Increased incidence and severity of the systemic inflammatory response syndrome in patients deficient in mannose-binding lectin

The role of mannose-binding lectin (MBL) in diabetic retinopathy: A scoping review

Diabetes mellitus (DM) is a chronic systemic disease characterized by a multifactorial nature, which may lead to several macro and microvascular complications. Diabetic retinopathy (DR) is one of the most severe microvascular complications of DM, which can result in permanent blindness. The mechanisms involved in the pathogenesis of DR are multiple and still poorly understood. Factors such as dysregulation of vascular regeneration, oxidative and hyperosmolar stress in addition to inflammatory processes have been associated with the pathogenesis of DR. Furthermore, compelling evidence shows that components of the immune system, including the complement system, play a relevant role in the development of the disease. Studies suggest that high concentrations of mannose-binding lectin (MBL), an essential component of the complement lectin pathway, may contribute to the development of DR in patients with DM. This review provides an update on the possible role of the complement system, specifically the lectin pathway, in the pathogenesis of DR and discusses the potential of MBL as a non-invasive biomarker for both, the presence and severity of DR, in addition to its potential as a therapeutic target for intervention strategies.

Mannose-Binding Lectin 2 as a Potential Therapeutic Target for Hepatocellular Carcinoma: Multi-Omics Analysis and Experimental Validation

Mannose-binding lectin 2 (MBL2), a member of the multimeric lectin family, is crucial in immune regulation and tumor development. MBL2 gene polymorphisms are associated with the risk and prognosis of various tumors, including hepatocellular carcinoma (HCC). Its functional role in HCC remains largely unclear. In this study, we aimed to identify whether MBL2 is a key regulator and a potential therapeutic target for HCC. A bioinformatics analysis revealed close relationships among MBL2 downregulation, the tumor-associated proliferation and metastasis pathway, and tumor immunosuppressive microenvironments. Lower expression of MBL2 in HCC patients was linked to an unfavorable prognosis. A cell counting kit-8 assay, colony formation assay, transwell migration assay, and wound healing assay further confirmed that the overexpression of MBL2 could directly inhibit the proliferation and metastasis of HCC. Moreover, MBL2 expression was regulated by miR-34c-3p, as confirmed by the dual-luciferase reporter assay, thereby demonstrating tumor progression in HCC cells. Thus, our study offers the first comprehensive confirmation of the role of MBL2 in the development of HCC through multi-omics analysis and experimental validation. Furthermore, miR-34c-3p was found to be an upstream mechanism of the downregulation of MBL2 expression and could be a promising therapeutic target, expanding treatment options for patients with HCC.

Development and validation of a patient-specific model to predict postoperative SIRS in older patients: A two-center study

Introduction

Postoperative systemic inflammatory response syndrome (SIRS) is common in surgical patients especially in older patients, and the geriatric population with SIRS is more susceptible to sepsis, MODS, and even death. We aimed to develop and validate a model for predicting postoperative SIRS in older patients.

Methods

Patients aged ≥65 years who underwent general anesthesia in two centers of Third Affiliated Hospital of Sun Yat-sen University from January 2015 to September 2020 were included. The cohort was divided into training and validation cohorts. A simple nomogram was developed to predict the postoperative SIRS in the training cohort using two logistic regression models and the brute force algorithm. The discriminative performance of this model was determined by area under the receiver operating characteristics curve (AUC). The external validity of the nomogram was assessed in the validation cohort.

Results

A total of 5,904 patients spanning from January 2015 to December 2019 were enrolled in the training cohort and 1,105 patients from January 2020 to September 2020 comprised the temporal validation cohort, in which incidence rates of postoperative SIRS were 24.6 and 20.2%, respectively. Six feature variables were identified as valuable predictors to construct the nomogram, with high AUCs (0.800 [0.787, 0.813] and 0.822 [0.790, 0.854]) and relatively balanced sensitivity (0.718 and 0.739) as well as specificity (0.718 and 0.729) in both training and validation cohorts. An online risk calculator was established for clinical application.

Conclusion

We developed a patient-specific model that may assist in predicting postoperative SIRS among the aged patients.

Mannose-binding lectin gene polymorphism and the susceptibility of sepsis: A meta-analysis

Objective

To assess the association between the Mannose-binding lectin (MBL) gene polymorphism and the susceptibility to sepsis using a meta-analysis.

Methods

The publications were searched on PubMed, Embase, and Web of Science databases up to December 1, 2019 for relevant literature.

Results

A total of 32 studies (21 adult and 11 pediatric studies) were selected for analysis. Overall, in the three models of MBL +54 A/B gene polymorphisms, namely the dominant model BB + AB vs. AA ( p = 0.03), the recessive model BB vs. AB + AA ( p < 0.00001), and the allele model B vs. A ( p = 0.04), MBL +54 A/B was significantly related to the risk of sepsis. In the adult group, the MBL A/O gene polymorphism was associated with the risk of sepsis in the dominant model AO + OO vs. AA ( p = 0.006) as well as in the allele model O vs. A ( p = 0.04). The MBL +54 A/B gene polymorphism was significantly related to the risk of sepsis in the recessive model and, therefore, may increase the risk of sepsis. In the pediatric group, no polymorphic loci were significantly associated with sepsis in any of the three models. The results of the publication bias test demonstrated no publication bias in an unadjusted estimate of the relationship between MBL A/O and −211Y/X gene polymorphism and sepsis.

Conclusions

The polymorphisms of MBL that are related to the occurrence of sepsis are primarily A/O and +54 A/B, while −221Y/X and −550H/L have no clear relationship with the susceptibility of sepsis in various age groups or different models.

Status of mannose-binding lectin (MBL) and complement system in COVID-19 patients and therapeutic applications of antiviral plant MBLs

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by a virus called "Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)." In the majority of patients, infection with COVID-19 may be asymptomatic or may cause only mild symptoms. However, in some patients, there can also be immunological problems, such as macrophage activation syndrome (CSS) that results in cytokine storm syndrome (CSS) and acute respiratory distress syndrome (ARDS). Comprehension of host-microbe communications is the critical aspect in the advancement of new therapeutics against infectious illnesses. Endogenous animal lectins, a class of proteins, may perceive non-self glycans found on microorganisms. Serum mannose-binding lectin (sMBL), as a part of the innate immune framework, recognizes a wide range of microbial microorganisms and activates complement cascade via an antibody-independent pathway. Although the molecular basis for the intensity of SARS-CoV-2 infection is not generally understood, scientific literature indicates that COVID-19 is correlated with unregulated activation of the complement in terms of disease severity. Disseminated intravascular coagulation (DIC), inflammation, and immune paralysis contribute to unregulated complement activation. Pre-existing genetic defects in MBL and their association with complement play a major role in immune response dysregulation caused by SARS-CoV-2. In order to generate anti-complement-based therapies in Covid-19, an understanding of sMBL in immune response to SARS-CoV-2 and complement is therefore essential. This review highlights the role of endogenous sMBL and complement activation during SARS-CoV-2 infection and their therapeutic management by various agents, mainly plant lectins, since antiviral mannose-binding plant lectins (pMBLs) offer potential applications in the prevention and control of viral infections.

Levels of mannose-binding lectin (MBL) associates with sepsis-related in-hospital mortality in women

Background

Mannose-binding lectin (MBL) mediates the innate immune response either through direct opsonisation of microorganisms or through activation of the complement system. There are conflicting data whether MBL deficiency leads to increased susceptibility to infections or not. The aim of this study was to determine if low levels of mannose-binding lectin (MBL) predict sepsis development, sepsis severity and outcome from severe sepsis or septic shock.

