Crystal Structure of an Anti-meningococcal Subtype P1.4 PorA Antibody Provides Basis for Peptide–Vaccine Design

In various western countries, subtype P1.4 of Neisseria meningitidis serogroup B causes the greatest incidence of meningococcal disease. To investigate the molecular recognition of this subtype, we crystallised a peptide (P1HVVVNNKVATH(P11)), corresponding to the subtype P1.4 epitope sequence of outer membrane protein PorA, in complex with a Fab fragment of the bactericidal antibody MN20B9.34 directed against this epitope. Structure determination at 1.95 A resolution revealed a unique complex of one P1.4 antigen peptide bound to two identical Fab fragments. One Fab recognises the putative epitope residues in a 2:2 type I beta-turn at residues P5NNKV(P8), whereas the other Fab binds the C-terminal residues of the peptide that we consider a crystallisation artefact. Interestingly, recognition of the P1.4 epitope peptide is mediated almost exclusively through the complementarity-determining regions of the heavy chain. We exploited the observed turn conformation for designing conformationally restricted cyclic peptides for use as a peptide vaccine. The conformational stability of the two peptide designs was assessed by molecular dynamics simulations. Unlike the linear peptide, both cyclic peptides, conjugated to tetanus toxoid as a carrier protein, elicited antibody responses in mice that recognised meningococci of subtype P1.7-2,4. Serum bactericidal assays showed that some, but not all, of the sera induced with the cyclic peptide conjugates could activate the complement system with titres that were very high compared to the titres induced by complete PorA protein in its native conformation administered in outer membrane vesicles.

Overexpression, refolding, and purification of the major immunodominant outer membrane porin OmpC from Salmonella typhi: characterization of refolded OmpC

The major immunodominant integral outer membrane protein C (OmpC) from Salmonella typhi Ty21a was overexpressed, without the signal peptide, in Escherichia coli. The protein aggregates as inclusion bodies (IBs) in the cytoplasm. OmpC from IBs was solubilized with 4 M urea and refolded. This involved rapid dilution of unfolded OmpC into a refolding buffer containing polyoxyethylene-9-lauryl ether (C(12)E(9)) and glycerol. The refolded OmpC (rfOmpC) was shown to be structurally similar to the native OmpC by SDS-PAGE, Western blotting, tryptic digestion, ultrafiltration, circular dichroism, and fluorescence spectroscopic techniques. Crystals of rfOmpC were obtained in preliminary crystallization trials. The rfOmpC also sets a stage for rational design by recombinant DNA technology for vaccine design and high resolution structure determination.

Multivalent liposome-based vaccines containing different serosubtypes of PorA protein induce cross-protective bactericidal immune responses against Neisseria meningitidis

Four serosubtypes (P1.7, 16, P1.7-2, 4, P1.19, 15 and P1.5-1, 10-4) of the PorA outer-membrane protein of Neisseria meningitidis were purified as recombinant proteins and incorporated into liposomes to investigate their immunogenicity. Each serosubtype induced high levels of bactericidal activity against the homologous strain. In addition, liposome preparations containing multiple serosubtypes induced high levels of bactericidal activity against each of the four strains. Significantly, antisera raised against monovalent and multivalent liposomes also showed cross-reactive bactericidal activity against heterologous strains. These data demonstrate that multivalent liposome vaccines, containing multiple PorA serosubtypes, have the potential to provide protection against a broad range of meningococcal strains.

