Association of low ficolin-2 concentration in cord serum with respiratory distress syndrome in preterm newborns

Introduction

Ficolin-2 is a serum pattern recognition molecule, involved in complement activation via the lectin pathway. This study aimed to investigate the association of ficolin-2 concentration in cord blood serum with complications related to premature birth.

Methods

546 premature neonates were included. The concentration of ficolin-2 in cord blood serum was determined by a sandwich TRIFMA method. FCN2 genetic variants were analysed with RFLP-PCR, allele-specific PCR, Sanger sequencing or allelic discrimination using TaqMan probes method.

Findings

Cord blood serum ficolin-2 concentration correlated positively with Apgar score and inversely with the length of hospitalisation and stay at Neonatal Intensive Care Unit (NICU). Multivariate logistic regression analysis indicated that low ficolin-2 increased the possibility of respiratory distress syndrome (RDS) diagnosis [OR=2.05, 95% CI (1.24-3.37), p=0.005]. Median ficolin-2 concentration was significantly lower in neonates with RDS than in premature babies without this complication, irrespective of FCN2 gene polymorphisms localised to promoter and 3'untranslated regions: for patients born <33 GA: 1471 ng/ml vs. 2115 ng/ml (p=0.0003), and for patients born ≥33 GA 1610 ng/ml vs. 2081 ng/ml (p=0.012). Ficolin-2 level was also significantly lower in neonates requiring intubation in the delivery room (1461 ng/ml vs. 1938 ng/ml, p=0.023) and inversely correlated weakly with the duration of respiratory support (R=-0.154, p<0.001). Interestingly, in the neonates born at GA <33, ficolin-2 concentration permitted differentiation of those with/without RDS [AUC=0.712, 95% CI (0.612-0.817), p<0.001] and effective separation of babies with mild RDS from those with moderate/severe form of the disease [AUC=0.807, 95% CI (0.644-0.97), p=0.0002].

Conclusion

Low cord serum ficolin-2 concentration (especially in neonates born at GA <33 weeks) is associated with a higher risk of developing moderate/severe RDS, requiring respiratory support and intensive care.

Polymorphisms of the FCN2 Gene 3'UTR Region and Their Clinical Associations in Preterm Newborns

Ficolin-2 is regarded as an important innate immunity factor endowed with both lectin (carbohydrate recognition) qualities and ability to induce complement activation. The aim of this study was to investigate the association of the FCN2 3'-untranslated region (3'UTR) polymorphisms with ficolin-2 expression and perinatal complications in preterm neonates. The sequencing analysis allowed us to identify six 3'UTR polymorphisms with minor allele frequency (MAF) >1%: rs4521835, rs73664188, rs11103564, rs11103565, rs6537958 and rs6537959. Except for rs4521835, all adhered to Hardy-Weinberg expectations. Moreover, rs6537958 and rs6537959 were shown to be in perfect linkage disequilibrium (LD) with nine other genetic polymorphisms: rs7040372, rs7046516, rs747422, rs7847431, rs6537957, rs6537960, rs6537962, rs11462298 and rs7860507 together stretched on a distance of 1242 bp and very high LD with rs11103565. The 3'UTR region was shown to bind nuclear extract proteins. The polymorphisms at rs4521835 and rs73664188 were found to influence serum ficolin-2 concentration significantly. All polymorphisms identified create (together with exon 8 polymorphism, rs7851696) two haplotype blocks. Among 49 diplotypes (D1-D49) created from rs7851696 (G>T), rs4521835 (T>G), rs73664188 (T>C), rs11103564 (T>C), rs11103565 (G>A) and rs6537959 (T>A), twenty two occurred with frequency >1%. Two diplotypes: D13 (GTTTGT/GGTCGT) and D10 (GTTTGT/GGTCGA), were significantly more frequent among preterm neonates with early onset of infection and pneumonia, compared with newborns with no infectious complications (OR 2.69 and 2.81, respectively; both p<0.05). The minor (C) allele at rs73664188 was associated with an increased risk of very low (≤1500 g) birthweight (OR=1.95, p=0.042) but was associated with the opposite effect at rs11103564 (OR=0.11, p=0.005).

The Plasma Proteome Fingerprint Associated with Circulating Carotenoids and Retinol in Older Adults

BACKGROUND

Although diets rich in carotenoids are associated with reduced risks of cardiovascular disease, age-related macular degeneration, disability, and other adverse aging outcomes, the underlying biological mechanisms are not fully elucidated.

