The mannan-binding-lectin pathway of the innate immune response

Large Mammals Have More Powerful Antibacterial Defenses Than Expected from Their Metabolic Rates

AbstractTerrestrial mammals span seven orders of magnitude in body size, ranging from the <2-g Etruscan pygmy shrew (Suncus etruscus) to the >3,900-kg African elephant (Loxodonta africana). Although body size profoundly affects the behavior, physiology, ecology, and evolution of species, how investment in functional immune defenses changes with body size across species is unknown. Here, we (1) developed a novel 12-point dilution curve approach to describe and compare antibacterial capacity against three bacterial species among >160 terrestrial species of mammals and (2) tested published predictions about the scaling of immune defenses. Our study focused on the safety factor hypothesis, which predicts that broad, early-acting immune defenses should scale hypermetrically with body mass. However, our three statistical approaches demonstrated that antibacterial activity in sera across mammals exhibits isometry; killing capacity did not change with body size across species. Intriguingly, this result indicates that the serum of a large mammal is less hospitable to bacteria than would be predicted by its metabolic rates. In other words, if metabolic rates underlie the rates of physiological reactions as postulated by the metabolic theory of ecology, large species should have disproportionately lower antibacterial capacity than small species, but they do not. These results have direct implications for effectively modeling the evolution of immune defenses and identifying potential reservoir hosts of pathogens.

Mannose-binding lectin conjugated to quantum dots as fluorescent nanotools for carbohydrate tracing

Quantum dots (QDs) have stood out as nanotools for glycobiology due to their photostability and ability to be combined with lectins. Mannose-binding lectin (MBL) is involved in the innate immune system and plays important roles in the activation of the complement cascade, opsonization, and elimination of apoptotic and microbial cells. Herein, adsorption and covalent coupling strategies were evaluated to conjugate QDs to a recombinant human MBL (rhMBL). The most efficient nanoprobe was selected by evaluating the conjugate ability to labelCandida albicansyeasts by flow cytometry. The QDs-rhMBL conjugate obtained by adsorption at pH 6.0 was the most efficient, labelingca.100% of cells with the highest median fluorescence intensity. The conjugation was also supported by Fourier transform infrared spectroscopy, zeta potential, and size analyses.C. albicanslabeling was calcium-dependent; 12% and <1% of cells were labeled in buffers without calcium and containing EDTA, respectively. The conjugate promoted specific labeling (based on cluster effect) since, after inhibition with mannan, there was a reduction of 80% in cell labeling, which did not occur with methyl-α-D-mannopyranoside monosaccharide. Conjugates maintained colloidal stability, bright fluorescence, and biological activity for at least 8 months. Therefore, QDs-rhMBL conjugates are promising nanotools to elucidate the roles of MBL in biological processes.

Secretome Profiling and Computational Biology of Human Leiomyoma Samples Unravel Molecular Signatures with Potential for Diagnostic and Therapeutic Interventions

In recent years, significant advancements have been made in the way the complex proteome samples are compared but the ultimate goal of routine biomarker discovery has yet to be achieved. Based on reverse genetic strategy, our study involved the spotting of genes showing expressional variability in uterine leiomyoma females. Serum samples were taken from uterine leiomyomas subjects (n=6) and healthy control subjects (n=6) for proteomic studies. Additionally, leiomyoma tissue samples (n=25) and normal myometrium samples (n=25) were taken for validation studies. In this study, we profiled the proteomes of uterine leiomyoma patient's serum and healthy control, along with relative quantification using Nano LC-MS/MS analysis. A total of 146 proteins were reported to be significantly differentially expressed (P value less than 0.05) in case and control sample. Statistical analysis identified a number of molecular signatures distinguishing healthy from diseased serum. Among these, five proteins lumican, ficolin, MASP2, EMSY, and kallistatin were further chosen according to their function for validation. Kallistatin was downregulated while ficolin, MASP2, lumican, and EMSY were found to be upregulated in the diseased sample. The expression modulations in the identified genes were further validated in twenty-five cases. Interactions among the differentially expressed proteins were identified followed with network analysis. Network analysis emphasized important pathways that are highly deregulated in myoma, and functional significance of these pathways in the pathology of the disease was discussed. Comparative expression analysis reveals distinct molecular signatures and their probable role in diagnosis of the disease.

Nanobodies Provide Insight into the Molecular Mechanisms of the Complement Cascade and Offer New Therapeutic Strategies

The complement system is part of the innate immune response, where it provides immediate protection from infectious agents and plays a fundamental role in homeostasis. Complement dysregulation occurs in several diseases, where the tightly regulated proteolytic cascade turns offensive. Prominent examples are atypical hemolytic uremic syndrome, paroxysmal nocturnal hemoglobinuria and Alzheimer’s disease. Therapeutic intervention targeting complement activation may allow treatment of such debilitating diseases. In this review, we describe a panel of complement targeting nanobodies that allow modulation at different steps of the proteolytic cascade, from the activation of the C1 complex in the classical pathway to formation of the C5 convertase in the terminal pathway. Thorough structural and functional characterization has provided a deep mechanistic understanding of the mode of inhibition for each of the nanobodies. These complement specific nanobodies are novel powerful probes for basic research and offer new opportunities for in vivo complement modulation.

Elevated C-reactive protein and complement C3 levels are associated with preterm birth: a nested case-control study in Chinese women

BACKGROUND

Currently, there are many studies researched the associations between maternal serum inflammatory indicators (i.e. ferritin, C-reactive protein [CRP], C3 and C4) and preterm birth (PTB). The results, however, are inconsistent. Therefore, the aim of this study was to estimate the relationship between maternal serum inflammatory indicators and PTB in a nested case-control (NCC)study.

METHODS

A NCC study was conducted by Guangxi Birth Cohort Study which enrolled a total of 6203 pregnant women between 5^0/7 and 34^6/7 weeks of gestational age (wGA) from six cities in China between 2015 and 2016. There were 206women who delivered preterm (< 37^0/7 wGA), and 412 women who delivered term birth, those women were matched by maternal age, birth place, gender of infants, and wGA at blood collection. The inflammatory indicators were quantified by immunoturbidimetric methods.

