Mannose-binding lectin recognizes peptidoglycan via the N-acetyl glucosamine moiety, and inhibits ligand-induced proinflammatory effect and promotes chemokine production by macrophages

Vicia ervilia lectin (VEA) has an antibiofilm effect on both Gram-positive and Gram-negative pathogenic bacteria

Bacterial growing resistance to antibiotics poses a critical threat to global health. This study investigates, for the first time, the antibiofilm properties of Vicia ervilia agglutinin (VEA) from six different V. ervilia accessions against pathogenic bacteria, and the yeast Candida albicans. In the absence of antimicrobial properties, purified VEA significantly inhibited biofilm formation, both in Gram-positive and Gram-negative bacteria, but not in C. albicans. With an inhibitory concentration ranging from 100 to 500 µg/ml, the VEA antibiofilm activity was more relevant against the Gram-positive bacteria Streptococcus aureus and Staphylococcus epidermidis, whose biofilm was reduced up to 50% by VEA purified from accessions #5 and #36. VEA antibiofilm variability between accessions was observed, likely due to co-purified small molecules rather than differences in VEA protein sequences. In conclusion, VEA seed extracts from the accessions with the highest antibiofilm activity could represent a valid approach for the development of an effective antibiofilm agent.

MBL2 gene variants and susceptibility to meningitis in Egyptian patients

BACKGROUND

Meningitis is inflammation of the membranes enclosing the brain and spinal cord. It is a fatal disease with severe morbidity and mortality. Mannose binding lectin (MBL) encoded by MBL2 gene activates complement system through lectin pathway in innate immunity to defense against the infections.

OBJECTIVE

the current study aimed to investigate the promoter and exon 1 variants of MBL2 gene among Egyptian patients having meningitis to explore their role in disease susceptibility.

PATIENTS AND METHODS

This case-control study, included 53 patients and 50 sex and age matched controls. MBL2 genotyping was done using Sanger sequencing.

RESULTS

The frequency of one promoter (c.-290C>G) and four in exon 1 (c.161G>A, c.170G>A, c.154C>T and c.132C>T) as well as another one located in its 5'utranslated part (c.-66C>T) variants were estimated. The incidence of the four individual exonic variants was not significantly different between cases and healthy individuals (all P> 0.05). The promoter variant, c.-290C>G was found in all examined patients (84.9% of the patients in homozygote state and 15.1% of patients in heterozygous state) with a highly significant variance in the prevalence of this variant between cases and control group (p=0.0001). Additionally, UTR variant (c.-66C>T) was also significantly higher in patients than controls (P=0.033).In comparison with clinical outcome, it was found that c.170G>A variant named C allele was associated with favorable outcome in the studied patients (P=0.025).

CONCLUSION

The results obtained showed that the Promoter (c.-290C>G) and UTR (c.-66 C>T) variants of MBL2 gene may be potential risk factors for disease susceptibility in Egyptian cases with meningitis. Our results also proposed that c.170G>A (C allele and CC genotype) could affect the severity and play a protective role in these patients. The other genetic variants of MBL2 gene, including c.132C>T, c.161G>A (A>B), and c.154C>T (A>D) that were investigated, did not show any association with susceptibility or severity of meningitis.

On the origin of the functional versatility of macrophages

Macrophages represent the most functionally versatile cells in the animal body. In addition to recognizing and destroying pathogens, macrophages remove senescent and exhausted cells, promote wound healing, and govern tissue and metabolic homeostasis. In addition, many specialized populations of tissue-resident macrophages exhibit highly specialized functions essential for the function of specific organs. Sometimes, however, macrophages cease to perform their protective function and their seemingly incomprehensible response to certain stimuli leads to pathology. In this study, we address the question of the origin of the functional versatility of macrophages. To this end, we have searched for the evolutionary origin of macrophages themselves and for the emergence of their characteristic properties. We hypothesize that many of the characteristic features of proinflammatory macrophages evolved in the unicellular ancestors of animals, and that the functional repertoire of macrophage-like amoebocytes further expanded with the evolution of multicellularity and the increasing complexity of tissues and organ systems. We suggest that the entire repertoire of macrophage functions evolved by repurposing and diversification of basic functions that evolved early in the evolution of metazoans under conditions barely comparable to that in tissues of multicellular organisms. We believe that by applying this perspective, we may find an explanation for the otherwise counterintuitive behavior of macrophages in many human pathologies.

Recent Advances in the Synthesis and Biological Applications of Peptidoglycan Fragments

The biosynthesis, breakdown, and modification of peptidoglycan (PG) play vital roles in both bacterial viability and in the response of human physiology to bacterial infection. Studies on PG biochemistry are hampered by the fact that PG is an inhomogeneous insoluble macromolecule. Chemical synthesis is therefore an important means to obtain PG fragments that may serve as enzyme substrates and elicitors of the human immune response. This review outlines the recent advances in the synthesis and biochemical studies of PG fragments, PG biosynthetic intermediates (such as Park's nucleotides and PG lipids), and PG breakdown products (such as muramyl dipeptides and anhydro-muramic acid-containing fragments). A rich variety of synthetic approaches has been applied to preparing such compounds since carbohydrate, peptide, and phospholipid chemical methodologies must all be applied.

Rapid Detection of Gram-Positive and -Negative Bacteria in Water Samples Using Mannan-Binding Lectin-Based Visual Biosensor

Waterborne bacterial infection is a health threat worldwide, making accurate and timely bacteria detection crucial to prevent waterborne disease outbreaks. Inspired by the intrinsic capability of mannan-binding lectin (MBL) in recognizing the pathogen-associated molecular patterns (PAMPs), a visual biosensor is developed here for the on-site detection of both Gram-positive and -negative bacteria. The biosensor was synthesized by immobilization of the MBL protein onto the blue carboxyl-functionalized polystyrene microparticles (PSM), which is then used in a two-step assay to detect bacterial cells in water samples. The first step involved a 20 min incubation following the MBL-PSM and calcium chloride solution addition to the samples. The second step was to add ethanol to the resultant blue mixture and observe the color change with the naked eye after 15 min. The biosensor had a binary (all-or-none) response, which in the presence of bacterial cells kept its blue color, while in their absence the color changed from blue to colorless. Testing the water samples spiked with four Gram-negative bacteria including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa and two Gram-positive bacteria of Enterococcus faecalis and Staphylococcus aureus showed that the biosensor could detect all tested bacteria with a concentration as low as 10^1.5 CFU/ml. The performance of biosensor using the water samples from a water treatment plant also confirmed its capability to detect the pathogens in real-life water samples without the need for instrumentation.

Association of Mannose-Binding Lectin 2 Gene Polymorphism with Tuberculosis Based on Mycobacterium tuberculosis Lineages

Purpose

Polymorphisms in MBL2 may contribute to the susceptibility to tuberculosis. The aim of the present study was to determine the associations of the polymorphisms of five loci (rs1800450, rs1800451, rs7096206, rs7095891, and rs11003125) in the MBL2 gene with susceptibility to tuberculosis and specific lineages of Mycobacterium tuberculosis causing tuberculosis in the Uyghur population of Xinjiang, China.

Methods

From January 2019 to January 2020, we enrolled 170 Uyghur tuberculosis patients as the case group and 147 Uyghur staff with no clinical symptoms as the control group from four designated tuberculosis hospitals in southern Xinjiang, China. The polymorphisms of five loci in MBL2 of human were detected by sequencing. Whole-genome sequencing was applied in 68 M. tuberculosis isolates from the case group and the data were used to perform genealogy analysis.

