development of an imaging strategy described herein designed to quantitatively measure local complement C3 fixation, have relevance to therapeutic and diagnostic strategies targeting the complement system.

RIG-I in RNA virus recognition

Antiviral immunity is initiated upon host recognition of viral products via non-self molecular patterns known as pathogen-associated molecular patterns (PAMPs). Such recognition initiates signaling cascades that induce intracellular innate immune defenses and an inflammatory response that facilitates development of the acquired immune response. The retinoic acid-inducible gene I (RIG-I) and the RIG-I-like receptor (RLR) protein family are key cytoplasmic pathogen recognition receptors that are implicated in the recognition of viruses across genera and virus families, including functioning as major sensors of RNA viruses, and promoting recognition of some DNA viruses. RIG-I, the charter member of the RLR family, is activated upon binding to PAMP RNA. Activated RIG-I signals by interacting with the adapter protein MAVS leading to a signaling cascade that activates the transcription factors IRF3 and NF-κB. These actions induce the expression of antiviral gene products and the production of type I and III interferons that lead to an antiviral state in the infected cell and surrounding tissue. RIG-I signaling is essential for the control of infection by many RNA viruses. Recently, RIG-I crosstalk with other pathogen recognition receptors and components of the inflammasome has been described. In this review, we discuss the current knowledge regarding the role of RIG-I in recognition of a variety of virus families and its role in programming the adaptive immune response through cross-talk with parallel arms of the innate immune system, including how RIG-I can be leveraged for antiviral therapy.

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RIG-I is a cytosolic pathogen recognition receptor.

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RIG-I binds to PAMP RNA.

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RIG-I initiates the immune response to RNA virus infection.

Low ficolin-2 levels in common variable immunodeficiency patients with bronchiectasis

Common variable immunodeficiency (CVID) encompasses a heterogeneous group of antibody deficiencies characterized by susceptibility to recurrent infections and sequelae, including bronchiectasis. We investigated the relevance of the lectin complement pathway in CVID patients by analysing ficolin-2 and ficolin-3 serum levels and genotyping single nucleotide polymorphisms (SNPs) in the FCN2 and FCN3 genes. Our results show that ficolin-2 levels in CVID patients are significantly lower (P < 0.0001) than in controls. The lowest ficolin-2 levels are found in CVID patients with bronchiectasis (P = 0.0004) and autoimmunity (P = 0.04). Although serum levels of ficolin-3 were similar in CVID patients and controls, CVID patients with bronchiectasis again showed lower levels when compared to controls (P = 0.0001). Analysis of single nucleotide polymorphisms in the FCN2 gene confirmed known influences on ficolin-2 serum levels, but did not support a genetic basis for the observed ficolin-2 deficiency in CVID. We found that CVID patients with bronchiectasis have very low levels of ficolin-2. The reason for the deficiency of ficolin-2 in CVID and any possible causal relationship is currently unknown. However, as bronchiectasis is a very important factor for morbidity and mortality in CVID, ficolin-2 could also serve as biomarker for monitoring disease complications such as bronchiectasis.

A novel IgM-H-ficolin complement pathway to attack allogenic cancer cells in vitro

The pentameric serum IgMs are critical to immune defense and surveillance through cytotoxicity against microbes and nascent cancer cells. Ficolins, a group of oligomeric lectins with an overall structure similar to C1q and mannose-binding lectin (MBL) participate in microbe infection and apoptotic cell clearance by activating the complement lectin pathway or a primitive opsonophagocytosis. It remains unknown whether serum IgMs interplay with ficolins in cancer immunosurveillance. Here we report a natural cancer killing of different types of cancer cells by sera from a healthy human population mediated by a novel IgM-H-ficolin complement activation pathway. We demonstrate for the first time that H-ficolin bound to a subset of IgMs in positive human sera and IgM-H-ficolin deposited on cancer cells to activate complement attack in cancer cells. Our data suggest that the IgM-H-ficolin -mediated complement activation pathway may be another defensive strategy for human cancer immunosurveillance.

