Ficolin-3 activity towards the opportunistic pathogen, Hafnia alvei

Ficolin-3 and MASP-2 gene variants in Siberian arctic populations: Summarized evidence of selective pressure for the high frequency of lectin complement pathway deficiency

Herewith, we provide novel original data about the prevalence of FCN3 rs532781899 and MASP2 rs72550870 variants among the newborns of aboriginal Siberian Arctic populations (Nenets and Dolgan-Nganasans) and Russians of East Siberia. This novel data has been analysed along with the genetic data about other proteins of the lectin pathway of the complement system (mannose-binding lectin and ficolin-2) obtained earlier. A total of 926 specimens of dried blood spots of the newborns were genotyped. The newborns represented four populations: Nenets, Dolgan-Nganasans, Mixed aboriginal population, and Russians (Caucasians) to study the prevalence of single nucleotide polymorphisms of FCN3 rs532781899 and MASP2 rs72550870. The prevalence of the deletion allele of the rs532781899 variant in the FCN3 gene associated with the decreased production of ficolin-3 was found to be increased in Russians compared to the Nenets aboriginal populations (P = .002). The prevalence of the rs72550870*G allele in the MASP2 gene associated with low serum protease activity was found to be increased in Russians compared with Nenets and Dolgan-Nganasans (P < .001 and P = .03, respectively). The results of the current study and our previous findings corroborate with a hypothesis that human evolution has been directed toward the accumulation of genotypes associated with low activity of the lectin complement activation pathway.

Proteins of the lectin pathway of the complement system activation: immunobiological functions, genetics and involvement in the pathogenesis of human diseases

The complement system is the most ancient components in the innate immunity, mainly functioning to primarily eliminate bacterial agents intravascularly. Moreover, the complement complex proteins play a role as a bridge between the systems of innate and adaptive immunity providing adequate conditions for maturation and differentiation of B- and T-lymphocytes. The complement system consists of plasma proteins and membrane receptors. Plasma proteins interact with each other via the three described cascade pathways lectin (which is most ancient phylogenetically), alternative and classical. Lectins are proteins comprising a separate superfamily of pattern-recognizing receptors able to sense molecules of oligo- and polysaccharide nature and induce their aggregation. Among all the lectins, ficolins (FCN) (common domain fibrinogen) and collectins (common domain collagen) mannose-binding lectin (MBL), hepatic and renal collectins have exert unique functions by complexing with carbohydrate components of microbial wall. Formation of a compound complex microbial wall polysaccharides + collectin/ficolin + specific mannose-binding lectin-associated serine proteases (MARP) results in the complement system activation, inflammatory reaction and bacterium elimination. Such scenario is proceeded along the lectin pathway compared to the two other pathways called classical and alternative. Examining a role of the complement system and congenital protein defects in the pathogenesis of various diseases is of topical interest because inborn deficiency of the complement components comprises at least 5% out of total primary immunodeficiency rate, whereas the aspects of their prevalence and pathogenesis remain unexplored. Relevance of investigating the complement system components for diverse populations is tremendous, taking into consideration accumulated evidence regarding an important role of the lectin pathway in viral infections. Lectins, the main proteins in the lectin pathway of the complement activation, are encoded by polymorphic genes, wherein single nucleotide polymorphisms (SNPs) result in altered protein conformation and expression, which, in turn, affects functionality and potential to respond to a pathogen. The distribution of the lectin polymorphic gene frequencies and their haplotypes displays extremely marked population differences. According to analyzing available data, population SNP frequencies including those associated with inborn deficiencies for components of the lectin pathway have been currently scarce or unexplored. hence, here we review major lectins and their functions, their functionally significant SNPs in diverse populations and their pathogenetic importance for host defense functions.