Results

The distributions of allele and genotype frequencies of five loci in MBL2 varied little between the case and control groups and varied little among the groups, including those infected with different lineages of M. tuberculosis and the control (except those of rs11003125), the P values were all >0.05. The distribution of alleles of rs11003125 was statistically different between patients infected with lineages 3 and 4 M. tuberculosis (χ²=7.037, P=0.008). The C allele and CC genotype of rs11003125 were found to be protective factors against lineage 4 infection when compared to lineage 3 (ORs were 0.190 and 0.158, respectively; 95% confidence intervals were 0.053~0.690 and 0.025~0.999, respectively).

Conclusion

Our results suggested that human’s susceptibility to tuberculosis is affected both by the host genetic polymorphisms and the lineage of the M. tuberculosis that people were exposed to. However, due to the limitation of the sample size in the present study, larger sample size and more rigorous design should be guaranteed in future studies.

Current State of Carbohydrate Recognition and C-Type Lectin Receptors in Pneumocystis Innate Immunity

Pneumocystis jirovecii is one of the most common fungal pathogens in immunocompromised individuals. Pneumocystis jirovecii pneumonia (PJP) causes a significant host immune response that is driven greatly by the organism’s cell wall components including β-glucans and major surface glycoprotein (Msg). These ligands interact with a number of C-type lectin receptors (CLRs) leading to downstream activation of proinflammatory signaling pathways. This minireview provides a brief overview summarizing known CLR/Pneumocystis interactions.

Citral alleviates peptidoglycan-induced inflammation and disruption of barrier functions in porcine intestinal epithelial cells

Peptidoglycan (PGN) is a major polymer in bacterial cell walls and may constrain gut functionality and lower intestinal efficiencies in livestock. Citral has been reported to exhibit antibacterial and anti-inflammatory biological activities, improving the gastrointestinal function of swine. However, the protective effect of citral against PGN-elicited cellular responses and possible underlying mechanisms are unknown. In this study, the porcine jejunal epithelial cell line (IPEC-J2) was challenged with PGN from Staphylococcus aureus (S. aureus) or Bacillus subtilis (B. subtilis) to explore PGN-induced inflammatory responses. Our data showed that the inflammatory response stimulated by PGN from harmful bacteria (S. aureus) was more potent than that from commensal bacteria (B. subtilis) in IPEC-J2 cells. Based on the inflammatory model by PGN from S. aureus, it was demonstrated that PGN could significantly induce inflammatory cytokine production and influence nutrient absorption and barrier function in a dose-dependent manner. However, the PGN-mediated immune responses were remarkably suppressed by citral. In addition, citral significantly attenuated the effect of PGN on the intestine nutrient absorption and barrier function. The expression of TLR2 was strongly induced by PGN stimulation, which was suppressed by citral. All data nominated that citral downregulated PGN-induced inflammation via TLR2-mediated activation of the NF-κB signaling pathway in IPEC-J2 cells. Furthermore, the results also indicate that the PGN degradation through the inclusion of enzymes (e.g., muramidase) as well as the inclusion of citral for attenuating inflammation may improve pig gut health and functionality.

Lymph Node-Targeted Synthetically Glycosylated Antigen Leads to Antigen-Specific Immunological Tolerance

Inverse vaccines that tolerogenically target antigens to antigen-presenting cells (APCs) offer promise in prevention of immunity to allergens and protein drugs and treatment of autoimmunity. We have previously shown that targeting hepatic APCs through intravenous injection of synthetically glycosylated antigen leads to effective induction of antigen-specific immunological tolerance. Here, we demonstrate that targeting these glycoconjugates to lymph node (LN) APCs under homeostatic conditions leads to local and increased accumulation in the LNs compared to unmodified antigen and induces a tolerogenic state both locally and systemically. Subcutaneous administration directs the polymeric glycoconjugate to the draining LN, where the glycoconjugated antigen generates robust antigen-specific CD4+ and CD8+ T cell tolerance and hypo-responsiveness to antigenic challenge via a number of mechanisms, including clonal deletion, anergy of activated T cells, and expansion of regulatory T cells. Lag-3 up-regulation on CD4+ and CD8+ T cells represents an essential mechanism of suppression. Additionally, presentation of antigen released from the glycoconjugate to naïve T cells is mediated mainly by LN-resident CD8+ and CD11b+ dendritic cells. Thus, here we demonstrate that antigen targeting via synthetic glycosylation to impart affinity for APC scavenger receptors generates tolerance when LN dendritic cells are the cellular target.

CNS-localized myeloid cells capture living invading T cells during neuroinflammation

To study the role of myeloid cells in the central nervous system (CNS) in the pathogenesis of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), we used intravital microscopy, assessing local cellular interactions in vivo in EAE animals and ex vivo in organotypic hippocampal slice cultures. We discovered that myeloid cells actively engulf invading living Th17 lymphocytes, a process mediated by expression of activation-dependent lectin and its T cell–binding partner, N-acetyl-D-glucosamine (GlcNAc). Stable engulfment resulted in the death of the engulfed cells, and, remarkably, enhancement of GlcNAc exposure on T cells in the CNS ameliorated clinical EAE symptoms. These findings demonstrate the ability of myeloid cells to directly react to pathogenic T cell infiltration by engulfing living T cells. Amelioration of EAE via GlcNAc treatment suggests a novel first-defense pathway of myeloid cells as an initial response to CNS invasion and demonstrates that T cell engulfment by myeloid cells can be therapeutically exploited in vivo.

Innate Immune Pattern Recognition Receptors of Mycobacterium tuberculosis: Nature and Consequences for Pathogenesis of Tuberculosis

Innate immunity against Mycobacterium tuberculosis is a critical early response to prevent the establishment of the infection. Despite recent advances in understanding the host-pathogen dialogue in the early stages of tuberculosis (TB), much has yet to be learnt. The nature and consequences of this dialogue ultimately determine the path of infection: namely, either early clearance of M. tuberculosis, or establishment of M. tuberculosis infection leading to active TB disease and/or latent TB infection. On the frontline in innate immunity are pattern recognition receptors (PRRs), with soluble factors (e.g. collectins and complement) and cell surface factors (e.g. Toll-like receptors and other C-type lectin receptors (Dectin 1/2, Nod-like receptors, DC-SIGN, Mincle, mannose receptor, and MCL) that play a central role in recognising M. tuberculosis and facilitating its clearance. However, in a 'double-edged sword' scenario, these factors can also be involved in enhancement of pathogenesis as well. Furthermore, innate immunity is also a critical bridge in establishing the subsequent adaptive immune response, which is also responsible for granuloma formation that cordons off M. tuberculosis infection, establishing latency and acting as a reservoir for bacterial persistence and dissemination of future disease. This chapter discusses the current understanding of pattern recognition of M. tuberculosis by innate immunity and the role this plays in the pathogenesis and protection against TB.

