Bordetella pertussis Infection or Vaccination Substantially Protects Mice against B. bronchiseptica Infection

Although B. bronchiseptica efficiently infects a wide range of mammalian hosts and efficiently spreads among them, it is rarely observed in humans. In contrast to the many other hosts of B. bronchiseptica, humans are host to the apparently specialized pathogen B. pertussis, the great majority having immunity due to vaccination, infection or both. Here we explore whether immunity to B. pertussis protects against B. bronchiseptica infection. In a murine model, either infection or vaccination with B. pertussis induced antibodies that recognized antigens of B. bronchiseptica and protected the lower respiratory tract of mice against three phylogenetically disparate strains of B. bronchiseptica that efficiently infect naïve animals. Furthermore, vaccination with purified B. pertussis-derived pertactin, filamentous hemagglutinin or the human acellular vaccine, Adacel, conferred similar protection against B. bronchiseptica challenge. These data indicate that individual immunity to B. pertussis affects B. bronchiseptica infection, and suggest that the high levels of herd immunity against B. pertussis in humans could explain the lack of observed B. bronchiseptica transmission. This could also explain the apparent association of B. bronchiseptica infections with an immunocompromised state.     

Structural basis for antibody binding to adenylate cyclase toxin reveals RTX linkers as neutralization-sensitive epitopes

RTX leukotoxins are a diverse family of prokaryotic virulence factors that are secreted by the type 1 secretion system (T1SS) and target leukocytes to subvert host defenses. T1SS substrates all contain a C-terminal RTX domain that mediates recruitment to the T1SS and drives secretion via a Brownian ratchet mechanism. Neutralizing antibodies against the Bordetella pertussis adenylate cyclase toxin, an RTX leukotoxin essential for B. pertussis colonization, have been shown to target the RTX domain and prevent binding to the α_Mβ₂ integrin receptor. Knowledge of the mechanisms by which antibodies bind and neutralize RTX leukotoxins is required to inform structure-based design of bacterial vaccines, however, no structural data are available for antibody binding to any T1SS substrate. Here, we determine the crystal structure of an engineered RTX domain fragment containing the α_Mβ₂-binding site bound to two neutralizing antibodies. Notably, the receptor-blocking antibodies bind to the linker regions of RTX blocks I–III, suggesting they are key neutralization-sensitive sites within the RTX domain and are likely involved in binding the α_Mβ₂ receptor. As the engineered RTX fragment contained these key epitopes, we assessed its immunogenicity in mice and showed that it elicits similar neutralizing antibody titers to the full RTX domain. The results from these studies will support the development of bacterial vaccines targeting RTX leukotoxins, as well as next-generation B. pertussis vaccines.     

Proteomics-Identified Bvg-Activated Autotransporters Protect against Bordetella pertussis in a Mouse Model

Pertussis is a highly infectious respiratory disease of humans caused by the bacterium Bordetella pertussis. Despite high vaccination coverage, pertussis has re-emerged globally. Causes for the re-emergence of pertussis include limited duration of protection conferred by acellular pertussis vaccines (aP) and pathogen adaptation. Pathogen adaptations involve antigenic divergence with vaccine strains, the emergence of strains which show enhanced in vitro expression of a number of virulence-associated genes and of strains that do not express pertactin, an important aP component. Clearly, the identification of more effective B. pertussis vaccine antigens is of utmost importance. To identify novel antigens, we used proteomics to identify B. pertussis proteins regulated by the master virulence regulatory system BvgAS in vitro. Five candidates proteins were selected and it was confirmed that they were also expressed in the lungs of naïve mice seven days after infection. The five proteins were expressed in recombinant form, adjuvanted with alum and used to immunize mice as stand-alone antigens. Subsequent respiratory challenge showed that immunization with the autotransporters Vag8 and SphB1 significantly reduced bacterial load in the lungs. Whilst these antigens induced strong opsonizing antibody responses, we found that none of the tested alum-adjuvanted vaccines - including a three-component aP - reduced bacterial load in the nasopharynx, suggesting that alternative immunological responses may be required for efficient bacterial clearance from the nasopharynx.     