OBJECTIVES

To characterize the plasma proteome fingerprint associated with circulating carotenoid and retinol concentrations in older adults.

METHODS

In 728 adults ≥65 y participating in the Invecchiare in Chianti (InCHIANTI) Study, plasma α-carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene were measured using HPLC. The SOMAscan assay was used to measure 1301 plasma proteins. Multivariable linear regression models were used to examine the relationship of individual carotenoids and retinol with plasma proteins. A false discovery rate approach was used to deal with multiple comparisons using a q-value < 0.05.

RESULTS

Plasma β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene were associated with 85, 39, 4, 2, and 5 plasma proteins, respectively, in multivariable linear regression models adjusting for potential confounders (q < 0.05). No proteins were associated with α-carotene or retinol. Two or more carotenoids were positively associated with ferritin, 6-phosphogluconate dehydrogenase (decarboxylating), hepcidin, thrombospondin-2, and choline/ethanolamine kinase. The proteins associated with circulating carotenoids were related to energy metabolism, sirtuin signaling, inflammation and oxidative stress, iron metabolism, proteostasis, innate immunity, and longevity.

CONCLUSIONS

The plasma proteomic fingerprint associated with elevated circulating carotenoids in older adults provides insight into the mechanisms underlying the protective role of carotenoids on health.

Association of mannose-binding lectin, ficolin-2 and immunoglobulin concentrations with future exacerbations in patients with chronic obstructive pulmonary disease: secondary analysis of the randomized controlled REDUCE trial

BACKGROUND

The innate and adaptive immune system is involved in the airway inflammation associated with acute exacerbations in patients with chronic obstructive pulmonary disease (COPD). We evaluated the association of mannose-binding lectin (MBL), immunoglobulin (Ig) and ficolin-2 concentrations with COPD exacerbations and according to the glucocorticoid treatment duration for an index exacerbation.

METHODS

Post-hoc analysis of the randomized, double-blind, placebo-controlled REDUCE trial of 5 vs. 14 days of glucocorticoid treatment for an index exacerbation. MBL, ficolin-2 and total IgG/IgA and subclass concentrations were determined in stored samples drawn (n = 178) 30 days after the index exacerbation and associated with the risk of re-exacerbation during a 180-day follow-up period.

RESULTS

IgG and subclass concentrations were significantly lower after 14 days vs. 5 days of glucocorticoid treatment. Patients with higher MBL concentrations were more likely to suffer from a future exacerbation (multivariable hazard ratio 1.03 per 200 ng/ml increase (95% confidence interval (CI) 1.00-1.06), p = 0.048), whereas ficolin-2 and IgG deficiency were not associated. The risk was most pronounced in patients with high MBL concentrations, IgG deficiency and 14 days of glucocorticoid treatment pointing towards an interactive effect of MBL and IgG deficiency in the presence of prolonged glucocorticoid treatment duration [Relative excess risk due to interaction 2.13 (95% CI - 0.41-4.66, p = 0.10)]. IgG concentrations were significantly lower in patients with frequent re-exacerbations (IgG, 7.81 g/L vs. 9.53 g/L, p = 0.03).

CONCLUSIONS

MBL modified the short-term exacerbation risk after a recent acute exacerbation of COPD, particularly in the setting of concurrent IgG deficiency and recent prolonged systemic glucocorticoid treatment. Ficolin-2 did not emerge as a predictor of a future exacerbation risk.

The Role of Glycosylation in Infectious Diseases

Glycosylation plays an important role in infectious diseases. Many important interactions between pathogens and hosts involve their carbohydrate structures (glycans). Glycan interactions can mediate adhesion, recognition, invasion, and immune evasion of pathogens. To date, changes in many protein N/O-linked glycosylation have been identified as biomarkers for the development of infectious diseases and cancers. In this review, we will discuss the principal findings and the roles of glycosylation of both pathogens and host cells in the context of human important infectious diseases. Understanding the role and mechanism of glycan-lectin interaction between pathogens and hosts may create a new paradigm for discovering novel glycan-based therapies that can lead to eradication or functional cure of pathogens infection.

Impact of mannose-binding lectin 2 gene polymorphisms on disease severity in noncystic fibrosis bronchiectasis in children

BACKGROUND

Mannose-binding lectin (MBL) is a complement protein involved in the innate immune system, and is associated with some chronic respiratory diseases including noncystic fibrosis (non-CF) bronchiectasis in adults. The aim of this study was to investigate the frequency of MBL2 gene polymorphisms in children with non-CF bronchiectasis, and the effect of MBL deficiency on disease severity.