Molecular basis of morphological changes in mitochondrial membrane accompanying induction of permeability transition, as revealed by immuno-electron microscopy

The mitochondrial inner membrane typically shows a condensed structure when examined by electron microscopy. However, this typical structure is known to disappear upon induction of the mitochondrial permeability transition (PT). This change in the appearance of the mitochondrial membrane structure that accompanies the induction of PT is thought to reflect changes in the permeability of inner mitochondrial membrane; however, its molecular basis has remained uncertain. In the present study, changes in membrane status were examined by immuno-electron microscopy using antibodies against the voltage-dependent anion channel (VDAC), beta-subunit of F1-ATPase (F1beta), and cytochrome c (cyt. c). In control mitochondria, antibody against VDAC was observed at the rim of the mitochondria, whereas antibodies against F1beta and cytochrome c bound these molecules inside of the mitochondria. However, in PT-induced mitochondria, all three antibodies were observed at the mitochondrial rim. These results strongly suggest that the inner mitochondrial membrane is shoved to the rim region of mitochondria upon induction of mitochondrial PT.

Effect of sequence variation in meningococcal PorA outer membrane protein on the effectiveness of a hexavalent PorA outer membrane vesicle vaccine in toddlers and school children

Though meningococcal conjugate vaccines are effective against serogroup C, there is currently no vaccine solution for serogroup B disease. PorA outer membrane protein (OMP) is a potential serogroup B vaccine candidate. A hexavalent PorA outer membrane vesicle (OMV) vaccine has been evaluated in phase I and II trials with promising results. However, considerable sequence variation occurs in the variable regions (VRs) encoding these serosubtypes. By using five wild type P1.19,15 variant strains we examined the serum bactericidal antibody (SBA) titres from sera collected from toddlers and school children pre- and post-vaccination. The numbers of subjects with SBA titres of <4, 4 and > or = 8 varied greatly between the different strains. This was also reflected when > or = 4-fold rises in SBA titres were examined. This finding in sera from toddlers and school children may have implications for PorA based vaccines.

Mass tag-assisted identification of naturally processed HLA class II-presented meningococcal peptides recognized by CD4+ T lymphocytes

The meningococcal class I outer membrane protein porin A plays an important role in the development of T cell-dependent protective immunity against meningococcal serogroup B infection and is therefore a major component of candidate meningococcal vaccines. T cell epitopes from porin A are poorly characterized because of weak in vitro memory T cell responses against purified Ag and strain variation. We applied a novel strategy to identify relevant naturally processed and MHC class II-presented porin A epitopes, based on stable isotope labeling of Ag. Human immature HLA-DR1-positive dendritic cells were used for optimal uptake and MHC class II processing of (14)N- and (15)N-labeled isoforms of the neisserial porin A serosubtype P1.5-2,10 in bacterial outer membrane vesicles. HLA-DR1 bound peptides, obtained after 48 h of Ag processing, contained typical spectral doublets in mass spectrometry that could easily be assigned to four porin A regions, expressed at diverging densities ( approximately 30-4000 copies/per cell). Epitopes from two of these regions are recognized by HLA-DR1-restricted CD4(+) T cell lines and are conserved among different serosubtypes of meningococcal porin A. This mass tag-assisted approach provides a useful methodology for rapid identification of MHC class II presented bacterial CD4(+) T cell epitopes relevant for vaccine development.

A C1q-binding 40kDa porin from Aeromonas salmonicida: Cloning, sequencing, role in serum susceptibility and fish immunoprotection

A 40 kDa C1q-binding outer membrane protein from Aeromonas salmonicida was identified by direct-binding assay with biotinylated C1q, a subcomponent of the complement classical pathway component C1. The 40 kDa porin structural gene from the A450 A. salmonicida typical strain (A+:O+) was cloned in Escherichia coli and sequenced. The amino acid sequence of the 40 kDa A. salmonicida porin, its ability to bind C1q in an antibody independent process, and its immunological cross-reaction with the A. hydrophila AH-3 porin II, allow us to determine the role of this protein in serum susceptibility. Furthermore, we obtained defined A. salmonicida 40 kDa porin insertion mutants in serum sensitive or resistant strains, and we complemented these mutants with a plasmid harboring only the 40 kDa porin gene from A. salmonicida A450 in order to define its role as an important surface molecule involved in serum susceptibility and C1q binding. Similar complementation was obtained using the A. hydrophila AH-3 porin II gene. The 40 kDa porin gene and/or protein was present in all the A. salmonicida typical or atypical strains tested. Furthermore, the A. hydrophila AH-3 porin II seems to be an important molecule for fish immunoprotection against either A. salmonicida or A. hydrophila strains.