Pertactin contributes to shedding and transmission of Bordetella bronchiseptica

Whooping cough is resurging in the United States despite high vaccine coverage. The rapid rise of Bordetella pertussis isolates lacking pertactin (PRN), a key vaccine antigen, has led to concerns about vaccine-driven evolution. Previous studies showed that pertactin can mediate binding to mammalian cells in vitro and act as an immunomodulatory factor in resisting neutrophil-mediated clearance. To further investigate the role of PRN in vivo, we examined the functions of pertactin in the context of a more naturally low dose inoculation experimental system using C3H/HeJ mice that is more sensitive to effects on colonization, growth and spread within the respiratory tract, as well as an experimental approach to measure shedding and transmission between hosts. A B. bronchiseptica pertactin deletion mutant was found to behave similarly to its wild-type (WT) parental strain in colonization of the nasal cavity, trachea, and lungs of mice. However, the pertactin-deficient strain was shed from the nares of mice in much lower numbers, resulting in a significantly lower rate of transmission between hosts. Histological examination of respiratory epithelia revealed that pertactin-deficient bacteria induced substantially less inflammation and mucus accumulation than the WT strain and in vitro assays verified the effect of PRN on the induction of TNF-α by murine macrophages. Interestingly, only WT B. bronchiseptica could be recovered from the spleen of infected mice and were further observed to be intracellular among isolated splenocytes, indicating that pertactin contributes to systemic dissemination involving intracellular survival. These results suggest that pertactin can mediate interactions with immune cells and augments inflammation that contributes to bacterial shedding and transmission between hosts. Understanding the relative contributions of various factors to inflammation, mucus production, shedding and transmission will guide novel strategies to interfere with the reemergence of pertussis.     

Immunisation With Immunodominant Linear B Cell Epitopes Vaccine of Manganese Transport Protein C Confers Protection against Staphylococcus aureus Infection

Vaccination strategies for Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA) infections have attracted much research attention. Recent efforts have been made to select manganese transport protein C, or manganese binding surface lipoprotein C (MntC), which is a metal ion associated with pathogen nutrition uptake, as potential candidates for an S. aureus vaccine. Although protective humoral immune responses to MntC are well-characterised, much less is known about detailed MntC-specific B cell epitope mapping and particularly epitope vaccines, which are less-time consuming and more convenient. In this study, we generated a recombinant protein rMntC which induced strong antibody response when used for immunisation with CFA/IFA adjuvant. On the basis of the results, linear B cell epitopes within MntC were finely mapped using a series of overlapping synthetic peptides. Further studies indicate that MntC113-136, MntC209-232, and MntC263-286 might be the original linear B-cell immune dominant epitope of MntC, furthermore, three-dimensional (3-d) crystal structure results indicate that the three immunodominant epitopes were displayed on the surface of the MntC antigen. On the basis of immunodominant MntC113-136, MntC209-232, and MntC263-286 peptides, the epitope vaccine for S. aureus induces a high antibody level which is biased to TH2 and provides effective immune protection and strong opsonophagocytic killing activity in vitro against MRSA infection. In summary, the study provides strong proof of the optimisation of MRSA B cell epitope vaccine designs and their use, which was based on the MntC antigen in the development of an MRSA vaccine.     

An ultrapotent pan-β-coronavirus lineage B (β-CoV-B) neutralizing antibody locks the receptor-binding domain in closed conformation by targeting its conserved epitope

