Relationship between gene polymorphisms of mannose-binding lectin (MBL) and two molecular forms of MBL

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.

The ambiguous role of mannose-binding lectin (MBL) in human immunity

Mannose-binding lectin (MBL) and lectin complement pathway have become targets of increasing clinical interest. Many aspects of MBL have been recently explored, including the structural properties that allow it to distinguish self from non-self/altered-self structures. Experimental evidences have declared the additional 5′- and 3′-variants that in amalgamation with well-known secretor polymorphisms change MBL function and concentration. Moreover, the current review highlights the differential behavior of MBL on exposure with extra/intracellular pathogens and in autoimmune diseases, stressing the fact that “high MBL levels can increase diseases susceptibility,” a paradox that needs justification. Attributable to these discrepancies, no absolute level of MBL deficiency could be defined so far and thus must be interpreted for specific diseases through case–control population-specific designs. Overall, it is evident that further research is needed about MBL and the lectin pathway of complement. Particularly, the transformative role of MBL over evolution is of interest and its role with regard to pathogenesis of different diseases and potential therapeutic targets within the respective pathways should be further explored. Apart from this, it is necessary to adopt an extensive locus-wide methodology to apprehend the clinical significance of MBL2 polymorphisms in a variety of infectious diseases by the future studies.

Role of MIF-173G/C and Mbl2 Codon 54A/B Variants in the Risk of Multiple Myeloma: An Association Study

BACKGROUND

Multiple myeloma (MM) is a malignant disease manifested by the clonal proliferation of atypical plasma cells. Macrophage inhibitory factor (MIF) is one of the pleiotropic regulators in various biological and cellular processes. Mannose-binding lectin (MBL) is a crucial protein involved in the lectin pathway of the immune system.

OBJECTIVE

We aimed to assess whether variants of MIF and MBL2 genes are associated with MM among a Turkish population.

METHODS

We analyzed the MIF-173G/C (rs755622) and MBL2 codon 54A/B (rs1800450) variants in 200 patients with MM and 200 healthy control subjects using a polymerase chain reaction (PCR) followed by restriction endonuclease digestion. There was also an evaluation of the patients undergoing autologous stem-cell transplantation (ASCT) for these variants.

RESULTS

AA and BB genotypes of MBL2 codon 54A/B increased in the patients as compared to the controls (p=0.008, p=0.001, respectively). The subjects carrying AA and BB genotypes of MBL2 were at high risk of development of susceptibility to MM by 7.377 and 8.812 times, respectively. The distribution of MBL2 codon 54A/B alleles was similar between the groups (p>0 .05). There was no statistical difference between the patients and controls in the genotype and allele frequencies of the MIF- 173G/C variant (p>0 .05). The patients undergoing ASCT, MBL2 codon 54A/B AA and BB genotypes also showed association with increased risk for MM (p=0.004, p=0.001, respectively).

CONCLUSION

As far as we know, this is the first report of the study on an association between these variants and MM in our population. Our results indicate that the MBL2 codon 54A/B variant may be associated with susceptibility to MM.

Use of Mannose-Binding Lectin Gene Polymorphisms and the Serum MBL Level for the Early Detection of Neonatal Sepsis

Background  Mannose-binding lectin (MBL) is a component of innate immunity and is particularly important in neonates, in whom adaptive immunity has not yet completely developed. MBL deficiency and MBL2 gene polymorphisms are associated with an opsonization defect and have been associated with neonatal sepsis. Aim  The aim of our study was to assess serum MBL levels and genotype MBL2 genes to determine whether they can serve as markers for predicting neonatal sepsis in neonatal intensive care units. Patients and Methods  A case-control study was conducted with 114 neonates classified into two groups: the septic group included 64 neonates (41 preterm and 23 full-term infants), and the non-septic control group included 50 neonates (29 preterm and 21 full-term infants). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was used to genotype MBL2 gene exon 1 (rs1800450) and (rs1800451) SNPs. Enzyme-linked immunosorbent assay (ELISA) was used to measure MBL serum concentrations. Results  The polymorphic genotypes BB and AC at codons 54 and 57, respectively, showed higher frequencies than the wild-type genotype (AA) (14.1% versus 12.9% and 28.1% versus 19.4% respectively) in both groups, and this difference was greater in the septic group than in the non-septic group; however, the differences did not reach statistical significance. The B and C allele frequencies were also higher in the septic group than in the non-septic group, but the differences did not reach statistical significance ( p  = 0.282 and 0.394, respectively). The serum levels of MBL were significantly lower in the septic group than in the non-septic group ( p  = 0.028). Conclusion  This study found no association between MBL levels or MBL2 exon 1 genotypes or alleles and neonatal sepsis risk. Further studies with larger sample sizes are needed to determine the role of the MBL2 gene as a risk factor and early predictor of neonatal sepsis.

Molecular profile of mannan-binding lectin in hepatitis C patients with MBL gene polymorphisms by a modified mannan-coated nitrocellulose assay

The aim of this study was to develop an assay to analyze the serum profile of Mannose-binding lectin (MBL) through a simple and "in-house" method (called "dot-N-man"). Furthermore, the study attempted to associate molecular masses of MBL to the profile of MBL gene polymorphisms in patients with hepatitis C. Heterogeneity in molecular masses of MBL is due to the impairment of oligomers formation, which is linked to genetic polymorphisms in the MBL gene. Individuals with AA genotype (wild-type) produce high-molecular-mass proteins, whereas AO and OO individuals produce intermediate and low-molecular-mass proteins, respectively. Sera of thirty patients carrying the hepatitis C virus (HCV) were investigated using MBL binding assay with mannan-coated nitrocellulose (dot-N-man). Purified MBL was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Dot-N-Man assay yielded MBL with molecular masses ranging between 55 and 320 kDa, comparable to low and high molecular mass forms of MBL. Nonreducing SDS-PAGE showed high molecular mass bands in all AA individuals while bands of 270 and 205 kDa were observed in sera for a number of patients with AO and OO genotypes, respectively. Immunoblotting confirmed the MBL samples obtained from the dot-N-man. These results provide new insights to understand the MBL molecular forms profile in patients infected with HCV- which could be useful in future investigations on the influence of the MBL structure/genotype on both the progression of infection and the response to hepatitis C therapy.

Genetic and Phenotypic Screening of Mannose-Binding Lectin in Relation to Risk of Recurrent Vulvovaginal Infections in Women of North India: A Prospective Cohort Study

Recurrent Vulvovaginal Infections (RVVI) is common problem associated with women of reproductive age. The function and deleterious effect of Mannose Binding Lectin 2 (MBL2) common polymorphisms are reported to be associated with various diseases. However, the role of MBL2 promoter gene polymorphisms and their combined effect with structural variant along with Serum Mannose Binding Lectin (sMBL) levels in RVVI has not been investigated. The study included 258 RVVI cases and 203 age matched healthy controls. These were investigated for the distribution of MBL2 codon 54 and promoter polymorphisms by Amplification Refractory Mutation System-Polymerase Chain Reaction (ARMS-PCR). sMBL levels were quantified by Enzyme Linked Immnosorbent Assay (ELISA). The frequency of X allele and its genotypes was significantly high in cases than controls conferring risk toward RVVI and its types (p < 0.05). The HXPA (OR; 2.0), LXQB (OR; 1.43) haplotypes were associated with susceptibility to RVVI cases while haplotype LYQB significantly protected against RVVI (OR; 0.58), Bacterial Vaginosis (BV) (OR; 0.27) and Mixed Infections (MI) cases (OR; 0.62) with high frequency observed in controls (p < 0.05). Mean sMBL levels were significantly low in RVVI, BV, Vulvovaginal Candidiasis (VVC), and MI cases compared to controls (p < 0.05). VVC patient showed significantly low sMBL levels than RVVI and MI cases (p < 0.05). The mean sMBL levels segregated based on MBL2 genotypes and haplotypes showed significant difference in different cases groups with controls. The findings of the present study suggested that MBL2 Y/X polymorphism and low sMBL levels were associated with susceptibility to RVVI either it is BV, VVC, or MI. Thus MBL deficiency in women with RVVI may contribute to decreased efficiency in clearing of pathogens. Hence, specific measures like administration of purified or recombinant MBL might decrease the incidence of vaginal infections recurrences and more-effective treatment.