[Expression and immunity reaction of a novel gene OmpL17 of the strong virulent L. interrogans serovar Lai in China]

This study was conducted to potentiate the expression of outer membrane protein OmpL17 of the strong virulent L. interrogans serovar Lai and investigate its immunogenicity in rabbits. The OmpL17 was cloned into prokaryotic expression vector pGEX-1lambdaT. The recombination expression plasmid pGEX-OmpL17 was transformed into E. Coli JM109. The GST fused protein GST-OmpL17 was expressed after induction by IPTG, then GST-tag was by thrombin and purified using Bulk GST purification Modules. SDS-PAGE and Western blotting analysis indicated that the molecular weight of GST-OmpL17 and OmpL17 was about 54 KDa and 28 KDa respectively. The outer membrane protein OmpL17 was subcutaneously injected into rabbits and high titre anti-OmpL17 antibody was obtained (1:4896) which could conjugate specifical with OmpL17. In conclusion, OmpL17 and specifical anti-OmpL17 antibody were obtained, which provided an experimental basis for researching pathogenic effect and immunity functions of OmpL17.

Protection against P. aeruginosa with an adenovirus vector containing an OprF epitope in the capsid

Pseudomonas aeruginosa is an important opportunistic pathogen that can cause chronic and often life-threatening infections of the respiratory tract, particularly in individuals with cystic fibrosis (CF). Because infections with P. aeruginosa remain the major cause of the high morbidity and mortality of CF, a vaccine against P. aeruginosa would be very useful for preventing this disorder. The outer membrane protein F (OprF) of P. aeruginosa is a promising vaccine candidate and various B cell epitopes within OprF have been identified. Given that adenovirus (Ad) vectors have strong immunogenic potential and can function as adjuvants for genetic vaccines, the present study evaluates the immunogenic and protective properties of a novel replication-deficient Ad vector in which the Ad hexon protein was modified to include a 14-amino acid epitope of P. aeruginosa OprF (Epi8) in loop 1 of the hypervariable region 5 of the hexon (AdZ.Epi8). Immunization of C57BL/6 mice with AdZ.Epi8 resulted in detectable serum anti-P. aeruginosa and anti-OprF humoral responses. These responses were haplotype dependent, with higher serum anti-OprF titers in CBA mice than in BALB/c or C57BL/6 mice. AdZ.Epi8 induced Epi8-specific IFN-gamma-positive CD4 and CD8 T cell responses and resulted in protection against a lethal pulmonary challenge with agar-encapsulated P. aeruginosa. Importantly, repeated administration of AdZ.Epi8 resulted in boosting of the anti-OprF humoral and anti-Epi8 cellular response, whereas no boosting effect was present in the response against the transgene beta-galactosidase. These observations suggest that Ad vectors expressing pathogen epitopes in their capsid will protect against an extracellular pathogen and will allow boosting of the epitope-specific humoral response with repeated administration, a strategy that should prove useful in developing Ad vectors as vaccines where humoral immunity will be protective.

[Construction and expression of the major outer membrane protein PI of Neisseria gonorrhoeae in Escherichia coli]

OBJECTIVE

To construct Neisseria gonorrhoeae major outer membrane protein PI gene recombinants for expression of the target protein in E. coli.

METHODS

Four clinic isolates of Neisseria gonorrhoeae were collected, and then the genome DNA of these strains was extracted. The gene encoding for PI of Neisseria gonorrhoeae was amplified by PCR, inserted into the cloning vector pBS-T; the recombinant plasmids pBS-T-PI-NG were constructed and sequence analysis was performed. Then PI gene fragments were inserted into expression vector pET30b to form pET30b-PI-NG recombinants. The PI protein expression was induced by adding IPTG in the inocula. The expressed proteins were analyzed by SDS-PAGE.

