Collectin liver 1 and collectin kidney 1 and other complement-associated pattern recognition molecules in systemic lupus erythematosus

CL-11 circulates in serum as functionally distinct isoforms

Collectin-11 (CL-11) is a pattern recognition molecule of the lectin pathway capable of interacting with collectin-10 (CL-10) and the MASPs to activate the complement cascade. Alternative splicing of the COLEC11 gene gives rise to two different isoforms found in serum (A and D). These isoforms vary in the length of their collagen-like region, which is involved in the stabilization of the trimeric subunit and the interaction with the MASPs. Here we aim at elucidating the biological differences of naturally occurring CL-11 isoforms A and D. We produced recombinant CL-11 as independent isoforms (CL-11A and CL-11D) and together with CL-10 (CL-10/11A, CL-10/11D). Both CL-11 isoforms associated with CL-10, but CL-11D did so to a lesser extent. CL-10/11 heterocomplexes were composed of trimeric subunits of CL-10 and CL-11, as opposed to CL-10 and CL-11 homotrimers. Heterocomplexes were more stable and migrated with higher apparent molecular weights. Immunoprecipitation of serum CL-11 and subsequent mass spectrometry analysis confirmed that native CL-11 circulates in the form of CL-10/11 heterocomplexes that associate with MASP-1, and MASP-3, but not necessarily MASP-2. Despite a shorter collagen region, CL-11D was capable to bind to the MASPs, suggesting that the missing exon 4 is not required for MASP association CL-11D had a reduced ligand binding compared to full-length CL-11A. Based on its reduced ability to oligomerize, form CL-10/11 heterocomplexes, and bind to ligands, we hypothesize that CL-11D may have a limited complement activation potential compared to full-length CL-11A.

Potential biomarkers for psoriasis topical treatment by in-depth serum proteomics

BACKGROUND

Psoriasis is a chronic skin disease, and topical sequential therapy with a combination of calcipotriol and calcipotriol betamethasone is currently approved topical treatment. However, the exact mechanism by which this treatment regimen relieves psoriasis is unknown.

METHOD

We assembled a cohort of 65 psoriasis patients and divided post-treatment cohort into responder group and non-responder group according to the Psoriasis Area Severity Index (PASI) score after 12-week treatment. We measured the expression levels of proteins in collected 130 serum samples using our in-depth proteomics platform with a data-independent acquisition mass spectrometer and antibody microarray. We performed bioinformatics analyses of the biologic processes and signaling pathways that were changed in the responder group and constructed a proteomics landscape of psoriasis pathogenesis response to treatment. We then validated the biomarkers of disease severity in an independent cohort of 88 samples using an enzyme-linked immunosorbent assay.

RESULTS

We first identified 174 differentially expressed proteins (DEPs) for comparative analysis of proteins between responders and non-responders at baseline (p < 0.05). Then pathway analysis showed that the responders focused more on signaling molecules and interaction, complement and coagulation cascades, whereas the non-responders more on signal transduction and IL-17 signaling pathways. We further identified four candidate biomarkers (COLEC11, C1QA, BNC2, ITIH4) response to treatment. We also found 125 DEPs (p < 0.05) after treatment compared with before treatment in responder group. Pathway analysis showed an enrichment in pathways related to complement and coagulation cascades, phagosome, ECM-receptor interaction, cholesterol metabolism, vitamin digestion and absorption. CD14 was validated as potential biomarkers for the disease severity of psoriasis and treatment targets.

CONCLUSION

In this work, we analyzed the response to topical sequential therapy and finally identified four biomarkers. Additionally, we found that topical sequential therapy may alleviate psoriasis by regulating lipid metabolism and modulating the immune response by affecting the complement activation process.