RESULTS

Highest quartile concentrations of all inflammatory indicators were determined versus median. After adjusting for maternal age, high levels of CRP (CRP > 16.60 mg/L) are related to the risk of PTB (OR = 2.16, 95% CI: 1.02-4.56, p = 0.044) in the first trimester. The association of C3 was extremely related to those who delivered PTB (OR = 2.53, 95% CI: 1.14-5.64, p = 0.023) in the first trimester. Moreover, no significant associations were found in C4 (p = 0.079) and ferritin (p = 0.067) between PTB.

CONCLUSIONS

Elevated concentrations of CRP and C3 in the first trimester were associated with increased risk of PTB. Inflammatory indicators may act a pivotal part in early diagnosis and prognosis of PTB.

Polysaccharide Fraction Extracted from Endophytic Fungus Trichoderma atroviride D16 Has an Influence on the Proteomics Profile of the Salvia miltiorrhiza Hairy Roots

Trichoderma atroviride develops a symbiont relationship with Salvia miltiorrhiza and this association involves a number of signaling pathways and proteomic responses between both partners. In our previous study, we have reported that polysaccharide fraction (PSF) of T. atroviride could promote tanshinones accumulation in S.miltiorrhiza hairy roots. Consequently, the present data elucidates the broad proteomics changes under treatment of PSF. Furthermore, we reported several previously undescribed and unexpected responses, containing gene expression patterns consistent with biochemical stresses and metabolic patterns inside the host. In summary, the PSF-induced tanshinones accumulation in S.miltiorrhiza hairy roots may be closely related to Ca2+ triggering, peroxide reaction, protein phosphorylation, and jasmonic acid (JA) signal transduction, leading to an increase in leucine-rich repeat (LRR) protein synthesis. This results in the changes in basic metabolic flux of sugars, amino acids, and protein synthesis, along with signal defense reactions. The results reported here increase our understanding of the interaction between T.atroviride and S.miltiorrhiza and specifically confirm the proteomic responses underlying the activities of PSF.

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

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

Genetic predisposition to necrotizing enterocolitis in premature infants: Current knowledge, challenges, and future directions

The role of genetics in the pathogenesis of necrotizing enterocolitis (NEC) was initially informed by epidemiological data indicating differences in prevalence among different ethnic groups as well as concordance in twins. These early observations, together with major advances in genomic research, paved the way for studies that begin to reveal the contribution of genetics to NEC. Using the candidate gene or pathway approach, several potential pathogenic variants for NEC in premature infants have already been identified. More recently, genome-wide association studies and exome-sequencing based studies for NEC have been reported. These advances, however, are tempered by the lack of adequately powered replication cohorts to validate the accuracy of these discoveries. Despite many challenges, genetic research in NEC is expected to increase, providing new insights into its pathogenesis and bringing the promise of personalized care closer to reality. In this review we provide a summary of genetic studies in NEC along with defining the challenges and possible future approaches.

Altered plasma proteins released from platelets and endothelial cells are associated with human patent ductus arteriosus

Patent ductus arteriosus is the third most common congenital heart disease and resulted from the persistence of ductal patency after birth. Ductus arteriosus closure involves functional and structural remodeling, controlled by many factors. The changes in plasma protein levels associated with PDA closure are not known. Here we for the first time demonstrate six key differential plasma proteins in human patent ductus arteriosus patients using proteomic technology and present a model to illustrate the constriction and closure of ductus arteriosus. Differentially expressed proteins were analyzed by using isobaric tags for relative and absolute quantification and validated by enzyme-linked immunosorbent assay in new samples. The proteomic data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD008568. We found 74 upregulated and 98 downregulated proteins in the plasma of patients with PDA. Five decreased proteins (platelet factor 4, fibrinogen, von Willebrand factor, collagen, and mannose binding lectin-associated serine protease-2) and one increased protein (fibronectin) may increase the risk of patent ductus arteriosus. Those proteins are closely related to platelet activation and coagulation cascades, complement mannan-binding-lectin, and other systemic signaling pathways. Our findings for the first time indicate that the differential proteins involved in different pathways may play key roles in the nonclosure of the ductus arteriosus in humans and may be developed as biomarkers for diagnosis. All those findings may be served as the basis of understanding the etiology and pathogenesis of patent ductus arteriosus.

Peptidyl-prolyl cis-trans isomerase A - A novel biomarker of multi-episodic (recurrent) ocular toxoplasmosis

Ocular toxoplasmosis (OT) is the most common etiology of posterior uveitis. The high incidence of macular scarring associated with OT is a leading cause of visual morbidity. Serum biomarkers of the disease would aid in its diagnosis. This study sought, for the first time, to elucidate serum biomarkers for OT by mass spectrometry. Blood samples were collected from four groups of nine patients each; toxoplasmosis IgG-with no history of uveitis, non-toxoplasmosis uveitis, first episode OT, and symptomatic recurrent OT. Serum was isolated and subjected to proteomics analysis using 2-dimensional gel electrophoresis (2D-GE) and surface-enhanced laser desorption ionization mass spectrometry (SELDI-MS). Selected proteins were further separated by SDS-PAGE and sequenced using tandem MS. Results were cross-validated with a T. gondii outbreak biomarker database that occurred in Brazil. Fifty markers of OT and 46 markers of recurrent disease were discovered by SELDI-MS of which 30 and 15, respectively, were cross-validated. 2D-GE analysis yielded 57 bands, selected based on the intensity of the bands, leading to the identification of 20 proteins. Eleven of those identified candidates were also found by SELDI-MS. Four candidates were chosen for immunoblotting. One serum protein, peptidyl-prolyl cis-trans isomerase A (PPIA), was confirmed as a biomarker of multi-episodic OT by immunoblotting in patients. PPIA can identify the patient with active recurrent OT from acute OT, other forms of uveitis and other parasitic infections. A validated PPIA assay may have a role in the diagnosis of the atypical OT patient before more invasive anterior chamber or vitreous tap is performed for PCR analysis or for Goldmann-Witner coefficient calculations. Base-line PPIA levels need to be studied to understand its possible use when deciding for prophylactic antibiotic use in the immunosuppressed sero-positive patient.

