Ficolins in complement activation

Ficolin-A induces macrophage polarization to a novel pro-inflammatory phenotype distinct from classical M1

BACKGROUND

Macrophages are key inflammatory immune cells that orchestrate the initiation and progression of autoimmune diseases. The characters of macrophage in diseases are determined by its phenotype in response to the local microenvironment. Ficolins have been confirmed as crucial contributors to autoimmune diseases, with Ficolin-2 being particularly elevated in patients with autoimmune diseases. However, whether Ficolin-A stimulates macrophage polarization is still poorly understood.

METHODS

We investigated the transcriptomic expression profile of murine bone marrow-derived macrophages (BMDMs) stimulated with Ficolin-A using RNA-sequencing. To further confirm a distinct phenotype activated by Ficolin-A, quantitative RT-PCR and Luminex assay were performed in this study. Additionally, we assessed the activation of underlying cell signaling pathways triggered by Ficolin-A. Finally, the impact of Ficolin-A on macrophages were investigated in vivo through building Collagen-induced arthritis (CIA) and Dextran Sulfate Sodium Salt (DSS)-induced colitis mouse models with Fcna-/- mice.

RESULTS

Ficolin-A activated macrophages into a pro-inflammatory phenotype distinct to LPS-, IFN-γ- and IFN-γ + LPS-induced phenotypes. The transcriptomic profile induced by Ficolin-A was primarily characterized by upregulation of interleukins, chemokines, iNOS, and Arginase 1, along with downregulation of CD86 and CD206, setting it apart from the M1 and M2 phenotypes. The activation effect of Ficolin-A on macrophages deteriorated the symptoms of CIA and DSS mouse models, and the deletion of Fcna significantly alleviated the severity of diseases in mice.

CONCLUSION

Our work used transcriptomic analysis by RNA-Seq to investigate the impact of Ficolin-A on macrophage polarization. Our findings demonstrate that Ficolin-A induces a novel pro-inflammatory phenotype distinct to the phenotypes activated by LPS, IFN-γ and IFN-γ + LPS on macrophages.

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.

Identification of FCN1 as a novel macrophage infiltration-associated biomarker for diagnosis of pediatric inflammatory bowel diseases

BACKGROUND

The incidence of pediatric inflammatory bowel disease (PIBD) has been steadily increasing globally. Delayed diagnosis of PIBD increases the risk of complications and contributes to growth retardation. To improve long-term outcomes, there is a pressing need to identify novel markers for early diagnosis of PIBD.

METHODS

The candidate biomarkers for PIBD were identified from the GSE117993 dataset by two machine learning algorithms, namely LASSO and mSVM-RFE, and externally validated in the GSE126124 dataset and our PIBD cohort. The role of ficolin-1 (FCN1) in PIBD and its association with macrophage infiltration was investigated using the CIBERSORT method and enrichment analysis of the single-cell dataset GSE121380, and further validated using immunoblotting, qRT-PCR, and immunostaining in colon biopsies from PIBD patients, a juvenile murine DSS-induced colitis model, and THP-1-derived macrophages.

RESULTS

FCN1 showed great diagnostic performance for PIBD in an independent clinical cohort with the AUC of 0.986. FCN1 expression was upregulated in both colorectal biopsies and blood samples from PIBD patients. Functionally, FCN1 was associated with immune-related processes in the colonic mucosa of PIBD patients, and correlated with increased proinflammatory M1 macrophage infiltration. Furthermore, single-cell transcriptome analysis and immunostaining revealed that FCN1 was almost exclusively expressed in macrophages infiltrating the colonic mucosa of PIBD patients, and these FCN1⁺ macrophages were related to hyper-inflammation. Notably, proinflammatory M1 macrophages derived from THP-1 expressed high levels of FCN1 and IL-1β, and FCN1 overexpression in THP-1-derived macrophages strongly promoted LPS-induced activation of the proinflammatory cytokine IL-1β via the NLRP3-caspase-1 axis.

CONCLUSIONS

FCN1 is a novel and promising diagnostic biomarker for PIBD. FCN1⁺ macrophages enriched in the colonic mucosa of PIBD exhibit proinflammatory phenotypes, and FCN1 promotes IL-1β maturation in macrophages via the NLRP3-caspase-1 axis.

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.

Calcium-dependent reversible coaggregation activity of C-reactive protein and M-ficolin

C-reactive protein (CRP) and M-ficolin are the pattern recognition proteins of the innate immune system. In this report, a mixture of CRP and M-ficolin reversibly co-aggregated in a calcium-dependent manner. This coaggregation was enhanced at low pH (6.5) or low salt (35 mM NaCl) concentrations. The co-aggregate was dissolved by adding EDTA and reformed by adding calcium. The M-ficolin fibrinogen-like domain (FD1), the ligand-binding domain of M-ficolin, also showed calcium-dependent coaggregation with CRP, indicating that reversible coaggregation is caused by CRP interacting with FD1. Interestingly, adding phosphocholine (PC), the ligand of CRP, to a CRP-FD1 mixture abolished the reversible coaggregation activity. PC also inhibited the interaction between CRP and FD1. These results indicate that CRP retains PC-binding activity in the coaggregation state and that FD1 binds specifically to the PC-binding site on CRP but does not fully occupy the five PC-binding sites on a CRP pentamer as judged by SDS-PAGE analysis of precipitates. Coaggregation analysis using FD1 mutants showed that FD1 also retains ligand-binding activity in the coaggregation state and that coaggregation requires the trimeric form of FD1. It was also found that modifications to the ligand-binding site of FD1 affect coaggregation efficiency. Although the biological functions of the coaggregation activity of CRP and M-ficolin remain unresolved, the co-aggregates may function as bacteria-trapping particles with affinities for ligands of CRP and M-ficolin. In addition, coaggregation may be involved in CRP deposition in the lesions of several arterial diseases, such as atherosclerosis.

How to get away with murder: The multiple strategies employed by pathogenic protozoa to avoid complement killing

Parasitic protozoa are eukaryotic unicellular organisms that depend on a variety of living organisms and can develop intra- and extracellularly inside their hosts. In humans, these parasites cause diseases with a significant impact on public health, such as malaria, toxoplasmosis, Chagas disease, leishmaniasis and amebiasis. The ability of a parasite in establishing a successful infection depends on a series of intricate evolutionarily selected adaptations, which include the development of molecular and cellular strategies to evade the host immune system effector mechanisms. The complement system is one of the main effector mechanisms and the first humoral shield of hosts innate immunity against pathogens. For unicellular pathogens, such as protozoa, bacteria and fungi, the activation of the complement system may culminate in the elimination of the invader mainly via 1- the formation of a pore that depolarizes the plasma membrane of the parasite, causing cell lysis; 2- opsonization and killing by phagocytes; 3- increasing vascular permeability while also recruiting neutrophils to the site of activation. Numerous strategies to avoid complement activation have been reported for parasitic protozoa, such as 1- sequestration of complement system regulatory proteins produced by the host, 2- expression of complement system regulatory proteins, 3- proteolytic cleavage of different complement effector molecules, 4- formation of a physical glycolipid barrier that prevents deposition of complement molecules on the plasma membrane, and 5- removal, by endocytosis, of complement molecules bound to plasma membrane. In this review, we revisit the different strategies of blocking various stages of complement activation described for the main species of parasitic protozoa, present the most recent discoveries in the field and discuss new perspectives on yet neglected strategies and possible new evasion mechanisms.

