J L DiFabio

Bio: J L DiFabio is an academic researcher from Brigham and Women's Hospital. The author has contributed to research in topics: Toxoid & Conjugate vaccine. The author has an hindex of 5, co-authored 5 publications receiving 540 citations.

Immunogenicity in animals of a polysaccharide-protein conjugate vaccine against type III group B Streptococcus.

Abstract: The native capsular polysaccharide of type III group B Streptococcus elicits a specific antibody response in only 60% of nonimmune human subjects. To enhance the immunogenicity of this polysaccharide, we coupled the type III polysaccharide to tetanus toxoid. Prior to coupling, aldehyde groups were introduced on the polysaccharide by controlled periodate oxidation, resulting in the conversion of 25% of the sialic acid residues of the polysaccharide to residues of the 8-carbon analogue of sialic acid, 5-acetamido-3,5-dideoxy-D-galactosyloctulosonic acid. Tetanus toxoid was conjugated to the polysaccharide by reductive amination, via the free aldehyde groups present on the partially oxidized sialic acid residues. Rabbits vaccinated with the conjugate vaccine produced IgG antibodies that reacted with the native type III group B streptococcal polysaccharide (3/3 rabbits), while rabbits immunized with the unconjugated type III polysaccharide failed to respond (0/3 rabbits). Sera from animals receiving conjugate vaccine opsonized type III group B streptococci for phagocytic killing by human peripheral blood leukocytes, and protected mice against lethal challenge with live type III group B streptococci. The results suggest that this method of conjugation to a carrier protein may be a useful strategy to improve the immunogenicity of the type III group B Streptococcus polysaccharide in human subjects.

Effects of chain length on the immunogenicity in rabbits of group B Streptococcus type III oligosaccharide-tetanus toxoid conjugates.

Abstract: One method to improve the immunogenicity of polysaccharide antigens is the covalent coupling of the native polysaccharide or a derivative oligosaccharide to a carrier protein. In general, T cell-dependent properties are enhanced in conjugates of smaller saccharides, but a conformational epitope of the native polysaccharide may be better expressed in conjugates of larger saccharides. We have reported previously the synthesis and immunogenicity in animals of an oligosaccharide-tetanus toxoid conjugate vaccine against type III group B Streptococcus. In this study, we sought to determine the optimal size of group B Streptococcus type III oligosaccharide for use in a conjugate vaccine by evaluating the relative immunogenicity of conjugate vaccines containing oligosaccharides that were twofold smaller (7,000 Mr) or larger (27,000 Mr) than that reported previously (14,500 Mr). All three type III oligosaccharide conjugate vaccines were immunogenic in rabbits, in contrast to native, uncoupled group B Streptococcus type III polysaccharide. However, with respect to eliciting specific antibodies that were protective in vivo, the vaccine containing the intermediate-size oligosaccharide was superior to the smaller or larger conjugate vaccine. Analysis of opsonic activity of vaccine-induced antibodies demonstrated a predominance of IgG antibodies, thought to reflect T cell dependence, in response to shorter chain length conjugates, while the conformational epitope of the native polysaccharide was maximally expressed on longer chain length conjugates. These opposing trends may account for the optimal immunogenicity of an intermediate-size group B Streptococcus type III oligosaccharide conjugate vaccine.

Isolation and characterization of type IV group B Streptococcus capsular polysaccharide.

Abstract: An antigenically distinct serotype, type IV, has recently been added to the recognized serotypes of group B streptococci (GBS). We isolated and purified the capsular polysaccharide antigen from a prototype type IV GBS strain. The type IV capsular polysaccharide formed a precipitin line with rabbit antiserum to type IV GBS organisms but not with antiserum to organisms of GBS serotype Ia, Ib, II, or III. Enzyme-linked immunosorbent assay inhibition experiments showed no cross-reaction between type IV antiserum and other GBS serotypes. Capsular polysaccharide released from the bacterial cells with mutanolysin and that isolated from the culture supernatant had similar elution profiles on Sepharose CL-6B, with a Kav of 0.30 and an estimated Mr of 200,000. The purified type IV polysaccharide was found to contain galactose, glucose, N-acetylglucosamine, and N-acetylneuraminic acid (sialic acid) as exclusive sugars. The polysaccharide contained 23% (by weight) sialic acid and galactose, glucose, and N-acetylglucosamine in a relative ratio of (1):1.10:0.55. These results are compatible with a repeating structure of six monosaccharide residues containing galactose, glucose, N-acetylglucosamine, and sialic acid in a molar ratio of 2:2:1:1. Unlike type Ia, II, and III GBS polysaccharides, desialylation of the type IV polysaccharide produced an antigen which formed a line of identity with the native type IV antigen in double diffusion in agar against homologous antiserum. This result suggests that sialic acid is not as critical to the immunodeterminant structure of the type IV antigen as it is for other GBS capsular types.