Method

Patients aged 18 years or more with documented sepsis within 24 h after admission to the intensive care unit were included if they had participated in a health survey and donated blood samples prior to the sepsis event. A subset of these patients had stored plasma also from the acute phase. Two matched referents free of known sepsis were selected for each case. Plasma levels MBL were determined in stored samples from health surveys (baseline) and from ICU admission (acute phase). The association between MBL and sepsis, sepsis severity and in-hospital mortality were determined with 1300 ng/mL as cut-off for low levels.

Results

We identified 148 patients (61.5% women) with a first-time sepsis event 6.5 years (median with IQR 7.7) after participation in a health survey, of which 122 also had samples from the acute septic phase. Both high MBL levels in the acute phase (odds ratio [95% confidence interval]) (2.84 [1.20-6.26]), and an increase in MBL levels from baseline to the acute phase (3.76 [1.21-11.72]) were associated with increased risk for in-hospital death in women, but not in men (0.47 [0.11-2.06]). Baseline MBL levels did not predict future sepsis, sepsis severity or in-hospital mortality.

Conclusions

An increase from baseline to the acute phase as well as high levels in the acute phase associated with an unfavourable outcome in women.

Targeting the complement system in bacterial meningitis

Bacterial meningitis is most commonly caused by Streptococcus pneumoniae and Neisseria meningitidis and continues to pose a major public health threat. Morbidity and mortality of meningitis are driven by an uncontrolled host inflammatory response. This comprehensive update evaluates the role of the complement system in upregulating and maintaining the inflammatory response in bacterial meningitis. Genetic variation studies, complement level measurements in blood and CSF, and experimental work have together led to the identification of anaphylatoxin C5a as a promising treatment target in bacterial meningitis. In animals and patients with pneumococcal meningitis, the accumulation of neutrophils in the CSF was mainly driven by C5-derived chemotactic activity and correlated positively with disease severity and outcome. In murine pneumococcal meningitis, adjunctive treatment with C5 antibodies prevented brain damage and death. Several recently developed therapeutics target C5 conversion, C5a, or its receptor C5aR. Caution is warranted because treatment with C5 antibodies such as eculizumab also inhibits the formation of the membrane attack complex, which may result in decreased meningococcal killing and increased meningococcal disease susceptibility. The use of C5a or C5aR antagonists to specifically target the harmful anaphylatoxins-induced effects, therefore, are most promising and present opportunities for a phase 2 clinical trial.

No association of complement mannose-binding lectin deficiency with cardiovascular disease in patients with Systemic Lupus Erythematosus

Cardiovascular (CV) morbidity is the major cause of death in patients with Systemic Lupus Erythematosus (SLE). Previous studies on mannose-binding lectin (MBL) gene polymorphisms in SLE patients suggest that low levels of complement MBL are associated with cardiovascular disease (CVD). However, as large studies on MBL deficiency based on resulting MBL plasma concentrations are lacking, the aim of our study was to analyze the association of MBL concentrations with CVD in SLE patients. Plasma MBL levels SLE patients included in the Swiss SLE Cohort Study were quantified by ELISA. Five different CV organ manifestations were documented. Of 373 included patients (85.5% female) 62 patients had at least one CV manifestation. Patients with MBL deficiency (levels below 500 ng/ml or 1000 ng/ml) had no significantly increased frequency of CVD (19.4% vs. 15.2%, P = 0.3 or 17.7% vs. 15.7%, P = 0.7). After adjustment for traditional CV risk factors, MBL levels and positive antiphospholipid serology (APL+) a significant association of CVD with age, hypertension, disease duration and APL+ was demonstrated. In our study of a large cohort of patients with SLE, we could not confirm previous studies suggesting MBL deficiency to be associated with an increased risk for CVD.

Mannan-Binding Lectin Regulates Inflammatory Cytokine Production, Proliferation, and Cytotoxicity of Human Peripheral Natural Killer Cells

Natural killer (NK) cells represent the founding members of innate lymphoid cells (ILC) and play critical roles in inflammation and the immune response. NK cell effector functions are regulated and fine-tuned by various immune modulators. Mannan (or mannose)-binding lectin (MBL), a soluble C-type lectin, is traditionally recognized as an initiator of the complement pathway. Recently, it is also considered as an immunomodulator by its interaction with kinds of immune cells. However, the effect of MBL on NK cell function remains unexplored. In this study, we found that human plasma MBL could interact directly with peripheral NK cells partially via its collagen-like region (CLR). This MBL binding markedly suppressed the interleukin-2- (IL-2-) induced inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) production but increased the IL-10 production in NK cells. In addition, the expression of activation surface markers such as CD25 and CD69 declined after MBL treatment. Also, MBL impaired the proliferation and lymphokine-activated killing (LAK) of NK cells. Moreover, we demonstrated that MBL inhibited IL-2-induced signal transducers and activators of transcription 5 (STAT5) activation in NK cells. In conclusion, we have uncovered a far unknown regulatory role of MBL on NK cells, a new clue that could be important in the immunomodulatory networks of immune responses.

Is mannose-binding lectin serum concentration a reliable predictor for recurrent vulvovaginal candidiasis?

Recurrent vulvovaginal candidiasis (RVVC) is a common opportunistic, mucosal fungal infection, predominantly caused by the fungus Candida albicans. Mannose-binding lectin (MBL) is an acute-phase protein that plays a key role in the innate immunity defence against infectious disease. This study was conducted to evaluate the relationship between the MBL serum level and the relative expression of MBL mRNA in RVVC using real-time PCR for the first time. The case-control study included 40 female participants suffering from RVVC and 40 healthy individuals. The MBL serum level was measured using a commercial ELISA kit. The relative mRNA expression of the MBL gene was quantified using real-time PCR. Data analysis was carried out by spss software. The MBL concentration was significantly higher in the participants suffering from RVVC compared to the control group (0.330 ng/mL vs 0.253 ng/mL). The prognostic value (P < .001) for RVVC diagnosis has been calculated. Quantitative RT-PCR results from 35 samples showed a low to significant values for mRNA levels corresponding to MBL gene expression (1-352 folds) (P < .001). The results of this study suggest that MBL plays a main role in the innate immunity and it is also affected by environmental factors and other genetic variations. Therefore, the MBL gene expression profile does not reflect precise phenotypic levels in the serum.

Serial Changes in Mannose-Binding Lectin in Patients with Sepsis

Background

Mannose-binding lectin (MBL) deficiency leads to increased susceptibility to infection. We investigated whether serial changes in MBL levels are associated with the prognosis of patients diagnosed with septic shock, and correlated with cytokine levels.

Methods

We enrolled 131 patients with septic shock in the study. We analyzed the serum samples for MBL and cytokine levels at baseline and 7 days later. Samples on day 7 were available in 73 patients.

Results

We divided the patients with septic shock into four groups according to serum MBL levels (<1.3 µg/mL or ≥1.3 µg/mL) on days 1 and 7. Patients with low MBL levels on day 1 and high MBL levels on day 7 showed a favorable prognosis for 28-day survival (odds ratio, 1.96, 95% confidence interval, 1.10–2.87; p=0.087). The high MBL group on day 7 showed a significant decrease in monocyte chemoattractant protein 1, interleukin (IL)-1β, IL-6, IL-8, interferon-γ, and granulocyte macrophage colony-stimulating factor levels compared with the low MBL group on day 7.

Conclusion

The increase in MBL levels of patients with septic shock may suggest a favorable prognosis and attenuate pro-inflammatory and anti-inflammatory responses.

