Effect of molecular size on the ability of zwitterionic polysaccharides to stimulate cellular immunity

Cleavage and Noncleavage Chemistry in Reactive Oxygen Species (ROS)-Responsive Materials for Smart Drug Delivery

The design and development of advanced drug delivery systems targeting reactive oxygen species (ROS) have gained significant interest in recent years for treating various diseases, including cancer, psychiatric diseases, cardiovascular diseases, neurological diseases, metabolic diseases, and chronic inflammations. Integrating specific chemical bonds capable of effectively responding to ROS and triggering drug release into the delivery system is crucial. In this Review, we discuss commonly used conjugation linkers (chemical bonds) and categorize them into two groups: cleavable linkers and noncleavable linkers. Our goal is to clarify their unique drug release mechanisms from a chemical perspective and provide practical organic synthesis approaches for their efficient production. We showcase numerous significant examples to demonstrate their synthesis routes and diverse applications. Ultimately, we strive to present a comprehensive overview of cleavage and noncleavage chemistry, offering insights into the development of smart drug delivery systems that respond to ROS.

Toll-like receptors in inflammatory bowel disease: A review of the role of phytochemicals

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammation within the gastrointestinal tract with a remarkable impact on patients' quality of life. Toll-like receptors (TLR), as a key contributor of immune system in inflammation, has a critical role in the pathogenesis of IBD and thus, can be a suitable target of therapeutic agents. Medicinal plants have long been considered as a source of bioactive agents for different diseases, including IBD.

PURPOSE

This review discusses current state of the art on the role of plant-derived compounds for the management of IBD with a focus on TLRs.

METHODS

Electronic database including PubMed, Web of Science, and Scopus were searched up to January 2023 and all studies in which anticolitis effects of a phytochemical was assessed via modulation of TLRs were considered.

RESULTS

Different categories of phytochemicals, including flavonoids, lignans, alkaloids, terpenes, saccharides, and saponins have demonstrated modulatory effects on TLR in different animal and cell models of bowel inflammation. Flavonoids were the most studied phytochemicals amongst others. Also, TLR4 was the most important type of TLRs which were modulated by phytochemicals. Other mechanisms such as inhibition of pro-inflammatory cytokines, nuclear factor-κB pathway, nitric oxide synthesis pathway, cyclooxygenase-2, lipid peroxidation, as well as induction of endogenous antioxidant defense mechanisms were also reported for phytochemicals in various IBD models.

CONCLUSION

Taken together, a growing body of pre-clinical evidence support the efficacy of herbal compounds for the treatment of IBD via modulation of TLRs. Future clinical studies are recommended to assess the safety and efficacy of these compounds in human.

Total Synthesis and Structural Studies of Zwitterionic Bacteroides fragilis Polysaccharide A1 Fragments

Zwitterionic polysaccharides (ZPSs) are exceptional carbohydrates, carrying both positively charged amine groups and negatively charged carboxylates, that can be loaded onto MHC-II molecules to activate T cells. It remains enigmatic, however, how these polysaccharides bind to these receptors, and to understand the structural features responsible for this "peptide-like" behavior, well-defined ZPS fragments are required in sufficient quantity and quality. We here present the first total synthesis of Bacteroides fragilis PS A1 fragments encompassing up to 12 monosaccharides, representing three repeating units. Key to our successful syntheses has been the incorporation of a C-3,C-6-silylidene-bridged "ring-inverted" galactosamine building block that was designed to act as an apt nucleophile as well as a stereoselective glycosyl donor. Our stereoselective synthesis route is further characterized by a unique protecting group strategy, built on base-labile protecting groups, which has allowed the incorporation of an orthogonal alkyne functionalization handle. Detailed structural studies have revealed that the assembled oligosaccharides take up a bent structure, which translates into a left-handed helix for larger PS A1 polysaccharides, presenting the key positively charged amino groups to the outside of the helix. The availability of the fragments and the insight into their secondary structure will enable detailed interaction studies with binding proteins to unravel the mode of action of these unique oligosaccharides at the atomic level.

Towards a better understanding of the relationships between the structure and antitumor activity of Gastrodia elata polysaccharides by asymmetrical flow field-flow fractionation

To better understand the structure-function relationship of Gastrodia elata polysaccharides (PGEs), PGEs were extracted by ultrasound-assisted extraction method and the effects of extraction time on the structure and conformation of PGEs were evaluated by asymmetrical flow field-flow fractionation (AF4) coupled online with multiangle light scattering (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI). Besides separation, AF4-MALS-dRI can provide more information about PGEs, such as size and molecular weight (M_w) distributions, apparent density, and conformation. The effects of PGEs on the proliferation, apoptosis, and cell cycle of MCF-7 cells were investigated. The cell activity assay indicated that the PGEs can inhibit the growth of MCF-7 cells by inducing late apoptosis. The results indicated that PGEs with a spherical conformation and compact structure seem to be beneficial to inducing MCF-7 cells late apoptosis. Moreover, results demonstrated that the information obtained by AF4-MALS-dRI is valuable for better understanding of the relationship of structure-activity of PGEs.

Chemical structure, chain conformation and rheological properties of pectic polysaccharides from soy hulls

We obtained a new acidic soy hull polysaccharide (SHP-1) with a molecular weight (Mw) of 4.81 × 105 g/mol through ammonium oxalate and microwave assisted extraction. SHP-1 was mainly composed of galacturonic acid, galactose, rhamnose and arabinose (molar ratio = 46.59%:17.95%:14.77%:13.97%) with small amounts of fucose, glucose, mannose and xylose. The chemical structure was presumed to be of pectin-I type, consisting of 2/3 HGA and 1/3 RG-I. Furthermore, the rheological information and the chain morphology of SHP-1 were different in five solvents. Surfactant, salt and alkali solutions enhanced the solubility and flexibility of the polysaccharide, but the polysaccharide showed decreased fluidity under acidic conditions. The addition of ions and alkali increased the consistency coefficient of the solution, but the effect was far less than that of the cross-linking morphology. The structural and morphological information of purified SHP should aid in further study of its structure-function relationships and applications.

