Recognition of bacterial capsular polysaccharides and lipopolysaccharides by the macrophage mannose receptor

Macrophages exploit the mannose receptor and JAK-STAT1-MHC-II pathway to drive antigen presentation and the antimycobacterial immune response after BCG vaccination

Tuberculosis (TB), caused by Mycobacterium tuberculosis ( M. tb), remains one of the leading causes of fatal infectious diseases worldwide. The only licensed vaccine, Mycobacterium bovis Bacillus Calmette-Guérin (BCG), has variable efficacy against TB in adults. Insufficiency of immune cell function diminishes the protective effects of the BCG vaccine. It is critical to clarify the mechanism underlying the antimycobacterial immune response during BCG vaccination. Macrophage mannose receptor (MR) is important for enhancing the uptake and processing of glycoconjugated antigens from pathogens for presentation to T cells, but the roles of macrophage MR in the BCG-induced immune response against M. tb are not yet clear. Here, we discover that macrophage MR deficiency impairs the antimycobacterial immune response in BCG-vaccinated mice. Mechanistically, macrophage MR triggers JAK-STAT1 signaling, which promotes antigen presentation via upregulated MHC-II and induces IL-12 production by macrophages, contributing to CD4 + T cell activation and IFN-γ production. MR deficiency in macrophages reduces the vaccine efficacy of BCG and increases susceptibility to M. tb H37Ra challenge in mice. Our results suggest that MR is critical for macrophage antigen presentation and the antimycobacterial immune response to BCG vaccination and offer valuable guidance for the preventive strategy of BCG immunization.

Synthetic BSA-conjugated disaccharide related to the Streptococcus pneumoniae serotype 3 capsular polysaccharide increases IL-17A Levels, γδ T cells, and B1 cells in mice

The disaccharide (β-D-glucopyranosyluronic acid)-(1→4)-β-D-glucopyranoside represents a repeating unit of the capsular polysaccharide of Streptococcus pneumoniae serotype 3. A conjugate of the disaccharide with BSA (di-BSA conjugate) adjuvanted with aluminum hydroxide induced - in contrast to the non-adjuvanted conjugate - IgG1 antibody production and protected mice against S. pneumoniae serotype 3 infection after intraperitoneal prime-boost immunization. Adjuvanted and non-adjuvanted conjugates induced production of Th1 (IFNγ, TNFα); Th2 (IL-5, IL-13); Th17 (IL-17A), Th1/Th17 (IL-22), and Th2/Th17 cytokines (IL-21) after immunization. The concentration of cytokines in mice sera was higher in response to the adjuvanted conjugate, with the highest level of IL-17A production after the prime and boost immunizations. In contrast, the non-adjuvanted conjugate elicited only weak production of IL-17A, which gradually decreased after the second immunization. After boost immunization of mice with the adjuvanted di-BSA conjugate, there was a significant increase in the number of CD45+/CD19+ B cells, TCR+ γδ T cell, CD5+ В1 cells, and activated cells with MHC II+ expression in the spleens of the mice. IL-17A, TCR+ γδ T cells, and CD5+ В1 cells play a crucial role in preventing pneumococcal infection, but can also contribute to autoimmune diseases. Immunization with the adjuvanted and non-adjuvanted di-BSA conjugate did not elicit autoantibodies against double-stranded DNA targeting cell nuclei in mice. Thus, the molecular and cellular markers associated with antibody production and protective activity in response to immunization with the di-BSA conjugate adjuvanted with aluminum hydroxide are IL-17A, TCR+ γδ T cells, and CD5+ В1 cells against the background of increasing MHC II+ expression.

Sulfated oligosaccharide activates endothelial Notch for inducing macrophage-associated arteriogenesis to treat ischemic diseases

Ischemic diseases lead to considerable morbidity and mortality, yet conventional clinical treatment strategies for therapeutic angiogenesis fall short of being impactful. Despite the potential of biomaterials to deliver pro-angiogenic molecules at the infarct site to induce angiogenesis, their efficacy has been impeded by aberrant vascular activation and off-target circulation. Here, we present a semisynthetic low-molecular sulfated chitosan oligosaccharide (SCOS) that efficiently induces therapeutic arteriogenesis with a spontaneous generation of collateral circulation and blood reperfusion in rodent models of hind limb ischemia and myocardial infarction. SCOS elicits anti-inflammatory macrophages' (Mφs') differentiation into perivascular Mφs, which in turn directs artery formation via a cell-to-cell communication rather than secretory factor regulation. SCOS-mediated arteriogenesis requires a canonical Notch signaling pathway in Mφs via the glycosylation of protein O-glucosyltransferases 2, which results in promoting arterial differentiation and tissue repair in ischemia. Thus, this highly bioactive oligosaccharide can be harnessed to direct efficiently therapeutic arteriogenesis and perfusion for the treatment of ischemic diseases.

Exploring the enzymatic activity of depolymerase gp531 from Klebsiella pneumoniae jumbo phage RaK2

Klebsiella pneumoniae poses a major global challenge due to its virulence, multidrug resistance, and nosocomial nature. Thus, bacteriophage-derived proteins are extensively being investigated as a means to combat this bacterium. In this study, we explored the enzymatic specificity of depolymerase gp531, encoded by the jumbo bacteriophage vB_KleM_RaK2 (RaK2). We used two different methods to modify the reducing end of the oligosaccharides released during capsule hydrolysis with gp531. Subsequent acidic cleavage with TFA, followed by TLC and HPLC-MS analyses, revealed that RaK2 gp531 is a β-(1→4)-endoglucosidase. The enzyme specifically recognizes and cleaves the capsular polysaccharide (CPS) of the Klebsiella pneumoniae K54 serotype, releasing K-unit monomers (the main product), dimers, and trimers. Depolymerase gp531 remains active from 10 to 50 °C and in the pH 3-8 range, indicating its stability and versatility. Additionally, we demonstrated that gp531's activity is not affected by CPS acetylation, which is influenced by the growth conditions of the bacterial culture. Overall, our findings provide valuable insights into the enzymatic activity of the first characterized depolymerase targeting the capsule of the clinically relevant K54 serotype of K. pneumoniae.

Identification of three capsule depolymerases in a bacteriophage infecting Klebsiella pneumoniae capsular types K7, K20, and K27 and therapeutic application

BACKGROUND

Klebsiella pneumoniae capsular types K1, K2, K5, K20, K54, and K57 are prevalent hypervirulent types associated with community infections, and worrisomely, hypervirulent strains that acquired drug resistance have been found. In the search for alternative therapeutics, studies have been conducted on phages that infect K. pneumoniae K1, K2, K5, and K57-type strains and their phage-encoded depolymerases. However, phages targeting K. pneumoniae K20-type strains and capsule depolymerases capable of digesting K20-type capsules have rarely been reported. In this study, we characterized a phage that can infect K. pneumoniae K20-type strains, phage vB_KpnM-20.

METHODS

A phage was isolated from sewage water in Taipei, Taiwan, its genome was analyzed, and its predicted capsule depolymerases were expressed and purified. The host specificity and capsule-digesting activity of the capsule depolymerases were determined. The therapeutic effect of the depolymerase targeting K. pneumoniae K20-type strains was analyzed in a mouse infection model.