Prevalence of the polymorphic H-ficolin (FCN3) genes and mannosebinding lectin-associated serine protease-2 (MASP2) in indigenous populations from the Russian Arctic regions

Lectins, being the main proteins of the lectin pathway activating the complement system, are encoded by polymorphic genes, wherein point mutations cause the protein conformation and expression to change, which turns out to have an effect on the functionality and ability to respond to the pathogen. In the current study, largescale data on the population genotype distribution of the genes for H-ficolin FCN3 rs28357092 and mannose-binding lectin-associated serine protease MASP2 rs72550870 among the indigenous peoples of the Russian Arctic regions (Nenets, Dolgans and Nganasans, a mixed population and Russians: a total sample was about 1000 newborns) have been obtained for the first time. Genotyping was carried out using RT-PCR. The frequency of the homozygous variant del/del FCN3 rs28357092 associated with the total absence of the most powerful activator of the lectin complement pathway, N-ficolin, was revealed; 0 % in the Nenets, 0.8 % in the Dolgans and Nganasans, and 3.5 % among the Russians ( p < 0.01). Analysis of the prevalence of the MASP2 genotypes has shown the predominance of the homozygous variant AA in all studied populations, which agrees with the available world data. The heterozygous genotype AG rs72550870 associated with a reduced level of protease was found to occur rarely in the Nenets, Dolgans and Nganasans compared to newborns of Caucasoid origin from Krasnoyarsk: 0.5 % versus 3.3 %, respectively. Moreover, among 323 examined Nenets, one AG carrier was identified, whereas in Russians, 16 out of 242 examined newborns were found to be AG carriers ( p < 0.001). A homozygous variant (GG) in total absence of protease with impaired binding of both MBL and ficolins was not detected in any of the 980 examined newborns. An additional analysis of infectious morbidity in Arctic populations allows one to find phenotypic characteristics related to a high functional activity of the lectin pathway of complement activation as an most important factor for the first-line of anti-infectious defense, including such new viral diseases as COVID-19.

ITIH4 acts as a protease inhibitor by a novel inhibitory mechanism

Inter-α-inhibitor heavy chain 4 (ITIH4) is a poorly characterized plasma protein that is proteolytically processed in multiple pathological conditions. However, no biological function of ITIH4 has been identified. Here, we show that ITIH4 is cleaved by several human proteases within a protease-susceptible region, enabling ITIH4 to function as a protease inhibitor. This is exemplified by its inhibition of mannan-binding lectin-associated serine protease-1 (MASP-1), MASP-2, and plasma kallikrein, which are key proteases for intravascular host defense. Mechanistically, ITIH4 acts as bait that, upon cleavage, forms a noncovalent, inhibitory complex with the executing protease that depends on the ITIH4 von Willebrand factor A domain. ITIH4 inhibits the MASPs by sterically preventing larger protein substrates from accessing their active sites, which remain accessible and fully functional toward small substrates. Thus, we demonstrate that ITIH4 functions as a protease inhibitor by a previously undescribed inhibitory mechanism.

Time course analysis of immunity-related gene expression in the sea cucumber Apostichopus japonicus during exposure to thermal and hypoxic stress

Temperature and dissolved oxygen concentration are important abiotic factors that can limit the growth and survival of sea cucumbers by affecting their immune systems. As global warming intensifies, sea cucumbers are increasingly exposed to adverse environmental conditions, which can cause severe economic losses and limit the sustainable development of sea cucumber aquaculture. It is therefore important to better understand how sea cucumbers respond to environmental stress, especially with regard to its effects on immunity. In the present study, the time series of immunity-related gene expression in sea cucumbers under thermal and hypoxic stresses were analyzed separately. The expression trends of 17 genes related to the nuclear factor κB (NF-κB) pathway, the protease family, the complement system, heat shock proteins (HSPs) and the transferrin family during exposure to two stresses at eight time points were concluded. These genes have interconnected roles in stress defense. The expression levels of genes relating to the NF-κB pathways and HSPs were strongly affected in the sea cucumber thermal stress response, while melanotransferrin (Mtf), ferritin (Ft) and mannan-binding C-type lectin (MBCL) were affected by hypoxia. In contrast, complement factor B (Bf), myosin V (Mys) and serine protease inhibitor (SPI) were not that sensitive during the initial period of environmental stress. Similar expression patterns under both thermal and hypoxic stress for certain genes, including an increase in Hsp90 and decreases in lysozyme (Lys), major yolk protein (MYP) and cathepsin C (CTLC) were observed in sea cucumbers. Conversely, NF-κB and Hsp70 were differentially affected by the two stress treatments. Lysozyme-induced immune defense was inconstant in sea cucumbers coping with stress. A gene ontology (GO) analysis of the selected genes revealed that the most co-involved terms related to immunity and iron ion. Our analysis suggests that sea cucumbers demonstrate complex and varied immune responses to different types of stresses. This dynamic image of the immune responses and stress tolerance of sea cucumbers provides new insights into the adaptive strategies of holothurians in adverse environments.