Mannose-Binding Lectin-Deficient Donors Increase the Risk of Bacterial Infection and Bacterial Infection-Related Mortality After Liver Transplantation

Mannose-binding lectin (MBL) is synthesized by the liver and binds to microbes. MBL2 gene polymorphisms produce intermediate/low/null or normal MBL serum levels (MBL-deficient or MBL-sufficient phenotypes, respectively). We aimed to evaluate the incidence and severity of infection, rejection, and survival within 1 year after liver transplantation (LT) according to donor and recipient MBL2 gene polymorphisms. A repeated-event analysis for infection episodes (negative binomial regression, Andersen-Gill model) was performed in 240 LTs. Four hundred twenty-eight infectious episodes (310 bacterial, 15 fungal, 65 cytomegalovirus [CMV]-related, and 38 viral non-CMV-related episodes) and 48 rejection episodes were recorded. The main bacterial infections were urinary (n = 82, 26%) and pneumonia (n = 69, 22%). LT recipients of MBL-deficient livers had a higher risk of bacterial infection (incidence rate ratio [IRR] 1.48 [95% confidence interval 1.04-2.09], p = 0.028), pneumonia (IRR 2.4 [95% confidence interval 1.33-4.33], p = 0.013), and septic shock (IRR 5.62 [95% confidence interval 1.92-16.4], p = 0.002) compared with recipients of MBL-deficient livers. The 1-year bacterial infection-related mortality was higher in recipients of MBL-deficient versus MBL-sufficient livers (65.8% vs. 56.1%, respectively; p = 0.0097). The incidence of rejection, viral, or fungal infection was similar in both groups. Recipient MBL2 genotype did not significantly increase the risk of bacterial infection. LT recipients of MBL-deficient livers have a higher risk of bacterial infection, pneumonia, septic shock, and 1-year bacterial infection-related mortality after LT.

Mannose-Binding Lectin Levels in Critically Ill Children With Severe Infections

OBJECTIVES

Low mannose-binding lectin levels and haplotypes associated with low mannose-binding lectin production have been associated with infection and severe sepsis. We tested the hypothesis that mannose-binding lectin levels would be associated with severe infection in a large cohort of critically ill children.

DESIGN

Prospective cohort study.

SETTING

Medical and Surgical PICUs, Boston Children's Hospital.

PATIENTS

Children less than 21 years old admitted to the ICUs from November 2009 to November 2010.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured mannose-binding lectin levels in 479 of 520 consecutively admitted children (92%) with severe or life-threatening illness. We genotyped 213 Caucasian children for mannose-binding lectin haplotype tagging variants and assigned haplotypes. In the univariate analyses of mannose-binding lectin levels with preadmission characteristics, levels were higher in patients with preexisting renal disease. Patients who received greater than 100 mL/kg of fluids in the first 24 hours after admission had markedly lower mannose-binding lectin, as did patients who underwent spinal fusion surgery. Mannose-binding lectin levels had no association with infection status at admission, or with progression from systemic inflammatory response syndrome to sepsis or septic shock. Although mannose-binding lectin haplotypes strongly influenced mannose-binding lectin levels in the predicted relationship, low mannose-binding lectin-producing haplotypes were not associated with increased risk of infection.

CONCLUSIONS

Mannose-binding lectin levels are largely genetically determined. This relationship was preserved in children during critical illness, despite the effect of large-volume fluid administration on mannose-binding lectin levels. Previous literature evaluating an association between mannose-binding lectin levels and severe infection is inconsistent; we found no relationship in our PICU cohort. We found that mannose-binding lectin levels were lower after aggressive fluid resuscitation and suggest that studies of mannose-binding lectin in critically ill patients should assess mannose-binding lectin haplotypes to reflect preillness levels.

Mannose-Binding Lectin: Biologic Characteristics and Role in the Susceptibility to Infections and Ischemia-Reperfusion Related Injury in Critically Ill Neonates

The mannose-binding lectin (MBL) is a member of the collectin family, belonging to the innate immunity system. Genetic, biologic, and clinical properties of MBL have been widely investigated throughout the last decades, although some interesting aspects of its potential clinical relevance are still poorly understood. Low circulating concentrations of MBL have been associated with increased risk of infection and poor neurologic outcome in neonates. On the other hand, an excessive and uncontrolled inflammatory response by the neonatal intestine after the exposure to luminal bacteria, leading to an increased production of MBL, may be involved in the onset of necrotizing enterocolitis. The purpose of the present review is to summarize the current knowledge about genetic and biologic characteristics of MBL and its role in the susceptibility to infections and to ischemia-reperfusion related tissue injuries to better explore its clinical relevance during the perinatal period and the possible future therapeutic applications.

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.

Association of mannose-binding lectin levels and invasive fungal disease in hematologic malignancy patients receiving myelosuppressive chemotherapy or allogeneic hematopoietic stem cell transplantation

Several studies have suggested an association of mannose-binding lectin (MBL) deficiency with infections. In this study, we investigated the association between MBL deficiency and invasive fungal disease (IFD) in hematologic malignancy patients receiving myelosuppressive chemotherapy or hematopoietic stem cell transplant. MBL levels were quantified at the start of treatment in 152 patients who were followed for 6 months and scored as developing IFD or not. Forty-five patients (29.6%) developed IFD, of which 21 (46.7% of IFD cases and 13.8% of patients) were proven or probable IFD. Fifty-nine (38.8%) had MBL levels <1000 ng/mL. The rates of all IFD in patients with MBL levels below and above 1000 ng/mL were 33.9% and 26.9%, respectively (P=0.356). The rates of proven or probable IFD in patients with MBL levels below and above 1000 ng/mL were 11.9% and 15.1%, respectively (P=0.579). MBL levels <1000 ng/mL were not predictors of death (P=0.233). As expected, IFD was associated with death (P<0.0001). Our findings indicate that MBL levels <1000 ng/mL were not associated with an increased risk of developing IFD or overall survival.

Confirmation of Host Genetic Determinants in the CFH Region and Susceptibility to Meningococcal Disease in a Central European Study Sample

BACKGROUND

Invasive meningococcal disease (IMD) is a leading cause of meningitis and severe sepsis in children and adolescents. Genetic factors are important in determining the susceptibility to and outcome of IMD. Recently, a genome-wide association study from the United Kingdom showed significant associations of single-nucleotide polymorphisms within complement factor H (CFH; rs1065489) and in CFH-related protein 3 (rs426736) with susceptibility of IMD. We report data of a genetic replication study in Central European children.

METHODS

The study was conducted as a retrospective case-reference study involving 248 patients with confirmed diagnosis of IMD from Austria and Germany and 835 healthy reference individuals from a multicenter German birth cohort.

RESULTS

Carriers of the minor alleles of rs1065489 and rs426736 were at lower risk of IMD [allelic odds ratio = 0.60 (0.44-0.82); P = 0.001 and 0.61 (0.45-0.83); P = 0.001]. Also, 2 major haplotypes (GT and TC) derived from the 2 single-nucleotide polymorphisms were significantly associated with IMD (P = 0.001 and P = 0.003, respectively).

CONCLUSIONS

The consistency of the results between the genome-wide association study and our study population strengthens the association of CFH polymorphisms to the susceptibility of IMD. Our results support the conclusion that CFH is a critical determinant in acquiring meningococcal disease.