New threats posed by the emerging circulating variants of SARS-CoV-2 highlight the need to find conserved neutralizing epitopes for therapeutic antibodies and efficient vaccine design. Here, we identified a receptor-binding domain (RBD)-binding antibody, XG014, which potently neutralizes β-coronavirus lineage B (β-CoV-B), including SARS-CoV-2, its circulating variants, SARS-CoV and bat SARSr-CoV WIV1. Interestingly, antibody family members competing with XG014 binding show reduced levels of cross-reactivity and induce antibody-dependent SARS-CoV-2 spike (S) protein-mediated cell-cell fusion, suggesting a unique mode of recognition by XG014. Structural analyses reveal that XG014 recognizes a conserved epitope outside the ACE2 binding site and completely locks RBD in the non-functional “down” conformation, while its family member XG005 directly competes with ACE2 binding and position the RBD “up”. Single administration of XG014 is effective in protection against and therapy of SARS-CoV-2 infection in vivo. Our findings suggest the potential to develop XG014 as pan-β-CoV-B therapeutics and the importance of the XG014 conserved antigenic epitope for designing broadly protective vaccines against β-CoV-B and newly emerging SARS-CoV-2 variants of concern.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13238-021-00871-6.     

Defining Immune Engagement Thresholds for In Vivo Control of Virus-Driven Lymphoproliferation

Persistent infections are subject to constant surveillance by CD8⁺ cytotoxic T cells (CTL). Their control should therefore depend on MHC class I-restricted epitope presentation. Many epitopes are described for γ-herpesviruses and form a basis for prospective immunotherapies and vaccines. However the quantitative requirements of in vivo immune control for epitope presentation and recognition remain poorly defined. We used Murid Herpesvirus-4 (MuHV-4) to determine for a latently expressed viral epitope how MHC class-I binding and CTL functional avidity impact on host colonization. Tracking MuHV-4 recombinants that differed only in epitope presentation, we found little latitude for sub-optimal MHC class I binding before immune control failed. By contrast, control remained effective across a wide range of T cell functional avidities. Thus, we could define critical engagement thresholds for the in vivo immune control of virus-driven B cell proliferation.     

Identification of neutralizing and nonneutralizing epitopes in the porcine reproductive and respiratory syndrome virus GP5 ectodomain

After infection of swine with porcine reproductive and respiratory syndrome virus (PRRSV), there is a rapid rise of PRRSV-specific nonneutralizing antibodies (NNA), while neutralizing antibodies (NA) are detectable not sooner than 3 weeks later. To characterize neutralizing epitopes, we selected phages from a 12-mer phage display library using anti-PRRSV neutralizing monoclonal antibody (MAb) ISU25-C1. In addition, phages carrying peptides recognized by swine antibodies with high seroneutralizing titer were isolated after subtracting from the library those clones binding to swine anti-PRRSV serum with no neutralizing activity. Two epitopes located in the ectodomain of PRRSV GP5 were identified. One of these epitopes, which we named epitope B, was recognized both by neutralizing MAb ISU25-C1 and swine neutralizing serum (NS) but not by swine nonneutralizing serum (NNS), indicating that it is a neutralizing epitope. Epitope B is sequential, conserved among isolates, and not immunodominant. Antibodies directed against it are detected in serum late after infection. In contrast, the other epitope, which we named epitope A, is hypervariable and immunodominant. Antibodies against it appear early after infection with PRRSV. This epitope is recognized by swine NNA but is not recognized by either neutralizing MAb ISU25-C1 or swine NA, indicating that it is not involved in PRRSV neutralization. During infection with PRRSV, epitope A may act as a decoy, eliciting most of the antibodies directed to GP5 and delaying the induction of NA against epitope B for at least 3 weeks. These results are relevant to the design of vaccines against PRRSV.     

Potent neutralization of botulinum neurotoxin/b by synergistic action of antibodies recognizing protein and ganglioside receptor binding domain

Background

Botulinum neurotoxins (BoNTs), the causative agents for life-threatening human disease botulism, have been recognized as biological warfare agents. Monoclonal antibody (mAb) therapeutics hold considerable promise as BoNT therapeutics, but the potencies of mAbs against BoNTs are usually less than that of polyclonal antibodies (or oligoclonal antibodies). The confirmation of key epitopes with development of effective mAb is urgently needed.