Pathogenic bacteria defense and complement activation function analysis of Collectin-10 from Hexagrammos otakii

With the tremendous success of the artificial breeding of Hexagrammos otakii, the yield has been substantially improved. However, intensive farming often results in bacterial diseases; hence it is imperative to find new antimicrobial molecules. In the present study, we identified a homologous cDNA fragment of collectin-10 from H. otakii, designated as HoCL-10. The cDNA length is 899 bp, which contains an open reading frame (ORF) of 816 bp encoding a secreted protein with 272 amino acid residues. The peptide of HoCL-10 contains an N-terminal collagen domain, a neck region, and a C-terminal carbohydrate recognition domain. The qRT-PCR results revealed that HoCL-10 mRNA was highest expressed in the liver and skin and was significantly induced post-LPS stimulation. The sugar and bacteria binding assay suggested that the recombinant HoCL-10 (rHoCL-10) could recognize various pathogen-associated molecular patterns (PAMPs) and bacteria. For effect on cells, rHoCL-10 enhanced the phagocytosis and migration ability of the macrophage indicated using pro-phagocytosis assay and trans-well assay. To determine the role of HoCL-10 in the complement system, the interaction between HoCL-10 and mannose-binding lectin associated serine protease 1, 2 (MASP-1, 2) were analyzed and demonstrated using ELISA and Far-western. And in vivo, the concentration of membrane-attack complex (MAC) in fish plasma was significantly down-regulated post-injection with HoCL-10 antibody. Finally, the bacteria challenge experiment was performed, implying that HoCL-10 may assist the host in defending against microbial invasion. The findings suggest that HoCL-10 may play crucial roles in host defense against microorganisms, possibly through opsonizing pathogens and activating the complement system.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Serum Proteomic Analysis by Tandem Mass Tag-Based Quantitative Proteomics in Pediatric Obstructive Sleep Apnea

Pediatric obstructive sleep apnea (OSA) is a frequent respiratory disorder with an estimated prevalence of 3–6% in the general population. However, the underlying pathophysiology of OSA remains unclear. Recently, proteomic analysis using high-resolution and high-throughput mass spectrometry has been widely used in the field of medical sciences. In the present study, tandem mass tag (TMT)-based proteomic analysis was performed in the serum of patients with OSA. The proteomic analysis revealed a set of differentially expressed proteins that may be associated with the pathophysiology of OSA. The differentially expressed proteins in patients with OSA were enriched in pathways including phagosome and glycan synthesis/degradation, immune response, and the hedgehog signaling pathway, indicating that such functions are key targets of OSA. Moreover, the experimental validation studies revealed that four proteins including ANTXR1, COLEC10, NCAM1, and VNN1 were reduced in the serum from patients with moderate and severe OSA, while MAN1A1 and CSPG4 protein levels were elevated in the serum from patients with severe OSA. The protein levels of ANTXR1, COLEC10, NCAM1, and VNN1 were inversely correlated with apnea-hypopnea index (AHI) in the recruited subjects, while the protein level of MAN1A1 was positively correlated with AHI, and no significant correlation was detected between CSPG4 protein and AHI. In summary, the present study for the first time identified differentially expressed proteins in the serum from OSA patients with different severities by using TMT-based proteomic analysis. The functional enrichment studies suggested that several signaling pathways may be associated with the pathophysiology of OSA. The experimental validation results indicated that six proteins including ANTXR1, COLEC10, NCAM1, VNN1, CGPG4, and MAN1A1 may play important roles in the pathophysiology of OSA, which requires further mechanistic investigation.

A Plausible Role for Collectins in Skin Immune Homeostasis

The skin is a complex organ that faces the external environment and participates in the innate immune system. Skin immune homeostasis is necessary to defend against external microorganisms and to recover from stress to the skin. This homeostasis depends on interactions among a variety of cells, cytokines, and the complement system. Collectins belong to the lectin pathway of the complement system, and have various roles in innate immune responses. Mannose-binding lectin (MBL), collectin kidney 1, and liver (CL-K1, CL-L1) activate the lectin pathway, while all have multiple functions, including recognition of pathogens, opsonization of phagocytosis, and modulation of cytokine-mediated inflammatory responses. Certain collectins are localized in the skin, and their expressions change during skin diseases. In this review, we summarize important advances in our understanding of how MBL, surfactant proteins A and D, CL-L1, and CL-K1 function in skin immune homeostasis. Based on the potential roles of collectins in skin diseases, we suggest therapeutic strategies for skin diseases through the targeting of collectins and relevant regulators.