Genetic alterations in necrotizing enterocolitis

An underlying genetic predisposition to necrotizing enterocolitis (NEC) is increasingly being recognized. Candidate gene or pathway approaches as well as genome-wide approaches are beginning to identify potential pathogenic variants for NEC in premature infants. However, a majority of these studies have not yielded definitive results because of limited sample size and lack of validation. Despite these challenges, understanding the contribution of genetic variation to NEC is important for providing new insights into the pathogenesis of NEC as well as allowing for targeted care of infants with inherent susceptibility. In this review we provide a summary of published genetic association studies in NEC along with defining the challenges and possible future approaches.

A novel exopolysaccharide elicitor from endophytic fungus Gilmaniella sp. AL12 on volatile oils accumulation in Atractylodes lancea

Endophytes and plants can establish specific long-term symbiosis through the accumulation of secondary metabolites. Previous studies have shown that the endophytic fungus Gilmaniella sp. AL12 can stimulate Atractylodes lancea to produce volatile oils. The purpose of this report is to investigate key factors involved in the stimulation of A. lancea by AL12 and reveal the mechanism. We identified the active component from AL12 as an extracellular mannan with a polymerization degree of 26–42. Differential membrane proteomics of A. lancea was performed by 2D electrophoresis. The results showed that there were significant differences in the expression of 83 proteins. Based on these results, we conclude that AL12 secreted mannan contributes to the antagonistic balance seen in interactions between AL12 and A. lancea. One portion of the mannan was degraded to mannose for hexokinase activation, promoting photosynthesis and energy metabolism, with a potential metabolic fluxes flowing towards terpenoid biosynthesis. The other portion of the mannan directly enhanced autoimmunity of A. lancea through G protein-mediated signal transduction and the mannan-binding lectin pathway. Volatile oil accumulation was ultimately promoted in subsequent defense reactions. This study provides a new perspective on the regulation of secondary metabolites by endophytic fungal elicitors in medicinal plants.

Low serum ficolin-3 levels are associated with severity and poor outcome in traumatic brain injury

Background

Ficolin-mediated activation of the lectin pathway of complement contributes to the complement-independent inflammatory processes of traumatic brain injury. Lower serum ficolin-3 levels have been demonstrated to be highly associated with unfavorable outcome after ischemic stroke. This prospective observatory study was designed to investigate the relationships between serum ficolin-3 levels and injury severity and clinical outcomes after severe traumatic brain injury.

Methods

Serum ficolin-3 levels of 128 patients and 128 healthy controls were measured by sandwich immunoassays. An unfavorable outcome was defined as Glasgow Outcome Scale score of 1–3. Study endpoints included mortality at 1 week and 6 months and unfavorable outcome at 6 months after head trauma. Injury severity was assessed by Glasgow Coma Scale score. Multivariate logistic models were structured to evaluate the relationships between serum ficolin-3 levels and study endpoints and injury severity.

Results

Compared with the healthy controls, serum ficolin-3 levels on admission were statistically decreased in patients with severe traumatic brain injury. Serum ficolin-3 levels were independently correlated with Glasgow Coma Scale scores. Ficolin-3 was also identified as an independent prognostic predictor for 1-week mortality, 6-month mortality, and 6-month unfavorable outcome. Under receiver operating characteristics curves, ficolin-3 has similar prognostic predictive values for all study endpoints compared with Glasgow Coma Scale scores.

Conclusions

It was proposed that lower serum ficolin-3 levels, correlated with injury severity, had the potential to be the useful, complementary tool to predict short- or long-term clinical outcomes after severe traumatic brain injury.

Exopolysaccharides isolated from hydrothermal vent bacteria can modulate the complement system

The complement system is involved in the defence against bacterial infection, or in the elimination of tumour cells. However, disturbances in this system contributes to the pathogenesis of various inflammatory diseases. The efficiency of therapeutic anti-tumour antibodies is enhanced when the complement system is stimulated. In contrast, cancer cells are able to inhibit the complement system and thus proliferate. Some marine molecules are currently being developed as new drugs for use in humans. Among them, known exopolyssacharides (EPSs) generally originate from fungi, but few studies have been performed on bacterial EPSs and even fewer on EPSs extracted from deep-sea hydrothermal vent microbes. For use in humans, these high molecular weight EPSs must be depolymerised. Furthermore, the over-sulphation of EPSs can modify their biological activity. The aim of this study was to investigate the immunodulation of the complement system by either native or over-sulphated low molecular weight EPSs isolated from vent bacteria in order to find pro or anti-activators of complement.

Genome-wide association study for serum complement C3 and C4 levels in healthy Chinese subjects

Complement C3 and C4 play key roles in the main physiological activities of complement system, and their deficiencies or over-expression are associated with many clinical infectious or immunity diseases. A two-stage genome-wide association study (GWAS) was performed for serum levels of C3 and C4. The first stage was conducted in 1,999 healthy Chinese men, and the second stage was performed in an additional 1,496 subjects. We identified two SNPs, rs3753394 in CFH gene and rs3745567 in C3 gene, that are significantly associated with serum C3 levels at a genome-wide significance level (P = 7.33×10⁻¹¹ and P = 1.83×10⁻⁹, respectively). For C4, one large genomic region on chromosome 6p21.3 is significantly associated with serum C4 levels. Two SNPs (rs1052693 and rs11575839) were located in the MHC class I area that include HLA-A, HLA-C, and HLA-B genes. Two SNPs (rs2075799 and rs2857009) were located 5′ and 3′ of C4 gene. The other four SNPs, rs2071278, rs3763317, rs9276606, and rs241428, were located in the MHC class II region that includes HLA-DRA, HLA-DRB, and HLA-DQB genes. The combined P-values for those eight SNPs ranged from 3.19×10⁻²² to 5.62×10⁻⁹⁷. HBsAg-positive subjects have significantly lower C3 and C4 protein concentrations compared with HBsAg-negative subjects (P<0.05). Our study is the first GWAS report which shows genetic components influence the levels of complement C3 and C4. Our significant findings provide novel insights of their related autoimmune, infectious diseases, and molecular mechanisms.