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

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

Factors involved in initiation and regulation of complement lectin pathway influence postoperative outcome after pediatric cardiac surgery involving cardiopulmonary bypass

Congenital heart disease (CHD) often requires surgical intervention, and is sometimes associated with life-threatening post-operative complications. We have investigated some factors of the innate immune system involved in the initiation or regulation of complement lectin pathway activation (MASP-1, MASP-2 MASP-3, MAp19, MAp44, ficolin-3) and related them to complications and prognosis in 190 pediatric patients undergoing CHD repair with the use of cardiopulmonary bypass (CPB). Patients with MAp44 levels ≤1.81 µg/ml more frequently experienced low cardiac output syndrome (LCOS), renal insufficiency, systemic inflammatory response syndrome (SIRS) and multiorgan dysfunction (MODS). Low MASP-3 (≤5.18 µg/ml) and high MASP-1 (≥11.7 µg/ml) levels were often associated with fatal outcome. Low ficolin-3 concentrations (≤10.1 µg/ml) were more common among patients experiencing SIRS and MODS than in those without complications. However, patients suffering from SIRS and MODS with low ficolin-3 had a much better prognosis (91% survival vs. 37% among other patients; p = 0.007). A discriminating value of 12.7 µg/ml ficolin-3 yielded 8% vs. 60% mortality (p = 0.001). Our data extend the knowledge concerning involvement of proteins of the lectin pathway in development of post-CPB complications. The potential prognostic value of low preoperative MAp44 and high preoperative ficolin-3 seems promising and warrants independent confirmation.

Ficolins and the Recognition of Pathogenic Microorganisms: An Overview of the Innate Immune Response and Contribution of Single Nucleotide Polymorphisms

Ficolins are innate pattern recognition receptors (PRR) and play integral roles within the innate immune response to numerous pathogens throughout the circulation, as well as within organs. Pathogens are primarily removed by direct opsonisation following the recognition of cell surface carbohydrates and other immunostimulatory molecules or via the activation of the lectin complement pathway, which results in the deposition of C3b and the recruitment of phagocytes. In recent years, there have been a number of studies implicating ficolins in the recognition and removal of numerous bacterial, viral, fungal, and parasitic pathogens. Moreover, there has been expanding evidence highlighting that mutations within these key immune proteins, or the possession of particular haplotypes, enhance susceptibility to colonization by pathogens and dysfunctional immune responses. This review will therefore encompass previous knowledge on the role of ficolins in the recognition of bacterial and viral pathogens, while acknowledging the recent advances in the immune response to fungal and parasitic infections. Additionally, we will explore the various genetic susceptibility factors that predispose individuals to infection.

Interactions of ficolin-3 with ovarian cancer cells

BACKGROUND

Ficolin-3 is a pattern-recognition molecule with the ability to activate the lectin pathway of complement. It is found in lung, liver and blood, but its physiological role is unclear. We have investigated interaction of recombinant ficolin-3 with malignant cells and tissues.

MATERIAL AND METHODS

Cells of various lines of human origin as well as ovarian tissue sections have been studied with the use of flow cytometry and immunohistochemistry.

