L-MBP is expressed in epithelial cells of mouse small intestine

The Lectin Pathway of the Complement System-Activation, Regulation, Disease Connections and Interplay with Other (Proteolytic) Systems

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.

Regulation of the innate immune response and gut microbiome by p53

p53 is a key tumor suppressor mutated in half of human cancers. In recent years, p53 was shown to regulate a wide variety of functions. From the transcriptome analysis of 24 tissues of irradiated mice, we identified 553 genes markedly induced by p53. Gene Ontology (GO) enrichment analysis found that the most associated biological process was innate immunity. 16S rRNA-seq analysis revealed that Akkermansia, which has anti-inflammatory properties and is involved in the regulation of intestinal barrier integrity, was decreased in p53-knockout (p53-/- ) mice after radiation. p53-/- mice were susceptible to radiation-induced GI toxicity and had a significantly shorter survival time than p53-wild-type (p53+/+ ) mice following radiation. However, administration of antibiotics resulted in a significant improvement in survival and protection against GI toxicity. Mbl2 and Lcn2, which have antimicrobial activity, were identified to be directly transactivated by p53 and secreted by liver into the circulatory system. We also found the expression of MBL2 and LCN2 was decreased in liver cancer tissues with p53 mutations compared with those without p53 mutations. These results indicate that p53 is involved in shaping the gut microbiome through its downstream targets related to the innate immune system, thus protecting the intestinal barrier.

Complement Initiation Varies by Sex in Intestinal Ischemia Reperfusion Injury

Intestinal ischemia reperfusion (IR)-induced tissue injury represents an acute inflammatory response with significant morbidity and mortality. The mechanism of IR-induced injury is not fully elucidated, but recent studies suggest a critical role for complement activation and for differences between sexes. To test the hypothesis that complement initiation differs by sex in intestinal IR, we performed intestinal IR on male and female WT C57B6L/, C1q-/-, MBL-/-, or properdin (P)-/- mice. Intestinal injury, C3b and C5a production and ex vivo secretions were analyzed. Initial studies demonstrated a difference in complement mRNA and protein in male and female WT mice. In response to IR, male C1q-, MBL- and P-deficient mice sustained less injury than male WT mice. In contrast, only female MBL-/- mice sustained significantly less injury than female wildtype mice. Importantly, wildtype, C1q-/- and P-/- female mice sustained significant less injury than the corresponding male mice. In addition, both C1q and MBL expression and deposition increased in WT male mice, while only elevated MBL expression and deposition occurred in WT female mice. These data suggested that males use both C1q and MBL pathways, while females tend to depend on lectin pathway during intestinal IR. Females produced significantly less serum C5a in MBL-/- and P-/- mice. Our findings suggested that complement activation plays a critical role in intestinal IR in a sex-dependent manner.

Interaction of Mannose-Binding Lectin With Lipopolysaccharide Outer Core Region and Its Biological Consequences

Lipopolysaccharide (LPS, endotoxin), the main surface antigen and virulence factor of Gram-negative bacteria, is composed of lipid A, core oligosaccharide, and O-specific polysaccharide (O-PS) regions. Each LPS region is capable of complement activation. We have demonstrated that LPS of Hafnia alvei, an opportunistic human pathogen, reacts strongly with human and murine mannose-binding lectins (MBLs). Moreover, MBL-LPS interactions were detected for the majority of other Gram-negative species investigated. H. alvei was used as a model pathogen to investigate the biological consequences of these interactions. The core oligosaccharide region of H. alvei LPS was identified as the main target for human and murine MBL, especially l-glycero-d-manno-heptose (Hep) and N-acetyl-d-glucosamine (GlcNAc) residues within the outer core region. MBL-binding motifs of LPS are accessible to MBL on the surface of bacterial cells and LPS aggregates. Generally, the accessibility of outer core structures for interaction with MBL is highest during the lag phase of bacterial growth. The LPS core oligosaccharide-MBL interactions led to complement activation and also induced an anaphylactoid shock in mice. Unlike Klebsiella pneumoniae O3 LPS, robust lectin pathway activation of H. alvei LPS in vivo was mainly the result of outer core recognition by MBL; involvement of the O-PS is not necessary for anaphylactoid shock induction. Our results contribute to a better understanding of MBL-LPS interaction and may support development of therapeutic strategies against sepsis based on complement inhibition.

Migration ofFasciola hepaticanewly excysted juveniles is inhibited by high-mannose and oligomannose-typeN-glycan-binding lectins

Fasciola hepaticahas both zoonotic importance and high economic impact in livestock worldwide. After ingestion by the definitive host, the Newly Excysted Juveniles (NEJ) penetrate the intestine before reaching the peritoneal cavity. The role of some NEJ-derived proteins in invasion has been documented, but the role of NEJ glycans or lectin-binding receptors during initial infection in the gut is still unknown. To address these questions, the migration of NEJ through rat intestine was recorded at 30 min intervals up to 150 min by twoex vivomethods. Firstly, jejunal sheets were challenged with NEJ incubated with biotinylated lectins. Secondly, untreated NEJ were incubated with distal jejunum pre-treated with lectins. BothConcanavalin A(ConA) andGalanthus nivalis(GNL), which recognize mannose-typeN-glycans, significantly inhibited NEJ migration across the jejunum. Most of the lectins bound to the tegument and oral sucker of the NEJ, but only ConA and GNL maintained this interaction over 150 min. None of the lectins examined significantly reduced NEJ migration when pre-incubated with jejunal sheets, suggesting that host glycans might not be essential for initial binding/recognition of the gut by NEJ. Agents capable of blocking mannose-typeN-glycans on the NEJ tegument may have potential for disrupting infection.

Purification, characterization and functional analysis of the immune molecule lectin from the haemolymph of blue swimmer crab Portunus pelagicus and their antibiofilm properties

The present study reveals purification and characterization of immune molecule lectin from the haemolymph of blue swimmer crab Portunus pelagicus (Pp-Lec). The Pp-Lec was purified by affinity chromatography with mannose coupled sepharose CL-4B column and it exhibits single band with a molecular weight of 155 kDa in SDS-PAGE. The surface morphology of purified Pp-Lec displays the homogeneous nature of protein. A distinct peak with a retention time of 3.3 min was appeared in high performance liquid chromatography (HPLC) and X-ray diffraction (XRD) analysis expresses a single peak at 31.5° which shows the purity and crystalline nature of the protein respectively. Functional analysis of purified Pp-Lec exhibits encapsulation activity against sepharose beads and yeast agglutination activity against Saccharomyces cerevisiae. Moreover, the purified Pp-Lec has the ability to agglutinates with the human erythrocytes among tested and which was observed by light microscopy. In addition, purified Pp-Lec showed the broad spectrum of antibacterial activity against Gram-positive Bacillus pumulis, Bacillus thuringiensis, Enterococcus faecalis and Gram negative Citrobacter amalonaticus, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Proteus vulgaris, Citrobacter murliniae, Citrobacter freundii, Morganella morganii. Antibiofilm potential of purified Pp-Lec against selective Gram-negative bacteria showed the disruption of biofilm architecture at the concentration of 50 μg ml^-1.