RESULTS

The isolated Klebsiella phage, vB_KpnM-20, infects K. pneumoniae K7, K20, and K27-type strains. Three capsule depolymerases, K7dep, K20dep, and K27dep, encoded by the phage were specific to K7, K20, and K27-type capsules, respectively. K20dep also recognized Escherichia coli K30-type capsule, which is highly similar to K. pneumoniae K20-type. The survival of K. pneumoniae K20-type-infected mice was increased following administration of K20dep.

CONCLUSIONS

The potential of capsule depolymerase K20dep for the treatment of K. pneumoniae infections was revealed using an in vivo infection model. In addition, K7dep, K20dep, and K27dep capsule depolymerases could be used for K. pneumoniae capsular typing.

Molecularly imprinted nanoparticles for pathogen visualisation

Saccharides displayed on the cell surface of pathogens play critical roles in many activities such as adhesion, recognition and pathogenesis, as well as in prokaryotic development. In this work, we report the synthesis of molecularly imprinted nanoparticles (nanoMIPs) against pathogen surface monosaccharides using an innovative solid-phase approach. These nanoMIPs can serve as robust and selective artificial lectins specific to one particular monosaccharide. The evaluation of their binding capabilities has been implemented against bacterial cells (E. coli and S. pneumoniae) as model pathogens. The nanoMIPs were produced against two different monosaccharides: mannose (Man), which is present mainly on the surface of Gram-negative bacteria, and N-acetylglucosamine (GlcNAc) exposed on the surface of the majority of bacteria. Herein, we assessed the potential use of nanoMIPs for pathogen cell imaging and detection via flow cytometry and confocal microscopy.

A Polysaccharide-RBD-Fc-Conjugated COVID-19 Vaccine, SCTV01A, Showed High Immunogenicity and Low Toxicity in Animal Models

We previously developed a polysaccharide-–RBD-conjugated nanoparticle vaccine which induced protective efficacy against SARS-CoV-2 in a mouse model. Here, we newly developed a vaccine, SCTV01A, by chemically conjugating recombinant SARS-CoV-2 RBD-Fc and PPS14 (Streptococcus pneumoniae serotype type 14 capsular polysaccharide). The immunogenicity and toxicity of SCTV01A were evaluated in animal models. The PPS14 conjugation enhanced the immunogenicity of RBD-Fc in C57BL/6 mice whether formulated with SCT-VA02B or Alum adjuvant. SCTV01A also induced high opsonophagocytic activity (OPA) against S. pneumoniae serotype 14. In addition, SCTV01A stimulated potent neutralizing titers in rhesus macaques and effectively reduced lung inflammation after SARS-CoV-2 infection with neither antibody-dependent enhancement (ADE) nor vaccine-enhanced diseases (VED) phenomenon. Importantly, the long-term toxicity study of SCTV01A in rhesus macaques did not cause any abnormal toxicity and was tolerated at the highest tested dose (120 μg). The existing immunogenicity and toxicological evaluation results have demonstrated the safety and efficacy of SCTV01A, which will be a promising and feasible vaccine to protect against SARS-CoV-2 infection.

Identification and functional analysis of Mannose receptor in Asian swamp eel (Monopterus albus) in response to bacterial infection

Mannose receptor (MR), as a member of the C-type lectin (CLEC) family, plays an important role in the internalize pathogen-associated ligands and activate immune response. In the present study, MR was identified and characterized from Asian swamp eel (Monopterus albus) (namely MaMR). The open reading frame of MaMR was 4311 bp in length encoding 1437 amino acids of a ∼162.308 kDa protein, including a cysteine-rich (CR) domain, a fibronectin type II (FNII) domain, eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short cytoplasmic domain. Phylogenetic analysis indicated that MaMR shared the highest similarity with that of Paralichthys olivaceus. The expression of MaMR was found in all the examined tissues, with the highest expression in the spleen and kidney. After injection with Edwardsiella tarda, the transcript level of MaMR was initially reduced and then significantly elevated in the liver, spleen, foregut and hindgut. In the isolated peripheral blood leukocytes, the expression of MaMR was significantly induced post stimulated with LPS and LTA. Then the MaMR-CTLD4-8 recombinant protein was purified. Bacterial agglutination and binding assay showed that rMaMR-CTLD4-8 could bind with both Gram-positive and Gram-negative bacteria and agglutinate bacteria in the presence of calcium in vitro. Further analysis revealed that MaMR and TLR2 coordinately induced the expression of TRAF6 and promoted the phosphorylation level of p65, leading to the expression of proinflammatory cytokines il-1β and tnf-α in EPC cells. Taken together, these results reveal that MaMR plays an important role in the immune response of fish to pathogen infections.

Comparison of the Toponomes of Alveolar Macrophages From Wild Type and Surfactant Protein A Knockout Mice and Their Response to Infection

Background

Surfactant protein-A (SP-A) plays a critical role in lung innate immunity by regulating alveolar macrophages (AM), expression of inflammatory mediators, and other host defense proteins. The toponome imaging system (TIS), a serial immunostainer, was used to study the AM toponome because it characterizes the localization of multiple markers and identifies marker combinations in each pixel as combinatorial molecular phenotypes (CMPs). We used TIS to study the AM toponome from wild type (WT) and SP-A knockout (KO) mice and changes following Klebsiella pneumoniae exposure.

Methods

WT or KO mice received intratracheal K. pneumoniae or vehicle and AM were obtained by bronchoalveolar lavage after one hour. AM were attached to slides and underwent TIS analysis. Images were analyzed to characterize all pixels. AM CMPs from WT vehicle (n=3) and infected (n=3) mice were compared to each other and to AM from KO (n=3 vehicle; n=3 infected). Histograms provided us with a tool to summarize the representation of each marker in a set of CMPs.

Results

Using the histograms and other tools we identified markers of interest and observed that: 1) Both comparisons had conserved (present in all group members) CMPs, only in vehicle AM and only in infected AM, or common to both vehicle and infected AM, (i.e., unaffected by the condition). 2) the CMP number decreased with infection in WT and KO versus vehicle controls. 3) More infection-specific CMPs in WT vs KO AM. 4) When AM from WT and KO vehicle or infected were compared, there were more unique CMPs exclusive to the KO AM. 5) All comparisons showed CMPs shared by both groups.

Conclusions

The decrease of CMPs exclusive to infected AM in KO mice may underlie the observed susceptibility of KO mice to infection. However, both KO groups had more exclusive CMPs than the corresponding WT groups, perhaps indicating a vigorous effort by KO to overcome deficits in certain proteins and CMPs that are dysregulated by the absence of SP-A. Moreover, the presence of shared CMPs in the compared groups indicates that regulation of these CMPs is not dependent on either infection or the presence or absence of SP-A.

In Vitro and In Vivo Assessments of Two Newly Isolated Bacteriophages against an ST13 Urinary Tract Infection Klebsiella pneumoniae

Antibiotic resistance represents a major public health concern requiring new alternatives including phage therapy. Klebsiella pneumoniae belongs to the ESKAPE bacteria and can cause urinary tract infections (UTIs). The aims of this study were to isolate and characterize new bacteriophages against a K. pneumoniae strain isolated from UTIs and to assess their efficacy in vitro and in vivo in a Galleria (G.) mellonella larvae model. For this purpose, two bacteriophages were newly isolated against an ST13 K. pneumoniae strain isolated from a UTI and identified as K3 capsular types by wzi gene PCR. Genomic analysis showed that these bacteriophages, named vB_KpnP_K3-ULINTkp1 and vB_KpnP_K3-ULINTkp2, belong to the Drulisvirus genus. Bacteriophage vB_KpnP_K3-ULINTkp1 had the narrowest host spectrum (targeting only K3), while vB_KpnP_K3-ULINTkp2 also infected other Klebsiella types. Short adsorption times and latent periods were observed for both bacteriophages. In vivo experiments showed their ability to replicate in G. mellonella larvae and to decrease host bacterial titers. Moreover, both bacteriophages improved the survival of the infected larvae. In conclusion, these two bacteriophages had different in vitro properties and showed in vivo efficacy in a G. mellonella model with a better efficiency for vB_KpnP_K3-ULINTkp2.