Emerging role of ficolins in autoimmune diseases

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

The Immunopathology of Complement Proteins and Innate Immunity in Autoimmune Disease

The complement is a powerful cascade of the innate immunity and also acts as a bridge between innate and acquired immune defence. Complement activation can occur via three distinct pathways, the classical, alternative and lectin pathways, each resulting in the common terminal pathway. Complement activation results in the release of a range of biologically active molecules that significantly contribute to immune surveillance and tissue homeostasis. Several soluble and membrane-bound regulatory proteins restrict complement activation in order to prevent complement-mediated autologous damage, consumption and exacerbated inflammation. The crucial role of complement in the host homeostasis is illustrated by association of both complement deficiency and overactivation with severe and life-threatening diseases. Autoantibodies targeting complement components have been described to alter expression and/or function of target protein resulting in a dysregulation of the delicate equilibrium between activation and inhibition of complement. The spectrum of diseases associated with complement autoantibodies depends on which complement protein and activation pathway are targeted, ranging from autoimmune disorders to kidney and vascular diseases. Nevertheless, these autoantibodies have been identified as differential biomarkers for diagnosis or follow-up of disease only in a small number of clinical conditions. For some autoantibodies, a clear relationship with clinical manifestations has been identified, such as anti-C1q, anti-Factor H, anti-C1 Inhibitor antibodies and C3 nephritic factor. For other autoantibodies, the origin and the functional consequences still remain to be elucidated, questioning about the pathophysiological significance of these autoantibodies, such as anti-mannose binding lectin, anti-Factor I, anti-Factor B and anti-C3b antibodies. The detection of autoantibodies targeting complement components is performed in specialized laboratories; however, there is no consensus on detection methods and standardization of the assays is a real challenge. This review summarizes the current panorama of autoantibodies targeting complement recognition proteins of the classical and lectin pathways, associated proteases, convertases, regulators and terminal components, with an emphasis on autoantibodies clearly involved in clinical conditions.

Plasma levels of H- and L-ficolin are increased in axial spondyloarthritis: improvement of disease identification

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily affects the axial skeleton. A predominance of innate versus adaptive immune responses have been reported in axSpA, indicating a prominent autoinflammatory component of the disease. Little is known about the lectin pathway proteins (LPPs) of the complement system in relation to axSpA. We have investigated LPPs in patients with axSpA and control individuals. Plasma samples were obtained from a cross-sectional cohort of 120 patients with a clinical diagnosis of axSpA and from 144 age- and gender-matched controls. The plasma concentrations of 11 LPPs were measured, using sandwich-type time-resolved immunofluorometric assays in patients and controls, and related to clinical diagnosis and disease activity. Three LPPs [H-ficolin (ficolin-3), L-ficolin (ficolin-2) and collectin liver 1 (CL-L1)] were significantly higher in axSpA patients than in controls (P < 0·0001) and one LPP, collectin kidney 1 (CL-K1), was significantly lower (P < 0·0001). Further, combining H- or L-ficolin concentrations above the 75th percentile of the respective H- or L-ficolin concentration measured in controls with human leucocyte antigen (HLA)-B27 positivity yielded axSpA diagnostic specificities of 99/99% and positive likelihood ratios of 68/62, respectively. H-ficolin and L-ficolin plasma concentrations were found to be elevated in axSpA patients regardless of time since diagnosis. H-ficolin and L-ficolin may represent diagnostic biomarkers for patients with axSpA and should be further evaluated. Our results showed no association between disease activity and the measured LPP concentrations. This result might be due to the cross-sectional design, and should be further investigated.

Effect of long-term remote ischemic conditioning on inflammation and cardiac remodeling