Methods and Findings

We selected 3 neutralizing mAbs which recognize different non-overlapping epitopes of BoNT/B from a panel of neutralizing antibodies against BoNT/B. By comparing the neutralizing effects among different combination groups, we found that 8E10, response to ganglioside receptor binding site, could synergy with 5G10 and 2F4, recognizing non-overlapping epitopes within Syt II binding sites. However, the combination of 5G10 with 2F4 blocking protein receptor binding sites did not achieve synergistical effects. Moreover, we found that the binding epitope of 8E10 was conserved among BoNT A, B, E, and F, which might cross-protect the challenge of different serotypes of BoNTs in vivo.

Conclusions

The combination of two mAbs recognizing different receptors'' binding domain in BoNTs has a synergistic effect. 8E10 is a potential universal partner for the synergistical combination with other mAb against protein receptor binding domain in BoNTs of other serotypes.     

An Epitope-Substituted DNA Vaccine Improves Safety and Immunogenicity against Dengue Virus Type 2

Dengue virus (DENV), a global disease, is divided into four serotypes (DENV1-4). Cross-reactive and non-neutralizing antibodies against envelope (E) protein of DENV bind to the Fcγ receptors (FcγR) of cells, and thereby exacerbate viral infection by heterologous serotypes via antibody-dependent enhancement (ADE). Identification and modification of enhancing epitopes may mitigate enhancement of DENV infection. In this study, we characterized the cross-reactive DB21-6 and DB39-2 monoclonal antibodies (mAbs) against domain I-II of DENV; these antibodies poorly neutralized and potently enhanced DENV infection both in vitro and in vivo. In addition, two enhancing mAbs, DB21-6 and DB39-2, were observed to compete with sera antibodies from patients infected with dengue. The epitopes of these enhancing mAbs were identified using phage display, structural prediction, and mapping of virus-like particle (VLP) mutants. N8, R9, V12, and E13 are the reactive residues of DB21-6, while N8, R9, and E13 are the reactive residues of DB39-2. N8 substitution tends to maintain VLP secretion, and decreases the binding activity of DB21-6 and DB39-2. The immunized sera from N8 substitution (N8R) DNA vaccine exerted greater neutralizing and protective activity than wild-type (WT)-immunized sera, both in vitro and in vivo. Furthermore, treatment with N8R-immunized sera reduced the enhancement of mortality in AG129 mice. These results support identification and substitution of enhancing epitope as a novel strategy for developing safe dengue vaccines.     

In silico Identification and Validation of a Linear and Naturally Immunogenic B-Cell Epitope of the Plasmodium vivax Malaria Vaccine Candidate Merozoite Surface Protein-9

Synthetic peptide vaccines provide the advantages of safety, stability and low cost. The success of this approach is highly dependent on efficient epitope identification and synthetic strategies for efficacious delivery. In malaria, the Merozoite Surface Protein-9 of Plasmodium vivax (PvMSP9) has been considered a vaccine candidate based on the evidence that specific antibodies were able to inhibit merozoite invasion and recombinant proteins were highly immunogenic in mice and humans. However the identities of linear B-cell epitopes within PvMSP9 as targets of functional antibodies remain undefined. We used several publicly-available algorithms for in silico analyses and prediction of relevant B cell epitopes within PMSP9. We show that the tandem repeat sequence EAAPENAEPVHENA (PvMSP9_E795-A808) present at the C-terminal region is a promising target for antibodies, given its high combined score to be a linear epitope and located in a putative intrinsically unstructured region of the native protein. To confirm the predictive value of the computational approach, plasma samples from 545 naturally exposed individuals were screened for IgG reactivity against the recombinant PvMSP9-RIRII_729-972 and a synthetic peptide representing the predicted B cell epitope PvMSP9_E795-A808. 316 individuals (58%) were responders to the full repetitive region PvMSP9-RIRII, of which 177 (56%) also presented total IgG reactivity against the synthetic peptide, confirming it validity as a B cell epitope. The reactivity indexes of anti-PvMSP9-RIRII and anti-PvMSP9_E795-A808 antibodies were correlated. Interestingly, a potential role in the acquisition of protective immunity was associated with the linear epitope, since the IgG1 subclass against PvMSP9_E795-A808 was the prevalent subclass and this directly correlated with time elapsed since the last malaria episode; however this was not observed in the antibody responses against the full PvMSP9-RIRII. In conclusion, our findings identified and experimentally confirmed the potential of PvMSP9_E795-A808 as an immunogenic linear B cell epitope within the P. vivax malaria vaccine candidate PvMSP9 and support its inclusion in future subunit vaccines.     