METHODS

Fifty children with non-CF bronchiectasis (bronchiectasis group) and 50 healthy controls (control group) were included. The demographic findings, number of acute pulmonary exacerbations in the previous year, airway cultures, pulmonary function tests, and radiologic scores of the bronchiectasis group were recorded. DNA extraction was performed in both groups and MBL2 gene polymorphisms in codons 52, 54, 57 in exon 1 and H/L, Y/X in the promoter region were studied using real-time polymerase chain reaction. Haplotypes were made by genotypes, and MBL serum expression was classified according to the genotypes in the literature.

RESULTS

The bronchiectasis group consisted of 23 (46%) patients with primary ciliary dyskinesia, 5 (10%) with primary immunodeficiency diseases, and 22 (44%) with idiopathic bronchiectasis. There were no statistically significant differences between the bronchiectasis and control groups in terms of allele and genotype frequencies of polymorphisms in codons 52, 54, 57 in exon 1 and promoter H/L. However, the YX heterozygote genotype was more frequent in the control group (82%) compared with the bronchiectasis group (50%) (P = .002). The frequency of patients with intermediate serum MBL expression genotype was higher in the bronchiectasis group (20%) than in the control group (0%) (P = .001). In the bronchiectasis group, there were no significant differences in growth, annual pulmonary exacerbation rates in the last year, pulmonary function tests, radiologic scores, and microbiologic findings between low, intermediate, and high-expressing genotypes.

CONCLUSIONS

In children with non-CF bronchiectasis, MBL genotype was different from healthy controls. MBL deficiency associated only with MBL genotype was not related to disease severity in this group of patients.

Insufficient serum L-ficolin is associated with disease presence and extent of pulmonary Mycobacterium avium complex disease

BACKGROUND

The incidence of infectious disease caused by nontuberculous mycobacteria is increasing worldwide. Pulmonary Mycobacterium avium complex (MAC) disease is difficult to treat with chemotherapy, and its mechanism of infection, infection route, disease onset, and severity remain unknown. Ficolins are oligomeric defense lectins. L-ficolin plays an important role in innate immunity. This study's aim was to identify L-ficolin's role in patients with pulmonary MAC disease.

METHODS

Between April 2011 and September 2017, 61 Japanese patients with pulmonary MAC disease were seen at our hospital. A control group, comprising 30 healthy individuals, without respiratory disease were enrolled in our study. The relationship between serum L-ficolin levels and disease severity was assessed, and L-ficolin's antibacterial role was examined.

RESULTS

Serum L-ficolin levels were significantly lower in patients with pulmonary MAC disease than in healthy subjects (1.69 ± 1.27 μg/ml vs. 3.96 ± 1.42 μg/ml; p < 0.001). The cut-off value, based on receiver operating characteristic (ROC) analysis results, was 2.48 μg/ml (area under the curve (AUC) 0.90, sensitivity and specificity 83.6 and 86.7%, respectively). Serum L-ficolin levels were significantly lower in the patients with nodular bronchiectatic type disease compared with the patients with fibrocavitary type disease and were lower in the high-resolution computed tomography high-scoring group compared with low-scoring group. An in vitro analysis showed that purified recombinant L-ficolin bound to M. avium and its major cell wall component, lipoarabinomannan, in a concentration-dependent manner. In addition, recombinant L-ficolin suppressed M. avium growth in a concentration-dependent manner.

CONCLUSIONS

Insufficient serum L-ficolin is associated with disease progression in pulmonary MAC disease, and the level of serum L-ficolin is a possible biomarker.

TRIAL REGISTRATION

This study is registered with UMIN ( UMIN000022392 ).

A Rare Genetic Defect of MBL2 Increased the Risk for Progression of IgA Nephropathy

The aim of this study was to investigate the association between lectin pathway-related genetic variations and progression in IgA nephropathy. Biopsy-proven IgAN patients with eGFR ≥15 ml/min/1.73 m2 at baseline and a minimum follow-up of 12-months were enrolled. A total of 1,007 patients and 121 healthy controls were enrolled from two Chinese renal centers. The discovery cohort consisted of 606 patients, and the validation cohort consisted of 401 patients. First, promoters, all exons and their boundary regions of MBL2 and FCN2 were sequenced in 50 patients, and then 37 variations were identified. Of these variations, 7 expression-associated variations were selected and genotyped in the whole discovery cohort. We found that rs1800450 in MBL2 and rs7851696 in FCN2 were associated with an increased risk for ESRD as well as serum MBL or L-ficolin levels. However, only rs1800450 was successively validated for its association with ESRD (HR, 15.91; 3.27-77.34; P = 0.001) in the fully adjusted model in the validation cohort. In addition, 2.7% of patients, and 2.5% of healthy controls carried rs1800450-AA. IgAN patients with rs1800450-AA lacked expression of MBL in both serum and renal tissue and had more severe tubulointerstitial damage. Furthermore, a combined effect of rs1800450-AA with a previously reported clinical risk score was observed in which patients with both a high clinical risk score (≥1%) and rs1800450-AA had a strikingly increased 10-years ESRD risk by 37.1-fold (7.17 to 192.13-fold). In summary, IgAN patients carrying MBL2 rs1800450-AA have a high risk for renal function deterioration, probably due to inactivation of the complement MBL pathway.

