Umbilical cord mannan-binding lectin and infections in early childhood

Collectins and ficolins in neonatal health and disease

The immune system starts to develop early in embryogenesis. However, at birth it is still immature and associated with high susceptibility to infection. Adaptation to extrauterine conditions requires a balance between colonization with normal flora and protection from pathogens. Infections, oxidative stress and invasive therapeutic procedures may lead to transient organ dysfunction or permanent damage and perhaps even death. Newborns are primarily protected by innate immune mechanisms. Collectins (mannose-binding lectin, collectin-10, collectin-11, collectin-12, surfactant protein A, surfactant protein D) and ficolins (ficolin-1, ficolin-2, ficolin-3) are oligomeric, collagen-related defence lectins, involved in innate immune response. In this review, we discuss the structure, specificity, genetics and role of collectins and ficolins in neonatal health and disease. Their clinical associations (protective or pathogenic influence) depend on a variety of variables, including genetic polymorphisms, gestational age, method of delivery, and maternal/environmental microflora.

Antimicrobial peptide LL-37 and recombinant human mannose-binding lectin express distinct age- and pathogen-specific antimicrobial activity in human newborn cord blood in vitro

Background: There is a need to prevent and treat infection in newborns. One approach is administration of antimicrobial proteins and peptides (APPs) such as LL-37, a membrane-active cathelicidin antimicrobial peptide, and mannose-binding lectin (MBL), a pattern-recognition protein that binds to microbial surface polysaccharides resulting in opsonization and complement activation. Low plasma/serum levels of LL-37 and of MBL have been correlated with infection and exogenous administration of these agents may enhance host defense. Methods: The antimicrobial activity of LL-37 (15 µg/ml) or rMBL (0.5, 2 and 10 µg/ml) was tested in hirudin-anticoagulated preterm and term human cord blood (N = 12-14) against Staphylococcus aureus (SA) USA 300 (2x10 4 CFU/ml), Staphylococcus epidermis (SE) 1457 (2x10 4 CFU/ml) and Candida albicans (CA) SC5314 (1x10 4 CFU/ml). After incubation (1, 45, or 180 min), CFUs were enumerated by plating blood onto agar plates. Supernatants were collected for measurement of MBL via ELISA. Results: Preterm cord blood demonstrated impaired endogenous killing capacity against SA and SE compared to term blood. Addition of LL-37 strongly enhanced antimicrobial/antifungal activity vs SA, SE and CA in term blood and SE and CA in preterm blood. By contrast, rMBL showed modest fungistatic activity vs CA in a sub-analysis of term newborns with high basal MBL levels. Baseline MBL levels varied within preterm and term cohorts with no correlation to gestational age. In summary, exogenous LL-37 demonstrated significant antimicrobial activity against SA, SE and CA in term and SE and CA in preterm human blood tested in vitro. rMBL demonstrated modest antifungal activity in term cord blood of individuals with high baseline MBL levels. Conclusions: To the extent that our in vitro results predict the effects of APPs in vivo, development of APPs for prevention and treatment of infection should take into account host age as well as the target pathogen.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

The potential role of the lectin pathway of complement in the host defence of full-term intrauterine growth restricted neonates at birth

OBJECTIVE

To prospectively investigate the potential role of the lectin pathway of complement in intrauterine-growth-restriction (IUGR, associated with impaired immunocompetence and increased risk for neonatal infections), by determining cord blood concentrations of mannose-binding lectin (MBL), H-ficolin and L-ficolin (important mediators of neonatal innate immunity) in IUGR and appropriate for gestational age (AGA) pregnancies. Furthermore, we aimed to describe correlations among cord blood MBL, H- and L-ficolin concentrations and with several demographic parameters of the infants at birth.

METHODS

Serum MBL, H- and L-ficolin concentrations were determined by ELISA in 154 mixed arteriovenous cord blood samples from IUGR (n = 50) and AGA (n = 104) singleton full-term infants.

RESULTS

Cord blood MBL concentrations were significantly lower in IUGR cases than AGA controls (p = 0.029). No differences in cord blood H- and L-ficolin concentrations were observed between groups. In the IUGR group, cord blood MBL concentrations negatively correlated with respective L-ficolin ones (r = -0.442, p = 0.001).

