Protection from group B streptococcal infection in neonatal mice by maternal immunization with recombinant Sip protein

The protective potential of antibodies directed against group B streptococcus (GBS) Sip surface protein was determined by using the mouse neonatal infection model. Rabbit Sip-specific antibodies administered passively to pregnant mice protected their pups against a GBS lethal challenge. In addition, active immunization with purified recombinant Sip protein of female CD-1 mice induced the production of specific antibodies that also confer protection to the newborn pups against GBS strains of serotypes Ia/c, Ib, II, III, and V. These data confirm that Sip-specific antibodies can cross the placenta and conferred protective immunity against GBS infections.     

Characterization of a novel leucine-rich repeat protein antigen from group B streptococci that elicits protective immunity

Group B streptococci (GBS) usually behave as commensal organisms that asymptomatically colonize the gastrointestinal and urogenital tracts of adults. However, GBS are also pathogens and the leading bacterial cause of life-threatening invasive disease in neonates. While the events leading to transmission and disease in neonates remain unclear, GBS carriage and level of colonization in the mother have been shown to be significant risk factors associated with invasive infection. Surface antigens represent ideal vaccine targets for eliciting antibodies that can act as opsonins and/or inhibit colonization and invasion. Using a genetic screen for exported proteins in GBS, we identified a gene, designated lrrG, that encodes a novel LPXTG anchored surface antigen containing leucine-rich repeat (LRR) motifs found in bacterial invasins and other members of the LRR protein family. Southern blotting showed that lrrG was present in all GBS strains tested, representing the nine serotypes, and revealed the presence of an lrrG homologue in Streptococcus pyogenes. Recombinant LrrG protein was shown in vitro to adhere to epithelial cells in a dose-dependent manner, suggesting that it may function as an adhesion factor in GBS. More importantly, immunization with recombinant LrrG elicited a strong immunoglobulin G response in CBA/ca mice and protected against lethal challenge with virulent GBS. The data presented in this report suggest that this conserved protein is a highly promising candidate antigen for use in a GBS vaccine.     

Isolation of a C (Ibc) protein from group B Streptococcus which elicits mouse protective antibody

The C (Ibc) proteins of group B Streptococcus (GBS) have been shown to induce mouse protective antibodies when present as immunogens on whole organisms. However, characterization of specific proteins responsible for inducing protection has not been reported. We have grown type Ic GBS in a dialysate of Todd Hewitt broth and analyzed the proteins extruded into the broth. Multiple proteins of varying size were visualized by SDS-PAGE. Ultrafiltration was used to separate the GBS components by molecular weight (MW) into 2 pools, those below 30,000 MW but above 10,000 MW (P10) and those above 30,000 MW (P30). The P10 contained 4 major proteins, including a 14,000 MW protein. Balb-c mice were immunized with the P10 fraction and the antisera used in mouse protection studies. This immune sera protected 100% of mice against challenge with type Ib GBS and protection was not altered by prior absorption of the sera with type Ia or Ib capsular polysaccharide. The P10 was fractionated by column chromatography and eluted proteins examined by SDS-PAGE and Western blot with the mouse protective antisera elicited to the P10. There was one major immunologically reactive protein at 14,000 MW which eluted in a partially purified form from the column. The 14,000 MW protein was reisolated from preparative SDS-PAGE gels and used to elicit antiserum in a rabbit. In mouse protection studies this rabbit antiserum protected mice against subsequent challenge with type Ib GBS (89% protection). Surface antigens were extracted from 125I-labelled type Ic GBS and immunoprecipitated with antiserum to the 14,000 MW protein. The 14,000 MW protein and multiple higher molecular weight proteins were immunologically cross-reactive suggesting the presence of shared epitopes. Thus the 14,000 MW protein from type Ic GBS that is antigenic and elicits mouse protective antibodies against the heterologous type Ib GBS fulfills the criteria for a C protein of GBS.     

Identification of group B streptococcal antigen with lectin-bound polystyrene particles.