Polymorphisms in the Mannose-Binding Lectin Gene are Associated with Defective Mannose-Binding Lectin Functional Activity in Crohn's Disease Patients

Mannose-binding lectin, together with mannose-associated serine proteases, activates the lectin pathway of the complement system and subsequent inflammatory mechanisms. An association between mannose-binding lectin deficiency and anti-Saccharomyces cerevisiae antibody levels is observed in Crohn’s disease and this deficiency is frequently associated with a severe Crohn’s disease phenotype. In the present study, we assessed the relationship between serum concentrations of mannose-binding lectin, mannose-binding lectin functional activity, MBL2 and NOD2 polymorphisms, anti-S. cerevisiae antibody levels and clinical Crohn’s disease phenotype in 69 Crohn’s disease patients and 30 age- and sex-matched healthy controls. The results show that the MBL2 variant rs5030737 at codon 52 was associated with a low level of mannose-binding lectin and impaired mannose-binding lectin–mannose-associated serine protease (MBL-MASP) functional activity in Crohn’s disease patients. This MBL2 variant was also associated with a higher level of anti-S. cerevisiae antibodies. In addition, the NOD2 variant rs2066844, which is associated with susceptibility to Crohn’s disease, was significantly correlated with an impairment in MBL-MASP functional activity. These results provide evidence that Crohn’s disease patients have an impairment in MBL-MASP functional activity and that this defect is associated with MBL2 and NOD2 variants.

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.

Complement Activation by Giardia duodenalis Parasites through the Lectin Pathway Contributes to Mast Cell Responses and Parasite Control

Infection with Giardia duodenalis is one of the most common causes of diarrheal disease in the world. While numerous studies have identified important contributions of adaptive immune responses to parasite control, much less work has examined innate immunity and its connections to the adaptive response during this infection. We explored the role of complement in immunity to Giardia using mice deficient in mannose-binding lectin (Mbl2) or complement factor 3a receptor (C3aR). Both strains exhibited delayed clearance of parasites and a reduced ability to recruit mast cells in the intestinal submucosa. C3aR-deficient mice had normal production of antiparasite IgA, butex vivo T cell recall responses were impaired. These data suggest that complement is a key factor in the innate recognition of Giardia and that recruitment of mast cells and activation of T cell immunity through C3a are important for parasite control.

Elevated plasma CL-K1 level is associated with a risk of developing disseminated intravascular coagulation (DIC)

Collectin kidney 1 (CL-K1) is a recently identified collectin that is synthesized in most organs and circulates in blood. CL-K1 is an innate immune molecule that may play a significant role in host defense. As some collectins also play a role in coagulation, we hypothesized that an effect of CL-K1 may be apparent in disseminated intravascular coagulation (DIC), a gross derangement of the coagulation system that occurs in the setting of profound activation of the innate immune system. DIC is a grave medical condition with a high incidence of multiple organ failure and high mortality and yet there are no reliable biomarkers or risk factors. In our present study, we measured plasma CL-K1 concentration in a total of 659 specimens, including 549 DIC patients, 82 non-DIC patients and 27 healthy volunteers. The median plasma CL-K1 levels in these cohorts were 424, 238 and 245 ng/ml, respectively, with no significant difference in the latter two groups. The incidence of elevated plasma CL-K1 was significantly higher in the DIC patients compared to the non-DIC patients, resulting in an odds ratio of 1.929 (confidence interval 1.041-3.866). Infection, renal diseases, respiratory diseases, and cardiac diseases were more frequently observed in the DIC group than in the non-DIC group. In the DIC group, vascular diseases were associated with elevated plasma CL-K1 levels while age and acute illness had little effect on plasma CL-K1 levels. Independent of DIC, elevated plasma CL-K1 levels were associated with respiratory disease and coagulation disorders. These results suggest that specific diseases may affect CL-K1 synthesis in an organ dependent manner and that elevated plasma CL-K1 levels are associated with the presence of DIC. Further investigations in cohorts of patients are warranted. We propose that elevated plasma CL-K1 may be a new useful risk factor and possibly biomarker for the prediction of developing DIC.

Enhanced permeability across Caco-2 cell monolayers by specific mannosylating ligand of buserelin acetate proliposomes

CONTEXT

Oral delivery of peptide and protein drugs still remains the area of challenges due to their low stability and permeability across GI tract. Among numerous attempts, the receptor-mediated drug targeting is a promising approach to enhance GI permeability.

OBJECTIVE

The aim of this study was to prepare mannosylated buserelin acetate (MANS-BA) proliposome powders grafted with N-octadecyl-d-mannopyranosylamine (SAMAN) as targeting moiety and evaluate their permeability across Caco-2 cell monolayers.

MATERIALS AND METHODS

The MANS-BA proliposome powders were prepared by coprecipitation method. The targeting moiety SAMAN was synthesized in-house and confirmed by characterization using Fourier transform infrared (FTIR) and differential scanning calorimeter (DSC).

RESULTS

The MANS-BA liposomes reconstituted from proliposome powders exhibited the oligolamellar vesicular structure of phospholipid bilayer. Their size, zeta potential and entrapment efficiency were in the ranges of 93.11-218.95 nm, -24.03 to -37.15 mV and 21.12-33.80%, respectively. The permeability of reconstituted MANS-BA liposomes across Caco-2 cell monolayers was significantly enhanced to about 1.2- and 2.2-fold over those of conventional BA liposomes and solution, respectively.

DISCUSSION

Increase in dicetylphosphate, cholesterol and SAMAN contents resulted in significant increase in size and zeta potential of reconstituted MAN-BA liposomes. The entrapment efficiency was increased with increasing dicetylphosphate and mannitol contents in liposomes containing cholesterol.

CONCLUSIONS

The significantly enhanced permeability across Caco-2 cell monolayers of MANS-BA liposomes might be due to the role of mannose receptor on intestinal enterocytes.

The consequence of low mannose-binding lectin plasma concentration in relation to susceptibility to Salmonella Infantis in chickens

Mannose-binding lectin (MBL) is a key protein in innate immunity. MBL binds to carbohydrates on the surface of pathogens, where it initiates complement activation via the lectin-dependent pathway or facilitates opsonophagocytosis. In vitro studies have shown that human MBL is able to bind to Salmonella, but knowledge in relation to chicken MBL and Salmonella is lacking. In order to study this relation day-old chickens from two selected lines L10H and L10L, differing in MBL serum concentration, were either orally infected with S. Infantis (S.123443) or kept as non-infected controls. The differences between healthy L10H and L10L chicken sublines were more profound than differences caused by the S. Infantis infection. The average daily body weight was higher for L10H than for L10L, regardless of infection, indicating beneficial effects of MBL selection on growth. Salmonella was detected in cloacal swabs and the number of Salmonella positive chickens during the experiment was significantly higher in L10L than L10H, indicating that MBL may affect the magnitude of Salmonella colonisation in day-old chickens. MBL expression was determined in ceca tissue by real-time RT-PCR. L10H chickens showed a significantly higher relative expression than L10L at days 1 and 41 pi, regardless of infection. Finally, flow cytometric analysis of whole blood from infected chickens showed that L10H had a significantly higher count of all assessed leucocyte subsets on day 5 pi, and also a higher count of monocytes on day 12 pi than L10L. No difference was observed between infected and non-infected L10L chicken.