Diagnosis of Whooping Cough: Comparison of Serological Tests with Isolation of Bordetella Pertussis

Antibody titres for Bordetella pertussis in paired sera from 223 children with suspected whooping cough showed good correlation by complement fixation and agglutination techniques. The patient''s age was related to serological responses and in a different way to B. pertussis isolations: in 73 children under 6 months of age B. pertussis was isolated from nasopharyngeal secretions in 42% and serological findings were positive in 19%; in 11 patients over 1 year of age serological tests were positive in 65% and cultures in 19%.B. pertussis was isolated from 59 out of 210 patients, while rising antibody titres were found in a further 43 from whom no isolations were made; thus 102 (49%) out of 210 showed evidence of infection with B. pertussis. Serotype 1,3 was the commonest serotype isolated from both immunized and unimmunized children. Previous immunization appeared to reduce the chances of isolating B. pertussis.     

Pertactin antigens extracted from Bordetella pertussis and Bordetella bronchiseptica differ in the isoelectric point

Pertactin, which is a membrane-associated antigen of Bordetella pertussis and which is present in many acellular vaccines against whooping cough, has been reported to be similar to the homologous protein in Bordetella bronchiseptica. By running parallel experiments using proteins derived from the two species, we show that the isoelectric point of pertactin from B. pertussis is lower than reported and clearly distinguishable from the homologous protein of B. bronchiseptica. Received: 9 April 1997 / Accepted: 20 May 1997     

Equivalent T Cell Epitope Promiscuity in Ecologically Diverse Human Pathogens

Background

The HLA (human leukocyte antigen) molecules that present pathogen-derived epitopes to T cells are highly diverse. Correspondingly, many pathogens such as HIV evolve epitope variants in order to evade immune recognition. In contrast, another persistent human pathogen, Mycobacterium tuberculosis, has highly conserved epitope sequences. This raises the question whether there is also a difference in the ability of these pathogens’ epitopes to bind diverse HLA alleles, referred to as an epitope’s binding promiscuity. To address this question, we compared the in silico HLA binding promiscuity of T cell epitopes from pathogens with distinct infection strategies and outcomes of human exposure.

Methods

We used computer algorithms to predict the binding affinity of experimentally-verified microbial epitope peptides to diverse HLA-DR, HLA-A and HLA-B alleles. We then analyzed binding promiscuity of epitopes derived from HIV and M. tuberculosis. We also analyzed promiscuity of epitopes from Streptococcus pyogenes, which is known to exhibit epitope diversity, and epitopes of Bacillus anthracis and Clostridium tetani toxins, as these bacteria do not depend on human hosts for their survival or replication, and their toxin antigens are highly immunogenic human vaccines.

Results

We found that B. anthracis and C. tetani epitopes were the most promiscuous of the group that we analyzed. However, there was no consistent difference or trend in promiscuity in epitopes contained in HIV, M. tuberculosis, and S. pyogenes.

Conclusions

Our results show that human pathogens with distinct immune evasion strategies and epitope diversities exhibit equivalent levels of T cell epitope promiscuity. These results indicate that differences in epitope promiscuity do not account for the observed differences in epitope variation and conservation.     