CONCLUSIONS

The relatively decreased MBL expression in IUGR fetuses at term could possibly contribute to IUGR-associated neonatal immunodeficiency, predisposing to increased susceptibility to infections. The negative correlation between MBL and L-ficolin concentrations in the IUGR group might suggest an underlying immune variation and needs to be further investigated.

Factors of the lectin pathway of complement activation and their clinical associations in neonates

This paper summarizes the data concerning soluble defense lectins (mannan-binding lectin, M-ficolin, L-ficolin, and H-ficolin) with the unique ability to activate complement and their associated serine proteases (MASPs) in neonates. The clinical importance of deficiencies of these immune factors is presented in aspects of perinatal mortality, premature births, and low birthweight. Prenatal serum concentrations of L-ficolin, H-ficolin, and MASP-2 (and probably M-ficolin) correlate with gestational age and birthweight. The relationship of serum MBL to gestational age is controversial. The MBL2 genotypes XA/O and O/O (associated with low-serum MBL) are associated with perinatal infections, whereas the high serum MBL-conferring A/A genotypes may be associated with prematurity. Low-serum L-ficolin concentrations, but not low-serum H-ficolin concentrations, are also associated with perinatal infections. Much of the literature is inconsistent, and the relationships reported so far require independent confirmation at both gene and protein levels. Our preliminary conclusion is that these soluble defense lectins play a protective role in the neonate, and that insufficiency of such factors contributes to the adverse consequences of prematurity and low birthweight.

Serum mannose-binding lectin (MBL) gene polymorphism and low MBL levels are associated with neonatal sepsis and pneumonia

OBJECTIVE

The aim of this study was to determine the serum mannose-binding lectin (MBL) levels and the frequency of MBL gene polymorphisms in infants with neonatal sepsis.

STUDY DESIGN

Between January 2008 and January 2010, a total of 93 infants were included in this study and 53 of them had neonatal sepsis diagnosis as study group and 40 infants who had no sepsis according to clinical and laboratory findings as control group.

RESULT

Serum MBL levels were found to be low in 17 of 93 infants. Eleven of them were in the sepsis group and six of them were in the control group. Serum MBL levels were significantly lower in infants with sepsis compared with the control group. Frequencies of genotype AB and BB were also significantly higher in the study group compared with the control group. Most importantly, presence of B allele of MBL exon 1 gene was found to be associated with an increased risk for neonatal sepsis. Additionally, in the study group, the mean serum MBL levels were found to be significantly lower in the premature infants compared with the term infants. Pneumonia, bronchopulmonary dysplasia (BPD) and intraventricular hemorrhage (IVH) were significantly higher in infants with MBL deficiency compared with infants with normal MBL levels.

CONCLUSION

Low MBL levels and presence of B allele of MBL exon 1 gene were found to be important risk factors for development of both neonatal sepsis and pneumonia, especially in premature infants. Low MBL levels and MBL gene polymorphisms might also be associated with inflammation-related neonatal morbidities such as BPD and IVH.

H-ficolin (ficolin-3) concentrations and FCN3 gene polymorphism in neonates

Serum H-ficolin (ficolin-3) concentrations (n=613) and FCN3 genotypes (n=529) from a large group of neonates are presented. Both pre-term deliveries and low birthweight (independently of gestational age) were significantly associated with low H-ficolin concentrations but not with heterozygosity for the FCN3 1637delC frameshift mutation. The presence of the variant allele, however, apparently influenced the protein level. No association of FCN3 gene heterozygosity or relative functional H-ficolin insufficiency (determined as serum level ≤8.6 μg/ml) with perinatal infections was found. One premature newborn, with confirmed infection caused by Streptococcus agalactiae, was H-ficolin-deficient (FCN3 variant homozygote, no detectable protein). We present what is only the fourth case report of total H-ficolin deficiency in the world literature. This neonate was however previously found to be mannan-binding lectin (MBL) as well as MBL-associated serine protease-2 (MASP-2) deficient and also had low serum L-ficolin.

Mannose-binding lectin (MBL) and the risk for febrile neutropenia and infection in pediatric oncology patients with chemotherapy

BACKGROUND

We determined whether mannose-binding lectin (MBL) deficiency is associated with an increased risk of febrile neutropenia (FN) and/or infection in pediatric oncology patients.