Collectins: Innate Immune Pattern Recognition Molecules

Collectins are collagen-containing C-type (calcium-dependent) lectins which are important pathogen pattern recognising innate immune molecules. Their primary structure is characterised by an N-terminal, triple-helical collagenous region made up of Gly-X-Y repeats, an a-helical coiled-coil trimerising neck region, and a C-terminal C-type lectin or carbohydrate recognition domain (CRD). Further oligomerisation of this primary structure can give rise to more complex and multimeric structures that can be seen under electron microscope. Collectins can be found in serum as well as in a range of tissues at the mucosal surfaces. Mannanbinding lectin can activate the complement system while other members of the collectin family are extremely versatile in recognising a diverse range of pathogens via their CRDs and bring about effector functions designed at the clearance of invading pathogens. These mechanisms include opsonisation, enhancement of phagocytosis, triggering superoxidative burst and nitric oxide production. Collectins can also potentiate the adaptive immune response via antigen presenting cells such as macrophages and dendritic cells through modulation of cytokines and chemokines, thus they can act as a link between innate and adaptive immunity. This chapter describes the structure-function relationships of collectins, their diverse functions, and their interaction with viruses, bacteria, fungi and parasites.

Staphylococci evade the innate immune response by disarming neutrophils and forming biofilms

Staphylococcus aureus and Staphylococcus epidermidis can cause many types of infections, ranging from skin infections to implant-associated infections. The primary innate immune response against bacterial infections involves complement activation, recruitment of phagocytes (most importantly neutrophils), and subsequent killing of the pathogen. However, staphylococci are not innocent bystanders; they actively obstruct this immune attack. To do that, S. aureus secretes several immune-evasion proteins to resist attack by the innate immune system. Furthermore, S. aureus and S. epidermidis are known for their ability to form biofilms on implanted medical devices and host tissues, which provides another important immune-evasion mechanism. Understanding these different strategies to resist immune attack will help to develop novel therapies against staphylococcal infections.

Molecular and functional characterisation of a mannose-binding lectin-like gene from Japanese sea bass (Lateolabrax japonicus)

Mannose-binding lectin (MBL) plays an important role in host immune responses against pathogens. LjMBL-like-1 was identified from Japanese sea bass (Lateolabrax japonicas), which has selectivity for galactose. Herein, this lectin might be better designated as galactose-binding lectin (LjGalBL-1). LjGalBL-1 transcripts were detected in all tested tissues, with highest expression in liver. Upon Vibrio harveyi infection, LjGalBL-1 mRNA expression was increased in major immune-related tissues, and protein levels in serum were also upregulated. Recombinant LjGalBL-1 (rLjGalBL-1) bound to monosaccharides and polysaccharides, and both rLjGalBL-1 and native LjGalBL-1 (nLjGalBL-1) agglutinated three Gram-positive bacteria (Staphylococcus aureus, Streptococcus iniae and Micrococcus luteus) and four Gram-negative bacteria (Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum and V. harveyi) in a Ca²⁺-dependent manner in vitro. Moreover, rLjGalBL-1 increased the survival rate of V. harveyi-infected fish and decreased bacterial load in liver, spleen, kidney and blood. Thus, LjGalBL-1 protects L. japonicas against V. harveyi infection.

Bacterial Peptidoglycan as a Driver of Chronic Brain Inflammation

Peptidoglycan (PGN) is a cell wall component of both Gram-positive and Gram-negative bacteria. Signature fragments of PGN are proinflammatory through engagement of pattern recognition receptors (PRR) on resident tissue cells and circulating leukocytes. Despite its abundance in the gut microbiota, there is limited recognition that PGN could contribute to chronic neuroinflammation. This review highlights current insights into the roles of PGN as a determinant of brain inflammation, notably in multiple sclerosis (MS) and its experimental autoimmune encephalomyelitis (EAE) models. Recent studies demonstrate PGN in blood of healthy adult humans. PGN amplifies autoimmune pathology via activation of innate immune cells. Novel uptake routes through (altered) gut mucosa by myeloid leukocyte subsets promote PGN transport to the brain.

Utilization of complement receptors in immune cell-microbe interaction

The complement system is a major humoral component of immunity and is essential for the fast elimination of pathogens invading the body. In addition to its indispensable role in innate immunity, the complement system is also involved in pathogen clearance during the effector phase of adaptive immunity. The fastest way of killing the invader is lysis by the membrane attack complex, which is formed by the terminal components of the complement cascade. Not all pathogens are lysed however and, if opsonized by a variety of molecules, they undergo phagocytosis and disposal inside immune cells. The most important complement-derived opsonins are C1q, the first component of the classical pathway, MBL, the initiator of the lectin pathway and C3-derived activation fragments, including C3b, iC3b and C3d, which all serve as ligands for their corresponding receptors. In this review, we discuss how complement receptors are utilized by various immune cells to tackle invading microbes, or by pathogens to evade host response.

Deconstructing the Chlamydial Cell Wall

The evolutionary separated Gram-negative Chlamydiales show a biphasic life cycle and replicate exclusively within eukaryotic host cells. Members of the genus Chlamydia are responsible for many acute and chronic diseases in humans, and Chlamydia-related bacteria are emerging pathogens. We revisit past efforts to detect cell wall material in Chlamydia and Chlamydia-related bacteria in the context of recent breakthroughs in elucidating the underlying cellular and molecular mechanisms of the chlamydial cell wall biosynthesis. In this review, we also discuss the role of cell wall biosynthesis in chlamydial FtsZ-independent cell division and immune modulation. In the past, penicillin susceptibility of an invisible wall was referred to as the "chlamydial anomaly." In light of new mechanistic insights, chlamydiae may now emerge as model systems to understand how a minimal and modified cell wall biosynthetic machine supports bacterial cell division and how cell wall-targeting beta-lactam antibiotics can also act bacteriostatically rather than bactericidal. On the heels of these discussions, we also delve into the effects of other cell wall antibiotics in individual chlamydial lineages.

Peptidoglycan Muropeptides: Release, Perception, and Functions as Signaling Molecules

Peptidoglycan (PG) is an essential molecule for the survival of bacteria, and thus, its biosynthesis and remodeling have always been in the spotlight when it comes to the development of antibiotics. The peptidoglycan polymer provides a protective function in bacteria, but at the same time is continuously subjected to editing activities that in some cases lead to the release of peptidoglycan fragments (i.e., muropeptides) to the environment. Several soluble muropeptides have been reported to work as signaling molecules. In this review, we summarize the mechanisms involved in muropeptide release (PG breakdown and PG recycling) and describe the known PG-receptor proteins responsible for PG sensing. Furthermore, we overview the role of muropeptides as signaling molecules, focusing on the microbial responses and their functions in the host beyond their immunostimulatory activity.

Mannan-Binding Lectin Suppresses Peptidoglycan-Induced TLR2 Activation and Inflammatory Responses

Peptidoglycan (PGN), as the major components of the bacterial cell wall, is known to cause excessive proinflammatory cytokine production. Toll-like receptor 2 (TLR2) is abundantly expressed on immune cells and has been shown to be involved in PGN-induced signaling. Although more and more evidences have indicated that PGN is recognized by TLR2, the role of TLR2 PGN recognition is controversial. Mannan-binding lectin (MBL), a plasma C-type lectin, plays a key role in innate immunity. More and more evidences show that MBL could suppress the amplification of inflammatory signals. Whether MBL can alter PGN-elicited cellular responses through TLR2 in macrophages is still unknown, and possible mechanism underlying it should be investigated. In this study, we found that MBL significantly attenuated PGN-induced inflammatory cytokine production, including TNF-α and IL-6, in PMA-stimulated THP-1 cells at both mRNA and protein levels. The expression of TLR2 was strongly induced by PGN stimulation. Furthermore, the administration of TLR2-neutralized antibody effectively suppressed PGN-induced TNF-α and IL-6 expression. These results supplied the evidence that PGN from Saccharomyces cerevisiae could be recognized by TLR2. In addition, we also found that MBL decreased PGN-induced TLR2 expression and suppressed TLR2-mediated downstream signaling, including the phosphorylation of IκBα, nuclear translocation of NF-κBp65, and phosphorylation of MAPK p38 and ERK1/2. Administration of MBL alone did not have an effect on the expression of TLR2. Finally, our data showed that PGN-mediated immune responses were more severely suppressed by preincubation with MBL and indicated that MBL can combine with both TLR2 and PGN to block the inflammation cytokine expression induced by PGN. All these data suggest that MBL could downregulate inflammation by modulating PGN/TLR2 signaling pathways. This study supports an important role for MBL in immune regulation and signaling pathways involved in inflammatory responses.

