The innate pattern recognition molecule Ficolin-1 is secreted by monocytes/macrophages and is circulating in human plasma

Diagnostic biomarkers and immune infiltration profiles common to COVID-19, acute myocardial infarction and acute ischaemic stroke using bioinformatics methods and machine learning

BACKGROUND

COVID-19 is a disease that affects people globally. Beyond affecting the respiratory system, COVID-19 patients are at an elevated risk for both venous and arterial thrombosis. This heightened risk contributes to an increased probability of acute complications, including acute myocardial infarction (AMI) and acute ischemic stroke (AIS). Given the unclear relationship between COVID-19, AMI, and AIS, it is crucial to gain a deeper understanding of their associations and potential molecular mechanisms. This study aims to utilize bioinformatics to analyze gene expression data, identify potential therapeutic targets and biomarkers, and explore the role of immune cells in the disease.

METHODS

This study employed three Gene Expression Omnibus (GEO) datasets for analysis, which included data on COVID-19, AMI and AIS. We performed enrichment analysis on the co-DEGs for these three diseases to clarify gene pathways and functions, and also examined the relationship between co-DEGs and immune infiltration. Machine learning techniques and protein-protein interaction networks (PPI) were used to identify hub genes within the co-DEGs. Finally, we employed a dual validation strategy integrating independent GEO datasets and in vitro experiments with human blood samples to comprehensively assess the reliability of our experimental findings.

RESULTS

We identified 88 co-DEGs associated with COVID-19, AMI and AIS. Enrichment analysis results indicated that co-DEGs were significantly enriched in immune inflammatory responses related to leukocytes and neutrophils. Immune infiltration analysis revealed significant differences in immune cell populations between the disease group and the normal group. Finally, genes selected through machine learning methods included: CLEC4E, S100A12, and IL1R2. Based on the PPI network, the top ten most influential DEGs were identified as MMP9, TLR2, TLR4, ITGAM, S100A12, FCGR1A, CD163, FCER1G, FPR2, and CLEC4D. The integration of the protein-protein interaction (PPI) network with machine learning techniques facilitated the identification of S100A12 as a potential common biomarker for early diagnosis and a therapeutic target for all three diseases. Ultimately, validation of S100A12 showed that it was consistent with our experimental results, confirming its reliability as a biomarker. Moreover, it demonstrated good diagnostic performance for the three diseases.

CONCLUSION

We employed bioinformatics methods and machine learning to investigate common diagnostic biomarkers and immune infiltration characteristics of COVID-19, AMI and AIS. Functional and pathway analyses indicated that the co-DEGs were primarily enriched in immune inflammatory responses related to leukocytes and neutrophils. Through two machine learning approaches and the PPI network, and subsequent validation and evaluation, we identified S100A12 as a potential common therapeutic target and biomarker related to immune response that may influence these three diseases.

The Role of Ficolins in Lung Injury

BACKGROUND

Respiratory diseases seriously threaten human health worldwide, and lung injury is an important component of respiratory disease. Complement activation is an important function of the innate immune system. Complement activation helps the body defend against invasion by external microorganisms, whereas excessive complement activation can exacerbate tissue damage or lead to unwanted side effects. Ficolins are a class of immune-related proteins in the lectin pathway that play important roles in the body's immune defense. Although individual ficolins are not well understood, current information suggests that ficolins may play an important regulatory role in lung injury.

SUMMARY

Several studies have shown that ficolins are involved in the immune response in the lung, particularly in the response to infectious and inflammatory processes.

KEY MESSAGES

This review summarizes the role of ficolins in lung injury. Ficolins may influence the development and repair of lung injury by recognizing and binding pathogenic microorganisms, modulating the inflammatory response, and promoting the clearance of immune cells. In addition, ficolins are associated with the development and progression of lung diseases (such as pneumonia and ARDS) and may have an important impact on the pathophysiological processes of inflammatory diseases.

Sources of biases in the in vitro testing of nanomaterials: the role of the biomolecular corona

The biological fate of nanomaterials (NMs) is driven by specific interactions through which biomolecules, naturally adhering onto their surface, engage with cell membrane receptors and intracellular organelles. The molecular composition of this layer, called the biomolecular corona (BMC), depends on both the physical-chemical features of the NMs and the biological media in which the NMs are dispersed and cells grow. In this work, we demonstrate that the widespread use of 10% fetal bovine serum in an in vitro assay cannot recapitulate the complexity of in vivo systemic administration, with NMs being transported by the blood. For this purpose, we undertook a comparative journey involving proteomics, lipidomics, high throughput multiparametric in vitro screening, and single molecular feature analysis to investigate the molecular details behind this in vivo/in vitro bias. Our work indirectly highlights the need to introduce novel, more physiological-like media closer in composition to human plasma to produce realistic in vitro screening data for NMs. We also aim to set the basis to reduce this in vitro-in vivo mismatch, which currently limits the formulation of NMs for clinical settings.

Ficolin B secreted by alveolar macrophage exosomes exacerbates bleomycin-induced lung injury via ferroptosis through the cGAS-STING signaling pathway

Pathogenesis exploration and timely intervention of lung injury is quite necessary as it has harmed human health worldwide for years. Ficolin B (Fcn B) is a recognition molecule that can recognize a variety of ligands and play an important role in mediating the cell cycle, immune response, and tissue homeostasis in the lung. However, the role of Fcn B in bleomycin (BLM)-induced lung injury is obscure. This study aims to investigate the sources of Fcn B and its mechanism in BLM-induced lung injury. WT, Fcna-/-, and Fcnb-/- mice were selected to construct the BLM-induced lung injury model. Lung epithelial cells were utilized to construct the BLM-induced cell model. Exosomes that were secreted from alveolar macrophages (AMs) were applied for intervention by transporting Fcn B. Clinical data suggested M-ficolin (homologous of Fcn B) was raised in plasma of interstitial lung disease (ILD) patients. In the mouse model, macrophage-derived Fcn B aggravated BLM-induced lung injury and fibrosis. Fcn B further promoted the development of autophagy and ferroptosis. Remarkably, cell experiment results revealed that Fcn B transported by BLM-induced AMs exosomes accelerated autophagy and ferroptosis in lung epithelial cells through the activation of the cGAS-STING pathway. In contrast, the application of 3-Methyladenine (3-MA) reversed the promotion effect of Fcn B from BLM-induced AMs exosomes on lung epithelial cell damage by inhibiting autophagy-dependent ferroptosis. Meanwhile, in the BLM-induced mice model, the intervention of Fcn B secreted from BLM-induced AMs exosomes facilitated lung injury and fibrosis via ferroptosis. In summary, this study demonstrated that Fcn B transported by exosomes from AMs exacerbated BLM-induced lung injury by promoting lung epithelial cells ferroptosis through the cGAS-STING signaling pathway.