PROCEDURE

We systematically searched and reviewed all the literature on MBL and infections in children with cancer, identified from a literature search of Medline, Embase, and Central (1966-April 2010). We extracted information on the type of study, patient characteristics, definition of MBL deficiency, definition of infection and method of detection, follow-up period and the results of the outcome in different groups. The validity of each study was assessed.

RESULTS

Six cohort studies were retrieved, consisting of 581 children with leukemia (n = 2) or varying types of cancer (n = 4). Many different outcome definitions were used. In only one out of three genotype studies, variant MBL2 genotypes, as well as MBL levels < 1,000 µg/L, were associated with an increased duration of FN. In one additional MBL level study the number of FN episodes, bacteremia and severe bacterial infection were increased in patients with MBL levels < 100 µg/L as compared to those with MBL levels of 100-999 µg/L. Sepsis, pneumonia, viral infection, and fungal infection were not associated with either MBL levels or genotypes in any of the studies.

CONCLUSIONS

MBL deficiency could not be identified as an independent risk factor for FN or infection in pediatric oncology patients. A multicenter study of children with comparable chemotherapy regimens, relevant and equal outcome definitions and measuring both MBL levels and genotypes, will be required to avoid clinical and methodological inconsistencies.

Mannose-binding lectin cord blood levels and respiratory symptoms during infancy: a prospective birth cohort study

Respiratory infections cause considerable morbidity during infancy. The impact of innate immunity mechanisms, such as mannose-binding lectin (MBL), on respiratory symptoms remains unclear. The aims of this study were to investigate whether cord blood MBL levels are associated with respiratory symptoms during infancy and to determine the relative contribution of MBL when compared with known risk factors. This is a prospective birth cohort study including 185 healthy term infants. MBL was measured in cord blood and categorized into tertiles. Frequency and severity of respiratory symptoms were assessed weekly until age one. Association with MBL levels was analysed using multivariable random effects Poisson regression. We observed a trend towards an increased incidence rate of severe respiratory symptoms in infants in the low MBL tertile when compared with infants in the middle MBL tertile [incidence rate ratio (IRR) = 1.59; 95% confidence interval (CI): 0.95-2.66; p = 0.076]. Surprisingly, infants in the high MBL tertile suffered significantly more from severe and total respiratory symptoms than infants in the middle MBL tertile (IRR = 1.97; 95% CI: 1.20-3.25; p = 0.008). This association was pronounced in infants of parents with asthma (IRR = 3.64; 95% CI: 1.47-9.02; p = 0.005). The relative risk associated with high MBL was similar to the risk associated with well-known risk factors such as maternal smoking or childcare. In conclusion the association between low MBL levels and increased susceptibility to common respiratory infections during infancy was weaker than that previously reported. Instead, high cord blood MBL levels may represent a so far unrecognized risk factor for respiratory morbidity in infants of asthmatic parents.

Two factors of the lectin pathway of complement, l-ficolin and mannan-binding lectin, and their associations with prematurity, low birthweight and infections in a large cohort of Polish neonates

Ficolins and one collectin, mannan-binding lectin (MBL), are the only factors known to activate the lectin pathway (LP) of complement. There is considerable circumstantial evidence that MBL insufficiency can increase susceptibility to various infections and influence the course of several non-infectious diseases complicated by infections. Much less information is available concerning l-ficolin. We report the results of a prospective study to investigate any association between either MBL deficiency or l-ficolin deficiency with prematurity, low birthweight or perinatal infections in a large cohort of Polish neonates, representing an ethnically homogenous population (n=1832). Cord blood samples were analysed to determine mbl-2 gene variants, MBL concentrations and MBL-MASP-2 complex activities (MBL-dependent lectin pathway activity) as well as l-ficolin levels. Median concentrations of l-ficolin and MBL were 2500 and 1124 ng/ml, respectively, while median LP activity was 272 mU/ml. After genotyping, 60.6% of babies were mbl-2 A/A, 35.4% were A/O and 4% were O/O genotypes. We found relative l-ficolin deficiency to be associated with prematurity, low birthweight and infections. l-Ficolin concentration correlated with gestational age and with birthweight, independently of gestational age. Preterm deliveries (<38 weeks) occurred more frequently among neonates with low LP activity but not with those having low serum MBL levels. Similarly, no association of serum MBL deficiency with low birthweight was found, but there was a correlation between LP activity and birthweight. Genotypes conferring very low serum MBL concentrations were associated with perinatal infections, and high-MBL-conferring genotypes were associated with prematurity. Our findings suggest that l-ficolin participates in host defence during the perinatal period and constitute the first evidence that relative l-ficolin deficiency may contribute to the adverse consequences of prematurity. Some similar trends were found with facets of MBL deficiency, but the observed relationships were weaker and less consistent.