EDIII-DENV3 nanospheres drive immature dendritic cells into a mature phenotype in an in vitro model

Domain III of E protein of dengue virus (DENV) is a target for vaccine development. Unfortunately, this protein based platform has low general immunogenicity. To circumvent this problem, the use of an adjuvant-nanoparticle delivery system to facilitate immunogenicity of soluble DENV-EDIII protein was investigated. One of the key features of this delivery system is its ability to simultaneously deliver antigens and exert adjuvanticity on specialized immune cells. In this study, N-trimethyl chitosan (TMC) nanoparticles (NPs) were generated to be used as adjuvant and carrier for soluble E-domain III of dengue virus serotype 3 (sEDIII-D3). Using ionotropic gelation, purified sEDIII-D3 was encapsulated into TMC NPs to form EDIII-D3 TMC NPs. After optimization, EDIII-D3 TMC particles exhibited a loading efficiency of 81% and a loading capacity of 41%. The immunogenicity of EDIII-D3 TMC NPs was tested using monocyte-derived dendritic cells (MoDCs). It was found that EDIII-D3 TMC NPs were well taken up by MoDCs. In addition, EDIII-D3 TMC NP treated MoDCs significantly upregulated maturation markers (CD80, CD83, CD86 and HLA-DR) and induced secretion of various cytokines and chemokines (IFN-α, IL-1β, IL-6, IL-2, IL-12p70, IFN-γ, IL-4, IL-10, IL-8, MCP-1, macrophage inflammatory protein-1β, granulocyte-colony stimulating factor, granulocyte-macrophage colony-stimulating factor and IL-7). These results indicate that EDIII-D3 TMC NPs are potent immunogens, at least in vitro, with the ability to induce maturation of DCs and highlight the potential use of TMC NPs for enhancing immunogenicity of a non-replicating dengue vaccine.

Surfactant protein D delays Fas- and TRAIL-mediated extrinsic pathway of apoptosis in T cells

Only a few extracellular soluble proteins are known to modulate apoptosis. We considered that surfactant-associated protein D (SP-D), an innate immune collectin present on many mucosal surfaces, could regulate apoptosis. Although SP-D is known to be important for immune cell homeostasis, whether SP-D affects apoptosis is unknown. In this study we aimed to determine the effects of SP-D on Jurkat T cells and human T cells dying by apoptosis. Here we show that SP-D binds to Jurkat T cells and delays the progression of Fas (CD95)-Fas ligand and TRAIL-TRAIL receptor induced, but not TNF-TNF receptor-mediated apoptosis. SP-D exerts its effects by reducing the activation of initiator caspase-8 and executioner caspase-3. SP-D also delays the surface exposure of phosphatidylserine. The effect of SP-D was ablated by the presence of caspase-8 inhibitor, but not by intrinsic pathway inhibitors. The binding ability of SP-D to dying cells decreases during the early stages of apoptosis, suggesting the release of apoptotic cell surface targets during apoptosis. SP-D also delays FasL-induced death of primary human T cells. SP-D delaying the progression of the extrinsic pathway of apoptosis could have important implications in regulating immune cell homeostasis at mucosal surfaces.

Prospective Observational Study on the Association Between Serum Mannose-Binding Lectin Levels and Severe Outcome in Critically Ill Patients with Pandemic Influenza Type A (H1N1) Infection

Background

Mannose-binding lectin (MBL) plays an important role in the innate immune response. In addition to activating the complement, MBL can induce cytokine production and contribute to a deleterious inflammatory response with severe A(H1N1)pdm09 virus infection. Our aim was to determine if serum MBL levels correlate with the risk of mortality in intensive care units (ICU) patients with A(H1N1)pdm09 infection.

Methods

Prospective observational study was performed in ICU patients with acute respiratory distress syndrome due to influenza A(H1N1)pdm09 virus. Demographic characteristics and severity indices were recorded at ICU admission. MBL was assayed from blood drawn at influenza diagnosis within 24–48 h following the ICU admission. Outcomes were compared according to MBL levels. Results are expressed as median and interquartile range.

Results

Serum MBL levels were studied in 27 patients (age: 56 [IQR 29] years) with severe A(H1N1)pdm09 infection and in 70 healthy controls. Median admission SAPSII and SOFA scores were 49 [IQR 26] and 12 [IQR 5], respectively. Mortality rate after a 30-day was 37%. MBL was significantly higher in non-survivors (3741 [IQR 2336] ng/ml) vs survivors (215 [IQR 1307] ng/ml), p = 0.006, as well as control group (1814 [IQR 2250] ng/ml), p = 0.01. In contrast, MBL levels in survivors group were significantly lower than the controls group (215 [IQR 1307] ng/ml vs. 1814 [IQR 2250] ng/ml, p = 0.005). MBL cut-off > 1870 ng/ml had a sensitivity of 80% and a specificity of 88.2% for mortality [AUC = 0.82 (95% CI 0.63–0.94)]. Kaplan–Meier analysis demonstrated a strong association between MBL levels and mortality (log-rank 7.8, p = 0.005). MBL > 1870 ng/ml was independently associated with mortality (HR = 8.7, 95% CI 1.2–29.1, p = 0.007).

Conclusions

This study shows that baseline MBL > 1870 ng/ml is associated with higher mortality in ICU patients with severe A(H1N1)pdm09 infection.

Surfactant protein D regulates caspase-8-mediated cascade of the intrinsic pathway of apoptosis while promoting bleb formation

Surfactant-associated protein D (SP-D) is a soluble innate immune collectin present on many mucosal surfaces. We recently showed that SP-D suppresses the extrinsic pathway of apoptosis by downregulating caspase-8 activation. However, the effects of SP-D on the intrinsic pathway of apoptosis are not clearly understood. In the intrinsic pathway, cytochrome c is released by mitochondria into the cytoplasm. Oxidation of cytochrome c by cytochrome c oxidase activates the apoptosome and caspase-9 cascade. Both caspase-8- and caspase-9-mediated branches are activated in the intrinsic pathway of apoptosis; however, little is known about the relevance of the caspase-8 pathway in this context. Here we studied the effects of SP-D on different branches of the intrinsic pathway of apoptosis using UV-irradiated Jurkat T-cells. We found that SP-D does not inhibit the caspase-9 branch of apoptosis and the relevance of the caspase-8-related branch became apparent when the caspase-9 pathway was inhibited by blocking cytochrome c oxidase. Under these conditions, SP-D reduces the activation of caspase-8, executioner caspase-3 and exposure of phosphatidylserine (PS) on the membranes of dying cells. By contrast, SP-D increases the formation of nuclear and membrane blebs. Inhibition of caspase-8 confirms the effect of SP-D is unique to the caspase-8 pathway. Overall, SP-D suppresses certain aspects of the intrinsic pathway of apoptosis via reduction of caspase-8 activation and PS flipping while at the same time increasing membrane and nuclear bleb formation. This novel regulatory aspect of SP-D could help to regulate intrinsic pathway of apoptosis to promote effective blebbing and breakdown of dying cells.