Gingival Transcriptome of Innate Antimicrobial Factors and the Oral Microbiome With Aging and Periodontitis

The epithelial barrier at mucosal sites comprises an important mechanical protective feature of innate immunity, and is intimately involved in communicating signals of infection/tissue damage to inflammatory and immune cells in these local environments. A wide array of antimicrobial factors (AMF) exist at mucosal sites and in secretions that contribute to this innate immunity. A non-human primate model of ligature-induced periodontitis was used to explore characteristics of the antimicrobial factor transcriptome (n = 114 genes) of gingival biopsies in health, initiation and progression of periodontal lesions, and in samples with clinical resolution. Age effects and relationship of AMF to the dominant members of the oral microbiome were also evaluated. AMF could be stratified into 4 groups with high (n = 22), intermediate (n = 29), low (n = 18) and very low (n = 45) expression in healthy adult tissues. A subset of AMF were altered in healthy young, adolescent and aged samples compared with adults (e.g., APP, CCL28, DEFB113, DEFB126, FLG2, PRH1) and were affected across multiple age groups. With disease, a greater number of the AMF genes were affected in the adult and aged samples with skewing toward decreased expression, for example WDC12, PGLYRP3, FLG2, DEFB128, and DEF4A/B, with multiple age groups. Few of the AMF genes showed a >2-fold increase with disease in any age group. Selected AMF exhibited significant positive correlations across the array of AMF that varied in health and disease. In contrast, a rather limited number of the AMF significantly correlated with members of the microbiome; most prominent in healthy samples. These correlated microbes were different in younger and older samples and differed in health, disease and resolution samples. The findings supported effects of age on the expression of AMF genes in healthy gingival tissues showing a relationship to members of the oral microbiome. Furthermore, a dynamic expression of AMF genes was related to the disease process and showed similarities across the age groups, except for low/very low expressed genes that were unaffected in young samples. Targeted assessment of AMF members from this large array may provide insight into differences in disease risk and biomolecules that provide some discernment of early transition to disease.

A fibrinogen-related protein mediates the recognition of various bacteria and haemocyte phagocytosis in oyster Crassostrea gigas

The family of fibrinogen-related proteins (FREPs) is a group of proteins with fibrinogen-like (FBG) domains, which play important roles as pattern recognition receptors (PRRs) in the innate immune responses. In the present study, a fibrinogen-like protein was identified from the oyster Crassostrea gigas (defined as CgFREP1). The open reading frame of CgFREP1 was of 966 bp that encoded a predicted polypeptide of 321 amino acids comprising a signal peptide and a fibrinogen-like domain. The mRNA expression of CgFREP1 was detected in all the examined tissues. The recombinant CgFREP1 (rCgFREP1) displayed binding activities to lipopolysaccharide (LPS), mannose (MAN), as well as Gram-positive bacteria (Micrococcus luteus and Staphylococcus aureus) and Gram-negative bacteria (Vibrio splendidus and Escherichia coli). The rCgFREP1 displayed the agglutinating activity towards M. luteus, V. splendidus and E. coli in the presence of Ca²⁺. rCgFREP1 was able to enhance the phagocytic activity of haemocytes towards V. splendidus, and exhibited binding activity to the CUB domain of CgMASPL-1. These results suggest that CgFREP1 not only serves as a PRR to recognize and agglutinate different bacteria but also mediates the haemocytes phagocytosis towards V. splendidus.

Complement Proteins as Soluble Pattern Recognition Receptors for Pathogenic Viruses

The complement system represents a crucial part of innate immunity. It contains a diverse range of soluble activators, membrane-bound receptors, and regulators. Its principal function is to eliminate pathogens via activation of three distinct pathways: classical, alternative, and lectin. In the case of viruses, the complement activation results in effector functions such as virion opsonisation by complement components, phagocytosis induction, virolysis by the membrane attack complex, and promotion of immune responses through anaphylatoxins and chemotactic factors. Recent studies have shown that the addition of individual complement components can neutralise viruses without requiring the activation of the complement cascade. While the complement-mediated effector functions can neutralise a diverse range of viruses, numerous viruses have evolved mechanisms to subvert complement recognition/activation by encoding several proteins that inhibit the complement system, contributing to viral survival and pathogenesis. This review focuses on these complement-dependent and -independent interactions of complement components (especially C1q, C4b-binding protein, properdin, factor H, Mannose-binding lectin, and Ficolins) with several viruses and their consequences.

The clinical value of ficolin-3 gene polymorphism in rheumatic heart disease. An Egyptian adolescents study

OBJECTIVE

Ficolin-3 is one of the innate immunity molecules that was thought to play a pivotal role in Streptococcus pyogenes autoimmunity and its complications; rheumatic fever (RF) and rheumatic heart disease (RHD). We aimed to disclose if there is an association between ficolin-3 (FCN3) gene polymorphisms (rs4494157 and rs10794501) and RF with or without RHD for the first time in Egyptian adolescents.

RESULTS

Serum ficolin-3 level was significantly elevated in patients suffering from RF with and without RHD in comparison with control. Regarding FCN3 gene (rs4494157) polymorphism, a significant correlation was found between the A allele and the susceptibility to RF with or without RHD (OR = 2.93, P = 0.0002 and OR = 2.23, P = 0.008 respectively). Besides, AA homozygous genotype showed a significant association with RHD risk (OR = 3.47, P = 0.026). Patients carrying the A allele (CA + AA) had significantly higher serum ficolin-3 than those carrying the CC genotype (P ˂ 0.0001). While the frequency of (rs10794501) polymorphism revealed no significant differences between the controls and RF patients with or without RHD (OR = 1.43, P = 0.261 and OR = 1.48, P = 0.208 respectively).

Emerging role of ficolins in autoimmune diseases

Ficolins are pattern-recognition molecules (PRMs) that could form complexes with mannose-binding lectin-associated serine proteases (MASPs) to trigger complement activation via the lectin pathway, thereby mediating a series of immune responses including opsonization, phagocytosis and cytokine production. In the past few decades, accumulating evidence have suggested that ficolins play a major role in the onset and development of several autoimmune diseases (ADs), including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc), Type 1 diabetes (T1D), inflammatory bowel disease (IBD), etc. In this review, we synthesized previous literatures and recent advances to elucidate the immunological regulations of ficolins and discuss the potential diagnostic ability of ficolins in ADs, as well as giving an insight into the future therapeutic options for ficolins in ADs.

Ficolin-3 in rheumatic fever and rheumatic heart disease

Rheumatic fever (RF) and chronic rheumatic heart disease (RHD) are complications of oropharyngeal infection caused by Streptococcus pyogenes. Despite the importance of the complement system against infections and autoimmunity diseases, studies on the role of the lectin pathway in RF and RHD are scarce. Thus, our aim was to evaluate the association of ficolin-3 serum levels, FCN3 polymorphisms and haplotypes with the susceptibility to RF and RHD. We investigated 179 patients with a history of RF (126 RHD and 53 RF only) and 170 healthy blood donors as control group. Ficolin-3 serum concentrations were measured using enzyme-linked immunosorbent assay (ELISA). Three FCN3 single nucleotide polymorphisms (SNPs rs532781899, rs28362807 and rs4494157) were genotyped through the sequence-specific PCR method. Lower ficolin-3 serum levels were observed in RF patients when compared to controls (12.81 μg/mL vs. 18.14 μg/mL respectively, p < 0.0001, OR 1.22 [1.12-1.34]), and in RHD in comparison to RF only (RFo) (12.72 μg/mL vs. 14.29 μg/mL respectively, p = 0.016, OR 1.38 [1.06-1.80]). Low ficolin-3 levels (<10.7 μg/mL) were more common in patients (39.5 %, 30/76) than controls (20.6 %, 13/63, p = 0.018, OR = 2.51 [1.14-5.31]), and in RHD (44.4 %, 28/63) than RFo (15.4 %, 2/13, p = 0.007, OR = 3.08 [1.43-6.79]). On the other hand, FCN3 polymorphism/haplotypes were not associated with ficolin-3 serum levels or the disease. Low ficolin-3 levels might be associated with RF, being a potential marker of disease progression.