Background. Remote ischemic conditioning (RIC) protects against acute ischemia-reperfusion injury and may have beneficial effects in patients with stable cardiovascular disease. We investigated the effect of long-term RIC treatment in patients with chronic ischemic heart failure (CIHF). Methods. Prespecified post-hoc analysis of a prospective, exploratory and outcome-assessor blinded study. Twenty-one patients with compensated CIHF and 21 matched controls without heart failure or ischemic heart disease were treated with RIC once daily for 28 ± 4 days. RIC was conducted as 4 cycles of 5 minutes upper arm ischemia followed by 5 minutes of reperfusion. We evaluated circulating markers of inflammation and cardiac remodeling at baseline and following long-term RIC. Results. RIC reduced C-reactive protein from 1.5 (0.6-2.5) to 1.3 (0.6-2.1) mg/l following long-term RIC treatment (p = .02) and calprotectin from 477 (95% CI 380 to 600) to 434 (95% CI 354 to 533) ng/ml (p = .03) in patients with CIHF, but not in matched controls. Overall, RIC did not affect circulating markers related to adaptive or innate immunology or cardiac remodeling in patients with CIHF. Among patients with CIHF and N-terminal pro-brain natriuretic peptide (NT-proBNP) plasma levels above the geometric mean of 372 ng/l, long-term RIC treatment reduced soluble ST2 (n = 9) from 22.0 ± 3.7 to 20.3 ± 3.9 ng/ml following long-term RIC treatment (p = .01). Conclusion. Our findings suggest that long-term RIC treatment has mild anti-inflammatory effects in patients with compensated CIHF and anti-remodeling effects in those with increased NT-proBNP levels. This should be further investigated in a randomized sham-controlled trial.

Changes in the Lectin Pathway Following Intracerebral or Spontaneous Subarachnoid Hemorrhage

Previous research indicates that the complement system is activated after occurrence of intracerebral hemorrhage (ICH) and spontaneous subarachnoid hemorrhage (SAH). The role of the lectin pathway (LP) of the complement system in this activation has only scarcely been investigated. The aim of this study was to determine the plasma concentration of the LP proteins in patients with ICH or SAH at admission compared to healthy individuals. Secondly, ICH and SAH patients were followed during the initial 24 h of disease, to investigate changes in LP protein concentrations during the critical acute phase. This prospective, observational study included 30 ICH and 33 SAH patients. EDTA plasma samples were collected at admission, 6 and 24 h after symptom onset. Time-resolved immuno-flourometric assays (TRIFMA) were used to measure all proteins of the LP in patient samples and in samples from age- and gender-matched healthy individuals. Compared to healthy individuals, ICH and SAH patients had increased levels of H-ficolin (p = 0.04, p = 0.03), M-ficolin (both p < 0.0001), and MAp44 (both p = 0.01) at admission. M-ficolin, H-ficolin, CL-L1, MASP-1, MASP-3, and MAp44 decreased significantly in both ICH and SAH patients during the initial 24 h after symptom onset. In conclusion, we observed significant differences in lectin pathway protein concentrations between patients with ICH or SAH and healthy individuals. Significant dynamics in lectin pathway protein levels were demonstrated during the initial 24 h after symptom onset. This indicates a potential role of the LP proteins during the acute phase of SAH and ICH.

Development of a Quantitative Assay for the Characterization of Human Collectin-11 (CL-11, CL-K1)

Collectin-11 (CL-11) is a pattern recognition molecule of the lectin pathway of complement with diverse functions spanning from host defense to embryonic development. CL-11 is found in the circulation in heterocomplexes with the homologous collectin-10 (CL-10). Abnormal CL-11 plasma levels are associated with the presence of disseminated intravascular coagulation, urinary schistosomiasis, and congenital disorders. Although there has been a marked development in the characterization of CL-11 there is still a scarcity of clinical tools for its analysis. Thus, we generated monoclonal antibodies and developed a quantitative ELISA to measure CL-11 in the circulation. The antibodies were screened against recombinant CL-11 and validated by ELISA and immunoprecipitation of serum and plasma. The best candidates were pairwise compared to develop a quantitative ELISA. The assay was validated regarding its sensitivity, reproducibility, and dilution linearity, demonstrating a satisfactory variability over a working range of 0.29–18.75 ng/ml. The mean plasma concentration of CL-11 in healthy controls was determined to be 289.4 ng/ml (range 143.2–459.4 ng/ml), highly correlated to the levels of CL/10/11 complexes (r = 0.729). Plasma CL-11 and CL-10/11 co-migrated in size exclusion chromatography as two major complexes of ~400 and >600 kDa. Furthermore, we observed a significant decrease at admission in CL-11 plasma levels in patients admitted to intensive care with systemic inflammatory response syndrome. By using the in-house antibodies and recombinant CL-11, we found that CL-11 can bind to zymosan independently of calcium by a separate site from the carbohydrate-binding region. Finally, we showed that CL-11/MASP-2 complexes trigger C4b deposition on zymosan. In conclusion, we have developed a specific and sensitive ELISA to investigate the ever-expanding roles of CL-11 in health and disease and shown a novel interaction between CL-11 and zymosan.