Mannose-binding lectin (MBL) insufficiency protects against the development of systemic inflammatory response after pediatric cardiac surgery

We investigated MBL2 and MASP2 genotypes, serum MBL (mannose-binding lectin) levels and activities of its complexes with associated serine proteases (MASP-1, MASP -2), in relation to complications following cardiac surgery in 195 children. The incidence of SIRS was lower in patients carrying MBL2 A/O and O/O genotypes (p=0.024). Children with MBL levels <500ng/ml had a lower risk of SIRS (p=0.014) and fever (p=0.044). Median MBL concentration was higher in patients who developed SIRS (p=0.048) but lower in those with post-operative infections (p=0.046). MBL-MASP-2 activities <100mU/ml protected from SIRS (p=0.007), low cardiac output syndrome (p=0.03) and multiorgan failure (p=0.012). In contrast, MBL2 YA/YA genotypes were associated with SIRS (p=0.018), low cardiac output syndrome (p=0.018), fever (p=0.018) and high inotropic score (VIS>30) (p=0.021). Thus, low MBL concentrations and associated genotypes may protect patients from systemic inflammation while high MBL serum levels and corresponding genotypes are risk factors of postoperative complications.

Circulating mannan-binding lectin, M-, L-, H-ficolin and collectin-liver-1 levels in patients with acute liver failure

BACKGROUND & AIMS

The complement system is activated in liver diseases including acute liver failure (ALF); however, the role of the lectin pathway of complement has scarcely been investigated in ALF. The pathway is initiated by soluble pattern recognition molecules: mannan-binding lectin (MBL), M-, L-, and H-ficolin and collectin-liver-1 (CL-L1), which are predominantly synthesized in the liver. We aimed to study lectin levels in ALF patients and associations with clinical outcome.

METHODS

Serum samples from 75 patients enrolled by the US ALF Study Group were collected on days 1 and 3. We included 75 healthy blood donors and 20 cirrhosis patients as controls. Analyses were performed using sandwich-type immunoassays (ELISA, TRIFMA).

RESULTS

At day 1, the MBL level in ALF patients was 40% lower compared with healthy controls {[median (interquartile range) 0.72 μg/ml(0.91) vs. 1.15 (1.92)(P = 0.02]}, and increased significantly by day 3 [0.83 μg/ml(0.94)(P = 0.01)]. The M-ficolin level was 60% lower [0.54 μg/ml(0.50) vs. 1.48(1.01)(P < 0.0001)]. The CL-L1 level at day 1 was slightly higher compared with healthy controls [3.20 μg/ml(2.37) vs. 2.64(0.72)(P = 0.11)]; this was significant at day 3 [3.35(1.84)(P = 0.006)]. H- and L-ficolin levels were similar to healthy controls. Spontaneous ALF survivors had higher levels of MBL at day 1 [0.96 μg/ml(1.15) vs. 0.60(0.60)(P = 0.02)] and lower levels of L-ficolin by day 3 compared with patients who died or were transplanted [1.61 μg/ml(1.19) vs. 2.17(2.19)(P = 0.02)].

CONCLUSION

We observed significant dynamics in lectin levels in ALF patients, which may suggest they play a role in ALF pathogenesis. High MBL and low L-ficolin levels are associated with survival.

Low mannose-binding lectin (MBL) levels and MBL genetic polymorphisms associated with the risk of neonatal sepsis: An updated meta-analysis

BACKGROUND

Relatively low serum mannose-binding lectin (MBL) levels and MBL genetic polymorphisms have been implicated as high risk factors for neonatal sepsis. However, different studies have reported conflicting findings and have generally been underpowered to exclude modest effect sizes.

METHODS

Standard methodology of systematic reviews and meta-analyses was followed. PubMed, Embase, Cochrane, Web of Science, and Scopus databases were searched from January 1996 to December 2013. The eligible studies were collected and analyzed using Review Manager 5.2. Meta-Disc version 1.4 was used to describe and calculate sensitivity, specificity, summary receiver operator characteristic (SROC) curves and area under the curve. SROC curve analysis was used to summarize the overall performance. Funnel plots, Egger's test and Begg's test were used to investigate publication bias.

RESULTS

Seven studies addressing low MBL levels and MBL genetic polymorphisms (structure variant A/O, A/B of Exon1) were analyzed for susceptibility to neonatal sepsis, respectively. All of these control studies were of reasonable methodological quality. The pooled unadjusted odds ratio showed that low MBL levels were significantly associated with neonatal sepsis (P=0.0002; odds ratio=4.94, 95% confidence interval=2.16-11.29) and MBL genetic polymorphisms were also significantly associated with neonatal sepsis (P=0.03; odds ratio=1.41, 95% confidence interval=1.03-1.94). In subgroup analysis based on gestational age, increased risk was found in the preterm infants in the dominant model (RR 2.33, 95%CI 1.06-5.13, P=0.03). However, no association was observed for term infants in subgroup analysis. Additionally, the SROC curve of low MBL levels in the prediction of neonatal sepsis indicated a poor predictive ability. The area under curve was 0.80 (95% confidence interval=0.74-0.86).

CONCLUSION

Currently available evidence shows that neonates with low serum MBL levels are more than four times more likely to have neonatal sepsis compared to those with higher serum MBL levels. Neonates with MBL genetic polymorphisms are also susceptible to developing neonatal sepsis. However, a low serum MBL level was only of moderate value in detecting neonatal sepsis.

If there is an evolutionary selection pressure for the high frequency of MBL2 polymorphisms, what is it?

Either immune selection or stochastic processes may have influenced the frequency of highly polymorphic genes such as mannose-binding lectin 2 (MBL2). This pattern recognition receptor of the innate immune system recognizes and binds to pathogenic microorganisms and apoptotic cells leading to lectin pathway complement killing or clearance. In almost all of a large number of studies in different ethnic groups worldwide there is 20-25% carriage of low MBL2 haplotypes, with 8-10% of each population having no MBL detectable in the blood. The source of this high variability of MBL2 remains cryptic. It arises from six main snps in the prompter and exon regions of the gene that assort into seven common haplotypes under linkage disequilibrium. While global studies of MBL2 show that it is not under immune selection pressure, these results are not the same when the same population genetic tools are used on large national studies. Other analyses point to the silenced MBL1 pseudogene and development of promoter polymorphisms in humans as evidence of selection pressure favouring low-producing haplotypes. While these analyses cannot be reconciled readily, there are two processes by which MBL heterozygosity could have been advantageous in an evolutionary sense; protection against adverse effects of various infectious diseases and lethal manifestations of atherosclerosis - a disease that now seems to have a more ancient history than assumed previously. Ultimately, consideration of the context for possible future therapeutic manipulation of MBL means that this can proceed independently of resolution of the evolutionary forces that have shaped MBL2 polymorphism.

Mannose-binding lectin polymorphisms and the risk of sepsis: evidence from a meta-analysis

Several studies have evaluated the association between mannose-binding lectin (MBL) polymorphisms and sepsis. However, the results are inconclusive and conflicting. To better understand the roles of MBL polymorphisms in sepsis, we conducted a comprehensive meta-analysis. All relevant studies were searched from PubMed, EMBASE and Web of Knowledge databases, with the last report up to 7 May 2013. Twenty-nine studies addressing four MBL polymorphisms (-550G/C, -221G/C, structure variant A/O, Gly54Asp) were analysed for susceptibility to sepsis and one study for sepsis-related mortality. Overall, significant associations between structure variant A/O and susceptibility to sepsis were observed for AO + OO vs. AA [odds ratio (OR) 1·27, 95% confidence interval (CI) 1·05-1·52, P = 0·01] and O vs. A (OR 1·19, 95% CI 1·02-1·40, P = 0·03). In subgroup analysis based on age group, increased risk was found in the paediatric group in the dominant model (OR 1·72, 95% CI 1·16-2·56, P = 0·007). Moreover, there was a slight association between the +54A/B polymorphism and susceptibility to sepsis in Caucasians (recessive model: OR 10·64, 95% CI 1·24-91·65, P = 0·03). However, no association was observed for -550G/C and -221G/C polymorphisms both overall and in subgroup analysis. For sepsis-related mortality, only one study suggested AO/OO was associated with in-hospital mortality in pneumococcal sepsis patients after controlling for confounding variables. Our meta-analysis indicated that MBL structure variants might be associated with susceptibility to sepsis but further studies with a large sample size should be conducted to confirm these findings.