Transcriptome and proteome analysis of dogs with precursor targeted immune-mediated anemia treated with splenectomy

Precursor-targeted immune-mediated anemia (PIMA) in dogs is characterized by persistent non-regenerative anemia and ineffective erythropoiesis, and it is suspected to be an immune-mediated disease. Most affected dogs respond to immunosuppressive therapies; however, some are resistant. In this study, we carried out splenectomy as an alternative therapy for refractory PIMA in dogs, and analyzed gene expression levels in the spleen of dogs with or without PIMA and in serum before and after splenectomy. A total of 1,385 genes were found to express differentially in the spleens from dogs with PIMA compared with healthy dogs by transcriptome analysis, of which 707 genes were up-regulated, including S100A12, S100A8, and S100A9 that are linked directly to the innate immune system and have been characterized as endogenous damage-associated molecular patterns. Furthermore, immunohistochemistry confirmed that S100A8/A9 protein expression levels were significantly higher in dogs with PIMA compared with those in healthy dogs. A total of 22 proteins were found to express differentially between the serum samples collected before and after splenectomy by proteome analysis, of which 12 proteins were up-regulated in the samples before. The lectin pathway of complement activation was identified by pathway analysis in pre-splenectomy samples. We speculated that S100A8/9 expression may be increased in the spleen of dogs with PIMA, resulting in activation of the lectin pathway before splenectomy. These findings further our understanding of the pathology and mechanisms of splenectomy for PIMA.

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.

Distinct Roles of Classical and Lectin Pathways of Complement in Preeclamptic Placentae

Pre-eclampsia is a pregnancy complication characterized by defective vascular remodeling in maternal decidua responsible for reduced blood flow leading to functional and structural alterations in the placenta. We have investigated the contribution of the complement system to decidual vascular changes and showed that trophoblasts surrounding unremodeled vessels prevalent in preeclamptic decidua fail to express C1q that are clearly detected in cells around remodeled vessels predominant in control placenta. The critical role of C1q is supported by the finding that decidual trophoblasts of female C1qa^-/- pregnant mice mated to C1qa^+/+ male mice surrounding remodeled vessels express C1q of paternal origin. Unlike C1qa^-/- pregnant mice, heterozygous C1qa^+/- and wild type pregnant mice share a high percentage of remodeled vessels. C1q was also found in decidual vessels and stroma of normal placentae and the staining was stronger in preeclamptic placentae. Failure to detect placental deposition of C1r and C1s associated with C1q rules out complement activation through the classical pathway. Conversely, the intense staining of decidual endothelial cells and villous trophoblast for ficolin-3, MASP-1 and MASP-2 supports the activation of the lectin pathway that proceeds with the cleavage of C4 and C3 and the assembly of the terminal complex. These data extend to humans our previous findings of complement activation through the lectin pathway in an animal model of pre-eclampsia and provide evidence for an important contribution of C1q in decidual vascular remodeling.

FCN1 polymorphisms are not the markers of dental caries susceptibility in Polish children: A case-control study

OBJECTIVE

To examine the association of four FCN1 SNPs: -542G>A (rs10120023), -144C>A (rs10117466), +6658C>T (rs148649884), and +7895A>G (rs150625869) with dental caries in Polish children.

SUBJECTS AND METHODS

The study group consisted of 261 15-year-old Polish teenagers: 82 children with "higher" caries experience (having Decayed Missing Filled Teeth, DMFT >5) and 179 children with "lower" caries experience (having DMFT ≤5). Moreover, in additional comparison, a group of 229 children with caries experience (DMFT ≥1) was compared to a caries-free (DMFT =0) group of 32 children. Extraction of genomic DNA was performed from buccal swabs, and genotyping was performed by Real-Time PCR.

RESULTS

FCN1 SNPs +6658C>T and +7895A>G appeared to be monomorphic in our sample. The genotype, allele, or haplotype distributions in FCN1 SNPs -542G>A and -144C>A in children with "higher" caries experience did not differ significantly from those in "lower" caries experience group. Similar results with no significant differences were demonstrated for subjects with DMFT ≥1 compared to subjects with DMFT =0.

CONCLUSION

FCN1 SNPs are not the markers of dental caries susceptibility in Polish children.

Single-Cell Sequencing Reveals an Intrinsic Heterogeneity of the Preovulatory Follicular Microenvironment

The follicular microenvironment, including intra-follicular granulosa cells (GCs), is responsible for oocyte maturation and subsequent ovulation. However, the functions of GCs and cellular components of the follicular microenvironment in preovulatory follicles have not been extensively explored. Here, we surveyed the single-cell transcriptome of the follicular microenvironment around MII oocytes in six human preovulatory follicles in in vitro fertilization. There were six different cell types in the preovulatory follicles, including GCs and various immune cells. In GCs, we identified nine different functional clusters with different functional transcriptomic profiles, including specific clusters involved in inflammatory responses and adhesive function. Follicular macrophages are involved in immune responses, extracellular matrix remoulding and assist GCs in promoting the oocyte meiotic resumption. Interestingly, we observed that the specific terminal state subcluster of GCs with high levels of adhesive-related molecules should result in macrophage recruitment and residence, further contributing to an obvious heterogeneity of the immune cell proportion in preovulatory follicles from different patients. Our results provide a comprehensive understanding of the transcriptomic landscape of the preovulatory follicular microenvironment at the single-cell level. It provides valuable insights into understanding the regulation of the oocyte maturation and ovulation process, offering potential clues for the diagnosis and treatment of oocyte-maturation-related and ovulation-related diseases.

Host factors: Implications in immunopathogenesis of COVID-19

Coronavirus disease 2019 (COVID-19) is a viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is more serious in people with underlying diseases, but the cause of healthy people with progressive disease is largely unknown. Host genetic factors such as ACE2 variants, IFITM-3, HLA, TMRSS2, and furin polymorphisms appear to be one of the agents involved in the progression of the COVID-19 and outcome of the disease. This review discusses the general characteristics of SARS-CoV-2, including viral features, receptors, cell entry, clinical findings, and the main human genetic factors that may contribute to the pathogenesis of COVID-19 and get the patients' situation more complex. Further knowledge in this context may help to find a way to prevent and treat this viral pneumonia.

MASP-1 and MASP-3 Bind Directly to Aspergillus fumigatus and Promote Complement Activation and Phagocytosis

Activation of the complement system is mediated by the interaction between pathogens and pattern recognition molecules (PRMs); mannose-binding lectin (MBL), ficolins, and collectin-10/-11 from the lectin pathway and C1q from the classical pathway. Lectin pathway activation specifically depends on proteases named MBL-associated serine proteases (MASPs) that are found in complexes with PRMs. In this study, we hypothesize that MASPs can recognize selected pathogens independently of PRMs. Using different clinical strains of opportunistic fungi, we have observed that MASPs directly recognize certain fungal pathogens in a way that can facilitate complement activation. Among these were Aspergillus fumigatus - a dangerous pathogen, especially for immunocompromised patients. In flow cytometry and fluorescence microscopy, we found that MASP-1 and -3 bound to all A. fumigatus growth stages (conidia, germ tubes, and hyphae), whereas rMASP-2 and the nonproteolytic rMAP-1 did not. Bound rMASPs could recruit rMBL and rficolin-3 to A. fumigatus conidia in a nonclassical manner and activate complement via rMASP-2. In experiments using recombinant and purified components, rMASP-1 increased the neutrophilic phagocytosis of conidia. In serum where known complement activation pathways were blocked, phagocytosis could be mediated by rMASP-3. We have encountered an unknown pathway for complement activation and found that MASP-1 and MASP-3 have dual functions as enzymes and as PRMs.

Lectin complement pathway initiators after subarachnoid hemorrhage - an observational study

Background

This exploratory study investigated the time-course of lectin complement pathway (LCP) initiators in cerebrospinal fluid (CSF) and plasma in patients with subarachnoid hemorrhage (SAH), as well as their relationship to delayed cerebral ischemia (DCI) and functional outcome.