FCN2 inhibits epithelial-mesenchymal transition-induced metastasis of hepatocellular carcinoma via TGF-β/Smad signaling

Hepatocellular carcinoma (HCC) is currently still a major cause of cancer-related deaths. Identifying early metastatic biomarkers and therapeutic targets for HCC is of great importance. Emerging evidence suggest that epithelial-mesenchymal transitions (EMTs) play important roles in tumor metastasis and recurrence. Understanding molecular mechanisms that regulate the EMT process is crucial for improving HCC. In this study, we find Ficolin-2 (FCN2) plays an essential role in metastasis and EMT of HCC. FCN2 expression is downregulated in HCC cells and tissues. Low level of FCN2 in HCCs is correlated with aggressive metastatic features, and would be a prognostic factor for overall disease-free survival of HCC patients. Ectopic expression of FCN2 markedly inhibits HCC cells migration, invasion as well as EMT in vitro and in vivo. Moreover, TGF-β is found contribute to the function of FCN2 in suppressing metastasis and EMT of HCC. Collectively, our data suggest that FCN2 may have prognostic value in HCC metastasis. Additionally, the FCN2/ TGF-β/EMT axis identified in this study provides novel insight into the mechanisms of HCC metastasis, which may facilitate the development of new therapeutics against HCC.

Six-SOMAmer Index Relating to Immune, Protease and Angiogenic Functions Predicts Progression in IPF

RATIONALE

Biomarkers in easily accessible compartments like peripheral blood that can predict disease progression in idiopathic pulmonary fibrosis (IPF) would be clinically useful regarding clinical trial participation or treatment decisions for patients. In this study, we used unbiased proteomics to identify relevant disease progression biomarkers in IPF.

METHODS

Plasma from IPF patients was measured using an 1129 analyte slow off-rate modified aptamer (SOMAmer) array, and patient outcomes were followed over the next 80 weeks. Receiver operating characteristic (ROC) curves evaluated sensitivity and specificity for levels of each biomarker and estimated area under the curve (AUC) when prognostic biomarker thresholds were used to predict disease progression. Both logistic and Cox regression models advised biomarker selection for a composite disease progression index; index biomarkers were weighted via expected progression-free days lost during follow-up with a biomarker on the unfavorable side of the threshold.

RESULTS

A six-analyte index, scaled 0 to 11, composed of markers of immune function, proteolysis and angiogenesis [high levels of ficolin-2 (FCN2), cathepsin-S (Cath-S), legumain (LGMN) and soluble vascular endothelial growth factor receptor 2 (VEGFsR2), but low levels of inducible T cell costimulator (ICOS) or trypsin 3 (TRY3)] predicted better progression-free survival in IPF with a ROC AUC of 0.91. An index score ≥ 3 (group ≥ 2) was strongly associated with IPF progression after adjustment for age, gender, smoking status, immunomodulation, forced vital capacity % predicted and diffusing capacity for carbon monoxide % predicted (HR 16.8, 95% CI 2.2-126.7, P = 0.006).

CONCLUSION

This index, derived from the largest proteomic analysis of IPF plasma samples to date, could be useful for clinical decision making in IPF, and the identified analytes suggest biological processes that may promote disease progression.