The complement system plays important roles in the innate and adaptive immune functions. C3 and C4 participate in almost all physiological activities and activated pathways as key complement members and host defense proteins. Identifying the genes that influence serum levels of C3 and C4 may help to elucidate the factors and mechanisms underlying the complement system. The genome-wide association studies (GWAS) have shown great success in revealing robust associations in both quantitative and qualitative traits. In this study, we performed a two-stage GWAS in a large cohort from the Chinese male population to examine the roles of common genetic variants on serum C3 and C4 levels. Our research identified genetic determinants associated with the quantitative levels of C3 and C4. Overall, our study highlights an intricate regulation of complement levels and potentially reveals novel mechanisms that may be followed up with additional functional studies.

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.

Proteome reference map of the skin mucus of Atlantic cod (Gadus morhua) revealing immune competent molecules

The skin mucosal proteome of Atlantic cod (Gadus morhua) was mapped using a 2D PAGE, LC-MS/MS coupled approach. Mucosal proteins from naive fish were identified primarily by similarity searches across various cod EST databases. The identified proteins were clustered into 8 groups based on gene ontology classification for biological process. Most of the proteins identified from the gel are hitherto unreported for cod. Galectin-1, mannan binding lectin (MBL), serpins, cystatin B, cyclophilin A, FK-506 binding protein, proteasome subunits (alpha-3 and -7), ubiquitin, and g-type lysozyme are considered immune competent molecules. Five of the aforementioned proteins were cloned and their tissue distribution was analysed by RT-PCR.

Infections of people with complement deficiencies and patients who have undergone splenectomy

The complement system comprises several fluid-phase and membrane-associated proteins. Under physiological conditions, activation of the fluid-phase components of complement is maintained under tight control and complement activation occurs primarily on surfaces recognized as "nonself" in an attempt to minimize damage to bystander host cells. Membrane complement components act to limit complement activation on host cells or to facilitate uptake of antigens or microbes "tagged" with complement fragments. While this review focuses on the role of complement in infectious diseases, work over the past couple of decades has defined several important functions of complement distinct from that of combating infections. Activation of complement in the fluid phase can occur through the classical, lectin, or alternative pathway. Deficiencies of components of the classical pathway lead to the development of autoimmune disorders and predispose individuals to recurrent respiratory infections and infections caused by encapsulated organisms, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. While no individual with complete mannan-binding lectin (MBL) deficiency has been identified, low MBL levels have been linked to predisposition to, or severity of, several diseases. It appears that MBL may play an important role in children, who have a relatively immature adaptive immune response. C3 is the point at which all complement pathways converge, and complete deficiency of C3 invariably leads to severe infections, including those caused by meningococci and pneumococci. Deficiencies of the alternative and terminal complement pathways result in an almost exclusive predisposition to invasive meningococcal disease. The spleen plays an important role in antigen processing and the production of antibodies. Splenic macrophages are critical in clearing opsonized encapsulated bacteria (such as pneumococci, meningococci, and Escherichia coli) and intraerythrocytic parasites such as those causing malaria and babesiosis, which explains the fulminant nature of these infections in persons with anatomic or functional asplenia. Paramount to the management of patients with complement deficiencies and asplenia is educating patients about their predisposition to infection and the importance of preventive immunizations and seeking prompt medical attention.

Surface membrane proteins of Biomphalaria glabrata embryonic cells bind fucosyl determinants on the tegumental surface of Schistosoma mansoni primary sporocysts

Previous observations that in vitro adherence of Biomphalaria glabrata embryonic (Bge) cells to sporocyst larval stages of Schistosoma mansoni was strongly inhibited by fucoidan, a sulfated polymer of L-fucose, suggested a role for lectinlike Bge cell receptors in sporocyst binding interactions. In the present investigation, monoclonal antibodies with specificities to 3 major glycan determinants found on schistosomes, LacdiNAc, fucosylated LacdiNAc (LDNF), and the Lewis X antigen, were used in adhesion blocking studies to further analyze the molecular interactions at the host-parasite interface. Results showed that only the anti-LDNF antibody significantly reduced snail Bge cell adhesion to the surface of sporocysts, suggesting that fucosyl determinants may be important in larval-host cell interactions. Affinity chromatographic separation of fucosyl-reactive Bge cell proteins from fucoidan-bound Sepharose 4B revealed the presence of polypeptides ranging from 6 to 200 kDa after elution with fucoidan-containing buffer. Pre-elution of the Bge protein-bound affinity column with dextran (Dex) and dextran sulfate (DexS) before introduction of the fucoidan buffer served as controls for protein binding based on nonspecific sugar or negative charge interactions. A subset of polypeptides (approximately 35-150 kDa) released by fucoidan elution was identified as Bge surface membrane proteins, representing putative fucosyl-binding proteins. Far-western blot analysis also demonstrated binding reactivity between Bge cell and sporocyst tegumental proteins. The finding that several of these parasite-binding Bge cell proteins were also fucoidan-reactive suggests the possible involvement of these molecules in mediating cellular interactions with sporocyst tegumental carbohydrates. It is concluded that Bge cells have surface protein(s) that may be playing a role in facilitating host cell adhesion to the surface of schistosome primary sporocysts through larval fucosylated glycoconjugates.

Analysis of Rickettsia typhi-infected and uninfected cat flea (Ctenocephalides felis) midgut cDNA libraries: deciphering molecular pathways involved in host response to R. typhi infection

Murine typhus is a flea-borne febrile illness that is caused by the obligate intracellular bacterium, Rickettsia typhi. The cat flea, Ctenocephalides felis, acquires R. typhi by imbibing a bloodmeal from a rickettsemic vertebrate host. To explore which transcripts are expressed in the midgut in response to challenge with R. typhi, cDNA libraries of R. typhi-infected and uninfected midguts of C. felis were constructed. In this study, we examined midgut transcript levels for select C. felis serine proteases, GTPases and defence response genes, all thought to be involved in the fleas response to feeding or infection. An increase in gene expression was observed for the serine protease inhibitors and vesicular trafficking proteins in response to feeding. In addition, R. typhi infection resulted in an increase in gene expression for the chymotrypsin and rab5 that we studied. Interestingly, R. typhi infection had little effect on expression of any of the defence response genes that we studied. We are unsure as to the physiological significance of these gene expression profiles and are currently investigating their potential roles as it pertains to R. typhi infection. To our knowledge, this is the first report of differential expression of flea transcripts in response to infection with R. typhi.