Methods

Concentrations of ficolin-1, ficolin-2, ficolin-3, and mannose-binding lectin (MBL) were analyzed in CSF and plasma from patients with SAH. Samples were collected daily from admission until day 9 (CSF; N__PATIENTS = 63, n__SAMPLES = 399) and day 8 (plasma; N__PATIENTS = 50, n__SAMPLES = 358), respectively. Twelve neurologically healthy patients undergoing spinal anesthesia and 12 healthy blood donors served as controls. The development of DCI during hospitalization and functional outcome at 3 months (modified Rankin Scale) were registered for patients.

Results

On admission, CSF levels of all LCP initiators were increased in SAH patients compared with healthy controls. Levels declined gradually over days in patients; however, a biphasic course was observed for ficolin-1. Increased CSF levels of all LCP initiators were associated with a poor functional outcome in univariate analyses. This relationship persisted for ficolin-1 and MBL in multivariate analysis after adjustments for confounders (age, sex, clinical severity, distribution and amount of blood on CT-imaging) and multiple testing (1.87 ng/mL higher in average, 95% CI, 1.17 to 2.99 and 1.69 ng/mL higher in average, 95% CI, 1.09 to 2.63, respectively). In patients who developed DCI compared with those without DCI, CSF levels of ficolin-1 and MBL tended to increase slightly more over time (p_interaction = 0.021 and 0.033, respectively); however, no association was found after adjustments for confounders and multiple testing (p-adj_interaction = 0.086 and 0.098, respectively). Plasma ficolin-1 and ficolin-3 were lower in SAH patients compared with healthy controls on all days. DCI and functional outcome were not associated with LCP initiator levels in plasma.

Conclusion

Patients with SAH displayed elevated CSF levels of ficolin-1, ficolin-2, ficolin-3, and MBL. Increased CSF levels of ficolin-1 and MBL were associated with a poor functional outcome.

Trial registration

This study was a retrospective analysis of samples, which had been prospectively sampled and stored in a biobank. Registered at clinicaltrials.gov (NCT01791257, February 13, 2013, and NCT02320539, December 19, 2014).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-01979-y.

Association between serum ficolin-1 level and disease progression in primary biliary cholangitis

Pattern recognition molecules (PRMs) in the complement system contribute to homeostasis as mediators of complement activation. The contribution of PRMs to primary biliary cholangitis (PBC) is unknown. In the current study, we aimed to assess the association between PRMs and the clinical findings of PBC. A total of 122 PBC patients and 20 healthy controls were enrolled. We measured four different PRMs (mannose-binding lectin [MBL], ficolin-1, ficolin-2 and ficolin-3) using stored sera, and retrospectively analyzed the associations between PRMs and laboratory findings, histological findings, and the development of cirrhosis-related conditions. Ficolin-1 levels were significantly higher in the PBC patients than in the healthy controls (152 ng/mL vs 102 ng/mL, P = 0.034), but no significant differences were observed regarding MBL, ficolin-2, and ficolin-3 levels. Ficolin-1 was significantly correlated with alkaline phosphatase (ALP). Low ficolin-1 levels were significantly associated with the development of cirrhosis-related conditions independent for histological stage and ALP levels (hazard ratio: 0.933; 95% confidence interval: 0.875-0.994; P = 0.032). Patients with low levels of ficolin-1 (< 77 ng/mL) had a significantly increased rate of developing cirrhosis-related conditions. Low ficolin-1 levels were associated with disease progression independent of histological stage and ALP levels in patients with PBC.

Rationale for targeting complement in COVID-19

A novel coronavirus, SARS-CoV-2, has recently emerged in China and spread internationally, posing a health emergency to the global community. COVID-19 caused by SARS-CoV-2 is associated with an acute respiratory illness that varies from mild to the life-threatening acute respiratory distress syndrome (ARDS). The complement system is part of the innate immune arsenal against pathogens, in which many viruses can evade or employ to mediate cell entry. The immunopathology and acute lung injury orchestrated through the influx of pro-inflammatory macrophages and neutrophils can be directly activated by complement components to prime an overzealous cytokine storm. The manifestations of severe COVID-19 such as the ARDS, sepsis and multiorgan failure have an established relationship with activation of the complement cascade. We have collected evidence from all the current studies we are aware of on SARS-CoV-2 immunopathogenesis and the preceding literature on SARS-CoV-1 and MERS-CoV infection linking severe COVID-19 disease directly with dysfunction of the complement pathways. This information lends support for a therapeutic anti-inflammatory strategy against complement, where a number of clinically ready potential therapeutic agents are available.

Ficolin A derived from local macrophages and neutrophils protects against lipopolysaccharide-induced acute lung injury by activating complement

Ficolins are important and widely distributed pattern recognition molecules that can induce lectin complement pathway activation and initiate the innate immune response. Although ficolins can bind lipopolysaccharide (LPS) in vitro, the sources, dynamic changes and roles of local ficolins in LPS-induced pulmonary inflammation and injury remain poorly understood. In this study, we established a ficolin knockout mouse model by clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) technology, and used flow cytometry and hematoxylin and eosin staining to study the expressions and roles of local ficolins in LPS-induced pulmonary inflammation and injury. Our results show that besides ficolin B (FcnB), ficolin A (FcnA) is also expressed in leukocytes from the bone marrow, peripheral blood, lung and spleen. Further analyses showed that macrophages and neutrophils are the main sources of FcnA and FcnB, and T and B cells also express a small amount of FcnB. The intranasal administration of LPS induced local pulmonary inflammation with the increased recruitment of macrophages and neutrophils. LPS stimulation induced increased expression of FcnA and FcnB in neutrophils at the acute stage and in macrophages at the late stage. The severity of the lung injury and local inflammation of Fcna-/- mice was increased by the induction of extracellular complement activation. The recovery of LPS-induced local lung inflammation and injury was delayed in Fcnb-/- mice. Hence, these findings suggested that the local macrophage- and neutrophil-derived FcnA protects against LPS-induced acute lung injury by mediating extracellular complement activation.

Ficolin-1 is a promising therapeutic target for autoimmune diseases

Previously, we reported that mRNA expression of ficolin-1 (FCN1), a component of the complement lectin pathway, is elevated in peripheral blood mononuclear cells of patients with vasculitis syndrome, and that FCN1-positive cells infiltrate into inflamed regions in patient specimens. In addition, we reported that the serum FCN1 concentration is elevated in patients with Kawasaki disease (KD), a pediatric vasculitis, but dramatically decreases after intravenous immunoglobulin (IVIG) treatment. Furthermore, we showed that FCN1 binds to IgG1 in a pull-down assay. These results suggested that removal of FCN1 may be a therapeutic mechanism of IVIG. In this study, we prepared anti-FCN1 monoclonal antibody (mAb) and examined its therapeutic potential in mice treated with Candida albicans water-soluble fraction (CAWS), which induces KD-like vasculitis in the coronary artery. Indeed, treatment with anti-FCN1 mAb decreased the histological score of vasculitis (P = 0.03). To investigate the role of FCN1, we assessed blood samples of patients with various autoimmune diseases and demonstrated that serum levels of FCN1 were elevated not only in patients with vasculitis, but also in those with rheumatoid arthritis. Additionally, FCN1-targeted treatment of a mouse model of arthritis [collagen antibody-induced arthritis (CAIA)] revealed that administration of anti-FCN1 mAb ameliorated symptoms of arthritis (P < 0.01). These results suggest that FCN1 is involved in the pathogenesis of autoimmune diseases, and that targeting FCN1 represents a promising strategy for treating these diseases.

