Differential microorganism-induced mannose-binding lectin activation

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

Direct, Rapid Detection of Pathogens from Urine Samples

The problem of rapidly detecting pathogens directly from clinical samples poses significant analytical challenges. Addressing this issue in relation to urinary tract infections, we propose an effective protocol and related immunomagnetic test kits enabling versatile screening for the presence of pathogenic bacteria in unprocessed urine samples. To achieve this, the components of a typical immunomagnetic separation protocol were optimized towards the sensitive assessment of the aggregates formed out of immunomagnetically tagged target pathogens collected from clinical samples. Specifically, a dedicated immunomagnetic material was developed via the functionalization of standardized, micron-sized magnetic beads with generic antibodies against gram-specific bacterial constituents with mannan binding lectin. As such, we demonstrate efficient procedures for achieving the enhanced, specific, and pathogen-mediated cluster formation of these tailored affinity-coated magnetic beads in complex samples. We further show how cluster analysis, in conjunction with the use of nonspecific, inexpensive fluorescent dye, allows for a straightforward optical assessment of the bacterial load directly from urine samples. The optimized sensing protocol and related kits provide, in less than 60 min, qualitative (positive/negative) information on the bacterial load with 85% specificity and 96% sensitivity, which is appropriate to empower clinical microscopy with a new analytic dimension. The procedure is prone to automation, can be conveniently used in clinical microbiology laboratories and, since it preserves the viability of the captured bacteria, can be interfaced with downstream analyses and antimicrobial susceptibility testing. Moreover, the study emphasizes a suite of practical validation assays that are useful for bringing the tool-box of immunomagnetic materials outside the academic laboratory and into real-life applications.

Importance of mannose-binding lectin2 polymorphism (rs1800450) in infections in children

PURPOSE

Mannose-binding lectin (MBL) is a serine protease belonging to the collectins and an important factor in the inherited immune system. We aimed to reveal the distribution of different MBL2 genotypes in patients diagnosed with acute bronchiolitis and pneumonia.

MATERIAL AND METHODS

A total of 147 patients who applied to Paediatric Emergency between 01.12.2019 and 31.12.2020 were included in the study. Patients were divided into two subgroups: Bronchiolitis and pneumonia.

RESULTS

AA genotype was found to be significantly higher in healthy controls (p = 0.039). In the pneumonia group, both AB/BB genotype was significantly higher compared to healthy controls (p = 0.001). While the AA genotype was more common in patients with acute bronchiolitis, AB/BB genotypes were more common in the pneumonia group (p = 0.001). The presence of fever, crepitation, tachypnoea, pathological x-ray finding, and high leukocyte count are significantly more common in patients with AA genotype, while more than 3 days of follow-up duration and severe clinical picture were more common in patients with AB/BB genotypes (p < 0.05, for all).

CONCLUSIONS

Genotypes with low MBL expression were significantly more common in patients with pneumonia and severe infection. All these results reveal the importance of MBL polymorphisms and their expression in infections.

Structure, preparation, modification, and bioactivities of β-glucan and mannan from yeast cell wall: A review

In order to solve the antibiotic resistance, the research on antibiotic substitutes has received an extensive attention. Many studies have shown that β-glucan and mannan from yeast cell wall have the potential to replace antibiotics for the prevention and treatment of animal diseases, thereby reducing the development and spread of antibiotic-resistant bacterial pathogens. β-Glucan and mannan had a variety of biological functions, including improving the intestinal environment, stimulating innate and acquired immunity, adsorbing mycotoxins, enhancing antioxidant capacity, and so on. The biological activities of β-glucan and mannan can be improved by chemically modifying its primary structure or reducing molecular weight. In this paper, the structure, preparation, modification, and biological activities of β-glucan and mannan were reviewed, which provided future perspectives of β-glucan and mannan.

Broad-spectrum capture of clinical pathogens using engineered Fc-mannose-binding lectin enhanced by antibiotic treatment

Background: Fc-mannose-binding lectin (FcMBL), an engineered version of the blood opsonin MBL that contains the carbohydrate recognition domain (CRD) and flexible neck regions of MBL fused to the Fc portion of human IgG1, has been shown to bind various microbes and pathogen-associated molecular patterns (PAMPs). FcMBL has also been used to create an enzyme-linked lectin sorbent assay (ELLecSA) for use as a rapid (<1 h) diagnostic of bloodstream infections. Methods: Here we extended this work by using the ELLecSA to test FcMBL's ability to bind to more than 190 different isolates from over 95 different pathogen species. Results: FcMBL bound to 85% of the isolates and 97 of the 112 (87%) different pathogen species tested, including bacteria, fungi, viral antigens and parasites. FcMBL also bound to PAMPs including, lipopolysaccharide endotoxin (LPS) and lipoteichoic acid (LTA) from Gram-negative and Gram-positive bacteria, as well as lipoarabinomannan (LAM) and phosphatidylinositol mannoside 6 (PIM 6) from Mycobacterium tuberculosis. Conclusions: The efficiency of pathogen detection and variation between binding of different strains of the same species could be improved by treating the bacteria with antibiotics, or mechanical disruption using a bead mill, prior to FcMBL capture to reveal previously concealed binding sites within the bacterial cell wall. As FcMBL can bind to pathogens and PAMPs in urine as well as blood, its broad-binding capability could be leveraged to develop a variety of clinically relevant technologies, including infectious disease diagnostics, therapeutics, and vaccines.