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.

Association of MBL2 exon1 polymorphisms with high-risk human papillomavirus infection and cervical cancers: a meta-analysis

PURPOSE

High-risk human papillomavirus (HR-HPV) infection is the main known cause of cervical cancer. Mannose-binding lectin (MBL) is a recognition molecule that mediates phagocytosis and activates complement.

METHODS

We performed a meta-analysis to investigate the association of MBL-2 functional polymorphisms with HPV infection and cervical cancer (CC).

RESULTS

The meta-analyses indicated an association between the MBL2 exon 1 polymorphisms and susceptibility to HPV infection in the recessive model (OO vs. AA + AO, p = 0.042, 95 % CI 1.02-3.15), and O/O vs. A/A mode (P = 0.023, 95 % CI 1.10-3.40) in Caucasian. Meanwhile, there was a significant association between MBL2 exon 1 polymorphisms and cervical cancer risk in AO vs. AA model (p = 0.035, 95 % CI 1.03-2.26), and Allelic model (O vs. A, p = 0.022, 95 % CI 1.05-1.96) as compared to HR-HPV-infected patients with CC vs. healthy controls in Caucasian. In addition, no an association was observed between MBL2 -550 H/L and -221 X/Y polymorphisms and HPV infection among Caucasians, but we found an association between the MBL2 -550 H/L polymorphism and susceptibility to HR-HPV infection in recessive model (HH vs. LL + LH, p = 0.003, 95 % CI 1.18-2.23), HH vs. LL model (p = 0.021, 95 % CI 1.07-2.19), and allelic model(H vs. L, p = 0.042, 95 % CI 1.01-1.40) in Asians.

CONCLUSIONS

Collectively, we suggest that the MBL2 gene exon1 polymorphisms are associated with increased risk of high-risk HPV infection and cervical cancer development among Caucasians. Additionally, no significant association was found between the MBL2 -550 H/L or -221 X/Y polymorphisms and HPV infection in Caucasians, but there may be potential links in Asians.

A comprehensive in silico analysis of non-synonymous and regulatory SNPs of human MBL2 gene

Mannose binding lectin (MBL) is a liver derived protein which plays an important role in innate immunity. Mannose binding lectin gene 2 (MBL2) polymorphisms are reported to be associated with various diseases. In spite of being exhaustively studied molecule, no attempt has been made till date to comprehensively and systematically analyze the SNPs of MBL2 gene. The present study was carried out to identify and prioritize the SNPs of MBL2 gene for further genotyping and functional studies. To predict the possible impact of SNPs on MBL structure and function SNP data obtained from dbSNP database were analyzed using various bioinformatics tools. Out of total 661 SNPs, only 37 validated SNPs having minor allele frequency ≥0.10 were considered for the present study. These 37 SNPs includes one in 3' near gene, nine in 3' UTR, one non-synonymous SNP (nsSNP), thirteen intronic SNPs and thirteen in 5' near gene. From these 37 SNPs, 11 non-coding SNPs were identified to be of functional significance and evolutionary conserved. Out of these, 4 SNPs from 3' UTR were found to play role in miRNA binding, 7 SNPs from 5' near and intronic region were predicted to involve in transcription factor binding and expression of MBL2 gene. One nsSNP Gly54Asp (rs1800450) was found to be deleterious and damaging by both SIFT and Polyphen-2 servers and thus affecting MBL2 protein stability and expression. Protein structural analysis with this amino acid variant was performed by using I-TASSER, RAMPAGE, Swiss-PdbViewer, Chimera and I-mutant. Information regarding solvent accessibility, molecular dynamics and energy minimization calculations showed that this variant causes clashes with neighboring amino acids residues that must interfere in the normal triple helix formation of trimeric subunit and further with the normal assembly of MBL oligomeric form, hence decrease in stability. Thus, findings of the present study indicated 12 SNPs of MBL2 gene to be functionally important. Exploration of these variants may provide novel remedial markers for various diseases.

Role of collectins and complement protein C1q in pregnancy and parturition

Collectins such as surfactant proteins SP-A, SP-D, and mannan-binding lectin (MBL), as well as complement protein C1q are evolutionarily conserved innate immune molecules. They are known to opsonize a range of microbial pathogens (bacteria, fungi, virus, and parasites) and trigger effector clearance mechanisms involving phagocytosis and/or complement activation. Collectins and C1q have also attracted attention in studies involving pregnancy as they are expressed in the female reproductive tissues during pregnancy; a unique state of immune suppression with increased susceptibility to infectious diseases. Recent studies are beginning to unravel their functional significance in implantation, placentation, pregnancy maintenance and parturition in normal and adverse pregnancies. Collectins and C1q, expressed in gestational tissues during pregnancy, might alter the status of mother's immune response to the allogenic fetus and the microenvironment, thereby serving as important regulators of fetus-mother interaction. Here, we discuss the functional roles that have been assigned to SP-A, SP-D, MBL and C1q in pregnancy and parturition.

MBL2 polymorphisms in women with atypical squamous cells of undetermined significance

Infection with high risk Human papillomavirus (HPV) is the main known cause of cervical cancer. HPV induces different grades of lesions: among them, Atypical squamous cells of undetermined significance are abnormal lesions that could evolve in pre-cancer lesions or spontaneously regress. The mannose binding lectin (MBL) is an innate immunity serum protein also found in cervico-vaginal mucosa, whose expression is known to be affected by polymorphisms in exon 1 and promoter of the MBL2 gene. In the present study the possible association between MBL2 functional polymorphisms and susceptibility to develop atypical squamous cells of undetermined significance was investigated in a group of women from North-East of Italy, stratified for HPV infection status. The MBL2 D and O alleles and the deficient producer combined genotypes, responsible for low MBL production, were more represented among atypical squamous cells of undetermined significance positive women than healthy controls and the results were confirmed when only HPV negative samples were considered. These results suggest a possible involvement of MBL2 functional polymorphisms in atypical squamous cells of undetermined significance susceptibility.

Mannose-binding lectin gene as a modifier of the cystic fibrosis phenotype in Argentinean pediatric patients

BACKGROUND

There is a considerable variation in the phenotype and course of the disease in cystic fibrosis (CF) even in patients with the same CFTR genotype, suggesting that other factors are important for prognosis. Mannose-binding lectin (MBL) has been proposed as one of these factors. We therefore investigated the influence of MBL2 gene variants on disease severity, age at acquisition of Pseudomonas aeruginosa, and survival in CF patients.

