Pathogenesis, pathology and chemotherapy of experimental Legionella pneumophila infection

Legionella pneumophila is the causative agent of a severe, often fatal pneumonic illness known as Legionnaires\u27 disease. The mechanisms by which L. pneumophila attaches to U937 (transformed human-like fibroblasts) were investigated. Experimental parameters for adherence assays were established prior to blocking studies designed to identify microbial adhesins and/or eukaryotic receptors that mediate bacterial attachment to target cells. Results from these studies indicated that a lectin-like component(s) associated with L. pneumophila may be responsible, at least in part, for microbial adherence to these eukaryotic host cells. Erythromycin is the drug of choice for the treatment of clinical legionellosis; however, difficulties with this antibiotic have been reported resulting in the need to seek alternative therapeutic regimens. In these studies, the effect of clinically relevant antibiotics that inhibited bacterial cell wall, protein and DNA synthesis of this pathogen was evaluated in vitro by growth and viability studies as well as morphologically by negative stain, scanning and thin-section electron microscopy. Of those tested, cefotaxime, an antibiotic of limited value in clinical trials, was most effective. The pathogenicity of L. pneumophila was assessed by LD\sb{50} and bacterial growth estimations in the chick embryo animal system in ovo. In addition, histopathological and electron microscopic examination of the cellular and sub-cellular pathology induced in the organs of embryos previously infected with 100 times the yolk sac (YS)LD\sb{50} of L. pneumophila was made as a prelude to chemotherapeutic treatment with a range of clinically putative antimicrobial agents. The promising new quinolone derivative, ciprofloxacin, was most effective in these trials. Results from these studies may be indicative of novel preventative and control measures for the therapy of human Legionnaires\u27 disease

Polysaccharide Processing and Presentation by the MHCII Pathway

AbstractThe 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

MHCII glycosylation modulates Bacteroides fragilis carbohydrate antigen presentation

N-linked glycans on class II MHC molecules are required for the presentation of glycoantigens, but not peptide antigens

T Cells Activated by Zwitterionic Molecules Prevent Abscesses Induced by Pathogenic Bacteria

Immunologic paradigms classify bacterial polysaccharides as T cell-independent antigens. However, these models fail to explain how zwitterionic polysaccharides (Zps) confer protection against intraabdominal abscess formation in a T cell-dependent manner. Here, we demonstrate that Zps elicit a potent CD4+ T cell response in vitro that requires available major histocompatibility complex class II molecules on antigen-presenting cells. Specific chemical modifications to Zps show that: 1) the activity is specific for carbohydrate structure, and 2) the proliferative response depends upon free amino and carboxyl groups on the repeating units of these polysaccharides. Peptides synthesized to mimic the zwitterionic charge motif associated with Zps also exhibited these biologic properties. Lysine-aspartic acid (KD) peptides with more than 15 repeating units stimulated CD4+ T cells in vitro and conferred protection against abscesses induced by bacteria such as Bacteroides fragilis and Staphylococcus aureus. Evidence for the biologic importance of T cell activation by these zwitterionic polymers was provided when human CD4+ T cells stimulated with these molecules in vitro and adoptively transferred to rats in vivo conferred protection against intraabdominal abscesses induced by viable bacterial challenge. These studies demonstrate that bacterial polysaccharides with a distinct charge motif activate T cells and that this activity confers immunity to a distinct pathologic response to bacterial infection

EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies ), 2013. Scientific Opinion on the substantiation of a health claim related to Yestimun ® and defence against pathogens in the upper respiratory tract pursuant to Article 13(5) of R egulation (EC) No 1924/2006

Following an application from Leiber GmbH, submitted for authorisation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of Germany, the Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to Yestimun® and defence against pathogens in the upper respiratory tract. The food that is the subject of the health claim, Yestimun®, which consists of (1,3)-(1,6)-β-D-glucans from brewer’s yeast cell wall, is sufficiently characterised. The claimed effect, defence against pathogens in the upper respiratory tract, is a beneficial physiological effect. No human intervention studies from which conclusions could be drawn for the scientific substantiation of the claim were provided by the applicant. The Panel concludes that a cause and effect relationship has not been established between the consumption of Yestimun® ((1,3)-(1,6)-β-D-glucans from brewer’s yeast cell wall) and defence against pathogens in the upper respiratory tract