Biomarker of Aflatoxin Ingestion: ¹H NMR-Based Plasma Metabolomics of Dairy Cows Fed Aflatoxin B₁ with or without Sequestering Agents

The study applied ¹H NMR-based plasma metabolomics to identify candidate biomarkers of aflatoxin B1 (AFB₁) ingestion in dairy cows fed no sequestering agents and evaluate the effect of supplementing clay and/or a Saccharomyces cerevisiae fermentation product (SCFP) on such biomarkers. Eight lactating cows were randomly assigned to 1 of 4 treatments in a balanced 4 × 4 Latin square design with 2 squares. Treatments were: control, toxin (T; 1725 µg AFB₁/head/day), T with clay (CL; 200 g/head/day), and CL with SCFP (CL + SCFP; 35 g of SCFP/head/day). Cows in T, CL, and CL + SCFP were dosed with AFB₁ from d 26 to 30. The sequestering agents were top-dressed from d 1 to 33. On d 30 of each period, 15 mL of blood was taken from the coccygeal vessels and plasma samples were prepared by centrifugation. Compared to the control, T decreased plasma concentrations of alanine, acetic acid, leucine, arginine and valine. In contrast, T increased plasma ethanol concentration 3.56-fold compared to control. Treatment with CL tended to reduce sarcosine concentration, whereas treatment with CL + SCFP increased concentrations of mannose and 12 amino acids. Based on size of the area under the curve (AUC) of receiver operating characteristic and fold change (FC) analyses, ethanol was the most significantly altered metabolite in T (AUC = 0.88; FC = 3.56); hence, it was chosen as the candidate biomarker of aflatoxin ingestion in dairy cows fed no sequestering agent.

Combination of Helicobacter pylori infection and the interleukin 8 -251 T > A polymorphism, but not the mannose-binding lectin 2 codon 54 G > A polymorphism, might be a risk factor of gastric cancer

Background

Mannose-binding lectin (MBL) acts in the innate immune response to Helicobacter pylori. Interleukin 8 (IL-8) is a potent cytokine produced by gastric epithelial cells in response to H. pylori. We aimed to investigate whether polymorphisms in MBL2 and IL-8 influence susceptibility to H. pylori infection, and the associations of these polymorphisms with the risk of gastroduodenal diseases in a Korean population.

Methods

We consecutively enrolled 176 H. pylori-negative control subjects, 221 subjects with H. pylori-positive non-atrophic gastritis, 52 mild atrophic gastritis (AG), 61 severe AG, 175 duodenal ulcer, and 283 gastric cancer (GC). Allele-specific PCR-RFLP was conducted for polymorphisms in MBL2 exon 1 (codon 52, 54, and 57) and IL-8 -251 T > A. IL-8 levels in gastric mucosal tissues and serum MBL levels were measured by enzyme-linked immunosorbent assay.

Results

MBL2 exon 1 polymorphic variants were found only in codon 54, and the allele frequencies did not differ significantly between the control and disease groups. Although serum MBL levels in codon 54 A/A mutants were markedly low, it did not influence susceptibility to H. pylori infection or the risk of gastroduodenal diseases. IL-8 levels were significantly different between T/T wild type, T/A heterozygote, and A/A mutant genotypes. IL-8 -251 A allele carriers (A/A + T/A) showed increased IL-8 levels, and were significantly associated with the risk of severe AG and GC.

Conclusions

We suggest that a combination of H. pylori infection and the IL-8 -251 T > A polymorphism might increase the risk of severe AG and GC in a Korean population.

Mannose-binding lectin 2 (Mbl2) gene polymorphisms are related to protein plasma levels, but not to heart disease and infection by Chlamydia

The presence of the single nucleotide polymorphisms in exon 1 of the mannose-binding lectin 2 (MBL2) gene was evaluated in a sample of 159 patients undergoing coronary artery bypass surgery (71 patients undergoing valve replacement surgery and 300 control subjects) to investigate a possible association between polymorphisms and heart disease with Chlamydia infection. The identification of the alleles B and D was performed using real time polymerase chain reaction (PCR) and of the allele C was accomplished through PCR assays followed by digestion with the restriction enzyme. The comparative analysis of allelic and genotypic frequencies between the three groups did not reveal any significant difference, even when related to previous Chlamydia infection. Variations in the MBL plasma levels were influenced by the presence of polymorphisms, being significantly higher in the group of cardiac patients, but without representing a risk for the disease. The results showed that despite MBL2 gene polymorphisms being associated with the protein plasma levels, the polymorphisms were not enough to predict the development of heart disease, regardless of infection with both species of Chlamydia.

Shared characteristics between Mycobacterium tuberculosis and fungi contribute to virulence

Mycobacterium tuberculosis, an etiologic agent of tuberculosis, exacts a heavy toll in terms of human morbidity and mortality. Although an ancient disease, new strains are emerging as human population density increases. The emergent virulent strains appear adept at steering the host immune response from a protective Th1 type response towards a Th2 bias, a feature shared with some pathogenic fungi. Other common characteristics include infection site, metabolic features, the composition and display of cell surface molecules, the range of innate immune receptors engaged during infection, and the ability to form granulomas. Literature from these two distinct fields of research are reviewed to propose that the emergent virulent strains of M. tuberculosis are in the process of convergent evolution with pathogenic fungi, and are increasing the prominence of conserved traits from environmental phylogenetic ancestors that facilitate their evasion of host defenses and dissemination.