RESULTS

The pET30b-PI-NG expression recombinants for four clinic isolates of Neisseria gonorrhoeae were constructed successfully; three of the four expression recombinants were expressed successfully.

CONCLUSION

The expressed PI protein will be applied in the further research for PI antigenicity and immunological activity. This will be very helpful for the further construction of preventive vaccines directed against Neisseria gonorrhoeae infection.

Porin of Shigella dysenteriae enhances Toll-like receptors 2 and 6 of mouse peritoneal B-2 cells and induces the expression of immunoglobulin M, immunoglobulin G2a and immunoglobulin A

Porin of Shigella dysenteriae type 1 increased the mRNA levels for Toll-like receptors TLR2 and TLR6, by 1.8-fold and twofold, respectively, in peritoneal cavity B-2 cells from C57BL/6 mice, implicating that the co-expression of TLR2 and TLR6 occurs as a combinatorial repertoire in response to porin. Among the two key TLRs, TLR2 and TLR4, which are primarily responsible for recognizing the majority of bacterial products, TLR2 alone participates in porin recognition. TLR2 expression was increased on B-2 cells, whereas the expression of TLR4 remained unaffected. Besides TLRs, mRNA for myeloid differentiation factor 88 (MyD88), an effector molecule associated with the TLR-mediated response, was enhanced by twofold, suggesting its involvement in the activity of porin. The B-2 cells showed a 1.8-fold increase in mRNA expression of the signalling molecule, nuclear factor-kappa B (NF-kappaB), in the presence of porin. Porin treatment of B-2 cells selectively up-regulated the expression of the costimulatory molecule, CD86, by 4.4-fold. Porin induced the cell-surface expression of immunoglobulin (Ig)M, of IgG2a preferentially among the IgG subclasses, and of IgA, on B-2 cells. The porin-mediated inductions of IgG2a and IgA were augmented by interleukin-6 on B-2 cells, by 2.7- and 1.6-fold, respectively.

Voltage-dependent anion-selective channel 1 (VDAC1)—a mitochondrial protein, rediscovered as a novel enzyme in the plasma membrane

The eukaryotic porin or voltage-dependent anion-selective channel (VDAC1) is a pore-forming protein discovered twenty five years ago in the mitochondrial outer membrane. Its gene in eukaryotes is known, but its tertiary structure has never been solved. Structure predictions highlight the presence of several amphipathic beta-strands possibly organised in a beta-barrel. VDAC1 has recently been described as being a NADH:ferricyanide reductase in the plasma membrane. There it affects the regulation of cell growth and death. Physiological cell death (apoptosis) has become a major research focus of biomedical research. Regulation of the enzyme will have impacts on cancer and autoimmune diseases (insufficient apoptosis) as well as neurodegenerative diseases (excessive apoptosis). VDAC1 in the plasma membrane establishes a novel level of apoptosis regulation putatively via its redox activity.

Gene conversion: a mechanism for generation of heterogeneity in the tprK gene of Treponema pallidum during infection

The tprK gene sequence of Treponema pallidum subspecies pallidum (T. pallidum) is heterogeneous within and among isolates. Heterogeneity in the tprK open reading frame is localized in seven discrete variable (V) regions, and variability results from apparent base changes, insertions or deletions. The TprK V regions are the focus of anti-TprK antibodies arising during infection. To test our hypothesis that V region sequences change during infection and passage, we developed a clonal isolate from the Chicago strain of T. pallidum and confirmed V region diversification during passage of this isolate. We describe the sequence anatomy of the seven V regions of tprK and the identification of putative donor sites for new V region sequences, and we propose a model for generation of new V regions by segmental gene conversion. These findings suggest that antigenic variation of TprK occurs in T. pallidum and may be important in immune evasion and persistence.