RESULTS

Recombinant (but not serum-derived) ficolin-3 was found to bind strongly to the ovarian cancer cell lines, SKOV-3, OVCAR-3 and ES-2, at concentrations of 2.5 μg/ml and above. Moreover, His-tagged recombinant ficolin-3 (10 μg/ml) preferentially stained ovarian tissue sections from patients with malignant tumours compared with those from patients without. Binding to cell lines was inhibited by EDTA and specific carbohydrate ligands, indicating involvement of the fibrinogen-like domain. Binding was enhanced under mildly acidic conditions and at physiological pH after pre-incubation of cells with mildly acidic buffer.

CONCLUSION

Basing on data concerning recombinant protein, it may be suggested that ficolin-3 is involved in immune response in ovarian cancer. However, unidentified serum factor(s) seem(s) to protect cancer cells from recognition by natural or rficolin-3.

Interaction of Mannose-Binding Lectin With Lipopolysaccharide Outer Core Region and Its Biological Consequences

Lipopolysaccharide (LPS, endotoxin), the main surface antigen and virulence factor of Gram-negative bacteria, is composed of lipid A, core oligosaccharide, and O-specific polysaccharide (O-PS) regions. Each LPS region is capable of complement activation. We have demonstrated that LPS of Hafnia alvei, an opportunistic human pathogen, reacts strongly with human and murine mannose-binding lectins (MBLs). Moreover, MBL-LPS interactions were detected for the majority of other Gram-negative species investigated. H. alvei was used as a model pathogen to investigate the biological consequences of these interactions. The core oligosaccharide region of H. alvei LPS was identified as the main target for human and murine MBL, especially l-glycero-d-manno-heptose (Hep) and N-acetyl-d-glucosamine (GlcNAc) residues within the outer core region. MBL-binding motifs of LPS are accessible to MBL on the surface of bacterial cells and LPS aggregates. Generally, the accessibility of outer core structures for interaction with MBL is highest during the lag phase of bacterial growth. The LPS core oligosaccharide-MBL interactions led to complement activation and also induced an anaphylactoid shock in mice. Unlike Klebsiella pneumoniae O3 LPS, robust lectin pathway activation of H. alvei LPS in vivo was mainly the result of outer core recognition by MBL; involvement of the O-PS is not necessary for anaphylactoid shock induction. Our results contribute to a better understanding of MBL-LPS interaction and may support development of therapeutic strategies against sepsis based on complement inhibition.

Dectin-2 Recognizes Mannosylated O-antigens of Human Opportunistic Pathogens and Augments Lipopolysaccharide Activation of Myeloid Cells

LPS consists of a relatively conserved region of lipid A and core oligosaccharide and a highly variable region of O-antigen polysaccharide. Whereas lipid A is known to bind to the Toll-like receptor 4 (TLR4)-myeloid differentiation factor 2 (MD2) complex, the role of the O-antigen remains unclear. Here we report a novel molecular interaction between dendritic cell-associated C-type lectin-2 (Dectin-2) and mannosylated O-antigen found in a human opportunistic pathogen, Hafnia alvei PCM 1223, which has a repeating unit of [-Man-α1,3-Man-α1,2-Man-α1,2-Man-α1,2-Man-α1,3-]. H. alvei LPS induced higher levels of TNFα and IL-10 from mouse bone marrow-derived dendritic cells (BM-DCs), when compared with Salmonella enterica O66 LPS, which has a repeat of [-Gal-α1,6-Gal-α1,4-[Glc-β1,3]GalNAc-α1,3-GalNAc-β1,3-]. In a cell-based reporter assay, Dectin-2 was shown to recognize H. alvei LPS. This binding was inhibited by mannosidase treatment of H. alvei LPS and by mutations in the carbohydrate-binding domain of Dectin-2, demonstrating that H. alvei LPS is a novel glycan ligand of Dectin-2. The enhanced cytokine production by H. alvei LPS was Dectin-2-dependent, because Dectin-2 knock-out BM-DCs failed to do so. This receptor cross-talk between Dectin-2 and TLR4 involved events including spleen tyrosine kinase (Syk) activation and receptor juxtaposition. Furthermore, another mannosylated LPS from Escherichia coli O9a also bound to Dectin-2 and augmented TLR4 activation of BM-DCs. Taken together, these data indicate that mannosylated O-antigens from several Gram-negative bacteria augment TLR4 responses through interaction with Dectin-2.