Understanding the molecular differential recognition of muramyl peptide ligands by LRR domains of human NOD receptors

Human nucleotide-binding oligomerization domain proteins, hNOD1 and hNOD2, are host intracellular receptors with C-terminal leucine-rich repeat (LRR) domains, which recognize specific bacterial peptidoglycan (PG) fragments as their ligands. The specificity of this recognition is dependent on the third amino acid of the stem peptide of the PG ligand, which is usually meso-diaminopimelic acid (mesoDAP) or l-lysine (l-Lys). Since the LRR domains of hNOD receptors had been experimentally shown to confer the PG ligand-sensing specificity, we developed three-dimensional structures of hNOD1-LRR and the hNOD2-LRR to understand the mechanism of differential recognition of muramyl peptide ligands by hNOD receptors. The hNOD1-LRR and hNOD2-LRR receptor models exhibited right-handed curved solenoid shape. The hot-spot residues experimentally proved to be critical for ligand recognition were located in the concavity of the NOD-LRR and formed the recognition site. Our molecular docking analyses and molecular electrostatic potential mapping studies explain the activation of hNOD-LRRs, in response to effective molecular interactions of PG ligands at the recognition site; and conversely, the inability of certain PG ligands to activate hNOD-LRRs, by deviations from the recognition site. Based on molecular docking studies using PG ligands, we propose few residues — G825, D826 and N850 in hNOD1-LRR and L904, G905, W931, L932 and S933 in hNOD2-LRR, evolutionarily conserved across different host species, which may play a major role in ligand recognition. Thus, our integrated experimental and computational approach elucidates the molecular basis underlying the differential recognition of PG ligands by hNOD receptors.

Mannose-binding lectin and l-ficolin polymorphisms in patients with community-acquired pneumonia caused by intracellular pathogens

Community-acquired pneumonia (CAP) is the leading infectious disease requiring hospitalization in the western world. Genetic variability affecting the host response to infection may play a role in susceptibility and outcome in patients with CAP. Mannose-binding lectin (MBL) and l-ficolin (l-FCN) are two important activators of the complement system and they can enhance phagocytosis by opsonization. In a prospective cohort of 505 Dutch patients with CAP and 227 control participants we studied whether polymorphisms in the MBL (MBL2) and FCN (FCN2) genes influenced susceptibility and outcome. No difference in frequency of these genotypes was found between patients with CAP in general and controls. However, the +6424G>T single nucleotide polymorphism (SNP) in FCN2 was more common in patients with a Coxiella burnetii pneumonia (P = 0·014). Moreover, the haplotypes coding for the highest MBL serum levels (YA/YA and YA/XA) predisposed to atypical pneumonia (C. burnetii, Legionella or Chlamydia species or Mycoplasma pneumoniae) compared with controls (P = 0·016). Furthermore, patients with these haplotypes were more often bacteraemic (P = 0·019). It can therefore be concluded that MBL2 and FCN2 polymorphisms are not major risk factors for CAP in general, but that the +6424G>T SNP in the FCN2 gene predisposes to C. burnetii pneumonia. In addition, patients with genotypes corresponding with high serum MBL levels are at risk for atypical pneumonia, possibly caused by enhanced phagocytosis, thereby promoting cell entry of these intracellular bacteria.

Mannose-Binding Lectin: Biologic Characteristics and Role in the Susceptibility to Infections and Ischemia-Reperfusion Related Injury in Critically Ill Neonates

The mannose-binding lectin (MBL) is a member of the collectin family, belonging to the innate immunity system. Genetic, biologic, and clinical properties of MBL have been widely investigated throughout the last decades, although some interesting aspects of its potential clinical relevance are still poorly understood. Low circulating concentrations of MBL have been associated with increased risk of infection and poor neurologic outcome in neonates. On the other hand, an excessive and uncontrolled inflammatory response by the neonatal intestine after the exposure to luminal bacteria, leading to an increased production of MBL, may be involved in the onset of necrotizing enterocolitis. The purpose of the present review is to summarize the current knowledge about genetic and biologic characteristics of MBL and its role in the susceptibility to infections and to ischemia-reperfusion related tissue injuries to better explore its clinical relevance during the perinatal period and the possible future therapeutic applications.

Bacterial peptidoglycan with amidated meso-diaminopimelic acid evades NOD1 recognition: an insight into NOD1 structure–recognition

Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) is an intracellular pattern recognition receptor that recognizes bacterial peptidoglycan (PG) containing meso-diaminopimelic acid (mesoDAP) and activates the innate immune system. Interestingly, a few pathogenic and commensal bacteria modify their PG stem peptide by amidation of mesoDAP (mesoDAPNH2). In the present study, NOD1 stimulation assays were performed using bacterial PG containing mesoDAP (PGDAP) and mesoDAPNH2 (PGDAPNH2) to understand the differences in their biomolecular recognition mechanism. PGDAP was effectively recognized, whereas PGDAPNH2 showed reduced recognition by the NOD1 receptor. Restimulation of the NOD1 receptor, which was initially stimulated with PGDAP using PGDAPNH2, did not show any further NOD1 activation levels than with PGDAP alone. But the NOD1 receptor initially stimulated with PGDAPNH2 responded effectively to restimulation with PGDAP. The biomolecular structure–recognition relationship of the ligand-sensing leucine-rich repeat (LRR) domain of human NOD1 (NOD1–LRR) with PGDAP and PGDAPNH2 was studied by different computational techniques to further understand the molecular basis of our experimental observations. The d-Glu–mesoDAP motif of GMTPDAP, which is the minimum essential motif for NOD1 activation, was found involved in specific interactions at the recognition site, but the interactions of the corresponding d-Glu–mesoDAP motif of PGDAPNH2 occur away from the recognition site of the NOD1 receptor. Hot-spot residues identified for effective PG recognition by NOD1–LRR include W820, G821, D826 and N850, which are evolutionarily conserved across different host species. These integrated results thus successfully provided the atomic level and biochemical insights on how PGs containing mesoDAPNH2 evade NOD1–LRR receptor recognition.

Atherogenesis in rheumatology

Atherosclerosis is a chronic inflammatory disorder characterized by immune cell activation, inflammation driven plaque formation and subsequent destabilization. In other disorders of an inflammatory nature, the chronic inflammatory state per se has been linked to acceleration of the atherosclerotic process which is underlined by an increased incidence of cardiovascular disease (CVD) in disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and antiphopholipid (Hughes) syndrome (APS). In addition to systemic inflammation, additional mechanisms have been put forward that are more specific for the pathophysiology of the individual chronic inflammatory disorders.