Rational Development of a Polysaccharide-Protein-Conjugated Nanoparticle Vaccine Against SARS-CoV-2 Variants and Streptococcus pneumoniae

The ongoing COVID-19 pandemic caused by SARS-CoV-2 has led to millions of deaths worldwide. Streptococcus pneumoniae (S. pneumoniae) remains a major cause of mortality in underdeveloped countries. A vaccine that prevents both SARS-CoV-2 and S. pneumoniae infection represents a long-sought "magic bullet". Herein, a nanoparticle vaccine, termed SCTV01B, is rationally developed by using the capsular polysaccharide of S. pneumoniae serotype 14 (PPS14) as the backbone to conjugate with the recombinant receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. The final formulation of conjugated nanoparticles in the network structure exhibits high thermal stability. Immunization with SCTV01B induces potent humoral and Type 1/Type 2 T helper cell (Th1/Th2) cellular immune responses in mice, rats, and rhesus macaques. In particular, SCTV01B-immunized serum not only broadly cross-neutralizes all SARS-CoV-2 variants of concern (VOCs), including the most recent Omicron variant, but also shows high opsonophagocytic activity (OPA) against S. pneumoniae serotype 14. Finally, SCTV01B vaccination confers protection against challenges with the SARS-CoV-2 mouse-adapted strain and the original strain in established murine models. Collectively, these promising preclinical results support further clinical evaluation of SCTV01B, highlighting the potency of polysaccharide-RBD-conjugated nanoparticle vaccine platforms for the development of vaccines for COVID-19 and other infectious diseases.

Measurement of erythrocyte membrane mannoses to assess splenic function

Red blood cells (RBCs) lose plasma membrane in the spleen as they age, but the cells and molecules involved are yet to be identified. Sickle cell disease and infection by Plasmodium falciparum cause oxidative stress that induces aggregates of cross‐linked proteins with N‐linked high‐mannose glycans (HMGs). These glycans can be recognised by mannose‐binding lectins, including the mannose receptor (CD206), expressed on macrophages and specialised phagocytic endothelial cells in the spleen to mediate the extravascular haemolysis characteristic of these diseases. We postulated this system might also mediate removal of molecules and membrane in healthy individuals. Surface expression of HMGs on RBCs from patients who had previously undergone splenectomy was therefore assessed: high levels were indeed observable as large membrane aggregates. Glycomic analysis by mass spectrometry identified a mixture of Man_5‐9GlcNAc₂ structures. HMG levels correlated well with manual pit counts (r = 0.75–0.85). To assess further whether HMGs might act as a splenic reticuloendothelial function test, we measured levels on RBCs from patients with potential functional hyposplenism, some of whom exhibited high levels that may indicate risk of complications.

Functional vulnerability of liver macrophages to capsules defines virulence of blood-borne bacteria

Many encapsulated bacteria use capsules to cause invasive diseases. However, it remains largely unknown how the capsules enhance bacterial virulence under in vivo infection conditions. Here we show that the capsules primarily target the liver to enhance bacterial survival at the onset of blood-borne infections. In a mouse sepsis model, the capsules enabled human pathogens Streptococcus pneumoniae and Escherichia coli to circumvent the recognition of liver-resident macrophage Kupffer cells (KCs) in a capsular serotype-dependent manner. In contrast to effective capture of acapsular bacteria by KCs, the encapsulated bacteria are partially (low-virulence types) or completely (high-virulence types) “untouchable” for KCs. We finally identified the asialoglycoprotein receptor (ASGR) as the first known capsule receptor on KCs to recognize the low-virulence serotype-7F and -14 pneumococcal capsules. Our data identify the molecular interplay between the capsules and KCs as a master controller of the fate and virulence of encapsulated bacteria, and suggest that the interplay is targetable for therapeutic control of septic infections.

A programmable encapsulation system improves delivery of therapeutic bacteria in mice

Living bacteria therapies have been proposed as an alternative approach to treating a broad array of cancers. In this study, we developed a genetically encoded microbial encapsulation system with tunable and dynamic expression of surface capsular polysaccharides that enhances systemic delivery. Based on a small RNA screen of capsular biosynthesis pathways, we constructed inducible synthetic gene circuits that regulate bacterial encapsulation in Escherichia coli Nissle 1917. These bacteria are capable of temporarily evading immune attack, whereas subsequent loss of encapsulation results in effective clearance in vivo. This dynamic delivery strategy enabled a ten-fold increase in maximum tolerated dose of bacteria and improved anti-tumor efficacy in murine models of cancer. Furthermore, in situ encapsulation increased the fraction of microbial translocation among mouse tumors, leading to efficacy in distal tumors. The programmable encapsulation system promises to enhance the therapeutic utility of living engineered bacteria for cancer.

Transient capsule induction allows engineered bacteria to evade initial immune surveillance in a colorectal cancer model.

A hexasaccharide from capsular polysaccharide of carbapenem-resistant Klebsiella pneumoniae KN2 is a ligand of Toll-like receptor 4

Klebsiella pneumoniae serotype KN2 is a carbapenem-resistant strain and leads to the health care-associated infections, such as bloodstream infections. Its capsular polysaccharide (CPS) was isolated and cleaved by a specific enzyme from a bacteriophage into a hexasaccharide-repeating unit. With GC-MS, NMR, and Mass analyses, the structure of KN2 CPS was determined to be {→3)-β-D-Glcp-(1→3)-[α-D-GlcpA-(1→4)-β-D-Glcp-(1→6)]-α-D-Galp-(1→6)-β-D-Galp-(1→3)-β-D-Galp-(1→}_n. We demonstrated that 1 μg/mL CPS could stimulate J774A.1 murine macrophages to release tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in vitro. Also, we proved that KN2 CPS induced the immune response through Toll-like receptor 4 (TLR4) in the human embryonic kidney (HEK)-293 cells. Strikingly, the hexasaccharide alone shows the same immune response as the CPS, suggesting that the hexasaccharide can shape the adaptive immunity to be a potential vaccine adjuvant. The glucuronic acid (GlcA) on other polysaccharides can affect the immune response, but the GlcA-reduced KN2 CPS and hexasaccharide still maintain their immunomodulatory activities.

Metagenomic and metatranscriptomic analyses reveal minor-yet-crucial roles of gut microbiome in deep-sea hydrothermal vent snail

BACKGROUND

Marine animals often exhibit complex symbiotic relationship with gut microbes to attain better use of the available resources. Many animals endemic to deep-sea chemosynthetic ecosystems host chemoautotrophic bacteria endocellularly, and they are thought to rely entirely on these symbionts for energy and nutrition. Numerous investigations have been conducted on the interdependence between these animal hosts and their chemoautotrophic symbionts. The provannid snail Alviniconcha marisindica from the Indian Ocean hydrothermal vent fields hosts a Campylobacterial endosymbiont in its gill. Unlike many other chemosymbiotic animals, the gut of A. marisindica is reduced but remains functional; yet the contribution of gut microbiomes and their interactions with the host remain poorly characterised.