An electrochemical immunosensor for quantitative detection of ficolin-3

Diabetes mellitus (DM) is one of the most common metabolic disorders in the world, of which more than 90% is type-2 diabetes mellitus (T2DM). There is a rather urgent need for reliable, sensitive and quick detection techniques in clinical application of T2DM. Ficolin-3 is a potential biomarker of T2DM, because serum ficolin-3 levels are associated with insulin resistance and predict the incidence of T2DM. Herein, a sandwich-type electrochemical immunosensor was developed for the detection of ficolin-3 in human serum. Cyclic voltammetry and the amperometric current versus time were used to characterize the performance of the immunosensor. Under optimal conditions, the detection limitation of ficolin-3 was 100 ng ml(-1) and the linear dynamic range was between 2 and 50 μg ml(-1). The method has ideal accuracy, excellent stability and selectivity and has wide application prospects in clinical research.

Mycobacterial antigen 85 complex (Ag85) as a target for ficolins and mannose-binding lectin

The pattern recognition molecules (PRMs) able to activate complement via the lectin pathway are suspected to be involved in the interaction between pathogenic Mycobacteria and the host immune response. Recently, we have found strong interactions between 25 and 35kDa mycobacterial cell fractions and mannose-binding lectin (MBL) and ficolins. Here we demonstrate that two biologically important mycobacterial structures, mannosylated lipoarabinomannan (ManLAM) and the antigen 85 (Ag85) complex, induce activation of the lectin pathway of complement. The strong interaction of recombinant MBL with purified ManLAM was confirmed, but no binding of recombinant ficolins (ficolin-1, -2, -3) with this structure was observed. Interestingly, all PRMs tested reacted with the mycobacterial antigen 85 (Ag85) complex. Based on the use of specific inhibitors (mannan for MBL, acetylated bovine serum albumin for ficolin-1 and -2, Hafnia alvei PCM 1200 lipopolysaccharide for ficolin-3), we concluded that carbohydrate-recognition (MBL) and fibrinogen-like domains (ficolins) were involved in these interactions. Our results indicate that the mycobacterial antigen 85 complex is a target for ficolins and MBL. Furthermore, those PRMs also bound to fibronectin and therefore might influence the Ag85 complex-dependent interaction of Mycobacterium with the extracellular matrix.

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.

Frequency and distribution of FCN2 and FCN3 functional variants among MBL2 genotypes

The six types of pattern recognition molecules (PRMs) that initiate complement via the lectin pathway (LP) comprise collectins and ficolins. The importance of having various PRMs to initiate the LP is currently unclear. Mannan-binding lectin (MBL) is a collectin member of the LP PRMs. MBL deficiency is common with mild clinical consequence. Thus, the lack of MBL may be compensated for by the other PRMs. We hypothesized that variants FCN2 + 6424 and FCN3 + 1637delC that cause gene-dose-dependent reduction in ficolin-2 and ficolin-3 levels, respectively, may be rare in MBL-deficient individuals due to the importance of compensation within the LP. The aim of this study was to investigate the distribution and frequency of these variants among MBL2 genotypes in healthy subjects. The allele frequency of FCN2 + 6424 and FCN3 + 1637delC was 0.099 and 0.015, respectively, in the cohort (n = 498). The frequency of FCN2 + 6424 tended to be lower among MBL-deficient subjects (n = 53) than among MBL-sufficient subjects (n = 445) (0.047 versus 0.106, P = 0.057). In addition, individuals who were homozygous for FCN2 + 6424 were sufficient MBL producers. The frequency of FCN3 + 1637delC did not differ between the groups. The frequency of FCN2 + 6424 was similar in FCN3 + 1637delC carriers (n = 15) versus wild type (n = 498). Furthermore, subjects that were heterozygote carriers of both FCN2 + 6424 and FCN3 + 1637delC were sufficient MBL producers. In conclusion, FCN2 + 6424 carriers with MBL deficiency tend to be rare among healthy individuals. MBL-deficient individuals with additional LP PRM defects may be at risk to morbidity.