Extraction of polysaccharides from maca: Characterization and immunoregulatory effects on CD4+ T cells

The immunomodulatory effects of maca polysaccharides (MCPs) on macrophages have been demonstrated in many studies. However, the effects of MCPs on CD4⁺ T cells have not been studied. Four water-soluble MCPs, labeled MCP1 (weight-average molecular weights [Mws] of 896.1 and 276.6 kDa), MCP2 (Mws of 337.8 and 219.0 kDa), MCP3 (Mws of 110.6, 58.1, and 38.9 kDa), and MCP4 (Mws of 15.7, 12.6, and 12.1 kDa), were obtained from maca by graded ethanol precipitation. The immunoregulatory effects of MCPs on CD4⁺ T cells were evaluated for the first time. The experimental results indicated that all MCPs had immunoregulatory effects on CD4⁺ T cells. However, the effects of MCP2 were stronger compared to the other three components, not only in promoting the proliferation of CD4⁺ T cells but also in terms of secretion of interferon-γ (IFN-γ). The molecular weight and monosaccharide compositions of MCPs were analyzed to explore the structure-activity relationship. The results suggested that the molecular weight and the galactosamine (GalN) of MCPs might be determining factors for its bioactivity. These findings suggest that the MCP2 isolated in our study have immune potentiation effects on CD4⁺ T cells.

Glycoconjugate vaccines: some observations on carrier and production methods

Glycoconjugate vaccines use protein carriers to improve the immune response to polysaccharide antigens. The protein component allows the vaccine to interact with T cells, providing a stronger and longer-lasting immune response than a polysaccharide interacting with B cells alone. Whilst in theory the mere presence of a protein component in a vaccine should be sufficient to improve vaccine efficacy, the extent of improvement varies. In the present review, a comparison of the performances of vaccines developed with and without a protein carrier are presented. The usefulness of analytical tools for macromolecular integrity assays, in particular nuclear magnetic resonance, circular dichroism, analytical ultracentrifugation and SEC coupled to multi-angle light scattering (MALS) is indicated. Although we focus mainly on bacterial capsular polysaccharide-protein vaccines, some consideration is also given to research on experimental cancer vaccines using zwitterionic polysaccharides which, unusually for polysaccharides, are able to invoke T-cell responses and have been used in the development of potential all-polysaccharide-based cancer vaccines.A general trend of improved immunogenicity for glycoconjugate vaccines is described. Since the immunogenicity of a vaccine will also depend on carrier protein type and the way in which it has been linked to polysaccharide, the effects of different carrier proteins and production methods are also reviewed. We suggest that, in general, there is no single best carrier for use in glycoconjugate vaccines. This indicates that the choice of carrier protein is optimally made on a case-by-case basis, based on what generates the best immune response and can be produced safely in each individual case.Abbreviations: AUC: analytical ultracentrifugation; BSA: bovine serum albumin; CD: circular dichroism spectroscopy; CPS: capsular polysaccharide; CRM197: Cross Reactive Material 197; DT: diphtheria toxoid; Hib: Haemophilius influenzae type b; MALS: multi-angle light scattering; Men: Neisseria menigitidis; MHC-II: major histocompatibility complex class II; NMR: nuclear magnetic resonance spectroscopy; OMP: outer membrane protein; PRP: polyribosyl ribitol phosphate; PSA: Polysaccharide A1; Sa: Salmonella; St.: Streptococcus; SEC: size exclusion chromatography; Sta: Staphylococcus; TT: tetanus toxoid; ZPS: zwitterionic polysaccharide(s).

Peripheral CD4 T follicular cells induced by a conjugated pneumococcal vaccine correlate with enhanced opsonophagocytic antibody responses in younger individuals

BACKGROUND

PCV13 (conjugated polysaccharide) and PPSV23 (polysaccharide only) are two licensed vaccines targeting S. pneumoniae. The role of CD4 T-cell responses in pneumococcal vaccines among healthy participants and their impact on antibodies is not yet known.

METHODS

Ten adults (5 old and 5 young) received PCV13 (prime) and a year later PPSV23 (boost). Blood samples were collected prior to and multiple time points after vaccination. CD4 T cells responding to CRM₁₉₇, polysaccharide (PS), CRM₁₉₇ conjugated polysaccharide (CPS), PCV13 and PPSV23 vaccines were measured by flow cytometry. Serum antibodies were analyzed via multiplex opsonophagocytosis (MOPA) and pneumococcal IgG assays.

RESULTS

Vaccine-specific CD4 T cells were induced in all ten vaccinees post PCV13. Older vaccinees mounted higher peak responses and those specific for PCV13 and conjugated PS-1 were more polyfunctional compared to the younger group. Vaccine-elicited peripheral T follicular helper (Tfh) cells were only detected in the younger group who also exhibited a higher fold change in OPA titers post both vaccines. Importantly, Tfh cells following PCV13 correlated only with PCV13 serotype specific OPA titers after PPSV23 vaccination.

CONCLUSIONS

These findings demonstrate age related differences in immune response and the potential importance of Tfh in modulating functional antibody responses following pneumococcal vaccination.

Chemoenzymatic synthesis of homogeneous chondroitin polymers and its derivatives

Chondroitin sulfate is a linear glycosaminoglycan widely distributed as an important extracellular matrix component of mammalian cells. It participates in numerous pathological processes, however, illustration of its diverse biological roles is hampered by the unavailability of structurally defined chondroitin polymers and their derivatives. Herein, we report a novel homogeneous chondroitin polymers synthetic strategy which combines stepwise oligosaccharides synthesis with one-pot homogeneous chondroitin chain polymerization. Exogenous trisaccharide was proved to be the necessary acceptor for PmCS-catalyzed homogeneous chondroitin polymers synthetic reactions. The strategy exhibited a well-controlled relationship between the final sugar chain length and the molar ratios of reaction substrates that could synthesize homogenous chondroitin polymers with unprecedented narrow molecular weight distribution. More importantly, the strategy was further expanded to synthesis of unnatural zwitterionic and N-sulfonated chondroitin polymers by incorporation of sugar nucleotide derivatives into the synthetic approach.

Differences in Zwitterionic Sulfobetaine and Carboxybetaine Dextran-Based Hydrogels

Zwitterionic sulfobetaine (SB) and carboxybetaine (CB) have been extensively investigated for their noticeable antifouling properties. Both SB and CB have cationic and anionic groups in the molecule, but they differ in negatively charged groups. Molecular simulations have been conducted to investigate the different properties induced by structure changes. However, few studies have focused on the differences between SB and CB materials, especially zwitterionic polysaccharides. Two zwitterionic sulfobetaine and carboxybetaine dextran hydrogels were designed and used as models to compare their properties. Results showed that the equilibrium swelling ratios of the SB-DEX hydrogels were much higher than CB-DEX ones, and larger interior pores were observed in the SB-DEX hydrogels due to their higher hydrophilicity. The rheological storage modulus of the SB-DEX hydrogels was lower than that of CB-DEX ones as a result of higher water content of SB-DEX. These results were consistent with molecular modeling. Additionally, both CB-DEX and SB-DEX had remarkable biocompatibilities, and the in vitro release studies showed that the SB-DEX and CB-DEX hydrogels released DOX in a sustained manner under acidic condition (pH 5.0), indicating their promise as an effective drug-delivery system.