METHODS

MBL2 variants were studied in 106 Argentinean pediatric CF patients carrying two severe CFTR mutations. Clinical phenotype was defined according to the Shwachman score and lung function tests. Age at infection with P. aeruginosa and age at death were also recorded.

RESULTS

MBL insufficiency was associated with a 3.5-fold risk of having a severe phenotype (CI 95%: 1.2-10.3, p=0.03). It was also associated with an earlier onset of infection with P. aeruginosa (p=0.035). No statistically significant differences were found in FEV1 and survival.

CONCLUSIONS

MBL insufficiency was associated with detrimental progression of the disease. These results together with previous findings suggest that the effect of MBL2 expression may be a major determinant of the severity of the clinical phenotype in patients with CF.

Restoration of MBL-deficiency: redefining the safety, efficacy and viability of MBL-substitution therapy

MBL-deficiency is a commonly occurring deficiency of the innate immune system, affecting a substantial part of the population and has been extensively studied. MBL appears to function as a disease modifier. The role of MBL in different conditions is context-dependent. Many clinical studies show conflicting results, which can be partially explained by different definitions of MBL-deficiency, including phenotype- and genotype-based approaches. In this review we give an overview of literature of MBL, its role in different pathologies, diseases and patient populations. We review MBL replacement studies, and discuss the potential of MBL substitution therapy. We finally suggest that new MBL substitution trials should be conducted within a predefined patient population. MBL-deficiency should be based on serum levels and confirmed by genotyping.

Oxidative stress decreases functional airway mannose binding lectin in COPD

We have previously established that a defect in the ability of alveolar macrophages (AM) to phagocytose apoptotic cells (efferocytosis) and pathogens is a potential therapeutic target in COPD. We further showed that levels of mannose binding lectin (MBL; required for effective macrophage phagocytic function) were reduced in the airways but not circulation of COPD patients. We hypothesized that increased oxidative stress in the airway could be a cause for such disturbances. We therefore studied the effects of oxidation on the structure of the MBL molecule and its functional interactions with macrophages. Oligomeric structure of plasma derived MBL (pdMBL) before and after oxidation (oxMBL) with 2,2′-azobis(2-methylpropionamidine)dihydrochroride (AAPH) was investigated by blue native PAGE. Macrophage function in the presence of pd/oxMBL was assessed by measuring efferocytosis, phagocytosis of non-typeable Haemophilus influenzae (NTHi) and expression of macrophage scavenger receptors. Oxidation disrupted higher order MBL oligomers. This was associated with changed macrophage function evident by a significantly reduced capacity to phagocytose apoptotic cells and NTHi in the presence of oxMBL vs pdMBL (eg, NTHi by 55.9 and 27.0% respectively). Interestingly, oxidation of MBL significantly reduced macrophage phagocytic ability to below control levels. Flow cytometry and immunofluorescence revealed a significant increase in expression of macrophage scavenger receptor (SRA1) in the presence of pdMBL that was abrogated in the presence of oxMBL. We show the pulmonary macrophage dysfunction in COPD may at least partially result from an oxidative stress-induced effect on MBL, and identify a further potential therapeutic strategy for this debilitating disease.

MBL2 variations and malaria susceptibility in Indian populations

Human mannose-binding lectin (MBL) encoded by the MBL2 gene is a pattern recognition protein and has been associated with many infectious diseases, including malaria. We sought to investigate the contribution of functional MBL2 gene variations to Plasmodium falciparum malaria in well-defined cases and in matched controls. We resequenced the 8.7 kb of the entire MBL2 gene in 434 individuals clinically classified with malaria from regions of India where malaria is endemic. The study cohort included 176 patients with severe malaria, 101 patients with mild malaria, and 157 ethnically matched asymptomatic individuals. In addition, 830 individuals from 32 socially, linguistically, and geographically diverse endogamous populations of India were investigated for the distribution of functional MBL2 variants. The MBL2 -221C (X) allelic variant is associated with increased risk of malaria (mild malaria odds ratio [OR] = 1.9, corrected P value [P(Corr)] = 0.0036; severe malaria OR = 1.6, P(Corr) = 0.02). The exon1 variants MBL2*B (severe malaria OR = 2.1, P(Corr) = 0.036; mild versus severe malaria OR = 2.5, P(Corr) = 0.039) and MBL2*C (mild versus severe malaria OR = 5.4, P(Corr) = 0.045) increased the odds of having malaria. The exon1 MBL2*D/*B/*C variant increased the risk for severe malaria (OR = 3.4, P(Corr) = 0.000045). The frequencies of low MBL haplotypes were significantly higher in severe malaria (14.2%) compared to mild malaria (7.9%) and asymptomatic (3.8%). The MBL2*LYPA haplotypes confer protection, whereas MBL2*LXPA increases the malaria risk. Our findings in Indian populations demonstrate that MBL2 functional variants are strongly associated with malaria and infection severity.

MBL serum concentration in women with HPV presenting CIN III lesions

PURPOSE

This study proposes to assess MBL serum concentrations in HPV positive women that developed high risk preinvasive lesions, CIN III.

MATERIALS AND METHODS

A total of 90 consecutive women (mean age 32.2 years, range 18-45 years) with CIN III lesions confirmed by cone biopsy were enrolled as cases at the gynecology cancer department of the Erasto Gaertner Hospital, a center of reference for cancer treatment in Southern Brazil. All the patients were HPV positive. In addition, 81 healthy women, voluntary blood donors, were enrolled as healthy control subjects (mean age 33.3 years, range 14-71 years) with no evidence of HPV infection, tested by hybrid capture, or CIN lesions, from the same geographic area.

RESULTS

The median concentration of MBL in the cases was 912 ng/ml (IQR: 100-5820 ng/ml) and in the controls was 1207.3 ng/ml (IQR 100-4320.6 ng/ml). No statistically significant difference was observed between cases and controls.

CONCLUSION

This study reports data on MBL serum concentrations in HPV infected women for the first time. The analysis of our findings did not show a statistically significant difference between MBL serum concentrations in HPV women that developed CIN III lesions and healthy controls.

Mannose-binding lectin genotype and serum levels in patients with chronic and allergic pulmonary aspergillosis

Several studies suggest mannose-binding lectin (MBL) deficiency is associated with various manifestations of aspergillosis. MBL serum levels and function are genetically determined, but levels rise during inflammation. We address the relative frequency of deficient genotypes, the relationship between serum level and genotype and both age and disease manifestations in patients with chronic pulmonary (CPA) and allergic bronchopulmonary aspergillosis (ABPA) and severe asthma with fungal sensitization (SAFS). DNA was extracted from blood samples, and MBL2 genotyping was performed using the INNO-LiPA MBL2 kit. Serum MBL concentrations were determined using ELISA. One hundred and eight patients were evaluated, 70 (65%) with CPA, 38 (35%) with allergic disease (ABPA, SAFS or undefined) and 13 (12%) had both CPA and ABPA. The mean MBL serum level was 1849 μg L(-1) and did not differ between groups. Forty subjects (37%) had exon 1 genotypes producing nonfunctional MBL (A/B, A/C, A/D and O/O), a frequency not different from published normal controls. A/A subjects with CPA had higher levels (2981 μg L(-1)) compared with allergic A/A subjects (2202 μg L(-1)) (pc0.012). No single haplotype, genotype or allele was significantly related to any aspergillosis phenotype. Worse breathlessness was associated with higher MBL levels among A/A subjects (P = 0.009) and conversely nonfunctional genotypes. Mean MBL values were higher in those with an Medical Research Council (MRC) breathlessness score of 5 compared with those with and MRC score of 1 (P = 0.023). A/A allergic subjects (n = 27) in this study were ≈ 11 years younger than allergic A/O subjects (n = 11, P = 0.02). Subjects with worse respiratory status or more severe CPA had higher MBL serum levels (P = 0.023; P = 0.034). Bronchiectasis was not associated with MBL levels in CPA or allergic aspergillosis. MBL genotype and serum level modulate progression of aspergillosis.