Pediatric bronchiectasis: No longer an orphan disease

Bronchiectasis is described classically as a chronic pulmonary disorder characterized by a persistent productive cough and irreversible dilatation of one or more bronchi. However, in children unable to expectorate, cough may instead be wet and intermittent and bronchial dilatation reversible in the early stages. Although still considered an orphan disease, it is being recognized increasingly as causing significant morbidity and mortality in children and adults in both affluent and developing countries. While bronchiectasis has multiple etiologies, the final common pathway involves a complex interplay between the host, respiratory pathogens and environmental factors. These interactions lead to a vicious cycle of repeated infections, airway inflammation and tissue remodelling resulting in impaired airway clearance, destruction of structural elements within the bronchial wall causing them to become dilated and small airway obstruction. In this review, the current knowledge of the epidemiology, pathobiology, clinical features, and management of bronchiectasis in children are summarized. Recent evidence has emerged to improve our understanding of this heterogeneous disease including the role of viruses, and how antibiotics, novel drugs, antiviral agents, and vaccines might be used. Importantly, the management is no longer dependent upon extrapolating from the cystic fibrosis experience. Nevertheless, substantial information gaps remain in determining the underlying disease mechanisms that initiate and sustain the pathophysiological pathways leading to bronchiectasis. National and international collaborations, standardizing definitions of clinical and research end points, and exploring novel primary prevention strategies are needed if further progress is to be made in understanding, treating and even preventing this often life-limiting disease.

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.

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.

Heparin-coated cardiopulmonary bypass circuits selectively deplete the pattern recognition molecule ficolin-2 of the lectin complement pathway in vivo

The complement system can be activated via the lectin pathway by the recognition molecules mannose-binding lectin (MBL) and the ficolins. Ficolin-2 exhibits binding against a broad range of ligands, including biomaterials in vitro, and low ficolin-2 levels are associated with increased risk of infections. Thus, we investigated the biocompatibility of the recognition molecules of the lectin pathway in two different types of cardiopulmonary bypass circuits. Bloods were drawn at five time-points before, during and postoperatively from 30 patients undergoing elective cardiac surgery. Patients were randomized into two groups using different coatings of cardiopulmonary bypass circuits, Phisio® (phosphorylcholine polymer coating) and Bioline® (albumin-heparin coating). Concentrations of MBL, ficolin-1, -2 and -3 and soluble C3a and terminal complement complex (TCC) in plasma samples were measured. Ficolin-3-mediated complement activation potential was evaluated with C4, C3 and TCC as output. There was no significant difference between the two circuit materials regarding MBL, ficolin-1 and -3. In the Bioline® group the ficolin-2 levels decreased significantly after initiation of surgery (P < 0.0001) and remained reduced throughout the sampling period. This was not seen for Phisio®-coated circuits. Ficolin-3-mediated complement activation potential was reduced significantly in both groups after start of operation (P < 0.0001), whereas soluble C3a and TCC in the samples were increased (P < 0.0001). Ficolin-2 was depleted from plasma during cardiac surgery when using heparin-coated bypass circuits and did not reach baseline level 24 h postoperation. These findings may have implications for the postoperative susceptibility to infections in patients undergoing extracorporeal circulation procedures.

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

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

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.

Serum ficolin-2 in hospitalised patients with community-acquired pneumonia

Mannose binding lectin (MBL) and ficolins contribute to host defence through activation of the lectin pathway of complement. In this study, serum levels of ficolin-2 and MBL were determined in 276 patients with community-acquired pneumonia (CAP). MBL deficiency and ficolin-2 insufficiency were defined using previously validated cut-offs. No differences were observed in MBL or ficolin-2 between patients and controls. MBL-deficient patients (<500 ng/ml) were not at higher risk of 30-day mortality odds ratio (OR) 0.97 (0.38-2.48,p=0.9) or a composite outcome of mortality, mechanical ventilation, vasopressor support (MV/VS) or complications OR 0.89 (0.44-1.77, p=0.9). Although no significant relationship between ficolin-2 insufficiency and outcome was observed, very low ficolin-2 levels (<1,200 ng/ml) were associated with an OR 1.23 (0.15-10.1), p=0.6 for 30-day mortality, 3.05 (0.61-15.2, p=0.2) for MV/VS and OR 2.05 (0.52-8.1, p=0.2) for the composite outcome. Low serum levels of MBL and ficolin-2 are not associated with CAP susceptibility. The high frequency of ficolin-2 insufficiency in patients with severe CAP would justify a larger investigation of ficolin-2 as a modifier of CAP severity.