RESULTS

Metagenomic and metatranscriptomic analyses showed that the gut microbiome of A. marisindica plays key nutritional and metabolic roles. The composition and relative abundance of gut microbiota of A. marisindica were different from those of snails that do not depend on endosymbiosis. The relative abundance of microbial taxa was similar amongst three individuals of A. marisindica with significant inter-taxa correlations. These correlations suggest the potential for interactions between taxa that may influence community assembly and stability. Functional profiles of the gut microbiome revealed thousands of additional genes that assist in the use of vent-supplied inorganic compounds (autotrophic energy source), digest host-ingested organics (carbon source), and recycle the metabolic waste of the host. In addition, members of five taxonomic classes have the potential to form slime capsules to protect themselves from the host immune system, thereby contributing to homeostasis. Gut microbial ecology and its interplay with the host thus contribute to the nutritional and metabolic demands of A. marisindica.

CONCLUSIONS

The findings advance the understanding of how deep-sea chemosymbiotic animals use available resources through contributions from gut microbiota. Gut microbiota may be critical in the survival of invertebrate hosts with autotrophic endosymbionts in extreme environments.

The Mannose Receptor: From Endocytic Receptor and Biomarker to Regulator of (Meta)Inflammation

The mannose receptor is a member of the C-type lectin (CLEC) family, which can bind and internalize a variety of endogenous and pathogen-associated ligands. Because of these properties, its role in endocytosis as well as antigen processing and presentation has been studied intensively. Recently, it became clear that the mannose receptor can directly influence the activation of various immune cells. Cell-bound mannose receptor expressed by antigen-presenting cells was indeed shown to drive activated T cells towards a tolerogenic phenotype. On the other hand, serum concentrations of a soluble form of the mannose receptor have been reported to be increased in patients suffering from a variety of inflammatory diseases and to correlate with severity of disease. Interestingly, we recently demonstrated that the soluble mannose receptor directly promotes macrophage proinflammatory activation and trigger metaflammation. In this review, we highlight the role of the mannose receptor and other CLECs in regulating the activation of immune cells and in shaping inflammatory responses.

Fc-conjugated C-type lectin receptors: Tools for understanding host-pathogen interactions

The use of soluble fusion proteins of pattern recognition receptors (PRRs) used in the detection of exogenous and endogenous ligands has helped resolve the roles of PRRs in the innate immune response to pathogens, how they shape the adaptive immune response, and function in maintaining homeostasis. Using the immunoglobulin (Ig) crystallizable fragment (Fc) domain as a fusion partner, the PRR fusion proteins are soluble, stable, easily purified, have increased affinity due to the Fc homodimerization properties, and consequently have been used in a wide range of applications such as flow cytometry, screening of protein and glycan arrays, and immunofluorescent microscopy. This review will predominantly focus on the recognition of pathogens by the cell membrane-expressed glycan-binding proteins of the C-type lectin receptor (CLR) subgroup of PRRs. PRRs bind to conserved pathogen-associated molecular patterns (PAMPs), such as glycans, usually located within or on the outer surface of the pathogen. Significantly, many glycans structures are identical on both host and pathogen (e.g. the Lewis (Le) X glycan), allowing the use of Fc CLR fusion proteins with known endogenous and/or exogenous ligands as tools to identify pathogen structures that are able to interact with the immune system. Screens of highly purified pathogen-derived cell wall components have enabled identification of many unique PAMP structures recognized by CLRs. This review highlights studies using Fc CLR fusion proteins, with emphasis on the PAMPs found in fungi, bacteria, viruses, and parasites. The structure and unique features of the different CLR families is presented using examples from a broad range of microbes whenever possible.

Macrophage targeted theranostic strategy for accurate detection and rapid stabilization of the inflamed high-risk plaque

Rationale: Inflammation plays a pivotal role in the pathogenesis of the acute coronary syndrome. Detecting plaques with high inflammatory activity and specifically treating those lesions can be crucial to prevent life-threatening cardiovascular events. Methods: Here, we developed a macrophage mannose receptor (MMR)-targeted theranostic nanodrug (mannose-polyethylene glycol-glycol chitosan-deoxycholic acid-cyanine 7-lobeglitazone; MMR-Lobe-Cy) designed to identify inflammatory activity as well as to deliver peroxisome proliferator-activated gamma (PPARγ) agonist, lobeglitazone, specifically to high-risk plaques based on the high mannose receptor specificity. The MMR-Lobe-Cy was intravenously injected into balloon-injured atheromatous rabbits and serial in vivo optical coherence tomography (OCT)-near-infrared fluorescence (NIRF) structural-molecular imaging was performed. Results: One week after MMR-Lobe-Cy administration, the inflammatory NIRF signals in the plaques notably decreased compared to the baseline whereas the signals in saline controls even increased over time. In accordance with in vivo imaging findings, ex vivo NIRF signals on fluorescence reflectance imaging (FRI) and plaque inflammation by immunostainings significantly decreased compared to oral lobeglitazone group or saline controls. The anti-inflammatory effect of MMR-Lobe-Cy was mediated by inhibition of TLR4/NF-κB pathway. Furthermore, acute resolution of inflammation altered the inflamed plaque into a stable phenotype with less macrophages and collagen-rich matrix. Conclusion: Macrophage targeted PPARγ activator labeled with NIRF rapidly stabilized the inflamed plaques in coronary sized artery, which could be quantitatively assessed using intravascular OCT-NIRF imaging. This novel theranostic approach provides a promising theranostic strategy for high-risk coronary plaques.

Development of a compound oral liquid containing herbal extracts and its effect on immunity and gastric mucosa

Nowadays, consumers have an increasing demand for health products. In this study, an oral liquid was developed using a compound extract consisting of three herbal extracts (Dendrobium nobile Lindl., Lycium barbarum, and Puerariae lobatae Radix) because the compound extract (a combination of all three extracts) was superior to every single extract in promoting the phagocytic capacity of RAW264.7 macrophages and the proliferation ability of GES-1 cells. In this oral liquid, the dosage of the stabilizer and the sweetener was selected using a stability test and sensory quality evaluation. When 0.30% (m/v) xanthan gum and 0.20% (m/v) mogroside were added, the oral liquid had not only a good stability but also the highest sensory score for overall acceptability. The chemical composition analysis showed that the oral liquid had various functional ingredients including polysaccharides, phenols, alkaloids, and so forth. The immune-enhancing efficacy of the oral liquid was evaluated in BALB/c mice by measuring the levels of different immune indicators. The results indicated that the oral liquid obviously enhanced nonspecific and specific immunity. A rat model with ethanol-induced gastric ulcer was used to examine the protective effect of the oral liquid on the gastric mucosa and to explore the related mechanisms. The oral administration of the oral liquid for days significantly prevented the formation of gastric ulcer. This study provided an effective oral liquid that could enhance immunity and protect gastric mucosa.