Low Mannose Binding Lectin, but Not L-Ficolin, Is Associated With Spontaneous Clearance of Hepatitis C Virus After Infection

Some individuals can spontaneously clear the hepatitis C virus (HCV) after infection, whereas others develop a chronic infection. The exact mechanism of this phenomenon is unknown. We aimed to evaluate the association of plasma levels of MBL, L-ficolin, and cytokines with outcome of HCV infections in two groups of patients who cleared HCV spontaneously (CHS), and who developed chronic HCV infections (CHC). Altogether, 86 patients and 183 healthy controls were included. Of 86 patients, 36 had CHS and 50 had CHC. Concentrations of plasma MBL and L-ficolin were measured in patients and controls. Twenty plasma cytokines and adhesion molecules, including GM-CSF, ICAM-1, IFN-γ, IFN-α, IL-1α, IL-1β, IL-10, IL-12p70, IL-13, IL-17A, IL-4, IL-8, IP-10, MCP-1, IL-6, MIP-1α, MIP-1β, sE-Selectin, sP-Selectin, and TNF-α, were determined in all patients and randomly selected 45 controls. The level of MBL was significantly lower in subjects with CHS than in healthy controls (median: 293.10 vs. 482.64 ng/ml, p = 0.008), whereas the level of MBL was significantly higher in patients with CHC than in controls (median: 681.32 vs. 482.64 ng/ml, p = 0.001). No such differences in plasma L-ficolin were observed. Plasma levels of all cytokines and adhesion molecules, except ICAM-1, were significantly higher in patients than in controls. Moreover, patients with CHC had significantly higher levels of IFN-γ, IFN-α, IL-1α, IL-10, IL-13, IL-4, IL-6, and TNF-α than those with CHS. These findings implicate that lower levels of plasma MBL, together with lower levels of above mentioned cytokines may play a part in virus clearance of HCV infection.

CCN1 is an opsonin for bacterial clearance and a direct activator of Toll-like receptor signaling

Expression of the matricellular protein CCN1 (CYR61) is associated with inflammation and is required for successful wound repair. Here, we show that CCN1 binds bacterial pathogen-associated molecular patterns including peptidoglycans of Gram-positive bacteria and lipopolysaccharides of Gram-negative bacteria. CCN1 opsonizes methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa and accelerates their removal by phagocytosis and increased production of bactericidal reactive oxygen species in macrophages through the engagement of integrin α_vβ₃. Mice with myeloid-specific Ccn1 deletion and knock-in mice expressing CCN1 unable to bind α_vβ₃ are more susceptible to infection by S. aureus or P. aeruginosa, resulting in increased mortality and organ colonization. Furthermore, CCN1 binds directly to TLR2 and TLR4 to activate MyD88-dependent signaling, cytokine expression and neutrophil mobilization. CCN1 is therefore a pattern recognition receptor that opsonizes bacteria for clearance and functions as a damage-associated molecular pattern to activate inflammatory responses, activities that contribute to wound healing and tissue repair.

CCN1 is a matricellular protein with a variety of functions, including an effect on wound healing and an association with inflammation. Here, the authors identify a possible mechanism by showing that CCN1 mediates the clearance of bacterial infections in mice and activates TLR signalling.

The potential sensing molecules and signal cascades for protecting teleost fishes against lipopolysaccharide

Lipopolysaccharide (LPS) is a classical pathogen-associated molecular pattern that can trigger strong inflammatory response mainly by TLR4-mediated signaling pathway in mammals, but the molecular mechanism of anti-LPS immunity is unclear in teleost fishes. In this study, we analyzed the gene expression features based on transcriptome analysis in Schizothorax prenanti (S. prenanti), after stimulation with two sources of LPS from Aeromonas hydrophila and Escherichia coli (Ah. LPS and Ecoli. LPS). 921 different expression genes (DEGs) after Ah. LPS stimulation and 975 DEGs after Ecoli.LPS stimulation were acquired, but only 706 and 750 DEGs were successfully annotated into the databases, respectively. Both of two groups of DGEs were significantly enriched into immune-related pathways by KEGG enrichment analysis, such as "Toll-like receptor signaling pathway", "Cytokine-cytokine receptor interaction" and "JAK-STAT signaling pathway". The annotated DEGs from Ah. LPS and Ecoli. LPS stimulation shared 470 DEGs, including 88 immune-related DEGs (IRGs) identified mainly by KEGG enrichment to immune-related signaling pathways. Among the shared IRGs, four pattern-recognition genes (TLR5, TLR25, PTX3 and C1q) were induced with high expression foldchange, and IFN-γ and relative genes also showed higher expression levels than control. Meanwhile, inflammatory signals were highlighted by upregulating the expression of inflammatory cytokines (IL-1β, IL-10 and IL-8). Moreover, some non-shared IRGs (including TLR2 and TLR4) were identified, suggesting that different sources of LPS own different potentials for the induction of immune gene expression. In conclusion, TLR5, TLR25, PTX3 and C1q may function as the sensing molecules to catch the invasion signal of LPS. The anti-LPS immune response may be involved into TLR25/TLR5-mediated inflammatory signals that regulate subsequently the activation of PTX3/C1q-modulated complement pathway upon the induction of PTX3 expression, and the crosstalk between IFN-γ and TLR signaling pathways in teleost fishes. This study will contribute to further explore the molecular mechanism of LPS-induced immunity in teleost fishes.

Genetic Basis of Myocarditis: Myth or Reality?

The genetic basis of myocarditis remains an intriguing concept, at least as long as the definition of myocarditis constitutes the definitive presence of myocardial inflammation sufficient to cause the observed ventricular dysfunction in the setting of cardiotropic infections. Autoimmune or immune-mediated myocardial inflammation constitutes a complex area of clinical interest, wherein numerous and not yet fully understood role of hereditary auto-inflammatory diseases can result in inflammation of the pericardium and myocardium. Finally, myocardial involvement in hereditary immunodeficiency diseases, cellular and humoral, is a possible trigger for infections which may complicate the diseases themselves. Whether the role of constitutional genetics can make the patient susceptible to myocardial inflammation remains yet to be explored.

Pattern Recognition Molecules of the Lectin Pathway-Screening of Patients with Suspected Immunodeficiency

PURPOSE

To compare plasma concentrations of all lectin pathway (LP) pattern recognition molecules (PRMs) in patients referred for laboratory evaluation due to recurrent infections with healthy individuals.

METHODS

Patients were divided into categories according to referral: recurrent airway infections (RAI), recurrent abscesses, common variable immunodeficiency (CVID), lung transplantation candidates (LTX), and 'other causes'. LP PRMs (mannose-binding lectin (MBL), collectin liver 1 (CL-L1), H-ficolin, L-ficolin, M-ficolin) and C-reactive protein (CRP) were determined in 332 patients and 150 healthy blood donors using time-resolved immunofluorometric assays.