Ficolins and infectious diseases

Ficolins are serum complement lectins, with a structure similar to mannose-binding lectin (MBL) and lung surfactant protein (SP)-A and SP-D. Ficolins activate the lectin complement system and play important roles in host innate immunity. Ficolins are members of the collectin family of proteins, which act as pattern recognition receptors (PRRs). They are soluble oligomeric defense proteins with lectin-like activity, and are able to recognize pathogen-associated molecular patterns (PAMPs), which are carbohydrate molecules on the surface of pathogens, and of apoptotic, necrotic, and malignant cells. Upon binding to their specific PAMPs, ficolins may trigger activation of the immune system either (1) by initiating activation of complement via the lectin pathway, (2) by a primitive type of opsonophagocytosis, or (3) by stimulating secretion of the inflammatory cytokines interferon (IFN)-Γ, interleukin (IL)-17, IL-6, and tumor necrosis factor (TNF)-α, and production of nitric oxide (NO) by macrophages, thus limiting the infection and concurrently orchestrating the subsequent adaptive immune response. Recently, a number of reports have shown that dysfunction or abnormal expression of ficolins may play crucial roles in viral and bacterial diseases and in inflammation. This review summarizes the reports on the roles of ficolins in the infectious diseases, and provides insight into ficolins as novel innate immune therapeutic options to treat these diseases.

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.

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.

The relationship between FCN2 genotypes and serum ficolin-2 (L-ficolin) protein concentrations from a large cohort of neonates

The human FCN2 gene codes for ficolin-2 (L-ficolin), a major pattern recognition molecule and activator of the lectin pathway of complement. Seven single nucleotide polymorphisms of this gene were investigated in a large series of cord blood DNA samples. Mutations from the majority to the minority alleles at -602, -4 and +6359 were associated with an increase, while mutations at -986, -557, -64 and +6424 were associated with a decrease, in protein concentration. Full (7 loci) genotypes were obtained for 1229 unrelated neonates, 12 sets of twin siblings and one set of triplets. Forty-four separate genotypes were detected. Four genotypes accounted for more than half the unrelated neonates, and >90% had one of the 12 commonest genotypes. Genotypes were associated with significant differences in mean serum ficolin-2, but the intra-genotype concentration ranges were large and greater than the inter-genotype differences. Consequently, there were no associations between genotypes and low birthweight babies or perinatal infections, and only a weak relationship with preterm deliveries, despite all three adverse pregnancy features being significantly associated with serum ficolin-2 protein. FCN2 genotyping may be of value in clinical studies, but not as a substitute for total serum ficolin-2 protein measurement.

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.

The overlap of bronchiectasis and immunodeficiency with asthma

Bronchiectasis should be considered as a differential diagnosis for, as well as a comorbidity in, patients with asthma, especially severe or long-standing asthma. Chronic airway inflammation is thought to be the primary cause, as with chronic or recurrent pulmonary infection and autoimmune conditions that involve the airways. Consequently, immunodeficiencies with associated increased susceptibility to respiratory tract infections or chronic inflammatory airways also increase the risk of developing bronchiectasis. Chronic bronchiectasis is associated with impaired mucociliary clearance and increased bronchial secretions, leading to airway obstruction and airflow limitation, which can lead to exacerbation of underlying asthma or increased asthma symptoms.

Polymorphisms in the lectin pathway genes as a possible cause of early chronic Pseudomonas aeruginosa colonization in cystic fibrosis patients

Genes of innate immunity may be involved in early onset of chronic Pa (Pseudomonas aeruginosa) colonization (cPaC) in cystic fibrosis (CF) patients. We studied 19 single nucleotide polymorphisms (SNPs) in 5 genes coding for proteins of the lectin complement pathway: MBL2 (Mannose binding lectin 2), MASP 1, 2, 3 (MBL-associated serine Protease) and FCN 1, 2 (Ficolin) gene in 96 CF patients. Association survival analysis using different genetic models was performed looking for an association between SNPs and age at onset of cPaC. CF patients who are MBL deficient are earlier chronic Pa colonized compared to MBL sufficient patients. Also patients with MBL2 genotype YO/YO, YO/XA, XA/XA, YA/YO and YA/XA are earlier chronic Pa colonized. CF patients heterozygous or homozygous for mutant alleles of two linked SNPs in the FCN1 gene (rs2989727 and rs1071583) are earlier colonized with Pa. Similarly, earlier onset of Pa colonization is seen in CF patients heterozygous for linked SNPs of FCN2 gene (rs7865453 and rs7851696) and MASP3 gene (rs7851696). Variants in MBL2, FCN1, FCN2 and MASP3 genes are significantly associated with earlier onset of chronic P. aeruginosa colonization.