Components of the lectin pathway of complement activation in paediatric patients of intensive care units

Infections are a major cause of childhood mortality. We investigated components of the lectin pathway of complement activation in the context of sepsis at both genetic and protein levels in neonates, infants and older children. Major components of the lectin pathway and two genes for Toll-like receptors were studied in 87 neonates with confirmed sepsis and compared with 40 babies with infections who did not develop sepsis (disease controls) and 273 infection-free neonatal controls. A second cohort comprised 47 older children with sepsis and 87 controls. Low MBL-conferring genotypes (LXA/O+O/O) were more frequent in sepsis patients than in healthy controls but no significant differences in the frequency of SNPs of other lectin pathway genes (FCN1, FCN2, FCN3, MASP1/3, MASP2) or TLR receptor genes (TLR2, TLR4) were found. One case of primary MASP-2 deficiency was found among healthy pre-terms and one neonate suffering from SIRS was heterozygous for the rare FCN1 gene mutation, +6658 G>A. Generally, sepsis was associated with low serum MBL and low ficolin-2 concentrations on admission. Among neonates, ficolin-1 and MASP-2 levels were elevated in sepsis relative to healthy, but not disease, controls. Unlike neonates, ficolin-3 and MASP-2 levels were lower in older patients than in healthy controls while no difference was found for ficolin-1. With the possible exception of MBL, inherited lectin pathway insufficiencies do not seem to predispose to sepsis, rather changes in protein concentrations reflect alterations in disease course.

Fibrinogen-Related Proteins in Tissue Repair: How a Unique Domain with a Common Structure Controls Diverse Aspects of Wound Healing

Significance: Fibrinogen-related proteins (FRePs) comprise an intriguing collection of extracellular molecules, each containing a conserved fibrinogen-like globe (FBG). This group includes the eponymous fibrinogen as well as the tenascin, angiopoietin, and ficolin families. Many of these proteins are upregulated during tissue repair and exhibit diverse roles during wound healing. Recent Advances: An increasing body of evidence highlights the specific expression of a number of FRePs following tissue injury and infection. Upon induction, each FReP uses its FBG domain to mediate quite distinct effects that contribute to different stages of tissue repair, such as driving coagulation, pathogen detection, inflammation, angiogenesis, and tissue remodeling. Critical Issues: Despite a high degree of homology among FRePs, each contains unique sequences that enable their diversification of function. Comparative analysis of the structure and function of FRePs and precise mapping of regions that interact with a variety of ligands has started to reveal the underlying molecular mechanisms by which these proteins play very different roles using their common domain. Future Directions: Fibrinogen has long been used in the clinic as a synthetic matrix serving as a scaffold or a delivery system to aid tissue repair. Novel therapeutic strategies are now emerging that harness the use of other FRePs to improve wound healing outcomes. As we learn more about the underlying mechanisms by which each FReP contributes to the repair response, specific blockade, or indeed potentiation, of their function offers real potential to enable regulation of distinct processes during pathological wound healing.

Primary Ficolin-3 deficiency--Is it associated with increased susceptibility to infections?

Ficolin-3 (also called H-ficolin or Hakata antigen) is the most potent activator of the lectin pathway of complement in vitro. Its genetically determined deficiency in Caucasians is associated with a frame-shift mutation +1637delC (rs28357092) of the FCN3 gene. When it was described for the first time, it was postulated to be strictly associated with enhanced susceptibility to infections. At present, with our knowledge extended by several other patients that issue seems to be more complicated and less clear-cut. Two new cases of primary Ficolin-3 deficiency are reported here: a 50-year old male, suffering from membranous nephropathy and an 11-month old male infant who was operated on to repair congenital heart disease. Based on those cases and a literature review, we conclude that the clinical consequences of congenital Ficolin-3 deficiency are still unclear and such questions as whether it may be life-threatening or acts as a disease modifier remain to be elucidated.