C-type lectins: their network and roles in pathogen recognition and immunity

CARD9 Is Required for Classical Macrophage Activation and the Induction of Protective Immunity against Pulmonary Cryptococcosis

Caspase recruitment domain-containing protein 9 (CARD9) is a critical adaptor molecule triggered by the interaction of C-type lectin receptors (CLRs) with carbohydrate motifs found in fungi. Consequently, clinical and animal studies indicate that CARD9 is an important regulator of protective immunity against fungal pathogens. Previous studies suggest that CARD9 is important for the induction of protection against Cryptococcus neoformans, an opportunistic fungal pathogen that causes life-threatening infections of the central nervous system in immunocompromised patients. However, the effect of CARD9 deficiency on the induction of protective immune responses against C. neoformans is unknown. Immunization with a C. neoformans mutant that overexpresses the transcription factor zinc finger 2, denoted LW10, results in protection against an otherwise lethal challenge with wild-type (WT) C. neoformans Our results showed that CARD9 is essential for the induction of vaccine-mediated immunity against C. neoformans infection. We observed significant decreases in interleukin-17 (IL-17) production and significant increases in Th2-type cytokine (IL-4, IL-5, and IL-13) production in CARD9-deficient mice after inoculation with strain LW10. While leukocyte infiltration to the lungs of CARD9-deficient mice was similar in LW10 and WT C. neoformans-infected mice, macrophages derived from CARD9-deficient mice inherently skewed toward an M2 activation phenotype, were unable to contain the growth of LW10, and failed to produce nitric oxide in response to infection with LW10 or stimulation with lipopolysaccharide. These results suggest that CARD9-mediated signaling is required for M1 macrophage activation and fungicidal activity necessary for the induction of vaccine-mediated immunity against C. neoformansIMPORTANCECryptococcus neoformans is a fungal pathogen that is found throughout the environment and can cause life-threatening infections of the lung and central nervous system in severely immunocompromised individuals. Caspase recruitment domain-containing protein 9 (CARD9) is a critical molecule that is activated after interactions of C-type lectin receptors (CLRs) found on the surfaces of specific immune cells, with carbohydrate structures associated with fungi. Patients with defects in CARD9 are significantly more susceptible to a multitude of fungal infections. C. neoformans contains several carbohydrate structures that interact with CLRs on immune cells and activate CARD9. Consequently, these studies evaluated the necessity of CARD9 for the induction of protective immunity against C. neoformans infection. These results are important, as they advance our understanding of cryptococcal pathogenesis and host factors necessary for the induction of protective immunity against C. neoformans.

Allostery in C-type lectins

C-type lectins are the largest and most diverse family of mammalian carbohydrate-binding proteins. They share a common protein fold, which provides the unifying basis for calcium-mediated carbohydrate recognition. Their involvement in a multitude of biological functions is remarkable. Here, we review the variety of tasks these lectins are involved in alongside with the structural demands on the overall protein architecture. Subtle changes of the protein structure are implemented to cope with such diverse functional requirements. The presence of a high level of structural dynamics over a broad palette of time scales is paired with the presence of secondary binding sites and allosteric coordination of remote sites and renders this lectin fold a highly adaptable scaffold.

Protective effects of Clec11a in islets against lipotoxicity via modulation of proliferation and lipid metabolism in mice

The lipotoxicity is considered as one of the risk for diabetes. Here we report C-type lectin domain family 11, member A (Clec11a) as a new regulator in islet playing a protective role in lipotoxicity induced dysfunction. Islet transcriptome sequencing was performed using the high-fat diet induced obesity (DIO) mice model. We found a significant decrease of Clec11a expression in islets of DIO mice compared to normal control mice, which was further confirmed by real-time PCR. Immunostaining demonstrated the localization of the Clec11a protein in mouse islets. Administration of recombinant human Clec11a (rClec11a) protein promoted the proliferation of islet cells and rescued the inhibition of fatty acid on cell proliferation, which involved the activation of Erk signaling pathway. We also found that the rClec11a altered the expression of genes involved in lipid metabolism.

Solution structure, glycan specificity and of phenol oxidase inhibitory activity of Anopheles C-type lectins CTL4 and CTLMA2

Malaria, the world's most devastating parasitic disease, is transmitted between humans by mosquitoes of the Anopheles genus. An. gambiae is the principal malaria vector in Sub-Saharan Africa. The C-type lectins CTL4 and CTLMA2 cooperatively influence Plasmodium infection in the malaria vector Anopheles. Here we report the purification and biochemical characterization of CTL4 and CTLMA2 from An. gambiae and An. albimanus. CTL4 and CTLMA2 are known to form a disulfide-bridged heterodimer via an N-terminal tri-cysteine CXCXC motif. We demonstrate in vitro that CTL4 and CTLMA2 intermolecular disulfide formation is promiscuous within this motif. Furthermore, CTL4 and CTLMA2 form higher oligomeric states at physiological pH. Both lectins bind specific sugars, including glycosaminoglycan motifs with β1-3/β1-4 linkages between glucose, galactose and their respective hexosamines. Small-angle x-ray scattering data supports a compact heterodimer between the CTL domains. Recombinant CTL4/CTLMA2 is found to function in vivo, reversing the enhancement of phenol oxidase activity in dsCTL4-treated mosquitoes. We propose these molecular features underline a common function for CTL4/CTLMA2 in mosquitoes, with species and strain-specific variation in degrees of activity in response to Plasmodium infection.

Gold Nanoparticles Coimmobilized with Small Molecule Toll-Like Receptor 7 Ligand and α-Mannose as Adjuvants

Adjuvants enhance the immune response during vaccination. Among FDA-approved adjuvants, aluminum salts are most commonly used in vaccines. Although aluminum salts enhance humoral immunity, they show a limited effect for cell-mediated immune responses. Thus, further development of adjuvants that induce T-cell-mediated immune response is needed. Toll-like receptors (TLRs) recognizing specific pathogen-associated molecular patterns activate innate immunity, which is crucial to shape adaptive immunity. Using TLR ligands as novel adjuvants in vaccines has therefore attracted substantial attention. Among them a small molecule TLR7 ligand, imiquimod, has been approved for clinical use, but its use is restricted to local administration due to unwanted adverse side effects when used systematically. Since TLR7 is mainly located in the endosomal compartment of immune cells, efficient transport of the ligand into the cells is important for improving the potency of the TLR7 ligand. In this study we examined gold nanoparticles (GNPs) immobilized with α-mannose as carriers for a TLR7 ligand to target immune cells. The small molecule synthetic TLR7 ligand, 2-methoxyethoxy-8-oxo-9-(4-carboxy benzyl)adenine (1V209), and α-mannose were coimmobilized via linker molecules consisting of thioctic acid on the GNP surface (1V209-αMan-GNPs). The in vitro cytokine production activity of 1V209-αMan-GNPs was higher than that of the unconjugated 1V209 derivative in mouse bone marrow-derived dendritic cells and in human peripheral blood mononuclear cells. In the in vivo immunization study, 1V209-αMan-GNPs induced significantly higher titers of IgG2c antibody specific to ovalbumin as an antigen than did unconjugated 1V209, and splenomegaly and weight loss were not observed. These results indicate that 1V209-αMan-GNPs could be useful as safe and effective adjuvants for development of vaccines against infectious diseases and cancer.