The role of humoral innate immunity in hepatitis C virus infection

Infection with Hepatitis C Virus (HCV) causes chronic disease in approximately 80% of cases, resulting in chronic inflammation and cirrhosis. Current treatments are not completely effective, and a vaccine has yet to be developed. Spontaneous resolution of infection is associated with effective host adaptive immunity to HCV, including production of both HCV-specific T cells and neutralizing antibodies. However, the supporting role of soluble innate factors in protection against HCV is less well understood. The innate immune system provides an immediate line of defense against infections, triggering inflammation and playing a critical role in activating adaptive immunity. Innate immunity comprises both cellular and humoral components, the humoral arm consisting of pattern recognition molecules such as complement C1q, collectins and ficolins. These molecules activate the complement cascade, neutralize pathogens, and recruit antigen presenting cells. Here we review the current understanding of anti-viral components of the humoral innate immune system that play a similar role to antibodies, describing their role in immunity to HCV and their potential contribution to HCV pathogenesis.

Association of mannose-binding lectin gene polymorphism with tuberculosis susceptibility and sputum conversion time

Mannose-binding lectin (MBL) plays an important role in innate immunity. The effect of low MBL levels producing variants of MBL2 gene on tuberculosis (TB) has been controversial with some studies reporting it to confer protection against the disease, whereas others estimating a susceptibility relation. Other than conducting a case-control study to evaluate the role of MBL A/B polymorphism on TB, we conducted a longitudinal study to check whether this MBL variant can influence the host response to Mycobacterium tuberculosis infection. A total of 357 TB patients (286 pulmonary TB, 71 extrapulmonary (EP) TB) and 392 healthy controls belonging to same ethnicity were included in the study. We found the mutant allele 'B' allele confers a protective role against TB in our study population. This effect was absent in EP patients. On stratification on the basis of sex, the protective role of the 'B' allele was found to be limited to females only and males reported no significant difference. No effect of MBL A/B polymorphism on sputum conversion time was reported. We conclude that MBL 'B' allele is associated with protection against TB, but no influence was found on sputum conversion rate.

A clinical case-control study on the association between mannose-binding lectin and susceptibility to HIV-1 infection among northern Han Chinese population

Mannose-binding lectin (MBL) is a key molecule of the innate immune system and a competent to bind carbohydrates of a variety of microorganisms, resulting in complement activation and opsonophagocytosis against various pathogens. However, there is no systemic investigation on the MBL's role in innate immune responses against HIV-1 infection among northern Han Chinese. This study investigated the association between MBL and HIV-1 infection susceptibility among northern Han Chinese. A total of 91 HIV-1 infected patients and 91 HIV-1 seronegative healthy individuals were recruited. Six polymorphisms of MBL2 gene were genotyped by pyrosequencing. The quantitative measurement of serum MBL concentration and MBL complex activity were performed by ELISA. The CD4+ T-cell counts were determined by flow cytometry. The plasma viral loads of 91 HIV-1 infected patients were determined by bDNA method. The results show that there is an association between MBL and HIV-1 infection susceptibility among northern Han Chinese. The individuals with B variant, low serum MBL concentration and low MBL complex activity are more susceptible to HIV-1 infection.

Association between mannose-binding lectin gene polymorphisms and pre-eclampsia in Brazilian women

PROBLEM

Mannose-binding lectin (MBL) is involved in the maintenance of an inflammatory environment in uterus. High MBL levels have been associated with successful pregnancies whereas low levels are involved in pre-eclampsia (PE) development. Here, we evaluated MBL2 gene polymorphisms in the structural and promoter regions addressing their association with PE.

METHOD OF STUDY

DNA samples from 162 control pregnant women and 157 pregnant PE women were genotyped and data compared with demographic and clinical characteristics.

RESULTS

High frequency of C and D alleles (related to low MBL levels) was observed in PE women when compared to controls (C: 0.08 versus 0.03, P = 0.006; D: 0.10 versus 0.05, P = 0.009). Grouping the MBL genotypes according to phenotype, a higher frequency of OO genotype was observed in PE women when compared to control women (0.15 versus 0.04, P = 0.007).

CONCLUSION

Our data suggest that women with genotypes associated with low MBL levels could be potential PE developers.

The role of mannose-binding lectin gene polymorphisms in susceptibility to HIV-1 infection in Southern Brazilian patients

OBJECTIVE

This study investigates the role of mannose-binding lectin (MBL) in the susceptibility to HIV-1 infection analyzing polymorphisms located at the MBL2 promoter and exon 1 regions.

MATERIALS AND METHODS

The prevalence of MBL2 variant alleles was investigated in 410 HIV-1-infected patients from the South Brazilian HIV cohort and in 345 unexposed uninfected healthy individuals. The promoter variants were genotyped using polymerase chain reaction with sequence-specific primers (PCR-SSP) and exon 1 variants were analyzed by real-time PCR using a melting temperature assay and were confirmed by PCR-restriction fragment length polymorphism (RFLP). MBL2 genotypic and allelic frequencies were compared between HIV-1-infected patients and controls using the chi-squared tests.

RESULTS

The analyses were performed subdividing the individuals according to their ethnic origin. Among Euro-derived individuals a higher frequency of the LX/LX genotype was observed in patients when compared to controls (P < 0.001). The haplotypic analysis also showed a higher frequency of the haplotypes associated with lower MBL levels among HIV-1-infected patients (P = 0.0001). Among Afro-derived individuals the frequencies of LY/LY and HY/HY genotypes were higher in patients when compared to controls (P = 0.009 and P = 0.02).

CONCLUSIONS

An increased frequency of MBL2 genotypes associated with low MBL levels was observed in Euro-derived patients, suggesting a potential role for MBL in the susceptibility to HIV-1 infection in Euro-derived individuals.

Mannose-binding lectin codon 54 gene polymorphism in relation to risk of nosocomial invasive fungal infection in preterm neonates in the neonatal intensive care unit

OBJECTIVE

Preterm neonates are susceptible to infection due to a combination of sub-optimal immunity and increased exposure to invasive organisms. Invasive fungal infections are associated with significant morbidity and mortality among preterm infants cared for in the neonatal intensive care unit (NICU). Mannose-binding lectin (MBL) is a component of the innate immune system, which may be especially important in the neonatal setting. The objective of this study was to investigate the presence of any association between MBL gene polymorphism and nosocomial invasive fungal infection in preterm neonates.

METHODS

Codon 54 (B allele) polymorphism in exon 1 of the MBL gene was investigated in 31 patients diagnosed as nosocomial invasive fungal infection and 30 control preterm neonates.