RESULTS

None of the LP PRMs was found in lower concentration in the patient categories; however, several PRMs were detected in higher concentrations. M-ficolin was found in higher concentrations in all patient categories. Patients suffering from RAI had higher concentrations of CL-L1 and H-ficolin. Patients suffering from abscesses exhibited higher concentrations of MBL and CL-L1, whereas LTX had higher concentrations of MBL. Patients with other causes of referral had higher concentrations of MBL and CL-L1. Prevalence of combined deficiencies of PRMs in patient categories and controls did not differ. CRP was used as a marker of ongoing inflammation and was significantly higher among all patient categories. Furthermore, CRP was found to correlate with both M-ficolin and L-ficolin.

CONCLUSION

The results suggest that neither single nor combined deficiencies of LP PRMs are more frequent among patients referred for an immunological evaluation than in healthy individuals. Future studies are needed and should focus on deficiencies of LP PRMs combined with deficiencies in other parts of the immune system.

Derivatives of the lectin complement pathway in Lophotrochozoa

A plethora of non-overlapping immune molecular mechanisms in metazoans is the most puzzling issue in comparative immunobiology. No valid evolutionary retrospective on these mechanisms has been developed. In this study, we aimed to reveal the origin and evolution of the immune complement-like system in Lophotrochozoa. For this, we analyzed publicly available transcriptomes of prebilaterian and lophotrochozoan species, mapping lineage-specific molecular events on the phylogenetic tree. We found that there were no orthologs of mannose-binding lectin (MBL) and ficolins (FCN) in Lophotrochozoa but C1q-like proteins (C1qL), bearing both a collagen domain and a globular C1q domain, were omnipresent in them. This suggests that among all complement-like activators the C1qL-specific domain architecture was an evolutionarily first. Two novel protostomian MASP-Related Molecules, MReM1 and MReM2, might hypothetically compensate for the loss of a prebilaterian MASP-orthologous gene and act in complex with C1qL and C1qDC as a "proto-activator" of an ancient "proto-complement". We proposed a new model of the complement evolution predicting that numerous lineage-specific complement-like systems should have evolved from a stem "antique" molecular complex. First evolved in the common ancestor of coelomic animals, the "antique" humoral complex consisted of a TEP molecule, the common ancestor of TEP-associated proteases (C2/Bf/Сf/Lf), the common ancestor of MASP-like proteases (MASP/C1r/C1s, MReM1/MReM2) and multimeric recognition proteins (C1q-, MBL- and FCN-homologs). Further evolutionary specialization and expansion of the complex was independent and lineage-specific, examples being the mammalian complement system and the Apogastropoda complement-like complex. The latter includes an impressive array of multimeric recognition proteins, the variable immunoglobulin and lectin domain containing molecules (VIgL), homologous to C1q, MBL, FCN and other lectins. Four novel polymorphic subfamilies of VIgLs were found to be expressed in Apogastropoda: C1q-related proteins (QREP), zona pellucida-related proteins (ZREP), Scavenger Receptor Cys-Rich-related proteins (SREP) and HPA-lectin related proteins (HREP). The transcriptional response of fibrinogen-related proteins of VIgL family (LlFREP), LlQREP and LlSREP to infestation of common periwinkle, Littorina littorea, with digenean parasite Himasthla elongata correlates with that of LlMReM1, supporting the model suggested in this study.

Ficolin-2 binds to serotype 35B pneumococcus as it does to serotypes 11A and 31, and these serotypes cause more infections in older adults than in children

Among 98 serotypes of Streptococcus pneumoniae, only a small subset regularly causes invasive pneumococcal diseases (IPD). We previously demonstrated that serotype 11A binds to ficolin-2 and has low invasiveness in children. Epidemiologic data suggested, however, that serotype 11A IPD afflicts older adults, possibly indicating reduced ficolin-2-mediated immune protection. Therefore, we studied the epidemiology of ficolin-2-bound serotypes. We obtained IPD case data from the United States Centers for Disease Control and Prevention. We studied three prominent ficolin-2-bound serotypes and their acetyltransferase-deficient variants for ficolin-2 binding and ficolin-2-mediated complement deposition with flow-cytometry. We determined the age distributions of these serotypes from the obtained epidemiologic data. We discovered that the serotype 35B capsule is a novel ficolin-2 ligand due to O-acetylation via WciG. Ficolin-2-mediated complement deposition was observed on serotypes 11A and 35B but not serotype 31 or any O-acetyl transferase deficient derivatives of these serotypes. Serotypes 11A, 35B, and 31 cause more IPD among older adults than children. Studies of the three serotypes provide additional evidence for ficolin-2 providing innate immunity against IPD. The skewed age distribution of the three serotypes suggests that older adults have reduced ficolin-2-mediated immunity and are more susceptible to these serotypes.

Sickening or Healing the Heart? The Association of Ficolin-1 and Rheumatic Fever

Rheumatic fever (RF) and its subsequent progression to rheumatic heart disease (RHD) are chronic inflammatory disorders prevalent in children and adolescents in underdeveloped countries, and a contributing factor for high morbidity and mortality rates worldwide. Their primary cause is oropharynx infection by Streptococcus pyogenes, whose acetylated residues are recognized by ficolin-1. This is the only membrane-bound, as well as soluble activator molecule of the complement lectin pathway (LP). Although LP genetic polymorphisms are associated with RF, FCN1 gene's role remains unknown. To understand this role, we haplotyped five FCN1 promoter polymorphisms by sequence-specific amplification in 193 patients (138 with RHD and 55, RF only) and 193 controls, measuring ficolin-1 serum concentrations in 78 patients and 86 controls, using enzyme-linked immunosorbent assay (ELISA). Patients presented lower ficolin-1 serum levels (p < 0.0001), but did not differ according to cardiac commitment. Control's genotype distribution was in the Hardy-Weinberg equilibrium. Four alleles (rs2989727: c.-1981A, rs10120023: c.-542A, rs10117466: c.-144A, and rs10858293: c.33T), all associated with increased FCN1 gene expression in whole blood or adipose subcutaneous tissue (p = 0.000001), were also associated with increased protection against the disease. They occur within the *3C2 haplotype, associated with an increased protection against RF (OR = 0.41, p < 0.0001) and with higher ficolin-1 levels in patient serum (p = 0.03). In addition, major alleles of these same polymorphisms comprehend the most primitive *1 haplotype, associated with increased susceptibility to RF (OR = 1.76, p < 0.0001). Nevertheless, instead of having a clear-cut protective role, the minor c.-1981A and c.-144A alleles were also associated with additive susceptibility to valvar stenosis and mitral insufficiency (OR = 3.75, p = 0.009 and OR = 3.37, p = 0.027, respectively). All associations were independent of age, sex or ethnicity. Thus, minor FCN1 promoter variants may play a protective role against RF, by encouraging bacteria elimination as well as increasing gene expression and protein levels. On the other hand, they may also predispose the patients to RHD symptoms, by probably contributing to chronic inflammation and tissue injury, thus emphasizing the dual importance of ficolin-1 in both conditions.

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.