A novel C-type lectin from spotted knifejaw, Oplegnathus punctatus possesses antibacterial and anti-inflammatory activity

C-type lectin is a type of carbohydrate-binding protein and plays significant roles in innate immune response against pathogen infection. To date, thousands of C-type lectin had been identified in teleost. In the present study, we isolated a novel isoform of C-type lectin (OppCTL) from spotted knifejaw (Oplegnathus punctatus). The OppCTL encoded a typical Ca²⁺-dependent carbohydrate-binding protein, and was mainly expressed in liver in a tissue specific fashion. The expression of OppCTL was significantly up-regulated following Vibrio anguillarum infection in vivo, suggesting involvement in immune response. Hemagglutination analysis showed that the recombinant OppCTL (rOppCTL) could agglutinate erythrocyte from Mus musculus, Oplegnathus punctatus, Sebastes schlegelii and Paralichthys olivaceus. The rOppCTL could bind and agglutinate all tested bacteria. The rOppCTL possessed capacities of calcium-dependent agglutination to all tested bacteria. Sugar binding assay revealed that rOppCTL could also bind to the glycoconjugates of the bacterial surface, including lipopolysaccharide and peptidoglycan. Interestingly, Dual-luciferase analysis revealed that OppCTL could inhibit the activity of NF-κB in HEK-293T cells after OppCTL overexpression. Taken together, these results indicate that OppCTL has immune activity capable of defending invading pathogens and possesses potential immunoregulatory activity, enriching our understanding of the function of C-type lectin.

CTLGA9 Interacts with ALP1 and APN Receptors To Modulate Cry11Aa Toxicity in Aedes aegypti

The mosquito Aedes aegypti is associated with the spread of many viral diseases in humans, including Dengue virus (DENVs), Yellow fever virus (YFV), Zika virus (ZIKV), and Chikungunya virus (CHIKV). Bacillus thuringiensis (Bt) is widely used as a biopesticide, which produces Cry toxins for mosquito control. The Cry toxins bind mainly to important receptors, including alkaline phosphatase (ALP) and aminopeptidase-N (APN). This work investigated the function of a C-type lectin, CTLGA9, in A. aegypti in response to Cry toxins. Our results showed by far-western blot and ELISA methods that the CTLTGA9 protein interacted with brush border membrane vesicles (BBMVs) of A. aegypti larvae and with ALP1, APN, and Cry11Aa proteins. Furthermore, molecular docking showed overlapping binding sites in ALP1 and APN for binding to Cry11Aa and CTLGA9. The toxicity assays further demonstrated that CTLGA9 inhibited the larvicidal activity of Cry toxins. According to the results of molecular docking, CTLGA9 may compete with Cry11Aa for binding to ALP1 and APN receptors and thus decreases the mosquitocidal toxicity of Cry11Aa. Our results provide further insights into better understanding the mechanism of Cry toxins and help improve the Cry toxicity for mosquito control.

Human thioredoxin, a damage-associated molecular pattern and Malassezia-crossreactive autoallergen, modulates immune responses via the C-type lectin receptors Dectin-1 and Dectin-2

Human thioredoxin (hTrx), which can be secreted from cells upon stress, functions in allergic skin inflammation as a T cell antigen due to homology and cross-reactivity with the fungal allergen Mala s13 of the skin-colonizing yeast Malassezia sympodialis. Recent studies have shown that cell wall polysaccharides of Malassezia are detected by the immune system via the C-type lectin receptors Dectin-1 and Dectin-2, which are expressed on myeloid cells. Therefore, this study aimed to investigate a putative interaction between Dectin-1, Dectin-2 and the allergens Mala s13 and hTrx. Stimulation of human monocyte-derived dendritic cells or macrophages with Mala s13 or hTrx resulted in remarkable secretion of IL-1β and IL-23. Blocking experiments suggest that hTrx induces IL-23 by Dectin-1 binding and IL-1β by binding to either Dectin-1 or Dectin-2. Regarding Mala s13, Dectin-1 appears to be involved in IL-1β signaling. Interference of Syk kinase function was performed to investigate downstream signaling, which led to diminished hTrx responses. In our experiments, we observed rapid internalization of Mala s13 and hTrx upon cell contact and we were able to confirm direct interaction with Dectin-1 as well as Dectin-2 applying a fusion protein screening platform. We hypothesize that this cytokine response may result in a Th2/Th17-polarizing milieu, which may play a key role during the allergic sensitization in the skin, where allergen presentation to T cells is accompanied by microbial colonization and skin inflammation.

Selenoglycosides as Lectin Ligands: 77 Se-Edited CPMG-HSQMBC NMR Spectroscopy To Monitor Biomedically Relevant Interactions

The fundamental importance of protein-glycan recognition calls for specific and sensitive high-resolution techniques for their detailed analysis. After the introduction of 19 F NMR spectroscopy to study the recognition of fluorinated glycans, a new 77 Se NMR spectroscopy method is presented for complementary studies of selenoglycans with optimised resolution and sensitivity, in which direct NMR spectroscopy detection on 77 Se is replaced by its indirect observation in a 2D 1 H,77 Se HSQMBC spectrum. In contrast to OH/F substitution, O/Se exchange allows the glycosidic bond to be targeted. As an example, selenodigalactoside recognition by three human galectins and a plant toxin is readily indicated by signal attenuation and line broadening in the 2D 1 H,77 Se HSQMBC spectrum, in which CPMG-INEPT long-range transfer ensures maximal detection sensitivity, clean signal phases, and reliable ligand ranking. By monitoring competitive displacement of a selenated spy ligand, the selective 77 Se NMR spectroscopy approach may also be used to screen non-selenated compounds. Finally, 1 H,77 Se CPMG-INEPT transfer allows further NMR sensors of molecular interaction to be combined with the specificity and resolution of 77 Se NMR spectroscopy.

The diversity of pattern recognition receptors (PRRs) involved with insect defense against pathogens

Through evolution, selection pressures cause both insects and the pathogens attacking them to adapt so that they will both survive and this has been called the co-evolutionary 'arms race'. Insects expand their repertoire of pattern recognition receptors (PRRs), a fundamental and core component of their immune systems, to adapt to the constantly changing and unpredictable diversity of pathogens. In this review, we discuss the diversity of PRRs based on studies conducted in recent years. The strategies associated with PRR diversity summarized here are genetic evolution, isoform diversity based on alternative splicing, 'part-time' PRRs, PRRs with opsonin function, and regulation of complex signaling pathways. Taken together, these data indicate that the function of PRRs in insect immunity is far more complex and possesses more features than originally thought.