Dangerous liaisons: complement, coagulation, and kallikrein/kinin cross-talk act as a linchpin in the events leading to thromboinflammation

Innate immunity is fundamental to our defense against microorganisms. Physiologically, the intravascular innate immune system acts as a purging system that identifies and removes foreign substances leading to thromboinflammatory responses, tissue remodeling, and repair. It is also a key contributor to the adverse effects observed in many diseases and therapies involving biomaterials and therapeutic cells/organs. The intravascular innate immune system consists of the cascade systems of the blood (the complement, contact, coagulation, and fibrinolytic systems), the blood cells (polymorphonuclear cells, monocytes, platelets), and the endothelial cell lining of the vessels. Activation of the intravascular innate immune system in vivo leads to thromboinflammation that can be activated by several of the system's pathways and that initiates repair after tissue damage and leads to adverse reactions in several disorders and treatment modalities. In this review, we summarize the current knowledge in the field and discuss the obstacles that exist in order to study the cross-talk between the components of the intravascular innate immune system. These include the use of purified in vitro systems, animal models and various types of anticoagulants. In order to avoid some of these obstacles we have developed specialized human whole blood models that allow investigation of the cross-talk between the various cascade systems and the blood cells. We in particular stress that platelets are involved in these interactions and that the lectin pathway of the complement system is an emerging part of innate immunity that interacts with the contact/coagulation system. Understanding the resulting thromboinflammation will allow development of new therapeutic modalities.

Ficolins do not alter host immune responses to lipopolysaccharide-induced inflammation in vivo

Ficolins are a family of pattern recognition molecules that are capable of activating the lectin pathway of complement. A limited number of reports have demonstrated a protective role of ficolins in animal models of infection. In addition, an immune modulatory role of ficolins has been suggested. Yet, the contribution of ficolins to inflammatory disease processes remains elusive. To address this, we investigated ficolin deficient mice during a lipopolysaccharide (LPS)-induced model of systemic inflammation. Although murine serum ficolin was shown to bind LPS in vitro, there was no difference between wildtype and ficolin deficient mice in morbidity and mortality by LPS-induced inflammation. Moreover, there was no difference between wildtype and ficolin deficient mice in the inflammatory cytokine profiles after LPS challenge. These findings were substantiated by microarray analysis revealing an unaltered spleen transcriptome profile in ficolin deficient mice compared to wildtype mice. Collectively, results from this study demonstrate that ficolins are not involved in host response to LPS-induced systemic inflammation.

Complementary Roles of the Classical and Lectin Complement Pathways in the Defense against Aspergillus fumigatus

Aspergillus fumigatus infections are associated with a high mortality rate for immunocompromised patients. The complement system is considered to be important in protection against this fungus, yet the course of activation is unclear. The aim of this study was to unravel the role of the classical, lectin, and alternative pathways under both immunocompetent and immunocompromised conditions to provide a relevant dual-perspective on the response against A. fumigatus. Conidia (spores) from a clinical isolate of A. fumigatus were combined with various human serum types (including serum deficient of various complement components and serum from umbilical cord blood). We also combined this with inhibitors against C1q, mannose-binding lectin (MBL), and ficolin-2 before complement activation products and phagocytosis were detected by flow cytometry. Our results showed that alternative pathway amplified complement on A. fumigatus, but required classical and/or lectin pathway for initiation. In normal human serum, this initiation came primarily from the classical pathway. However, with a dysfunctional classical pathway (C1q-deficient serum), lectin pathway activated complement and mediated opsonophagocytosis through MBL. To model the antibody-decline in a compromised immune system, we used serum from normal umbilical cords and found MBL to be the key complement initiator. In another set of experiments, serum from patients with different kinds of immunoglobulin insufficiencies showed that the MBL lectin pathway contribution was highest in the samples with the lowest IgG/IgM binding. In conclusion, lectin pathway appears to be the primary route of complement activation in the absence of anti-A. fumigatus antibodies, whereas in a balanced immune state classical pathway is the main activator. This suggests a crucial role for the lectin pathway in innate immune protection against A. fumigatus in immunocompromised patients.

A journey through the lectin pathway of complement-MBL and beyond

Mannose-binding lectin (MBL), collectin-10, collectin-11, and the ficolins (ficolin-1, ficolin-2, and ficolin-3) are soluble pattern recognition molecules in the lectin complement pathway. These proteins act as mediators of host defense and participate in maintenance of tissue homeostasis. They bind to conserved pathogen-specific structures and altered self-antigens and form complexes with the pentraxins to modulate innate immune functions. All molecules exhibit distinct expression in different tissue compartments, but all are found to a varying degree in the circulation. A common feature of these molecules is their ability to interact with a set of serine proteases named MASPs (MASP-1, MASP-2, and MASP-3). MASP-1 and -2 trigger the activation of the lectin pathway and MASP-3 may be involved in the activation of the alternative pathway of complement. Furthermore, MASPs mediate processes related to coagulation, bradykinin release, and endothelial and platelet activation. Variant alleles affecting expression and structure of the proteins have been associated with a variety of infectious and non-infectious diseases, most commonly as disease modifiers. Notably, the severe 3MC (Malpuech, Michels, Mingarelli, and Carnevale) embryonic development syndrome originates from rare mutations affecting either collectin-11 or MASP-3, indicating a broader functionality of the complement system than previously anticipated. This review summarizes the characteristics of the molecules in the lectin pathway.

Cholesterol Crystals Activate the Lectin Complement Pathway via Ficolin-2 and Mannose-Binding Lectin: Implications for the Progression of Atherosclerosis

Cholesterol crystals (CC) play an essential role in the formation of atherosclerotic plaques. CC activate the classical and the alternative complement pathways, but the role of the lectin pathway is unknown. We hypothesized that the pattern recognition molecules (PRMs) from the lectin pathway bind CC and function as an upstream innate inflammatory signal in the pathophysiology of atherosclerosis. We investigated the binding of the PRMs mannose-binding lectin (MBL), ficolin-1, ficolin-2, and ficolin-3, the associated serine proteases, and complement activation products to CC in vitro using recombinant proteins, specific inhibitors, as well as deficient and normal sera. Additionally, we examined the deposition of ficolin-2 and MBL in human carotid plaques by immunohistochemistry and fluorescence microscopy. The results showed that the lectin pathway was activated on CC by binding of ficolin-2 and MBL in vitro, resulting in activation and deposition of complement activation products. MBL bound to CC in a calcium-dependent manner whereas ficolin-2 binding was calcium-independent. No binding was observed for ficolin-1 or ficolin-3. MBL and ficolin-2 were present in human carotid plaques, and binding of MBL to CC was confirmed in vivo by immunohistochemistry, showing localization of MBL around CC clefts. Moreover, we demonstrated that IgM, but not IgG, bound to CC in vitro and that C1q binding was facilitated by IgM. In conclusion, our study demonstrates that PRMs from the lectin pathway recognize CC and provides evidence for an important role for this pathway in the inflammatory response induced by CC in the pathophysiology of atherosclerosis.

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.