Protective effect of three glucomannans from different plants against DSS induced colitis in female BALB/c mice

Glucomannans (GMs) from diverse natural plants have great potentiality in enhancing the host immune system.

Finding a needle in a haystack: Bacteroides fragilis polysaccharide A as the archetypical symbiosis factor

Starting from birth, all animals develop a symbiotic relationship with their resident microorganisms that benefits both the microbe and the host. Recent advances in technology have substantially improved our ability to direct research toward the identification of important microbial species that affect host physiology. The identification of specific commensal molecules from these microbes and their mechanisms of action is still in its early stages. Polysaccharide A (PSA) of Bacteroides fragilis is the archetypical example of a commensal molecule that can modulate the host immune system in health and disease. This zwitterionic polysaccharide has a critical impact on the development of the mammalian immune system and also on the stimulation of interleukin 10-producing CD4⁺ T cells; consequently, PSA confers benefits to the host with regard to experimental autoimmune, inflammatory, and infectious diseases. In this review, we summarize the current understanding of the immunomodulatory effects of B. fragilis PSA and discuss these effects as a novel immunological paradigm. In particular, we discuss recent advances in our understanding of the unique functional mechanisms of this molecule and its therapeutic potential, and we review the recent literature in the field of microbiome research aimed at discovering new commensal products and their immunomodulatory potential.

Enhanced control of Mycobacterium tuberculosis extrapulmonary dissemination in mice by an arabinomannan-protein conjugate vaccine

Currently there are a dozen or so of new vaccine candidates in clinical trials for prevention of tuberculosis (TB) and each formulation attempts to elicit protection by enhancement of cell-mediated immunity (CMI). In contrast, most approved vaccines against other bacterial pathogens are believed to mediate protection by eliciting antibody responses. However, it has been difficult to apply this formula to TB because of the difficulty in reliably eliciting protective antibodies. Here, we developed capsular polysaccharide conjugates by linking mycobacterial capsular arabinomannan (AM) to either Mtb Ag85b or B. anthracis protective antigen (PA). Further, we studied their immunogenicity by ELISA and AM glycan microarrays and protection efficacy in mice. Immunization with either Abg85b-AM or PA-AM conjugates elicited an AM-specific antibody response in mice. AM binding antibodies stimulated transcriptional changes in Mtb. Sera from AM conjugate immunized mice reacted against a broad spectrum of AM structural variants and specifically recognized arabinan fragments. Conjugate vaccine immunized mice infected with Mtb had lower bacterial numbers in lungs and spleen, and lived longer than control mice. These findings provide additional evidence that humoral immunity can contribute to protection against Mtb.

Vaccine design in the TB field has been driven by the imperative of attempting to elicit strong cell-mediated responses. However, in recent decades evidence has accumulated that humoral immunity can protect against many intracellular pathogens through numerous mechanisms. In this work, we demonstrate that immunization with mycobacterial capsular arabinomannan (AM) conjugates elicited responses that contributed to protection against Mtb infection. We developed two different conjugates including capsular AM linked to the Mtb related protein Ag85b or the Mtb unrelated PA from B. anthracis and found that immunization with AM conjugates elicited antibody populations with different specificities. These surface-specific antibodies could directly modify the transcriptional profile and metabolism of mycobacteria. In addition, we observed a prolonged survival and a reduction in bacterial numbers in lungs and spleen in mice immunized with Ag85b-AM conjugates after infection with Mtb and that the presence of AM-binding antibodies was associated with modest prolongation in survival and a marked reduction in mycobacterial dissemination. Finally, we show that AM is antigenically variable and could potentially form the basis for a serological characterization of mycobacteria based on serotypes.

Transcriptional Reprogramming at Genome-Scale of Lactobacillus plantarum WCFS1 in Response to Olive Oil Challenge

Dietary fats may exert selective pressures on Lactobacillus species, however, knowledge on the mechanisms of adaptation to fat stress in these organisms is still fragmentary. This study was undertaken to gain insight into the mechanisms of adaptation of Lactobacillus plantarum WCFS1 to olive oil challenge by whole genome transcriptional profiling using DNA microarrays. A set of 230 genes were differentially expressed by L. plantarum WCFS1 to respond to this vegetable oil. This response involved elements typical of the stringent response, as indicated by the induction of genes involved in stress-related pathways and downregulation of genes related to processes associated with rapid growth. A set of genes involved in the transport and metabolism of compatible solutes were downregulated, indicating that this organism does not require osmoprotective mechanisms in presence of olive oil. The fatty acid biosynthetic pathway was thoroughly downregulated at the transcriptional level, which coincided with a diminished expression of genes controlled by this pathway in other organisms and that are required for the respiratory function, pyruvate dehydrogenase activity, RNA processing and cell size setting. Finally, a set of genes involved in host-cell signaling by L. plantarum were differentially regulated indicating that olive oil can influence the expression of metabolic traits involved in the crosstalk between this bacterium and the host.

Characteristics and Antitumor Activity of Morchella esculenta Polysaccharide Extracted by Pulsed Electric Field

Polysaccharides from Morchella esculenta have been proven to be functional and helpful for humans. The purpose of this study was to investigate the chemical structure and anti-proliferating and antitumor activities of a Morchella esculenta polysaccharide (MEP) extracted by pulsed electric field (PEF) in submerged fermentation. The endo-polysaccharide was separated and purified by column chromatography and Gel permeation chromatography, and analyzed by gas chromatography. The MEP with an average molecular weight of 81,835 Da consisted of xylose, glucose, mannose, rhamnose and galactose at the ratio of 5.4:5.0:6.5:7.8:72.3. Structure of MEP was further analyzed by Fourier-transform infrared spectroscopy and ¹H and ¹³C liquid-state nuclear magnetic resonance spectroscopy. Apoptosis tests proved that MEP could inhibit the proliferation and growth of human colon cancer HT-29 cells in a time- and dose-dependent manner within 48 h. This study provides more information on chemical structure of anti-proliferating polysaccharides isolated from Morchella esculenta.