The role of mannose-binding lectin in severe sepsis and septic shock

Severe sepsis and septic shock are a primary cause of death in patients in intensive care unit (ICU). Investigations upon genetic susceptibility profile to systemic complications during severe infections are a field of increasing scientific interest. Particularly when adaptive immune system is compromised or immature, innate immunity plays a key role in the immediate defense against invasive pathogens. Mannose-binding lectin (MBL) is a serum protein that recognizes a wide range of pathogenic microorganisms and activates complement cascade via the antibody-independent pathway. More than 30% of humans harbor mutations in MBL gene (MBL2) resulting in reduced plasmatic levels and activity. Increased risk of infection acquisition has been largely documented in MBL-deficient patients, but the real impact of this form of innate immunosuppression upon clinical outcome is not clear. In critically ill patients higher incidence and worse prognosis of severe sepsis/septic shock appear to be associated with low-producers haplotypes. However an excess of MBL activation might be also harmful due to the possibility of an unbalanced proinflammatory response and an additional host injury. Strategies of replacement therapies in critically ill patients with severe infections are under investigation but still far to be applied in clinical practice.

Significance of mannose-binding lectin deficiency and nucleotide-binding oligomerization domain 2 polymorphisms in Staphylococcus aureus bloodstream infections: a case-control study

BACKGROUND

Pathways coordinated by innate pattern recognition receptors like mannose-binding lectin (MBL) and nucleotide-binding oligomerization domain 2 (NOD2) are among the first immune responses to Staphylococcus aureus (S. aureus) bloodstream infections (BSI) in animal models, but human data are limited. Here, we investigated the role of MBL deficiency and NOD2 mutations in the predisposition to and severity of S. aureus BSI.

PATIENTS AND METHODS

A matched case-control study was undertaken involving 70 patients with S. aureus BSI and 70 age- and sex-matched hospitalized controls. MBL levels, MBL2 and NOD2 polymorphisms were analyzed.

RESULTS

After adjusting for potential confounders, MBL deficiency (<0.5 µg/ml) was found less frequently in cases than controls (26 vs. 41%, OR 0.4, 95% confidence interval (CI) 0.20-0.95, p=0.04) as were low producing MBL genotypes (11 vs. 23%, OR 0.2, 95% CI 0.08-0.75, p=0.01), whereas NOD2 polymorphisms were similarly distributed. Cases with NOD2 polymorphisms had less organ dysfunction as shown by a lower SOFA score (median 2.5 vs. 4.5, p=0.02), whereas only severe MBL deficiency (<0.1 µg/ml) was associated with life-threatening S. aureus BSI (OR 5.6, 95% CI 1.25-24.85, p=0.02).

CONCLUSIONS

Contrary to animal model data, our study suggests MBL deficiency may confer protection against acquiring S. aureus BSI. NOD2 mutations were less frequently associated with multi-organ dysfunction. Further human studies of the innate immune response in S. aureus BSI are needed to identify suitable host targets in sepsis treatment.

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

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

Mannose-binding lectin genotype influences frequency and duration of infectious complications in children with malignancy

Children with cancer receiving identical treatment differ in their experience of infection, suggesting that variations in immunity may influence susceptibility to infection. Studies of the influence of mannose-binding lectin (MBL), an important component of the innate immune system, in children with febrile neutropenia (FN) have yielded conflicting results. We examined the role of MBL in infection susceptibility in the largest cohort of children with cancer reported to date. MBL levels were measured and genotyping performed on children (≤16 y) receiving chemotherapy for cancer in London, UK. Clinical data from FN episodes were recorded prospectively. MBL status was assessed in 269 children; 513 episodes of FN were captured from 211 patients. Patients with MBL2 polymorphisms experienced more FN episodes than wildtype genotype (median 2 vs. 1, respectively; P = 0.074) and more episodes with documented infection (P = 0.045). Patients experiencing multiple FN episodes had lower MBL levels (P = 0.036). MBL genotype influenced duration of episode in some groups: high-risk MBL-deficient patients spent up to 5 nights longer/episode in hospital than equivalent wildtypes. These results indicate that MBL deficiency influences both susceptibility to and outcome of FN episodes and may be most important in those patients at higher risk of complications of FN.

Impact of mannose-binding lectin deficiency on radiocontrast-induced renal dysfunction: a post-hoc analysis of a multicenter randomized controlled trial

Background

Local renal ischemia is regarded as an important factor in the development of contrast-induced nephropathy (CIN). Mannose-binding lectin (MBL) is involved in the tissue damage during experimental ischemia/reperfusion injury of the kidneys. The aim of the present study was to investigate the association of MBL deficiency with radiocontrast-induced renal dysfunction in a large prospective cohort.

Methods

246 patients with advanced non–dialysis-dependent renal dysfunction who underwent radiographic contrast procedures were included in the study. Baseline serum MBL levels were analyzed according to the occurrence of a creatinine-based (increase of ≥0.5 mg/dL or ≥25% within 48 hours) or cystatin C-based (increase of ≥10% within 24 hours) CIN.

Results

The incidence of creatinine-based and cystatin C-based CIN was 6.5% and 24%, respectively. MBL levels were not associated with the occurrence of creatinine-based CIN. However, patients that experienced a cystatin C increase of ≥10% showed significantly higher MBL levels than patients with a rise of <10% (median 2885 (IQR 1193–4471) vs. 1997 (IQR 439–3504)ng/mL, p = 0.01). In logistic regression analysis MBL deficiency (MBL levels≤500 ng/ml) was identified as an inverse predictor of a cystatin C increase ≥10% (OR 0.34, 95% CI 0.15-0.8, p = 0.01).

Conclusion

MBL deficiency was associated with a reduced radiocontrast-induced renal dysfunction as reflected by the course of cystatin C. Our findings support a possible role of MBL in the pathogenesis of CIN.

The developing human preterm neonatal immune system: a case for more research in this area

Neonates, particularly those born prematurely, are among the most vulnerable age group for morbidity and mortality due to infections. Immaturity of the innate immune system and a high need for invasive medical procedures in the context of a preterm birth make these infants highly susceptible to common neonatal pathogens. Preterm infants who survive may also suffer permanent disabilities due to organ damage resulting from either the infection itself or from the inflammatory response generated under an oxidative stress. Infections in preterm infants continue to pose important healthcare challenges. Yet, developmental maturation events in the innate immune system that underlie their excessively high vulnerability to infection remain largely understudied. In this review article, we identify pertinent knowledge gaps that must be filled in order to orient future translational research.

A pilot study of host genetic variants associated with influenza-associated deaths among children and young adults

Low-producing MBL2 genotypes may have increased risk for MRSA co-infection.