The lectin of the tomato, Lycopersicon esculentum, or of the potato, Solanum tuberosum, can be passively coupled to amide-modified polystyrene spheres to be used as a detection reagent for the specific identification of group B streptococcal cultures grown in selective or nonselective Todd-Hewitt broth for 5 and 4 h, respectively. Agglutination occurred when the lectin reagents were allowed to react with either the cell suspension, clarified broth, or antigen extracts from group B streptococci grown in Todd-Hewitt broth. No agglutination occurred when these lectins were allowed to react with strains of serogroup A, C, D, F, or G streptococci. False-negative agglutination responses may occur with certain serotype of group B streptococci grown on Columbia sheep blood agar. A 20-min staining time permitted the specific labeling of fixed smears of group B streptococci with fluorescein-conjugated Lycopersicon lectin. The lectin from the solanaceous plant Datura stramonium did not agglutinate group B streptococci or other clinically significant streptococcal serogroups.     

Multivalent group A streptococcal vaccine elicits bactericidal antibodies against variant M subtypes

Group A streptococci cause a wide spectrum of clinical illness. One of several strategies for vaccine prevention of these infections is based on the type-specific M protein epitopes. A multivalent M protein-based vaccine containing type-specific determinants from 26 different M serotypes is now in clinical trials. Recent epidemiologic studies have shown that, within some serotypes, the amino-terminal M protein sequence may show natural variation, giving rise to subtypes. This raises the possibility that vaccine-induced antibodies against the parent type may not be as effective in promoting bactericidal killing of variant subtypes. In the present study we used rabbit antisera against the 26-valent M protein-based vaccine in bactericidal tests against M1, M3, and M5 streptococci, which were represented by multiple subtypes. We show that the vaccine antibodies effectively promoted in vitro bactericidal activity despite the fact that the M proteins contained naturally occurring variant sequences in the regions corresponding to the vaccine sequence. Our results show that the variant M proteins generally do not result in significant differences in opsonization promoted by rabbit antisera raised against the 26-valent vaccine, suggesting that a multivalent M protein vaccine may not permit variant subtypes of group A streptococci to escape in a highly immunized population.     

Characterization of PepB, a group B streptococcal oligopeptidase.

Group B streptococci were recently reported to possess a cell-associated collagenase. Although the enzyme hydrolyzed the synthetic collagen-like substrate N-(3-[2-furyl]acryloyl)-Leu-Gly-Pro-Ala, we found that neither the highly purified enzyme nor crude group B streptococcal cell lysate solubilized a film of reconstituted rat tail collagen, an activity regarded as obligatory for a true collagenase. We cloned and sequenced the gene for the enzyme (pepB). The deduced amino acid sequence showed 66.4% identity to the PepF oligopeptidase from Lactococcus lactis, a member of the M3 or thimet family of zinc metallopeptidases. The group B streptococcal enzyme also showed oligopeptidase activity and degraded a variety of small bioactive peptides, including bradykinin, neurotensin, and peptide fragments of substance P and adrenocorticotropin.     

B族链球菌表面蛋白LrrG的分段表达及其免疫原性和功能研究

目的研究LrrG蛋白不同片段的免疫原性及保护功能,为B族链球菌(GBS)蛋白疫苗及组分疫苗的研究奠定基础。方法采用生物信息学的方法预测LrrG蛋白的抗原表位,结合该蛋白的一级结构特征构建3个多肽片段(Gn、Gr、Gc)并重组表达;通过免疫动物及萃取组织液检测其免疫原性;体外调理吞噬试验检测各多肽片段的保护功能。结果成功构建和表达纯化了Gn、Gr、Gc多肽片段,且3个多肽片段均可在小鼠血清诱导产生较高水平的特异性IgG抗体,Gn免疫原性好于Gr、Gc。Gr、Gc 30μg剂量的免疫原性均好于其10μg和50μg剂量。除了Gr在肺、直肠组织产生的IgA抗体有较明显升高外,Gn、Gc对黏膜及血清IgA无明显刺激作用。体外调理吞噬试验表明3个多肽片段的抗体均具有促进吞噬细胞对GBS的吞噬功能。Gr、Gc的调理吞噬活性高于Gn,与B细胞表位预测结果相符。结论重组多肽片段均具有较强的免疫原性,在一定免疫剂量范围内,血清特异性IgG水平呈剂量依赖关系;皮下免疫对黏膜免疫影响不大;调理吞噬作用可能是LrrG蛋白具有保护作用的机制,3个多肽片段均具有潜在保护作用,支持将其作为GBS蛋白疫苗及组分疫苗的候选成分。     