Entirely Carbohydrate-Based Vaccines: An Emerging Field for Specific and Selective Immune Responses

Carbohydrates are regarded as promising targets for vaccine development against infectious disease because cell surface glycans on many infectious agents are attributed to playing an important role in pathogenesis. In addition, oncogenic transformation of normal cells, in many cases, is associated with aberrant glycosylation of the cell surface glycan generating tumor associated carbohydrate antigens (TACAs). Technological advances in glycobiology have added a new dimension to immunotherapy when considering carbohydrates as key targets in developing safe and effective vaccines to combat cancer, bacterial infections, viral infections, etc. Many consider effective vaccines induce T-cell dependent immunity with satisfactory levels of immunological memory that preclude recurrence. Unfortunately, carbohydrates alone are poorly immunogenic as they do not bind strongly to the MHCII complex and thus fail to elicit T-cell immunity. To increase immunogenicity, carbohydrates have been conjugated to carrier proteins, which sometimes can impede carbohydrate specific immunity as peptide-based immune responses can negate antibodies directed at the targeted carbohydrate antigens. To overcome many challenges in using carbohydrate-based vaccine design and development approaches targeting cancer and other diseases, zwitterionic polysaccharides (ZPSs), isolated from the capsule of commensal anaerobic bacteria, will be discussed as promising carriers of carbohydrate antigens to achieve desired immunological responses.

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10(2) μM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10(2) μM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro.

Mechanistic insights into cellular immunity of chondroitin sulfate A and its zwitterionic N-deacetylated derivatives

As a major component in extracellular matrix of the tissue, chondroitin sulfate A (CS-A) has been shown to exhibit either pro- or anti-inflammatory immune response which was largely dependent on its molecular size and cell types. In this study, we determined the signaling pathway involved in immune response of CS and its N-deacetylated derivative (dCS). Our data indicated that both CS and dCS could activate the NF-κB transcription factor in antigen presenting cells and induce TNF-α production through the TLR/MyD88 pathway. Further studies demonstrated that both CS and dCS had a potential in promoting the proliferation of spleen lymphocytes, and promoting the cytokines secretion by OVA-sensitized splenocytes. Thus, our finding provided a mechanistic insight into the understanding of cellular immunity of CS and dCS, which might be helpful to develop CS-based immune modulators against chronic inflammatory conditions, autoimmunity, infectious diseases, allergies and asthmatic conditions.

Synthesis of conjugation-ready zwitterionic oligosaccharides by chemoselective thioglycoside activation

A method to chemoselectively activate thioglycosides in the presence of thioethers is developed and applied in the total synthesis of repeating units of S. pneumoniae Sp1 and B. fragilis PS A1. Biochemical evaluation of these glycans is performed after conjugation to reporter moieties.

Biosynthetic assembly of the Bacteroides fragilis capsular polysaccharide A precursor bactoprenyl diphosphate-linked acetamido-4-amino-6-deoxygalactopyranose

The sugar capsule capsular polysaccharide A (CPSA), which coats the surface of the mammalian symbiont Bacteroides fragilis, is a key mediator of mammalian immune system development. In addition, this sugar polymer has shown therapeutic potential in animal models of multiple sclerosis and other autoimmune disorders. The structure of the CPSA polymer includes a rare stereoconfiguration sugar acetamido-4-amino-6-deoxygalactopyranose (AADGal) that we propose is the first sugar linked to a bactoprenyl diphosphate scaffold in the production of CPSA. In this report, we have utilized a heterologous system to reconstitute bactoprenyl diphosphate-linked AADGal production. Construction of this system included a previously reported Campylobacter jejuni dehydratase, PglF, coupled to a B. fragilis-encoded aminotransferase (WcfR) and initiating hexose-1-phosphate transferase (WcfS). The function of the aminotransferase was confirmed by capillary electrophoresis and a novel high-performance liquid chromatography (HPLC) method. Production of the rare uridine diphosphate (UDP)-AADGal was confirmed through a series of one- and two-dimensional nuclear magnetic resonance experiments and high-resolution mass spectrometry. A spectroscopically unique analogue of bactoprenyl phosphate was utilized to characterize the transfer reaction catalyzed by WcfS and allowed HPLC-based isolation of the isoprenoid-linked sugar product. Importantly, the entire heterologous system was utilized in a single-pot reaction to biosynthesize the bactoprenyl-linked sugar. This work provides the first critical step in the in vitro reconstitution of CPSA biosynthesis.

The yin yang of bacterial polysaccharides: lessons learned from B. fragilis PSA

Over the past several years, there have been remarkable advances in our understanding of how commensal organisms shape host immunity. Although the full cast of immunogenic bacteria and their immunomodulatory molecules remains to be elucidated, lessons learned from the interactions between bacterial zwitterionic polysaccharides (ZPSs) and the host immune system represent an integral step toward better understanding how the intestinal microbiota effect immunologic changes. Somewhat paradoxically, ZPSs, which are found in numerous commensal organisms, are able to elicit both proinflammatory and immunoregulatory responses; both these outcomes involve fine-tuning the balance between T-helper 17 cells and interleukin-10-producing regulatory T cells. In this review, we discuss the immunomodulatory effects of the archetypal ZPS, Bacteroides fragilis PSA. In addition, we highlight some of the opportunities and challenges in applying these lessons in clinical settings.

Adaptive immune defects against glycoantigens in chronic granulomatous disease via dysregulated nitric oxide production

Chronic granulomatous disease (CGD) is a primary immunodeficiency defined by mutations in the NADPH oxidase complex leading to reduced superoxide production, increased susceptibility to infection, chronic inflammation, and recurring abscess and granuloma formation. Here, we found that CGD mice were hyperresponsive to abscess-inducing T-cell-dependent carbohydrate antigens (glycoantigens) due to a ten-fold increase in NO production within APCs, which is known to be necessary for glycoantigen presentation on MHC class II. CGD mice exhibited increased Th1 pro-inflammatory T-cell responses in vitro and in vivo, characterized by more severe abscess pathology. This phenotype was also seen in WT animals following adoptive transfer of neutrophil-depleted APCs from CGD animals, demonstrating that this phenotype was independent of neutrophil and T-cell defects. Finally, pharmacological attenuation of NO production to WT levels in vivo reduced abscess incidence and severity in CGD without overt increases in inflammation or the ability to clear infection, suggesting a potential new treatment option for early stage CGD-associated infections.

Total synthesis of the Bacteroides fragilis zwitterionic polysaccharide A1 repeating unit

Nearly all bacteria capsular polysaccharides are T-cell-independent antigens that do not promote immunoglobulin class switching from IgM to IgG nor memory responses. In contrast, zwitterionic polysaccharides activate T-cell-dependent immune responses by major histocompatability complex class II presentation, a mechanism previously believed to be reserved for peptidic antigens. The best studied zwitterionic polysaccharide, polysaccharide A1 (PS A1) is found on the capsule of the commensal bacteria Bacteroides fragilis . Its potent immunomodulatory properties have been linked to postoperative intra-abdominal abscess formation. Here, we report the synthesis of the PS A1 tetrasaccharide repeating unit (2) as a tool to investigate the biological role of this polysaccharide. A modular synthetic strategy originating from the reducing end of the PS A1 repeating unit was unsuccessful and illustrated the limitations of glycosylation reactions between highly armed glycosylating agents and poor nucleophiles. Thus, a [3 + 1] glycosylation relying on trisaccharide 5 and pyruvalated galactose 6 was used to complete the first total synthesis of the PS A1 repeating unit (2).