Immunogenicity and bactericidal activity in mice of an outer membrane protein vesicle vaccine against Neisseria meningitidis serogroup A disease

Serogroup A Neisseria meningitidis organisms of the subgroup III have caused epidemics of meningitis in sub-Saharan Africa since their introduction into the continent in 1987. The population structure of these bacteria is basically clonal, and these meningococci are strikingly similar in their major outer membrane antigens PorA and PorB. Protein-based vaccines might be an alternative to prevent epidemics caused by these meningococci; thus, we developed an outer membrane vesicle (OMV) vaccine from a serogroup A meningococcal strain of subgroup III. The serogroup A OMV vaccine was highly immunogenic in mice and elicited significant bactericidal activity towards several other serogroup A meningococci of subgroup III. The IgG antibodies generated were in immunoblot shown to be mainly directed towards the PorA outer membrane protein. The results presented demonstrate the potential of an OMV vaccine as an optional strategy to protect against meningococcal disease caused by serogroup A in Africa.

Up-regulation of CD80-CD86 and IgA on mouse peritoneal B-1 cells by porin of Shigella dysenteriae is Toll-like receptors 2 and 6 dependent

Porin of Shigella dysenteriae type 1 increased the mRNA levels for Toll-like receptor (TLR) 2 and TLR6 by 1.5- and 2.9-fold respectively, of peritoneal cavity B-1a and B-1b cells, implicating that coexpression of TLR2 and TLR6 is essential as a combinatorial repertoire for recognition of porin by the B-1 cells. Among the two key TLRs, TLR2 and TLR4, which are primarily responsible for recognizing majority of the bacterial products, TLR2 and not TLR4, participates in porin recognition. TLR2 got increased on both the B-1 cell populations whereas the TLR4 expression remained unaffected. Besides TLRs, mRNA for MyD88, an effector molecule associated with TLR-mediated response was enhanced by 1.8-fold that suggests of its involvement in the activity of porin. Both of the B-1 cell populations expressed strongly the mRNA for NF-kappaB in the presence of porin, that was 2.4-fold more than untreated control, conforming to the earlier finding that coexpression of TLR2 and TLR6, resulted in robust NF-kappaB activation for signaling. Porin treatment of B-1 cell populations of C57BL/6 mice, and C3H/HeJ mice in particular, selectively up-regulated the expression of the costimulatory molecules. CD80 expression got enhanced on the B-1a cells whereas CD86 got solely expressed on B-1b cells. Porin-induced cell surface expression of IgM and IgA on B-1 cell populations from C57BL/6 mice. The IgA-generating capacity, hallmark of mucosal immune response, was confirmed with B-1 cells of C3H/HeJ, the lipopolysaccharide non-responder mouse, in response to the protein. The porin-mediated induction of IgA was augmented by interleukin-6 on B-1a and B-1b cells, by 2.4- and 2.6-fold, respectively. The IgA expressed on both B-1a and B-1b cell surfaces after 72 h of culture was found to bind to the 38 kDa monomer of porin confirming it to be anti-porin IgA antibody.

Human antibody responses to a Chlamydia-secreted protease factor

We have previously identified a chlamydia-secreted protein (designated chlamydial proteasome/protease-like activity factor, or CPAF) in the cytosol of chlamydia-infected cells. Although CPAF is known to degrade host transcription factors required for major histocompatibility complex antigen expression in cultured cells, it is not clear whether CPAF is produced and maintains similar functions in humans infected with chlamydial organisms. We now report that CPAF does not preexist in chlamydial organisms and that CPAF synthesis requires live organism replication in cultured cells. Mice inoculated with live, but not mice inoculated with dead, chlamydial organisms produced a strong antibody response to CPAF, correlating CPAF-specific antibody production with CPAF synthesis in animals. Sera from women diagnosed with Chlamydia trachomatis cervicitis displayed higher levels of antibodies to CPAF than to either chlamydial major outer membrane protein or heat shock protein 60, suggesting that CPAF is both produced and immunogenic during human chlamydial infection.