Mannose-binding lectin in term newborns and their mothers: genotypic and phenotypic relationship

Functional mannose-binding lectin (f-MBL) plays an important role in the innate neonatal immune system. We studied the origin of f-MBL in umbilical cord blood (UCB) by measuring maternal MBL (n=47), collected before elective cesarean section, and neonatal MBL (n=43) in arterial umbilical cord blood. In a subgroup, arterial and venous UCB MBL levels were measured. In addition, MBL expression was correlated with genetic mutations. The f-MBL levels in term infants were lower than in their mothers (0.70 microg/ml vs 1.11 microg/ml, p<0.01) and maternal and neonatal MBL levels were only weakly correlated (R=0.32, p<0.001), which suggests a fetal origin of f-MBL. Arterial and venous UCB median MBL levels did not differ (0.98 microg/ml vs. 1.40 microg/ml, p=0.20). No homozygous mutations were found. MBL was lower in mothers and infants with a (compound) heterozygous mutation than in those with a wild type. One new (HYPB) and two rare haplotypes (HXPA, LYPD) were reported in our population. Levels of MBL differed depending on the genotype of the mother or the infant. Because the role of MBL in host defense is still unclear, both f-MBL and haplotype should be measured to determine the clinical implications of MBL deficiency in infants.

Deciphering Dorin M glycosylation by mass spectrometry

The soft tick, Ornithodoros moubata, is a vector of several bacterial and viral pathogens including Borrelia duttoni, a causative agent of relapsing fever and African swine fever virus. Previously, a sialic acid-specific lectin Dorin M was isolated from its hemolymph. Here, we report on the complete characterization of the primary sequence of Dorin M. Using liquid chromatography coupled to mass spectrometry, we identified three different glycopeptides in the tryptic digest of Dorin M. The peptide, as well as the glycan part of all glycopeptides, were further fully sequenced by means of tandem mass spectrometry (MS2) and multiple-stage mass spectrometry (MS3). Two classical N-glycosylation sites were modified by high-mannose-type glycans containing up to nine mannose residues. The third site bore a glycan with four to five mannose residues and a deoxyhexose (fucose) attached to the proximal N-acetylglycosamine. The microheterogeneity at each site was estimated based on chromatographic behavior of different glycoforms. The fourth, a non-classical N-glycosylation site (Asn-Asn-Cys), was not glycosylated, probably due to the involvement of the cysteine residue in a disulfide bridge.

Effects of complement regulators bound to Escherichia coli K1 and Group B Streptococcus on the interaction with host cells

Escherichia coli K1 and Group B Streptococcus (GBS) are the most common bacteria that cause meningitis during the neonatal period. Complement, the first line of defence in the host, acts on these bacteria to opsonize with various components of complement for subsequent presentation to phagocytes. To counteract these opsonization effects, E. coli and GBS bind to the complement regulators C4 binding protein and Factor H, respectively. Nonetheless, the deposition of complement components on these two bacteria from neonatal serum and their effect on the host cell interaction is unclear. Here we demonstrated that the deposition of complement proteins from adult serum prevented the invasion of E. coli into human brain microvascular endothelial cells, whereas the invasion of GBS was enhanced. In contrast, treatment with cord serum had no effect on the invasion of both these bacteria. We also examined the effect of the deposited complement proteins on phagocytosis using THP-1 cells and THP-1 cells differentiated into macrophages. Escherichia coli treated with adult serum neither attached nor entered these cells, whereas GBS was phagocytosed and survived efficiently. We further demonstrate that the inhibitory effect of complement proteins is the result of the bound complement inhibitors C4b-binding protein, in the case of E. coli, and Factor H, in the case of GBS. Taken together, these results suggest that E. coli and GBS utilize contrasting mechanisms of complement-mediated interactions with their target cells for successful establishment of disease.

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.

A complement response may activate metamorphosis in the ascidian Boltenia villosa

Ascidian metamorphosis transforms a free-swimming larval chordate ascidian into a sessile adult through a distinct series of metamorphic events. Initially, larvae must become competent to respond to settlement cues. Settlement is then marked by dramatic body plan remodeling and may be accompanied by attachment to the substrate. Subtractive hybridization has revealed that many innate immunity transcripts are upregulated during metamorphosis in the ascidian Boltenia villosa. Several of these genes have well-known roles in the mannose-binding lectin (MBL)-complement pathway of innate immunity, including MBL and MBL-activated serine protease (MASP). MBL recognizes and binds to bacterial pathogens, activates MASP, and triggers the complement cascade. In B. villosa, larvae upregulate BvMASP at the time of competency to initiate settlement. We show that several bacterial strains can induce settlement and that the timing of BvMASP expression in the papillae-associated tissue (PAT) cells is tightly correlated with larval competency. We further demonstrate that serine protease inhibitors used to block the complement response also block metamorphosis, allowing tail resorption, but preventing further morphological changes. Based on these experiments, we propose that the MBL-complement pathway may be important for competency, bacterial substrate detection and body plan remodeling during metamorphosis.

Phase I Safety, Tolerability, and Pharmacokinetic Study of Recombinant Human Mannan-Binding Lectin

Mannan-binding lectin (MBL), a human plasma protein, plays an important role in the innate immune defence. MBL recognizes microorganisms through surface carbohydrate structures. Due to genetic polymorphisms, MBL plasma concentrations range from 5 to 10,000 ng/mL. Approximately 30% of the human population have low levels of MBL (below 500 ng/mL). MBL deficiency is associated with increased susceptibility to infections in immunosuppressed individuals, e.g., during chemotherapeutically induced neutropenia. Replacement therapy with MBL may be beneficial in this patient group, and recombinant human MBL (rhMBL) is in development as a novel therapeutic approach. To assess the safety, tolerability, and pharmacokinetics of rhMBL, a placebo-controlled double-blinded study was performed in MBL-deficient healthy male subjects. rhMBL was administered as both single intravenous (i.v.) infusions (0.01, 0.05, 0.1, and 0.5 mg/kg) and repeated i.v. infusions (0.1 or 0.3 mg/kg given at 3-day intervals). There were no difference in incidence and type of adverse events reported in the study between the groups of subjects receiving rhMBL and the placebo group. All adverse events reported as drug-related were mild and no serious adverse events were recorded. There were no clinically significant changes in laboratory evaluations, ECG or vital signs, and no anti-MBL antibodies were detected following rhMBL administration. After single i.v. doses of rhMBL the maximal plasma levels increased in a dose-dependent manner reaching a geometric mean of 9710 ng/mL+/-10.5% in the highest dose group (0.5 mg/kg), with an elimination half-life of approximately 30 h. No rhMBL accumulation in plasma was observed following repeat dosing. Administration of rhMBL restored the ability to activate the MBL pathway of the complement system without non-specific activation of the complement cascade. In conclusion, no safety or tolerability concern was raised following rhMBL administration no signs of immunogenicity detected, and an rhMBL plasma level judged sufficient to achieve therapeutic benefit (>1000 ng/mL) can be achieved.