Oxidative depolymerization of polysaccharides by reactive oxygen/nitrogen species

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are constantly produced and are tightly regulated to maintain a redox balance (or homeostasis) together with antioxidants (e.g. superoxide dismutase and glutathione) under normal physiological circumstances. These ROS/RNS have been shown to be critical for various biological events including signal transduction, aging, apoptosis, and development. Despite the known beneficial effects, an overproduction of ROS/RNS in the cases of receptor-mediated stimulation and disease-induced oxidative stress can inflict severe tissue damage. In particular, these ROS/RNS are capable of degrading macromolecules including proteins, lipids and nucleic acids as well as polysaccharides, and presumably lead to their dysfunction. The purpose of this review is to highlight (1) chemical mechanisms related to cell-free and cell-based depolymerization of polysaccharides initiated by individual oxidative species; (2) the effect of ROS/RNS-mediated depolymerization on the successive cleavage of the glycosidic linkage of polysaccharides by glycoside hydrolases; and (3) the potential biological outcome of ROS/RNS-mediated depolymerization of polysaccharides.

Carbohydrate oxidation acidifies endosomes, regulating antigen processing and TLR9 signaling

Phagocytes kill encapsulated microbes through oxidative cleavage of surface carbohydrates, releasing glycan fragments and microbial contents that serve as ligands for immune receptors, which tailor the immune response against the offending pathogen. The glycan fragments serve as MHC class II (MHC II) ligands and innate receptor agonists, whereas microbial proteins serve as substrates for proteolytic cleavage and MHC II presentation, and released nucleic acids activate innate pattern-recognition receptors (e.g., TLR9). In the current study, confocal microscopy of live macrophages and dendritic cells revealed that endocytosis of carbohydrates lead to vesicular acidification independent of proton pump activity. Acidification was dependent on NO-mediated oxidation in the presence of the ingested carbohydrate and was sufficient to negatively regulate T cell-dependent polysaccharide Ag cleavage, promote acid-dependent protein Ag processing, and facilitate CpG-mediated TLR9 signaling. Our findings lead to a model in which oxidation of carbohydrates from encapsulated microbes facilitates adaptive immune responses against microbial protein and carbohydrate Ags through promoting Ag processing for MHC II-mediated presentation as well as innate responses against released microbial DNA via TLR9 signaling.

Interleukin-6 is essential for zwitterionic polysaccharide-mediated abscess formation

Abscess formation associated with secondary peritonitis causes severe morbidity and can be fatal. Formation of abscesses requires the presence of CD4+ T-cells. Zwitterionic polysaccharides (ZPSs) represent a novel class of immunomodulatory bacterial antigens that stimulate CD4+ T-cells in a major histocompatibility complex (MHC) class II-dependent manner. The capsular polysaccharide Sp1 of Streptococcus pneumoniae serotype 1 possesses a zwitterionic charge with free amino groups and promotes T-cell-dependent abscess formation in an experimental mouse model. So far, nothing is known about the function of Interleukin (IL)-6 in intraperitoneal abscess formation. Here, we demonstrate that macrophages and dendritic cells (DCs), the most prevalent professional antigen-presenting cells involved in the formation of abscesses, secrete Interleukin (IL)-6 and are incorporated in the abscess capsule. Sp1 inhibits apoptosis of CD4 + T-cells and causes IL-17 expression by CD4+ T-cells in an IL-6-dependent manner. Abrogation of the Sp1-induced pleiotropic effects of IL-6 in IL-6-deficient mice and mice treated with an IL-6-specific neutralizing antibody results in significant inhibition of abscess formation. The data delineate the essential role of IL-6 in the linkage of innate and adaptive immunity in polysaccharide-mediated abscess formation.

Toll-like receptor 2 dependent immunogenicity of glycoconjugate vaccines containing chemically derived zwitterionic polysaccharides

Group B Streptococcus (GBS) causes serious infection in neonates and is an important target of vaccine development. Zwitterionic polysaccharides (ZPS), obtained through chemical introduction of positive charges into anionic polysaccharides (PS) from GBS, have the ability to activate human and mouse antigen presenting cells (APCs) through toll-like receptor 2 (TLR2). To generate a polysaccharide vaccine with antigen (Ag) and adjuvant properties in one molecule, we have conjugated ZPS with a carrier protein. ZPS-glycoconjugates induce higher T-cell and Ab responses to carrier and PS, respectively, compared to control PS-glycoconjugates made with the native polysaccharide form. The increased immunogenicity of ZPS-conjugates correlates with their ability to activate dendritic cells (DCs). Moreover, protection of mothers or neonate offspring from lethal GBS challenge is better when mothers are immunized with ZPS-conjugates compared to immunization with PS-conjugates. In TLR2 knockout mice, ZPS-conjugates lose both their increased immunogenicity and protective effect after vaccination. When ZPS are coadministered as adjuvants with unconjugated tetanus toxoid (TT), they have the ability to increase the TT-specific antibody titer. In conclusion, glycoconjugates containing ZPS are potent vaccines. They target Ag to TLR2-expressing APCs and activate these APCs, leading to better T-cell priming and ultimately to higher protective Ab titers. Thus, rational chemical design can generate potent PS-adjuvants with wide application, including glycoconjugates and coadministration with unrelated protein Ags.

Mechanisms in the serotype-independent pneumococcal immunity induced in mice by intranasal vaccination with the cell wall polysaccharide

We previously reported that cell wall polysaccharide (CWPS) given to mice intranasally with adjuvant induces serotype-independent immunity to pneumococci. Some strains make CWPS with one phosphocholine group (CWPS/1), but most express two per tetrasaccharide repeat unit (CWPS/2). Here, CWPS/1 and CWPS/2 were equally protective against colonization by CWPS/2-type pneumococci, but the related Streptococcus mitis polymer lacking phosphocholine was non-protective. Previously the protection was shown to be CD4+T cell-dependent, abrogated by antiserum to interleukin (IL)-17A, and demonstrable in antibody-defective mice. Here, CWPS failed to protect IL-17A receptor knockout mice, further indicating IL-17A-dependence. When commercial CWPS/1 was size-fractionated preparatively, the larger exceeded the smaller molecules in their capacity to prime for IL-17A responses, and only the larger protected against pneumococcal colonization. However, a CWPS-tetanus toxoid conjugate - despite raising high titers of phosphocholine antibody - was non-protective, confirming the irrelevance of humoral immunity in this model. The results strengthen the concept that IL-17A-mediated T cell immunity is inducible by zwitterionic polysaccharides with sufficient chain length to provide coiled secondary structure. Coupling CWPS to protein, which paradoxically prevents protection, may occlude this regular linear conformation. We suggest that mucosal immunization with CWPS primes T(H)17 cells, which - upon contact with the phosphocholine of colonizing pneumococci - elaborate IL-17A, enhancing phagocytosis.