Mannose-binding lectin deficiency and acute exacerbations of chronic obstructive pulmonary disease

Background:

Mannose-binding lectin is a collectin involved in host defense against infection. Whether mannose-binding lectin deficiency is associated with acute exacerbations of chronic obstructive pulmonary disease is debated.

Methods:

Participants in a study designed to determine if azithromycin taken daily for one year decreased acute exacerbations had serum mannose-binding lectin concentrations measured at the time of enrollment.

Results:

Samples were obtained from 1037 subjects (91%) in the trial. The prevalence of mannose-binding lectin deficiency ranged from 0.5% to 52.2%, depending on how deficiency was defined. No differences in the prevalence of deficiency were observed with respect to any demographic variable assessed, and no differences were observed in time to first exacerbation, rate of exacerbations, or percentage of subjects requiring hospitalization for exacerbations in those with deficiency versus those without, regardless of how deficiency was defined.

Conclusion:

In a large sample of subjects with chronic obstructive pulmonary disease selected for having an increased risk of experiencing an acute exacerbation of chronic obstructive pulmonary disease, only 1.9% had mannose-binding lectin concentrations below the normal range and we found no association between mannose-binding lectin concentrations and time to first acute exacerbation or frequency of acute exacerbations during one year of prospective follow-up.

Genetic predisposition to respiratory infection and sepsis

Genetic variations, in part, determine individual susceptibility to sepsis and pneumonia. Advances in genetic sequence analysis as well as high throughput platform analysis of gene expression has allowed for a better understanding of immunopathogenesis during sepsis. Differences in genes can also modulate immune and inflammatory response during sepsis thereby translating to differences in clinical outcomes. An increasing number of candidate genes have been implicated to play a role in sepsis susceptibility, most of which are controversial with few exceptions. This does not refute the significance of genetic polymorphisms in sepsis, but rather highlights the difficulties and pitfalls related to genetic association studies. These difficulties include differences in study design such as heterogeneous patient cohorts and differences in pathogenic organisms, linkage disequilibrium, and lack of power for detailed haplotype analysis or examination of gene-gene interactions. There is extensive diversity in the pathways of inflammation and immune response during sepsis making it even harder to prove the functional and clinical significance of one single genetic polymorphism which could be easily masqueraded or compensated by other upstream or downstream events of the pathway involved. The majority of studies have analysed candidate genes in isolation from other possible polymorphisms. It is likely that susceptibility to sepsis is the result of polymorphisms from multiple genes rather than one single mutation. Future studies should aim for multi-centered collaborative approach looking at genome wide association or gene profiling to provide a more complete appraisal of the key genetic players in determining genetic susceptibility to sepsis. This review paper will summarise the prominent candidate gene polymorphisms with known functional changes or those with haplotype data. In addition, a summary of the expanding research in the field of epigenetics and post-sepsis immunosuppression will be discussed.

Characterization of mannose-binding lectin plasma levels and genetic polymorphisms in HIV-1-infected individuals

INTRODUCTION

The present study investigated the association between mannose-binding lectin (MBL) gene polymorphism and serum levels with infection by HIV-1.

METHODS

Blood samples (5 mL) were collected from 97 HIV-1-infected individuals resident in Belém, State of Pará, Brazil, who attended the Special Outpatient Unit for Infections and Parasitic Diseases (URE-DIPE). CD4+ T-lymphocyte count and plasma viral load were quantified. A 349bp fragment of exon 1 of the MBL was amplified via PCR, using genomic DNA extracted from controls and HIV-1-infected individuals, following established protocols. MBL plasma levels of the patients were quantified using an enzyme immunoassay kit.

RESULTS

Two alleles were observed: MBL*O, with a frequency of 26.3% in HIV-1-infected individuals; and the wild allele MBL*A (73.7%). Similar frequencies were observed in the control group (p > 0.05). Genotype frequencies were distributed according to the Hardy-Weinberg equilibrium in both groups. Mean MBL plasma levels varied by genotype, with statistically significant differences between the AA and AO (p < 0.0001), and AA and OO (p < 0.001) genotypes, but not AO and OO (p = 0.17). Additionally, CD4+ T-lymphocytes and plasma viral load levels did not differ significantly by genotype (p > 0.05).

CONCLUSIONS

The results of this study do not support the hypothesis that MBL gene polymorphism or low plasma MBL concentrations might have a direct influence on HIV-1 infection, although a broader study involving a large number of patients is needed.