Decreased expression of COLEC10 predicts poor overall survival in patients with hepatocellular carcinoma

Purpose

Collectin subfamily member 10 (COLEC10) encodes for collectin liver 1 (CL-L1), which is highly expressed in normal liver. Nevertheless, the association between COLEC10 and the prognosis of patients with hepatocellular carcinoma (HCC) remains unclear. To address this question, the prognostic value of COLEC10 expression in HCC was explored in this study.

Patients and methods

Data from The Cancer Genome Atlas were used to compared transcriptional levels of COLEC10 in HCC samples and samples from healthy controls. In addition, COLEC10 mRNA and protein expression levels were analyzed in HCC tissue samples from Chinese patients and matched adjacent nontumorous tissue samples, by quantitative reverse-transcription polymerase chain reaction and immunohistochemistry, respectively. The prognostic value of COLEC10 was further examined using the Gene Expression Profiling Interactive Analysis online tool.

Results

Both the mRNA and protein levels of COLEC10 were found to be downregulated in HCC tissues compared with normal controls. Survival analysis indicated that decreased mRNA and protein levels of COLEC10 were related with shorter overall survival in patients with HCC. In addition, univariate and multivariate analysis demonstrated that COLEC10 is an independent prognostic factor for overall survival of HCC patients.

Conclusion

Together, the results suggest that decreased expression of COLEC10 may predict poor overall survival in patients with HCC.

Substitution of Mannan-Binding Lectin (MBL)-Deficient Serum With Recombinant MBL Results in the Formation of New MBL/MBL-Associated Serine Protease Complexes

The lectin pathway (LP) of complement activation depends on the activation of the MBL-associated serine proteases (MASPs) circulating in complex with mannan-binding lectin (MBL). MBL deficiency is the most common complement deficiency and has been associated with several pathological conditions. As we had previously shown, plasma-derived MBL (pdMBL) contains pre-activated MASPs that upon in vivo pdMBL substitution results in restoration of MBL concentrations but no LP functionality due to immediate inactivation of pdMBL-MASP complexes upon infusion. In this study, we analyzed MBL-sufficient and -deficient serum by size-exclusion chromatography for complexes of LP activation. In both sera, we identified non-bound free forms of MASP-2 and to lesser extent MASP-1/3. After addition of recombinant MBL (rMBL) to MBL-deficient serum, these free MASPs were much less abundantly present, which is highly suggestive for the formation of high-molecular complexes that could still become activated upon subsequent ligand binding as shown by a restoration of C4-deposition of MBL-deficient serum. Ficolin (FCN)-associated MASPs have been described to redistribute to ligand-bound MBL, hereby forming new MBL/MASP complexes. However, reconstitution of MBL-deficient serum with rMBL did not change the relative size of the FCN molecules suggestive for a limited redistribution in fluid phase of already formed complexes. Our findings demonstrate that rMBL can associate with free non-bound MASPs in fluid phase while preserving full restoration of LP functionality. In contrast to pdMBL products containing pre-activated MASPs which become inactivated almost immediately, these current data provide a rationale for substitution studies using rMBL instead.

The Lectin Pathway of Complement Activation in Patients with Systemic Lupus Erythematosus

OBJECTIVE

The pathogenesis of systemic lupus erythematosus (SLE) involves complement activation. Activation of complement through the classical pathway (CP) is well established. However, complement activation through pattern recognition not only happens through the CP, but also through the lectin pathway (LP). We investigated the hypothesis that the LP is activated in SLE and involved in the pathogenesis of the disease.

METHODS

Using immunoassays developed in-house, we measured concentrations of LP proteins in a cohort of 372 patients with SLE and 170 controls. We estimated complement activation measuring total C3, and investigated whether LP protein concentrations were associated with complement activation and disease activity. Protein changes and disease activity over time were assessed in a cohort of 52 patients with SLE followed with repeated samples over a 5-year period.