Red blood cell mannoses as phagocytic ligands mediating both sickle cell anaemia and malaria resistance

In both sickle cell disease and malaria, red blood cells (RBCs) are phagocytosed in the spleen, but receptor-ligand pairs mediating uptake have not been identified. Here, we report that patches of high mannose N-glycans (Man_5-9GlcNAc₂), expressed on diseased or oxidized RBC surfaces, bind the mannose receptor (CD206) on phagocytes to mediate clearance. We find that extravascular hemolysis in sickle cell disease correlates with high mannose glycan levels on RBCs. Furthermore, Plasmodium falciparum-infected RBCs expose surface mannose N-glycans, which occur at significantly higher levels on infected RBCs from sickle cell trait subjects compared to those lacking hemoglobin S. The glycans are associated with high molecular weight complexes and protease-resistant, lower molecular weight fragments containing spectrin. Recognition of surface N-linked high mannose glycans as a response to cellular stress is a molecular mechanism common to both the pathogenesis of sickle cell disease and resistance to severe malaria in sickle cell trait.

A 14 bp indel polymorphism in the promoter region is associated with different responses to porcine circovirus type 2 infection by regulating MRC1 transcription

Mannose receptor, C type 1 (MRC1) is a key factor in regulating the body's immune response to resist pathogen invasions. In this study, mRNA expressions of MRC1 gene in nine porcine organs/tissues were compared between Laiwu (LW) and Yorkshire × Landrace crossbred (YL) pigs prior to and post PCV2 infection. We found that, for pigs uninfected with PCV2, MRC1 mRNA expressions in the lung, spleen, large intestine, small intestine and mesenteric lymph node tissues of LW were significantly higher than those of YL pigs (P < 0.05). After PCV2 infection, MRC1 mRNA levels in the liver, kidney and mesenteric lymph node were significantly increased in LW pigs (P < 0.05); while, significantly decreased in the heart and lung tissues of YL pigs (P < 0.05). The transcriptional activity of porcine MRC1 promoter was further analyzed to investigate the molecular mechanism underlying these expressional differences in response to PCV2 infection. Luciferase assay indicated that a 14 bp indel polymorphism "GTTTTTTTTTTTTT" at the site -864 of MRC1 promoter contributed to the transcriptional activity. The frequency of 14 bp insertion in LW and Dapulian pigs, generally resistant to PCV2 infection, was higher than that in Duroc, Landrace and Yorkshire pigs, which were sensitive to PCV2 infection. The promoter with 14 bp insertion displayed higher MRC1 transcription level both prior to and post PCV2 infection compared with that carrying no insertion in PK15 cells (P < 0.01). The results suggest that this 14 bp indel polymorphism is associated with different responses to PCV2 infection by regulating MRC1 transcription.

Panax quinquefolius (North American Ginseng) Polysaccharides as Immunomodulators: Current Research Status and Future Directions

Panax quinquefolius (North American ginseng, NAG) is a popular medicinal plant used widely in traditional medicine. NAG products are currently available in various forms such as roots, extracts, nutraceuticals, dietary supplements, energy drinks, etc. NAG polysaccharides are recognized as one of the major bioactive ingredients. However, most NAG reviews are focused on ginsenosides with little information on polysaccharides. NAG polysaccharides have demonstrated a therapeutic activity in numerous studies, in which many of the bioactivities involve regulation of the immune response. The purpose of this review is to summarize the structural features and the immunomodulatory properties of crude, partially purified, and pure polysaccharides isolated from NAG. Receptors of the innate immune system that potentially bind to NAG polysaccharides and the respective signal transduction pathways initiated by these compounds are discussed. Major challenges, recent innovations, and future directions in NAG polysaccharide research are also summarized.

Higher Cytokine and Opsonizing Antibody Production Induced by Bovine Serum Albumin (BSA)-Conjugated Tetrasaccharide Related to Streptococcus pneumoniae Type 3 Capsular Polysaccharide

A number of studies have demonstrated the limited efficacy of S. pneumoniae type 3 capsular polysaccharide (CP) in the 13-valent pneumococcal conjugate vaccine against serotype 3 invasive pneumococcal diseases and carriage. Synthetic oligosaccharides (OSs) may provide an alternative to CPs for development of novel conjugated pneumococcal vaccines and diagnostic test systems. A comparative immunological study of di-, tri-, and tetra-bovine serum albumin (BSA) conjugates was performed. All oligosaccharides conjugated with biotin and immobilized on streptavidin-coated plates stimulated production of IL-1α, IL-2, IL-4, IL-5, IL-10, IFNγ, IL-17A, and TNFα, but not IL-6 and GM-CSF in monocultured mice splenocytes. The tetrasaccharide-biotin conjugate stimulated the highest levels of IL-4, IL-5, IL-10, and IFNγ, which regulate expression of specific immunoglobulin isotypes. The tetra-BSA conjugate adjuvanted with aluminum hydroxide elicited high levels of IgM, IgG1, IgG2a, and IgG2b antibodies (Abs). Anti-CP-induced Abs could only be measured using the biotinylated tetrasaccharide. The tetrasaccharide ligand possessed the highest binding capacity for anti-OS and antibacterial IgG Abs in immune sera. Sera to the tetra-BSA conjugate promoted greater phagocytosis of bacteria by neutrophils and monocytes than the CRM197-CP-antisera. Sera of mice immunized with the tetra-BSA conjugate exhibited the highest titer of anti-CP IgG1 Abs compared with sera of mice inoculated with the same doses of di- and tri-BSA conjugates. Upon intraperitoneal challenge with lethal doses of S. pneumoniae type 3, the tri- and tetra-BSA conjugates protected mice more significantly than the di-BSA conjugate. Therefore, it may be concluded that the tetrasaccharide ligand is an optimal candidate for development of a semi-synthetic vaccine against S. pneumoniae type 3 and diagnostic test systems.

Increased Levels of Soluble CD206 Associated with Rapidly Progressive Interstitial Lung Disease in Patients with Dermatomyositis

Objective

Soluble CD206 (sCD206) is considered a macrophage activation marker, and a previous study proved it as a potential biomarker to predict the severity of anti-melanoma differentiation-associated gene 5- (anti-MDA-5-) positive dermatomyositis- (DM-) associated interstitial lung disease (ILD). To investigate the role of sCD206 in various subtypes of DM, we evaluated the serum level of sCD206 in patients with different myositis-specific autoantibodies besides anti-MDA-5 and clarified its clinical significance.

Methods

Commercial enzyme-linked immunosorbent assay kits were used to detect serum concentrations of sCD206 in 150 patients with DM and 52 healthy controls (HCs). Correlations between sCD206 levels and clinical features, laboratory examinations, and pulmonary function test parameters were analysed.

Results

The median concentrations of serum sCD206 in DM patients were significantly higher than those in HCs (p < 0.0001). Furthermore, median sCD206 levels were elevated in patients with ILD (p = 0.001), especially in those with rapidly progressive ILD (RP-ILD) (p < 0.0001). In addition, sCD206 levels were negatively correlated with the pulmonary function test results, including the percent predicted forced vital capacity (r = −0.234, p = 0.023), percent predicted forced expiratory volume in one second (r = −0.225, p = 0.030), and percent predicted carbon monoxide diffusion capacity (r = −0.261, p = 0.014). Age- and gender-adjusted multivariable analysis showed that sCD206 was an independent prognostic factor for RP-ILD in patients with DM. A longitudinal study showed that sCD206 levels were positively correlated with the physician global assessment visual analog scale scores (β = 54.201, p = 0.001).

Conclusion

Serum sCD206 levels were significantly increased in patients with DM and significantly associated with RP-ILD, suggesting that sCD206 is an important biological predictor of RP-ILD in patients with DM.