Mannose-binding lectin is produced by vaginal epithelial cells and its level in the vaginal fluid is influenced by progesterone

Mannose-binding lectin (MBL) is a recognition molecule of the complement (C) system and binds to carbohydrate ligands present on a wide range of pathogenic bacteria, viruses, fungi, and parasites. MBL has been detected in the cervico-vaginal cavity where it can provide a first-line defence against infectious agents colonizing the lower tract of the reproductive system. Analysis of the cervico-vaginal lavage (CVL) obtained from 11 normal cycling women at different phases of the menstrual cycle revealed increased levels of MBL in the secretive phase. Part of this MBL derives from the circulation as indicated by the presence of transferrin in CVL tested as a marker of vascular and tissue permeability. The local synthesis of MBL is suggested by the finding that its level is substantially higher than that of transferrin in the secretive phase. The contribution of endometrium is negligible since the MBL level did not change before and after hysterectomy. RT-PCR and in situ RT-PCR analysis showed that the vaginal tissue, and in particular the basal layer of the epithelium, is a source of MBL which binds to the basal membrane and to cells of the outer layers of the epithelium. In conclusion, we have shown that MBL detected in CVL derives both from plasma as result of transudation and from local synthesis and its level is progesterone dependent increasing in the secretive phase of the menstrual cycle.

Association between mannose-binding lectin and HIV infection and progression in a Chinese population

Mannose-binding lectin (MBL) is a circulating pattern recognition molecule involved in the innate immune system that mediates phagocytosis and activates complement by binding to a carbohydrate extremity. Some MBL genetic polymorphisms result in deficient protein levels and increased susceptibility to infection. The objective of this study was to investigate the association between MBL2 exon 1 polymorphisms, serum levels of normal MBL, and HIV-1 infection and progression in a Chinese population. A total of 1075 adult patients infected with HIV-1 (532 male and 543 female) were recruited. The genotype of 145 patients was determined and the genotype frequencies compared with healthy population controls. The disease status of patients was evaluated for different MBL2 genotypes and normal MBL serum levels. MBL2 exon 1 polymorphisms (A/O or O/O) were significantly more common in HIV-1-infected patients than in the healthy controls. Patients in clinical categories B/C with severe diseases were significantly more likely to have one variant allele. There was a statistical relationship between MBL2 genotypes and MBL serum levels. In addition, higher CD4(+) T cell counts and ratios of CD4(+) T cells:CD8(+) T cells were observed in patients with medium MBL levels than with low or high MBL levels. Patients with mild diseases were also more likely to have medium MBL levels than high levels. Analysis of MBL levels with respect to sex yielded differences. Median MBL levels were substantially higher in males than in females in HIV-1-infected patients. Lower CD4(+) T cell counts were detected in males with low MBL levels, but the opposite was observed in females. Our results suggest that genetic polymorphisms resulting in MBL deficiency are associated with increased susceptibility to HIV-1 infection and disease progression in the studied population. Moreover, serum circulating levels of normal MBL in HIV-1-infected patients could be an important auxiliary biological marker in association with CD4(+) T cell counts in the evaluation of HIV-1 disease progression. The sex differences in the regulation of MBL serum levels during infection merit further exploration.

Mannose-binding lectin deficiency and respiratory tract infection

Mannose-binding lectin (MBL) is an innate immune system pattern recognition protein that kills a wide range of pathogenic microbes through complement activation. A substantial proportion of all human populations studied to date have MBL deficiency due to MBL2 polymorphisms, which potentially increases susceptibility to infectious disease. MBL binds numerous respiratory pathogens but the capsule of Streptococcus pneumoniae abrogates its efficient binding. Clinical studies in humans have shown that MBL deficiency appears to predispose to severe respiratory tract infection. A recent meta-analysis shows that MBL deficiency was associated with death in patients with pneumococcal infection after adjusting for bacteraemia and comorbidities. Human clinical studies have also shown associations between MBL deficiency and various less common respiratory infections. Intracellular infections like tuberculosis may be less common with MBL deficiency because of reduced opsonophagocytosis. Lung secretions contain small amounts of MBL that are potentially sufficient to activate complement, but their measurement is confounded by dilution inherent in collection techniques. Therefore, if this protein does play a role in pulmonary immunity it is presumably through prevention of haematogenous dissemination of respiratory pathogens while adding to mucosal defences. Ficolins are collectins that are structurally and functionally related to MBL and are either present in serum or expressed in tissues including the lung. Limited variation in serum levels of L- and H-ficolin result from the presence of FCN2 and FCN3 polymorphisms. Initial studies on the impact of FCN2 polymorphisms or low L-ficolin levels do not seem to show major associations with respiratory infection. MBL is being developed as a new immunotherapeutic agent for prevention of infection in immunocompromised hosts. The available literature suggests that it may also be of benefit in MBL deficient patients with severe pneumonia. This review concentrates on clinical associations between MBL deficiency and susceptibility to respiratory tract infection.

Mannose-binding lectin gene polymorphisms are not associated with susceptibility to hepatitis C virus infection in the Brazilian Amazon region

The present study compares the genotype frequencies between two population groups composed by 73 hepatitis C virus (HCV)-infected patients and 92 seronegative controls and investigates the role of allele variants as a possible factor in the susceptibility to HCV infection and the influence on disease progression. The identification of MBL*B and MBL*C alleles was performed by restriction fragment length polymorphism analysis of the 349-bp product using BanI and MboII restriction enzymes, respectively, and a polymerase chain reaction-sequence-specific polymorphism for discrimination of MBL*D. The analysis of allele and genotype frequencies between an HCV-infected group and seronegative controls did not indicate significant differences. The comparison of chronically infected subjects with and without liver cirrhosis was also not statistically significant. The odds ratio estimations were not significant, and the values obtained cannot suggest that the presence of allele variant MBL*B could have some influence in the risk of HCV infection progression to liver cirrhosis and that the presence of allele MBL*D could confer some protection against disease progression, but a larger sample size is necessary to confirm the present results.