Dynamic changes in cell-surface expression of mannose in the oral epithelium during the development of graft-versus-host disease of the oral mucosa in rats

Background

The role of cell-surface glycoconjugates in oral mucosal graft-versus-host disease (GVHD) is still unclear, even though molecular changes in the oral epithelium are essential for the pathogenesis of these lesions. In this study, we investigated changes in the binding of mannose (Man)-specific Lens culinaris lectin (LCA) in the oral mucosa of rats with GVHD.

Methods

Lewis rat spleen cells were injected into (Lewis x Brown Norway) F₁ rats to induce systemic GVHD, including oral mucosal lesions. Tongue and spleen samples were evaluated using lectin histochemistry, immunohistochemistry, Western blotting, transwell migration assays and Stamper-Woodruff binding assays.

Results

Binding of Man-specific LCA expanded to the epithelial layers of the tongue in GVHD-rats. An expansion of LCA binding was related to the increased expression of mannosyltransferase in the oral mucosa. CD8⁺ cells, effector cells of oral mucosal GVHD, expressed mannose-binding protein (MBP) and migrated to the medium containing Man in the transwell migration assay. Adherence of CD8⁺ cells to the oral epithelium could be inhibited by pretreating CD8⁺ cells with MBP antibody and/or by pretreating sections with Man-specific LCA.

Conclusions

Increased expression of Man on keratinocytes leads to the migration and/or adhesion of CD8⁺ cells in the surface epithelium, which is mediated in part by the MBP/Man-binding pathway during the development of oral mucosal GVHD.

Low mannose-binding lectin (MBL) is associated with paediatric inflammatory bowel diseases and ileal involvement in patients with Crohn disease

BACKGROUND

Mannose-binding lectin (MBL) is a pattern-recognition molecule of the innate immune system and may be involved in the pathogenesis of inflammatory bowel disease (IBD). Our aim was to assess the prevalence of MBL deficiency in a cohort of patients with paediatric-onset IBD and study whether it is associated with the clinical manifestations, serum antibody formation, or genetic factors.

METHODS

This prospective study included 159 paediatric patients (mean age: 14.0 years) with IBD [107 patients with Crohn disease (CD) and 52 patients with ulcerative colitis (UC)]. Furthermore, 95 controls were investigated. Serum samples were determined for MBL by enzyme-linked immunosorbent assay (ELISA) and for serologic markers [autoantibodies against Saccharomyces cerevisiae (ASCA) and perinuclear components of neutrophils (pANCA)] by indirect immunofluorescent assay. NOD2/CARD15 variants were tested by polymerase chain reaction/restriction fragment length polymorphism.

RESULTS

The MBL serum concentration was significantly lower in IBD patients(both with CD and UC) compared to controls (IBD, p=0.007, CD, p=0.04, UC p=0.004). Prevalence of low MBL level (<500 ng/mL) was significantly higher in both CD and UC groups compared to controls (p=0.002 and p=0.006). Furthermore, low MBL level was associated with isolated ileal involvement (p=0.01) and MBL deficiency (<100 ng/mL) with male gender (p=0.004) in patients with CD. We failed to confirm any correlation between MBL deficiency and serum autoantibodies or NOD2/CARD15 variants.

CONCLUSIONS

Our results suggest that low MBL associated with paediatric-onset IBD and ileal CD may be considered an additional marker of the IBD pathogenesis.

Mannose-binding lectin regulates host resistance and pathology during experimental infection with Trypanosoma cruzi

Mannose-binding lectin (MBL) is a humoral pattern-recognition molecule important for host defense. Although recent genetic studies suggest an involvement of MBL/MASP2-associated pathways in Chagas’ disease, it is currently unknown whether MBL plays a role in host resistance to the intracellular protozoan Trypanosoma cruzi, the causative agent of Chagas’ disease. In this study we employed MBL^−/− mice to assess the role of MBL in resistance to experimental infection with T. cruzi. T. cruzi infection enhanced tissue expression of MBL both at the mRNA and protein level. Similarly, symptomatic acute Chagas’ disease patients displayed increased serum concentrations of MBL compared to patients with indeterminate, asymptomatic forms of the disease. Furthermore, increased parasite loads in the blood and/or tissue were observed in MBL^−/− mice compared to WT controls. This was associated with reduced systemic levels of IL-12/23p40 in MBL^−/− mice. Importantly, MBL^−/− mice infected with a cardiotropic strain of T. cruzi displayed increased myocarditis and cardiac fibrosis compared to WT controls. The latter was accompanied by elevated hydroxyproline content and mRNA levels of collagen-1 and -6 in the heart. These observations point to a previously unappreciated role for MBL in regulating host resistance and cardiac inflammation during infection with a major human pathogen.

Association between mannose-binding lectin gene polymorphisms and necrotizing enterocolitis in preterm infants

OBJECTIVES

The aim of the present study was to evaluate whether polymorphisms of the mannose-binding lectin (MBL-2) gene and MBL serum levels on admission to neonatal intensive care unit are associated with necrotizing enterocolitis (NEC) in preterm infants and to verify MBL expression in NEC bowels.

METHODS

In this retrospective cohort study, 107 neonates (41 with NEC and 66 controls) were included. MBL-2 genotyping for the promoter polymorphism -221 and for the exon 1 variant alleles at codons 52, 54, and 57 was performed. MBL levels were determined by enzyme-linked immunosorbent assay in 55 infants. Immunohistochemical staining for MBL expression was performed on bowel specimens. The main study outcome was severe NEC (Bell stages II/III).

RESULTS

The -221 Y allele and the MBL-2 YY genotype were more frequent in neonates with severe NEC than in controls (P = 0.04 and P = 0.004, respectively). In the multivariate analysis, the MBL-2 YA/YA genotype was associated with NEC (odds ratio = 3.03, 95% confidence interval 1.13%-8.13%, P = 0.024). Neonates with NEC had MBL level on admission >400 ng/mL more frequently than controls (P = 0.043). Among neonates with severe NEC, the deceased neonates were carriers of high or intermediate producing MBL-2 genotypes (P = 0.035). Finally, MBL was highly expressed in intestinal tissue from infants with NEC.

CONCLUSIONS

MBL-2 genotypes associated with high MBL serum levels represent a risk factor for NEC. This finding, together with the MBL expression in bowel tissue, supports a role for MBL in the pathogenesis of NEC.