Mannan-binding lectin reduces CpG DNA-induced inflammatory cytokine production by human monocytes

Mannan-binding lectin (MBL) belongs to the collectin family and functions as an opsonin that can also initiate complement activation. Our previous study showed that MBL serves as a double-stranded RNA binding protein that attenuates polyriboinosinic-polyribocytidylic acid-induced TLR3 activation. Prompted by these findings, in the present study cross-talk between MBL and CpG-DNA-induced TLR9 activation was investigated. Here, it was found that MBL also interacts with the TLR9 agonist, CpG oligodeoxynucleotide (CpG-ODN), in a calcium-dependent manner. Purified MBL protein suppressed activation of nuclear factor-kappa B signaling and subsequent production of proinflammatory cytokines from human monocytes induced by CpG-ODN 2006. These observations indicate that MBL can down-regulate CpG DNA-induced TLR9 activation, emphasizing the importance of understanding the interaction of MBL with TLR agonist in host immune defense.

Functional characterisation and expression analysis of recombinant serum amyloid P isoform 1 (RbSAP1) from rock bream (Oplegnathus fasciatus)

Lectins are carbohydrate-binding proteins that play important roles in the recognition and elimination of pathogens via the innate immune system. Pentraxins (PTX) are humoral lectins, which are multifunctional proteins in vertebrates. Pentraxins can be divided into two groups based on their primary structure: short (C-reactive protein and serum amyloid P [SAP]) and long pentraxins (PTX3 and neuronal pentraxins). Previously, SAP was shown to have Ca(2+)-dependent binding specificity for various ligands and to be a major acute phase protein. In this study, we identified and characterised the gene encoding SAP isoform 1 in rock bream (Oplegnathus fasciatus) (RbSAP1) and analysed its expression in various tissues after a pathogen challenge. An alignment analysis conducted based on the deduced amino acid sequence of RbSAP1 (1918 bp full-length cDNA with a 699 bp open reading frame encoding 232 amino acids) and SAPs and PTXs isolated from other organisms, revealed that the pentraxin domain and cysteine residues of the deduced protein are conserved. RbSAP1, which was ubiquitously expressed in all tissues examined, was predominantly detected in head kidney, trunk kidney, peripheral blood leukocytes, and gills. RbSAP1 expression was dramatically up-regulated in the kidney and liver after infection with Edwardsiella tarda, Streptococcus iniae, or red seabream iridovirus. Purified rRbSAP1 was able to bind Gram-negative bacteria, Gram-positive bacteria, and pathogen-associated molecular patterns. Interestingly, rRbSAP1 aggregated Gram-negative bacteria in the presence of Ca(2+). The anti-pathogen activity of rRbSAP1 suggests that SAP functions in innate immunity in the rock bream.

Molecular characterization of a transmembrane C-type lectin receptor gene from ayu (Plecoglossus altivelis) and its effect on the recognition of different bacteria by monocytes/macrophages

C-type lectin receptors (CTLRs) play vital roles in immune responses as pattern-recognition receptors (PRRs). In this study, we identified a novel C-type lectin receptor (PaCTLRC) gene from ayu, Plecoglossus altivelis. Predicted PaCTLRC is a single transmembrane receptor with a typical carbohydrate recognition domain (CRD) at its C-terminus. Sequence comparison and phylogenetic tree analysis showed that PaCTLRC was most closely related to Atlantic salmon (Salmo salar) CLRC, but was significantly different from two other ayu CTLRs, aCLR and PaCD209L. PaCTLRC transcript was detected in all tested tissues and cells, with high levels in the liver; and its expression was significantly altered upon Vibrio anguillarum infection. Refolded recombinant PaCTLRC (rPaCTLRC) agglutinated three types of Gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus and Streptococcus iniae) and four types of Gram-negative bacteria (Aeromonas hydrophila, Escherichia coli, V. anguillarum and Vibrio parahaemolyticus) in a Ca(2+)-dependent manner in vitro, and Gram-positive bacteria were shown to be biologically relevant ligands for PaCTLRC. rPaCTLRC bound to d-mannose, d-galactose, l-fucose, N-acetyl-d-glucosamine (GlcNAc), lipopolysaccharide (LPS) and peptidoglycan (PGN), exhibiting a relative binding strength to d-mannose and PGN. d-Mannose, l-fucose, GlcNAc, LPS and PGN could inhibit the agglutinating activity of rPaCTLRC, while d-galactose did not functioned. PaCTLRC neutralization using anti-PaCTLRC IgG resulted in the inhibition of phagocytosis by ayu monocytes/macrophages (MO/MΦ) of S. aureus but not of E. coli, and produced a consistently higher survival rate of S. aureus than that of E. coli. d-Mannose, LPS and PGN treatment had no significant influence on the phagocytosis of ayu MO/MΦ. These results suggest that PaCTLRC may serve as a Gram-positive bacteria-preferred PRR which is involved in pathogen recognition and signal transduction in ayu MO/MΦ.

Identification of a C-type lectin with antiviral and antibacterial activity from pacific white shrimp Litopenaeus vannamei

C-type lectins (CTLs) play crucial roles in innate immune responses in invertebrates by recognizing and eliminating microinvaders. In this study, a CTL from pacific white shrimp Litopenaeus vannamei (LvCTL3) was identified. LvCTL3 contains a single C-type lectin-like domain (CTLD), which shows similarities to those of other shrimp CTLs and has a mutated 'EPD' motif in Ca(2+)-binding site 2. LvCTL3 mRNA can be detected in all tested tissues and expression of LvCTL3 in gills was up-regulated after Lipopolysaccharides, poly (I:C), Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenges, suggesting activation responses of LvCTL3 to bacterial, virus and immune stimulant challenges. The 5'flanking regulatory region of LvCTL3 was cloned and we identified a NF-κB binding motif in the LvCTL3 promoter region. Dual-luciferase reporter assays indicated that over-expression of L. vannamei dorsal can dramatically up regulate the promoter activity of LvCTL3, suggesting that LvCTL3 expression could be regulated through NF-κB signaling pathway. As far as we know, this is the first report on signaling pathway involve in shrimp CTLs expression. The recombinant LvCTL3 protein was expressed in Escherichia coli and purified by Ni-affinity chromatography. The purified LvCTL3 can agglutinate Gram-negative microbe Vibrio alginolyticus and V. parahaemolyticus and Gram-positive bacteria Bacillus subtilis in the presence of calcium ions, but cannot agglutinate Gram-positive bacteria Streptococcus agalactiae. The agglutination activity of LvCTL3 was abolished when Ca(2+) was chelated with EDTA, suggesting the function of LvCTL3 is Ca(2+)-dependent. In vivo challenge experiments showed that the recombinant LvCTL3 protein can significantly reduce the mortalities of V. parahemolyticus and WSSV infection, indicating LvCTL3 might play significant roles in shrimp innate immunity defense against bacterial and viral infection.

Neutrophil-Mediated Phagocytosis of Staphylococcus aureus

Initial elimination of invading Staphylococcus aureus from the body is mediated by professional phagocytes. The neutrophil is the major phagocyte of the innate immunity and plays a key role in the host defense against staphylococcal infections. Opsonization of the bacteria with immunoglobulins and complement factors enables efficient recognition by the neutrophil that subsequently leads to intracellular compartmentalization and killing. Here, we provide a review of the key processes evolved in neutrophil-mediated phagocytosis of S. aureus and briefly describe killing. As S. aureus is not helpless against the professional phagocytes, we will also highlight its immune evasion arsenal related to phagocytosis.

Human secreted stabilin-1-interacting chitinase-like protein aggravates the inflammation associated with rheumatoid arthritis and is a potential macrophage inflammatory regulator in rodents

OBJECTIVE

To study the relationship between the human secreted protein stabilin-1-interacting chitinase-like protein (SI-CLP) and rheumatoid arthritis (RA).