RESULTS

AB genotype was determined in 26% and 30% of patient and control groups, respectively, and the difference was not statistically significant. AA genotype was determined in 74% of the patient group and in 67% of the control group, and the difference was not statistically significant. B allele frequency was not different significantly in the patient group (13%) compared to the control group (18%).

CONCLUSIONS

In our study, no relationship was found between MBL codon 54 gene polymorphism and the risk of nosocomial invasive fungal infection in preterm neonates in NICU.

Relationship between oligomer and functional serum mannose-binding lectin in chronic renal failure

INTRODUCTION

Mannose-binding lectin (MBL) plays an important role in first-line host defence against pathogens via the lectin pathway. The binding affinity for ligands is greatly increased by oligomerization, although the basic triplet does not bind solid phase mannan and cannot activate complement. Besides, MBL is a positive acute-phase protein. In this study, we examined the relationship between oligomer and functional serum MBL in chronic renal failure patients who were either uraemic [Pre-haemodialysis (pre-HD) patients], or who were receiving maintenance haemodialysis treatment (HD patients).

MATERIALS AND METHODS

This study included a total of 20 Pre-HD patients, 130 HD patients and 28 healthy subjects. The oligomer and functional serum MBL levels were measured using enzyme-linked immunosorbent assays established previously.

RESULTS

The median serum functional MBL levels were significantly reduced in both Pre-HD and HD patients compared with healthy subjects (P<0·05 for both). Furthermore, the median functional MBL level in Pre-HD patients was significantly lower than that in HD patients (P<0·05). The median serum oligomer MBL levels in both Pre-HD and HD patients were significantly higher compared with healthy subjects (P<0·05 for both). Furthermore, the median oligomer MBL level in HD patients was significantly (P<0·05) higher than that in Pre-HD patients. The ratios of median serum functional MBL levels to oligomer MBL levels were significantly reduced in both Pre-HD and HD patients compared with healthy subjects (P<0·05 for both).

CONCLUSIONS

We found significant reductions in the ratios of serum functional MBL levels to oligomer MBL levels in HD and Pre-HD patients compared with healthy subjects.

New insights on the structural/functional properties of recombinant human mannan-binding lectin and its variants

Inefficient activation of complement lectin pathway in individuals with variant mannan-binding lectin (MBL) genotypes has been attributed to poor formation of higher order oligomers by MBL. But recent studies have shown the presence of large oligomers of MBL (approximately 450 kDa) in serum of individuals with variant MBL alleles. The recombinant forms of MBL (rMBL) variants except MBL/B that assemble into higher order oligomers have not yet been reported. In the present study, structural/functional properties of recombinant forms of wild type MBL (rMBL/A) and its three structural variants, rMBL/B, C, and D generated in insect cells were examined. Western blot analysis indicated covalently linked monomers to hexamers while gel filtration chromatography exhibited non-covalently linked higher order oligomers in addition to prevalent low oligomeric forms. Mannan binding determined by ELISA showed rMBL/A but not the structural variants bind to mannan. Apparent avidity of monoclonal antibody used was found to be about 18- to 52-fold weaker for rMBL structural variants than rMBL/A. Complement activation varied with maximum impairment apparent in rMBL/C followed by rMBL/B, but rMBL/D was functional to the same extent as rMBL/A. Comparison of rMBL/A to MBL purified from plasma (pMBL/A) indicated 8- and 24-fold weaker binding to mannan by BIAcore analysis and ELISA and about 5-fold lesser efficiency in activating complement. The findings provide new insights on the structural/functional properties of rMBL variants and imply that lectin pathway activation may be impaired in individuals, homozygous for the mutant alleles, MBL/C and to a lesser extent MBL/B but not MBL/D.

Independent effects of genetic variations in mannose-binding lectin influence the course of HIV disease: the advantage of heterozygosity for coding mutations

BACKGROUND

The in vivo impact of mannose-binding lectin (MBL), a molecule involved in innate immunity, on the pathogenesis of human immunodeficiency virus (HIV)-1 infection and AIDS is unknown.

METHODS

A total of 1102 HIV-positive and 2213 HIV-negative adult subjects were screened for polymorphisms in the coding and promoter regions of MBL2, the gene that encodes MBL.

RESULTS

Variations in MBL2 did not influence the risk of acquiring HIV-1. Heterozygosity for coding mutations (O allele) and homozygosity for the -221 promoter polymorphism (X allele) in MBL2 were associated with a delay in and an accelerated rate of disease progression, respectively. MBL2 variations influenced the rate of progression to AIDS-defining illnesses. In a multivariate model, the effects of MBL2 variations were independent of several parameters known to influence disease progression, including steady-state viral load, baseline CD4(+) T cell counts, and delayed-type hypersensitivity skin test responses, an in vivo marker of cell-mediated immunity. The effects of MBL2 variations were most evident in those who possessed protective genotypes of CCR5 and a high copy number of CCL3L1, the most potent HIV-suppressive CCR5 ligand.

CONCLUSIONS

MBL2 genotypes are independent determinants of HIV disease progression and heterozygosity for MBL2 coding mutations confer disease-retarding effects. MBL-dependent immune responses may play a role in the pathogenesis of HIV infection.

Complex two-gene modulation of lung disease severity in children with cystic fibrosis

Although cystic fibrosis (CF) is a monogenic disease, its clinical manifestations are influenced in a complex manner. Severity of lung disease, the main cause of mortality among CF patients, is likely modulated by several genes. The mannose-binding lectin 2 (MBL2) gene encodes an innate immune response protein and has been implicated as a pulmonary modifier in CF. However, reports have been conflicting, and interactions with other modifiers have not been investigated. We therefore evaluated the association of MBL2 with CF pulmonary phenotype in a cohort of 1,019 Canadian pediatric CF patients. MBL2 genotypes were combined into low-, intermediate-, and high-expression groups based on MBL2 levels in plasma. Analysis of age at first infection with Pseudomonas aeruginosa demonstrated that MBL2 deficiency was significantly associated with earlier onset of infection. This MBL2 effect was amplified in patients with high-producing genotypes of transforming growth factor beta 1 (TGFB1). Similarly, MBL2 deficiency was associated with more rapid decline of pulmonary function, most significantly in those carrying the high-producing TGFB1 genotype. These findings provide evidence of gene-gene interaction in the pathogenesis of CF lung disease, whereby high TGF-beta1 production enhances the modulatory effect of MBL2 on the age of first bacterial infection and the rate of decline of pulmonary function.

Association between MBL2 gene functional polymorphisms and high-risk human papillomavirus infection in Brazilian women

We studied the association between high-risk human papillomavirus (HPV) infection and MBL2 functional polymorphisms in a group of 180 high-risk HPV-infected women and 180 healthy control subjects. The most frequent high-risk HPV genotypes were 16 (47.2%), 31 (11.7%), 33 (5%), and 18 (2.2%), respectively. Of the 180 HPV-infected women, 99 presented with uterine cervical cancer and 81 did not. No differences in MBL2 genotype or in allelic or haplotype frequencies were found between HPV patients who developed cervical uterine cancer and those who did not. When considering combined genotypes grouped according to MBL production (designated as high, low, and deficient producers), we detected a significant difference between healthy controls and high-risk HPV-positive patients, the latter group showing increased frequencies of deficient-producer genotypes (14.4% vs 9.4% in the healthy control group, corrected p = 0.04). In conclusion, a correlation between MBL2 polymorphisms and high-risk HPV infection was found in this study.