Oligoclonal CD4+ T cells promote host memory immune responses to Zwitterionic polysaccharide of Streptococcus pneumoniae

Zwitterionic polysaccharides of the normal flora bacteria represent a novel class of antigens in that they correct systemic CD4(+) T-cell deficiencies and direct lymphoid organogenesis during colonization of the host. Presentation of these polysaccharides to CD4(+) T cells depends on major histocompatibility complex class II- and DM-dependent retrograde transport from lysosomes to the cell surface. Yet the phenotype and clonality of the immune response to the polysaccharide in the mature host immune system have not been studied. Using the zwitterionic capsular polysaccharide Sp1 of Streptococcus pneumoniae, a transient member of the bacterial flora, in an experimental mouse model of cellular immunity, we demonstrated the accumulation of TH1- and TH17-polarized CD4(+) CD44(high) CD62(low) CD25(-) memory T cells. Subcutaneous immunization with Sp1 resulted in an increase of serum immunoglobulin G (IgG), predominantly of the IgG1 subclass, and suggested the presence of a humoral memory response to the polysaccharide. CD4(+) T cells stimulated with polysaccharide in vitro and in vivo showed a nonrestricted pattern for the T-cell receptor (TCR) beta-chain variable region, as demonstrated by semiquantitative reverse transcription-PCR and flow cytometry. Clonotype mapping of in vivo and in vitro polysaccharide-activated CD4(+) T cells revealed clonotypic TCR transcripts. Taken together, the data show the induction of clonal expansion of CD4(+) T cells by polysaccharides of commensal bacteria. Cellular and humoral memory host responses imply the ability of these polysaccharides to mediate the expansion of T cells via recognition within the CDR3 region of the TCR.

Generation of antibody responses to pneumococcal capsular polysaccharides is independent of CD1 expression in mice

Streptococcus pneumoniae is a bacterial microorganism that frequently causes serious infection, particularly in children and the elderly. Protection against infection with S. pneumoniae is based mainly on the generation of antibodies to the pneumococcal capsular polysaccharides (caps-PS), but the mechanisms responsible for the generation of anticapsular antibodies remain incompletely understood. The aim of the present study was to evaluate the role of CD1-restricted T cells in the antibody response to caps-PS. When immunized with Pneumo23, wild-type mice and CD1 knockout mice on BALB/c and C57BL/6 backgrounds generated immunoglobulin M (IgM) and IgG antibody responses to soluble caps-PS that were comparable. Similar results were obtained after immunization with heat-inactivated S. pneumoniae. The IgM and IgG antibody response of wild-type mice to Pneumo23 was not affected by an antagonizing monoclonal anti-CD1 antibody treatment. In summary, our data provide evidence that the antibody response to caps-PS is generated independently of CD1 expression.

Introduction of zwitterionic motifs into bacterial polysaccharides generates TLR2 agonists able to activate APCs

It was shown previously that bacterial polysaccharides (PS), which naturally contain both positive and negative charges, are able to activate T cells and APCs. However, the vast majority of bacterial PS are anionic and do not have these properties. In this study, we show that chemical introduction of positive charges into naturally anionic bacterial PS confers to the resulting zwitterionic PS (ZPS) the ability to activate pure human monocytes, monocyte-derived dendritic cells, and mouse bone marrow-derived dendritic cells, as do natural bacterial ZPS. Cells are induced to up-regulate MHC class II and costimulatory molecules and to produce cytokines. In mixed monocyte-T cell cocultures, ZPS induce MHC II-dependent T cell proliferation and up-regulation of activation markers. These stimulatory qualities of ZPS disappear when the positive charge is chemically removed from the molecules and thus the zwitterionic motif is destroyed. The ability of natural and chemically derived ZPS to activate APCs can be blocked by anti-TLR2 mAbs, and TLR2 transfectants show reporter gene transcription upon incubation with ZPS. In conclusion, the generation of a zwitterionic motif in bacterial PS confers the ability to activate both APCs and T cells. This finding has important implications for the design of novel polysaccharide vaccines.

Transport of Streptococcus pneumoniae capsular polysaccharide in MHC Class II tubules

Bacterial capsular polysaccharides are virulence factors and are considered T cell–independent antigens. However, the capsular polysaccharide Sp1 from Streptococcus pneumoniae serotype 1 has been shown to activate CD4⁺ T cells in a major histocompatibility complex (MHC) class II–dependent manner. The mechanism of carbohydrate presentation to CD4⁺ T cells is unknown. We show in live murine dendritic cells (DCs) that Sp1 translocates from lysosomal compartments to the plasma membrane in MHCII-positive tubules. Sp1 cell surface presentation results in reduction of self-peptide presentation without alteration of the MHCII self peptide repertoire. In DM-deficient mice, retrograde transport of Sp1/MHCII complexes resulting in T cell–dependent immune responses to the polysaccharide in vitro and in vivo is significantly reduced. The results demonstrate the capacity of a bacterial capsular polysaccharide antigen to use DC tubules as a vehicle for its transport as an MHCII/saccharide complex to the cell surface for the induction of T cell activation. Furthermore, retrograde transport requires the functional role of DM in self peptide–carbohydrate exchange. These observations open new opportunities for the design of vaccines against microbial encapsulated pathogens.

Microorganisms are comprised of proteins, carbohydrates, lipids, and nucleic acids. Current immunologic paradigms state that activation of T lymphocytes required for humoral and cellular immune responses resulting in immunologic memory to the pathogens is solely brought about by proteinaceous antigens, processed and degraded to small peptides, loaded onto major histocompatibility complex (MHC) molecules, and transported as MHC/peptide complexes to the cell surface, where the MHC/peptide complex is recognized by the T cell antigen receptor. The findings of the present study elucidate the mechanism of MHC class II (MHCII)–dependent presentation of the bacterial capsular polysaccharide of Streptococcus pneumoniae serotype 1 (Sp1) that results in effective T cell activation. Sp1 is transported in MHCII-positive tubules from lysosomal compartments to the plasma membrane for presentation. In the absence of the DM molecule, known as an editor and catalyst of self and foreign peptide exchange, retrograde transport of carbohydrate/MHCII complexes resulting in dendritic cell engagement with T cells in vitro and T cell–dependent immune responses to the polysaccharide in vivo fail. The results suggest a fundamental shift in the immunologic paradigm, offering previously unrecognized opportunities for the design of new classes of vaccines against infectious diseases.