Low invasiveness of pneumococcal serotype 11A is linked to ficolin-2 recognition of O-acetylated capsule epitopes and lectin complement pathway activation

BACKGROUND

The divergent epidemiological behavior of Streptococcus pneumoniae serotypes suggests that serotype-specific features such as capsule O-acetylation influence the propensity of a strain to cause invasive pneumococcal disease (IPD). We hypothesize that innate host factors mediate the observed negative association between IPD and the serotype 11A (ST11A) capsule O-acetyltransferase gene, wcjE.

METHODS

We evaluated the ability of ficolin-2, an initiator of the lectin complement pathway that was previously shown to bind ST11A pneumococci, to recognize and mediate complement-dependent opsonophagocytosis of different pneumococcal serotypes. We supplemented findings with an epidemiological meta-analysis comparing invasiveness of the 30 most prevalent pneumococcal serotypes.

RESULTS

Ficolin-2 bound ST11A capsule polysaccharide and other wcjE-containing pneumococcal serotypes, except ST9V and ST20B. Ficolin-2 did not bind wcjE-null serotypes, including the wcjE-null variant of ST11A, ST11E. We observed C1q-independent complement deposition and phagocytic killing of pneumococci expressing ST11A but not those expressing ST11E. Inhibition of ficolin-2 binding abrogated ST11A-associated complement deposition and phagocytosis. In children, invasiveness of ST11A was the lowest among serotypes tested in our meta-analysis, while ST9V was among the highest.

CONCLUSIONS

Ficolin-2 mediates serum protection by recognizing specific O-acetylated epitopes of pneumococcal capsule polysaccharides, exemplifying a novel host-microbe interaction that innately offers serotype-specific immunity to IPD.

Commercially available complement component-depleted sera are unexpectedly codepleted of ficolin-2

The ficolins are a family of innate pattern recognition molecules that are known to bind acetylated compounds and activate complement through the association of mannose binding lectin (MBL)/ficolin-associated serine proteases (MASPs). Their importance has more recently become appreciated, as they have been shown to play a role in a variety of disease processes from infection to autoimmunity. While studying ficolin-2-mediated complement deposition on Streptococcus pneumoniae, we found that sera depleted of C1q or other complement components were also codepleted of ficolin-2 but not ficolin-1, ficolin-3, or MBL. MBL present in C1q-depleted sera was able to mediate complement deposition on Saccharomyces cerevisiae, suggesting the presence of MASPs. We found that complement was activated on pneumococci in C1q-depleted serum only after opsonization with exogenous recombinant ficolin-2 (rFicolin-2). Also, no complement deposition was observed in C1q-depleted serum when pneumococci were opsonized with rFicolin-2 mutated at its lysine-57 residue, where MASPs are known to associate. Thus, these depleted sera are a unique tool to study ficolin-2-mediated complement pathways; however, one should be aware that ficolin-2 is absent from complement component-depleted sera.

Effects of caste on the expression of genes associated with septic injury and xenobiotic exposure in the Formosan subterranean termite

As social insects, termites live in densely populated colonies with specialized castes under conditions conducive to microbial growth and transmission. Furthermore, termites are exposed to xenobiotics in soil and their lignocellulose diet. Therefore, termites are valuable models for studying gene expression involved in response to septic injury, immunity and detoxification in relation to caste membership. In this study, workers and soldiers of the Formosan subterranean termite, Coptotermes formosanus, were challenged by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of phenobarbital. Constitutive and induced expression of six putative immune response genes (two encoding for lectin-like proteins, one for a ficolin-precursor, one for the Down syndrome cell adhesion molecule, one for a chitin binding protein, and one for the gram-negative binding protein 2) and four putative detoxification genes (two encoding for cytochrome P450s, one for glutathione S-transferase, and one for the multi antimicrobial extrusion protein), were measured via quantitative real time polymerase chain reaction and compared within and among 1) colonies, 2) treatment types and 3) castes via ANOVA. Eight genes were inducible by septic injury, feeding with phenobarbital or both. Colony origin had no effect on inducibility or differential gene expression. However, treatment type showed significant effects on the expression of the eight inducible genes. Caste effects on expression levels were significant in five of the eight inducible genes with constitutive and induced expression of most target genes being higher in workers than in soldiers.