Immune response to the Chlamydia trachomatis outer membrane protein PorB

The antigenicity of the outer membrane protein PorB during exposure to Chlamydia trachomatis was evaluated in humans and its immunogenicity was tested in mice. Although natural human infection resulted in strong serological responses to the major outer membrane protein (OmpA), antibodies to PorB were low or absent. Analogous to the responses observed in humans, mice inoculated with EB or challenged with EB produced weak anti-PorB antibody responses. PorB immunization of mice previously exposed to EB elicited strong PorB antibody responses. These findings support the fact that OmpA antibodies dominate the humoral immune response during natural infections and demonstrate that immunization with PorB overcomes the lack of immune response to PorB elicited during natural infection.

Enhanced immunogenicity in the murine airway mucosa with an attenuated Salmonella live vaccine expressing OprF-OprI from Pseudomonas aeruginosa

We constructed an oral live vaccine based on the attenuated aroA mutant Salmonella enterica serovar Typhimurium strain SL3261 expressing outer membrane proteins F and I (OprF-OprI) from Pseudomonas aeruginosa and investigated it in a mouse model. Strains with in vivo inducible protein expression with the PpacC promoter showed good infection rates and immunogenicity but failed to engender detectable antibodies in the lung. However, a systemic booster vaccination following an oral primary immunization yielded high immunoglobulin A (IgA) and IgG antibody levels in both upper and lower airways superior to conventional systemic or mucosal booster vaccination alone. In addition, the proportion of IgG1 and IgG2a antibodies suggested that the systemic booster does not alter the more TH1-like type of response induced by the oral Salmonella primary vaccination. We conclude that an oral primary systemic booster vaccination strategy with an appropriate mucosal vector may be advantageous in diseases with the risk of P. aeruginosa airway infection, such as cystic fibrosis.

Relevance of serologic studies in inflammatory bowel disease

The serologic panel for inflammatory bowel disease (IBD) is rapidly expanding. Antineutrophil cytoplasmic antibodies (ANCA) and anti-Saccharomyces cerevisiae mannan antibodies (ASCA) have remained the most widely studied markers, but immune reactivity against a new group of bacterial antigens such as I2, OmpC (outer membrane porin C), and flagellin, has been described in Crohn's disease. Several clinical avenues have been explored, such as the usefulness of serologic markers as screening tools for IBD and in accelerating a diagnosis in patients with indeterminate colitis. Another area of interest is disease stratification. Emerging data suggest there is a diversity of qualitative and quantitative responses to environmental antigens that differs among groups of IBD patients and may be associated with different clinical behaviors. As a result, it may be possible to tailor therapy on the basis of serologic responses. Prospective studies are needed before translating this concept into clinical practice. Clustering of IBD patients into more homogeneous subgroups based on antibody responses may help to unravel the pathophysiology of subsets of IBD.

Serologic testing with ANCA, ASCA, and anti-OmpC in children and young adults with Crohn's disease and ulcerative colitis: diagnostic value and correlation with disease phenotype

OBJECTIVES

Serologic testing is increasingly being utilized to evaluate children with suspected inflammatory bowel disease (IBD). The aim of this paper was to evaluate the sensitivity and specificity of a currently available panel involving four antibodies: deoxyribonuclease (DNase)-sensitive perinuclear antineutrophil cytoplasmic antibody (DNase-sensitive pANCA), IgA and IgG antibodies to Saccharomyces cerevisiae (IgA and IgG ASCA), and antibody to Escherichia coli outer membrane porin (anti-OmpC). We also wished to determine whether antibody levels correlated with disease activity, and whether a specific antibody pattern correlated with location and outcome of disease in children.