A bacterial carbohydrate links innate and adaptive responses through Toll-like receptor 2

Commensalism is critical to a healthy Th1/Th2 cell balance. Polysaccharide A (PSA), which is produced by the intestinal commensal Bacteroides fragilis, activates CD4+ T cells, resulting in a Th1 response correcting the Th2 cell skew of germ-free mice. We identify Toll-like receptors as crucial to the convergence of innate and adaptive responses stimulated by PSA. Optimization of the Th1 cytokine interferon-γ in PSA-stimulated dendritic cell–CD4+ T cell co-cultures depends on both Toll-like receptor (TLR) 2 and antigen presentation. Synergy between the innate and adaptive responses was also shown when TLR2−/− mice exhibited impaired intraabdominal abscess formation in response to B. fragilis. Commensal bacteria, using molecules like PSA, potentially modulate the Th1/Th2 cell balance and the response to infection by coordinating both the innate and adaptive pathways

Antibody-Independent, Interleukin-17A-Mediated, Cross-Serotype Immunity to Pneumococci in Mice Immunized Intranasally with the Cell Wall Polysaccharide

Serotype-specific immunity to Streptococcus pneumoniae is conferred by antibodies to the capsular polysaccharides, which define the 90 known serotypes. Whether antibody to the species-common cell wall polysaccharide (C-Ps) is protective has been a matter of controversy. Here we show that C-Ps given intranasally with mucosal adjuvant increased the resistance of mice to experimental nasopharyngeal colonization by capsulated S. pneumoniae of serotype 6B. This immunity could be induced in mice congenitally lacking immunoglobulin but was dependent upon CD4+ T cells. Elimination of the charged amino group on the polymer backbone by N acetylation of C-Ps reduced the immunity, as did treatment of the mice with antibody to the cytokine interleukin-17A at the time of challenge, both consistent with the hypothesis of T-cell activation due to the zwitterionic motif of the polymer. C-Ps also protected in a model of fatal aspiration pneumonia by heavily capsulated serotype 3. These findings suggest a novel immunization strategy against S. pneumoniae

Streptococcus pneumoniae Serotype 1 Capsular Polysaccharide Induces CD8+CD28− Regulatory T Lymphocytes by TCR Crosslinking

Zwitterionic capsular polysaccharides (ZPS) of commensal bacteria are characterized by having both positive and negative charged substituents on each repeating unit of a highly repetitive structure that has an α-helix configuration. In this paper we look at the immune response of CD8+ T cells to ZPSs. Intraperitoneal application of the ZPS Sp1 from Streptococcus pneumoniae serotype 1 induces CD8+CD28− T cells in the spleen and peritoneal cavity of WT mice. However, chemically modified Sp1 (mSp1) without the positive charge and resembling common negatively charged polysaccharides fails to induce CD8+CD28− T lymphocytes. The Sp1-induced CD8+CD28− T lymphocytes are CD122lowCTLA-4+CD39+. They synthesize IL-10 and TGF-β. The Sp1-induced CD8+CD28− T cells exhibit immunosuppressive properties on CD4+ T cells in vivo and in vitro. Experimental approaches to elucidate the mechanism of CD8+ T cell activation by Sp1 demonstrate in a dimeric MHC class I-Ig model that Sp1 induces CD8+ T cell activation by enhancing crosslinking of TCR. The expansion of CD8+CD28− T cells is independent, of direct antigen-presenting cell/T cell contact and, to the specificity of the T cell receptor (TCR). In CD8+CD28− T cells, Sp1 enhances Zap-70 phosphorylation and increasingly involves NF-κB which ultimately results in protection versus apoptosis and cell death and promotes survival and accumulation of the CD8+CD28− population. This is the first description of a naturally occurring bacterial antigen that is able to induce suppressive CD8+CD28− T lymphocytes in vivo and in vitro. The underlying mechanism of CD8+ T cell activation appears to rely on enhanced TCR crosslinking. The data provides evidence that ZPS of commensal bacteria play an important role in peripheral tolerance mechanisms and the maintenance of the homeostasis of the immune system