Multiplex PCR assay for direct identification of group B streptococcal alpha-protein-like protein genes

We developed a group B streptococcus multiplex PCR assay which allows, by direct analysis of the amplicon size, determination of the surface protein antigen genes of alpha-C protein, epsilon protein, Rib, Alp2, Alp3, and Alp4. The multiplex PCR assay offers a rapid and simple method of subtyping Streptococcus agalactiae based on surface protein genes.     

Immuno-electronmicroscopic demonstration of alpha and beta components of group B streptococcal protein antigen c

Affinity purified and absorbed monospecific antibodies against the protein type antigen c components c alpha and c beta were used in immuno-electronmicroscopic studies. As demonstrated with protein A gold particles the c alpha specific antibodies reacted with the c alpha antigen, the c beta specific antibodies with the c beta antigen. The respective antigens were distributed over the whole surface of the bacterial cells, mainly at the outermost layer of the cell wall.     

Detection of group B streptococcal antigen in early-onset and late-onset group B streptococcal disease with the Wellcogen Strep B latex agglutination test.

The Wellcogen Strep B latex agglutination test (Wellcome Diagnostics, Dartford, England) was evaluated as a method of detecting group B streptococcal antigen in urine, cerebrospinal fluid, and serum from neonates with early-onset (less than or equal to 7 days of age) and late-onset group B streptococcal disease. Urine was the best source of antigen, which was detected in 100% of six neonates with early-onset group B streptococcal disease who had urine available in the first 12 h of illness and in 88% of 17 group B streptococcus-infected neonates with urine available in the first 48 h of illness. Antigen was not detected in any samples from patients without group B streptococcal disease except in the urine of one patient with Proteus mirabilis meningitis. The Wellcogen Strep B latex test of the lot tested compares favorably with a noncommercially available latex agglutination test.     

Tumor cell membrane-bound heat shock protein 70 elicits antitumor immunity

B cell hybridomas expressing class I and II MHC molecules and producing antibodies directed against hemagglutinin protein of Rinderpest virus and human Mucin-1 have been used as surrogate B cells to study T cell responses against the antigens. The observed CTL and lymphoproliferative response indicates that anti-idiotypic B cells termed Jerne cells stimulate both T helper and T cytotoxic cells by virtue of their ability to present recycled or regurgitated peptido-mimics of antigen to T helper cells through class II MHC and de novo synthesized peptido-mimics of antigens to CTLs. Thus, T cell memory response can be perpetuated by anti-idiotypic Jerne B cells and these findings lend support to the earlier proposed relay hypothesis for perpetuation of immunological memory (IM).     

The pspC gene of Streptococcus pneumoniae encodes a polymorphic protein, PspC, which elicits cross-reactive antibodies to PspA and provides immunity to pneumococcal bacteremia