METHODS

We studied sera from 81 children with Crohn's disease (CD), 54 with ulcerative colitis (UC), and 63 controls. Clinical data, disease activity, and disease diagnosis were gathered at the time of serum sampling, and charts were re-reviewed at time of the study to determine long-term outcome. Enzyme-linked immunosorbent assay was utilized to determine titers of antibodies to ASCA, DNase-sensitive pANCA, and anti-OmpC; the presence of perinuclear staining for ANCA was confirmed by immunofluorescence.

RESULTS

We identified ASCA antibodies in 44% of CD patients, 0% of UC patients, and 1 control patient. DNase-sensitive pANCA antibodies were found in 70% of patients with UC, 18% of CD patients (predominantly Crohn's colitis), and 3% of controls. Anti-OmpC as an isolated assay had low sensitivity for both CD (24%) and UC (11%), and displayed a 5% false-positive rate. However, anti-OmpC did identify a small number of IBD patients not detected by the other assays. If any one or more of the four antibodies was positive, the overall sensitivity of the four antibody panel was 65% for CD and 76% for UC, with a specificity of 94%. Patients who were ASCA-positive were more likely to have disease of the ileum or ileum and right colon than patients who were ASCA-negative (58%vs 18%, p < 0.001). Patients with ASCA-positive were also more likely to require ileocecal resection (36%vs 13%, p < 0.05).

CONCLUSIONS

A currently available commercial antibody panel has good sensitivity and excellent specificity for CD and UC. The ASCA antibodies, while highly specific for CD, identify predominantly the subset of children with disease of the ileum and ascending colon who may be at increased risk of surgery.

Outer membrane proteins of pathogenic spirochetes

Pathogenic spirochetes are the causative agents of several important diseases including syphilis, Lyme disease, leptospirosis, swine dysentery, periodontal disease and some forms of relapsing fever. Spirochetal bacteria possess two membranes and the proteins present in the outer membrane are at the site of interaction with host tissue and the immune system. This review describes the current knowledge in the field of spirochetal outer membrane protein (OMP) biology. What is known concerning biogenesis and structure of OMPs, with particular regard to the atypical signal peptide cleavage sites observed amongst the spirochetes, is discussed. We examine the functions that have been determined for several spirochetal OMPs including those that have been demonstrated to function as adhesins, porins or to have roles in complement resistance. A detailed description of the role of spirochetal OMPs in immunity, including those that stimulate protective immunity or that are involved in antigenic variation, is given. A final section is included which covers experimental considerations in spirochetal outer membrane biology. This section covers contentious issues concerning cellular localization of putative OMPs, including determination of surface exposure. A more detailed knowledge of spirochetal OMP biology will hopefully lead to the design of new vaccines and a better understanding of spirochetal pathogenesis.

Conformational epitope mapping of OmpC, a major cell surface antigen from Salmonella typhi

The outer membrane protein OmpC, a trimer made of 16 stranded beta-barrel monomers, is a major cell surface antigen from the human pathogen Salmonella typhi. The relative stability of the epitopes recognising a Salmonella specific MAb (referred as MPN5) and an Enterobacteria specific MAb (referred as P7D8) and the role of the trimeric organisation has been probed using gel electrophoresis and monoclonal antibodies. The assembly of the trimer and the stability of the beta-barrel are found to be important for epitope presentation. The Salmonella specific conformational epitope is found to be more stable than the Enterobacteria specific one. The important residues of the Salmonella specific (Asp 25 of loop 1, Asp 340 of loop 8, Lys 334 of loop 8, and Tyr 210 of loop 5) and the Enterobacteria specific (Asp 25 of loop 1, Tyr 210 of loop 5, and Lys 152 of loop 4) conformational epitope have been identified using monoclonal antibodies, chemical modification, and solid phase binding methods.