RESULTS

Concentrations of LP proteins in SLE were altered compared with controls. The differences observed in LP proteins associated with complement activation were reflected by a decrease in total C3. The pattern recognition molecules (M-ficolin, CL-L1, and CL-K1), the serine protease (MASP-3), and the associated protein (MAp19) displayed a negative correlation with disease activity. Changes in MASP-2 concentrations over time correlated significantly with increased disease activity. Association between active proteinuria and serum concentration was observed for MASP-3 and MAp19.

CONCLUSION

In patients with SLE, we measured specific changes in LP proteins that are associated with complement activation and disease activity, indicating that the LP is activated in patients with SLE. These novel findings substantiate the involvement of the LP in SLE.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Serum proteomics study reveals candidate biomarkers for systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease which is characterized by the presence of autoantibodies. It will be helpful if specific serum biomarkers can be used for monitoring the disease activity as well as differentiating SLE from other diseases. For this purpose, we used a label free-based two dimensional liquid chromatography mass spectrometry platform to analyze serum samples from SLE patients in active or inactivestage. Significant differences were found for 42 serum proteins implicated in pathways including complement and coagulation cascades. Further gene set enrichment analysis revealed that gene sets including formation of fibrin clot, ECM glycoproteins and innate immune system were highly correlated with the SLE disease activity. To further assess the validity of these findings, thrombospondin-4 was selected for subsequent ELISA assays. We also explored the autoantibody of three candidate biomarkers in larger cohorts including SLE, Rheumatoid arthritis, Sjogrensyndrome patients and normal controls. Our findings provided valuable information on the proteomic changes in the serum of different SLE disease activity. Serum properdin, collectin-11 and thrombospondin-4 were valuable in monitoring the disease activity of SLE, and the autoantibodies to them may be valuable in differentiating SLE from other diseases for clinical diagnosis in the future.

COLEC10 is mutated in 3MC patients and regulates early craniofacial development

3MC syndrome is an autosomal recessive heterogeneous disorder with features linked to developmental abnormalities. The main features include facial dysmorphism, craniosynostosis and cleft lip/palate; skeletal structures derived from cranial neural crest cells (cNCC). We previously reported that lectin complement pathway genes COLEC11 and MASP1/3 are mutated in 3MC syndrome patients. Here we define a new gene, COLEC10, also mutated in 3MC families and present novel mutations in COLEC11 and MASP1/3 genes in a further five families. The protein products of COLEC11 and COLEC10, CL-K1 and CL-L1 respectively, form heteromeric complexes. We show COLEC10 is expressed in the base membrane of the palate during murine embryo development. We demonstrate how mutations in COLEC10 (c.25C>T; p.Arg9Ter, c.226delA; p.Gly77Glufs*66 and c.528C>G p.Cys176Trp) impair the expression and/or secretion of CL-L1 highlighting their pathogenicity. Together, these findings provide further evidence linking the lectin complement pathway and complement factors COLEC11 and COLEC10 to morphogenesis of craniofacial structures and 3MC etiology.

The 3MC syndrome is a unifying term amalgamating four rare recessive genetic disorders with overlapping features namely; Mingarelli, Malpuech, Michels and Carnevale syndromes. It is characterised by facial malformations including, high-arched eyebrows, cleft lip/palate, hypertelorism, developmental delay and hearing loss. We previously reported that lectin complement pathway genes COLEC11 and MASP1/3 were mutated in 3MC syndrome patients. Here we describe a new gene from the same pathway, COLEC10, mutated in 3MC patients. Our results show that COLEC10 is expressed in craniofacial tissues during development. We demonstrate how CL-L1, the protein expressed by COLEC10, can act as a cellular chemoattractant in vitro, controlling cell movement and migration. We overexpressed constructs carrying COLEC10 non-sense mutations found in our patients, CL-L1 failed to be expressed and secreted. Moreover, when we expressed a missense COLEC10 construct, CL-L1 was expressed but failed to be secreted. In sum, we discovered a new gene, COLEC10, mutated in 3MC syndrome and we propose a pathogenic mechanism for 3MC relating to the failure of CL-L1 function and its craniofacial developmental consequences.