We compared the prevalence of 8 polymorphisms in the tumor necrosis factor and mannose-binding lectin genes among 105 children and young adults with fatal influenza with US population estimates and determined in subanalyses whether these polymorphisms were associated with sudden death and bacterial co-infection among persons with fatal influenza. No differences were observed in genotype prevalence or minor allele frequencies between persons with fatal influenza and the reference sample. Fatal cases with low-producing MBL2 genotypes had a 7-fold increased risk for invasive methicillin-resistant Staphylococcus aureus (MRSA) co-infection compared with fatal cases with high- and intermediate-producing MBL2 genotypes (odds ratio 7.1, 95% confidence interval 1.6–32.1). Limited analysis of 2 genes important to the innate immune response found no association between genetic variants and fatal influenza infection. Among children and young adults who died of influenza, low-producing MBL2 genotypes may have increased risk for MRSA co-infection.

MBL Deficiency as Risk of Infection and Autoimmunity

In pathogen recognition by C-type lectins, several levels of complexity can be distinguished; these might modulate the immune response in different ways. Firstly, the pathogen-associated molecular pattern repertoire expressed at the microbial surface determines the interactions with specific receptors (Fig. 42.1). Secondly, each immune cell type possesses a specific set of pathogen-recognition receptors. Thirdly, changes in the cell-surface distribution of C-type lectins regulate carbohydrate binding by modulating receptor affinity for different ligands. Crosstalk between these receptors results in a network of multimolecular complexes, adding a further level of complexity in pathogen recognition (Cambi and Figdor 2005; Thiel et al. 2006) (see 10.1007/978-3-7091-1065-2_23). MBL deficiency is genetically determined and predisposes to recurrent infections and chronic inflammatory diseases. MBL deficiency has been implicated in susceptibility and course of viral, bacterial, fungal, and protozoan infection. More than 10% of the general population may, depending on definition, be classified as MBL deficient, underlining the redundancy of the immune system. MBL-disease association studies have been a fruitful area of research, which implicates a role for MBL in infective, inflammatory and autoimmune disease processes. MBL deficiency predisposes both to infection by extra-cellular pathogens and to autoimmune disease.

Mannose-binding lectin (MBL) as prognostic factor in paediatric oncology patients

Deficiency of mannose-binding lectin (MBL) has been suggested to influence duration of febrile neutropenia and prognosis in paediatric oncology patients. However, there is no consensus on the definition of MBL deficiency. In a cohort of children with cancer, we investigated (i) how to determine MBL deficiency and (ii) whether MBL is a prognostic factor for disease severity. In 222 paediatric oncology patients, 92 healthy children and 194 healthy adults, MBL plasma levels and MBL2 genotype (wild-type: A, variant: O) were determined. Event-free survival (EFS), overall survival (OS) and paediatric intensive care unit (PICU) admissions were recorded prospectively. In febrile neutropenic patients admitted to the PICU, disease severity was assessed by clinical, microbiological and laboratory parameters. An optimal cut-off value for MBL deficiency was determined to be < 0·20 µg/ml. Wild-type MBL2 genotype patients, including the XA/XA haplotype, had increased MBL levels compared to healthy individuals. MBL deficiency was associated with decreased EFS (P = 0·03), but not with need for PICU admission. A trend for a twice increased frequency of septic shock (80% versus 38%, P = 0·14), multiple organ failure (40% versus 17%, P = 0·27) and death (40% versus 21%, P = 0·27) was observed in the absence of microbiological findings. MBL deficiency was associated with decreased EFS and possibly with an increased severity of disease during PICU admission after febrile neutropenia in the absence of any association with microbiological findings. These findings suggest prognosis to be worse in MBL-deficient compared to MBL-sufficient paediatric oncology patients.

Mannose-binding lectin deficiency is associated with smaller infarction size and favorable outcome in ischemic stroke patients

Background

The Mannose-binding lectin (MBL) pathway of complement plays a pivotal role in the pathogenesis of ischemia/reperfusion (I/R) injury after experimental ischemic stroke. As comparable data in human ischemic stroke are limited, we investigated in more detail the association of MBL deficiency with infarction volume and functional outcome in a large cohort of patients receiving intravenous thrombolysis or conservative treatment.

Methodology/Principal Findings

In a post hoc analysis of a prospective cohort study, admission MBL concentrations were determined in 353 consecutive patients with an acute ischemic stroke of whom 287 and 66 patients received conservative and thrombolytic treatment, respectively. Stroke severity, infarction volume, and functional outcome were studied in relation to MBL concentrations at presentation to the emergency department. MBL levels on admission were not influenced by the time from symptom onset to presentation (p = 0.53). In the conservative treatment group patients with mild strokes at presentation, small infarction volumes or favorable outcomes after three months demonstrated 1.5 to 2.6-fold lower median MBL levels (p = 0.025, p = 0.0027 and p = 0.046, respectively) compared to patients with more severe strokes. Moreover, MBL deficient patients (<100 ng/ml) were subject to a considerably decreased risk of an unfavorable outcome three months after ischemic stroke (adjusted odds ratio 0.38, p<0.05) and showed smaller lesion volumes (mean size 0.6 vs. 18.4 ml, p = 0.0025). In contrast, no association of MBL concentration with infarction volume or functional outcome was found in the thrombolysis group. However, the small sample size limits the significance of this observation.

Conclusions

MBL deficiency is associated with smaller cerebral infarcts and favorable outcome in patients receiving conservative treatment. Our data suggest an important role of the lectin pathway in the pathophysiology of cerebral I/R injury and might pave the way for new therapeutic interventions.

Expression of mannose binding lectin in HIV-1-infected brain: implications for HIV-related neuronal damage and neuroAIDS

Mannose binding lectin (MBL) activates complement pathway that leads to pathogen opsonization and phagocytosis. MBL deficiency is linked to HIV transmission and disease progression. We sought to determine the role of MBL in HIV encephalitis (HIVE) by evaluating its presence and distribution in the HIV-1-infected brain and by assessing its association with monocyte chemoattractant protein-1 (MCP-1) expression. This retrospective study utilized archived post-mortem brain tissues obtained from 35 individuals enrolled in a longitudinal study as part of the California NeuroAIDS Tissue Network. MBL, MCP-1 and brain cell markers in post-mortem brain tissues with or without HIVE were evaluated using immunocytochemistry, immunofluorescence, confocal microscopy, and western blots. MBL was expressed in neurons, astrocytes, microglia, and oligodendrocytes of the frontal cortex of the HIV-1-infected brain. Overall, there were 30% to 40% more MBL-positive brain cells in HIVE vs non-HIVE cases (P = 0.01, paired t-test). Specifically, there was an increased MBL expression in the neuronal axons of HIVE cases. Also, western blots showed 3- to 4-fold higher levels of 78 kD MBL trimers in HIVE vs non-HIVE cases. This MBL-HIVE link was further confirmed by MBL associated higher MCP-1 expression in HIVE vs non-HIVE cases. HIV negative healthy individuals and normal or the gp120 transgenic mice did not show any differential MBL expression. Increased MBL expression in the major brain cell types, specifically in the neuronal axons of HIVE brain, and MBL associated higher MCP-1 expression in HIVE suggest that MBL could cause neuroinflammation and neuronal injury through MBL complement activation pathway.