Development of mannosylated liposomes using synthesized N-octadecyl-D-mannopyranosylamine to enhance gastrointestinal permeability for protein delivery

The lysozyme (LZ)-entrapped mannosylated liposomes were prepared in this study by the use of N-octadecyl-D-mannopyranosylamine (SAMAN), which had been synthesized in-house and confirmed by characterization with FTIR and NMR. The reactant residues of synthesized SAMAN were found to be less than 1%. The mean sizes, zeta potentials, drug entrapment efficiencies, and loading capacities of all liposomal formulations were in the ranges of 234.7 to 431.0 nm, -10.97 to -25.80 mV, 7.52 to 14.10%, and 1.44 to 2.77%, respectively. The permeability of mannosylated LZ liposomes across Caco-2 cell monolayers was significantly enhanced to about 2.5- and 7-folds over those of conventional liposomes and solution, respectively, which might be due to the role of mannose receptor or mannose-binding protein on the intestinal enterocytes.

Mannose-binding lectin and the balance between immune protection and complication

The innate immune system is evolutionarily ancient and biologically primitive. Historically, it was first identified as an element of the immune system that provides the first-line response to pathogens, and increasingly it is recognized for its central housekeeping role and its essential functions in tissue homeostasis, including coagulation and inflammation, among others. A pivotal link between the innate immune system and other functions is mannose-binding lectin (MBL), a pattern recognition molecule. Multiple studies have demonstrated that MBL deficiency increases susceptibility to infection, and the mechanisms associated with this susceptibility to infection include reduced opsonophagocytic killing and reduced activation of the lectin complement pathway. Results from our laboratory have demonstrated that MBL and MBL-associated serine protease (MASP)-1/3 together mediate coagulation factor-like activities, including thrombin-like activity. MBL and/or MASP-1/3-deficient hosts demonstrate in vivo evidence that MBL and MASP-1/3 are involved with hemostasis following injury. Staphylococcus aureus-infected MBL null mice developed disseminated intravascular coagulation, which was associated with elevated blood IL-6 levels (but not TNF-α) and systemic inflammatory responses. Infected MBL null mice also develop liver injury. These findings suggest that MBL deficiency may manifest as disseminated intravascular coagulation and organ failure with infection. Beginning from these observations, this review focuses on the interaction of innate immunity and other homeostatic systems, the derangement of which may lead to complications in infection and other inflammatory states.

Mannose-binding lectin binds to amyloid β protein and modulates inflammation

Mannose-binding lectin (MBL), a soluble factor of the innate immune system, is a pattern recognition molecule with a number of known ligands, including viruses, bacteria, and molecules from abnormal self tissues. In addition to its role in immunity, MBL also functions in the maintenance of tissue homeostasis. We present evidence here that MBL binds to amyloid β peptides. MBL binding to other known carbohydrate ligands is calcium-dependent and has been attributed to the carbohydrate-recognition domain, a common feature of other C-type lectins. In contrast, we find that the features of MBL binding to Aβ are more similar to the reported binding characteristics of the cysteine-rich domain of the unrelated mannose receptor and therefore may involve the MBL cysteine-rich domain. Differences in MBL ligand binding may contribute to modulation of inflammatory response and may correlate with the function of MBL in processes such as coagulation and tissue homeostasis.

THE ROLE OF SPECIFIC IgG AND COMPLEMENT IN COMBATING A PRIMARY MUCOSAL INFECTION OF THE GUT EPITHELIUM

The role of complement and complement-fixing IgG isotypes at mucosal surfaces is ill defined. Previous data have demonstrated that survival of an infection with the attaching and effacing pathogen Citrobacter rodentium requires production of systemic and CD4+ T cell-dependent IgG. We have found that both complement and complement-fixing IgG isotypes are needed to survive a C. rodentium infection. Our results indicate that both IgG and complement C3b enter the gut lumen and bind epithelially adherent, and fecally shed C. rodentium. Furthermore, C3-deficient mice demonstrate a profound survival defect, though means to replenish C3 in systemic or mucosal sites restores the protective capacity of complement in the host. Our data provide evidence that both IgG and complement interact constructively on both sides of the epithelium to fight colonizing mucosal infections.

Influence of dietary ingredients on in vitro inflammatory response of intestinal porcine epithelial cells challenged by an enterotoxigenic Escherichia coli (K88)

Enterotoxigenic Escherichia coli (ETEC) K88 is the main bacterial cause of diarrhea in piglets around weaning and the adhesion of ETEC to the intestinal mucosa is a prerequisite step for its colonization. In this study, the adhesion of a fimbriated ETEC and a non-fimbriated E. coli (NFEC) to the intestinal cells and the activation of the innate immune system were evaluated using a porcine intestinal epithelial cell line (IPEC-J2). The impact of several feedstuffs (wheat bran (WB); casein glycomacropeptide (CGMP); mannan-oligosaccharides (MOS); locust bean extract (LB) and Aspergillus oryzae fermentation extract (AO)) on ETEC attachment and the inflammatory response were also studied. The gene expression of TLR-4; TLR-5; IL-1β; IL-8; IL-10 and TNF-α were quantified using Cyclophilin-A, as a reference gene, and related to a non-challenged treatment. The fimbriated strain was markedly better than the non-fimbriated strain at adherence to intestinal cells and inducing an inflammatory response. All the feedstuffs studied were able to reduce the adhesion of ETEC, with the greatest decrease with CGMP or MOS at highest concentration. Regarding the inflammatory response, the highest dose of WB promoted the lowest relative expression of cytokines and chemokines. All tested feedstuffs were able to reduce the adhesion of ETEC to IPEC-J2 and interfere on the innate inflammatory response; however WB should be further studied according to the beneficial results on the intestinal inflammatory process evidenced in this study.

High levels of mannose-binding lectin are associated with poor outcomes after lung transplantation

BACKGROUND

Mannose-binding lectin (MBL) is a key molecule of the innate immune system and, in addition to the classical and alternative pathways, a principle driver of complement activation. Genetic mutations of MBL are common, result in low serum levels of MBL, and are associated with increased infection risk in solid-organ transplant recipients.

METHODS

We performed a retrospective study of MBL2 genotype and plasma and bronchoalveolar lavage (BAL) MBL levels in 37 lung transplant recipients (LTR). Plasma MBL levels were measured pretransplant and both plasma and BAL MBL levels were measured at 3, 6, and 12 months after lung transplantation. MBL2 genotyping was performed on recipient and donor peripheral blood mononuclear cells. Clinical variables analyzed included primary graft dysfunction, intensive care unit stay, acute allograft rejection, infection, bronchiolitis obliterans syndrome (BOS), and mortality.

RESULTS

Plasma MBL levels posttransplant were predicted by recipient, and not donor MBL2 genotype. Compared with pretransplant levels, plasma MBL was significantly increased at 3, 6, and 12 months posttransplant (P<0.05). LTR who developed BOS or died during the study period had higher plasma MBL levels at 6 and 12 months posttransplant (P ≤ 0.05) compared with LTR with stable graft function. MBL was not routinely detected in the lung allograft; however if present in the BAL at 3 and 6 months posttransplant, it was associated with the later development of BOS (P<0.05).