Genetic and other factors determining mannose-binding lectin levels in American Indians: the Strong Heart Study

Background

Mannose-binding lectin (MBL) forms an integral part of the innate immune system. Persistent, subclinical infections and chronic inflammatory states are hypothesized to contribute to the pathogenesis of atherosclerosis. MBL gene (MBL2) variants with between 12 to 25% allele frequency in Caucasian and other populations, result in markedly reduced expression of functional protein. Prospective epidemiologic studies, including a nested, case-control study from the present population, have demonstrated the ability of MBL2 genotypes to predict complications of atherosclerosis,. The genetic control of MBL2 expression is complex and genetic background effects in specific populations are largely unknown.

Methods

The Strong Heart Study is a longitudinal, cohort study of cardiovascular disease among American Indians. A subset of individuals genotyped for the above mentioned case-control study were selected for analysis of circulating MBL levels by double sandwich ELISA method. Mean MBL levels were compared between genotypic groups and multivariate regression was used to determine other independent factors influencing MBL2 expression.

Results

Our results confirm the effects of variant structural (B, C, and D) and promoter (H and Y) alleles that have been seen in other populations. In addition, MBL levels were found to be positively associated with male gender and hemoglobin A1c levels, but inversely related to triglyceride levels. Correlation was not found between MBL and other markers of inflammation.

Conclusion

New data is presented concerning the effects of known genetic variants on MBL levels in an American Indian population, as well as the relationship of MBL2 expression to clinical and environmental factors, including inflammatory markers.

Possible disease-modifying factors: the mannan-binding lectin pathway and infections in hereditary angioedema of children and adults

Introduction

Hereditary angioedema (HAE) is caused by mutations in the C1inh gene, leading to dysfunction of the C1-esterase inhibitor (C1-INH). C1-INH interacts with MASP-1 and MASP-2 proteases, participating in the mannan-binding lectin (MBL) pathway of complement activation. The aim of the study was to investigate the contribution of possible changes in MBL/MASP-2 complex activity and Helicobacter pylori, hepatitis B virus (HBV), and hepatitis C virus (HCV) infections to the severity and frequency of clinical symptoms of HAE.

Materials and Methods

The study was performed in 65 patients with HAE and 113 healthy persons. The parameters measured were C1-INH, C4, MBL concentration and MBL/MASP-2 complex activity, and serological markers of H. pylori, HBV, and HCV infection. Scores for the frequency and severity of HAE symptoms were determined.

Results

HAE scores were significantly higher in patients whose C1-INH activity did not exceed 10% than in patients with activity of 10-52% (p=0.016). No significant differences were found in the median levels of MBL concentration and MBL/MASP-2 complex activity between patients and the control group. There was a slight association between contact with H. pylori in patients and HAE symptom score (p=0.052, not significant). Adult patients showed a 2.6-times higher frequency of anti-HBc than the general population. HBV DNA was negative in anti-HBc(+) patients.

Conclusions

These results suggest that the MBL complement activation pathway itself does not contribute to the frequency of angioedema attacks. Infections with H. pylori and HBV may slightly influence the disease score (not significant).

Association of polymorphisms in the mannose-binding lectin gene and pulmonary morbidity in preterm infants