Mannose-binding lectin deficiency influences innate and antigen-presenting functions of blood myeloid dendritic cells

Mannose-binding lectin (MBL) is a serum lectin that plays a significant role in innate host defence. Individuals with mutations in exon 1 of the MBL2 gene have reduced MBL ligand binding and complement activation function and increased incidence of infection. We proposed that, during infection, MBL deficiency may impact on dendritic cell (DC) function. We analysed the blood myeloid DC (MDC) surface phenotype, inflammatory cytokine production and antigen-presenting capacity in MBL-deficient (MBL-D) individuals and MBL-sufficient (MBL-S) individuals using whole blood culture supplemented with zymosan (Zy) or MBL-opsonized zymosan (MBL-Zy) as a model of infection. Zy-stimulated MDCs from MBL-D individuals had significantly increased production of interleukin (IL)-6 and tumour necrosis factor (TNF)-α. Stimulation with MBL-Zy significantly decreased IL-6 production by MDCs from MBL-D, but had no effect on TNF-α production. MDCs from both MBL-S and MBL-D individuals up-regulated expression of the activation molecule CD83, and down-regulated expression of homing (CXCR4), adhesion (CD62L, CD49d) and costimulatory (CD40, CD86) molecules in response to Zy and MBL-Zy. MDC from both MBL-D and MBL-S individuals induced proliferation of allogeneic (allo) T cells following Zy or MBL-Zy stimulation; however, MBL-D individuals demonstrated a reduced capacity to induce effector allo-T cells. These data indicate that MBL deficiency is associated with unique functional characteristics of pathogen-stimulated blood MDCs manifested by increased production of IL-6, combined with a poor capacity to induce effector allo-T-cell responses. In MBL-D individuals, these functional features of blood MDCs may influence their ability to mount an immune response.

New insights of an old defense system: structure, function, and clinical relevance of the complement system

The complement system was discovered a century ago as a potent defense cascade of innate immunity. After its first description, continuous experimental and clinical research was performed, and three canonical pathways of activation were established. Upon activation by traumatic or surgical tissue damage, complement reveals beneficial functions of pathogen and danger defense by sensing and clearing injured cells. However, the latest research efforts have provided a more distinct insight into the complement system and its clinical subsequences. Complement has been shown to play a significant role in the pathogenesis of various inflammatory processes such as sepsis, multiorgan dysfunction, ischemia/reperfusion, cardiovascular diseases and many others. The three well-known activation pathways of the complement system have been challenged by newer findings that demonstrate direct production of central complement effectors (for example, C5a) by serine proteases of the coagulation cascade. In particular, thrombin is capable of producing C5a, which not only plays a decisive role on pathogens and infected/damaged tissues, but also acts systemically. In the case of uncontrolled complement activation, “friendly fire” is generated, resulting in the destruction of healthy host tissue. Therefore, the traditional research that focuses on a mainly positive-acting cascade has now shifted to the negative effects and how tissue damage originated by the activation of the complement can be contained. In a translational approach including structure-function relations of this ancient defense system, this review provides new insights of complement-mediated clinical relevant diseases and the development of complement modulation strategies and current research aspects.

Genetic variability in complement activation modulates the systemic inflammatory response syndrome in children

OBJECTIVE

To determine the impact of genetic variability in complement activation on early development of the systemic inflammatory response syndrome (SIRS) in general pediatric critical care.

DESIGN

Prospective, observational, cohort study.

SETTING

A tertiary pediatric intensive care unit in the United Kingdom.

PATIENTS

Children with at least one organ failure expected to stay in the intensive care unit >12 hrs, or an expected death within 12 hrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 299 children were genotyped for functional polymorphisms in the complement activation cascade. We identified complement factor H as an important independent genetic modifier of SIRS/sepsis. Homozygosity for the complement factor H Y402H polymorphism, which is thought to reduce complement inhibition, was associated with less frequent SIRS/sepsis (the adjusted odds ratio for the homozygous variant complement factor H Y402H [CC] carriers was 0.3, 95% confidence interval, 0.1-0.7, p = .005). We also confirmed that structural and promoter variant mannose-binding lectin genotypes are a risk factor for SIRS/sepsis in pediatric critical care (adjusted odds ratio, 2.5; 95% confidence interval, 1.3-5.0, p = .008). Both findings were independent of clinical characteristics and other potentially confounding genetic polymorphisms in the innate immune system.

CONCLUSIONS

Functional polymorphisms in the complement activation cascade modify the risk for early SIRS/sepsis in general pediatric critical care. The complement factor H Y402H variant allele is protective, whereas the mannose-binding lectin variant polymorphisms increase risk. A genotype that permits vigorous complement activation to an infectious or inflammatory insult may offer protection from development of systemic inflammation.

Mannose-binding lectin levels and major infections in a cohort of very long-term survivors after allogeneic stem cell transplantation

BACKGROUND

Life-threatening infections are a major cause of death after allogeneic stem cell transplantation. Complement Mannose-binding lectin is a key component of innate immunity. Functional deficiency of mannose-binding lectin due to genetic polymorphism is frequent. Previous reports showed conflicting results with respect to the influence of functional mannose-binding lectin deficiency on infectious risk after allogeneic stem cell transplantation. The aim of this study was to clarify the impact of low mannose-binding lectin levels on infectious risk in a unique cohort of very long-term survivors after stem cell transplantation.

DESIGN AND METHODS

Incidence of major infections was evaluable in 43 out of 44 very long-term survivors (over ten years) and studied retrospectively in relation to mannose-binding lectin serum concentrations.

RESULTS

Recipients with mannose-binding lectin levels below 1,000 ng/mL were at increased risk to suffer from one or more major infections (P=0.002) during entire follow up. Infectious susceptibility was increased after neutrophil recovery, particularly until 24 months (Hazard Ratio 3.4) with sustained effects afterwards (Hazard Ratio 2.9). Mannose-binding lectin serum concentrations below 1,000 ng/mL were independently associated with major infections after neutrophil recovery (P=0.009). In subgroup analyses occurrence of severe herpes virus infections in particular was associated with significantly lower mannose-binding lectin levels (P=0.02).

CONCLUSIONS

Our findings indicate that low mannose-binding lectin levels may predict markedly increased susceptibility to severe infections with sustained effects even late after allogeneic stem cell transplantation. Determinations of mannose-binding lectin status should therefore be included into pre-transplantation risk assessment.

Genetic polymorphisms in the endotoxin receptor may influence platelet count as part of the acute phase response in critically ill children

PURPOSE

To determine if common polymorphisms in the endotoxin recognition complex influence the acute phase response as determined by the development of the systemic inflammatory response syndrome (SIRS) and platelet count on admission.

METHODS

This was a prospective observational cohort study. Paediatric intensive care patients (n = 913) were genotyped for common functional polymorphisms in the endotoxin recognition complex, including Toll-like receptor 4 (TLR4). We also selected potentially confounding polymorphisms in other genes of the innate immune system. SIRS was defined by age-specific consensus criteria. Platelet counts were recorded on admission.

RESULTS

The development of SIRS was primarily determined by the nature of the insult, but carriers of TLR4 variant alleles had lower platelet counts than children with wild-type genotype [mean +/- standard error of the mean (SEM) 143 +/- 7 vs. 175 +/- 4; p = 0.0001)--independent of other innate immune system polymorphisms. These findings were validated using a patient cohort of 1,170 adults with coronary artery disease. Carriers of TLR4 polymorphisms with a history of myocardial infarction (n = 573) had lower platelet counts than those with the wild-type genotype (217 +/- 7 vs. 237 +/- 2.8; p = 0.021).

CONCLUSIONS

Our results show that TLR4 variant alleles are associated with lower platelet counts across a range of ages and precipitating insults but that they do not influence the incidence of SIRS. This result may reflect redundancy and 'robustness' in the pathways leading to SIRS or the lack of specificity of this endpoint. Platelet count may vary with TLR4 genotype because it may be sufficiently sensitive and more linearly related to inflammation than other markers or, alternatively, there may be a direct TLR4-mediated platelet effect.