CONCLUSIONS

Plasma MBL levels increase after lung transplantation and persistently increased MBL levels are associated with poor long-term outcomes.

Functional analysis of agalactosyl IgG in inflammatory bowel disease patients

BACKGROUND

Agalactosyl immunoglobulin (Ig) G is increased in inflammatory bowel disease (IBD) similarly to rheumatoid arthritis (RA). The lectin complement pathway is shown to be activated through association of agalactosyl IgG with mannan-binding lectin (MBL) in RA. Functional changes of IgG agalactosylation in IBD, however, have not yet been clarified.

METHODS

The ratio of the agalactosyl/non-agalactosyl fraction in fucosylated IgG oligosaccharides (G0F/G2F) and serum MBL levels were analyzed in 59 patients with Crohn's disease (CD), 64 ulcerative colitis (UC), and 39 healthy volunteers (HV). The MBL levels associated with serum IgG were analyzed by enzyme-linked immunosorbent assay. MBL expression in the intestinal mucosa was analyzed by immunohistochemistry. Phagocytosis of sheep red blood cells (SRBC) reacted with either an agalactosyl or non-agalactosyl SRBC-specific IgG antibody was determined by flow cytometry.

RESULTS

The serum MBL levels were not significantly different among CD, UC, or HV. In patients with CD, the serum MBL levels were negatively correlated with the Crohn's Disease Activity Index (CDAI). The levels of MBL associated with agalactosyl IgG were not different from those associated with non-agalactosyl IgG. Immunoreactivity to MBL was less in the inflamed mucosa compared with the noninflamed mucosa. Phagocytic activity of SRBC was significantly higher in the presence of agalactosyl IgG compared to non-agalactosyl IgG.

CONCLUSIONS

Agalactosyl IgG oligosaccharides enhanced antibody-dependent phagocytosis in vitro but did not activate the lectin complement pathway. Oligosaccharide alterations of IgG are not only a marker of IBD but also functionally modulate the immune function of IBD.

Demonstration of substances of innate immunity in the esophageal epithelium of domesticated mammals: Part II--Defence mechanisms, including species comparison

The second part of our study deals with a comparative evaluation and discussion of the immunohistochemical results that were obtained. The cryoscanning electron microscopy (cryoSEM) observations confirmed a monolayer colonization of the esophageal surface with bacteria and fungi (yeasts); the latter in particular was prominent in the ruminant species studied. We demonstrated the existence of several innate immune parameters, including pathogen recognition receptors (PRRs), such as Toll-like receptor 2, which was primarily expressed in the stratum basale; however, the presence β-glucan receptors remained inconclusive. Furthermore, the group of cationic antimicrobial peptides (CAPs) was shown, comprising β-defensins 2 and 3 and cathelicidin. The less keratinized esophageal epithelium of the carnivorous cat was protected by high amounts of CAPs; whereas the more strongly keratinized epithelium of the herbivorous and omnivorous species with its characteristic layer structure exhibited clearly weaker reactions. Moreover, lysozyme could distinctly be demonstrated in the cells of the esophageal epithelium. It can be concluded that a first line of defence mechanisms of the innate immune system contributes to maintaining a microbial homeostasis on the surface of the esophageal epithelium of domesticated mammals. The results are discussed in comparison to findings from studies on the human esophagus.

Demonstration of substances of innate immunity in the esophageal epithelium of domesticated mammals. Part I--Methods and evaluation of comparative fixation

The aim of the investigation was to demonstrate that the esophageal epithelium of domesticated mammals exhibits characteristic features of innate immunity. The esophageal samples used were obtained immediately after euthanization from seven species of domesticated mammals of three nutrition groups (herbivores: horse, goat, cattle; omnivores: pig, dog, laboratory rat; carnivores: cat). The experimental basis was immunohistochemistry, which was evaluated in a qualitative and statistically relevant semi-quantitative manner. The first part of the study analyzed the influence of different fixation media on the immunohistochemical reactivities. Two formalin-based routine fixation solutions (Bouin's solution, Ca-acetate formalin) were compared with the recently introduced formalin-free HOPE® fixative. In this context, we clearly demonstrated a diminished immunoreactivity for Ca-formol fixed samples; satisfactory results were obtained, particularly, from samples fixed in Bouin's solution. The HOPE® fixation method offers a relatively cheap alternative, as the antibody amounts can be reduced. An application in routine diagnostic is not advisable, because of several variable parameters. It can be concluded that immunohistochemical results have always to be evaluated and discussed in close relation to the fixation medium used.

Recombinant chimeric lectins consisting of mannose-binding lectin and L-ficolin are potent inhibitors of influenza A virus compared with mannose-binding lectin

MBL structurally contains a type II-like collagenous domain and a carbohydrate recognition domain (CRD). We have recently generated three novel recombinant chimeric lectins (RCL), in which varying length of collagenous domain of mannose-binding lectin (MBL) is replaced with that of L-ficolin (L-FCN). CRD of MBL is used for target recognition because it has a broad spectrum in pathogen recognition compared with L-FCN. Results of our study demonstrate that these RCLs are potent inhibitors of influenza A virus (IAV). RCLs, against IAV, show dose-dependent activation of the lectin complement pathway, which is significantly higher than that of recombinant human MBL (rMBL). This activity is observed even without MBL-associated serine proteases (MASPs, provided by MBL deficient mouse sera), which have been thought to mediate complement activation. These observations suggest that RCLs are more efficient in associating with MASP-2, which predominantly mediates the activity. Yet, additional serum further increases the activity while RCL-mediated coagulation-like enzyme activities are diminished compared with rMBL, suggesting reduced association with MASP-1, which has been shown to mediate coagulation-like activity. These data suggest that RCLs may interfere less with host coagulation, which is advantageous to be a therapeutic drug. Importantly, these RCLs have surpassed rMBL for anti-viral activities, such as viral aggregation, reduction of viral hemagglutination (HA) and inhibition of virus-mediated HA and neuraminidase (NA) activities. These results are encouraging that novel RCLs could be used as anti-IAV agents with less side effect and that RCLs would be suitable candidates in developing a new anti-IAV therapy.

A Sequential Model of Host Cell Killing and Phagocytosis by Entamoeba histolytica

The protozoan parasite Entamoeba histolytica is responsible for invasive intestinal and extraintestinal amebiasis. The virulence of Entamoeba histolytica is strongly correlated with the parasite's capacity to effectively kill and phagocytose host cells. The process by which host cells are killed and phagocytosed follows a sequential model of adherence, cell killing, initiation of phagocytosis, and engulfment. This paper presents recent advances in the cytolytic and phagocytic processes of Entamoeba histolytica in context of the sequential model.

Lack of the pattern recognition molecule mannose-binding lectin increases susceptibility to influenza A virus infection

Background

Mannose-binding lectin (MBL), a pattern recognition innate immune molecule, inhibits influenza A virus infection in vitro. MBL deficiency due to gene polymorphism in humans has been associated with infection susceptibility. These clinical observations were confirmed by animal model studies, in which mice genetically lacking MBL were susceptible to certain pathogens, including herpes simplex virus 2.