Deficiency in the collectin mannose-binding lectin (MBL) increases the risk for pulmonary and systemic infections and its complications in children and adults. The aim of this prospective cohort study was to determine the genetic association of sequence variations within the MBL gene with systemic infections and pulmonary short- and long-term complications in preterm infants below 32 weeks gestational age (GA). Three single-nucleotide polymorphisms (SNPs) in the coding region and one SNP in the promotor region of MBL2 were genotyped by direct sequencing and with sequence-specific probes in 284 newborn infants <32 weeks GA. Clinical variables were comprehensively monitored. An association was found between two SNPs and the development of bronchopulmonary dysplasia (BPD), defined as persistent oxygen requirement at 36 weeks postmenstrual age, adjusting for covariates GA, grade of respiratory distress syndrome and days on mechanical ventilation (rs1800450 (exon 1 at codon 54, B variant): odds ratio dominant model (OR)=3.59, 95% confidence interval (CI)=1.62-7.98; rs7096206 (-221, X variant): OR=2.40, 95% CI=1.16-4.96). Haplotype analyses confirmed the association to BPD, and a single haplotype (frequency 56%) including all SNPs in their wild-type form showed a negative association with the development of BPD. We detected no association between the MBL gene variations and the development of early-onset infections or further pulmonary complications. Frequent variants of the MBL gene, leading to low MBL concentrations, are associated with the diagnosis of BPD in preterm infants. This provides a basis for potential therapeutic options and further genetic and proteomic analysis of the function of MBL in the resistance against pulmonary long-term complications in preterm infants.

Low Mannose-Binding Lectin Concentration Is Associated with Severe Infection in Patients with Hematological Cancer Who Are Undergoing Chemotherapy

BACKGROUND

Mannose-binding lectin (MBL) is a serum lectin involved in innate immune response. Low serum MBL concentration may constitute a risk factor for infection in patients receiving myelosuppressive chemotherapy.

METHODS

We conducted a prospective, observational study that assessed MBL concentration as a risk factor for infection in patients with hematological malignancy who were hospitalized to undergo at least 1 chemotherapy cycle. MBL deficiency was defined using an algorithm that considered the serum MBL concentration and the MBL genotype. The primary end point was the ratio of duration of febrile neutropenia to the duration of neutropenia. Secondary end points included the incidence of severe infection (e.g., sepsis, pneumonia, bacteremia, and invasive fungal infection). Logistic regression analysis was conducted, and Fisher's exact test was used to analyze binary outcomes, and Kaplan-Meier estimates and log rank tests were used for time-to-event variables.

RESULTS

We analyzed 255 patients who received 569 cycles of chemotherapy. The median duration of neutropenia per cycle was 7 days (interquartile range, 0-13 days). Sixty-two patients (24%) were found to have MBL deficiency. Febrile neutropenia occurred at least once in 200 patients. No difference in the primary outcome was seen. The incidence of severe infection was higher among MBL-deficient patients than among non-MBL-deficient patients (1.96 vs. 1.34 cases per 100 days for analysis of all patients [P=.008] and 1.85 vs. 0.94 cases per 100 days excluding patients with acute leukemia [P<.001]).

CONCLUSIONS

MBL deficiency does not predispose adults with hematological cancer to more-frequent or more-prolonged febrile episodes during myelosuppressive chemotherapy, but MBL-deficient patients have a greater number of severe infections and experience their first severe infection earlier, compared with nondeficient patients.

Mannose-binding lectin levels during pregnancy: a longitudinal study

BACKGROUND

Pregnancy is associated with changes in the immune system. Although previous studies have focussed mainly on adaptive immunity, there are indications that components of innate immunity, such as mannose-binding lectin (MBL), are associated with pregnancy outcome. Although this would suggest that pregnancy also involves adaptations in innate immunity, there are few studies in this area. Therefore, we aimed to determine whether MBL concentrations and the following steps in complement pathway activation are influenced by pregnancy.

METHODS

MBL and Ficolin-2 concentrations, MBL-MBL-associated serine protease (MASP) complex activity, MBL pathway activity and classical complement pathway activity were determined by enzyme-linked immunosorbent assay (ELISA) in sera from pregnant women (n=32) during each trimester and post-partum. MBL genotyping was performed by PCR.

RESULTS

During pregnancy, MBL concentrations increased to 140% [interquartile range (IQR) 116-181%, P < 0.0001]. This increase was already present at 12 weeks of pregnancy and was most pronounced in the high-production AA-genotype. Directly Post-partum MBL concentrations dropped to 57% of baseline (IQR 44-66%, P < 0.0001). Variations in MBL levels were reflected by similar changes in the following steps of complement activation, r > 0.93 (P < 0.01). Ficolin-2 levels and classical complement pathway activity were not similarly influenced by pregnancy.

CONCLUSIONS

Pregnancy and the post-partum period profoundly influence MBL serum concentration and MBL complement pathway activity.