Mechanisms of immune dysfunction and bacterial persistence in non-cystic fibrosis bronchiectasis

Bronchiectasis is a chronic inflammatory lung disease. The underlying cause is not identified in the majority of patients, but bronchiectasis is associated with a number of severe infections, immunodeficiencies and autoimmune disorders. Regardless of the underlying cause, the disease is characterised by a vicious cycle of bacterial colonisation, airway inflammation and airway structural damage. Inflammation in bronchiectasis is predominantly neutrophil driven. Neutrophils migrate to the airway under the action of pro-inflammatory cytokines such as interleukin-8, tumour necrosis factor-α and interleukin-1β, all of which are increased in the airway of patients with bronchiectasis. Bacterial infection persists in the airway despite large numbers of neutrophils that would be expected to phagocytose and kill pathogens under normal circumstances. Evidence suggests that neutrophils are disabled by multiple mechanisms including cleavage of phagocytic receptors by neutrophil elastase and inhibition of phagocytosis by neutrophil peptides. Complement activation is impaired and neutrophil elastase may cleave activated complement from pathogens preventing effective opsonisation. Organisms also evade clearance by adapting to chronic infection. The formation of biofilms, reduced motility and the down-regulation of virulence factors are among the strategies used to subvert innate immune mechanisms. Greater understanding of the mechanisms underlying chronic colonisation in bronchiectasis will assist in the development of new treatments for this important disease.

Birds, babies and blood

This is an autobiographical review describing the author's career in immunology research and summarizing his current understanding of the areas involved. Contributions to autoimmunity, immune deficiency, transfusion immunology, HLA-disease associations, reproductive immunology, cellular therapies, and innate immunity are included; also discussion of medical research ethics and various research-related activities.

Circulating ficolin-2 and ficolin-3 in normal pregnancy and pre-eclampsia

Ficolins are soluble molecules of the innate immune system that recognize carbohydrate molecules on microbial pathogens, apoptotic and necrotic cells. They act through two distinct routes: initiating the lectin pathway of complement activation and mediating a primitive opsonophagocytosis. In this study, we measured plasma levels of ficolin-2 and ficolin-3 in 60 pre-eclamptic patients, 60 healthy pregnant women and 59 healthy non-pregnant women by enzyme-linked immunosorbent assay (ELISA). Circulating levels of complement activation products (C4d, C3a, SC5b9), angiogenic factors (soluble fms-like tyrosine kinase-1, placental growth factor) and markers of endothelial activation (von Willebrand factor antigen), endothelial injury (fibronectin) and trophoblast debris (cell-free fetal DNA) were also determined. Plasma levels of ficolin-2 were significantly lower in healthy pregnant than in healthy non-pregnant women, while ficolin-3 levels did not differ significantly between the two groups. Furthermore, pre-eclamptic patients had significantly lower ficolin-2 and ficolin-3 concentrations than healthy non-pregnant and pregnant women. In the pre-eclamptic group, plasma ficolin-2 levels showed a significant positive correlation with serum placental growth factor (PlGF) concentrations and significant inverse correlations with serum levels of soluble fms-like tyrosine kinase-1 (sFlt-1), blood urea nitrogen and creatinine, serum lactate dehydrogenase activities, as well as with plasma VWF:antigen, fibronectin and cell-free fetal DNA concentrations. In conclusion, circulating levels of ficolin-2 are decreased in the third trimester of normal pregnancy. There is a further decrease in plasma ficolin-2 concentrations in pre-eclampsia, which might contribute to the development of the maternal syndrome of the disease through impaired removal of the trophoblast-derived material released into the maternal circulation by the hypoxic and oxidatively stressed pre-eclamptic placenta.

Relevance of the lectin pathway of complement in rheumatic diseases

Due to its importance both in the clearance of pathogens that contribute as rheumatic etiological agents and in the disposal of apoptotic bodies and potential autoimmune initiators, deficiencies of the components of the lectin pathway of complement have been found to increase susceptibility and modulate the severity of most rheumatic disorders. This chapter introduces the general aspects of the structure, function, and genetics of lectin pathway components and summarizes current knowledge of the field regarding rheumatic diseases predisposition and modulation.