METHODS

The expression of SI-CLP in peripheral blood mononuclear cells (PBMCs) and synovial fluid from patients with RA and the effects of cytokines on SI-CLP expression were examined by Western blotting. Fluorescence-activated cell sorting analysis was performed to investigate the binding between SI-CLP and cells. Bone marrow-derived macrophages were isolated from wild-type and SI-CLP(-/-) mice, and real-time quantitative polymerase chain reaction was performed to detect the levels of messenger RNA for cytokines or SI-CLP in SI-CLP- or cytokine-treated macrophages. Histologic studies were conducted to evaluate inflammation and the expression of interleukin-12 (IL-12), IL-13, and SI-CLP in lesions. Enzyme-linked immunosorbent assays were used to detect the cytokine levels in bone marrow-derived macrophages. Rats or mice with collagen-induced arthritis (CIA) and SI-CLP(-/-) mice were used to study the function of SI-CLP in RA.

RESULTS

SI-CLP expression was increased in PBMCs and detectable in synovial fluid from patients with RA. Administration of SI-CLP to rats with CIA aggravated arthritis-associated inflammation. SI-CLP was specifically attached to the surface protein of macrophages, which elevated the expression of IL-1β, IL-6, IL-12, and IL-13 in macrophages and mouse bone marrow-derived macrophages, up-regulating ERK phosphorylation. Moreover, SI-CLP was up-regulated by both IL-12 and IL-13 through JNK and JAK/STAT signaling, respectively. Knockout of SI-CLP resulted in a decrease in the expression of IL-1β, IL-6, IL-12, and IL-13 and lower susceptibility to CIA compared with wild-type mice. SI-CLP treatment also aggravated arthritis-related inflammation in wild-type and SI-CLP(-/-) mice.

CONCLUSION

SI-CLP functions as a regulator of the inflammatory response by macrophages. The decrease in inflammation-associated cytokine levels resulting from SI-CLP knockout may explain the lower susceptibility to CIA in SI-CLP(-/-) mice.

Age-dependent association of mannose-binding lectin polymorphisms with the development of pulmonary tuberculosis in Viet Nam

Mannose-binding lectin (MBL) binds to pathogens and induces complement-mediated opsonophagocytosis. Although the association between MBL2 polymorphisms and tuberculosis (TB) has been studied in various populations, the results are controversial. We explored the stages of TB associated with MBL2 polymorphisms. X/Y (rs7096206) and A/B (rs1800450) were genotyped in 765 new patients with active pulmonary TB without HIV infection and 556 controls in Hanoi, Viet Nam. The MBL2 nucleotide sequences were further analyzed, and plasma MBL levels were measured in 109 apparently healthy healthcare workers and 65 patients with TB. Latent TB infection (LTBI) was detected by interferon-gamma release assay (IGRA). The YA/YA diplotype, which exhibited high plasma MBL levels, was associated with protection against active TB in younger patients (mean age = 32)≦ 45 years old (odds ratio, 0.61; 95% confidence interval, 0.46-0.80). The resistant diplotype was less frequently found in the younger patients at diagnosis (P = 0.0021). MBL2 diplotype frequencies and plasma MBL levels were not significantly different between the IGRA-positive and -negative groups. MBL2 YA/YA exhibited a protective role against the development of TB in younger patients, whereas the MBL2 genotype and MBL levels were not associated with LTBI. High MBL levels may protect against the early development of pulmonary TB after infection.

Prognostic value of mannose-binding lectin: 90-day outcome in patients with acute ischemic stroke

Complement activation and inflammation have been suggested in the pathogenesis of stroke; mannose-binding lectin (MBL) was found to have roles during the process. We therefore evaluated the short-term prognostic value of serum MBL in Chinese patients with an acute ischemic stroke (AIS). Consecutive AIS patients admitted to the emergency department were identified. Clinical information was collected. Serum concentration of MBL and NIH Stroke Scale (NIHSS) was measured at the time of admission. Short-term functional outcome was measured by modified Rankin scale (mRS) 90 days after admission. Multivariate analyses were performed using logistic regression models. During the inclusion period, 231 patients were diagnosed with AIS, and 220 completed follow-up. The results indicated that the serum MBL levels were significantly (P = 0.000) higher in acutely ischemic stroke patients as compared with normal controls. MBL was an independent prognostic marker of short-term functional outcome and death (odds ratio (OR) 5.28 (2.88-10.67) and 6.99 (3.55-13.97), respectively, P = 0.000 for both, adjusted for NIHSS, other predictors, and vascular risk factors) in patients with AIS. MBL improved the area under the receiver operating characteristic curve of the NIHSS score for functional outcome from 0.826 (95 % CI 0.773-0.879) to 0.857 (95 % CI 0.808-0.905, P = 0.000) and for mortality from 0.768 (95 % CI 0.682-0.853) to 0.822 (95 % CI 0.747-0.896, P = 0.000). Serum MBL levels are a useful, complementary tool to predict functional outcome and mortality 90 days after stroke.

Mannan binding lectin attenuates double-stranded RNA-mediated TLR3 activation and innate immunity

Mannan binding lectin (MBL) functions as a pattern recognition molecule (PRM) which is able to initiate complement activation. Here, we characterize a previously unrecognized attribute of MBL as a double-stranded RNA (dsRNA) binding protein capable of modifying Toll like receptor 3 (TLR3) activation. MBL interacts with poly(I:C) and suppresses poly(I:C)-induced activation of TLR3 pathways and subsequent cytokine production. In addition, MBL binds to TLR3 directly. Surprisingly, disrupting the interaction between MBL and complement receptor 1 (CR1) or restraining the traffic of MBL to phagosome reversed the MBL limited TLR3 activation. We demonstrate the importance of MBL guided ligands intracellular localization, emphasizing the significance of understanding the dynamics of TLR agonists complexed with MBL or other PRMs inside the cell in immune defense.

Human SAP is a novel peptidoglycan recognition protein that induces complement-independent phagocytosis of Staphylococcus aureus

The human pathogen Staphylococcus aureus is responsible for many community-acquired and hospital-associated infections and is associated with high mortality. Concern over the emergence of multidrug-resistant strains has renewed interest in the elucidation of host mechanisms that defend against S. aureus infection. We recently demonstrated that human serum mannose-binding lectin binds to S. aureus wall teichoic acid (WTA), a cell wall glycopolymer--a discovery that prompted further screening to identify additional serum proteins that recognize S. aureus cell wall components. In this report, we incubated human serum with 10 different S. aureus mutants and determined that serum amyloid P component (SAP) bound specifically to a WTA-deficient S. aureus ΔtagO mutant, but not to tagO-complemented, WTA-expressing cells. Biochemical characterization revealed that SAP recognizes bacterial peptidoglycan as a ligand and that WTA inhibits this interaction. Although SAP binding to peptidoglycan was not observed to induce complement activation, SAP-bound ΔtagO cells were phagocytosed by human polymorphonuclear leukocytes in an FcγR-dependent manner. These results indicate that SAP functions as a host defense factor, similar to other peptidoglycan recognition proteins and nucleotide-binding oligomerization domain-like receptors.