Genetic polymorphisms associated with acute lung injury

Acute lung injury and acute respiratory distress syndrome are the result of intense inflammation in the lungs leading to respiratory failure. The causes of acute lung injury/acute respiratory distress syndrome are numerous (e.g., pneumonia, sepsis and trauma) but the reasons why certain individuals develop lung injury in response to these stimuli and others do not are not well understood. There is ample evidence in the literature that gene-host and gene-environment interactions may play a large role in the morbidity and mortality associated with this syndrome. In this review, we initially discuss methods for identification of candidate acute lung injury/acute respiratory distress syndrome susceptibility genes using a number of model systems including in vitro cell systems and inbred mice. We then describe examples of polymorphisms in genes that have been associated with the pathogenesis of acute lung injury/acute respiratory distress syndrome in human case-control studies. Systematic bench to bedside approaches to understand the genetic contribution to acute lung injury/acute respiratory distress syndrome have provided important insight to this complex disease and continuation of these investigations could lead to the development of novel prevention or intervention strategies.

Deficient serum mannose-binding lectin levels and MBL2 polymorphisms increase the risk of single and recurrent Cryptosporidium infections in young children

Mannose-binding lectin (MBL) is an evolutionarily conserved protein that functions in human innate immunity by binding to microbial surfaces and promoting opsonophagocytosis. MBL has been shown to bind to Cryptosporidium sporozoites, and earlier work has suggested that the protective role of MBL may be most important in childhood. We evaluated the association between polymorphisms in the MBL gene (MBL2), serum MBL deficiency, and infection with Cryptosporidium, Entamoeba histolytica, and Giardia intestinalis in children. A large, prospective cohort of Bangladeshi preschool children was followed up for >3 years. Clinical outcomes, serum MBL levels, and MBL2 polymorphisms and haplotypes were determined. Statistically significant associations with E. histolytica and G. intestinalis were not found. Serum MBL deficiency, polymorphisms in the -221 promoter region, and the YO/XA MBL2 haplotype were strongly associated with Cryptosporidium infections, particularly recurrent infection. Children with multiple infections with Cryptosporidium were more likely to be MBL deficient (odds ratio [OR], 10.45), carry the -221 promoter variant (OR, 4.02), and have the YO/XA haplotype (OR, 4.91). We have identified a potentially important component of the human innate immune response to Cryptosporidum infection. Further work is needed to evaluate the mechanism of protection of MBL in Cryptosporidium infection.

Association of mannose-binding lectin-2 genotype and serum levels with prognosis of sepsis

Introduction

Individuals deficient in mannose-binding lectin (MBL), an important component of the innate immune system, show increased susceptibility to infection. We investigated whether polymorphisms in the MBL2 gene and the serum level are associated with the severity and prognosis of sepsis.

Methods

A total of 266 patients with sepsis and 398 healthy controls were enrolled. We analyzed the three single nucleotide polymorphisms (Gly54Asp, -550, and +4) in the MBL2 gene. Serum samples collected on day 1 were analyzed for the levels of MBL.

Results

Patients who were heterozygous (A/B) or homozygous (B/B) at codon 54 (adjusted odds ratio (OR), 0.370; 95% confidence interval (CI), 0.207-0.661, P = 0.001) and who were heterozygous (H/L) or homozygous (L/L) at -550 (adjusted OR, 0.476; 95% CI, 0.249-0.910, P = 0.025) were less likely to have septic shock in the sepsis group. Using Cox regression analysis for 28-day mortality, an MBL level ≥ 1.3 microg/mL showed significantly lower 28-day mortality (P = 0.020; hazard ratio, 0.571; 95% CI, 0.355-0.916) in the septic shock group.

Conclusions

Homozygosity at codons 54 (A/A) and -550 (H/H) appears to be associated with the severity, but not the outcome, of sepsis, whereas a low MBL level may be an independent risk factor for mortality. These findings suggest that the genotype and serum level for MBL2 may have different clinical implications.

Donor mannose-binding lectin gene polymorphisms influence the outcome of liver transplantation

Mannose-binding lectin (MBL) is a C-type lectin produced mainly by the liver that binds to a wide range of pathogens. Polymorphisms at the promoter and exon 1 of the MBL2 gene are responsible for low serum levels of MBL and have been associated with an increased risk of infections. We prospectively analyzed 95 liver transplant recipients. Well-known functionally relevant polymorphisms of the MBL2 gene of the liver donor were examined by gene sequencing. Infectious events were collected prospectively. No differences in the incidence of infections were found according to the donor MBL2 genotypes. Survival was lower in patients receiving a liver graft from a donor with an exon 1 MBL2 variant genotype, and they had higher infection-related mortality (50% versus 14%, P = 0.040). No differences were found according to other polymorphisms involving the promoter and 5'-untranslated region. When we analyzed bacterial infection episodes, we found that patients receiving a liver from a donor with an exon 1 variant genotype had a higher incidence of septic shock (46% versus 11%, P = 0.004). Independent variables associated with graft or patient survival were as follows: receiving a graft from a donor with an exon 1 MBL2 variant genotype [adjusted hazard ratio (aHR), 9.64; 95% confidence interval (CI), 2.59-36.0], the Model for End-Stage Liver Disease score (aHR, 1.14; 95% CI, 1.05-1.23), and bacterial infections (aHR, 11.1; 95% CI, 2.73-44.9). Liver transplantation from a donor with a variant MBL2 exon 1 genotype was associated with a worse prognosis, mainly because of infections of higher severity.

Endothelial response to childhood infection: the role of mannose-binding lectin (MBL)

OBJECTIVE

To assess the influence of mannose-binding lectin (MBL) genotype on endothelial function in the presence and absence of infection in childhood.

METHODS

We studied 2176 children aged 10 years drawn from the Avon Longitudinal Study of Parents and Children. Endothelial function was assessed by flow mediated dilatation (FMD). Exon 1 and promoter polymorphisms in the MBL gene were determined by heteroduplexing procedures. Children were classified as AA (wild type) AO (heterozygotes) and OO (homozygotes).

RESULTS

During the vascular assessment, 544 children presented with current or recent (<2 weeks) infection (INF). FMD was reduced in the INF group compared to controls (10% reduction in FMD, p<0.001). MBL genotype was not associated with FMD in controls, although a relationship with the degree of impairment during INF was observed (8.0%, 7.6% and 26.6% lower FMD compared to controls for groups AA, AO, OO respectively, p<0.05). After multivariate analysis, OO was associated with reduced FMD in the INF group (odds ratio 2.95 [1.33, 6.52], p<0.001).

CONCLUSION

Homozygosity for MBL variant alleles is associated with greater impairment in FMD during infection in childhood. This suggests a gene-environment interaction operating in early life that may have relevance for the initiation and progression of atherosclerosis.

Humoral pattern recognition molecules: mannan-binding lectin and ficolins

Innate immunity comprises a sophisticated network of molecules, which recognize pathogens, and effector molecules, working together to establish a quick and efficient immune response to infectious agents. Complement activation triggered by mannan binding lectin (MBL) or ficolins represents a beautiful example of this network Both MBL and ficolins recognize specific chemical structures on the surface of antigens and pathogens, thus bind to a broad variety of pathogens. Once bound further complement deposition is achieved through a cascade of proteolytic reactions. MBL and ficolin induced complement activation is critical for adequate anti-bacterial, anti-fungal and anti-viral responses. This is well illustrated by numerous and convincing studies that demonstrate associations between MBL deficiency and infections. Recent work has also highlighted that MBL and ficolins recognize self-structures, thus extending the role of these molecules beyond the traditional view of first line defense molecules. It appears that MBL deficiency may modulate the prognosis of inflammatory and autoimmune diseases. What is known about the mechanisms behind this broad scope of activities of MBL and ficolins is discussed in this chapter.