Engineered probiotics biofilm enhances osseointegration via immunoregulation and anti-infection

Preventing multidrug-resistant bacteria-related infection and simultaneously improving osseointegration are in great demand for orthopedic implants. However, current strategies are still limited to a combination of non-U.S. Food and Drug Administration-approved antibacterial and osteogenic agents. Here, we develop a food-grade probiotic-modified implant to prevent methicillin-resistant Staphylococcus aureus (MRSA) infection and accelerate bone integration. Lactobacillus casei is cultured on the surface of alkali heat-treated titanium (Ti) substrates and inactivated by ultraviolet irradiation to avoid sepsis induced by viable bacteria. This inactivated L. casei biofilm shows excellent 99.98% antibacterial effectiveness against MRSA due to the production of lactic acid and bacteriocin. In addition, the polysaccharides in the L. casei biofilm stimulate macrophages to secrete abundant osteogenic cytokines such as oncostatin M and improve osseointegration of the Ti implant. Inactivated probiotics modification can be a promising strategy to endow implants with both excellent self-antibacterial activity and osteointegration ability.

Vpr Is a VIP: HIV Vpr and Infected Macrophages Promote Viral Pathogenesis

HIV infects several cell types in the body, including CD4+ T cells and macrophages. Here we review the role of macrophages in HIV infection and describe complex interactions between viral proteins and host defenses in these cells. Macrophages exist in many forms throughout the body, where they play numerous roles in healthy and diseased states. They express pattern-recognition receptors (PRRs) that bind viral, bacterial, fungal, and parasitic pathogens, making them both a key player in innate immunity and a potential target of infection by pathogens, including HIV. Among these PRRs is mannose receptor, a macrophage-specific protein that binds oligosaccharides, restricts HIV replication, and is downregulated by the HIV accessory protein Vpr. Vpr significantly enhances infection in vivo, but the mechanism by which this occurs is controversial. It is well established that Vpr alters the expression of numerous host proteins by using its co-factor DCAF1, a component of the DCAF1-DDB1-CUL4 ubiquitin ligase complex. The host proteins targeted by Vpr and their role in viral replication are described in detail. We also discuss the structure and function of the viral protein Env, which is stabilized by Vpr in macrophages. Overall, this literature review provides an updated understanding of the contributions of macrophages and Vpr to HIV pathogenesis.

Oncolytic bacteria: past, present and future

More than a century ago, independent groups raised the possibility of using bacteria to selectively infect tumours. Such treatment induces an immune reaction that can cause tumour rejection and protect the patient against further recurrences. One of the first holistic approximations to use bacteria in cancer treatment was performed by William Coley, considered the father of immune-therapy, at the end of XIX century. Since then, many groups have used different bacteria to test their antitumour activity in animal models and patients. The basis for this reactivity implies that innate immune responses activated upon bacteria recognition, also react against the tumour. Different publications have addressed several aspects of oncolytic bacteria. In the present review, we will focus on revisiting the historical aspects using bacteria as oncolytic agents and how they led to the current clinical trials. In addition, we address the molecules present in oncolytic bacteria that induce specific toxic effects against the tumors as well as the activation of host immune responses in order to trigger antitumour immunity. Finally, we discuss future perspectives that could be considered in the different fields implicated in the implementation of this kind of therapy in order to improve the current use of bacteria as oncolytic agents.

Macrophage Activation Markers, CD163 and CD206, in Acute-on-Chronic Liver Failure

Macrophages facilitate essential homeostatic functions e.g., endocytosis, phagocytosis, and signaling during inflammation, and express a variety of scavenger receptors including CD163 and CD206, which are upregulated in response to inflammation. In healthy individuals, soluble forms of CD163 and CD206 are constitutively shed from macrophages, however, during inflammation pathogen- and damage-associated stimuli induce this shedding. Activation of resident liver macrophages viz. Kupffer cells is part of the inflammatory cascade occurring in acute and chronic liver diseases. We here review the existing literature on sCD163 and sCD206 function and shedding, and potential as biomarkers in acute and chronic liver diseases with a particular focus on Acute-on-Chronic Liver Failure (ACLF). In multiple studies sCD163 and sCD206 are elevated in relation to liver disease severity and established as reliable predictors of morbidity and mortality. However, differences in expression- and shedding-stimuli for CD163 and CD206 may explain dissimilarities in prognostic utility in patients with acute decompensation of cirrhosis and ACLF.

A murine model demonstrates capsule-independent adaptive immune protection in survivors of Klebsiella pneumoniae respiratory tract infection

Klebsiella pneumoniae represents a growing clinical threat, given its rapid development of antibiotic resistance, necessitating new therapeutic strategies. Existing live-infection models feature high mortality rates, limiting their utility in the study of natural adaptive immune response to this pathogen. We developed a preclinical model of pneumonia with low overall mortality, in which previously exposed mice are protected from subsequent respiratory tract challenge with K. pneumoniae Histologic analyses of infected murine lungs demonstrate lymphocytic aggregates surrounding vasculature and larger airways. Initial exposure in RAG1 knockout mice (lacking functional B and T cells) failed to confer protection against subsequent K. pneumoniae challenge. While administration of isolated K. pneumoniae capsule was sufficient to provide protection, we also found that initial inoculation with K. pneumoniae mutants lacking capsule (Δcps), O-antigen (ΔwecA) or both conferred protection from subsequent wild-type infection and elicited K. pneumoniae-specific antibody responses, indicating that non-capsular antigens may also elicit protective immunity. Experiments in this model will inform future development of multivalent vaccines to prevent invasive K. pneumoniae infections.

In vitro and in vivo characterization of the interaction, proinflammatory, immunomodulatory and antigenic properties of capsular polysaccharide from Streptococcus pneumoniae serotype 1

Pneumococcal capsular polysaccharide (PCP) is the major virulence determinant of Streptococcus pneumoniae (pneumococcus). Strains devoid of the capsule are avirulent or highly attenuated. PCP is present in soluble form and on pneumococci in infected individuals. The present study was undertaken to study the interaction of PCP from serotype 1 (PCP1) with immune cells, and its proinflammatory, immunomodulatory and antigenic properties. Binding of PCP1 to the surface of immune cells led to proinflammatory cytokine production which was not cell line or cytokine restricted. HEK293T transfectants expressing TLR1 and TLR2 produced IL-8 upon stimulation with PCP1, untransfected cells did not do so. PCP1 failed to induce TNF-α production from RAW264.7 cells when pre-incubated with a TLR2 blocking antibody. The surface binding of PCP1 was abrogated in the presence of TLR2 blocking antibody. PCP1 failed to bind TLR2 deficient RAW264.7 cells and induce TNF-α production. Unlike PCP1, alkali-treated PCP1 failed to stimulate RAW264.7 cells to produce TNF-α indicating the importance of alkali-sensitive moieties like O-acetyl groups. Alkali-treated PCP1 elicited lower anti-PCP1 antibody response. Mice experiments suggested that alkali-sensitive groups are significant target of protective antibodies in PCP1 immunized mice. Our findings demonstrate that PCP1 is an important modulator of immune response against pneumococci.

C-type Lectins in Immunity to Lung Pathogens

The respiratory tract is tasked with responding to a constant and vast influx of foreign agents. It acts as an important first line of defense in the innate immune system and as such plays a crucial role in preventing the entry of invading pathogens. While physical barriers like the mucociliary escalator exert their effects through the clearance of these pathogens, diverse and dynamic cellular mechanisms exist for the activation of the innate immune response through the recognition of pathogen-associated molecular patterns (PAMPs). These PAMPs are recognized by pattern recognition receptors (PRRs) that are expressed on a number of myeloid cells such as dendritic cells, macrophages, and neutrophils found in the respiratory tract. C-type lectin receptors (CLRs) are PRRs that play a pivotal role in the innate immune response and its regulation to a variety of respiratory pathogens such as viruses, bacteria, and fungi. This chapter will describe the function of both activating and inhibiting myeloid CLRs in the recognition of a number of important respiratory pathogens as well as the signaling events initiated by these receptors.