Mouse mannose-binding lectin-A and ficolin-A inhibit lipopolysaccharide-mediated pro-inflammatory responses on mast cells

It is unknown how soluble pattern-recognition receptors in blood, such as mannose-binding lectin (MBL) and ficolins, modulate mast cell-mediated inflammatory responses. We investigate how mouse MBL-A or ficolin-A regulate mouse bone marrow-derived mast cells (mBMMCs)-derived inflammatory response against bacterial lipopolysaccharide (LPS) stimulation. LPS-mediated pro-inflammatory cytokine productions on mBMMCs obtained from Toll-like receptor4 (TLR4)-deficient mice, TLR2-defficient mice, and their wildtype, were specifically attenuated by the addition of either mouse MBL-A or ficolin-A in a dose-dependent manner. However, the inhibitory effects by mouse MBL-A or ficolin-A were restored by the addition of mannose or N-acetylglucosamine, respectively. These results suggest that mouse MBL-A and ficolin-A bind to LPS via its carbohydrate-recognition domain and fibrinogen-like domain, respectively, whereby cytokine production by LPS-mediated TLR4 in mBMMCs appears to be down-regulated, indicating that mouse MBL and ficolin may have an inhibitory function toward mouse TLR4-mediated excessive inflammation on the mast cells.

Mannose-binding lectin blunts macrophage polarization and ameliorates lupus nephritis

Background

Deficiency in clearance of self nuclear antigens, including DNA, is the hallmark of systemic lupus erythematosus (SLE), a chronic autoimmnue disease characterized by the production of various autoantibodies, immune complex deposition and severe organ damage. Our previous studies revealed that administration of syngeneic BALB/c mice with activated lymphocyte-derived DNA (ALD-DNA) could induce SLE disease. Mannose-binding lectin (MBL), a secreted pattern recognition receptor with binding activity to DNA, has been proved to be a modulator of inflammation, but whether MBL takes responsibility for DNA clearance, modulates the DNA-mediated immune responses, and is involved in the development of DNA-induced SLE disease remain poorly understood.

Methodology/Principal Findings

The levels of serum MBL significantly decreased in lupus mice induced by ALD-DNA and were negatively correlated with SLE disease. MBL blunted macrophage M2b polarization by inhibiting the MAPK and NF-κB signaling while enhancing the activation of CREB. Furthermore, MBL suppressed the ability of ALD-DNA–stimulated macrophages to polarize T cells toward Th1 cells and Th17 cells. Importantly, MBL supplement in vivo could ameliorate lupus nephritis.

Conclusion/Significance

These results suggest MBL supplement could alleviate SLE disease and might imply a potential therapeutic strategy for DNA-induced SLE, which would further our understanding of the protective role of MBL in SLE disease.

Secondary cell wall polymers of Enterococcus faecalis are critical for resistance to complement activation via mannose-binding lectin

The complement system is part of our first line of defense against invading pathogens. The strategies used by Enterococcus faecalis to evade recognition by human complement are incompletely understood. In this study, we identified an insertional mutant of the wall teichoic acid (WTA) synthesis gene tagB in E. faecalis V583 that exhibited an increased susceptibility to complement-mediated killing by neutrophils. Further analysis revealed that increased killing of the mutant was due to a higher rate of phagocytosis by neutrophils, which correlated with higher C3b deposition on the bacterial surface. Our studies indicated that complement activation via the lectin pathway was much stronger on the tagB mutant compared with wild type. In concordance, we found an increased binding of the key lectin pathway components mannose-binding lectin and mannose-binding lectin-associated serine protease-2 (MASP-2) on the mutant. To understand the mechanism of lectin pathway inhibition by E. faecalis, we purified and characterized cell wall carbohydrates of E. faecalis wild type and V583ΔtagB. NMR analysis revealed that the mutant strain lacked two WTAs with a repeating unit of →6)[α-l-Rhap-(1→3)]β-D-GalpNAc-(1→5)-Rbo-1-P and →6) β-D-Glcp-(1→3) [α-D-Glcp-(1→4)]-β-D-GalpNAc-(1→5)-Rbo-1-P→, respectively (Rbo, ribitol). In addition, compositional changes in the enterococcal rhamnopolysaccharide were noticed. Our study indicates that in E. faecalis, modification of peptidoglycan by secondary cell wall polymers is critical to evade recognition by the complement system.

Mannose-binding lectin contributes to deleterious inflammatory response in pandemic H1N1 and avian H9N2 infection

BACKGROUND

Mannose-binding lectin (MBL) is a pattern-recognition molecule, which functions as a first line of host defense. Pandemic H1N1 (pdmH1N1) influenza A virus caused massive infection in 2009 and currently circulates worldwide. Avian influenza A H9N2 (H9N2/G1) virus has infected humans and has the potential to be the next pandemic virus. Antiviral function and immunomodulatory role of MBL in pdmH1N1 and H9N2/G1 virus infection have not been investigated.

METHODS

In this study, MBL wild-type (WT) and MBL knockout (KO) murine models were used to examine the role of MBL in pdmH1N1 and H9N2/G1 virus infection.

RESULTS

Our study demonstrated that in vitro, MBL binds to pdmH1N1 and H9N2/G1 viruses, likely via the carbohydrate recognition domain of MBL. Wild-type mice developed more severe disease, as evidenced by a greater weight loss than MBL KO mice during influenza virus infection. Furthermore, MBL WT mice had enhanced production of proinflammatory cytokines and chemokines compared with MBL KO mice, suggesting that MBL could upregulate inflammatory responses that may potentially worsen pdmH1N1 and H9N2/G1 virus infections.

CONCLUSIONS

Our study provided the first in vivo evidence that MBL may be a risk factor during pdmH1N1 and H9N2/G1 infection by upregulating proinflammatory response.

N-acetyl-D-galactosamine-specific lectin isolated from the seeds of Carica papaya

N-Acetyl-D-galactosamine (GalNAc)-specific lectins are of great interest because they have been reported to detect tumor-associated antigens of malignant cells. We isolated a novel lectin from Carica papaya seeds, named C. papaya lectin (CPL). Purification of the lectin involved ammonium sulfate fractionation and DEAE anion exchange and repeated gel filtration chromatography. Inhibition of CPL causing hemagglutination on human erythrocytes showed that the lectin shows specificity to GalNAc and lactose. Surface plasmon resonance further revealed that the lectin possesses high specificity toward GalNAc with a dissociation constant of 5.5 × 10(-9) M. The lectin is composed of 38- and 40-kDa subunits with a molecular mass of ∼804 kDa estimated by size-exclusion high-performance liquid chromatography. Incubation of CPL with Jurkat T cells showed significant induction of IL-2 cytokine, which suggests that CPL has potent immunomodulatory effects on immune cells.

Toll-like receptors and their adapter molecules

Toll-like receptors (TLR) are among key receptors of the innate mammalian immune system. Receptors of this family are able to recognize specific highly conserved molecular regions (patterns) in pathogen structures, thus initiating reactions of both innate and acquired immune response finally resulting in the elimination of the pathogen. In this case every individual TLR type is able to bind a broad spectrum of molecules of microbial origin characterized by different chemical properties and structures. Recent data demonstrate the existence of a multistep mechanism of the TLR recognition of the pathogen in which, in addition to receptors proper, the involvement of different adapter molecules is necessary. However, functions of separate adapter molecules as well as the principles of formation of a multicomponent system of ligand-specific recognition are still not quite understandable. We describe all identified as well as possible (candidate) adapter TLR molecules by giving their brief characteristics, and we also propose generalized possible variants of the TLR ligand-specific recognition with involvement of adapter molecules.