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D L Kasper

Publications and source records attributed to D L Kasper.

At least 55 records · Page 3Linked to original sources
PubMed1997

NMR and molecular dynamics studies of the conformational epitope of the type III group B Streptococcus capsular polysaccharide and derivatives.

The conformational epitope of the type III group B Streptococcus capsular polysaccharide (GBSP III) exhibits unique properties which can be ascribed to the presence of sialic acid in its structure and the requirement for an extended binding site. By means of NMR and molecular dynamics studies on GBSP III and its fragments, the extended epitope of GBSP III was further defined. The influence of sialic acid on the conformational properties of GBSP III was examined by performing conformational analysis on desialylated GBSP III, which is identical to the polysaccharide of Streptococcus pneumoniae type 14, and also on oxidized and reduced GBSP III. Conformational changes were gauged by 1H and 13C chemical shift analysis, NOE, 1D selective TOCSY-NOESY experiments, J(HH) and J(CH) variations, and NOE of OH resonances. Changes in mobility were examined by 13C T1 and T2 measurements. Unrestrained molecular dynamics simulations with explicit water using the AMBER force field and the GLYCAM parameter set were used to assess static and dynamic conformational models, simulate the observable NMR parameters and calculate helical parameters. GBSP III was found to be capable of forming extended helices. Hence, the length dependence of the conformational epitope could be explained by its location on extended helices within the random coil structure of GBSP III. The interaction of sialic acid with the backbone of the PS was also found to be important in defining the conformational epitope of GBSP III.

Carbohydrate Conformation↗
PubMed1997

Group A and group B streptococcal vaccine development. A round table presentation.

The data presented above provide a broad overview of ongoing work to develop vaccines against group A and group B streptococcal infections. The encouraging results of human trials with conjugate group B polysaccharide vaccines suggest that this approach will lead to a safe and effective method for preventing these devastating infections in newborn infants. The results of preclinical studies of the various strategies to develop group A streptococcal vaccines are also encouraging. Whether one approach will be more advantageous or efficacious than another will need to await clinical trials. Nevertheless, we predict that in the next decade we will make significant strides in preventing streptococcal infections and their complications.

Adhesins, Bacterial↗
PubMed1997

Therapeutic potential of human antisera to group B streptococcal glycoconjugate vaccines in neonatal mice.

Experimental immunoglobulin preparations for treatment of group B streptococcal (GBS) infections contain low levels of functional antibody and exhibit lot-to-lot variability. GBS capsular polysaccharide-protein conjugate vaccines have recently been shown to produce high serum levels of type-specific antibody in healthy volunteers. Treatment of neonatal mice 4 h after inoculation with an ordinarily lethal dose of GBS type Ia, Ib, or III with pooled human serum from adults who had received GBS type Ia capsular polysaccharide-tetanus toxoid vaccine (Ia CPS-TT), Ib CPS-TT, or III CPS-TT resulted in 63%, 70%, and 75% survival, respectively. In contrast, < or = 17% of the infected mice treated with normal human serum or saline survived. These results demonstrate the therapeutic activity of GBS polysaccharide conjugate vaccine-induced antiserum and provide a rationale for the use of these vaccines in producing a functional, high-titered intravenous immunoglobulin preparation for clinical use.

Adult↗
PubMed1997

Immunogenicity and protective efficacy of the alpha C protein of group B streptococci are inversely related to the number of repeats.

Infection by group B streptococci (GBS) is an important cause of bacterial disease in neonates. Alpha C protein is a protective cell surface-associated protein of GBS. This protein contains a repeat region flanked by N and C termini. Variable expression of tandem repeating units of alpha C proteins had been found among clinical isolates of GBS. We examined the effect of the number of repeats on the immunogenicity of the alpha C protein and its ability to elicit protection from GBS infection in a neonatal mouse model. Mice were immunized with purified alpha C proteins of constructs containing various numbers of repeats (n = 1, 2, 9, and 16) and the N- and C-terminal regions. Both the N-terminal and the repeat regions contain protective and opsonic epitopes. Antibody responses to the alpha C protein constructs with various numbers of repeats were tested with enzyme-linked immunosorbent assay plates coated with either native, nine-repeat alpha C protein or "repeatless" N-terminal antigen. An inverse relationship was found between the number of repeats and the immunogenicity of the alpha C protein; this effect was most pronounced on titers of antibody to the N-terminal region. An inverse relationship was also observed between the number of repeats and protective efficacy, i.e., mouse dams immunized with 5 microg of one- or nine-repeat alpha C protein transferred protective immunity to 65 or 11% of their pups, respectively (P < 0.0001). Thus, the presence of multiple repeats appears to lessen the antibody response to the complete alpha C protein, and especially the antibody response to its N-terminal region, and suggests a mechanism whereby repeat elements contribute to the evasion of host immunity.