Early ficolin-1 is a sensitive prognostic marker for functional outcome in ischemic stroke

BACKGROUND

Several lines of evidence support the involvement of the lectin pathway of complement (LP) in the pathogenesis of acute ischemic stroke. The aim of this multicenter observational study was to assess the prognostic value of different circulating LP initiators in acute stroke.

METHODS

Plasma levels of the LP initiators ficolin-1, -2, and -3 and mannose-binding lectin (MBL) were measured in 80 stroke patients at 6 h only and in 85 patients at 48 h and later. Sixty-one age- and sex-matched healthy individuals served as controls. Stroke severity was measured on admission using the National Institutes of Health Stroke Scale (NIHSS). The outcome was measured at 90 days by the modified Rankin Scale (mRS).

RESULTS

Ficolin-1 was decreased in patients compared with controls measured at 6 h (median 0.13 vs 0.33 μg/ml, respectively, p < 0.0001). At 48 h, ficolin-1 was significantly higher (0.45 μg/ml, p < 0.0001) compared to the 6 h samples and to controls. Likewise, ficolin-2 was decreased at 6 h (2.70 vs 4.40 μg/ml, p < 0.0001) but not at 48 h. Ficolin-3 was decreased both at 6 and 48 h (17.3 and 18.23 vs 21.5 μg/ml, p < 0.001 and <0.05, respectively). For MBL no difference was detected between patients and controls or within patients at the different time points. In multivariate analysis, early ficolin-1 was independently associated with unfavorable mRS outcome (adjusted odds ratio (OR): 2.21, confidence interval (CI) 95 % 1.11-4.39, p = 0.023). Early ficolin-1 improved the discriminating ability of an outcome model including NIHSS and age (area under the curve (AUC) 0.95, CI 95 % 0.90-0.99, p = 0.0001).

CONCLUSIONS

The ficolins are consumed within 6 h after stroke implicating activation of the LP. Early ficolin-1 is selectively related to 3-month unfavorable outcome.

Studies of the binding of ficolin-2 and ficolin-3 from the complement lectin pathway to Leptospira biflexa, Pasteurella pneumotropica and Diarrheagenic Escherichia coli

Ficolins recognize pathogen associated molecular patterns and activate the lectin pathway of complement system. However, our knowledge regarding pathogen recognition of human ficolins is still limited. We therefore set out to explore and investigate the possible interactions of the two main serum ficolins, ficolin-2 and ficolin-3 with different Gram-negative bacteria. We used recombinant ficolin molecules and normal human serum, which were detected with anti-ficolin monoclonal antibodies. In addition we investigated the capacity of these pathogens to activate the lectin pathway of complement system. We show for the first time that human ficolin-2 recognizes the nonpathogenic spirochete Leptospira biflexa serovar Patoc, but not the pathogenic Leptospira interrogans serovar Kennewicki strain Fromm. Additionally, human ficolin-2 and ficolin-3 recognize pathogenic Pasteurella pneumotropica, enteropathogenic Escherichia coli (EPEC) serotype O111ab:H2 and enteroaggregative E. coli (EAEC) serogroup O71 but not four enterohemorrhagic E. coli, three EPEC, three EAEC and two nonpathogenic E. coli strains (DH5α and HB101). The lectin pathway was activated by Pasteurella pneumotropica, EPEC O111ab:H2 and EAEC O71 after incubation with C1q depleted human serum. In conclusion, this study provide novel insight in the binding and complement activating capacity of the lectin pathway initiation molecules ficolin-2 and ficolin-3 towards relevant Gram-negative pathogens of pathophysiological relevance.

New insights into the role of ficolins in the lectin pathway of innate immunity

In the innate immune system, a variety of recognition molecules provide the first-line host defense to prevent infection and maintain endogenous homeostasis. Ficolin is a soluble recognition molecule, which senses pathogen-associated molecular patterns on microbes and aberrant sugar structures on self-cells. It consists of a collagen-like stalk and a globular fibrinogen-like domain, the latter binding to carbohydrates such as N-acetylglucosamine. Ficolins have been widely identified in animals from higher invertebrates to mammals. In mammals, ficolins form complexes with mannose-binding lectin-associated serine proteases (MASPs), and ficolin-MASP complexes trigger complement activation via the lectin pathway. Once activated, complement mediates many immune responses including opsonization, phagocytosis, and cytokine production. Although the precise function of each ficolin is still under investigation, accumulating information suggests that ficolins have a crucial role in host defense by recognizing a variety of microorganisms and interacting with effector proteins.

The Lectin Pathway of Complement and Biocompatibility

In modern health technologies the use of biomaterials in the form of stents, haemodialysis tubes, artificial implants, bypass circuits etc. is rapidly expanding. The exposure of synthetic, foreign surfaces to the blood and tissue of the host, calls for strict biocompatibility in respect to contact activation, the coagulation system and the complement system. The complement system is an important part of the initial immune response and consists of fluid phase molecules in the blood stream. Three different activation pathways can initiate the complement system, the lectin, the classical and the alternative pathway, all converging in an amplification loop of the cascade system and downstream reactions. Thus, when exposed to foreign substances complement components will be activated and lead to a powerful inflammatory response. Biosurface induced complement activation is a recognised issue that has been broadly documented. However, the specific role of lectin pathway and the pattern recognition molecules initiating the pathway has only been transiently investigated. Here we review the current data on the field.

Interaction of lectin pathway of complement-activating pattern recognition molecules with mycobacteria

We have demonstrated that mannose-binding lectin (MBL) recognizes various slow-growing, pathogenic mycobacteria [Mycobacterium tuberculosis (MTB), M. bovis, M. kansasii, M. gordonae] as well as non-pathogenic M. smegmatis. Recognition resulted in activation of the lectin pathway (LP) of complement and an enhancement of phagocytosis (shown for M. tuberculosis). Although MBL may be considered the main factor activating the LP upon recognition of mycobacteria, involvement of ficolins has also to be considered. Interaction of ficolin-3 with M. tuberculosis, M. bovis and M. kansasii, and ficolin-1 with M. tuberculosis and M. bovis was shown for the first time. Binding of recombinant MBL or ficolin-3 to MTB H37 Rv led to the agglutination of bacteria and promoted their phagocytosis, but little effect was apparent with ficolin-1 or ficolin-2. Data from Western blots suggest mannosylated lipoarabinomannan (ManLAM) to be one of the main cell components of slow-growing mycobacteria, involved in LP activation. However, the LP was also activated by other cell fractions. Results presented here supplement considerably the data concerning the ability of complement-activating lectins to interact with mycobacteria. Ficolins (especially ficolin-3) might influence host response to infection and thus have clinical significance, at least as disease modifiers.

Lessons learned from mice deficient in lectin complement pathway molecules

The lectin pathway of the complement system is initiated when the pattern-recognition molecules, mannose-binding lectin (MBL), ficolins or collectin-11, bind to invading pathogens or damaged host cells. This leads to activation of MBL/ficolin/collectin-11 associated serine proteases (MASPs), which in turn activate downstream complement components, ultimately leading to elimination of the pathogen. Mice deficient in the key molecules of lectin pathway of complement have been generated in order to build knowledge of the molecular mechanisms of the lectin pathway in health and disease. Despite differences in the genetic arrangements of murine and human orthologues of lectin pathway molecules, the knockout mice have proven to be valuable models to explore the effect of deficiency states in humans. In addition, new insight and unexpected findings on the diverse roles of lectin pathway molecules in complement activation, pathogen infection, coagulation, host tissue injury and developmental biology have been revealed by in vivo investigations. This review provides an overview of the mice deficient in lectin pathway molecules and highlights some of the most important findings that have resulted from studies of these.