Surface (S) Layer Proteins of Lactobacillus acidophilus Block Virus Infection via DC-SIGN Interaction

Alphaviruses and flaviviruses are important human pathogens that include Chikungunya virus (CHIKV), Dengue virus (DENV), and Zika virus (ZIKV), which can cause diseases in humans ranging from arthralgia to hemorrhagic fevers and microcephaly. It was previously shown that treatment with surface layer (S-layer) protein, present on the bacterial cell-envelope of Lactobacillus acidophilus, is able to inhibit viral and bacterial infections by blocking the pathogen’s interaction with DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN), a trans-membrane protein that is a C-type calcium-dependent lectin. DC-SIGN is known to act as an attachment factor for several viruses including alphaviruses and flaviviruses. In the present study, we used alphaviruses as a model system to dissect the mechanism of S-layer inhibition. We first evaluated the protective effect of S-layer using 3T3 cells, either wild type or stably expressing DC-SIGN, and infecting with the alphaviruses Semliki Forest virus (SFV) and CHIKV and the flaviviruses ZIKV and DENV. DC-SIGN expression significantly enhanced infection by all four viruses. Treatment of the cells with S-layer prior to infection decreased infectivity of all viruses only in cells expressing DC-SIGN. In vitro ELISA experiments showed a direct interaction between S-layer and DC-SIGN; however, confocal microscopy and flow cytometry demonstrated that S-layer binding to the cells was independent of DC-SIGN expression. S-layer protein prevented SFV binding and internalization in DC-SIGN-expressing cells but had no effect on virus binding to DC-SIGN-negative cells. Inhibition of virus binding occurred in a time-dependent manner, with a significant reduction of infection requiring at least a 30-min pre-incubation of S-layer with DC-SIGN-expressing cells. These results suggest that S-layer has a different mechanism of action compared to mannan, a common DC-SIGN-binding compound that has an immediate effect in blocking viral infection. This difference could reflect slower kinetics of S-layer binding to the DC-SIGN present at the plasma membrane (PM). Alternatively, the S-layer/DC-SIGN interaction may trigger the activation of signaling pathways that are required for the inhibition of viral infection. Together our results add important information relevant to the potential use of L. acidophilus S-layer protein as an antiviral therapy.

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.

The CARD9-Associated C-Type Lectin, Mincle, Recognizes La Crosse Virus (LACV) but Plays a Limited Role in Early Antiviral Responses against LACV

La Crosse virus (LACV) is a mosquito-transmitted arbovirus and the main cause of virus-mediated neurological diseases in children. To date, little is known about the role of C-type lectin receptors (CLRs)—an important class of pattern recognition receptors—in LACV recognition. DC-SIGN remains the only well-described CLR that recognizes LACV. In this study, we investigated the role of additional CLR/LACV interactions. To this end, we applied a flow-through chromatography method for the purification of LACV to perform an unbiased high-throughput screening of LACV with a CLR-hFc fusion protein library. Interestingly, the CARD9-associated CLRs Mincle, Dectin-1, and Dectin-2 were identified to strongly interact with LACV. Since CARD9 is a common adaptor protein for signaling via Mincle, Dectin-1, and Dectin-2, we performed LACV infection of Mincle^−/− and CARD9^−/− DCs. Mincle^−/− and CARD9^−/− DCs produced less amounts of proinflammatory cytokines, namely IL-6 and TNF-α, albeit no reduction of the LACV titer was observed. Together, novel CLR/LACV interactions were identified; however, the Mincle/CARD9 axis plays a limited role in early antiviral responses against LACV.

Glycosylation of HIV Env Impacts IgG Subtype Responses to Vaccination

The envelope protein (Env) is the only surface protein of the human immunodeficiency virus (HIV) and as such the exclusive target for protective antibody responses. Experimental evidences from mouse models suggest a modulating property of Env to steer antibody class switching towards the less effective antibody subclass IgG1 accompanied with strong TH2 helper responses. By simple physical linkage we were able to imprint this bias, exemplified by a low IgG2a/IgG1 ratio of antigen-specific antibodies, onto an unrelated antigen, namely the HIV capsid protein p24. Here, our results indicate the glycan moiety of Env as the responsible immune modulating activity. Firstly, in Card9^−/− mice lacking specific C-Type lectin responsiveness, DNA immunization significantly increased the IgG2a/IgG1 ratio for the Env-specific antibodies while the antibody response against the F-protein of the respiratory syncytial virus (RSV) serving as control antigen remained unchanged. Secondly, sequential shortening of the Env encoding sequence revealed the C2V3 domain as responsible for the strong IgG1 responses and TH2 cytokine production. Removing all potential N-glycosylation sites from the C2V3 domain by site-specific mutagenesis reversed the vaccine-induced immune response towards a Th1-dominated T-cell response and a balanced IgG2a/IgG1 ratio. Accordingly, the stretch of oligomannose glycans in the C2V3 domain of Env might mediate a specific uptake and/or signaling modus in antigen presenting cells by involving interaction with an as yet unknown C-type lectin receptor. Our results contribute to a deeper understanding of the impact of Env glycosylation on HIV antigen-specific immune responses, which will further support HIV vaccine development.

Messages From the Past: New Insights in Plant Lectin Evolution

Lectins are a large and diverse class of proteins, found in all kingdoms of life. Plants are known to express different types of carbohydrate-binding proteins, each containing at least one particular lectin domain which enables them to specifically recognize and bind carbohydrate structures. The group of plant lectins is heterogeneous in terms of structure, biological activity and function. Lectins control various aspects of plant development and defense. Some lectins facilitate recognition of exogenous danger signals or play a role in endogenous signaling pathways, while others are considered as storage proteins or involved in symbiotic relationships. In this study, we revisit the origin of the different plant lectin families in view of the recently reshaped tree of life. Due to new genomic sampling of previously unknown microbial lineages, the tree of life has expanded and was reshaped multiple times. In addition, more plant genomes especially from basal Phragmoplastophyta, bryophytes, and Salviniales (e.g., Chara braunii, Marchantia polymorpha, Physcomitrella patens, Azolla filiculoides, and Salvinia cucullata) have been analyzed, and annotated genome sequences have become accessible. We searched 38 plant genome sequences including core eudicots, monocots, gymnosperms, fern, lycophytes, bryophytes, charophytes, chlorophytes, glaucophytes, and rhodophytes for lectin motifs, performed an extensive comparative analysis of lectin domain architectures, and determined the phylogenetic and evolutionary history of lectins in the plant lineage. In conclusion, we describe the conservation of particular domains in plant lectin sequences obtained from algae to higher plants. The strong conservation of several lectin motifs highlights their significance for plants.