Identification and characterization of a novel PRR of fibrinogen-related protein in Apostichopus japonicus

Fibrinogen-related proteins (FREPs) play important roles in innate immunity by recognizing pathogen associated molecular patterns on pathogenic bacteria surfaces via conserved fibrinogen-like domain (FBG). In this paper, the full-length cDNA of Apostichopus japonicus FREP (designated as AjFREP) was cloned combined with rapid amplification of cDNA ends (RACE) and transcriptome sequencing. The full-length cDNA of AjFREP was of 2110 bp with an open reading frame (ORF) of 1659 bp. SMART analysis revealed that the AjFREP contained a typical signal peptide of 19 amino acid residues, a FBG and two unusual epidermal growth factor-like domains (EGFs). Multiple sequence alignments suggested that FBG domain shared a remarkably high structural conservation in polypeptide binding site and Ca²⁺ binding site. Tissue distribution analysis revealed that AjFREP was constitutively expressed in all examined tissues with the largest magnitude in coelomocytes, indicating AjFREP might play an important role in immune defense. The mRNA level of AjFREP in coelomocytes was sharply up-regulated by Vibrio splendidus challenge, and reached its peak expression at 48 h. Knock-down AjFREP by specific siRNA could significantly repress the coelomocyte phagocytosis rate. Meantime, the survival number of V. splendidus in the coelomic fluid was promoted. All these current results indicated that AjFREP might be involved in pathogen clearance through mediating coelomocytes phagocytosis activity.

Structural and functional diversity of collectins and ficolins and their relationship to disease

Pattern recognition molecules are sensors for the innate immune system and trigger a number of pathophysiological functions after interaction with the corresponding ligands on microorganisms or altered mammalian cells. Of those pattern recognition molecules used by the complement system, collagen-like lectins (collectins) are an important subcomponent. Whereas the best known of these collectins, mannose-binding lectin, largely occurs as a circulating protein following production by hepatocytes, the most recently described collectins exhibit strong local biosynthesis. This local production and release of soluble collectin molecules appear to serve local tissue functions at extravascular sites, including a developmental function. In this article, we focus on the characteristics of collectin-11 (CL-11 or CL-K1), whose ubiquitous expression and multiple activities likely reflect a wide biological relevance. Collectin-11 appears to behave as an acute phase protein whose production associated with metabolic and physical stress results in locally targeted inflammation and tissue cell death. Early results indicate the importance of fucosylated ligand marking the injured cells targeted by collectin-11, and we suggest that further characterisation of this and related ligands will lead to better understanding of pathophysiological significance and exploitation for clinical benefit.

Progressive IgA Nephropathy Is Associated With Low Circulating Mannan-Binding Lectin-Associated Serine Protease-3 (MASP-3) and Increased Glomerular Factor H-Related Protein-5 (FHR5) Deposition

Introduction

IgA nephropathy (IgAN) is characterized by glomerular deposition of galactose-deficient IgA1 and complement proteins and leads to renal impairment. Complement deposition through the alternative and lectin activation pathways is associated with renal injury.

Methods

To elucidate the contribution of the lectin pathway to IgAN, we measured the 11 plasma lectin pathway components in a well-characterized cohort of patients with IgAN.

Results

M-ficolin, L-ficolin, mannan-binding lectin (MBL)-associated serine protease (MASP)-1 and MBL-associated protein (MAp) 19 were increased, whereas plasma MASP-3 levels were decreased in patients with IgAN compared with healthy controls. Progressive disease was associated with low plasma MASP-3 levels and increased glomerular staining for C3b/iC3b/C3c, C3d, C4d, C5b-9, and factor H-related protein 5 (FHR5). Glomerular FHR5 deposition positively correlated with glomerular C3b/iC3b/C3c, C3d, and C5b-9 deposition, but not with glomerular C4d. These observations, together with the finding that glomerular factor H (fH) deposition was reduced in progressive disease, are consistent with a role for fH deregulation by FHR5 in renal injury in IgAN.

Conclusion

Our data indicate that circulating MASP-3 levels could be used as a biomarker of disease severity in IgAN and that glomerular staining for FHR5 could both indicate alternative complement pathway activation and be a tissue marker of disease severity.

Evolution and Function of Thioester-Containing Proteins and the Complement System in the Innate Immune Response

The innate immune response is evolutionary conserved among organisms. The complement system forms an important and efficient immune defense mechanism. It consists of plasma proteins that participate in microbial detection, which ultimately results in the production of various molecules with antimicrobial activity. Thioester-containing proteins (TEPs) are a superfamily of secreted effector proteins. In vertebrates, certain TEPs act in the innate immune response by promoting recruitment of immune cells, phagocytosis, and direct lysis of microbial invaders. Insects are excellent models for dissecting the molecular basis of innate immune recognition and response to a wide range of microbial infections. Impressive progress in recent years has generated crucial information on the role of TEPs in the antibacterial and antiparasite response of the tractable model insect Drosophila melanogaster and the mosquito malaria vector Anopheles gambiae. This knowledge is critical for better understanding the evolution of TEPs and their involvement in the regulation of the host innate immune system.

The role of the complement system in hereditary angioedema

Hereditary angioedema (HAE) is a rare, but potentially life-threatening disorder, characterized by acute, recurring, and self-limiting edematous episodes of the face, extremities, trunk, genitals, upper airways, or the gastrointestinal tract. HAE may be caused by the deficiency of C1-inhibitor (C1-INH-HAE) but another type of the disease, hereditary angioedema with normal C1-INH function (nC1-INH-HAE) was also described. The patient population is quite heterogeneous as regards the location, frequency, and severity of edematous attacks, presenting large intra- and inter-individual variation. Here, we review the role of the complement system in the pathomechanism of HAE and also present an overview on the complement parameters having an importance in the diagnosis or in predicting the severity of HAE.

Morula cells as key hemocytes of the lectin pathway of complement activation in the colonial tunicate Botryllus schlosseri

The complement system is deeply rooted in the evolution of humoral mechanism of innate immunity. In addition to the alternative pathway of complement activation, lectins and associated serine proteases exert important roles in the recognition of non-self and activation of the effectors. In the colonial tunicate Botryllus schlosseri, we identified, characterized and studied the expression of three orthologues of genes involved in the lectin pathway of complement activation of vertebrates, i.e., genes for a mannose-binding lectin (MBL), a ficolin and a mannose-associated serine protease 1 (MASP1). All the genes are transcribed by hemocytes, and specifically by morula cells, the same immunocytes responsible for the transcription of C3 and Bf orthologues. The transcription levels of MASP1 and ficolin orthologues are not affected by zymosan challenge, indicating a constitutive expression of complement system associated serine proteases, whereas the MBL orthologue is up-regulated after 15 min of zymosan exposure. Collectively, our data suggest the presence of a complete lectin activation pathway in Botryllus.

The role of ficolin-like protein (PcFLP1) in the antibacterial immunity of red swamp crayfish (Procambarus clarkii)

In invertebrates, ficolin-like proteins (FLPs) play important roles in innate immunity against pathogens. Previous studies primarily investigated the functions of FLPs in immune recognition, activation, and regulation. However, limited research has examined the functions of FLPs as immune effectors. In this work, a ficolin-like protein was identified in red swam crayfish (Procambarus clarkii) and designated as PcFLP1. Quantitative RT-PCR and western blot were employed to analyze the distribution and expression profiles of PcFLP1 in the tissues of the crayfish. The results indicated that PcFLP1 was present in all tested tissues, including hemocytes, heart, hepatopancreas, gill, stomach, and mid-intestine. The expression level of PcFLP1 was up-regulated in hemocytes, hepatopancreas and mid-intestines of the crayfish challenged with Vibrio parahaemolyticus. Further study demonstrated that PcFLP1 could protect the hepatopancreatic cells of crayfish from V. parahaemolyticus infection. The recombinant PcFLP1 enhanced bacterial elimination in crayfish, whereas the antibacterial action was inhibited after PcFLP1 was knocked down. Furthermore, PcFLP1 could bound to bacteria and inhibited bacterial replication. These results demonstrated that PcFLP1 plays an important role in the anti-Vibrio immunity of red swamp crayfish.