A Critical Role of Natural Immunoglobulin M in Immediate Defense Against Systemic Bacterial Infection

Abstract: To evaluate the role of natural immunoglobulin (Ig)M in the immediate response against microbial infection, we tested mutant mice that are deficient in secreted (s)IgM in an acute peritonitis model induced by cecal ligation and puncture (CLP). 20% of wild-type mice died within 32 h of CLP, whereas 70% of sIgM-deficient mice died within the same time period. The increased susceptibility was associated with a reduced level of tumor necrosis factor (TNF)-α, a decreased neutrophil recruitment and an increased bacterial load in the peritoneum, and elevated levels of endotoxin and proinflammatory cytokines in the circulation. Resistance to CLP by sIgM-deficient mice was restored by reconstitution with polyclonal IgM from normal mouse serum. Reconstitution with a monoclonal IgM specific to phosphatidylcholine, a conserved cell membrane component, has a modest effect but a monoclonal IgM specific to phosphocholine is not protective. These findings demonstrate a critical role of natural IgM in the immediate defense against severe bacterial infection.

Studies of group B streptococcal infection in mice deficient in complement component C3 or C4 demonstrate an essential role for complement in both innate and acquired immunity

Abstract: Group B streptococci (GBS) cause sepsis and meningitis in neonates and serious infections in adults with underlying chronic illnesses. Specific antibodies have been shown to be an important factor in protective immunity for neonates, but the role of serum complement is less well defined. To elucidate the function of the complement system in immunity to this pathogen, we have used the approach of gene targeting in embryonic stem cells to generate mice totally deficient in complement component C3. Comparison of C3-deficient mice with mice deficient in complement component C4 demonstrated that the 50% lethal dose for GBS infection was reduced by approximately 50-fold and 25-fold, respectively, compared to control mice. GBS were effectively killed in vitro by human blood leukocytes in the presence of specific antibody and C4-deficient serum but not C3-deficient serum. The defective opsonization by C3-deficient serum in vitro was corroborated by in vivo studies in which passive immunization of pregnant dams with specific antibodies conferred protection from GBS challenge to normal and C4-deficient pups but not C3-deficient pups. These results indicate that the alternative pathway is sufficient to mediate effective opsonophagocytosis and protective immunity to GBS in the presence of specific antibody. In contrast, the increased susceptibility to infection of non-immune mice deficient in either C3 or C4 implies that the classical pathway plays an essential role in host defense against GBS infection in the absence of specific immunity.

A Population-Based Assessment of Invasive Disease Due to Group B Streptococcus in Nonpregnant Adults

Abstract: Background Group B streptococci (Streptococcus agalactiae) are a major cause of meningitis and septicemia in neonates and pregnant women, but the importance of group B streptococcal disease in nonpregnant adults has not been clearly defined. Methods We conducted a prospective surveillance of the pathogens responsible for meningitis for a period of 24 months in 35 hospitals and a referral laboratory in metropolitan Atlanta. We reviewed the clinical and laboratory records of all the nonpregnant adults identified as having invasive group B streptococcal disease during this period. Results During 1989 and 1990 there were 424 patients with invasive group B streptococcal disease (annual incidence, 9.2 cases per 100,000 population). Of these patients, 46 percent were 1 month of age or younger, 6 percent were older than 1 month but younger than 18 years of age, and 48 percent were 18 or older. Men and nonpregnant women accounted for 68 percent (n = 140) of all cases among adults (annual incidence, 4.4 per 100,000...