Results

We demonstrate that MBL is present in the lung of naïve healthy wild type (WT) mice and that MBL null mice are more susceptible to IAV infection. Administration of recombinant human MBL (rhMBL) reverses the infection phenotype, confirming that the infection susceptibility is MBL-mediated. The anti-viral mechanisms of MBL include activation of the lectin complement pathway and coagulation, requiring serum factors. White blood cells (WBCs) in the lung increase in WT mice compared with MBL null mice on day 1 post-infection. In contrast, apoptotic macrophages (MΦs) are two-fold higher in the lung of MBL null mice compared with WT mice. Furthermore, MBL deficient macrophages appear to be susceptible to apoptosis in vitro. Lastly, soluble factors, which are associated with lung injury, are increased in the lungs of MBL null mice during IAV infection. These results suggest that MBL plays a key role against IAV infection.

Conclusion

MBL plays a key role in clearing IAV and maintaining lung homeostasis. In addition, our findings also suggest that MBL deficiency maybe a risk factor in IAV infection and MBL may be a useful adjunctive therapy for IAV infection.

Collectin 11 (CL-11, CL-K1) is a MASP-1/3-associated plasma collectin with microbial-binding activity

Collectins play important roles in the innate immune defense against microorganisms. Recently, a new collectin, collectin 11 (CL-11 or CL-K1), was identified via database searches. In present work, we characterize the structural and functional properties of CL-11. Under nonreducing conditions, in gel permeation chromatography recombinant CL-11 forms disulfide-linked oligomers of 100 and 200 kDa. A mAb-based ELISA estimates the concentration of CL-11 in plasma to be 2.1 μg/ml, and the presence of CL-11 in plasma was further verified by Western blotting and mass spectrometry. Mannan-binding lectin-associated serine protease 1 (MASP-1) copurified with CL-11 and the interaction in plasma with MASP-1 and/or MASP-3 was further demonstrated using ELISA. We identified the adrenal glands, the kidneys, and the liver as primary sites of expression. CL-11 lectin activity was demonstrated by ELISA and showed that CL-11 has preference for l-fucose and d-mannose. We finally show that CL-11 binds to intact bacteria, fungi, and viruses and that CL-11 decreases influenza A virus infectivity and forms complexes with DNA. On the basis of the significant concentration of CL-11 in circulation and CL-11's interaction with various microorganisms and MASP-1 and/or MASP-3, it is conceivable that CL-11 plays a role in activation of the complement system and in the defense against invading microorganisms.

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

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

Mannose-binding lectin and its associated proteases (MASPs) mediate coagulation and its deficiency is a risk factor in developing complications from infection, including disseminated intravascular coagulation

The first line of host defense is the innate immune system that includes coagulation factors and pattern recognition molecules, one of which is mannose-binding lectin (MBL). Previous studies have demonstrated that MBL deficiency increases susceptibility to infection. Several mechanisms are associated with increased susceptibility to infection, including reduced opsonophagocytic killing and reduced lectin complement pathway activation. In this study, we demonstrate that MBL and MBL-associated serine protease (MASP)-1/3 together mediate coagulation factor-like activities, including thrombin-like activity. MBL and/or MASP-1/3 deficient hosts demonstrate in vivo evidence that MBL and MASP-1/3 are involved with hemostasis following injury. Staphylococcus aureus infected MBL null mice developed disseminated intravascular coagulation (DIC), which was associated with elevated blood IL-6 levels (but not TNF-α and multi-organ inflammatory responses). Infected MBL null mice also develop liver injury. These findings suggest that MBL deficiency may manifest into DIC and organ failure during infectious diseases.

Protective role of mouse MBL-C on intestinal mucosa during Shigella flexneri invasion

Mannan-binding lectin (MBL) is a C-type serum lectin, which is believed to play an important role in the innate immunity against a variety of pathogens. MBL can bind to sugar determinants of a wide variety of microorganisms, neutralize them and inhibit infection by complement activation through the lectin pathway and opsonization by collectin receptors. Given that small intestine is a predominant site of extrahepatic expression of MBL, here we addressed the question whether MBL is involved in mucosal innate immunity. The carbohydrate recognition domain (CRD) genes of mouse MBL-C (mMBL-C) were cloned and expressed in Escherichia coli. Recombinant mMBL-C-CRD binds to Shigella flexneri 2a in a calcium-dependent manner and that interaction could be blocked by the anti-mMBL-C-CRD antibody. mMBL-C-CRD protein could inhibit the adhesion of S. flexneri 2a to intestinal mucosa, while administration of anti-mMBL-C-CRD antibody caused an increased level of bacteria adhesion in vitro. Administration of recombinant mMBL-C-CRD protein reduced the secretion of IL-6 and monocyte chemoattractant protein 1 from primary intestinal epithelial cells stimulated with S. flexneri 2a. Furthermore, neutralization of MBL activity by anti-MBL-C-CRD resulted in a significant increase in the number of S. flexneri 2a that colonized the intestines of BALB/c mice and attenuated the severity of inflammation seen in the areas of bacterial invasion. These findings suggest that mMBL-C may protect host intestinal mucosa by directly binding to the bacteria.

Mannose-binding lectin null alleles are associated with preserved epithelial cell integrity following intestinal ischemia reperfusion in man

Mannose-binding lectin (MBL) deficiency is associated with reduced intestinal ischemia-reperfusion (IR) damage in rodents. We set out to investigate an association between frequently observed MBL deficiency and IR associated intestinal cell damage in man. Using a newly developed IR model of the human small intestine 29 patients were consecutively included. Part of the jejunum was subjected to 30 min of ischemia and reperfusion. The MBL genotype was assessed by means of quantitative-PCR analysis. Enterocyte loss was explored by measuring plasma intestinal-fatty acid binding protein (I-FABP) levels. Arterial and venous MBL plasma levels were measured to assess MBL consumption, MBL deposition was analyzed by immunofluorescence. Ethical approval and informed consent were obtained. The amount of epithelial cell damage varied significantly between the carriers of different mbl2 genotypes (ANOVA, p=0.02). I-FABP release, representing disintegration of differentiated enterocytes, observed in homozygous wildtype individuals was twice (p=0.03) that measured in heterozygous and ten times (p=0.04) that observed in homozygous variant individuals. No MBL deposition was observed over the course of reperfusion. The data indicate that MBL influences intestinal epithelial cell integrity in an immediate and non-complement dependent manner during ischemia and reperfusion.

C-type lectins and phagocytosis

To recognise and respond to pathogens, germ-line encoded pattern recognition receptors (PRRs) bind to conserved microbial structures and activate host defence systems, including microbial uptake by phagocytosis. Phagocytosis is a complex process that is instrumental in the control of extracellular pathogens, and this activity is mediated by several PRRs, including a number of C-type lectins. While some of these receptors have clearly been shown to mediate or regulate the uptake of pathogens, others are more contentious and are less well understood in terms of their phagocytic potential. Furthermore, very little is known about the underlying phagocytic mechanisms. Here, we review the phagocytic roles of the mannose receptor, Dectin-1, dendritic cell-specific ICAM grabbing non-integrin (DC-SIGN), DCL-1, mannose binding lectin and surfactant proteins A and D.