Animals↗
PubMed1996

Immune response to type III group B streptococcal polysaccharide-tetanus toxoid conjugate vaccine.

Group B Streptococcus (GBS) is an important perinatal pathogen. Because transplacentally acquired maternal antibodies to the GBS capsular polysaccharides (CPS) confer protection, prevention of infant disease may be possible after immunization of women. Unfortunately, the purified CPS of GBS are only variably immunogenic in adults; therefore to enhance immunogenicity we have designed and developed a CPS-protein conjugate vaccine. The lability of a conformationally dependent epitope on the III CPS containing a critical sialic acid residue was important to consider in vaccine design. 100 women were randomized to receive GBS type III CPS-tetanus toxoid conjugate (III-TT) vaccine at one of three doses; unconjugated GBS type III CPS; or saline. Serum samples were obtained before immunization and 2, 4, 8, and 26 wk thereafter, and specific antibody to type III CPS was measured. Vaccines were well tolerated. In sera from recipients of the highest dose of III-TT, CPS-specific IgG levels rose from a geometric mean of 0.09 microg/ml before immunization to 4.53 microg/ml 8 wk later, whereas levels in recipients of unconjugated type III CPS rose from 0.21 microg/ml to 1.41 microg/ml. Lower doses resulted in lower antibody levels. A > or = 4-fold rise in antibody concentration was achieved in 90% of recipients of III-TT compared with 50% of those that received III CPS (P = 0.0015). Antibodies evoked by the conjugate vaccine recognized a conformationally dependent epitope of the III-CPS, promoted opsonophagocytosis and killing of GBS, and, after maternal immunization, protected neonatal mice from lethal challenge with type III GBS. We conclude that directed coupling of type III GBS polysaccharide to a carrier protein yielded a conjugate vaccine with preserved expression of a highly labile conformational epitope involving sialic acid and enhanced immunogenicity compared with uncoupled CPS.

Adolescent↗
PubMed1996

Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein.

Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca) for this protein contains a series of tandem repeats (each encoding 82 aa) that are identical at the nucleotide level and express a protective epitope. We previously reported that GBS isolates from two of 14 human maternal and neonatal pairs differed in the number of repeats contained in their alpha C protein; in both pairs, the alpha C protein of the neonatal isolate was smaller in molecular size. We now demonstrate by PCR that the neonatal isolates contain fewer tandem repeats. Maternal isolates were susceptible to opsonophagocytic killing in the presence of alpha C protein-specific antiserum, whereas the discrepant neonatal isolates proliferated. An animal model was developed to further study this phenomenon. Adult mice passively immunized with antiserum to the alpha C protein were challenged with an alpha C protein-expressing strain of GBS. Splenic isolates of GBS from these mice showed a high frequency of mutation in bca--most commonly a decrease in repeat number. Isolates from non-immune mice were not altered. Spontaneous deletions in the repeat region were observed at a much lower frequency (6 x 10(-4)); thus, deletions in that region are selected for under specific antibody pressure and appear to lower the organism's susceptibility to killing by antibody specific to the alpha C protein. This mechanism of antigenic variation may provide a means whereby GBS evade host immunity.

Animals↗
PubMed1996

Structural and immunochemical characterization of the type VIII group B Streptococcus capsular polysaccharide.

The type VIII capsular polysaccharide has been isolated and purified from a newly described strain of group B Streptococcus which is a leading cause of sepsis and neonatal meningitis in Japan. The polysaccharide contains D-glucose, D-galactose, L-rhamnose, and sialic acid in the molar ratio 1:1:1:1. By means of high resolution 1H nuclear magnetic resonance (1H NMR), 13C NMR, and homo- and heterocorrelated NMR, the repeating unit structure of the type VIII polysaccharide was delineated as the following, [formula: see text] Enzymatic studies established this polysaccharide as the first from which sialic acid, linked to a branched beta-D-galactopyranosyl residue, is known to be removed by bacterial neuraminidase.

Antigens, Bacterial↗
PubMed1996

Quantitative determination of antibodies to type III group B streptococcal polysaccharide.

The susceptibility of neonates to invasive infection with type III group B streptococci (GBS) in a radioactive antigen-binding assay (RABA) has been correlated with low maternal serum levels of capsular polysaccharide-specific antibodies. An ELISA was developed using capsular polysaccharide covalently coupled to human serum albumin. In sera from 35 healthy women, the range of IgG antibodies to GBS III polysaccharide was 0.05-33.0 micrograms/mL, and specific IgA antibodies were 0.08-1.1 micrograms/mL; however, no GBS III capsular polysaccharide-specific antibodies of the IgM isotype were detected by the ELISA. The levels of naturally acquired and vaccine-induced antibodies obtained with this ELISA correlated well with the results of the RABA (Spearman's rank correlation coefficient, .92). The ELISA has two major advantages over the RABA: It measures specific isotypes and subclasses of antibodies, and it can detect type III polysaccharide-specific antibodies at lower concentrations.