Daphnia galeata responds to the exposure to an ichthyosporean gut parasite by down-regulation of immunity and lipid metabolism

BACKGROUND

Regulatory circuits of infection in the emerging experimental model system, water flea Daphnia and their microparasites, remain largely unknown. Here we provide the first molecular insights into the response of Daphnia galeata to its highly virulent and common parasite Caullerya mesnili, an ichthyosporean that infects the gut epithelium. We generated a transcriptomic dataset using RNAseq from parasite-exposed (vs. control) Daphnia, at two time points (4 and 48 h) after parasite exposure.

RESULTS

We found a down-regulation of metabolism and immunity-related genes, at 48 h (but not 4 h) after parasite exposure. These genes are involved in lipid metabolism and fatty acid biosynthesis, as well as microbe recognition (e.g. c-type lectins) and pathogen attack (e.g. gut chitin).

CONCLUSIONS

General metabolic suppression implies host energy shift from reproduction to survival, which is in agreement with the known drastic reduction in Daphnia fecundity after Caullerya infection. The down-regulation of gut chitin indicates a possible interaction between the peritrophic matrix and the evading host immune system. Our study provides the first description of host transcriptional responses in this very promising host-parasite experimental system.

Interactions of Surface Exopolysaccharides From Bifidobacterium and Lactobacillus Within the Intestinal Environment

Exopolysaccharides (EPS) are surface carbohydrate polymers present in most bacteria acting as a protective surface layer but also interacting with the surrounding environment. This review discusses the roles of EPS synthesized by strains of Lactobacillus and Bifidobacterium, many of them with probiotic characteristics, in the intestinal environment. Current knowledge on genetics and biosynthesis pathways of EPS in lactic acid bacteria and bifidobacteria, as well as the development of genetic tools, has created possibilities to elucidate the interplay between EPS and host intestinal mucosa. These include the microbiota that inhabits this ecological niche and the host cells. Several carbohydrate recognition receptors located in the intestinal epithelium could be involved in the interaction with bacterial EPS and modulation of immune response; however, little is known about the receptors recognizing EPS from lactobacilli or bifidobacteria and the triggered response. On the contrary, it has been clearly demonstrated that EPS play a relevant role in the persistence of the producing bacteria in the intestinal tract. Indeed, some authors postulate that some of the beneficial actions of EPS-producing probiotics could be related to the formation of a biofilm layer protecting the host against injury, for example by pathogens or their toxins. Nevertheless, the in vivo formation of biofilms by probiotics has not been proved to date. Finally, EPS produced by probiotic strains are also able to interact with the intestinal microbiota that populates the gut. In fact, some of these polymers can be used as carbohydrate fermentable source by some gut commensals thus being putatively involved in the release of bacterial metabolites that exert positive benefits for the host. In spite of the increasing knowledge about the role that these surface molecules play in the interaction of probiotic bacteria with the gut mucosal actors, both intestinal receptors and microbiota, the challenging issue is to demonstrate the functionality of EPS in vivo, which will open an avenue of opportunities for the application of EPS-producing probiotics to improve health.

Fluorinated Carbohydrates as Lectin Ligands: Synthesis of OH/F-Substituted N-Glycan Core Trimannoside and Epitope Mapping by 2D STD-TOCSYreF NMR spectroscopy

Glycan-protein interactions play an important role in a broad range of physiological processes, raising interest to elucidate the structural interplay. Yet, their dynamic nature limits the analysis by crystallography, whereas NMR spectroscopy suffers from the low ¹ H dispersion of glycans. Therefore, their sparse fluorination and NMR screening by 1D Saturation Transfer Difference with relay to ¹⁹ F (STDreF) was previously proposed to exploit the superior dispersion in ¹⁹ F NMR spectroscopy. A new 2D STD-TOCSYreF experiment is presented here that enables comprehensive epitope mapping of fluorinated glycans by combining the spectral resolution of ¹⁹ F with the spatial resolution and coverage of ¹ H. For an illustration, the 2-deoxy-2-fluoro derivative of the N-glycan core trimannoside was synthesised and its recognition of Pisum sativum agglutinin by either of the two terminal mannose residues was confirmed. Going beyond the crystallographic information, the 2D STD-TOCSYreF spectrum moreover visualised collateral contacts from the branching mannose and allowed to assess the ratio of both co-existing binding modes through the α1,3- (67 %) and α1,6-linked (33 %) terminal mannose moieties.

Probiotics for the airways: Potential to improve epithelial and immune homeostasis

Probiotics are live microorganisms that, when administered in adequate amounts, confer health benefit on the host. The therapeutic effects of probiotics have been mostly studied in the gastrointestinal tract, but recent evidence points toward the potential of these bacteria to prevent and/or treat chronic airway diseases. In this review, possible mechanisms of action of probiotics in the airways are described, with a particular focus on their capacity to modulate the epithelial barrier function and their mode of interaction with the immune system. Indeed, probiotic bacteria, mostly lactobacilli, can promote the expression and regulation of tight junctions and adherence junctions, resulting in the restoration of a defective epithelial barrier. These bacteria interact with the epithelial barrier and immune cells through pattern recognition receptors, such as Toll-like receptors, which upon activation can stimulate or suppress various immune responses. Finally, the clinical potential of probiotics to treat inflammatory diseases of the upper and lower respiratory tract, and the difference between their mode of application (eg, oral or nasal) are discussed here.

C-Type Lectin-20 Interacts with ALP1 Receptor to Reduce Cry Toxicity in Aedes aegypti

Aedes aegypti is a crucial vector for human diseases, such as yellow fever, dengue, chikungunya, and Zika viruses. Today, a major challenge throughout the globe is the insufficient availability of antiviral drugs and vaccines against arboviruses, and toxins produced by Bacillus thuringiensis (Bt) are still used as biological agents for mosquito control. The use of Cry toxins to kill insects mainly depends on the interaction between Cry toxins and important toxin receptors, such as alkaline phosphatase (ALP). In this study, we investigated the function of A. aegypti C-type lectin-20 (CTL-20) in the tolerance of Cry toxins. We showed that recombinant CTL-20 protein interacted with both Cry11Aa and ALP1 by the Far-Western blot and ELISA methods, and CTL-20 bound to A. aegypti larval brush border membrane vesicles (BBMVs). Binding affinity of CTL-20 to ALP1 was higher than that of Cry11Aa to ALP1. Furthermore, the survival rate of A. aegypti larvae fed with Cry11Aa toxin mixed with recombinant CTL-20 fusion protein was significantly increased compared with that of the control larvae fed with Cry11Aa mixed with thioredoxin. Our novel results suggest that midgut proteins like CTLs may interfere with interactions between Cry toxins and toxin receptors by binding to both Cry toxins and receptors to alter Cry toxicity.