Lessons learned from murine models of mannose-binding lectin deficiency

MBL (mannose-binding lectin) is a pattern recognition molecule and a component of innate immunity, the first line of the host defence system against foreign bodies and pathogens. MBL deficiency is common in humans and has been associated with immunodeficiency. We have generated mouse models of MBL deficiency in order to explore the molecular mechanisms of MBL function in disease and health. In addition to confirming findings from human clinical research, these model studies have uncovered unexpected roles of MBL and evidence of its interaction with other molecules of the innate immune system.

A novel C-type lectin from the shrimp Litopenaeus vannamei possesses anti-white spot syndrome virus activity

C-type lectins play key roles in pathogen recognition, innate immunity, and cell-cell interactions. Here, we report a new C-type lectin (C-type lectin 1) from the shrimp Litopenaeus vannamei (LvCTL1), which has activity against the white spot syndrome virus (WSSV). LvCTL1 is a 156-residue polypeptide containing a C-type carbohydrate recognition domain with an EPN (Glu(99)-Pro(100)-Asn(101)) motif that has a predicted ligand binding specificity for mannose. Reverse transcription-PCR analysis revealed that LvCTL1 mRNA was specifically expressed in the hepatopancreas of L. vannamei. Recombinant LvCTL1 (rLvCTL1) had hemagglutinating activity and ligand binding specificity for mannose and glucose. rLvCTL1 also had a strong affinity for WSSV and interacted with several envelope proteins of WSSV. Furthermore, we showed that the binding of rLvCTL1 to WSSV could protect shrimps from viral infection and prolong the survival of shrimps against WSSV infection. Our results suggest that LvCTL1 is a mannose-binding C-type lectin that binds to envelope proteins of WSSV to exert its antiviral activity. To our knowledge, this is the first report of a shrimp C-type lectin that has direct anti-WSSV activity.

C1q- and collectin-dependent phagocytosis of apoptotic host cells by the intestinal protozoan Entamoeba histolytica

BACKGROUND

Entamoeba histolytica, the cause of invasive amebiasis, phagocytoses apoptotic host cells during tissue invasion. In mammals, collectin family members (e.g., mannose-binding lectin [MBL]) and the structurally related protein C1q bind to apoptotic cells and stimulate macrophage phagocytosis via a conserved collagenous tail domain. The collectins also bind to bacteria, the usual source of nutrients for E. histolytica.

METHODS

To test the possibility that the collectins are ligands that stimulate E. histolytica phagocytosis, we used a flow cytometry-based assay for amebic phagocytosis, a method for making single-ligand particles to delineate a given ligand's ability to initiate phagocytosis, and purified human C1q, MBL, and collagenous collectin tails.

RESULTS

Apoptotic lymphocytes opsonized with serum or human C1q were phagocytosed more efficiently than control cells, an effect that was dependent on ligand density. C1q and the collectins alone were adequate to trigger amebic phagocytosis, because single-ligand particles coated with C1q, MBL, or purified collectin tails were phagocytosed more efficiently than control particles. Furthermore, C1q, MBL, and the tail domain of C1q were all chemoattractants for E. histolytica.

CONCLUSIONS

C1q and MBL can serve as opsonins on apoptotic cells that stimulate E. histolytica phagocytosis, an effect mediated at least in part by the collagenous collectin tail domain.

Role of glycan synthesis in colonization of the mammalian gut by the bacterial symbiont Bacteroides fragilis

Bacteroides species are the most abundant Gram-negative bacteria of the human colonic microbiota. These endogenous organisms are unique in that they synthesize an extensive number of phase-variable surface polysaccharides. Pathogenic bacteria phase vary expression of surface molecules for immune evasion, but the importance of the synthesis of multiple phase-variable polysaccharides to these commensal bacteria is unknown. We previously showed that a Bacteroides fragilis mutant unable to synthesize 4 of the 8 capsular polysaccharides and unable to glycosylate proteins properly is rapidly outcompeted by the wild-type strain for colonization of the gnotobiotic mouse intestine. In the present study, we constructed mutants defective only in capsule polysaccharide synthesis to define better the importance of these surface molecules to intestinal colonization. We discovered a key enzymatic activity required for synthesis of 7 of the 8 capsular polysaccharides. Deletion of its gene resulted in the first B. fragilis mutant able to synthesize only one phase-variable polysaccharide, and further mutation resulted in a stable acapsular mutant. We show that the acapsular mutant is rapidly outcompeted, but synthesis of a single polysaccharide is sufficient for the organism to colonize the gnotobiotic intestine competitively. These data demonstrate that initial colonization of the gnotobiotic mouse intestine by B. fragilis requires that the organism synthesize only a single polysaccharide and suggest that the synthesis of multiple phase-variable polysaccharides is important for the bacteria's long-term maintenance in the normally complex and competitive ecosystem.

On the hunt for helminths: innate immune cells in the recognition and response to helminth parasites

The generation of protective immunity to helminth parasites is critically dependent upon the development of a CD4(+) T helper type 2 cytokine response. However, the host-parasite interactions responsible for initiating this response are poorly understood. This review will discuss recent advances in our understanding of how helminth-derived products are recognized by innate immune cells. Specifically, interactions between helminth excretory/secretory products and host Toll-like receptors and lectins will be discussed as well as the putative functions of helminth proteases and chitin in activating and recruiting innate immune cells. In addition, the functional significance of pattern recognition by epithelial cells, granulocytes, dendritic cells and macrophages including expression of alarmins, thymic stromal lymphopoetin, interleukin (IL)-25, IL-33 and Notch ligands in the development of adaptive anti-parasite Th2 cytokine responses will be examined.

Binding and activation of human and mouse complement by Cryptosporidium parvum (Apicomplexa) and susceptibility of C1q- and MBL-deficient mice to infection

Cryptosporidium parvum is a protozoan parasite (Apicomplexa) that causes gastrointestinal disease in animals and humans. Whereas immunocompetent hosts can limit the infection within 1 or 2 weeks, immunocompromised individuals develop a chronic, life-threatening disease. The importance of the adaptive cellular immune response, with CD4+ T-lymphocytes being the major players, has been clearly demonstrated. Several non-adaptive immune mechanisms have been suggested to contribute to the host defence, such as interferon-gamma (IFN-gamma) from NK cells, certain chemokines, beta-defensins and pro-inflammatory cytokines, but the influence of the complement systems has been less well studied. We analysed the in vitro binding and activation of the human and mouse complement systems and tested the susceptibility to infection in complement-deficient mouse strains. We found that C. parvum can activate both the classical and lectin pathways, leading to the deposition of C3b on the parasite. Using real-time PCR, parasite development could be demonstrated in adult mice lacking mannan-binding lectin (MBL-A/C-/-) but not in mice lacking complement factor C1q (C1qA-/-) or in wild type C57BL/6 mice. The contribution of the complement system and the lectin pathway in particular to the host defence against cryptosporidiosis may become apparent in situations of immunodeficiency such as HIV infections or in early childhood.