Identification of an I-Ed-restricted T-cell epitope of Escherichia coli outer membrane protein F

A predominant T-cell epitope of Escherichia coli outer membrane protein F (OmpF) that encompasses amino acids 295 to 314 was identified in H-2(d) mice. BALB/c-derived T-cell hybridomas generated against this region were CD3(+), CD4(+), CD8(-), and T-cell receptor alphabeta(+) and secreted TH-1-associated cytokines (interleukin-2 [IL-2] and gamma interferon), but not a TH-2-associated cytokine (IL-4), when restimulated with peptide 295-314. Class II(+) mouse lymphoma (A20) cells, but not class II(-) mouse mastocytoma (P815) cells, supported IL-2 secretion of hybridomas when substituted for syngeneic splenocytes as antigen-presenting cells (APCs). Antibodies specific for I-E(d) blocked IL-2 secretion by hybridomas, but I-A(d)-specific antiserum did not. When transfected L cells expressing I-A(d) (AalphaAbeta(d)), I-E(d) (EalphaEbeta(d)), or the hybrid molecule I-EalphaAbeta(d) were used as APCs, hybridomas recognized peptide only when presented by the I-E(d)-transfected cells. When peptide 295-314 truncated at either the C or the N terminus of the sequence was used, the minimal epitope was determined. Critical residues were determined by using alanine-substituted peptide analogues. T-cell hybridomas were only stimulated by peptides that encompassed amino acids 295 to 303 (9-mer), and the core sequence required a minimum of three additional amino acids at either the amino or the carboxy terminus to induce IL-2 secretion. Critical residues were determined to be phenylalanine at position 295, threonine at position 300, and tyrosines at positions 301 and 302. This study is the first to identify a minimal T-cell epitope and major histocompatibility complex restriction element of the OmpF protein and confirms previous observations that there is considerable degeneracy in the length of peptides that can bind I-E(d) and variability in the amino acid composition of the C and N termini of these peptides.

PorA-specific differences in antibody avidity after vaccination with a hexavalent Men B outer membrane vesicle vaccine in toddlers and school children

A clinical phase II trial with an experimental hexavalent outer membrane vesicle (OMV) vaccine (HexaMen) containing six different porin A (PorAs) was carried out in toddlers (2-3 years) and schoolchildren (7-8 years) in The Netherlands. HexaMen exists of two OMVs each containing three different PorA types. The serum bactericidal activity (SBA) after vaccination against the six PorAs was significantly different and was higher in toddlers than in schoolchildren. After vaccination the SBA against P1.5-2,10 was 4-6 times higher than against P1.7-2,4. The aim of this study was to test whether the differences in SBA could be explained by a difference in subtype-specific antibody avidity maturation. The avidity index (AI) of antibodies against three subtypes (PorA types P1.5-2,10; P1.12-1,13 and P1.7-2,4) was measured by ELISA and evaluated in relation to SBA. A significant avidity maturation for the 3 PorA subtypes was found. This maturation was most pronounced for P1.5-2,10 (mean AI = 72%), correlating with the highest SBA titres. Generally, the avidity titre correlated best with SBA. No differences in avidity indices against the three tested PorAs were found between toddlers and school children indicating that avidity maturation induced by this vaccine is not age-dependent.

High-level serum antibodies to bacterial antigens are associated with antibiotic-induced clinical remission in Crohn's disease: a pilot study

In Crohn's disease, antibiotics are used with variable efficacy, suggesting that some patients are more likely to respond. The aim of this study was to determine whether Crohn's patients with predominant serum antibody reactivity toward bacterial antigens OmpC and/or I2 were more likely to achieve remission with antibiotics. Patients with ileal or ileal with right-sided colonic Crohn's disease were studied in a double-blind trial of budesonide alone or budesonide plus metronidazole and ciprofloxacin. In the budesonide plus metronidazole and ciprofloxacin group, patients with OmpC/I2 predominant profiles had the highest remission rate, whereas the group with no antibody predominant profiles had the lowest rate. In the budesonide group, patients with the OmpC/I2 predominant profile had the lowest remission rate, and the no-antibody group rate was higher. Although not statistically significant, these results support further testing to determine whether predominant serum reactivity to certain bacterial antigens may be a marker for efficacious use of antibiotics.