Sequence and Structure Based Binding Prediction Study of HLA Class I and cTAP Binding Peptides for Japanese Encephalitis Vaccine Development

Japanese encephalitis is a major threat in developing countries, even the availability of several conventional vaccines, which demand development of more effective vaccines. The present study used propred I and Immune Epitope Database Artificial Neural Network (ANN) algorithm (IEDB-ANN) to identify the conserve and promiscuous T cell epitopes from JEV proteome followed by structure based analysis of potential epitopes. Among all identified 102 epitopes, ten epitope were promiscuous but two epitopes of glycoprotein viz. ⁵⁵LVTVNPFVA⁶³ and ³⁸IPIVSVASL⁴⁶ were found most promiscuous, highly conserved and high population coverage in comparison of known antigenic positive control peptides. The B cell epitopes of glycoprotein also share these two T cell epitopes revealed by BCPred algorithm which can be a basis to confer the protection by neutralizing antibody combined with an effective cell-mediated response. Further, Autodock 4.2 and NAMD–VMD molecular dynamics simulation were used for docking and molecular dynamics simulation respectively, to validate epitope and allele complex binding stability. The 3D structure models were generated for epitopes and corresponding HLA allele by Pepstr and Modeller 9.10 respectively. Epitope LVTVNPFVA–B5101 allele complex showed best energy minimization and stability over the time window during simulation. Here we also present the binding sequel of epitope LVTVNPFVA and its eventual transport through cTAP1 (PDB ID: 1JJ7) revealed by Autodock 4.2, which is an essential path for HLA class I binding epitopes to elicit immune response. The docking experiment of epitope LVTVNPFVA and cTAP1 very well show a 2 H-bond with a binding energy of ?1.88 kcal/mol and other binding state of epitope forming no H-bond with a binding energy of ?1.13 kcal/mol in the lower area of cTAP1 cavity. These results show a smooth pass through of the epitope across the channel of cTAP1. Overall, identified peptides have potential application in the design and development of short peptide based vaccines and diagnostic agents for Japanese encephalitis.     

T- and B-Cell-Mediated Protection Induced by Novel,Live Attenuated Pertussis Vaccine in Mice. Cross Protection against Parapertussis

Background

Despite the extensive use of efficacious vaccines, pertussis still ranks among the major causes of childhood mortality worldwide. Two types of pertussis vaccines are currently available, whole-cell, and the more recent acellular vaccines. Because of reduced reactogenicity and comparable efficacy acellular vaccines progressively replace whole-cell vaccines. However, both types require repeated administrations for optimal efficacy. We have recently developed a live attenuated vaccine candidate, named BPZE1, able to protect infant mice after a single nasal administration.

Methodology/Principal Findings

We determined the protective mechanism of BPZE1-mediated immunity by using passive transfer of T cells and antibodies from BPZE1-immunized mice to SCID mice. Clearance of Bordetella pertussis from the lungs was mediated by both BPZE1-induced antibodies and CD4⁺, but not by CD8⁺ T cells. The protective CD4⁺ T cells comprised IFN-γ-producing and IL-17-producing subsets, indicating that BPZE1 induces both Th1 and Th17 CD4⁺ T cells. In addition, and in contrast to acellular pertussis vaccines, BPZE1 also cross-protected against Bordetella parapertussis infection, but in this case only the transfer of CD4⁺ T cells conferred protection. Serum from BPZE1-immunized mice was not able to kill B. parapertussis and did not protect SCID mice against B. parapertussis infection.

Conclusions/Significance

The novel live attenuated pertussis vaccine BPZE1 protects in a pre-clinical mouse model against B. pertussis challenge by both BPZE1-induced antibodies and CD4⁺ T cell responses. It also protects against B. parapertussis infection. However, in this case protection is only T cell mediated.     