Collectin Liver 1 and Collectin Kidney 1 of the Lectin Complement Pathway Are Associated With Mortality After Kidney Transplantation

Kidney transplanted patients still have significantly higher mortality compared with the general population. The innate immune system may play an important role during periods, with suppression of the adaptive immune system. In the present study, two soluble pattern recognition molecules of the innate immune system were investigated, collectin liver 1 (CL-L1) and collectin kidney 1 (CL-K1). Potential associations of their pretransplant levels and long-term graft and recipient survival were examined. The levels of CL-L1 and CL-K1 were measured at the time of transplantation in 382 patients (≥17 years) transplanted in 2000-2001. The cohort was subsequently followed until December 31, 2014. Data on patient and graft survival were obtained from the Norwegian Renal Registry. Both high CL-L1 (≥376 ng/mL) and high CL-K1 (≥304 ng/mL) levels were significantly associated with overall mortality in multivariate Cox analyses with hazard ration (HR) 1.50, 95% confidence interval (CI) 1.09-2.07, p = 0.013 and HR 1.43, 95% CI 1.02-1.99, p = 0.038, respectively. Moreover, high CL-K1 levels were significantly associated with cardiovascular mortality. No association between measured biomarkers and death-censored graft loss was found. Finally, there was a significant correlation between these two collectins, r = 0.83 (95% CI 0.80-0.86). In conclusion, CL-L1 and CL-K1 were significantly associated with mortality in kidney transplant recipients.

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.

The pattern recognition molecule collectin-L1 in critically ill children

BACKGROUND

Critically ill children are prone to nosocomial infections, which may lead to adverse outcome. Low serum concentrations upon admission to the pediatric intensive care unit (PICU) of the mannan-binding lectin (MBL)-associated serine protease (MASP)-3 protein of the lectin pathway of complement activation have been associated with risk of infection and prolonged need for intensive care. We hypothesized that also a low upon-admission concentration of collectin-L1 (CL-L1), a novel member of this pathway, is independently associated with these adverse outcomes.

METHODS

We quantified the serum concentrations of CL-L1 in 81 healthy children and in 700 critically ill children upon PICU admission.

RESULTS

CL-L1 concentrations were significantly lower in the critically ill children as compared with the healthy children. However, corrected for baseline characteristics, risk factors and several lectin pathway proteins, a higher CL-L1 concentration upon PICU admission was independently associated with an increased risk of acquiring a new infection and with a prolonged time to PICU discharge. In contrast, a low MASP-3 concentration remained independently associated with these adverse outcomes.

CONCLUSION

A high serum CL-L1 concentration in critically ill children upon PICU admission is associated with an increased risk of infection and prolonged need of intensive care, and counteracts the protective effect of having a high MASP-3 concentration.

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.

Mannose-binding lectin polymorphisms and rheumatoid arthritis: A short review and meta-analysis

Mannose-binding lectin (MBL) is a pattern recognition receptor of the lectin pathway of complement system. MBL binds to carbohydrates on microorganism's surfaces leading to complement activation, opsonization and phagocytosis. Polymorphisms in the MBL gene (MBL2) are associated with variations on MBL serum levels and with the susceptibility to various infectious and autoimmune diseases. The involvement of the lectin pathway in rheumatoid arthritis (RA) has been demonstrated by several studies and although MBL has been considered to have a dual role in the pathogenesis of the disease, the association between MBL and RA remains inconclusive. In an attempt to clarify this relationship, we developed this short review summarizing accumulated evidences in regard to MBL and RA and a meta-analysis to evaluate the influence of MBL2 polymorphisms on the susceptibility to RA. Among a total of 217 articles that were identified following a predefined search strategy on PubMed, Scopus, Scielo, EMBASE and Cochrane databases, only 13 met all inclusion criteria and were included in the meta-analysis. Data assessment was conducted by three independent investigators and presented in odds ratio (OR) and 95% confidence intervals (CIs) using forest plot charts. Both heterogeneity and publication bias were analyzed. The results of the meta-analysis evidenced that MBL2 low producing OO and XX genotypes do not confer higher risk to RA, even when data were analyzed according to cohort's ethnicity. Further studies are needed in order to clarify the importance of other genes of the lectin pathway in the pathogenesis of RA.