Acute-phase responsiveness of mannose-binding lectin in community-acquired pneumonia is highly dependent upon MBL2 genotypes

Mannose-binding lectin (MBL) is a pattern recognition receptor of the complement system and plays an important role in innate immunity. Whether or not MBL acts as an acute-phase response protein in infection has been an issue of extensive debate, because MBL responses have shown a high degree of heterogeneity. Single nucleotide polymorphisms (SNPs) in the promoter (wild-type Y versus X) and exon 1 (A versus 0) of the MBL2 gene can lead to MBL deficiency. This study investigated the influence of SNPs in the promoter and exon 1 of the MBL2 gene on the acute-phase responsiveness of MBL in 143 patients with community-acquired pneumonia. Acute-phase reactivity was observed only in MBL-sufficient genotypes (YA/YA, XA/YA, XA/XA and YA/0). In patients with wild-type exon 1 genotype A/A, positive acute-phase responses were associated with the presence of the YA haplotype and negative responses with its absence. Genotypes YA/0 and XA/XA produced equal levels of MBL in convalescence. In the acute phase, however, patients with genotype XA/XA displayed negative acute-phase responses more often than those with genotype YA/0. Correlation of MBL and C-reactive protein levels in the acute phase of pneumonia also depended upon the MBL2 genotype. In conclusion, acute-phase responsiveness of MBL was highly dependent upon the MBL2 genotype. These data suggest that heterogeneity in protein responses in the acute phase of disease should always be viewed in the light of possible influences of genetic differences in both structural and regulatory parts of the gene.

Mannose binding lectin plays a crucial role in innate immunity against yeast by enhanced complement activation and enhanced uptake of polymorphonuclear cells

BACKGROUND

Mannose binding lectin (MBL) is an important host defence protein against opportunistic fungal pathogens. This carbohydrate-binding protein, an opsonin and lectin pathway activator, binds through multiple lectin domains to the repeating sugar arrays displayed on the surface of a wide range of clinically relevant microbial species. We investigated the contribution of MBL to antifungal innate immunity towards C. parapsilosis in vitro.

RESULTS

High avidity binding was observed between MBL and C. albicans and C. parapsilosis. Addition of MBL to MBL deficient serum increased the deposition of C4 and C3b and enhanced the uptake of C. albicans, C. parapsilosis and acapsular C. neoformans by polymorphonuclear cells (PMNs). Compared to other microorganisms, such as Escherichia coli, Staphylococcus aureus and Cryptococcus neoformans, C. parapsilosis and Candida albicans were potent activators of the lectin pathway.

CONCLUSION

Our results suggest that MBL plays a crucial role in the innate immunity against infections caused by yeast by increasing uptake by PMN.

Deficient mannose-binding lectin-mediated complement activation despite mannose-binding lectin-sufficient genotypes in an outbreak of Legionella pneumophila pneumonia

Polymorphisms leading to deficiency of mannose-binding lectin (MBL) are associated with predisposition to infection. However, MBL deficiency can be protective against intracellular pathogens that use MBL to enter host cells. The role of MBL genotype and activity in infection with the intracellular pathogen Legionella pneumophila was studied in a large outbreak of legionellosis at a Dutch flower show. A total of 141 patients, 65 exposed asymptomatic exhibition staff members and 670 unexposed blood bank donors were included for the study of MBL2 genotypes and MBL-mediated complement activation. Genotypic MBL deficiency was equally prevalent in patients and controls. Deficient MBL-mediated complement activation was more prevalent in patients. Even in patients with genotypes that confer MBL sufficiency, 20.6% lacked MBL-mediated complement activation. In most patients with MBL-sufficient genotypes who lacked MBL-mediated activation at the acute phase of disease, lectin pathway functionality was restored at convalescence. In conclusion, genotypic MBL deficiency was not a risk factor for legionellosis. However, patients with legionellosis displayed deficient MBL-mediated complement activation even with MBL-sufficient genotypes. Together, these genotypical and functional data suggest that the observed deficiency of lectin pathway activation is an effect of legionellosis rather than a risk factor for acquiring it.

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.

Receptor-mediated uptake of Legionella pneumophila by Acanthamoeba castellanii and Naegleria lovaniensis

AIMS

Investigation of the attachment and uptake of Legionella pneumophila by Acanthamoeba castellanii and Naegleria lovaniensis, as these are two critical steps in the subsequent bacterial survival in both amoeba hosts.

METHODS AND RESULTS

Initially, the mode of Legionella uptake was examined using inhibitors of microfilament-dependent and receptor-mediated uptake phagocytosis. Secondly, the minimum saccharide structure to interfere with L. pneumophila uptake was determined by means of selected saccharides. Bacterial attachment and uptake by each of the amoeba species occurred through a receptor-mediated endocytosis, which required de novo synthesis of host proteins. Legionella pneumophila showed a high affinity to the alpha1-3D-mannobiose domain of the mannose-binding receptor located on A. castellanii. In contrast, L. pneumophila bacteria had a high affinity for the GalNAcbeta1-4Gal domain of the N-acetyl-D-galactosamine receptor of N. lovaniensis.