Low serum mannose-binding lectin level is not associated with disease severity in non-cystic fibrosis bronchiectasis

Deficiency of mannose-binding lectin (MBL), a serum protein involved in killing and promoting phagocytosis of pathogens, is associated with respiratory infection and disease progression in a number of acute and chronic lung diseases, including cystic fibrosis (CF)- associated bronchiectasis. No such association has been studied in non-CF bronchiectasis (nCF-Br). One hundred and thirty-three adult patients with nCF-Br were studied. Serum MBL levels were measured and deficiency defined using two cut-off levels, i.e. MBL ≤100 ng/ml and ≤600 ng/ml. Parameters of severity included lung function impairment, annual exacerbation and hospital admission rates, breathlessness, and Pseudomonas aeruginosa and Haemophilus influenzae infection rates. The incidence of MBL deficiency using cut-off levels of 100 ng/ml and 600 ng/ml was 10% and 26% respectively, similar to rates seen in the general population. There was no significant difference in mean FEV1% predicted between MBL deficient and sufficient patients at both cut-off levels (≤100 ng/ml: 63.8% vs . 64.6%, P = 0.91; ≤ 600 ng/ml: 66.5% vs . 63.9%, P = 0.56). In addition, exacerbation/hospital admission rates, symptoms of breathlessness and isolation/colonisation rates with P. aeruginosa and H. influenzae were similar in both groups at both cut-off levels. In conclusion, MBL deficiency is not associated with markers of disease severity in patients with nCF-Br.

Human L-ficolin (ficolin-2) and its clinical significance

Human L-ficolin (P35, ficolin-2) is synthesised in the liver and secreted into the bloodstream where it is one of the major pattern recognition molecules of plasma/serum. Like other ficolins, it consists of a collagen-like tail region linked to a fibrinogen-related globular head; a basic triplet subunit arises via a collagen-like triple helix, and this then forms higher multimers (typically a 12-mer, Mr 400K). Unlike other ficolins, it has a complex set of binding sites arranged within an internal cleft enabling it to recognise a variety of molecular patterns including acetylated sugars and certain 1,3-β-glucans. It is one of the few molecules known to activate the lectin pathway of complement. Recently, some disease association studies (at either the DNA or protein level) have implicated L-ficolin in innate immunity, where it might cooperate with pentraxins and collectins. Emerging lines of evidence point to a role for L-ficolin in respiratory immunity, where its affinity for Pseudomonas aeruginosa could be significant.

Ficolin-2 levels and genetic polymorphisms of FCN2 in malaria

Human ficolin-2 (L-ficolin; FCN2) is a serum protein binding to sugar moieties of different human micro-pathogens forcing phagocytosis. Here, we investigate the clinical significance of FCN2 in African children with either mild or severe malaria (n = 130 and n = 108, respectively) from Gabon by analyzing three promoter SNPs (-986G>A, -602G>A, and -4A>G) and one single nucleotide polymorphisms (SNP) in exon 8 (+6424G>T) using quantitative TaqMan, real-time polymerase chain reaction (PCR). In addition, we measured the ficolin-2 plasma levels at two time points: on admission (t(0), acute disease) and 4 weeks after treatment (t(1), healthy phase). Comparison of ficolin-2 plasma levels shows that ficolin-2 concentration is highest during acute severe disease. In addition, we determined polymorphisms in the promoter and all coding regions of FCN2 in 40 Gabonese. Linkage disequilibrium data revealed polymorphic allelic combination patterns in the FCN2 promoter region; strong allelic combinations at -986 and -4, and -557 and -64 were found. No FCN2 promoter haplotypes were significantly distributed between mild and severe cases.

L-ficolin (ficolin-2) insufficiency is associated with combined allergic and infectious respiratory disease in children

We previously reported an association between relative L-ficolin deficiency and recurrent respiratory infections co-existing with allergic disorders in children. To confirm and extend this preliminary finding, we performed a prospective study on children of a similar age (mean 8.9 years) designed to establish whether the principal relationship was with infection or allergy. Serum L-ficolin values in healthy children were normally distributed with a mean value of 3838 ng/ml. L-ficolin concentrations were generally lower in patients with asthma and/or allergic rhinitis with (mean 3413 ng/ml; p=0.02) or without (3512 ng/ml; p<0.07) respiratory infections, but not in patients with respiratory infections without allergic disease (3623 ng/ml; p=0.2). The lower average values in the group comprised of children with respiratory allergy and infections were largely due to a high proportion of very low values: 18.3% had values below 2150 ng/ml compared to only 5.5% of healthy controls (OR=3.9; p=0.01). This relationship was not apparent in the groups characterized by allergy without infection or infections without allergy. An association between mannan-binding lectin (MBL) insufficiency and recurrent respiratory infections was also confirmed. One of the patients was MASP-2 deficient, evidenced both by MASP2 genotyping and by lectin pathway activity measurement. In conclusion, L-ficolin may confer some protection from microorganisms that exacerbate allergic inflammation in the lung and its relative deficiency may contribute to enhanced susceptibility to respiratory infections. MBL insufficiency and MASP-2 deficiency are risk factors for recurrence of infections independently of allergic disease.