Animals↗
PubMed1996

Immunogenicity of group B Streptococcus type III polysaccharide-tetanus toxoid vaccine in baboons.

Maternal vaccination has been proposed as a rational approach for the prevention of neonatal group B streptococcal (GBS) disease. In this study, baboons were used as a nonhuman primate model to evaluate the immunogenicity of a GBS type III glycoconjugate vaccine. Type III-specific immunoglobulin G with opsonic activity was induced after vaccination with type III polysaccharide coupled to tetanus toxoid administered with an aluminum adjuvant. This suggests that baboons could be used in evaluating maternal transfer of GBS-specific antibodies by vaccination during pregnancy.

Animals↗
PubMed1996

Sequence of the toxic shock syndrome toxin gene (tstH) borne by strains of Staphylococcus aureus isolated from patients with Kawasaki syndrome.

To explore whether a novel staphylococcal clone or structural variant of toxic shock syndrome toxin 1 is associated with Kawasaki syndrome, six toxigenic strains of Staphylococcus aureus from Kawasaki syndrome patients were studied. The strains were divisible into two groups based on phenotypic and genotypic characteristics and are therefore unequivocally not clonal. Portions of the tstH genes of each strain were sequenced. Three were sequenced in their entirety, while the remainder were sequenced from codon 66 to codon 137 of the mature protein only. Two of the former group differed slightly in the sequences of their signal peptides relative to the sequence published for the tstH signal peptide. Those differences did not affect toxin processing or secretion. The sequenced portions of the regions encoding mature toxic shock syndrome toxin 1 were identical in all six strains and corresponded exactly to the published sequence of tstH. No evidence was found for the existence of a structural variant of tstH uniquely associated with Kawasaki syndrome.

Bacterial Toxins↗
PubMed1995

Structural elucidation of the novel type VII group B Streptococcus capsular polysaccharide by high resolution NMR spectroscopy.

The type VII capsular polysaccharide isolated from the newly discovered group B Streptococcus (GBS) strain contains D-glucose, D-galactose, N-acetyl-D-glucosamine and N-acetylneuraminic acid in the molar ratio 2:2:1:1. High-resolution one- and two-dimensional (1D and 2D) 1H and 13C NMR spectroscopy of the native and desialylated polysaccharides showed the type VII GBS capsular polysaccharide to contain the following branched hexasaccharide repeating unit: [formula: see text] Despite extensive structural similarity with the previously described GBS polysaccharides, the type VII polysaccharide showed no cross-reaction with the heterologous antisera.

Acetylglucosamine↗
PubMed1995

Structural elucidation of the capsular polysaccharide of Bacteroides fragilis strain 23745M1.

The capsule of Bacteroides fragilis (ATCC23745) consists of two distinct polysaccharides, the separation of which could not be accomplished. The mouse-passaged strain (23745M1), however, yielded a preponderant polysaccharide which was isolated and purified. Using mainly high resolution NMR spectroscopy, the structure of the polysaccharide was elucidated and it is composed of the following repeating unit: [formula see text]

Acetylglucosamine↗
PubMed1995

Structure and function of Bacteroides fragilis capsular polysaccharides: relationship to induction and prevention of abscesses.

The capsular polysaccharide complex (CPC) of Bacteroides fragilis exhibits unusual biological properties. This polysaccharide complex promotes the formation of intraabdominal abscesses and, when administered systemically, can prevent abscess induction in a rat model of intraabdominal sepsis. Each of these biological properties is mediated by a T cell-dependent immune mechanism. The CPC consists of two distinct polysaccharides, PS A and PS B, each with repeating units that have positively charged amino groups and negatively charge carboxyl or phosphate groups. Analysis of these polysaccharides as well as of other charged polysaccharides of bacterial origin, before and after chemical modification, revealed that the oppositely charged groups are required for promotion of intraabdominal abscesses as well as for the distinct properties associated with the B. fragilis CPC and delineate one mechanism by which these biological responses occur.

Abdominal Abscess↗
PubMed1995

Immunogenicity and protective activity in animals of a type V group B streptococcal polysaccharide-tetanus toxoid conjugate vaccine.