The first line of defence: insights into mechanisms and relevance of phagocytosis in epithelial cells

Epithelial tissues cover most of the external and internal surfaces of the body and its organs. Inevitably, these tissues serve as first line of defence against inorganic, organic, and microbial intruders. Epithelial cells are the main cell type of these tissues. Besides their function as cellular barrier, there is growing evidence that epithelial cells are of particular relevance as initial sensors of danger and also as executers of adequate defence responses. These cells feature various essential functions to maintain tissue integrity in health and disease. In this review, we survey some of the different innate immune functions of epithelial cells in mucosal tissues being constantly exposed to a plethora of harmless contaminants but also of pathogens. We discuss how epithelial cells avoid inadequate immune responses in such conditions. In particular, we will focus on the diverse types and mechanisms of phagocytosis used by epithelial cells to not only maintain homeostasis but to also harness the host response against invading pathogens.

The Intestinal Roundworm Ascaris suum Releases Antimicrobial Factors Which Interfere With Bacterial Growth and Biofilm Formation

Ascariasis is a widespread soil-transmitted helminth infection caused by the intestinal roundworm Ascaris lumbricoides in humans, and the closely related Ascaris suum in pigs. Progress has been made in understanding interactions between helminths and host immune cells, but less is known concerning the interactions of parasitic nematodes and the host microbiota. As the host microbiota represents the direct environment for intestinal helminths and thus a considerable challenge, we studied nematode products, including excretory-secretory products (ESP) and body fluid (BF), of A. suum to determine their antimicrobial activities. Antimicrobial activities against gram-positive and gram-negative bacterial strains were assessed by the radial diffusion assay, while effects on biofilm formation were assessed using the crystal violet static biofilm and macrocolony assays. In addition, bacterial neutralizing activity was studied by an agglutination assay. ESP from different A. suum life stages (in vitro-hatched L3, lung-stage L3, L4, and adult) as well as BF from adult males were analyzed by mass spectrometry. Several proteins and peptides with known and predicted roles in nematode immune defense were detected in ESP and BF samples, including members of A. suum antibacterial factors (ASABF) and cecropin antimicrobial peptide families, glycosyl hydrolase enzymes such as lysozyme, as well as c-type lectin domain-containing proteins. Native, unconcentrated nematode products from intestine-dwelling L4-stage larvae and adults displayed broad-spectrum antibacterial activity. Additionally, adult A. suum ESP interfered with biofilm formation by Escherichia coli, and caused bacterial agglutination. These results indicate that A. suum uses a variety of factors with broad-spectrum antibacterial activity to affirm itself within its microbe-rich environment in the gut.

Black rockfish C-type lectin, SsCTL4: A pattern recognition receptor that promotes bactericidal activity and virus escape from host immune defense

C-type lectin (CTL) is an immune receptor and is received extensive attention of its important roles in immune response and immune escape. Some CTL, such as CTL4, has been well characterized in human and several other mammals, but much less documentation exists about the immunological function of CTL4 in lower vertebrates. In the present study, a C-type lectin domain family 4 member, SsCTL4, which is also high homology with CD209 antigen-like protein, from the teleost fish black rockfish (Sebastes schlegelii) was identified and examined at expression and functional levels. The open reading frame of SsCTL4 is 765 bp, and the deduced amino acid sequence of SsCTL4 shares 78%-84% overall identities with the C-type lectin of several fish species. In silico analysis identified several conserved C-type lectin features, including a carbohydrate-recognition domain and four disulfide bond-forming cysteine residues. Expression of SsCTL4 occurred in multiple tissues and was upregulated during bacterial and viral infection. Recombinant SsCTL4 (rSsCTL4) exhibited apparent binding activities against bacteria (Edwardsiella tarda and Vibrio anguillarum) and virus (infectious spleen and kidney necrosis virus, ISKNV). rSsCTL4 was able to agglutinate the Gram-negative and Gram-positive bacteria in a Ca²⁺-dependent manner. The agglutinating ability of rSsCTL4 was abolished in the absence of calcium or presence of mannose. rSsCTL4 also increased macrophage bactericidal activity. In the presence of rSsCTL4, fish exhibited enhanced resistance against bacterial infection but increased susceptibility to viral infections. Collectively, these results indicate that SsCTL4 serves as a pattern recognition receptor that not only promotes bactericidal activity, but may also serve as targets for virus manipulation of host defense system.

Crystallization of a human galectin-3 variant with two ordered segments in the shortened N-terminal tail

Among members of the family of adhesion/growth-regulatory galectins, galectin-3 (Gal-3) bears a unique modular architecture. A N-terminal tail (NT) consisting of the N-terminal segment (NTS) and nine collagen-like repeats is linked to the canonical lectin domain. In contrast to bivalent proto- and tandem-repeat-type galectins, Gal-3 is monomeric in solution, capable to self-associate in the presence of bi- to multivalent ligands, and the NTS is involved in cellular compartmentalization. Since no crystallographic information on Gal-3 beyond the lectin domain is available, we used a shortened variant with NTS and repeats VII-IX. This protein crystallized as tetramers with contacts between the lectin domains. The region from Tyr101 (in repeat IX) to Leu114 (in the CRD) formed a hairpin. The NTS extends the canonical β-sheet of F1-F5 strands with two new β-strands on the F face. Together, crystallographic and SAXS data reveal a mode of intramolecular structure building involving the highly flexible Gal-3’s NT.

Immunoregulatory Effects of Myeloid-Derived Suppressor Cell Exosomes in Mouse Model of Autoimmune Alopecia Areata