Mannan-binding lectin MBL2 gene polymorphism in chronic hepatitis C: association with the severity of liver fibrosis and response to interferon therapy

Hepatitis C virus (HCV) is a major cause of hepatic disease and of liver transplantation worldwide. Mannan-binding lectin (MBL), encoded by the MBL2 gene, can have an important role as an opsonin and complement activating molecule in HCV persistence and liver injury. We assessed the MBL2 polymorphism in 102 Euro-Brazilian patients with moderate and severe chronic hepatitis C, paired for gender and age with 102 HCV seronegative healthy individuals. Six common single nucleotide polymorphisms in the MBL2 gene, three in the promoter (H/L, X/Y and P/Q) and three in exon 1 (A, the wild-type, and B, C or D also known as O) were evaluated using real-time polymerase chain reaction with fluorescent hybridization probes. The concentration of MBL in plasma was measured by enzyme-linked immunosorbent assay. The frequency of the YA/YO genotype was significantly higher in the HCV patients compared with the controls (P = 0.022). On the other hand, the genotypes associated with low levels of MBL (XA/XA, XA/YO and YO/YO) were decreased significantly in the patients with severe fibrosis (stage F4), when compared with the patients with moderate fibrosis (stage F2) (P = 0.04) and to the control group (P = 0.011). Furthermore, MBL2 genotypes containing X or O mutations were found to be associated with non-responsiveness to pginterferon and ribavirin treatment (P = 0.023). MBL2 polymorphisms may therefore be associated not only with the development of chronic hepatitis C, but also with its clinical evolution and response to treatment.

The role of mannose-binding lectin gene polymorphisms in women with recurrent bacterial vaginosis

OBJECTIVE

The objective of the study was to examine mannose-binding lectin gene (MBL2) polymorphisms in women with recurrent episodes of bacterial vaginosis (BV).

STUDY DESIGN

Seventy-one women with at least 4 episodes of BV in the last 12 months and 130 healthy controls were enrolled to evaluate all 3 variant alleles of the MBL2 gene (polymorphisms at positions 52, 54, and 57 in the first exon of the MBL2 gene).

RESULTS

No statistically significant differences in MBL2 polymorphism allelic and genotype frequencies were observed between women with recurrent BV and controls. Allele A (wild type) was present, respectively, in 78% of patients with recurrent BV and 77% of controls, whereas the allele 0 was present in 22% of women with recurrent BV and 23% of controls. MBL2 genotype and allelic frequencies were similar in the 2 groups, and the 2 populations were in accordance with the Hardy-Weiberg equilibrium.

CONCLUSION

Our results indicate that MBL2 gene polymorphisms do not seem to be involved in susceptibility to recurrences of BV in gynecological patients.

Evidence of an association between mannose binding lectin codon 54 polymorphism and adenoidectomy and/or tonsillectomy in children

Mannose binding lectin (MBL) is a calcium-dependent lectin that plays an important role innate immunity by activating the complement pathway. There have been a number of studies describing an association between the MBL genotype and disease susceptibility. MBL deficiency has been described as one of the factors leading to a number of infections in children with recurrent upper respiratory tractus infections (URTI). We hypothesized that MBL deficiency may be associated with recurrent URTI, which requires adenoidectomy and/or adenotonsillectomy. In this study to clarify this hypothesis we investigated whether there may be an association between two low producing MBL variants and adenoidectomy and/or tonsillectomy due to recurrent URTI in children. Blood samples were collected, adenoidectomy and/or tonsillectomy due to recurrent URTI and 50 controls (mean age 80.53 +/- 32.62 months). In all patients and controls codon 54 and codon 57 polymorphisms of the MBL gene were analyzed. None of the subjects from the patient group and control group carried codon 57 polymorphism of the MBL gene. The frequency of low-level MBL genotypes (AB and BB) for codon 54 polymorphism in the patient group was found to be significantly higher compared to the control subjects (55.7% versus 14%) (p<0.001). This study shows that the presence of low-level MBL alleles is associated with adenoidectomy and/or tonsillectomy caused by recurrent URTI in children.

Fluorochrome-linked immunoassay for functional analysis of the mannose binding lectin complement pathway to the level of C3 cleavage

The humoral response to invading pathogens is mediated by a repertoire of innate immune molecules and receptors able to recognize pathogen-associated molecular patterns. Mannose binding lectin (MBL) and ficolins are initiation molecules of the lectin complement pathway (LCP) that bridge innate and adaptive immunity. Activation of the MBL-dependent lectin pathway, to the level of C3 cleavage, requires functional MASP-2, C2, C4 and C3, all of which have been identified with genetic polymorphisms that can affect protein concentration and function. Current assays for MBL and MASP-2 lack the ability to assess activation of all components to the level of C3 cleavage in a single assay platform. We developed a novel, low volume, fluorochrome linked immunoassay (FLISA) that quantitatively assesses the functional status of MBL, MASP-2 and C3 convertase in a single well. The assay can be used with plasma or serum. Multiple freeze/thaw cycles of serum do not significantly alter the assay, making it ideal for high throughput of large sample databases with minimal volume use. The FLISA can be used potentially to identify specific human disease correlations between these components and clinical outcomes in already established databases.

Identification of the Site of Human Mannan-Binding Lectin Involved in the Interaction with Its Partner Serine Proteases: The Essential Role of Lys55

Mannan-binding lectin (MBL) is an oligomeric lectin that binds neutral carbohydrates on pathogens, forms complexes with MBL-associated serine proteases (MASP)-1, -2, and -3 and 19-kDa MBL-associated protein (MAp19), and triggers the complement lectin pathway through activation of MASP-2. To identify the MASP binding site(s) of human MBL, point mutants targeting residues C-terminal to the hinge region were produced and tested for their interaction with the MASPs and MAp19 using surface plasmon resonance and functional assays. Mutation Lys(55)Ala abolished interaction with the MASPs and MAp19 and prevented formation of functional MBL-MASP-2 complexes. Mutations Lys(55)Gln and Lys(55)Glu abolished binding to MASP-1 and -3 and strongly inhibited interaction with MAp19. Conversely, mutation Lys(55)Arg abolished interaction with MASP-2 and MAp19, but only weakened interaction with MASP-1 and -3. Mutation Arg(47)Glu inhibited interaction with MAp19 and decreased the ability of MBL to trigger the lectin pathway. Mutant Arg(47)Lys showed no interaction with the MASPs or MAp19, likely resulting from a defect in oligomerization. In contrast, mutation Arg(47)Ala had no impact on the interaction with the MASPs and MAp19, nor on the ability of MBL to trigger the lectin pathway. Mutation Pro(53)Ala only had a slight effect on the interaction with MASP-1 and -3, whereas mutations at residues Leu(49) and Leu(56) were ineffective. In conclusion, the MASP binding site of MBL involves a sequence stretch centered on residue Lys(55), which may form an ionic bond representing the major component of the MBL-MASP interaction. The binding sites for MASP-2/MAp19 and MASP-1/3 have common features but are not strictly identical.