The recent recognition of type V strains as a frequent cause of group B streptococcal (GBS) infection in both infants and adults prompted investigation of an effective vaccine against these organisms. Purified GBS type V polysaccharide was covalently linked to tetanus toxoid to form a type V polysaccharide-tetanus toxoid conjugate vaccine. The conjugate elicited type V polysaccharide-specific IgG antibodies in rabbits, while unconjugated type V polysaccharide did not. Conjugate-induced rabbit antibodies were opsonic in vitro and protected mice against challenge with type V GBS. Efficacy of the conjugate vaccine also was demonstrated in a maternal vaccination/neonatal challenge model in mice. A GBS type V polysaccharide-tetanus toxoid conjugate is an effective immunogen in animal models and may be a useful component for inclusion in a multivalent GBS vaccine for human use.

Animals↗
PubMed1995

Monoclonal antibodies to detect capsular diversity among Bacteroides fragilis isolates.

The capsular polysaccharide complex (CPC) of Bacteroides fragilis is composed of two distinct polysaccharides, designated PS A and PS B, and is a major virulence factor of this microorganism. In order to investigate the antigenic diversity of the CPCs of B. fragilis strains, we generated and characterized 10 monoclonal antibodies (MAbs) directed to the CPCs of three reference strains. The specificities of the MAbs were determined by enzyme-linked immunosorbent assay and dot-immunobinding assay. At least one MAb was specific for each PS A and PS B of the three strains. The MAbs were used to detect capsular antigens on the surface of 231 B. fragilis isolates from different geographical areas by a whole-cell dot-immunobinding assay. Over half of the strains, regardless of the country of origin, reacted with at least one MAb. Clinical extraintestinal infection isolates were significantly more reactive than fecal isolates, suggesting an association between capsular composition and the propensity to cause clinical infections. The patterns of reactivity of the isolates with the 10 MAbs were very different and sometimes extremely complex and indicated a sharing of epitopes among different capsular polysaccharides. The reactive strains could be grouped according to 32 different patterns; some patterns were relatively common, while others were rarer and were shown by only one or two strains. These results show that B. fragilis capsular polysaccharides are antigenically extremely diverse. This complexity and the large number of nonreactive strains indicate that a typing system based on B. fragilis capsular antigens will be difficult to establish.

Antibodies, Bacterial↗
PubMed1995

Polysaccharide-mediated protection against abscess formation in experimental intra-abdominal sepsis.

Abscess formation is a major complication of intra-abdominal sepsis that causes significant morbidity and mortality. In such cases, Bacteroides fragilis is the predominant anaerobic isolate. In a rat model of intra-abdominal sepsis, the capsular polysaccharide complex (CPC) from B. fragilis promotes abscess formation and when administered sub-cutaneously, protects against this host response by a T cell-dependent immune mechanism. In the present study, the polysaccharide A (PS A) component of CPC protected animals against challenge with live heterologous bacterial species (mixtures of anaerobes and facultative organisms) that are most commonly isolated from intra-abdominal abscesses in humans. Protection against heterologous bacterial challenge was transferred by T cells. Administration of PS A shortly before or even after challenge with B. fragilis protected against this host response. In experiments designed to simulate fecal contamination of the human peritoneal cavity, PS A protected animals against abscess formation induced by a rat cecal contents inoculum. The surprisingly broad protective activity of PS A indicates that this molecule is likely suppressing a nonspecific host tissue reaction that forms in response to a variety of abscess-inducing organisms and that it might be useful in preventing abscess formation associated with intra-abdominal sepsis in the clinical setting.

Abdominal Abscess↗
PubMed1995

Designer vaccines to prevent infections due to group B Streptococcus.

Group B streptococci (GBS) are the major cause of serious infections in neonates and an important cause of infection in adults, particularly peripartum women and patients with diabetes mellitus and malignancy. Immunity to GBS in neonates is associated with naturally acquired maternal antibodies to the type-specific capsular polysaccharides of these organisms. IgG class antibodies directed to these polysaccharides are passed transplacentally and protect the child from invasive GBS disease. Phase I and II clinical trials showed that the purified polysaccharides had limited immunogenicity. However, vaccine responders passed functional IgG class antibodies to their children. A glycoconjugate vaccine has been designed so that the type-specific polysaccharides are covalently linked to a carrier protein. This secondary amine linkage is between aldehyde groups created on the eighth carbon of a selected number of periodate-oxidized sialic acid residues of the polysaccharide and epsilon-amino groups on lysine residues of tetanus toxoid. Careful epitope mapping studies had demonstrated that modification by controlled periodate oxidation could be accomplished and that an important conformational epitope on the polysaccharide would be preserved. Preclinical testing of the glycoconjugate vaccines in animal models of GBS disease demonstrated the immunogenicity and protective efficacy of the vaccine-induced antibodies. Phase I clinical testing of the glycoconjugate vaccine is in progress, and the early results appear promising.

Bacterial Vaccines↗