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.

Purification, measurement of concentration, and functional complement assay of human ficolins

Ficolins constitute a group of lectins involved in innate immunity. L-Ficolin, H-ficolin, and M-ficolin are present in human serum. The human ficolins differ in carbohydrate-binding specificity, but they have in common the ability to recognize the acetyl group. L-Ficolin and H-ficolin are associated with serine proteases termed MASPs (MBL-associated serine proteases) and their truncated proteins, and the complexes (L/H-ficolin-MASP) activate the lectin pathway of complement upon binding to their ligands. Recombinant M-ficolin is also able to form a complex with MASP, resulting in complement activation. L-Ficolin and H-ficolin can be purified as a complex with MASP from serum by utilizing their binding specificities. These ficolin-MASP complexes have an ability to activate C4. Human ficolins are quantified by ELISA using specific antibodies or ligands.

Blood collection tubes influence serum ficolin-1 and ficolin-2 levels

The ficolins are members of a recently discovered family of host innate opsonins that can activate the lectin pathway of complement. The ficolins bind many ligands, although they are typically described as binding acetylated sugars. Ficolin-1 (M-ficolin) and ficolin-2 (L-ficolin) are known to bind Streptococcus pneumoniae serotypes 19C and 11A, respectively. While studying the binding of ficolins to pneumococci, we found variations in ficolin-2 binding among serum samples collected in different types of blood collection tubes. Plastic tubes, which contain a silica clot activator, yielded sera with reduced ficolin-2 binding and apparent ficolin-2 levels. We found that the silica clot activator eluted from plastic red-top tubes inhibited ficolin-2 ligand binding, while other related proteins, like mannose-binding lectin (MBL) and ficolin-1, were not affected. These tube types did not affect the concentrations of other related opsonins (C1q, MBL, or ficolin-3 [H-ficolin]). Interestingly, we also found that ficolin-1 levels were increased 2- to 3-fold in plastic serum separator tubes compared to the increases in other tube types. These findings have implications for future ficolin-1 and ficolin-2 studies, as proper sample collection and handling are essential.

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.

Immature mouse granulocytic myeloid cells are characterized by production of ficolin-B

Ficolins activate the lectin pathway of the complement system upon binding to carbohydrate patterns on pathogens. To characterize the producer cells of ficolin-B the expression of mouse ficolin-B, the orthologue of human M-ficolin, was studied in macrophages and dendritic cells during differentiation from bone marrow cells, in primary granulocytes, and during differentiation of granulocytes derived from ER-Hoxb8 cells. Expression of ficolin-B mRNA declined in all myeloid cell types to low levels during terminal differentiation. However, in contrast to macrophages and dendritic cells, ficolin-B expression was enhanced upon activation in granulocytes. High expression of ficolin-B was observed in primary immature neutrophilic CD11b(+) Ly-6C(int) Ly-6G(high) granulocytes when isolated from the bone marrow, in particular during sepsis. Ficolin-B was demonstrated in lysates of primary granulocytes, ER-Hoxb8-derived granulocytes, bone marrow-derived macrophages, and dendritic cells. Native ficolin-B from cell lysates and supernatants of granulocytes activated the lectin pathway as measured by binding to MASP-2 and inducing C4 deposition. Specific staining demonstrated intra-cellular or cell associated ficolin-B protein in activated immature granulocytes deposited in a granular fashion. This study shows that ficolin-B is stored in and set free from immature granulocytic myeloid cells indicating a role in the early infection-induced cellular response of these inflammatory cells.

Ficolin-1-PTX3 complex formation promotes clearance of altered self-cells and modulates IL-8 production

The long pentraxin 3 (PTX3) has been shown to be important in maintaining internal tissue homeostasis and in protecting against fungal Aspergillus fumigatus infection. However, the molecular mechanisms of how these functions are elicited are poorly delineated. Ficolin-1 is a soluble pattern recognition molecule that interacts with PTX3. We hypothesized that heterocomplexes between ficolin-1 and PTX3 might mediate the signals necessary for sequestration of altered self-cells and A. fumigatus. We were able to show that ficolin-1 interacts with PTX3 via its fibrinogen-like domain. The interaction was affected in a pH- and divalent cation-sensitive manner. The primary binding site for ficolin-1 on PTX3 was located in the N-terminal domain portion of PTX3. Ficolin-1 and PTX3 heterocomplex formation occurred on dying host cells, but not on A. fumigatus. The heterocomplex formation was a prerequisite for enhancement of phagocytosis by human monocyte-derived macrophages and downregulation of IL-8 production during phagocytosis. On A. fumigatus, PTX3 exposed the C-terminal portion of the molecule, probably resulting in steric hindrance of ficolin-1 interaction with PTX3. These results demonstrate that ficolin-1 and PTX3 heterocomplex formation acts as a noninflammatory "find me and eat me" signal to sequester altered-host cells. The fact that the ficolin-1-PTX3 complex formation did not occur on A. fumigatus shows that PTX3 uses different molecular effector mechanisms, depending on which domains it exposes during ligand interaction.

Ficolins in complement activation

Ficolins are a group of multimeric lectins made up of single subunits each of which is composed of a collagen-like domain and a fibrinogen-like domain. Most of the ficolins identified to date bind to acetylated compounds such as N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc). Ficolins in serum are complexed with MBL-associated serine proteases (MASPs) and their truncated proteins. These lectins play an important role in innate immunity. Binding of the ficolin-MASP complex to carbohydrates present on the surface of microbes initiates complement activation via the lectin pathway.

Structural and functional overview of the lectin complement pathway: its molecular basis and physiological implication

The complement system is an effector mechanism in immunity. It is activated in three ways, the classical, alternative and lectin pathways. The lectin pathway is initiated by the binding of mannose-binding lectin (MBL) or ficolins to carbohydrates on the surfaces of pathogens. In humans, MBL and three types of ficolins (L-ficolin, H-ficolin, and M-ficolin) are present in plasma. Of these lectins, at least, MBL, L-ficolin, and H-ficolin are complexed with three types of MBL-associated serine proteases (MASPs), MASP-1, MASP-2, and MASP-3 and their truncated proteins (MAp44 and sMAP). In the lectin pathway, the lectin-MASP complex (i.e., a complex of lectin, MASPs and their truncated proteins) binds to pathogens, resulting in the activation of C4 and C2 to generate a C3 convertase capable of activating C3. MASP-2 is involved in the activation of C4 and C2. MASP-1 activates C2 and MASP-2. The functions of MASP-3, sMAP, and MAp44 in the lectin pathway remain unknown. MASP-1 and MASP-3 also have a role in the alternative pathway. MBL and ficolins are able to bind to a variety of pathogens depending on their carbohydrate binding specificity, resulting in the activation of the lectin pathway. Deficiencies of the components of the lectin pathway are associated to susceptibility to infection, indicating an important role of the lectin pathway in innate immunity. The lectin-MASP complex is also involved in innate immunity by activating the coagulation system. Recent findings suggest a crucial role of MASP-3 in development.