Mannan binding lectin and viral hepatitis

Mannan binding lectin (MBL) is a pattern recognition molecule of the innate immune system that binds to sugars on the surface of invading micro-organisms. Target binding, complement activation and other functions of MBL are dependent on the presence of multiple carbohydrate recognition domains. Several polymorphisms in the promoter and structural regions of MBL2 adversely affect the plasma concentration and oligomeric state of MBL. The possession of mutant alleles has been linked to disease outcome for a variety of bacterial and viral infections. Viral hepatitis is caused by unrelated viruses referred to as hepatitis virus A-E. The disease usually has both acute and chronic phases, the latter leading to cirrhosis and hepatocellular carcinoma. Hepatitis viruses B and C (HBV and HCV, respectively) are a significant cause of morbidity worldwide. HBV encodes envelope glycoproteins termed large, middle, and small that may exist in glycosylated or unglycosylated forms on the virion. An interaction between HBV glycoproteins and MBL has been demonstrated in vitro. Significant associations between MBL levels, determined by MBL2 haplotypes, and HBV persistence and disease progression have been described. HCV encodes two highly glycosylated envelope proteins, E1 and E2, which are potential targets for interaction with MBL. Mutant MBL2 haplotypes have been linked to disease progression and response to therapy in HCV infection. Here we summarise the effect of MBL2 polymorphisms on MBL function and how this may relate to disease outcome in HBV and HCV infection.

Quantification of mannan-binding lectin

Mannan-binding lectin (MBL) is attracting considerable interest due to its role in the immune defense. The high frequency of congenital MBL deficiency makes it feasible to evaluate clinical relevance through epidemiological investigations on fairly limited numbers of patients. MBL deficiency is determined by three mutant allotypes termed B, C and D in the coding region as well as mutations in the promoter region. It has been suggested that individuals, with deficiency-associated allotypes, may present significant amounts of low molecular weight MBL. We have compared the quantification of MBL by four commercially available assays with results obtained by our own in-house assays. Most assays are selectively sensitive for the wild type MBL (allotype A), but special combinations of antibodies also detect mutant forms of MBL. Thus a sandwich-type time-resolved immunoflourometric assay (TRIFMA), with a mouse monoclonal antibody (93C) as the catching and detecting antibody, shows B/B and D/D homozygous individuals to present signals corresponding to up to 500 ng MBL per ml (with plasma from an A/A individual as standard) as compared to less than 50 ng/ml and 200 ng/ml, respectively, when measured in other assays. In GPC at isotonic conditions the MBL in B/B and D/D individuals showed a Mr of 450 kDa. This MBL cannot bind to mannan. We further present a new method for quantifying the amount of MBL polypeptide chain. By applying plasma samples on SDS-PAGE at reducing conditions followed by Western blotting and quantification by chemiluminescense, this approach presents single polypeptide chains to the antibody independent of allotype differences in the collagen-like region. Titrations of recombinant MBL served as standard. In sera from homozygous mutants (O/O) the MBL concentrations estimated on Western blot were in the range of 100 to 500 ng/ml and correlated with that measured in the 93C-based TRIFMA.

Degalactosylated and/or Denatured IgA, but Not Native IgA in Any Form, Bind to Mannose-Binding Lectin

Mannose-binding lectin (MBL) is reported to bind to agalactosyl IgG, but not to normally galactosylated (native) IgG. It was recently reported that serum polymeric IgA in its native form reacts with MBL, whereas a more recent report has claimed that native IgD and IgE, and possibly IgM, do not. This led us to investigate whether IgA is truly reactive with MBL. To accomplish this, we collected purified human Igs, of various classes, subclasses, and allotypes, and tested their ability to bind to MBL using an ELISA method. Among these preparations, only one (monoclonal IgA2m(2):Kur) exhibited significant MBL binding. In particular, polymeric or monomeric forms of our normal serum IgA preparation lacked any ability to bind to MBL whatsoever. However, all the Ig preparations which had not bound to MBL became able to do so when they were degalactosylated with a galactosidase treatment, and the binding was further enhanced by acidic denaturation of the Igs. Among the degalactosylated and/or acid-denatured IgA, the IgA2 subclass exhibited a higher level of MBL binding than did IgA1. Our results suggest that MBL does not bind to native Igs (viewed in principle as "self" components), and that only Igs with abnormal glycosylation (degalactosylated forms) and/or denaturation would be MBL reactive.

Diversity of the MBL2 gene in various Brazilian populations and the case of selection at the mannose-binding lectin locus

The mannose binding lectin (MBL2) polymorphism is responsible for a common immunodeficiency in the human species. There were suggestions that the MBL2 polymorphism has been under balancing selection, based on the high global frequency of alleles generating MBL deficiency and on the worldwide distribution of diseases negatively associated with them. To describe the distribution of MBL2 allelic haplotypes in Brazilian populations and to discuss the evolution of this polymorphism, we analyzed six South Brazilian populations (152 Guarani Amerindian, 239 Kaingang Amerindian, 107 admixed, Brazilian 32 Afro-Brazilian, 202 Euro-Brazilian and 16 Oriental-Brazilian). Eight haplotypes were observed: MBL2*HYPA, LYQA, LYPA, LXPA, LYPB, LYQC, HYPD, and LYPD. In addition, through sequencing of the promoter and exon 1 from Amerindian and Oriental individuals, three new single-nucleotide polymorphisms (SNPs) were found in the MBL2 promoter region in the Kaingang. Analysis of the sequencing data by neutrality tests (Tajima's D and Fu and Li's D* and F*) revealed no deviation from selective neutrality equilibrium in the Guarani and Kaingang. Significant Fay and Wu's H results are explained by the recent gene flow in these populations. Contrarily to previous thoughts, stochastic evolutionary factors seem therefore to have had a predominant role in shaping the MBL2 polymorphism, at least in the Amerindians.

Association of a new mannose-binding lectin variant with severe malaria in Gabonese children

Mannose-binding lectin (MBL2) variants that decrease the plasma level of the protein or encode dysfunctional proteins are frequently associated with the severity of a number of infections and autoimmune disorders. The high frequencies of these variants in most populations of the world are probably maintained by some selective advantage against widespread diseases. We found 14 new MBL2 allelic haplotypes, two of them with non-synonymous variants, by screening 136 children with uncomplicated malaria, 131 children with severe malaria and 39 older healthy schoolchildren. We also found a significant association of a novel variant with susceptibility to severe malaria (P=0.010). Increased MBL plasma levels and corresponding MBL2 genotypes were associated with lower concentration of several cytokines and chemokines in plasma of malaria patients. We suggest that malaria could have been one of the evolutionary driving forces shaping the MBL2 polymorphism in the African population.

Mannose-binding lectin and its genetic variants

Mannose-binding lectin (MBL) is a collagen-like serum protein that mediates activation of the complement system and is of importance for host defence. Common variant alleles situated both in the promoter and structural region of the human MBL gene (MBL2) influence the stability and the serum concentration of the protein. Epidemiological studies have suggested that genetically determined variation in MBL serum concentration influences the susceptibility to and the course of different types of infections, autoimmune, metabolic and cardiovascular diseases, but this is still a subject of debate. The fact that these genetic variations are very frequent indicates a dual role for MBL in host defence. In this survey, we summarize the current molecular understanding of human MBL genetics.