The treatment of autoimmune diseases still poses a major challenge, frequently relying on non-specific immunosuppressive drugs. Current efforts aim at reestablishing self tolerance using immune cells with suppressive activity like the regulatory T cells (Treg) or the myeloid-derived suppressor cells (MDSC). We have demonstrated therapeutic efficacy of MDSC in mouse Alopecia Areata (AA). In the same AA model, we now asked whether MDSC exosomes (MDSC-Exo) can replace MDSC. MDSC-Exo from bone marrow cells (BMC) cultures of healthy donors could substantially facilitate treatment. With knowledge on MDSC-Exo being limited, their suitability needs to be verified in advance. Protein marker profiles suggest comparability of BMC- to ex vivo collected inflammatory MDSC/MDSC-Exo in mice with a chronic contact dermatitis, which is a therapeutic option in AA. Proteome analyses substantiated a large overlap of function-relevant molecules in MDSC and MDSC-Exo. Furthermore, MDSC-Exo are taken up by T cells, macrophages, NK, and most avidly by Treg and MDSC-Exo uptake exceeds binding of MDSC themselves. In AA mice, MDSC-Exo preferentially target skin-draining lymph nodes and cells in the vicinity of remnant hair follicles. MDSC-Exo uptake is accompanied by a strong increase in Treg, reduced T helper proliferation, mitigated cytotoxic activity, and a slight increase in lymphocyte apoptosis. Repeated MDSC-Exo application in florid AA prevented progression and sufficed for partial hair regrowth. Deep sequencing of lymphocyte mRNA from these mice revealed a significant increase in immunoregulatory mRNA, including FoxP3 and arginase 1. Downregulated mRNA was preferentially engaged in prohibiting T cell hyperreactivity. Taken together, proteome analysis provided important insights into potential MDSC-Exo activities, these Exo preferentially homing into AA-affected organs. Most importantly, changes in leukocyte mRNA seen after treatment of AA mice with MDSC-Exo sustainably supports the strong impact on the adaptive and the non-adaptive immune system, with Treg expansion being a dominant feature. Thus, MDSC-Exo could potentially serve as therapeutic agents in treating AA and other autoimmune diseases.

ABO Antigens Active Tri- and Disaccharides Microarray to Evaluate C-type Lectin Receptor Binding Preferences

Understanding blood group antigen binding preferences for C-type lectin receptors holds promise for modulating immune responses, since several Gram-negative bacteria express blood group antigens as molecular mimicry to evade immune responses. Herein, we report the synthesis of ABO blood group antigen active tri and disaccharides to investigate the binding specificity with various C-type lectin receptors using glycan microarray. The results of binding preferences show that distinct glycosylation on the galactose and fucose motifs are key for C-type lectin receptor binding and that these interactions occur in a Ca²⁺-dependent fashion.

Trypanosomatid Infections: How Do Parasites and Their Excreted-Secreted Factors Modulate the Inducible Metabolism of l-Arginine in Macrophages?

Mononuclear phagocytes (monocytes, dendritic cells, and macrophages) are among the first host cells to face intra- and extracellular protozoan parasites such as trypanosomatids, and significant expansion of macrophages has been observed in infected hosts. They play essential roles in the outcome of infections caused by trypanosomatids, as they can not only exert a powerful antimicrobial activity but also promote parasite proliferation. These varied functions, linked to their phenotypic and metabolic plasticity, are exerted via distinct activation states, in which l-arginine metabolism plays a pivotal role. Depending on the environmental factors and immune response elements, l-arginine metabolites contribute to parasite elimination, mainly through nitric oxide (NO) synthesis, or to parasite proliferation, through l-ornithine and polyamine production. To survive and adapt to their hosts, parasites such as trypanosomatids developed mechanisms of interaction to modulate macrophage activation in their favor, by manipulating several cellular metabolic pathways. Recent reports emphasize that some excreted-secreted (ES) molecules from parasites and sugar-binding host receptors play a major role in this dialog, particularly in the modulation of the macrophage's inducible l-arginine metabolism. Preventing l-arginine dysregulation by drugs or by immunization against trypanosomatid ES molecules or by blocking partner host molecules may control early infection and is a promising way to tackle neglected diseases including Chagas disease, leishmaniases, and African trypanosomiases. The present review summarizes recent knowledge on trypanosomatids and their ES factors with regard to their influence on macrophage activation pathways, mainly the NO synthase/arginase balance. The review ends with prospects for the use of biological knowledge to develop new strategies of interference in the infectious processes used by trypanosomatids, in particular for the development of vaccines or immunotherapeutic approaches.

Linkage of Infection to Adverse Systemic Complications: Periodontal Disease, Toll-Like Receptors, and Other Pattern Recognition Systems

Toll-like receptors (TLRs) are a group of pattern recognition receptors (PRRs) that provide innate immune sensing of conserved pathogen-associated molecular patterns (PAMPs) to engage early immune recognition of bacteria, viruses, and protozoa. Furthermore, TLRs provide a conduit for initiation of non-infectious inflammation following the sensing of danger-associated molecular patterns (DAMPs) generated as a consequence of cellular injury. Due to their essential role as DAMP and PAMP sensors, TLR signaling also contributes importantly to several systemic diseases including cardiovascular disease, diabetes, and others. The overlapping participation of TLRs in the control of infection, and pathogenesis of systemic diseases, has served as a starting point for research delving into the poorly defined area of infection leading to increased risk of various systemic diseases. Although conflicting studies exist, cardiovascular disease, diabetes, cancer, rheumatoid arthritis, and obesity/metabolic dysfunction have been associated with differing degrees of strength to infectious diseases. Here we will discuss elements of these connections focusing on the contributions of TLR signaling as a consequence of bacterial exposure in the context of the oral infections leading to periodontal disease, and associations with metabolic diseases including atherosclerosis and type 2 diabetes.

Glycan Chains of Gangliosides: Functional Ligands for Tissue Lectins (Siglecs/Galectins)

Molecular signals on the cell surface are responsible for adhesion and communication. Of relevance in this respect, their chemical properties endow carbohydrates with the capacity to store a maximum of information in a minimum of space. One way to present glycans on the cell surface is their covalent conjugation to a ceramide anchor. Among the resulting glycosphingolipids, gangliosides are special due to the presence of at least one sialic acid in the glycan chains. Their spatial accessibility and the dynamic regulation of their profile are factors that argue in favor of a role of glycans of gangliosides as ligands (counterreceptors) for carbohydrate-binding proteins (lectins). Indeed, as discovered first for a bacterial toxin, tissue lectins bind gangliosides and mediate contact formation (trans) and signaling (cis). While siglecs have a preference for higher sialylated glycans, certain galectins also target the monosialylated pentasaccharide of ganglioside GM1. Enzymatic interconversion of ganglioside glycans by sialidase action, relevant for neuroblastoma cell differentiation and growth control in vitro, for axonogenesis and axon regeneration, as well as for proper communication between effector and regulatory T cells, changes lectin-binding affinity profoundly. The GD1a-to-GM1 "editing" is recognized by such lectins, for example, myelin-associated glycoprotein (siglec-4) losing affinity and galectin-1 gaining reactivity, and then translated into postbinding signaling. Orchestrations of loss/gain of affinity, of ganglioside/lectin expression, and of lectin presence in a network offer ample opportunities for fine-tuning. Thus glycans of gangliosides such as GD1a and GM1 are functional counterreceptors by a pairing with tissue lectins, an emerging aspect of ganglioside and lectin functionality.