CONCLUSIONS

Our data pointed to a remarkable adaptation of L. pneumophila to invade different amoeba hosts, as the uptake by both amoeba species is mediated by two different receptor families.

SIGNIFICANCE AND IMPACT OF THE STUDY

The fact that L. pneumophila is taken up by two different amoeba species using different receptor families adds further complexity to the host-parasite interaction process, as 14 amoeba species are known to be appropriate Legionella hosts.

Low mannose-binding lectin complement activation function is associated with predisposition to Legionnaires' disease

Innate immune system deficiency may predispose to severe infections such as Legionnaires' disease. We have investigated the role of mannose-binding lectin (MBL) deficiency in the Melbourne Aquarium Legionnaires' disease outbreak. Serum samples from patients and controls that were exposed but shown to be uninfected from the Melbourne Aquarium Legionnaires' disease outbreak were tested for MBL function (C4 deposition) and level (mannan-binding). MBL function was lower in Legionnaires' disease cases than in age- and sex-matched uninfected, exposed controls. The frequency of MBL deficiency with C4 deposition < 0.2 U/microl was significantly higher in Legionnaires' disease cases than in controls. This also applied to Legionnaires' disease cases requiring hospital care. There was no difference in MBL mannan-binding levels between Legionnaires' disease patients and controls. There was no significant interval change in MBL function or level after a mean of 46 days. MBL complement activation functional deficiency appears to predispose to Legionnaires' disease.

Mannose-binding lectin deficiency does not increase the prevalence of Helicobacter pylori seropositivity

BACKGROUND

Mannose-binding lectin is an immune molecule that can bind to pathogens and initiate the complement cascade. In certain clinical situations, often characterized by immune compromise, mannose-binding lectin deficiency can increase the risk of infectious complications. Helicobacter pylori is one of the most common human infections and can bind mannose-binding lectin. Therefore, we examined whether mannose-binding lectin status influences the prevalence of H. pylori infection.

METHODS

Two distinct populations were targeted. The first consisted of 166 volunteer blood donors, the second included 108 peripheral blood stem cell donors. All were tested for serological evidence of H. pylori infection, and had their mannose-binding lectin status characterized by genotyping, and quantification of mannose-binding lectin mannan-binding level and C4-deposition function in plasma.

RESULTS

H. pylori positive blood donors had higher blood mannose-binding lectin levels, as measured by C4 deposition (median 0.67 vs. 0.40, P=0.009, hazard ratio 2.82, 95% confidence interval 1.29-6.19) and mannan-binding assays (median 1.83 vs. 1.26, P=0.02, hazard ratio 1.28, 95% confidence interval 1.03-1.59). A trend was also found between the presence of an MBL2 coding mutation and a reduced prevalence of H. pylori. No significant associations were found in the second population.

CONCLUSIONS

Mannose-binding lectin deficiency does not increase the risk of H. pylori infection. The finding in one population that greater mannose-binding lectin activity might predispose to infection, suggests that this study should be repeated in other large cohorts of normal subjects.

Mannose-binding lectin and maladies of the bowel and liver

Mannose-binding lectin (MBL) is a pattern-recognition molecule that binds to characteristic carbohydrate motifs present on the surface of many different pathogens. MBL binding stimulates the immune system via the lectin pathway of complement activation. In certain clinical situations, often characterized by pre-existing immune compromise, MBL deficiency increases the risk of infectious and other disease-specific complications. Many of the key pathogenic processes inherent to common gastroenterological diseases, such as infection, immunological damage, and carcinogenesis, have been linked to MBL. This editorial reviews the biology of MBL, outlines key disease associations to document the breadth of influence of MBL, and finally, highlights the relevance of MBL to both gastroenterological health and disease.

Development of a fluorescence assay for the detection of L-ficolin-MASP in serum or purified samples

A fluorescence assay for the detection of L-ficolin-MASP in human serum or purified sample was developed by measuring the cleavage of fluorescent amide substrate by L-ficolin associated MASPs bound to the lipoteichoic acid (LTA). LTA (Staphylococcus aureus DSM 20233) was coated on NuncMaxisorp microtiter plates and serum or purified sample incubated overnight at 4 degrees C to allow the L-ficolin-MASP to bind LTA. Assay conditions for binding and complete cleavage of fluorescent amide substrate were standardized. The optimum temperature, incubation time and molarity of NaCl for LTA-ficolin binding were found to be 4 degrees C for 6 h at 1 M NaCl concentration. The optimum incubation time and pH for complete cleavage of fluorescent amide substrate by LTA bound L-ficolin associated MASP were found to be 2 h at pH 8.5. LTA-ficolin binding was found to be highly specific and was inhibited completely by LTA but not with mannose. A calibration curve was prepared by using the purified ficolin-MASP complex (1 to 12 mug/ml) and could be used to find concentration of ficolin-MASP complex in normal human serum.