High prevalence of mannose-binding lectin (MBL) deficiency in premature neonates

Mannose-binding lectin (MBL) is a component of innate immunity and thus particularly important in neonates in whom adaptive immunity is not yet completely developed. Promoter polymorphisms and structural exon-1 mutations in the MBL2 gene cause reduced or deficient MBL plasma concentrations. The aim of our study was to determine the prevalence of MBL deficiency in neonates admitted to the neonatal intensive care unit (NICU). Eighty-five NICU patients (69 premature) were included in the study. We measured MBL concentrations in umbilical cord and neonatal blood within 24 h after birth by ELISA technique. MBL2 genotypes (n = 67) were determined by Taqman analysis. MBL concentrations were measured longitudinally during three weeks in 26 premature neonates. The association between pre- and intra-partum clinical data and MBL concentrations was investigated. At birth, 29 (42%) premature and six (38%) term neonates had MBL plasma concentrations < or = 0.7 microg/ml which was regarded as deficient. Twenty-one (38%) premature and four (36%) term neonates had variant MBL2 haplotypes, corresponding to exon-1 mutations and the LXPA haplotype. MBL concentrations increased over time in neonates with wild-type MBL2 haplotypes, but not in neonates with variant haplotypes. Low MBL plasma concentrations were related to lower gestational age and variant MBL2 haplotypes. Umbilical cord and neonatal MBL plasma concentrations appeared to be similar. In conclusion, almost half of our NICU patients, especially the premature ones, were MBL-deficient at birth. These infants may be at increased risk of neonatal infections. MBL concentration can reliably be measured in umbilical cord blood and it is positively correlated with gestational and postnatal age.

The mannose-binding lectin: a prototypic pattern recognition molecule

The innate immune system is comprised of a sophisticated network of recognition and effector molecules that act together to protect the host in the first minutes or hours of exposure to an infectious challenge. The mannose-binding lectin (MBL) is an evolutionary conserved circulating host defense protein that acts as a broad-spectrum recognition molecule against a wide variety of infectious agents. Target binding triggers the MBL pathway of complement activation. MBL can be considered conceptually as an 'ante-antibody' because it has a role in mammals during the lag period that is required to develop an antibody response against infectious agents. Additionally, there are MBL-like homologues in animals that lack adaptive immunity that activate a primitive complement system, and under these circumstances these MBL-like molecules play an analogous role to antibodies in higher animals. These molecules might be considered to be functional antecedents of antibodies. Recent work also indicates that MBL recognizes altered self-antigens, and as such MBL has a role that extends beyond a traditional role in first line host defense as it appears to play a role as a modulator of inflammation.

Modulatory effect of mannose-binding lectin on cytokine responses: possible roles in HIV infection

BACKGROUND

Mannose-binding lectin (MBL) is a soluble receptor of the innate immune system, probably contributing to antimicrobial defence. The possible role of MBL in HIV infection is unclear.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) from 28 HIV-infected patients and 13 healthy controls were stimulated with MBL and costimulated with HIV-1 gp120 or mannan from Saccharomyces cerevisiae before inflammatory responses in PBMC cultures were examined by enzyme-linked immunosorbent assay (ELISA) and flow cytometry. HIV-1 RNA replication in vitro was assessed by quantitative reverse transcription polymerase chain reaction (RT-PCR) in supernatants from patients with measurable HIV-1 RNA levels.

RESULTS

(i) Enhanced TNF-alpha responses were observed when PBMCs from healthy controls and HIV-infected patients were stimulated with MBL and costimulated with HIV-1 gp120 or mannan. (ii) MBL stimulation induced increased HIV RNA replication in culture supernatants when costimulated with mannan.

CONCLUSIONS

The present study suggests a modulatory role of MBL on cytokine responses, and HIV replication after stimulation with microbial products. These effects of MBL on inflammatory responses and viral replication may be clinically relevant for HIV infection.

C1q-deficiency is neuroprotective against hypoxic-ischemic brain injury in neonatal mice

BACKGROUND AND PURPOSE

This study was undertaken to determine whether the initial component of the classical complement (C) activation pathway contributes to hypoxic-ischemic brain injury in neonatal mice.

METHODS

Hypoxia-ischemia (HI) was produced in C1q(-/-) and wild-type (WT) neonatal mice. At 24 hours after HI, neonatal mouse reflex performance and cerebral infarct volume were assessed. Long-term outcomes were measured by water-maze performance and degree of cerebral atrophy at 7 to 8 weeks after HI. Activation of circulating neutrophils, and C1q, C3, and neutrophil deposition in brains were examined.