N-Carboxyanhydride Polymerization of Glycopolypeptides That Activate Antigen-Presenting Cells through Dectin-1 and Dectin-2

The C-type lectins dectin-1 and dectin-2 contribute to innate immunity against microbial pathogens by recognizing their foreign glycan structures. These receptors are promising targets for vaccine development and cancer immunotherapy. However, currently available agonists are heterogeneous glycoconjugates and polysaccharides from natural sources. Herein, we designed and synthesized the first chemically defined ligands for dectin-1 and dectin-2. They comprised glycopolypeptides bearing mono-, di-, and trisaccharides and were built through polymerization of glycosylated N-carboxyanhydrides. Through this approach, we achieved glycopolypeptides with high molecular weights and low dispersities. We identified structures that elicit a pro-inflammatory response through dectin-1 or dectin-2 in antigen-presenting cells. With their native proteinaceous backbones and natural glycosidic linkages, these agonists are attractive for translational applications.

Dectin-1 Positive Dendritic Cells Expand after Infection with Leishmania major Parasites and Represent Promising Targets for Vaccine Development

Resistant mouse strains mount a protective T cell-mediated immune response upon infection with Leishmania (L.) parasites. Healing correlates with a T helper (Th) cell-type 1 response characterized by a pronounced IFN-γ production, while susceptibility is associated with an IL-4-dependent Th2-type response. It has been shown that dermal dendritic cells are crucial for inducing protective Th1-mediated immunity. Additionally, there is growing evidence that C-type lectin receptor (CLR)-mediated signaling is involved in directing adaptive immunity against pathogens. However, little is known about the function of the CLR Dectin-1 in modulating Th1- or Th2-type immune responses by DC subsets in leishmaniasis. We characterized the expression of Dectin-1 on CD11c+ DCs in peripheral blood, at the site of infection, and skin-draining lymph nodes of L. major-infected C57BL/6 and BALB/c mice and in peripheral blood of patients suffering from cutaneous leishmaniasis (CL). Both mouse strains responded with an expansion of Dectin-1+ DCs within the analyzed tissues. In accordance with the experimental model, Dectin-1+ DCs expanded as well in the peripheral blood of CL patients. To study the role of Dectin-1+ DCs in adaptive immunity against L. major, we analyzed the T cell stimulating potential of bone marrow-derived dendritic cells (BMDCs) in the presence of the Dectin-1 agonist Curdlan. These experiments revealed that Curdlan induces the maturation of BMDCs and the expansion of Leishmania-specific CD4+ T cells. Based on these findings, we evaluated the impact of Curdlan/Dectin-1 interactions in experimental leishmaniasis and were able to demonstrate that the presence of Curdlan at the site of infection modulates the course of disease in BALB/c mice: wild-type BALB/c mice treated intradermally with Curdlan developed a protective immune response against L. major whereas Dectin-1-/- BALB/c mice still developed the fatal course of disease after Curdlan treatment. Furthermore, the vaccination of BALB/c mice with a combination of soluble L. major antigens and Curdlan was able to provide a partial protection from severe leishmaniasis. These findings indicate that the ligation of Dectin-1 on DCs acts as an important checkpoint in adaptive immunity against L. major and should therefore be considered in future whole-organism vaccination strategies.

C-Type Lectin Receptor (CLR)-Fc Fusion Proteins As Tools to Screen for Novel CLR/Bacteria Interactions: An Exemplary Study on Preselected Campylobacter jejuni Isolates

C-type lectin receptors (CLRs) are carbohydrate-binding receptors that recognize their ligands often in a Ca²⁺-dependent manner. Upon ligand binding, myeloid CLRs in innate immunity trigger or inhibit a variety of signaling pathways, thus initiating or modulating effector functions such as cytokine production, phagocytosis, and antigen presentation. CLRs bind to various pathogens, including viruses, fungi, parasites, and bacteria. The bacterium Campylobacter jejuni (C. jejuni) is a very frequent Gram-negative zoonotic pathogen of humans, causing severe intestinal symptoms. Interestingly, C. jejuni expresses several glycosylated surface structures, for example, the capsular polysaccharide (CPS), lipooligosaccharide (LOS), and envelope proteins. This “Methods” paper describes applications of CLR–Fc fusion proteins to screen for yet unknown CLR/bacteria interactions using C. jejuni as an example. ELISA-based detection of CLR/bacteria interactions allows a first prescreening that is further confirmed by flow cytometry-based binding analysis and visualized using confocal microscopy. By applying these methods, we identified Dectin-1 as a novel CLR recognizing two selected C. jejuni isolates with different LOS and CPS genotypes. In conclusion, the here-described applications of CLR–Fc fusion proteins represent useful methods to screen for and identify novel CLR/bacteria interactions.

Glycomimetic, Orally Bioavailable LecB Inhibitors Block Biofilm Formation of Pseudomonas aeruginosa

The opportunistic Gram-negative bacterium Pseudomonas aeruginosa is a leading pathogen for infections of immuno-compromised patients and those suffering from cystic fibrosis. Its ability to switch from planktonic life to aggregates, forming the so-called biofilms, is a front-line mechanism of antimicrobial resistance. The bacterial carbohydrate-binding protein LecB is an integral component and necessary for biofilm formation. Here, we report a new class of drug-like low molecular weight inhibitors of the lectin LecB with nanomolar affinities and excellent receptor binding kinetics and thermodynamics. This class of glycomimetic inhibitors efficiently blocked biofilm formation of P. aeruginosa in vitro while the natural monovalent carbohydrate ligands failed. Furthermore, excellent selectivity and pharmacokinetic properties were achieved. Notably, two compounds showed good oral bioavailability, and high compound concentrations in plasma and urine were achieved in vivo.

Revealing biomedically relevant cell and lectin type-dependent structure–activity profiles for glycoclusters by using tissue sections as an assay platform

The increasing realization of the involvement of lectin-glycan recognition in (patho)physiological processes inspires envisioning therapeutic intervention by high-avidity/specificity blocking reagents. Synthetic glycoclusters are proving to have potential for becoming such inhibitors but the commonly used assays have their drawbacks to predict in vivo efficacy. They do not represent the natural complexity of (i) cell types and (ii) spatial and structural complexity of glycoconjugate representation. Moreover, testing lectins in mixtures, as present in situ, remains a major challenge, giving direction to this work. Using a toolbox with four lectins and six bi- to tetravalent glycoclusters bearing the cognate sugar in a model study, we here document the efficient and versatile application of tissue sections (from murine jejunum as the model) as a platform for routine and systematic glycocluster testing without commonly encountered limitations. The nature of glycocluster structure, especially core and valency, and of protein features, i.e. architecture, fine-specificity and valency, are shown to have an influence, as cell types can differ in response profiles. Proceeding from light microscopy to monitoring by fluorescence microscopy enables grading of glycocluster activity on individual lectins tested in mixtures. This work provides a robust tool for testing glycoclusters prior to considering in vivo experiments.

Introducing tissue sections for testing glycocluster activity as inhibitors of lectin binding close to in vivo conditions.