Possible immune functions of congerin, a mucosal galectin, in the intestinal lumen of Japanese conger eel

Congerin, a mucosal galectin of the Japanese conger eel, provides chemical fortification through its agglutinating and opsonizing activity. Congerin is produced in the epidermis, and the epithelia of the oral cavity to the esophagus, but not in the stomach or intestine. We hypothesized that congerin secreted from the upper digestive tract can reach and function in the intestinal lumen. We found that congerin possessed marked resistance against digestion by gastric and enteric enzymes of conger eel. It was not degraded until 6h of incubation with stomach extract or intestinal digestion juice. Western blotting demonstrated that congerin essentially remained in the intestinal mucus. The mucus agglutinated rabbit erythrocytes, and the agglutination was hampered by anti-congerin antibody. Furthermore, congerin could bind to some enteric bacteria. These results support the above hypothesis.

Association of deficiency for mannan-binding lectin with anti-mannan antibodies in Crohn's disease: a family study

BACKGROUND

Antibodies against mannan, a component of the yeast Saccharomyces cerevisiae cell wall, are more frequently found in Crohn's disease (CD) patients with low levels of mannan-binding lectin (MBL). MBL concentration depends on genetic polymorphisms. The aim of this study was to evaluate whether low MBL is related to ASCA production in healthy family members of CD patients.

METHODS

ASCA and MBL concentrations in sera from patients (n=52), and their 158 healthy relatives were measured by enzyme-linked immunosorbent assay (ELISA). Genetic MBL variants were determined by DNA sequencing.

RESULTS

Thirty-five (67%) patients were ASCA-positive. Twenty-six (74%) of the 35 ASCA-positive patients had low MBL levels (<500 ng/mL), whereas only 4 (24%) of the 17 ASCA-negative patients had low values for MBL (P=0.001). ASCA were found in 38 (24%) family members. Twenty-three (50%) of 46 family members with low values for MBL were ASCA-positive compared to 15 (13%) of 112 family members with normal values for MBL (P<0.0001). ASCA were found in 33 of 104 (32%) family members of ASCA-positive patients and in 5 family members (9%) of ASCA-negative patients (P=0.002). Relatives with mutations leading to MBL deficiency had significantly more frequent ASCA than relatives without these mutations (P=0.018).

CONCLUSIONS

MBL deficiency is associated with ASCA positivity not only in patients with CD, but also in their relatives. An impaired innate immune system defined by low MBL serum concentrations may lead to an increased reactivity of the specific immune system to mannan antigens, and therefore facilitate the generation of ASCA.

Binding of mouse mannan-binding lectins to different bacterial pathogens of mice

Humans have one mannan-binding lectin (MBL) in circulation but rodents, pigs, rabbits and rhesus monkeys have two, MBL-A and MBL-C. Plasma forms of these proteins have similar mannan-binding activity in vitro, but might differ in their ability to bind other microbial targets. In these studies, we compared carbohydrate-dependent binding of mouse plasma MBL-A and MBL-C to mannan-sepharose beads and to intact bacteria isolated as pathogens from mice. After incubation of mouse plasma with intact bacteria, MBL-A and MBL-C were eluted with N-acetylglucosamine (GlcNAc) and identified in nonreducing SDS-PAGE using Western blot analysis and MBL-A or MBL-C specific monoclonal antibodies. GlcNAc eluates of plasma incubated with mannan-sepharose beads, Klebsiella oxytoca and Staphylococcus aureus contained similar bands (mainly approximately 50kDa) that were immunoreactive with MBL-C antibody. Furthermore, a smaller form of MBL-C (approximately 45kDa) was detected bound to Pseudomonas aeruginosa. By comparison, immunoreactive MBL-A (a ladder of approximately 175kDa and larger bands) was identified in these GlcNAc eluates from mannan-sepharose beads, S. aureus and K. oxytoca but not P. aeruginosa. These studies demonstrate that mouse MBL-A and MBL-C in plasma are not equivalent in their ability to recognize bacteria that are pathogens for mice.

Burn injury reveals altered phenotype in mannan-binding lectin-deficient mice

Burn injury destroys skin, the second largest innate immune organ in the body, and triggers chaotic immune and inflammatory responses. The pattern recognition molecule, mannan-binding lectin (MBL), plays an important role in the first-line host defense against infectious agents. MBL initiates the lectin complement pathway and acts as an opsonin. Recent studies suggest that MBL also modulates inflammatory responses. We report that local responses after burn in MBL null mice differ from those found in wild-type (WT) mice in the following important biological markers: spontaneous eschar separation, thinned epidermis and dermis, upregulation of soluble factors including cytokines, chemokines, cell adhesion molecules, a growth factor-binding protein, and matrix metalloproteinases. Mice lacking C1q, C4, or C3 did not show the lack of eschar separation seen in MBL null-burn phenotype. These findings implicate MBL as an important molecule in the maintenance of the homeostatic balance.

Mannose-binding lectin and maladies of the bowel and liver

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

Characterization of a Novel C-Type Lectin, Bombyx mori Multibinding Protein, from the B. mori Hemolymph: Mechanism of Wide-Range Microorganism Recognition and Role in Immunity

To investigate the system used by insects to recognize invading microorganisms, we examined proteins from the larval hemolymph of Bombyx mori that bind to the cell surface of microorganisms. Two hemolymph proteins that bound to the cell surfaces of Micrococcus luteus and Saccharomyces cerevisiae were shown to be identical. This protein bound to all 11 microorganisms examined-5 Gram-negative bacteria, 3 Gram-positive bacteria, and 3 yeasts-and was consequently designated B. mori multibinding protein (BmMBP). The sequence of the cDNA encoding BmMBP revealed that it was a C-type lectin with two dissimilar carbohydrate-recognition domains (CRD1 and CRD2) distantly related to known insect C-type lectins. CRD1 and CRD2 were prepared as recombinant proteins and their binding properties were investigated using inhibition assays. Each domain had wide, dissimilar binding spectra to sugars. These properties enable BmMBP to bind to two sites on a microorganism, facilitating high-affinity binding to many types of microorganisms. The dissociation constants of BmMBP with M. luteus cells and S. cerevisiae were 1.23 x 10(-8) and 1.00 x 10(-11) M, respectively. rBmMBP triggered the aggregation of hemocytes from B. mori larvae in vitro and microorganisms recognized by BmMBP were surrounded by aggregated hemocytes in vivo, forming a nodule, which is the typical cellular reaction in insect immune responses. These observations suggest that BmMBP functions as a trigger for the nodule reaction and that the multirecognition characteristic of BmMBP plays an important role in the early stages of infection by a variety of microorganisms.