Ficolin-2 inhibitors are present in sera after prolonged storage at -80 °C

Ficolins can activate the lectin pathway of the complement system that provides innate immune protection against pathogens, marks host cellular debris for clearance, and promotes inflammation. Baseline inflammation increases with aging in a phenomenon known as “inflammaging.” Although IL-6 and C-reactive protein are known to increase with age, contributions of many complement factors, including ficolins, to inflammaging have been little studied.

Ficolin-2 is abundant in human serum and can recognize many target structures; therefore, ficolin-2 has potential to contribute to inflammaging. We hypothesized that inflammaging would alter ficolin-2 levels among older adults and examined 360 archived sera collected from older individuals. We found that these sera had apparently reduced ficolin-2 levels and that 84.2% of archived sera exhibited ficolin-2 inhibitors, which suppressed apparent amounts of ficolin-2 detected by enzyme-linked immunosorbent assay. Fresh serum samples were obtained from donors whose archived sera showed inhibitors, but the fresh sera did not have ficolin-2 inhibitors. Ficolin-2 inhibitors were present in other long-stored sera from younger persons. Furthermore, noninhibiting samples and fresh sera from older adults had apparently normal amounts of ficolin-2. Thus, ficolin-2 inhibitors may arise as an artifact of long-term storage of serum at −80 °C.

Association of Low Ficolin-Lectin Pathway Parameters with Cardiac Syndrome X

In patients with typical angina pectoris, inducible myocardial ischaemia and macroscopically normal coronaries (cardiac syndrome X (CSX)), a significantly elevated plasma level of terminal complement complex (TCC), the common end product of complement activation, has been observed without accompanying activation of the classical or the alternative pathways. Therefore, our aim was to clarify the role of the ficolin-lectin pathway in CSX. Eighteen patients with CSX, 37 stable angina patients with significant coronary stenosis (CHD) and 54 healthy volunteers (HC) were enrolled. Serum levels of ficolin-2 and ficolin-3, ficolin-3/MASP-2 complex and ficolin-3-mediated TCC deposition (FCN3-TCC) were determined. Plasma level of TCC was significantly higher in the CSX than in the HC or CHD group (5.45 versus 1.30 versus 2.04 AU/ml, P < 0.001). Serum levels of ficolin-2 and ficolin-3 were significantly lower in the CSX compared to the HC or CHD group (3.60 versus 5.80 or 5.20 μg/ml, P < 0.05; 17.80 versus 24.10 or 26.80 μg/ml, P < 0.05). The ficolin-3/MASP-2 complex was significantly lower in the CSX group compared to the HC group (92.90 versus 144.90 AU/ml, P = 0.006). FCN3-TCC deposition was significantly lower in the CSX group compared to the HC and CHD groups (67.8% versus 143.3% or 159.7%, P < 0.05). In the CSX group, a significant correlation was found between TCC and FCN3-TCC level (r = 0.507, P = 0.032) and between ficolin-3/MASP-2 complex level and FCN3-TCC deposition (r = 0.651, P = 0.003). In conclusion, in patients with typical angina and myocardial ischaemia despite macroscopically normal coronary arteries, low levels of several lectin pathway parameters were observed, indicating complement activation and consumption. Complement activation through the ficolin-lectin pathway might play a role in the complex pathomechanism of CSX.

A New Ligand-Based Method for Purifying Active Human Plasma-Derived Ficolin-3 Complexes Supports the Phenomenon of Crosstalk between Pattern-Recognition Molecules and Immunoglobulins

Despite recombinant protein technology development, proteins isolated from natural sources remain important for structure and activity determination. Ficolins represent a class of proteins that are difficult to isolate. To date, three methods for purifying ficolin-3 from plasma/serum have been proposed, defined by most critical step: (i) hydroxyapatite absorption chromatography (ii) N-acetylated human serum albumin affinity chromatography and (iii) anti-ficolin-3 monoclonal antibody-based affinity chromatography. We present a new protocol for purifying ficolin-3 complexes from human plasma that is based on an exclusive ligand: the O-specific polysaccharide of Hafnia alvei PCM 1200 LPS (O-PS 1200). The protocol includes (i) poly(ethylene glycol) precipitation; (ii) yeast and l-fucose incubation, for depletion of mannose-binding lectin; (iii) affinity chromatography using O-PS 1200-Sepharose; (iv) size-exclusion chromatography. Application of this protocol yielded average 2.2 mg of ficolin-3 preparation free of mannose-binding lectin (MBL), ficolin-1 and -2 from 500 ml of plasma. The protein was complexed with MBL-associated serine proteases (MASPs) and was able to activate the complement in vitro. In-process monitoring of MBL, ficolins, and total protein content revealed the presence of difficult-to-remove immunoglobulin G, M and A, in some extent in agreement with recent findings suggesting crosstalk between IgG and ficolin-3. We demonstrated that recombinant ficolin-3 interacts with IgG and IgM in a concentration-dependent manner. Although this association does not appear to influence ficolin-3-ligand interactions in vitro, it may have numerous consequences in vivo. Thus our purification procedure provides Ig-ficolin-3/MASP complexes that might be useful for gaining further insight into the crosstalk and biological activity of ficolin-3.

Alveolar recruitment of ficolin-3 in response to acute pulmonary inflammation in humans

BACKGROUND

Ficolins serve as soluble recognition molecules in the lectin pathway of complement. They are known to participate in the systemic host-response to infection but their role in local pulmonary defence is still incompletely understood. The purpose of this study was to clarify whether acute lung and systemic inflammation induce recruitment of lectins in humans.

METHODS

Fifteen healthy volunteers received LPS intravenously (IV) or in a lung subsegment on two different occasions. Volunteers were evaluated by consecutive blood samples and by bronchoalveolar lavage 2, 4, 6, 8, or 24h after LPS (n=3 in all groups), and gene expression patterns and protein levels of mannose-binding lectin (MBL) and ficolins were determined.

RESULTS

Endobronchial LPS was associated with an increase in alveolar ficolin-3 and MBL levels (p<0.04 and p<0.001, respectively). IV LPS elicited a pronounced acute phase response with an increase in CRP (p<0.001) and plasma ficolin-1 protein levels (p<0.001), whereas no changes were observed in ficolin-1 gene expression patterns (p=0.11) or plasma protein levels of MBL, ficolin-2, or ficolin-3.

CONCLUSIONS

LPS induces a tissue-specific recruitment of ficolin-3 and ficolin-1 in the lung and systemic compartment, respectively, suggesting an important role of distinct lectin complement pathway initiators in the local pulmonary and systemic host defence.

Serum opsonin ficolin-A enhances host-fungal interactions and modulates cytokine expression from human monocyte-derived macrophages and neutrophils following Aspergillus fumigatus challenge

Invasive aspergillosis is a devastating invasive fungal disease associated with a high mortality rate in the immunocompromised, such as leukaemia patients, transplant patients and those with HIV/AIDS. The rodent serum orthologue of human L-ficolin, ficolin-A, can bind to and opsonize Aspergillus fumigatus, the pathogen that causes invasive aspergillosis, and may participate in fungal defence. Using human monocyte-derived macrophages and neutrophils isolated from healthy donors, we investigated conidial association and fungal viability by flow cytometry and microscopy. Additionally, cytokine production was measured via cytometric bead arrays. Ficolin-A opsonization was observed to significantly enhance association of conidia, while also inhibiting hyphal growth and contributing to increased fungal killing following incubation with monocyte-derived macrophages and neutrophils. Additionally, ficolin-A opsonization was capable of manifesting a decrease in IL-8, IL-1β, IL-6, IL-10 and TNF-α production from MDM and IL-1β, IL-6 and TNF-α from neutrophils 24 h post-infection. In conclusion, rodent ficolin-A is functionally comparable to human L-ficolin and is capable of modulating the innate immune response to A. fumigatus, down-regulating cytokine production and could play an important role in airway immunity.