Mannan-binding lectin in children with chronic gastritis

The involvement of mannan-binding lectin (MBL) insufficiency in the pathogenesis of chronic gastritis (CG) in children was investigated. Blood samples were collected from 78 paediatric patients suffering from CG associated with Helicobacter pylori infection (group Hp(+)) and from 41 with the disease not associated with such an infection (group Hp(-)). Control group consisted of 77 children. The frequency of mbl-2 gene mutations and serum protein concentrations did not differ significantly in both groups as compared with controls. An expression of mbl-2 gene in gastric biopsies of CG patients was demonstrated. It was found to be stronger in H. pylori-infected children. The results presented in this paper suggest that MBL deficit/dysfunction probably does not contribute to an increased risk of CG (both associated and not associated with H. pylori infection) in children. However, MBL opsonic effect and/or the lectin pathway of complement activation may be taken into account as possible host defence mechanisms in gastric patients.

Deficiency of mannose-binding lectin greatly increases susceptibility to postburn infection with Pseudomonas aeruginosa

Burn injury disrupts the mechanical and biological barrier that the skin presents against infection by symbionts like the Pseudomonas aeruginosa, a Gram-negative bacteria. A combination of local factors, antimicrobial peptides, and resident effector cells form the initial response to mechanical injury of the skin. This activity is followed by an inflammatory response that includes influx of phagocytes and serum factors, such as complement and mannose-binding lectin (MBL), which is a broad-spectrum pattern recognition molecule that plays a key role in innate immunity. A growing consensus from studies in humans and mice suggests that lack of MBL together with other comorbid factors predisposes the host to infection. In this study we examined whether MBL deficiency increases the risk of P. aeruginosa infection in a burned host. We found that both wild-type and MBL null mice were resistant to a 5% total body surface area burn alone or s.c. infection with P. aeruginosa alone. However, when mice were burned then inoculated s.c. with P. aeruginosa at the burn site, all MBL null mice died by 42 h from septicemia, whereas only one-third of wild-type mice succumbed (p = 0.0005). This result indicates that MBL plays a key role in containing and preventing a systemic spread of P. aeruginosa infection following burn injury and suggests that MBL deficiency in humans maybe a premorbid variable in the predisposition to infection in burn victims.

Mannose-binding lectin gene polymorphism and its impact on human immunodeficiency virus 1 infection

Mannose-binding lectin (MBL) is a serum protein whose low concentration is associated with the occurrence of allele variants named MBL*B, MBL*C and MBL*D. The present study investigated the association between MBL gene polymorphism and the susceptibility to HIV-1 infection. The study of 145 HIV-1-infected subjects and 99 healthy controls showed the presence of alleles MBL*A, MBL*B and MBL*D, whose frequencies were 69%, 22% and 09% among patients and 71%, 13% and 16% among healthy controls, respectively. The presence of the variant MBL*B was associated with higher plasma viral load levels, suggesting the importance of the MBL gene polymorphism in the clinical evolution of HIV-1-infected patients.

The bovine innate immune response during experimentally-induced Pseudomonas aeruginosa mastitis

Almost half of all clinical cases of mastitis are caused by Gram-negative bacteria. Among these bacteria, intramammary infection by Pseudomonas aeruginosa remains one of the most refractory to antibiotic therapy. The ability to recognize potentially harmful pathogens whether previously encountered or not, as well as the induction of an initial pro-inflammatory response to these pathogens, are critical components of host innate immunity. Although the innate immune response to another Gram-negative mastitis-causing pathogen, Escherichia coli, has been well-characterized, little is known about the response to other Gram-negative bacteria, including P. aeruginosa. The objective of the current study was to characterize the systemic and localized bovine innate immune response to intramammary infection with P. aeruginosa. The contralateral quarters of ten mid-lactating Holstein cows were challenged with either saline or P. aeruginosa. Following the establishment of infection, milk samples were collected and assayed for changes in cytokine and growth factor concentrations, complement activation, and changes in the levels of soluble CD14 (sCD14) and lipopolysaccharide (LPS)-binding protein (LBP), two accessory molecules involved in host recognition of Gram-negative bacteria. Initial increases in milk somatic cell counts were evident within 12h of experimental challenge and remained elevated for >or=3 weeks. Increased permeability of the mammary gland vasculature, as evidenced by elevated milk levels of BSA, was initially observed 20 h post-infection and persisted for 2 weeks. Within 32 h of challenge, increased levels of IL-8, TNF-alpha, IL-10, and IL-12 were detected, however, the elevated levels of these cytokines were not sustained for longer than a 24h period. In contrast, elevations in IL-1beta, IFN-gamma, TGF-alpha, TGF-beta1, TGF-beta2, sCD14, LBP, and activated complement factor 5 (C5a) were sustained for periods of >48 h. Systemic changes were characterized by elevated body temperature, induction of the acute phase protein synthesis of serum amyloid A and LBP, and a transient decrease in circulating neutrophils and lymphocytes. Together, these data demonstrate the capability of the mammary gland to mount a robust innate immune response to P. aeruginosa that is characterized by the induction of pro-inflammatory cytokines, complement activation, and increased levels of accessory molecules involved in Gram-negative bacterial recognition.

Moraxella catarrhalisis only a weak activator of the mannose-binding lectin (MBL) pathway of complement activation

A hemolytic bystander assay was used to assess the functional serum mannose-binding lectin (MBL) activating capacity of five isolates of Moraxella catarrhalis obtained from children who suffered recurrent acute otitis media episodes. Results showed that this organism is only a poor activator of the lectin pathway of complement activation, with subsequent consequences for the etiology of otitis media by this organism.