Tick lectins: structural and functional properties

Few papers have been published on tick lectins so far, and therefore more data are needed to complete the mosaic of knowledge of their structural and functional properties. Tissue-specific lectin/haemagglutinin activities of both soft and hard ticks have been investigated. Some tick lectins are proteins with binding affinity for sialic acid, various derivatives of hexosamines and different glycoconjugates. Most tick lectin/haemagglutinin activities are blood meal enhanced, and could serve as molecular factors of self/non-self recognition in defence reactions against bacteria or fungi, as well as in pathogen/parasite transmission. Dorin M, the plasma lectin of Ornithodoros moubata, is the first tick lectin purified so far from tick haemolymph, and the first that has been fully characterized. Partial characterization of other tick lectins/haemagglutinins has been performed mainly with respect to their carbohydrate binding specificities and immunochemical features.

Mannan-binding lectin (MBL)-mediated opsonization is enhanced by the alternative pathway amplification loop

The complement system is a humoral effector in the innate immune system. Three activation pathways exist in the complement system, known as the classical pathway, the lectin pathway and the alternative pathway. Dysfunction of lectin pathway activation is caused by MBL deficiency. MBL deficiency in a cohort of healthy Caucasian blood bank donors was investigated with MBL genotyping and MBL plasma concentration. Recognition of the yeast-derived zymosan by MBL was investigated with Western blot. The involvement of the alternative pathway amplification loop in enhancing MBL-mediated opsonization of zymosan was investigated in a novel opsonophagocytosis assay for flow cytometry. Sera deficient for MBL, factor D or properdin were tested, and purified MBL, factor D or properdin were used to recover opsonization. The optimal receiver-operator characteristic (ROC) cut-off value for dividing the Caucasian cohort in MBL-sufficient and MBL-deficient was calculated at 0.7 microg/ml. Thirty-eight percent of the group had concentrations below 0.7 microg/ml. Zymosan eluates opsonized with MBL-sufficient sera contain high oligomers of MBL, while eluates from MBL-deficient donors contained hardly any MBL. The MBL-, factor D- and properdin-deficient sera showed reduced opsonophagocytosis by human control neutrophils, as compared to normal MBL-sufficient sera. This reduction in opsonization was restored to normal levels by addition of purified MBL, factor D and properdin. The absence of opsonization in the factor D- and properdin-deficient sera, but presence in normal serum after blocking with anti-C1q-F(ab)2 and anti-MBL-F(ab)2, demonstrates the involvement of the amplification loop in MBL-initiated zymosan opsonization, even at very low serum concentrations (up to 3%, v/v). In conclusion, our data demonstrate that the MBL-mediated route of complement activation depends on the alternative pathway amplification loop for optimal opsonization of zymosan.

The tick plasma lectin, Dorin M, is a fibrinogen-related molecule

A lectin, named Dorin M, previously isolated and characterized from the hemolymph plasma of the soft tick, Ornithodoros moubata, was cloned and sequenced. The immunofluorescence using confocal microscopy revealed that Dorin M is produced in the tick hemocytes. A tryptic cleavage of Dorin M was performed and the resulting peptide fragments were sequenced by Edman degradation and/or mass spectrometry. Two of three internal peptide sequences displayed a significant similarity to the family of fibrinogen-related molecules. Degenerate primers were designed and used for PCR with hemocyte cDNA as a template. The sequence of the whole Dorin M cDNA was completed by the method of RACE. The tissue-specific expression investigated by RT-PCR revealed that Dorin M, in addition to hemocytes, is significantly expressed in salivary glands. The derived amino-acid sequence clearly shows that Dorin M has a fibrinogen-like domain, and exhibited the most significant similarity with tachylectins 5A and 5B from a horseshoe crab, Tachypleus tridentatus. In addition, other protein and binding characteristics suggest that Dorin M is closely related to tachylectins-5. Since these lectins have been reported to function as non-self recognizing molecules, we believe that Dorin M may play a similar role in an innate immunity of the tick and, possibly, also in pathogen transmission by this vector.

Identification of the insulin-like growth factor II receptor as a novel receptor for binding and invasion by Listeria monocytogenes

The gram-positive bacterium Listeria monocytogenes causes a life-threatening disease known as listeriosis. The mechanism by which L. monocytogenes invades mammalian cells is not fully understood, but the processes involved may provide targets to prevent and treat listeriosis. Here, for the first time, we have identified the insulin-like growth factor II receptor (IGFIIR; also known as the cation-independent mannose 6-phosphate receptor (CI)M6PR or CD222) as a novel receptor for binding and invasion of Listeria species. Random peptide phage display was employed to select a peptide sequence by panning with immobilized L. monocytogenes cells; this peptide sequence corresponds to a sequence within the mannose 6-phosphate binding site of the IGFIIR. All Listeria spp. specifically bound the labeled peptide but not a control peptide, which was demonstrated using fluorescence spectrophotometry and fluorescence-activated cell sorting. Further evidence for binding of the receptor by L. monocytogenes and L. innocua was provided by affinity purification of the bovine IGFIIR from fetal calf serum by use of magnetic beads coated with cell preparations of Listeria spp. as affinity matrices. Adherence to and invasion of mammalian cells by L. monocytogenes was significantly inhibited by both the synthetic peptide and mannose 6-phosphate but not by appropriate controls. These observations indicate a role for the IGFIIR in the adherence and invasion of L. monocytogenes of mammalian cells, perhaps in combination with known mechanisms. Ligation of IGFIIR by L. monocytogenes may be a novel mechanism that contributes to the regulation of infectivity, possibly in combination with other mechanisms.