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.

Ficolin Gene Polymorphisms in Systemic Lupus Erythematosus and Rheumatoid Arthritis

Systemic lupus erythemathosus (SLE) and rheumatoid arthritis (RA) are complex autoimmune diseases characterized by an immune balance breakdown and by chronic inflammation. Several findings link SLE and RA development with the complement system and ficolin components have emerged as candidates for disease development. Since genetic association studies with ficolin genes in SLE and RA have not yet been conducted in a Brazilian population, the aim of this study was to determine whether polymorphisms of ficolin-1(FCN1) and ficolin-2 (FCN2) genes are associated with SLE and RA susceptibility as well as disease manifestation. Two SNPs within FCN1 (rs2989727 and 1071583) and three in FCN2 (rs17514136, rs3124954, and rs7851696) were studied in 208 SLE and184 RA patients as well as 264 healthy individuals in a Southeast Brazilian population. For SLE patients, the FCN2 rs17514136 SNP was associated with a more severe disease (SLICC) (p = 0.0067). Furthermore, an association between the occurrence of nephritis and the T/T genotype for FCN2 rs3124954 SNP (p = 0.047, OR = 3.17, 95%CI = 1.34-7.5) was observed. No association was observed between the studied polymorphisms and RA development. Thus, our data support involvement of the FCN2 gene in the SLE phenotype.

Complement activation, regulation, and molecular basis for complement-related diseases

The complement system is an essential element of the innate immune response that becomes activated upon recognition of molecular patterns associated with microorganisms, abnormal host cells, and modified molecules in the extracellular environment. The resulting proteolytic cascade tags the complement activator for elimination and elicits a pro-inflammatory response leading to recruitment and activation of immune cells from both the innate and adaptive branches of the immune system. Through these activities, complement functions in the first line of defense against pathogens but also contributes significantly to the maintenance of homeostasis and prevention of autoimmunity. Activation of complement and the subsequent biological responses occur primarily in the extracellular environment. However, recent studies have demonstrated autocrine signaling by complement activation in intracellular vesicles, while the presence of a cytoplasmic receptor serves to detect complement-opsonized intracellular pathogens. Furthermore, breakthroughs in both functional and structural studies now make it possible to describe many of the intricate molecular mechanisms underlying complement activation and the subsequent downstream events, as well as its cross talk with, for example, signaling pathways, the coagulation system, and adaptive immunity. We present an integrated and updated view of complement based on structural and functional data and describe the new roles attributed to complement. Finally, we discuss how the structural and mechanistic understanding of the complement system rationalizes the genetic defects conferring uncontrolled activation or other undesirable effects of complement.

Peptide Inhibitor of Complement C1 (PIC1) Rapidly Inhibits Complement Activation after Intravascular Injection in Rats

The complement system has been increasingly recognized to play a pivotal role in a variety of inflammatory and autoimmune diseases. Consequently, therapeutic modulators of the classical, lectin and alternative pathways of the complement system are currently in pre-clinical and clinical development. Our laboratory has identified a peptide that specifically inhibits the classical and lectin pathways of complement and is referred to as Peptide Inhibitor of Complement C1 (PIC1). In this study, we determined that the lead PIC1 variant demonstrates a salt-dependent binding to C1q, the initiator molecule of the classical pathway. Additionally, this peptide bound to the lectin pathway initiator molecule MBL as well as the ficolins H, M and L, suggesting a common mechanism of PIC1 inhibitory activity occurs via binding to the collagen-like tails of these collectin molecules. We further analyzed the effect of arginine and glutamic acid residue substitution on the complement inhibitory activity of our lead derivative in a hemolytic assay and found that the original sequence demonstrated superior inhibitory activity. To improve upon the solubility of the lead derivative, a pegylated, water soluble variant was developed, structurally characterized and demonstrated to inhibit complement activation in mouse plasma, as well as rat, non-human primate and human serum in vitro. After intravenous injection in rats, the pegylated derivative inhibited complement activation in the blood by 90% after 30 seconds, demonstrating extremely rapid function. Additionally, no adverse toxicological effects were observed in limited testing. Together these results show that PIC1 rapidly inhibits classical complement activation in vitro and in vivo and is functional for a variety of animal species, suggesting its utility in animal models of classical complement-mediated diseases.

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.

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.

Human ficolin-2 recognition versatility extended: an update on the binding of ficolin-2 to sulfated/phosphated carbohydrates

Ficolin-2 has been reported to bind to DNA and heparin, but the mechanism involved has not been thoroughly investigated. X-ray studies of the ficolin-2 fibrinogen-like domain in complex with several new ligands now show that sulfate and phosphate groups are prone to bind to the S3 binding site of the protein. Composed of Arg132, Asp133, Thr136 and Lys221, the S3 site was previously shown to mainly bind N-acetyl groups. Furthermore, DNA and heparin compete for binding to ficolin-2. Mutagenesis studies reveal that Arg132, and to a lesser extent Asp133, are important for this binding property. The versatility of the S3 site in binding N-acetyl, sulfate and phosphate groups is discussed through comparisons with homologous fibrinogen-like recognition proteins.

Activation of the ficolin-lectin pathway during attacks of hereditary angioedema

BACKGROUND

The activation of plasma enzyme systems is insufficiently controlled in hereditary angioedema due to the deficiency of C1-inhibitor (C1-INH) (HAE-C1-INH). Recently, it was suggested that the ficolin-lectin pathway (ficolin-LP) might play a more dominant role than the mannose-binding lectin-lectin pathway in the pathomechanism of HAE-C1-INH.

OBJECTIVE

Because the role of the ficolin-LP during edematous attacks is still enigmatic, we analyzed its activity during such episodes.

METHODS

Thirty-five patients with HAE-C1-INH, who have experienced severe attacks on 106 occasions, were enrolled. We analyzed blood samples drawn during attacks, and obtained 35 samples from the same patients during symptom-free periods. The serum levels of ficolin-2, ficolin-3, MASP-2, ficolin-3/MASP-2 complex, C1-INH, and C4, as well as the extent of ficolin-3-mediated terminal complement complex (FCN3-TCC) deposition, were measured using ELISA-based methods.

RESULTS

Levels of MASP-2 and of the ficolin-3/MASP-2 complex were elevated (P < .0001 and .033, respectively), whereas that of FCN3-TCC was lower (P < .0001) during attacks than during the symptom-free period. During symptom-free periods, FCN3-TCC deposition was significantly related to concentrations of ficolin-3 (R = 0.2778; P = .0022), antigenic C1-INH (R = 0.3152; P = .0006), and C4 (R = 0.5307; P < .0001). Both ficolin-3 and MASP-2 levels correlated inversely with the time from the onset of the attack until blood sampling.

CONCLUSIONS

There is a marked heterogeneity of the pathomechanism and development of hereditary angioedema attacks in different patients. Our results suggest that the activation of the ficolin-LP may deplete the innately low level of C1-INH and thus, it may contribute to the uncontrolled activation of plasma cascade systems, and thereby to edema formation.