The love-hate relationship between bacterial polysaccharides and the host immune system

This article explores the fascinating relationship between the mammalian immune system and the bacteria that are present in the mammalian gut. Every human is an ecosystem that hosts 10(13)-10(14) bacteria. We review the evidence that immunomodulatory molecules produced by commensal bacteria in the gut have a beneficial influence on the development of certain immune responses, through eliciting the clonal expansion of CD4(+) T-cell populations. This process seems to contribute to the overall health of the host by offering protection against various diseases and might provide supporting evidence at a molecular level for the 'hygiene hypothesis' of allergic immune disorders.

Structure and function relations with a T-cell-activating polysaccharide antigen using circular dichroism

Studies centered on understanding how molecular structure affects biological function have historically focused on proteins. Circular dichroism (CD) is commonly used to analyze protein secondary structure, yet its application to other molecules is far less explored. In fact, little is known about how glycan conformation might affect function, likely because of a lack of tools for measuring dynamic structural changes of carbohydrates. In the present study, we developed a method based on CD to monitor conformational changes in the zwitterionic T-cell-activating glycoantigen polysaccharide A1 (PSA). We found that PSA helical structure produces a CD spectrum that is strikingly similar to proteins rich in alpha-helical content and is equally sensitive to nonpolar solvents. Like conventional T-cell-dependent proteins, PSA requires processing before major histocompatibility complex class II (MHCII) binding. CD spectra of PSA fragments of varying sizes indicated that fragments smaller than three repeating units lack helical content and are incapable of MHCII binding. Likewise, neutralization of charged groups in the repeating unit resulted in major conformational changes as measured by CD, which correlated with a lack of MHCII presentation. These data represent two significant findings: CD can be used to measure conformational changes in carbohydrates and the functional epitope from PSA is dependent on a specific conformation that is stabilized by adjacent repeating units and a zwitterionic charge motif. As a result, this work demonstrates that CD is a valuable tool for use in functional glycomics efforts that seek to align chemical and conformational structure with biological activity.

Effect of B7-2 and CD40 signals from activated antigen-presenting cells on the ability of zwitterionic polysaccharides to induce T-Cell stimulation

Carbohydrates have been thought to stimulate immune responses independently of T cells; however, zwitterionic polysaccharides (ZPSs) from the capsules of some bacteria elicit potent CD4+-T-cell responses in vivo and in vitro. We demonstrated that HLA-DR on professional antigen-presenting cells (APCs) is required for ZPS-induced T-cell proliferation in vitro (15). Recently, it was shown that ZPSs are processed to low-molecular-weight carbohydrates by a nitric oxide-mediated mechanism in endosomes and locate in the major histocompatibility complex class II pathway (5, 15). The effect of the ZPS-mediated expression of HLA-DR and costimulatory molecules on the APC and T-cell engagement and subsequent T-cell activation has not been elucidated. Herein, we report that ZPS-mediated induction of HLA-DR-surface expression and T-cell proliferation are maximally enhanced after incubation of APCs for 8 h with ZPS. Treatment of APCs with bafilomycin A inhibits the up-regulation of ZPS-mediated HLA-DR surface expression and leads to inhibition of T-cell proliferation. Monoclonal antibodies (MAbs) to the costimulatory molecules B7-2 and CD40L specifically block ZPS-mediated T-cell activation, while a MAb to B7-1 does not. Surface expression of B7-2 and B7-1 but not of CD40 is maximally enhanced at 8 to 16 h of treatment of APCs with ZPS. The results demonstrate that the cellular immune response to ZPS depends on the translocation of HLA-DR to the cell surface and requires costimulation via B7-2 and CD40 on activated APCs. The implication is that activation of ZPS-specific T cells requires an orchestrated arrangement of both presenting and costimulatory molecules to form an immunological synapse.

Biological chemistry of immunomodulation by zwitterionic polysaccharides

Capsular polysaccharides isolated from pathogenic bacteria are comprised typically of many repeating units from one to eight or more monosaccharides in length. These polysaccharides stimulate the murine humoral immune system to elicit primarily IgM antibody responses. Studies conducted primarily in the mouse have characterized these polymers as T cell-independent antigens. These mouse studies and the relatively poor immunogenicity of polysaccharides in human hosts have led to the design of vaccines by coupling these polysaccharides to protein carriers to stimulate a T cell-dependent response. However, a newly described class of bacterial polysaccharides has been characterized that have the ability to modulate the cellular immune system. They are structurally diverse, but all share a zwitterionic charge motif that allows them to directly interact with T cells and antigen-presenting cells to initiate an immunomodulatory T cell response. These polymers, termed zwitterionic polysaccharides (ZPSs), elicit T cell-derived chemokines and cytokines that influence the immune response governing at least one classic host response to bacterial infection: abscess formation. This review will describe the biological and structural aspects of ZPSs that convey these activities.

Zwitterionic polysaccharides stimulate T cells with no preferential V beta usage and promote anergy, resulting in protection against experimental abscess formation

Zwitterionic polysaccharides (Zps) from pathogenic bacteria, such as Bacteroides fragilis, are virulence factors responsible for abscess formation associated with intra-abdominal sepsis. The underlying cellular mechanism for abscess formation requires T cell activation. Conversely, abscess formation can be prevented by prophylactic s.c. injection of purified Zps alone, a process also dependent on T cells. Hence, the modulatory role of T cells in abscess formation was investigated. We show that Zps interact directly with T cells with fast association/dissociation kinetics. Vbeta repertoire analysis using RT-PCR demonstrates that Zps have broad Vbeta usage. Zps-specific hybridomas responded to a variety of other Zps, but not to a nonzwitterionic polysaccharide, indicating cross-reactivity between different Zps. Furthermore, Zps-reactive T cell hybridomas could effectively transfer protection against abscess formation. Analysis of the proliferative capacity of T cells recovered from Zps-treated animals revealed that these T cells are anergic to subsequent stimulation by the different Zps or to alloantigens in an MLR. This anergic response was relieved by addition of IL-2. Taken together, the data show that this class of polysaccharides interacts directly with T cells in a nonbiased manner to elicit an IL-2-dependent anergic response that confers protection against abscess formation.