Kinetic studies on the interactions of heparin and complement proteins using surface plasmon resonance

Heparin is a naturally occurring polysaccharide known to interact with complement proteins and regulate multiple steps in the complement cascade. Quantitative information, in the form of affinity constants for heparin-complement interactions, is not generally available and there are no reports of a comprehensive analysis using the same interaction method. Such information should improve our understanding of how exogenously administered pharmaceutical heparin and the related endogenous polysaccharide, heparan sulfate, regulate complement activation. The current study provides the first comprehensively analysis of the binding of various complement proteins to heparin using surface plasmon resonance (SPR). Complement proteins C1, C2, C3, C4, C5, C6, C7, C8, C9, C1INH, factor I, factor H, factor B and factor P all bind heparin but exhibit different binding kinetics and dissociation constants (Kd) ranging from 2 to 320 nM. By taking into account these Kd values and the serum concentrations of these complement proteins, the percentage of each binding to exogenously administered heparin was calculated and found to range from 2% to 41%. This study provides essential information required for the rational design of new therapeutic agents capable of regulating the complement activation.

Mannose Binding Lectin Acute Phase Activity in Patients with Severe Infection

Mannose Binding Lectin (MBL) is a liver derived, circulating plasma protein that plays a pivotal role in innate immunity. MBL functions as a pathogen recognition molecule, opsonising organisms and initiating the complement cascade. MBL deficiency arising from mutations and promoter polymorphisms in the MBL2 gene is common and has been associated with risk, severity, and frequency of infection in a number of clinical settings. With MBL therapy on the horizon, the usefulness of replacement MBL therapy has been challenged by the notion, that as an acute phase protein, MBL levels may rise under stress to sufficient levels, in individuals who are usually deficient. This report demonstrates that in patients with sepsis and septic shock, the majority of patients do not display an MBL acute phase response: 41.4% of individuals maintained consistent MBL levels throughout hospital stay, 31.3% of individuals demonstrated a positive acute phase response, and a negative acute phase response was observed in 27.3% of individuals studied. Importantly, a positive acute phase response was generally observed in individuals with wild-type MBL2 genes. When a positive acute phase response was observed in individuals with coding mutation, these individuals demonstrated a normal MBL level on admission to hospital. Furthermore, no individual, regardless of genotype who was MBL deficient at admission was able to demonstrate a positive acute phase response into the normal MBL range. These findings indicate MBL demonstrates a variable acute phase response in the clinical setting of sepsis and septic shock.

Complexes between C1q and C3 or C4: novel and specific markers for classical complement pathway activation

Classical pathway activation is often assessed by measuring circulating levels of activated C4. However, this parameter does not discriminate between activation through the classical or the lectin pathway. We hypothesized that during classical pathway activation, complexes are formed between C1q and activated C4 or C3. Using ELISA, we investigated whether such complexes constitute specific markers for classical pathway activation. In vitro, C1q-C3d/C4d complexes were generated upon incubation of normal recalcified plasma with aggregated IgG or an anti-C1q mAb that activates C1 (mAb anti-C1q-130). In contrast, during incubation with C1s or trypsin, C1q-C3d/C4d complexes were not generated, which excludes an innocent bystander effect. Additionally, C1q-C3d/C4d complexes were not generated during activation of the alternative or the lectin pathway. Repeated freezing and thawing did not influence levels of C1q-C3d/C4d complexes in recalcified plasma. To measure C1q-complement complexes in plasma samples, we separated unbound complement proteins from C1q-C3d/C4d complexes in the samples prior to testing with ELISA. In samples from patients undergoing cardiopulmonary bypass surgery or suffering from rheumatoid arthritis, we found higher levels of C1q-C4 complexes than in samples from healthy individuals. We conclude that complexes between C1q and C4 or C3 are specific markers of classical complement pathway activation.

Recent advances in the innate immunity of invertebrate animals

Invertebrate animals, which lack adaptive immune systems, have developed other systems of biological host defense, so called innate immunity, that respond to common antigens on the cell surfaces of potential pathogens. During the past two decades, the molecular structures and functions of various defense components that participated in innate immune systems have been established in Arthropoda, such as, insects, the horseshoe crab, freshwater crayfish, and the protochordata ascidian. These defense molecules include phenoloxidases, clotting factors, complement factors, lectins, protease inhibitors, antimicrobial peptides, Toll receptors, and other humoral factors found mainly in hemolymph plasma and hemocytes. These components, which together compose the innate immune system, defend invertebrate from invading bacterial, fungal, and viral pathogens. This review describes the present status of our knowledge concerning such defensive molecules in invertebrates.

Basic Science for the Clinician 27

Ancient protective mechanisms are in place, deep within our defenses against infection and malignancy, often unappreciated until homologous proteins found within less phylogenetically advanced organisms are identified. Such is the case with 2 major recent finds, the Toll-like receptors (TLRs) and nucleotide oligomerization domain (NOD) families of innate immunity molecules. These families of receptors have high specificity, limited heterogeneity, and no plasticity; nonetheless, they play a pivotal role in rapid initial defenses against pathogens. Moreover, studies of the mechanisms of TLRs and NODs show how they and IL-1 and IL-18 stand at the threshold of the adaptive immune response and help to accelerate specific immune responsivity. Nonspecific reactivity of these preprogrammed receptors may be how relatively nonpathogenic organisms like yersinia and chlamydia may drive the inflammation of reactive arthritis and atherosclerosis. The inflammation of rheumatoid arthritis may be magnified, if not initiated, by these innate mechanisms as well.