PspC is one of three designations for a pneumococcal surface protein whose gene is present in approximately 75% of all Streptococcus pneumoniae strains. Under the name SpsA, the protein has been shown to bind secretory immunoglobulin A (S. Hammerschmidt, S. R. Talay, P. Brandtzaeg, and G. S. Chhatwal, Mol. Microbiol. 25:1113-1124, 1997). Under the name CbpA, the protein has been shown to interact with human epithelial and endothelial cells (C. Rosenow et al., Mol. Microbiol. 25:819-829, 1997). The gene is paralogous to the pspA gene in S. pneumoniae and was thus called pspC (A. Brooks-Walter, R. C. Tart, D. E. Briles, and S. K. Hollingshead, Abstracts of the 97th General Meeting of the American Society for Microbiology 1997). Sequence comparisons of five published and seven new alleles reveal that this gene has a mosaic structure, and modular domains have contributed to gene diversity during evolution. Two major clades exist: clade A alleles are larger and contain an extra module that is shared with many pspA alleles; clade B alleles are smaller and lack this pspA-like domain. All alleles have a proline-rich domain and a choline-binding repeat domain that show 0% divergence from similar domains in the PspA protein. Immunization of a rabbit with a recombinant clade B PspC molecule produced antiserum that cross-reacted with both PspC and PspA from 15 pneumococcal isolates. The cross-reactive antibodies afforded cross-protection in a mouse model system. Mice immunized with PspC were protected against challenge with a strain that expressed PspA but not PspC. The PspA- and PspC-cross-reactive antibodies were directed to the proline-rich domain present in both molecules.     

A lipid core peptide construct containing a conserved region determinant of the group A streptococcal M protein elicits heterologous opsonic antibodies

The study reported here investigated the immunogenicity and protective potential of a lipid core peptide (LCP) construct containing a conserved region determinant of M protein, defined as peptide J8. Parenteral immunization of mice with LCP-J8 led to the induction of high-titer serum immunoglobulin G J8-specific antibodies when the construct was coadministered with complete Freund's adjuvant (CFA) or administered alone. LCP-J8 in CFA had significantly enhanced immunogenicity compared with the monomeric peptide J8 given in CFA. Moreover, LCP-J8/CFA and LCP-J8 antisera opsonized four different group A streptococcal (GAS) strains, and the antisera did not cross-react with human heart tissue proteins. These data indicate the potential of an LCP-based M protein conserved region GAS vaccine in the induction of broadly protective immune responses in the absence of a conventional adjuvant.     

Molecular profiles of group B streptococcal surface protein antigen genes: relationship to molecular serotypes

The study of surface protein antigens of group B streptococci (GBS) is important for understanding of the pathogenesis and epidemiology of infection, and several of these antigens have been proposed as components of GBS conjugate vaccines. In a previous study, we developed a novel PCR-and-sequencing system for identification of GBS serotypes and serosubtypes based on the capsular polysaccharide synthesis (cps) gene cluster. In this study, we used published sequences to develop PCR assays for identification of genes encoding GBS surface proteins including C alpha (bca), C alpha-like proteins 2 and 3 (alp2 and alp3), Rib (rib), and C beta (bac). We showed that the prototype R reference strain, Prague 25/60, contained a novel alpha-like protein antigen gene (the proposed alp4), which presumably encodes an atypical, but antigenically similar, R-like protein. Initial evaluation of these gene-specific assays showed excellent specificity. By combining cps serotypes, serosubtypes, and surface protein gene profiles, we were able to divide 224 GBS isolates into 31 serovariants. GBS bac-positive strains could be further subtyped into 11 groups and 20 subgroups. Our results confirmed and extended reported associations between some cps serotypes and serosubtypes, on the one hand, and surface protein genes, on the other: serosubtypes III-1 and III-2 were associated with rib, serosubtype III-3 with alp2, serotype Ib with bca and bac, and serotype V with alp3. The associations between serotype Ia and bca, bca repetitive unit, and bca repetitive unit-like sequence-containing genes need to be studied further. These PCR-based methods will provide an alternative and objective tool for subtyping of GBS based on surface protein antigen genes.     

Guanine-plus-cytosine composition of five group B streptococcal serotypes.

The percent guanine-plus-cytosine content of deoxyribonucleic acid of each of the five serotypes of group B streptococci was determined by thermal denaturation. The range of guanine-plus-cytosine content was 35.1 to 36.9%, with a mean value of 35.9%. These values suggest a genetic homogeneity to the serotypes of the group B streptococci.