Polysaccharide Processing and Presentation by the MHCII Pathway

The adaptive immune system functions through the combined action of antigen-presenting cells (APCs) and T cells. Specifically, class I major histocompatibility complex antigen presentation to CD8(+) T cells is limited to proteosome-generated peptides from intracellular pathogens while the class II (MHCII) endocytic pathway presents only proteolytic peptides from extracellular pathogens to CD4(+) T cells. Carbohydrates have been thought to stimulate immune responses independently of T cells; however, zwitterionic polysaccharides (ZPSs) from the capsules of some bacteria can activate CD4(+) T cells. Here we show that ZPSs are processed to low molecular weight carbohydrates by a nitric oxide-mediated mechanism and presented to T cells through the MHCII endocytic pathway. Furthermore, these carbohydrates bind to MHCII inside APCs for presentation to T cells. Our observations begin to elucidate the mechanisms by which some carbohydrates induce important immunologic responses through T cell activation, suggesting a fundamental shift in the MHCII presentation paradigm.

Zwitterionic polysaccharides stimulate T cells by MHC class II-dependent interactions

Polysaccharides of pathogenic extracellular bacteria commonly have negatively charged groups or no charged groups at all. These molecules have been considered classic T cell-independent Ags that do not elicit cell-mediated immune responses in mice. However, bacterial polysaccharides with a zwitterionic charge motif (ZPSs), such as the capsular polysaccharides of many strains of Bacteroides fragilis, Staphylococcus aureus, and Streptococcus pneumoniae type 1 elicit potent CD4(+) T cell responses in vivo and in vitro. The cell-mediated response to ZPS depends on the presence of both positively charged and negatively charged groups on each repeating unit of the polysaccharide. In this study, we define some of the requirements for the presentation of ZPS to CD4(+) T cells. We provide evidence that direct interactions of T cells with APCs are essential for T cell activation by ZPS. Monocytes, dendritic cells, and B cells are all able to serve as APCs for ZPS-mediated T cell activation. APCs lacking MHC class II molecules do not support this activity. Furthermore, mAb to HLA-DR specifically blocks ZPS-mediated T cell activation, while mAbs to other MHC class II and class I molecules do not. Immunoprecipitation of lysates of MHC class II-expressing cells following incubation with ZPS shows binding of ZPS and HLA-DR. Electron microscopy reveals colocalization of ZPS with HLA-DR on the cell surface and in compartments of the endocytic pathway. These results indicate that MHC class II molecules expressing HLA-DR on professional APCs are required for ZPS-induced T cell activation. The implication is that binding of ZPS to HLA-DR may be required for T cell activation.

Immunochemical and biological characterization of three capsular polysaccharides from a single Bacteroides fragilis strain

Although Bacteroides fragilis accounts for only 0.5% of the normal human colonic flora, it is the anaerobic species most frequently isolated from intra-abdominal and other infections with an intestinal source. The capsular polysaccharides of B. fragilis are part of a complex of surface polysaccharides and are the organism's most important virulence factors in the formation of intra-abdominal abscesses. Two capsular polysaccharides from strain NCTC 9343, PS A1 and PS B1, have been characterized structurally. Their most striking feature is a zwitterionic charge motif consisting of both positively and negatively charged substituent groups on each repeating unit. This zwitterionic motif is essential for abscess formation. In this study, we sought to elucidate structural features of the capsular polysaccharide complex of a commonly studied B. fragilis strain, 638R, that is distinct from strain 9343. We sought a more general picture of the species to establish basic structure-activity and structure-biosynthesis relationships among abscess-inducing polysaccharides. Strain 638R was found to have a capsular polysaccharide complex from which three distinct carbohydrates could be isolated by a complex purification procedure. Compositional and immunochemical studies demonstrated a zwitterionic charge motif common to all of the capsular polysaccharides that correlated with their ability to induce experimental intra-abdominal abscesses. Of interest is the range of net charges of the isolated polysaccharides-from positive (PS C2) to balanced (PS A2) to negative (PS 3). Relationships among structural components of the zwitterionic polysaccharides and their molecular biosynthesis loci were identified.

Structural basis of the abscess-modulating polysaccharide A2 from Bacteroides fragilis

Zwitterionic capsular polysaccharides from pathogenic bacteria have peculiar immunological properties. They are capable of eliciting T-cell proliferation and modulating the course of abscess formation. To understand the molecular basis of this characteristic immune response, we are conducting detailed structure-function studies on these polysaccharides. We have identified, purified, and characterized an abscess-modulating polysaccharide, PS A2, from the clinical strain Bacteroides fragilis 638R. Here, we report the elucidation of both the chemical and three-dimensional structures of PS A2 by NMR spectroscopy, chemical methods, gas chromatography-mass spectrometry, and restrained molecular dynamics calculations. PS A2 consists of a pentasaccharide repeating unit containing mannoheptose, N-acetylmannosamine, 3-acetamido-3,6-dideoxyglucose, 2-amino-4-acetamido-2,4,6-trideoxygalactose, fucose, and 3-hydroxybutanoic acid. PS A2 is zwitterionic and carries one cationic free amine and one anionic carboxylate in each repeating unit. It forms an extended right-handed helix with two repeating units per turn and a pitch of 20 A. Positive and negative charges are exposed on the outer surface of the polymer in a regularly spaced pattern, which renders them easily accessible to other molecules. The helix is characterized by repeated large grooves whose lateral boundaries are occupied by the charges. The three-dimensional structure of PS A2 explicitly suggests mechanisms of interaction between zwitterionic polysaccharides and proteins.

Bacterial pathogens induce abscess formation by CD4(+) T-cell activation via the CD28-B7-2 costimulatory pathway

Abscesses are a classic host response to infection by many pathogenic bacteria. The immunopathogenesis of this tissue response to infection has not been fully elucidated. Previous studies have suggested that T cells are involved in the pathologic process, but the role of these cells remains unclear. To delineate the mechanism by which T cells mediate abscess formation associated with intra-abdominal sepsis, the role of T-cell activation and the contribution of antigen-presenting cells via CD28-B7 costimulation were investigated. T cells activated in vitro by zwitterionic bacterial polysaccharides (Zps) known to induce abscess formation required CD28-B7 costimulation and, when adoptively transferred to the peritoneal cavity of naïve rats, promoted abscess formation. Blockade of T-cell activation via the CD28-B7 pathway in animals with CTLA4Ig prevented abscess formation following challenge with different bacterial pathogens, including Staphylococcus aureus, Bacteroides fragilis, and a combination of Enterococcus faecium and Bacteroides distasonis. In contrast, these animals had an increased abscess rate following in vivo T-cell activation via CD28 signaling. Abscess formation in vivo and T-cell activation in vitro required costimulation by B7-2 but not B7-1. These results demonstrate that abscess formation by pathogenic bacteria is under the control of a common effector mechanism that requires T-cell activation via the CD28-B7-2 pathway.