The ancient origin of the complement system

The complement system has been thought to originate exclusively in the deuterostomes. Here, we show that the central complement components already existed in the primitive protostome lineage. A functional homolog of vertebrate complement 3, CrC3, has been isolated from a 'living fossil', the horseshoe crab (Carcinoscorpius rotundicauda). CrC3 resembles human C3 and shows closest homology to C3 sequences of lower deuterostomes. CrC3 and plasma lectins bind a wide range of microbes, forming the frontline innate immune defense system. Additionally, we identified CrC2/Bf, a homolog of vertebrate C2 and Bf that participates in C3 activation, and a C3 receptor-like sequence. Furthermore, complement-mediated phagocytosis of bacteria by the hemocytes of horseshoe crab was also observed. Thus, a primitive yet complex opsonic complement defense system is revealed in the horseshoe crab, a protostome species. Our findings demonstrate an ancient origin of the critical complement components and the opsonic defense mechanism in the Precambrian ancestor of bilateral animals.

Peptidoglycan recognition proteins: on and off switches for innate immunity

Insects rely on innate immune mechanisms to defend themselves against microbes. The inducible anti-microbial peptides constitute an important arm of this defense. In Drosophila, the Toll and the Imd pathways are the major routes to induce the peptides, and it has become clear that to a certain extent, these pathways can discriminate between different microbes and mount an appropriate response to eliminate the intruder. This review discusses the proteins responsible for this discriminatory recognition, the peptidoglycan recognition proteins (PGRPs). The serum protein PGRP-SA triggers a humoral cascade of proteases upon infection by certain gram-positive bacteria to activate the Toll pathway. The membrane-bound receptor PGRP-LC activates the Imd pathway in response to certain gram-negative bacteria or their peptidoglycans. Other PGRPs have enzymatic activity, cleaving lactylamide bonds in peptidoglycan to eliminate its immunogenicity, thus turning off the immune response. The PGRP family is conserved from insects to man. Short mammalian PGRP variants are synthesized in neutrophils and stored in granules. These PGRPs seem to influence the survival of phagocytosed non-pathogenic bacteria. Long PGRP variants are expressed in the liver and secreted into the bloodstream where their peptidoglycan-degrading activity might serve scavenger functions.

Genetic susceptibility to sepsis: A possible role for mannose-binding lectin

Sepsis is an increasing problem in modern medicine and the leading cause of death in noncoronary intensive care unit patients. Over the past few years, several studies have provided data indicating that relatively common polymorphisms in genes encoding proteins of importance for innate immune recognition, the inflammatory response, and for coagulation and fibrinolysis, are associated with susceptibility for and outcome of sepsis. Recently, several studies have shed light on the importance of deficiency of mannose-binding lectin (MBL) as a susceptibility factor for sepsis. This review summarizes the evidence that critically ill patients carrying MBL-variant alleles may be at increased risk for severe sepsis. The prospect for the future is that genetic profiling may guide in identifying critically ill patients at increased risk for sepsis and poor outcome, and in tailoring a more individual and effective therapy.

The potential role of mannan-binding lectin in the clearance of self-components including immune complexes

Mannan-binding lectin (MBL) is a pattern recognition receptor in the innate immune system. It recognizes certain sugar residues arranged in a pattern that enables MBL to bind with sufficient strength. Such sugar patterns are common on the surface of many microorganisms, and MBL has therefore been considered to be an agent that can discriminate between self and nonself. There is, however, increasing evidence supporting that MBL, like many membrane-bound C-type lectin-like receptors, also helps to dispose of various outworn or abnormal body components. Most self-components are protected with sialic acid or galactose that disrupt the pattern of the sugars that MBL can bind, but MBL may be significantly involved in the elimination of self-components that have lost these protective terminal residues. The role of MBL in the clearance of invading pathogens has previously been thoroughly reviewed. Here, we review some findings that support the notion that MBL may contribute to noninflammatory removal of immune complexes and abnormal cells by the reticuloendothelial system. Defects in this clearance mechanism may cause an accumulation of potentially dangerous self-components, thereby increasing the likelihood of chronic inflammation and autoimmunity.

Serum mannose-binding lectin levels and mbl2 gene polymorphisms in different age and gender groups of southern Chinese adults

Mannose-binding lectin (MBL) is an acute-phase serum protein, and its inherited deficiency has been shown to predispose to infections. The developmental profile of serum MBL in preterm infants has been demonstrated previously. To determine the profiles of serum MBL levels and mbl2 polymorphisms over age and genders in an adult population, samples from 689 southern Chinese (age range 16-57 years; 382 males and 307 females) were studied using enzyme-linked immunosorbent assay and high-throughput genotyping of mbl2. Serum MBL levels maintained within a narrow range from age groups of 16-20 years old to 31-40 years old (mean of 2050-2160 micro g/l) and declined to a mean of 1466 micro g/l in the last age group 41-57 years old. No significant differences were found in the distributions of mbl2 haplotypes (YA, XA and YB) among all these age groups. Between gender groups, no significant imbalance of MBL profile in terms of serum MBL levels and distribution of mbl2 haplotypes was found. Results suggest an important role of circulating MBL in first-line host defence because MBL maintains at fairly constant levels after childhood and no gender influence on the MBL profile.

Localization of the Serine Protease-binding Sites in the Collagen-like Domain of Mannose-binding Protein

Mutations in the collagen-like domain of serum mannose-binding protein (MBP) interfere with the ability of the protein to initiate complement fixation through the MBP-associated serine proteases (MASPs). The resulting deficiency in the innate immune response leads to susceptibility to infections. Studies have been undertaken to define the region of MBP that interacts with MASPs and to determine how the naturally occurring mutations affect this interaction. Truncated and modified MBPs and synthetic peptides that represent segments of the collagen-like domain of MBP have been used to demonstrate that MASPs bind on the C-terminal side of the hinge region formed by an interruption in the Gly-X-Y repeat pattern of the collagen-like domain. The binding sites for MASP-2 and for MASP-1 and -3 overlap but are not identical. The two most common naturally occurring mutations in MBP result in substitution of acidic amino acids for glycine residues in Gly-X-Y triplets on the N-terminal side of the hinge. Circular dichroism analysis and differential scanning calorimetry demonstrate that the triple helical structure of the collagen-like domain is largely intact in the mutant proteins, but it is more easily unfolded than in wild-type MBP. Thus, the effect of the mutations is to destabilize the collagen-like domain, indirectly disrupting the binding sites for MASPs. In addition, at least one of the mutations has a further effect on the ability of MBP to activate MASPs.