Macrophage Mannose Receptor CD206 Predicts Prognosis in Community-acquired Pneumonia

CD206, a mannose receptor, is mainly expressed on the surface of alternatively activated macrophages where it acts as a pattern recognition receptor and plays a role in innate and adaptive immunity. This study investigated serum soluble CD206 (sCD206) levels in community-acquired pneumonia (CAP) and examined their clinical significance. sCD206 concentrations were measured in the sera of two independent cohorts with CAP (127 and 125 patients, respectively) and 42 controls. The expression of CD206 in the lung from autopsied cases was also examined. Patients with CAP showed significantly elevated sCD206 levels than did the controls (p < 0.0001). Notably, fatal CAP patients had more than two-fold higher sCD206 concentrations than survivors in both cohorts (p < 0.0001). Serum sCD206 concentrations were associated with Pneumonia Severity Index (PSI) and CURB-65 values. Importantly, even fatal CAP patients classified as PSI I-IV, CURB65 0–2 or age <75 years had comparatively higher levels of sCD206 than those classified as PSI V, CURB-65 3–5 or age ≥75 years. Immunohistochemically, the infiltration of CD206⁺ macrophages was found in the lungs of fatal cases. Elevated levels of sCD206 are associated with CAP prognosis, suggesting sCD206 might be a potential biomarker to predict severity for CAP.

N-Glycosylation of mollusk hemocyanins contributes to their structural stability and immunomodulatory properties in mammals

Hemocyanins are widely used as carriers, adjuvants, and nonspecific immunostimulants in cancer because they promote Th1 immunity in mammals. Hemocyanins also interact with glycan-recognizing innate immune receptors on antigen-presenting cells, such as the C-type lectin immune receptors mannose receptor (MR), macrophage galactose lectin (MGL), and the Toll-like receptors (TLRs), stimulating proinflammatory cytokine secretion. However, the role of N-linked oligosaccharides on the structural and immunological properties of hemocyanin is unclear. Mollusk hemocyanins, such as Concholepas concholepas (CCH), Fissurella latimarginata (FLH), and Megathura crenulata (KLH), are oligomeric glycoproteins with complex dodecameric quaternary structures and heterogeneous glycosylation patterns, primarily consisting of mannose-rich N-glycans. Here, we report that enzyme-catalyzed N-deglycosylation of CCH, FLH, and KLH disrupts their quaternary structure and impairs their immunogenic effects. Biochemical analyses revealed that the deglycosylation does not change hemocyanin secondary structure but alters their refolding mechanism and dodecameric structure. Immunochemical analyses indicated decreased binding of N-deglycosylated hemocyanins to the MR and MGL receptors and TLR4 and reduced endocytosis concomitant with an impaired production of tumor necrosis factor α, and interleukins 6 and 12 (IL-6 and IL-12p40, respectively) in macrophages. Evaluating the function of N-deglycosylated hemocyanins in the humoral immune response and their nonspecific antitumor effects in the B16F10 melanoma model, we found that compared with native hemocyanins N-deglycosylated hemocyanins elicited reduced antibody titers, as well as partially diminished antitumor effects and altered carrier activities. In conclusion, the glycan content of hemocyanins is, among other structural characteristics, critically required for their immunological activities and should be considered in biomedical applications.

Pyruvate Substitutions on Glycoconjugates

Glycoconjugates are the most diverse biomolecules of life. Mostly located at the cell surface, they translate into cell-specific "barcodes" and offer a vast repertoire of functions, including support of cellular physiology, lifestyle, and pathogenicity. Functions can be fine-tuned by non-carbohydrate modifications on the constituting monosaccharides. Among these modifications is pyruvylation, which is present either in enol or ketal form. The most commonly best-understood example of pyruvylation is enol-pyruvylation of N-acetylglucosamine, which occurs at an early stage in the biosynthesis of the bacterial cell wall component peptidoglycan. Ketal-pyruvylation, in contrast, is present in diverse classes of glycoconjugates, from bacteria to algae to yeast-but not in humans. Mild purification strategies preventing the loss of the acid-labile ketal-pyruvyl group have led to a collection of elucidated pyruvylated glycan structures. However, knowledge of involved pyruvyltransferases creating a ring structure on various monosaccharides is scarce, mainly due to the lack of knowledge of fingerprint motifs of these enzymes and the unavailability of genome sequences of the organisms undergoing pyruvylation. This review compiles the current information on the widespread but under-investigated ketal-pyruvylation of monosaccharides, starting with different classes of pyruvylated glycoconjugates and associated functions, leading to pyruvyltransferases, their specificity and sequence space, and insight into pyruvate analytics.

Emerging concepts in the pathogenesis of the Streptococcus pneumoniae: From nasopharyngeal colonizer to intracellular pathogen

Streptococcus pneumoniae (the pneumococcus) is a human respiratory tract pathogen and a major cause of morbidity and mortality globally. Although the pneumococcus is a commensal bacterium that colonizes the nasopharynx, it also causes lethal diseases such as meningitis, sepsis, and pneumonia, especially in immunocompromised patients, in the elderly, and in young children. Due to the acquisition of antibiotic resistance and the emergence of nonvaccine serotypes, the pneumococcus has been classified as one of the priority pathogens for which new antibacterials are urgently required by the World Health Organization, 2017. Understanding molecular mechanisms behind the pathogenesis of pneumococcal infections and bacterial interactions within the host is crucial to developing novel therapeutics. Previously considered to be an extracellular pathogen, it is becoming evident that pneumococci may also occasionally establish intracellular niches within the body to escape immune surveillance and spread within the host. Intracellular survival within host cells also enables pneumococci to resist many antibiotics. Within the host cell, the bacteria exist in unique vacuoles, thereby avoiding degradation by the acidic lysosomes, and modulate the expression of its virulence genes to adapt to the intracellular environment. To invade and survive intracellularly, the pneumococcus utilizes a combination of virulence factors such as pneumolysin (PLY), pneumococcal surface protein A (PspA), pneumococcal adhesion and virulence protein B (PavB), the pilus‐1 adhesin RrgA, pyruvate oxidase (SpxB), and metalloprotease (ZmpB). In this review, we discuss recent findings showing the intracellular persistence of Streptococcus pneumoniae and its underlying mechanisms.

The macrophage-related biomarkers sCD163 and sCD206 are released by different shedding mechanisms

The hemoglobin receptor CD163 and the mannose receptor CD206 are both expressed on the surface of human macrophages. Upon inflammatory activation, the receptors are shed from the macrophage surface generating soluble products. The plasma concentration of both soluble CD163 (sCD163) and soluble CD206 (sCD206) are increased in several diseases, including inflammatory conditions and cancer. Here, we show that in contrast to CD163, LPS-mediated shedding of CD206 in humans is slow and a result of indirect signaling. Although both sCD163 and sCD206 were increased in response to LPS stimulation in vivo, only CD163 was shed from LPS-stimulated macrophages in vitro. Although both sCD163 and sCD206 were released from cultured macrophages stimulated with zymosan and PMA, shedding of CD206 was generally slower and less efficient and not reduced by inhibitors against the major protease classes. These data indicate that CD163 and CD206 are shed from the macrophages by very different mechanisms potentially involving distinctive inflammatory processes.