Structural and functional diversity of collectins and ficolins and their relationship to disease

Pattern recognition molecules are sensors for the innate immune system and trigger a number of pathophysiological functions after interaction with the corresponding ligands on microorganisms or altered mammalian cells. Of those pattern recognition molecules used by the complement system, collagen-like lectins (collectins) are an important subcomponent. Whereas the best known of these collectins, mannose-binding lectin, largely occurs as a circulating protein following production by hepatocytes, the most recently described collectins exhibit strong local biosynthesis. This local production and release of soluble collectin molecules appear to serve local tissue functions at extravascular sites, including a developmental function. In this article, we focus on the characteristics of collectin-11 (CL-11 or CL-K1), whose ubiquitous expression and multiple activities likely reflect a wide biological relevance. Collectin-11 appears to behave as an acute phase protein whose production associated with metabolic and physical stress results in locally targeted inflammation and tissue cell death. Early results indicate the importance of fucosylated ligand marking the injured cells targeted by collectin-11, and we suggest that further characterisation of this and related ligands will lead to better understanding of pathophysiological significance and exploitation for clinical benefit.

Glycopeptides as Targets for Dendritic Cells: Exploring MUC1 Glycopeptides Binding Profile toward Macrophage Galactose-Type Lectin (MGL) Orthologs

The macrophage galactose-type lectin (MGL) recognizes glycan moieties exposed by pathogens and malignant cells. Particularly, mucin-1 (MUC1) glycoprotein presents an altered glycosylation in several cancers. To estimate the ability of distinct MGL orthologs to recognize aberrant glycan cores in mucins, we applied evanescent-field detection to a versatile MUC1-like glycopeptide microarray platform. Here, as binding was sequence-dependent, we demonstrated that not only sugars but also peptide region impact the recognition of murine MGL1 (mMGL1). In addition, we observed for all three MGL orthologs that divalent glycan presentation increased the binding. To assess the utility of the glycopeptide binders of the MGL orthologs for MGL targeting, we performed uptake assays with fluorescein-MUC1 using murine dendritic cells. A diglycosylated MUC1 peptide was preferentially internalized in an MGL-dependent fashion, thus showing the utility for divalent MGL targeting. These findings may be relevant to a rational design of antitumor vaccines targeting dendritic cells via MGL.

A genetic algorithm for simulating correlated binary data from biomedical research

Correlated binary data arise in a large variety of biomedical research. In order to evaluate methods for their analysis, computer simulations of such data are often required. Existing methods can often not cover the full range of possible correlations between the variables or are not available as implemented software. We propose a genetic algorithm that approaches the desired correlation structure under a given marginal distribution. The procedure generates a large representative matrix from which the probabilities of individual observations can be derived or from which samples can be drawn directly. Our genetic algorithm is evaluated under different specified marginal frequencies and correlation structures, and is compared against two existing approaches. The evaluation checks the speed and precision of the approach as well as its suitability for generating also high-dimensional data. In an example of high-throughput glycan array data, we demonstrate the usability of our approach to simulate the power of global test procedures. An implementation of our own and two other methods were added to the R-package 'RepeatedHighDim'. The presented algorithm is not restricted to certain correlation structures. In contrast to existing methods it is also evaluated for high-dimensional data.

Deep transcriptome profiling sheds light on key players in nucleus implantation induced immune response in the pearl oyster Pinctada martensii

Immunological rejection of the pearl oysters following nucleus implantation is a major issue limiting the successful rate of cultured pearls. To date, the molecular mechanism of immune tolerance during pearl formation in the pearl oysters is still largely unknown. Through the RNA sequencing platform and comparative transcriptomic analysis, we investigated the chronic gene expression changes at seven time points (0, 5, 10, 15, 20, 30, 60 days post implantation or dpi) over a period of 60 days following nucleus implantation in the pearl oyster Pinctada martensii. A total of 81,390 unique transcripts (or unigenes) with a combined length of 96.8 million bp and a N50 value of 2227 bp were obtained. When compared with sequences in the nr, nt, Swiss-Prot, KEGG, COG and GO databases, 36,380 unigenes can find homologous genes. Pairwise comparison of gene expression among all the samples showed that the largest number (or 6846) of differentially expressed genes was observed at 10 dpi. The number then decreased to below 5000 at 15, 20 and 30 dpi and increased again to 6679 at 60 dpi. PCA analysis further showed that the seven time points can be roughly divided into four groups. Comparative transcriptomic analysis between the four groups identified a variety of genes showing differential expression at different time points, including many immune-related genes such as those encoding for toll-like receptor, lectin, scavenger receptor, and peroxidase. In addition, GO and KEGG enrichment analysis revealed that these differentially expressed genes were mainly associated with metabolism, ribosome function, immune response, signaling transduction, and cytoskeleton organization. Notably, two KEGG pathways, namely "cell adhesion molecules" and "primary immunodeficiency" were significantly enriched during the whole process. This finding indicates that genes in these pathways are likely to play critical roles in the immune tolerance of the pearl oysters. To conclude, the data obtained contribute to a better understanding of the molecular mechanisms of nucleus implantation induced immune response in the pearl oysters, and will facilitate the development of effective measures to improve the performance of pearl culture.

Structure, genetics and function of the pulmonary associated surfactant proteins A and D: The extra-pulmonary role of these C type lectins

The collectins family encompasses several collagenous Ca²⁺-dependent defense lectins that are described as pathogen recognition molecules. They play an important role in both adaptive and innate immunity. Surfactant proteins A and D are two of these proteins which were initially discovered in association with surfactant in the pulmonary system. The structure, immune and inflammatory functions, and genetic variations have been well described in relation to their roles, function and pathophysiology in the pulmonary system. Subsequently, these proteins have been discovered in a wide range of other organs and organ systems. The role of these proteins outside the pulmonary system is currently an active area of research. This review intends to provide a current overview of the genetics, structure and extra-pulmonary functions of the surfactant collectin proteins.

Myeloid C-Type Lectin Receptors in Viral Recognition and Antiviral Immunity

Recognition of viral glycans by pattern recognition receptors (PRRs) in innate immunity contributes to antiviral immune responses. C-type lectin receptors (CLRs) are PRRs capable of sensing glycans present in viral pathogens to activate antiviral immune responses such as phagocytosis, antigen processing and presentation, and subsequent T cell activation. The ability of CLRs to elicit and shape adaptive immunity plays a critical role in the inhibition of viral spread within the host. However, certain viruses exploit CLRs for viral entry into host cells to avoid immune recognition. To block CLR interactions with viral glycoproteins, antiviral strategies may involve the use of multivalent glycan carrier systems. In this review, we describe the role of CLRs in antiviral immunity and we highlight their dual function in viral clearance and exploitation by viral pathogens.