Mouse mannose-binding lectin-A and ficolin-A inhibit lipopolysaccharide-mediated pro-inflammatory responses on mast cells

It is unknown how soluble pattern-recognition receptors in blood, such as mannose-binding lectin (MBL) and ficolins, modulate mast cell-mediated inflammatory responses. We investigate how mouse MBL-A or ficolin-A regulate mouse bone marrow-derived mast cells (mBMMCs)-derived inflammatory response against bacterial lipopolysaccharide (LPS) stimulation. LPS-mediated pro-inflammatory cytokine productions on mBMMCs obtained from Toll-like receptor4 (TLR4)-deficient mice, TLR2-defficient mice, and their wildtype, were specifically attenuated by the addition of either mouse MBL-A or ficolin-A in a dose-dependent manner. However, the inhibitory effects by mouse MBL-A or ficolin-A were restored by the addition of mannose or N-acetylglucosamine, respectively. These results suggest that mouse MBL-A and ficolin-A bind to LPS via its carbohydrate-recognition domain and fibrinogen-like domain, respectively, whereby cytokine production by LPS-mediated TLR4 in mBMMCs appears to be down-regulated, indicating that mouse MBL and ficolin may have an inhibitory function toward mouse TLR4-mediated excessive inflammation on the mast cells.

Upregulation of genes for C-reactive protein and related pentraxin/complement proteins in photodynamic therapy-treated human tumor cells: enrolment of PI3K/Akt and AP-1

Treatment of mouse tumors by photodynamic therapy (PDT) was reported to trigger the production of serum amyloid P component (SAP), a prototypic acute phase reactant in the mouse, that occurs in the targeted tumor as well as distant sites dominated by host's liver. It was also shown that the SAP gene becomes upregulated and protein produced in mouse tumor cells treated by PDT in vitro. Present study revealed that, in addition to SAP, increased expression of genes encoding related pentraxin and complement proteins, including PTX3, C1q and ficolin B, can be found in mouse LLC tumor cells treated by PDT. Since in humans C-reactive protein (CRP) is more important acute phase reactant than SAP, the expression of gene encoding this pentraxin protein was examined in human lung tumor A549 cells treated by PDT. The results demonstrated a PDT dose-dependent upregulation of CRP gene, as well as of PTX3 and ficolin 1 genes in these cells. Investigation into the signal transduction process underlying PDT-induced human CRP gene upregulation using specific inhibitors of critical signaling elements revealed critical role played by PI3K/Akt pathway. Downstream DNA transcription factor largely responsible for this increased CRP gene expression is AP-1 with possible cooperation of HIF-1. It was suggested that cells sensing to have sustained a mortal injury from PDT can turn on molecular programs ensuring that the disposal of their corpses (facilitated by CRP and related pentraxin and complement components) is swift and efficient.

The role of fibrinogen, fibrin and fibrin(ogen) degradation products (FDPs) in tumor progression

Participation of fibrin, fibrinogen, and their degradation products in pathogenesis and progression of cancer may lead to complications of thromboembolic events. The tumor may be a source of fibrinogen. Fibrinogen inside the tumor is one of the factors of its growth and metastasis. Fibrinogen, fibrin and their degradation products possess proinflammatory activity. They indirectly stimulate endothelium to secrete von Willebrand factor, leading to activation of platelets accompanying neoplastic disorders. Fragments E and D are the end products of fibrin(ogen) degradation and E and DD are the end products of stabilized fibrin. E stimulates proliferation, migration and differentiation of endothelial cells, contributing to tumor vasculature. Increased levels of DD are observed in malignant neoplasms, such as breast, lung, colon and ovary cancers. In breast cancers DD correlates with progression of disease and metastasis. The role of fibrinogen and the products of its degradation in the progression of various tumors is not sufficiently understood.

Association of ficolin-3 with severity and outcome of chronic heart failure

BACKGROUND

Inflammatory mechanisms involving complement activation has been shown to take part in the pathophysiology of congestive heart failure, but the initiating mechanisms are unknown. We hypothesized that the main initiator molecules of the lectin complement pathway mannose-binding lectin (MBL), ficolin-2 and ficolin-3 were related to disease severity and outcome in chronic heart failure.

METHODS AND RESULTS

MBL, ficolin-2 and ficolin-3 plasma concentrations were determined in two consecutive cohorts comprising 190 patients from Hungary and 183 patients from Norway as well as controls. Disease severity and clinical parameters were determined at baseline, and all-cause mortality was registered after 5-years follow-up. In univariate analysis a low level of ficolin-3, but not that of MBL or ficolin-2, was significantly associated with advanced heart failure (New York Heart Association Class IV, p<0.001 for both cohorts) and showed inverse correlation with B- type natriuretic peptide (BNP) levels (r = -0.609, p<0.001 and r = -0.467, p<0.001, respectively). In multivariable Cox regression analysis, adjusted for age, gender and BNP, decreased plasma ficolin-3 was a significant predictor of mortality (HR 1.368, 95% CI 1.052-6.210; and HR 1.426, 95% CI 1.013-2.008, respectively). Low ficolin-3 levels were associated with increased complement activation product C3a and correspondingly decreased concentrations of complement factor C3.

CONCLUSIONS

This study provides evidence for an association of low ficolin-3 levels with advanced heart failure. Concordant results from two cohorts show that low levels of ficolin-3 are associated with advanced heart failure and outcome. The decrease of ficolin-3 was associated with increased complement activation.

The emerging role of complement lectin pathway in trypanosomatids: molecular bases in activation, genetic deficiencies, susceptibility to infection, and complement system-based therapeutics

The innate immune system is evolutionary and ancient and is the pivotal line of the host defense system to protect against invading pathogens and abnormal self-derived components. Cellular and molecular components are involved in recognition and effector mechanisms for a successful innate immune response. The complement lectin pathway (CLP) was discovered in 1990. These new components at the complement world are very efficient. Mannan-binding lectin (MBL) and ficolin not only recognize many molecular patterns of pathogens rapidly to activate complement but also display several strategies to evade innate immunity. Many studies have shown a relation between the deficit of complement factors and susceptibility to infection. The recently discovered CLP was shown to be important in host defense against protozoan microbes. Although the recognition of pathogen-associated molecular patterns by MBL and Ficolins reveal efficient complement activations, an increase in deficiency of complement factors and diversity of parasite strategies of immune evasion demonstrate the unsuccessful effort to control the infection. In the present paper, we will discuss basic aspects of complement activation, the structure of the lectin pathway components, genetic deficiency of complement factors, and new therapeutic opportunities to target the complement system to control infection.

Modulation of cytokine release and gene expression by the immunosuppressive domain of gp41 of HIV-1

The transmembrane envelope protein gp41 of the human immunodeficiency virus HIV-1 plays an important role during infection allowing fusion of the viral and cellular membrane. In addition, there is increasing evidence that gp41 may contribute to the immunodeficiency induced by HIV-1. Recombinant gp41 and a synthetic peptide corresponding to a highly conserved domain in gp41, the immunosuppressive (isu) domain, have been shown to inhibit mitogen-induced activation of human peripheral blood mononuclear cells (PBMCs) and to increase release of IL-6 and IL-10 from these cells. We recently reported that a single mutation in the isu domain of gp41 abrogated the immunosuppressive properties and that HIV-1 sequences containing such abrogating mutations had never been isolated from infected individuals. Here, we studied the influence of the isu peptide on the release of 66 cytokines and the expression of 27,000 genes in PBMCs. Incubation of PBMCs with isu peptide homopolymers increased the expression of 16 cytokines among them IL-6 and IL-10, and decreased that of IL-2 and CXCL9. Interestingly, the extend of cytokine modulation was donor-dependent. Among the genes up-regulated were IL-6, IL-8, IL-10 but also MMP-1, TREM-1 and IL-1beta. Most importantly, genes involved in innate immunity such as FCN1 and SEPP1 were found down-regulated. Many changes in cytokine expression demonstrated in our experiments were also found in HIV-1 infected individuals. These data indicate that the isu domain of gp41 has a broad impact on gene expression and cytokine release and therefore may be involved in HIV-1 induced immunopathogenesis.