Heteroligomeric forms of codon 54 mannose binding lectin (MBL) in circulation demonstrate reduced in vitro function

Mannose binding lectin (MBL) is a pattern recognition molecule that plays a pivotal role in innate immunity. This liver derived, circulating plasma protein binds organisms displaying high-density carbohydrate structures and flags them for destruction via opsonisation and initiation of the lectin pathway of the complement cascade. The present study reveals native, oligomeric forms of human MBL in plasma from healthy blood donors of differing genotypes and correlates the relative abundance of observed molecular weight species with mannan binding activity and C4 deposition in vitro. Wild type (A/A) individuals demonstrate predominately high molecular weight MBL that correlated with high mannan binding capacity and C4 deposition. A/C individuals demonstrated predominantly low molecular weight MBL with decreased mannan binding and C4 deposition activity. A/D individuals demonstrated both high molecular weight and low molecular weight MBL with reduced mannan binding and C4 deposition predominantly seen in combination with LX promoter. We identified A/B individuals as a unique group with large variation in MBL level, mannan binding activity and C4 deposition and propose a model for C4 deposition based on differential binding of MASP.

Characterization of Mannose-Binding Lectin Gene Polymorphism Among Human T-Cell Lymphotropic Virus 1 and 2–Infected Asymptomatic Subjects

The present study investigated the association between mannose-binding lectin (MBL) gene polymorphism and the susceptibility to human T-cell lymphotropic virus (HTLV) infection in a group of 83 HTLV-infected asymptomatic subjects (62 HTLV-1 and 21 HTLV-2) and 99 healthy controls. Detection of MBL*A, MBL*B, and MBL*C was performed by amplifying a fragment of 349 bp (exon 1) and submitting the product to restriction fragment length polymorphism analysis with BanI and MboII endonucleases. Allele MBL*D was investigated by sequence-specific primer-polymerase chain reaction. The frequency of MBL*A, MBL*B, and MBL*D was 63%, 22%, and 15% among seropositive subjects and 70%, 14%, and 16% among healthy controls, respectively. Genotype differences were statistically significant (chi2 = 11.57; p = 0.04); the presence of genotype BB was 9.6% among HTLV-infected patients compared with 1% among controls (chi2 = 7.151; p = 0.019). A significant difference of the genotype frequencies between HTLV-1 and HTLV-2 infections was observed, but this result could be attributed to the number of investigated HTLV-1-infected subjects. The odds ratio to the presence of BB genotype was 10.453 (1.279 < or = IC95% < or = 85.40; p = 0.019). Results reveal a strong association between MBL polymorphism and HTLV infection. Presence of genotype BB may be associated with the susceptibility to HTLV, but further studies, with a larger number of individuals, will be necessary. MBL polymorphism could possibly have an impact on diseases associated with HTLV infection.

The two major oligomeric forms of human mannan-binding lectin: chemical characterization, carbohydrate-binding properties, and interaction with MBL-associated serine proteases

Mannan-binding lectin (MBL) is an oligomeric C-type lectin assembled from homotrimeric structural units that binds to neutral carbohydrates on microbial surfaces. It forms individual complexes with MBL-associated serine proteases (MASP)-1, -2, -3 and a truncated form of MASP-2 (MAp19) and triggers the lectin pathway of complement through MASP-2 activation. To characterize the oligomerization state of the two major MBL forms present in human serum, both proteins were analyzed by mass spectrometry. Mass values of 228,098 +/- 170 Da (MBL-I) and 304,899 +/- 229 Da (MBL-II) were determined for the native proteins, whereas reduction of both species yielded a single chain with an average mass of 25,340 +/- 18 Da. This demonstrates that MBL-I and -II contain 9 and 12 disulfide-linked chains, respectively, and therefore are trimers and tetramers of the structural unit. As shown by surface plasmon resonance spectroscopy, trimeric and tetrameric MBL bound to immobilized mannose-BSA and N-acetylglucosamine-BSA with comparable K(D) values (2.2 and 0.55 nM and 1.2 and 0.96 nM, respectively). However, tetrameric MBL exhibited significantly higher maximal binding capacity and lower dissociation rate constants for both carbohydrates. In contrast, no significant difference was detected for binding of the recombinant MASPs or MAp19 to immobilized trimeric or tetrameric MBL. As shown by gel filtration, both MBL species formed 1:2 complexes with MASP-3 or MAp19. These results provide the first precise analysis of the major human MBL oligomers. The oligomerization state of MBL has a direct effect on its carbohydrate-binding properties, but no influence on the interaction with the MASPs.

L-ficolin in children with recurrent respiratory infections

The lectin pathway of complement activation is used by a collectin, mannan-binding lectin (MBL), and two ficolins, L-ficolin and H-ficolin, to opsonize microorganisms for phagocytosis. We published evidence recently that MBL insufficiency is associated with recurrent respiratory infections in childhood. We have now measured serum L-ficolin in 313 respiratory infection patients and 74 healthy control children. L-ficolin concentrations below the lower limit of the control group were found in 6% of the patients (P <0.02) and were associated most strongly with children having co-existing atopic disorders (11%; P=0.002). We suggest that L-ficolin may have a role in protection from microorganisms complicating allergic disease.

Mannose-binding lectin: laying the stepping stones from clinical research to personalized medicine

As a key component of the complement system, mannose-binding lectin (MBL) is one of the linchpins of innate immunity. It is, therefore, not surprising that MBL2 genetic variants affecting the quantity and activity of the MBL protein in serum have been associated with increased susceptibility to infection and autoimmune diseases, and with poorer prognostic outcomes. This enhanced risk is particularly the case for children and immunosuppressed patients, especially when immunity is further compromised by coexistent primary or secondary immune deficiencies. In several disease areas, such as sepsis, cystic fibrosis, and recurrent childhood infections, the association between low MBL-producing allelic variants and disease risk and/or severity is particularly strong. It is here that the use of MBL testing and replacement therapy has reached the threshold of personalized medicine. The role of MBL in health and disease, advances in MBL testing methodologies and key areas for possible applications of MBL replacement therapy are reviewed.

A population-based study of morbidity and mortality in mannose-binding lectin deficiency

Reduced levels of wild-type mannose-binding lectin (MBL) may increase susceptibility for infection, other common diseases, and death. We investigated associations between MBL deficiency and risk of infection, other common diseases, and death during 24, 24, and 8 yr of follow-up, respectively. We genotyped 9,245 individuals from the adult Danish population for three MBL deficiency alleles, B, C, and D, as opposed to the normal noncarrier A allele. Hospitalization incidence per 10,000 person · yr was 644 in noncarriers compared with 631 in heterozygotes (log-rank: P = 0.39) and 658 in deficiency homozygotes (P = 0.53). Death incidence per 10,000 person · yr was 235 in noncarriers compared with 244 in heterozygotes (P = 0.44) and 274 in deficiency homozygotes (P = 0.12). After stratification by specific cause of hospitalization or death, only hospitalization from cardiovascular disorders was increased in deficiency homozygotes versus noncarriers (P = 0.02). When retested in two case control studies, this association could not be confirmed. Incidence of hospitalization or death from infections or other serious common disorders did not differ between deficiency homozygotes and noncarriers. In conclusion, in this large study in an ethnically homogenous Caucasian population, there was no evidence for significant differences in infectious disease or mortality in MBL-deficient individuals versus controls. Our results suggest that MBL deficiency is not a major risk factor for morbidity or death in the adult Caucasian population.