Successful classification of macrophage-mannose receptor CD206 in severity of anti-MDA5 antibody positive dermatomyositis associated ILD

Objectives

Macrophage-mannose receptor, CD206, is a marker of alternatively activated macrophages. Activated macrophages play key roles in DM. Interstitial lung disease (ILD) is a leading cause of mortality in patients with DM/clinically amyopathic DM (CADM). In particular, patients with the anti-melanoma differential gene 5 antibody (MDA5) frequently develop fatal rapid progressive ILD. This study aimed to evaluate the clinical implications of alternatively activated macrophages in patients with CADM/DM-ILD with anti-MDA5 antibody (MDA5-CADM/DM-ILD).

Methods

We measured serum concentrations of soluble CD206 (sCD206) in 33 patients with MDA5-CADM/DM-ILD and 36 age- and sex-matched control subjects. Expression levels of CD206 in the lungs from MDA5-CADM/DM-ILD were also examined.

Results

Patients with MDA5-CADM/DM-ILD had higher levels of sCD206 than those in controls (P < 0.0001). Of the 33 patients, 10 MDA5-CADM/DM-ILD patients developed fatal respiratory failure. Concentrations of sCD206 in patients with fatal ILD cases were significantly higher than those in the survivors, and increased sCD206 levels were associated with a higher mortality rate (Log-rank test, P = 0.0009). Age- and gender-adjusted logistic regression analyses showed that sCD206 was an independent prognostic factor for MDA5-CADM/DM-ILD. Importantly, assessment by sCD206 together with PaO2 successfully divided into three groups by their prognosis (P < 0.005, respectively). Pathological analyses showed accumulations of CD206-positive macrophages in lungs from the fatal case rather than those in the non-fatal cases.

Conclusions

Levels of serum sCD206 are increased in MDA5-CADM/DM-ILD and associated with poor prognosis. sCD206 is a potential biomarker to predict the severity of MDA5-CADM/DM-ILD.

Pneumolysin and the bacterial capsule of Streptococcus pneumoniae cooperatively inhibit taxis and motility of microglia

Background

Streptococcus pneumoniae is the cause of a highly lethal form of meningitis in humans. Microglial cells in the brain represent the first line of defense against pathogens, and they participate in the inflammatory response. The cholesterol-dependent cytolysin pneumolysin and the bacterial capsule are key pathogenic factors, known to exacerbate the course of pneumococcal meningitis.

Methods

We utilized live imaging and immunostaining of glial cells in dissociated and acute brain slice cultures to study the effect of pneumococcal factors, including the cholesterol-dependent cytolysin pneumolysin and the pneumococcal capsule, on microglial motility and taxis.

Results

In brain tissue, primary microglia cells showed an enhanced response towards lysates from bacteria lacking capsules and pneumolysin as they moved rapidly to areas with an abundance of bacterial factors. The presence of bacterial capsules and pneumolysin cumulatively inhibited microglial taxis. In mixed cultures of astrocytes and microglia, the motility of microglia was inhibited by capsular components within minutes after exposure. The reduced motility was partially reversed by mannan, a mannose receptor inhibitor. The effects on microglia were not mediated by astrocytes because pure microglial cells responded to various pneumococcal lysates similarly with distinct cell shape changes as seen in mixed cultures.

Conclusions

Our data indicate that microglia possess the capacity for a very agile response towards bacterial pathogens, but key pathogenic factors, such as pneumococcal capsules and pneumolysin, inhibited this response shortly after a bacterial challenge. Furthermore, we demonstrate for the first time that the bacterial capsule affects cellular behaviors such as motility and taxis.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1491-7) contains supplementary material, which is available to authorized users.

The Pseudomonas aeruginosa lectin LecB binds to the exopolysaccharide Psl and stabilizes the biofilm matrix

Pseudomonas aeruginosa biofilms are composed of exopolysaccharides (EPS), exogenous DNA, and proteins that hold these communities together. P. aeruginosa produces lectins LecA and LecB, which possess affinities towards sugars found in matrix EPS and mediate adherence of P. aeruginosa to target host cells. Here, we demonstrate that LecB binds to Psl, a key matrix EPS, and this leads to increased retention of both cells and EPS in a growing biofilm. This interaction is predicted to occur between the lectin and the branched side chains present on Psl. Finally, we show that LecB coordinates Psl localization in the biofilm. This constitutes a unique function for LecB and identifies it as a matrix protein that contributes to biofilm structure through EPS interactions.

Identification of three podoviruses infecting Klebsiella encoding capsule depolymerases that digest specific capsular types

Klebsiella pneumoniae is an important human pathogen causing opportunistic nosocomial and community-acquired infections. A major public health concern regarding K. pneumoniae is the increasing incidence of multidrug-resistant strains. Here, we isolated three novel Klebsiella bacteriophages, KN1-1, KN3-1 and KN4-1, which infect KN1, KN3 and K56, and KN4 types respectively. We determined their genome sequences and conducted a comparative analysis that revealed a variable region containing capsule depolymerase-encoding genes. Recombinant depolymerase proteins were produced, and their enzymatic activity and specificity were evaluated. We identified four capsule depolymerases in these phages that could only digest the capsule types of their respective hosts. Our results demonstrate that the activities of these capsule depolymerases were correlated with the host range of each phage; thus, the capsule depolymerases are host specificity determinants. By generating a capsule mutant, we demonstrate that capsule was essential for phage adsorption and infection. Further, capsule depolymerases can enhance bacterial susceptibility to serum killing. The discovery of these phages and depolymerases lays the foundation for the typing of KN1, KN3, KN4 and K56 Klebsiella and could be useful alternative therapeutics for the treatment of K. pneumoniae infections.

Pneumolysin binds to the mannose receptor C type 1 (MRC-1) leading to anti-inflammatory responses and enhanced pneumococcal survival

Streptococcus pneumoniae (the pneumococcus) is a major cause of mortality and morbidity globally, and the leading cause of death in children under 5 years old. The pneumococcal cytolysin pneumolysin (PLY) is a major virulence determinant known to induce pore-dependent pro-inflammatory responses. These inflammatory responses are driven by PLY-host cell membrane cholesterol interactions, but binding to a host cell receptor has not been previously demonstrated. Here, we discovered a receptor for PLY, whereby pro-inflammatory cytokine responses and Toll-like receptor signalling are inhibited following PLY binding to the mannose receptor C type 1 (MRC-1) in human dendritic cells and mouse alveolar macrophages. The cytokine suppressor SOCS1 is also upregulated. Moreover, PLY-MRC-1 interactions mediate pneumococcal internalization into non-lysosomal compartments and polarize naive T cells into an interferon-γ^low, interleukin-4^high and FoxP3⁺ immunoregulatory phenotype. In mice, PLY-expressing pneumococci colocalize with MRC-1 in alveolar macrophages, induce lower pro-inflammatory cytokine responses and reduce neutrophil infiltration compared with a PLY mutant. In vivo, reduced bacterial loads occur in the airways of MRC-1-deficient mice and in mice in which MRC-1 is inhibited using blocking antibodies. In conclusion, we show that pneumococci use PLY-MRC-1 interactions to downregulate inflammation and enhance bacterial survival in the airways. These findings have important implications for future vaccine design.