Susceptibility to leprosy is associated with M-ficolin polymorphisms

PURPOSE

Mycobacterium leprae exploits complement activation and opsonophagocytosis to infect phagocytes. M-ficolin is encoded by the FCN1 gene and initiates the lectin pathway on monocyte surfaces. We investigated FCN1 promoter polymorphisms that could be responsible for the high interindividual variability of M-ficolin levels and for modulating leprosy susceptibility.

METHODS

We genotyped rs2989727 (-1981 G > A), rs28909068 (-791 G > A), rs10120023 (-542 G > A), rs17039495 (-399 G > A), rs28909976 (-271IndelT), rs10117466 (-144C > A) and rs10858293 (+33 T > G) in 400 controls and 315 leprosy patients from Southern Brazil, and in 296 Danish healthy individuals with known M-ficolin levels.

RESULTS

Ten haplotypes were identified with sequence-specific PCR and/or haplotype-specific sequencing. We found evidence for a protective codominant additive effect of FCN1*-542A-144C with leprosy in Euro-Brazilians (P=0.003, PBf =0.021, OR=0.243 [CI95% =0.083-0.71]), which was independent of age, ethnic group and gender effects (P=0.029). There was a trend for a positive association of the -399A variant in Afro-Brazilians (P=0.022, PBf =0.154, OR=4.151 [CI95% =1.115-15.454], as well as for a negative association of the FCN1*3A haplotype with lepromatous leprosy, compared with less severe forms of the disease (P=0.016, PBf =0.112, OR=0.324 [CI95% =0.123-0.858]). Danish individuals with this haplotype presented M-ficolin levels higher than the population average of circa 1,000 ng/ml, and -542A-144C, which is able to modify the recognition of transcription factors in silico, occurred in individuals with levels under the 25 percentil (P=0.031).

CONCLUSIONS

Our data provide the first evidence that FCN1 polymorphisms are associated with leprosy. M-ficolin may represent a novel key to understand the immunopathogenesis of M. leprae infection.

Mice deficient in ficolin, a lectin complement pathway recognition molecule, are susceptible to Streptococcus pneumoniae infection

Mannose-binding lectin (MBL) and ficolin are complexed with MBL-associated serine proteases, key enzymes of complement activation via the lectin pathway, and act as soluble pattern recognition molecules in the innate immune system. Although numerous reports have revealed the importance of MBL in infectious diseases and autoimmune disorders, the role of ficolin is still unclear. To define the specific role of ficolin in vivo, we generated model mice deficient in ficolins. The ficolin A (FcnA)-deficient (Fcna(-/-)) and FcnA/ficolin B double-deficient (Fcna(-/-)b(-/-)) mice lacked FcnA-mediated complement activation in the sera, because of the absence of complexes comprising FcnA and MBL-associated serine proteases. When the host defense was evaluated by transnasal infection with a Streptococcus pneumoniae strain, which was recognized by ficolins, but not by MBLs, the survival rate was significantly reduced in all three ficolin-deficient (Fcna(-/-), Fcnb(-/-), and Fcna(-/-)b(-/-)) mice compared with wild-type mice. Reconstitution of the FcnA-mediated lectin pathway in vivo improved survival rate in Fcna(-/-) but not in Fcna(-/-)b(-/-) mice, suggesting that both FcnA and ficolin B are essential in defense against S. pneumoniae. These results suggest that ficolins play a crucial role in innate immunity against pneumococcal infection through the lectin complement pathway.

Non-synonymous polymorphisms in the FCN1 gene determine ligand-binding ability and serum levels of M-ficolin

BACKGROUND

The innate immune system encompasses various recognition molecules able to sense both exogenous and endogenous danger signals arising from pathogens or damaged host cells. One such pattern-recognition molecule is M-ficolin, which is capable of activating the complement system through the lectin pathway. The lectin pathway is multifaceted with activities spanning from complement activation to coagulation, autoimmunity, ischemia-reperfusion injury and embryogenesis. Our aim was to explore associations between SNPs in FCN1, encoding M-ficolin and corresponding protein concentrations, and the impact of non-synonymous SNPs on protein function.

PRINCIPAL FINDINGS

We genotyped 26 polymorphisms in the FCN1 gene and found 8 of these to be associated with M-ficolin levels in a cohort of 346 blood donors. Four of those polymorphisms were located in the promoter region and exon 1 and were in high linkage disequilibrium (r(2)≥0.91). The most significant of those were the AA genotype of -144C>A (rs10117466), which was associated with an increase in M-ficolin concentration of 26% compared to the CC genotype. We created recombinant proteins corresponding to the five non-synonymous mutations encountered and found that the Ser268Pro (rs150625869) mutation lead to loss of M-ficolin production. This was backed up by clinical observations, indicating that an individual homozygote of Ser268Pro would be completely M-ficolin deficient. Furthermore, the Ala218Thr (rs148649884) and Asn289Ser (rs138055828) were both associated with low M-ficolin levels, and the mutations crippled the ligand-binding capability of the recombinant M-ficolin, as indicated by the low binding to Group B Streptococcus.

SIGNIFICANCE

Overall, our study interlinks the genotype and phenotype relationship concerning polymorphisms in FCN1 and corresponding concentrations and biological functions of M-ficolin. The elucidations of these associations provide information for future genetic studies in the lectin pathway and complement system.

Variation in FCN1 affects biosynthesis of ficolin-1 and is associated with outcome of systemic inflammation

Ficolin-1 is a recognition molecule of the lectin complement pathway. The ficolin-1 gene FCN1 is polymorphic, but the functional and clinical consequences are unknown.The concentration of ficolin-1 in plasma and FCN1 polymorphisms in positions -1981 (rs2989727), -791 (rs28909068), -542 (rs10120023), -271 (rs28909976), -144 (rs10117466) and +7918 (rs1071583) were determined in 100 healthy individuals. FCN1 expression by isolated monocytes and granulocytes and ficolin-1 levels in monocyte culture supernatants were assessed in 21 FCN1-genotyped individuals. FCN1 polymorphisms were determined in a cohort of 251 patients with systemic inflammation. High ficolin-1 plasma levels were significantly associated with the minor alleles in position -542 and -144. These alleles were also significantly associated with high FCN1 mRNA expression. The level of ficolin-1 in culture supernatants was significantly higher in individuals homozygous for the minor alleles at positions -542 and -144. Homozygosity for these alleles was significantly associated with fatal outcome in patients with systemic inflammation. None of the other investigated polymorphisms were associated with FCN1 and ficolin-1 expression, concentration or disease outcome. Functional polymorphic sites in the promoter region of FCN1 regulate both the expression and synthesis of ficolin-1 and are associated with outcome in severe inflammation.