Neutrophil-Mediated Phagocytosis of Staphylococcus aureus

Initial elimination of invading Staphylococcus aureus from the body is mediated by professional phagocytes. The neutrophil is the major phagocyte of the innate immunity and plays a key role in the host defense against staphylococcal infections. Opsonization of the bacteria with immunoglobulins and complement factors enables efficient recognition by the neutrophil that subsequently leads to intracellular compartmentalization and killing. Here, we provide a review of the key processes evolved in neutrophil-mediated phagocytosis of S. aureus and briefly describe killing. As S. aureus is not helpless against the professional phagocytes, we will also highlight its immune evasion arsenal related to phagocytosis.

The carbohydrate-binding promiscuity of Euonymus europaeus lectin is predicted to involve a single binding site

Euonymus europaeus lectin (EEL) is a carbohydrate-binding protein derived from the fruit of the European spindle tree. EEL was first identified for its erythrocyte agglutinating properties and specificity for B and H blood groups. However, a detailed molecular picture of the structural basis of carbohydrate recognition by EEL remains to be developed. In this study, we performed fluorescence titrations of a range of carbohydrates against EEL. Binding of EEL to a wide range of carbohydrates was observed, including a series of blood group-related carbohydrates, mannosides, chitotriose and sialic acid. Affinity was strongest for carbohydrates with H-related structures and the B trisaccharide. A homology model of EEL was produced from templates identified using the HHPred server, which employs hidden Markov models (HMMs) to identify templates. The HMM approach identified that the best templates for EEL were proteins featuring a ricin B-like (R-type) fold. Separate templates were used to model the core and binding site regions of the lectin. Through the use of constrained docking and spatial comparison with a template ligand, binding modes for the carbohydrate ligands were predicted. A relationship between the experimental binding energies and the computed binding energies of the selected docked poses was determined and optimized. Collectively, our results suggest that EEL utilizes a single site for recognition of carbohydrates terminating in a variety of monosaccharides.

The complement system in inflammatory bowel disease

Complement is well appreciated to be a potent innate immune defense against microbes and is important in the housekeeping act of removal of apoptotic and effete cells. It is also understood that hyperactivation of complement, or the lack of regulators, may underlie chronic inflammatory diseases. A pipeline of products to intervene in complement activation, some already in clinical use, is being studied in various chronic inflammatory diseases. To date, the role of complement in inflammatory bowel disease has not received a lot of research interest. Novel genetically modified laboratory animals and experiments using antagonists to complement effector molecules have kindled important research observations implicating the complement system in inflammatory bowel disease pathogenesis. We review the evidence base for the role and potential therapeutic manipulation of the complement cascade in inflammatory bowel disease.

Complement, c1q, and c1q-related molecules regulate macrophage polarization

Complement is a critical system of enzymes, regulatory proteins, and receptors that regulates both innate and adaptive immune responses. Natural mutations in complement molecules highlight their requirement in regulation of a variety of human conditions including infectious disease and autoimmunity. As sentinels of the immune system, macrophages are specialized to respond to infectious microbes, as well as normal and altered self, and dictate appropriate immune responses. Complement components such as anaphylatoxins (C3a and C5a) and opsonins [C3b, C1q, mannan binding lectin (MBL)] influence macrophage responses. While anaphylatoxins C3a and C5a trigger inflammasome activation, opsonins such as C1q and related molecules (MBL and adiponectin) downregulate inflammasome activation and inflammation, and upregulate engulfment of apoptotic cells consistent with a pro-resolving or M2 macrophage phenotype. This review summarizes our current understanding of the influence of the complement system on macrophage polarization with an emphasis on C1q and related molecules.

Complement activation and its prognostic role in post-cardiac arrest patients

Cardiac arrest causes generalized ischaemia/hypoxia, and subsequent resuscitation inflicts reperfusion injury, the pathology of which is not fully understood. Moreover, predicting the prognosis of comatose, post-cardiac arrest patients is a complex clinical challenge. We hypothesized that the extent of complement activation might be a reliable predictor of mortality in this population. Forty-six comatose cardiac arrest patients were enrolled into our prospective cohort study, conducted in a tertiary care university clinic. All subjects were cooled to 32-34 °C body temperature for 24 h and then allowed to rewarm to normothermia. All patients underwent diagnostic coronary angiography. On admission, at 6 and 24 h, blood samples were taken from the arterial catheter. In these, complement products (C3a, C3, C4d, C4, SC5b9 and Bb) were measured by ELISA in blood samples. Patients were followed up for 30 days; 22 patients (47.8%) died by the end of this period. We observed that complement activation (determined as the C3a to C3 ratio) was higher in non-survivors than in survivors at each time point. In the multivariate Cox regression analysis, the C3a/C3 ratio determined 24 h after the initiation of therapeutic hypothermia predicted 30-day mortality regardless of age, sex and the APACHE II score. Complement activation occurs in post-cardiac arrest patients, and its extent correlates with 30-day survival. The C3a/C3 ratio might prove useful for estimating the prognosis of comatose post-cardiac arrest patients.

The pattern recognition molecule ficolin-1 exhibits differential binding to lymphocyte subsets, providing a novel link between innate and adaptive immunity

Ficolin-1 is a soluble pattern recognition molecule synthesized by myeloid cells and capable of activating the lectin pathway of complement on the surface of pathogens. It is tethered to the membranes of monocytes and granulocytes; however, the biological significance of cell-associated ficolin-1 is unknown. Recognition of healthy host cells by a pattern recognition molecule constitutes a potential hazard to self cells and tissues, emphasizing the importance of further elucidating the reported self-recognition. In the current study we investigated the potential recognition of lymphocytes by ficolin-1 and demonstrated that CD56(dim) NK-cells and both CD4(+) and CD8(+) subsets of activated T-cells were recognized by ficolin-1. In contrast we did not detect binding of ficolin-1 to CD56(bright) NK-cells, NKT-cells, resting T-cells or B-cells. Furthermore, we showed that the protein-lymphocyte interaction occurred via the pathogen-recognition domain of ficolin-1 to sialic acid on the cell surface. Thus, the differential binding of ficolin-1 to lymphocyte subsets suggests ficolin-1 as a novel link between innate and adaptive immunity. Our results provide new insight about the recognition properties of ficolin-1 and point toward additional immune modulating functions of the molecule besides its role in pathogen recognition.

The lectin pathway of complement and rheumatic heart disease

The innate immune system is the first line of host defense against infection and is comprised of humoral and cellular mechanisms that recognize potential pathogens within minutes or hours of entry. The effector components of innate immunity include epithelial barriers, phagocytes, and natural killer cells, as well as cytokines and the complement system. Complement plays an important role in the immediate response against microorganisms, including Streptococcus sp. The lectin pathway is one of three pathways by which the complement system can be activated. This pathway is initiated by the binding of mannose-binding lectin (MBL), collectin 11 (CL-K1), and ficolins (Ficolin-1, Ficolin-2, and Ficolin-3) to microbial surface oligosaccharides and acetylated residues, respectively. Upon binding to target molecules, MBL, CL-K1, and ficolins form complexes with MBL-associated serine proteases 1 and 2 (MASP-1 and MASP-2), which cleave C4 and C2 forming the C3 convertase (C4b2a). Subsequent activation of complement cascade leads to opsonization, phagocytosis, and lysis of target microorganisms through the formation of the membrane-attack complex. In addition, activation of complement may induce several inflammatory effects, such as expression of adhesion molecules, chemotaxis and activation of leukocytes, release of reactive oxygen species, and secretion of cytokines and chemokines. In this chapter, we review the general aspects of the structure, function, and genetic polymorphism of lectin-pathway components and discuss most recent understanding on the role of the lectin pathway in the predisposition and clinical progression of Rheumatic Fever.