Mannan-binding lectin recognizes structures on ischaemic reperfused mouse kidneys and is implicated in tissue injury

Organ damage as a consequence of ischaemia and reperfusion (I/R) is a major clinical problem in an acute renal failure and transplantation. Ligands on surfaces of endothelial cells that are exposed due to the ischaemia may be recognized by pattern recognition molecules such as mannan-binding lectin (MBL), inducing complement activation. We examined the contribution of the MBL complement pathway in a bilateral renal I/R model (45 min of ischaemia followed by 24 h of reperfusion), using transgenic mice deficient in MBL-A and MBL-C [MBL double knockout (MBL DKO)] and in wildtype (WT) mice. Kidney damages, which were evaluated by levels of blood urea nitrogen (BUN) and creatinine, showed that MBL DKO mice were significantly protected compared with WT mice. MBL DKO mice, reconstituted with recombinant human MBL, showed a dose-dependent severity of kidney injury increasing to a comparable level to WT mice. Acute tubular necrosis was evident in WT mice but not in MBL DKO mice after I/R, confirming renal damages in WT mice. MBL ligands in kidneys were observed to be present after I/R but not in sham-operated mice. C3a (desArg) levels in MBL DKO mice were decreased after I/R compared with that in WT mice, indicating less complement activation that was correlated with less C3 deposition in the kidneys of MBL DKO mice. Our data implicate a role of MBL in I/R-induced kidney injury.

Role of YadA, Ail, and Lipopolysaccharide in Serum Resistance of Yersinia enterocolitica Serotype O:3

Complement attack is a host strategy leading to elimination of pathogens. Yersinia enterocolitica expresses several potential complement resistance factors: the outer membrane proteins YadA and Ail as well as lipopolysaccharide (LPS). To study the contribution of these factors to the survival of Y. enterocolitica serotype O:3 in nonimmune human serum, we constructed 23 mutant strains of Y. enterocolitica O:3 expressing different combinations of YadA, Ail, LPS O antigen, and LPS outer core. Survival of bacteria was analyzed in normal serum (with functional classical, lectin, and alternative complement activation pathways) and EGTA-Mg-treated serum (only alternative pathway functional). Kinetic killing tests revealed that the most potent single-serum resistance factor needed for long-term survival was YadA; Ail was also indispensable, but it provided short-term survival and delayed the bacterial killing. On the contrary, the LPS O antigen and outer core, when in combination with YadA, Ail, or both, had a minor and often negative effect on serum resistance. Bacteria in the exponential phase of growth were more resistant to serum killing than stationary-phase bacteria. After exposing bacteria to EGTA-Mg-treated serum, O antigen could prevent deposition of covalently bound C3b on bacteria at 3 min of incubation, even as a single factor. At later time points (15 and 30 min) it had to be accompanied by YadA, Ail, and outer core. In normal serum, the bacteria were less resistant to C3b deposition. However, no direct correlation between the C3 deposition pattern and bacterial resistance was observed.

A case of renal sarcoidosis with complement activation via the lectin pathway

A 57-year-old woman with pulmonary sarcoidosis was admitted to the hospital because of an elevation of serum creatinine and blood urea nitrogen. On admission, the laboratory data suggested interstitial nephritis without proteinuria and hematuria, whereas a renal biopsy showed granulomatous interstitial nephritis and mild mesangial proliferative glomerulonephritis. Immunoglobulin and C1q deposits were negative, but mannose-binding lectin, C3, C4d, and C5b-9 deposits were marked in the glomerular mesangial areas. The lectin pathway of complement activation may have contributed to the development of glomerular injury in this patient. DNA of Propionibacterium acnes , which is now strongly suspected as the pathogen of sarcoidosis, was detected in the patient's glomerular mesangial cells; tubular epithelial cells, which were involved in granulomatous inflammation; and mononuclear cells in epithelioid granulomas by in situ hybridization. These findings may add new insights to the pathogenesis of renal sarcoidosis, including its relation to infection, because mannose-binding lectin plays a crucial role in the host defense against various pathogens. From this case of renal sarcoidosis, it is hypothesized that P acnes may be involved in pathogenesis of granulomatous interstitial nephritis and that it plays a role in glomerular complement activation via the lectin pathway.

Effect of capsulation of opportunistic pathogenic bacteria on binding of the pattern recognition molecules mannan-binding lectin, L-ficolin, and H-ficolin

Mannan-binding lectin (MBL), L-ficolin, and H-ficolin are pattern recognition molecules of the innate immune system. We investigated their ability to bind to different serotypes and noncapsulated variants of two gram-positive bacterial species, Streptococcus pneumoniae and Staphylococcus aureus. MBL did not bind to capsulated S. aureus or capsulated S. pneumoniae but did bind to a noncapsulated S. aureus variant (Wood). L-ficolin bound to some capsulated S. aureus serotypes (serotypes 1, 8, 9, 11, and 12) and capsulated S. pneumoniae serotypes (11A, 11D, and 11F) but not to noncapsulated strains. H-ficolin did not bind to any of the S. pneumoniae and S. aureus serotypes included in this study but did bind to one strain of Aerococcus viridans. The concentrations of the three proteins in 97 plasma samples were estimated. The median concentrations were 0.8 mug per ml for MBL, 3.3 mug per ml for L-ficolin, and 18.4 mug per ml for H-ficolin.