RESULTS

C1q(-/-) mice were significantly protected against HI (mean+/-SE infarct volume in C1q(-/-) mice=17.3+/-5.5% versus 53.6+/-6.8% in WT mice; P<0.0001) and exhibited significantly less neurofunctional deficit compared with WT mice. Immunostaining revealed significantly greater deposition of C3 (and C1q) as well as granulocytes in the infarcted brains in WT mice compared with C1q(-/-) animals. Activation of circulating leukocytes was significantly decreased in C1q(-/-) mice compared with WT mice, which correlated strongly (r=0.7) with cerebral infarct volumes.

CONCLUSIONS

Cerebral deposition of C1q and C3 after hypoxic-ischemic insult is associated with significantly greater neurologic damage in WT mice compared with C1q(-/-) mice, providing strong evidence that the classical C pathway contributes to the hypoxic-ischemic brain injury. Significantly decreased activation of circulating neutrophils associated with diminished local accumulation and attenuation of brain injury in C1q(-/-) mice suggests a potential cellular mechanism by which C1q mediates neurodegeneration in HI.

Childhood levels of immunoglobulins and mannan-binding lectin in relation to infections and allergy

Respiratory tract infections, allergies and otitis media are common problems in early childhood. Our aim was to evaluate in a longitudinal community-based cohort study the association between maturation of immunoglobulin (Ig) and mannan-binding lectin (MBL) responses and disease manifestations in the first 4 years of life. Sustained low levels of IgA proved the strongest single indicator of susceptibility for recurrent otitis media (P = 0.008) and respiratory tract infections (P = 0.02), and this condition was also associated with low production of IgG subclasses. About 7% of the cohort had sustained low levels of MBL (<0.4 mg/l). Low MBL did not predispose to any ailments studied, but children with low IgA and recurrent otitis media had relatively low MBL at birth, which failed to increase during the study period and was significantly reduced at the age of 4 years (P = 0.04). MBL levels increased from birth to 2 years (P < 0.0001) and were higher in children than in adults (P = 0.001). The increase was 1.9-fold in children with no recorded clinical events and 1.7-fold in children with asthma or infections, but significantly lower, 1.2-fold, in children with recurrent otitis media. Low levels of IgA within the normal range may reveal disease susceptibility not detected by conventional criteria. Slow maturation of Ig appears to be the main factor of susceptibility during childhood, but a strong corollary role for MBL is indicated by the high levels produced during childhood as well as the precipitation of disease in children with low levels of MBL and Ig.

Human Plasma-Derived Mannose-Binding Lectin: A Phase I Safety and Pharmacokinetic Study

Mannose-binding lectin (MBL) is an important component of innate immunity that can bind to certain sugar residues on the surface of many types of pathogenic micro-organisms. On binding, MBL generates opsonic activity mainly through activation of the complement system. Genetically determined MBL deficiency is very common and can be associated with increased susceptibility to a variety of infections, especially in children and immunosuppressed individuals. The potential benefits of MBL reconstitution therapy therefore need to be evaluated. We have carried out a phase I safety and pharmacokinetic study on 20 MBL-deficient healthy adult volunteers. The MBL was prepared from plasma of nonremunerated, voluntary Danish donors tested and found negative for hepatitis B surface antigen, antibodies to human immunodeficiency virus (HIV) and hepatitis C virus. Each volunteer received a total of 18 mg of MBL in three 6 mg doses given intravenously, once weekly over a period of 3 weeks. The volunteers were closely monitored at the University Hospital in Reykjavik for 8 h after each infusion and daily thereafter for 5 days after each infusion. No adverse clinical or laboratory changes were observed in any of the 20 participants, and frequent measurements did not reveal any signs of infusion-associated complement activation. No antibodies to MBL, HIV or hepatitis viruses were observed 24 weeks after the last infusion. Serum MBL levels increased up to normal levels (1200-4500 ng/ml) immediately after each infusion, but the half-life of the infused MBL was highly variable, ranging from 18 to 115 h (mean 69.6). It is concluded that infusion of purified MBL as prepared by Statens Serum Institut (SSI) is safe. However, adults have to be given at least 6 mg twice or thrice weekly for maintaining protective MBL levels assumed to be about 1000 ng/ml.