The landscape of antibody binding in SARS-CoV-2 infection

The search for potential antibody-based diagnostics, vaccines, and therapeutics for pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has focused almost exclusively on the spike (S) and nucleocapsid (N) proteins. Coronavirus membrane (M), ORF3a, and ORF8 proteins are humoral immunogens in other coronaviruses (CoVs) but remain largely uninvestigated for SARS-CoV-2. Here, we use ultradense peptide microarray mapping to show that SARS-CoV-2 infection induces robust antibody responses to epitopes throughout the SARS-CoV-2 proteome, particularly in M, in which 1 epitope achieved excellent diagnostic accuracy. We map 79 B cell epitopes throughout the SARS-CoV-2 proteome and demonstrate that antibodies that develop in response to SARS-CoV-2 infection bind homologous peptide sequences in the 6 other known human CoVs. We also confirm reactivity against 4 of our top-ranking epitopes by enzyme-linked immunosorbent assay (ELISA). Illness severity correlated with increased reactivity to 9 SARS-CoV-2 epitopes in S, M, N, and ORF3a in our population. Our results demonstrate previously unknown, highly reactive B cell epitopes throughout the full proteome of SARS-CoV-2 and other CoV proteins.

Profiling of antibody binding from naïve and COVID-19 convalescent human sera to the entire proteome of SARS-CoV-2 and other human, bat and pangolin coronaviruses identifies 79 B cell epitopes throughout the SARS-CoV-2 proteome, finding that the most sensitive and specific binding occurred in the membrane (M) protein, and revealing cross-reactivity patterns.     

Human thyroid peroxidase: mapping of autoantibodies,conformational epitopes to the enzyme surface

Abstract

The enzyme, thyroid peroxidase (TPO), is a dominant antigen in thyroid autoimmune diseases. Autoantibodies recognised two major dominant conformational epitopes termed A and B. The epitopes have been defined by mAbs, but the amino acid residues which constitute these determinants remain unknown. Using a model of TPO, built from the structure of myeloperoxidase (MPO), we have synthesised peptides corresponding to exposed loops and generated rabbit antibodies to the peptides.

Antisera to peptide sequence 599–617 (peptide 14) representing a highly protrusive loop on the TPO, showed the highest inhibition in 65 sera from patients positive with anti-TPO antibodies. The inhibition was by 15–80% (mean 41%), and no other antibody showed any inhibition. Binding of hFabs to the B determinant on TPO was inhibited by anti-peptide 14 antibodies more then 85%, but not Fabs to the A determinant. In conclusion, the peptide 14 defines a sequence taking part in building up the B major conformational epitope.

None of generated anti-peptide antibodies alone inhibited the binding of human Fabs to the A epitope, however a combination of four anti-peptide antibodies (P1, P12, P14 and P18) inhibits Fabs binding to the A determinant by more then 60% and autoantibodies binding from 65% to 94%. Combination of antibodies reacting with peptides outside the surface defined by those four anti-peptide antibodies did not give any inhibition of Fabs to TPO.

The inhibition of Fabs and auto Abs to TPO by this combination of anti-peptide Abs is the result of steric hindrance as none of these Abs individually inhibited auto Abs' or Fabs' binding to TPO.

The four peptides define an area on the enzyme surface where the A and B major conformational epitopes are localised.     

Immunological features and efficacy of a multi-epitope vaccine CTB-UE against H. pylori in BALB/c mice model

Epitope vaccine is a promising option for prophylactic and therapeutic vaccination against Helicobacter pylori infection. Urease is an essential virulence factor and colonization factor for H. pylori. In this study, we constructed a multi-epitope vaccine named CTB-UE with mucosal adjuvant cholera toxin B subunit (CTB) and tandem copies of Th and B cell epitopes from H. pylori urease A and B subunits. The immunogenicity, specificity, ability to induce neutralizing antibodies against H. pylori urease, and prophylactic and therapeutic efficacy of the CTB-UE vaccine were evaluated in BALB/c mice model after purification. The experimental results indicated that CTB-UE could induce comparatively high levels of specific antibodies against native H. pylori urease, UreA, UreB, or the selected B cell epitopes UreA_183–203 and UreB_327–334 involved with the active site of urease and showed an effectively inhibitory effect on the enzymatic activity of urease. Besides, oral prophylactic or therapeutic immunization with CTB-UE significantly decreased H. pylori colonization compared with oral immunization with rUreB or PBS, and the protection was correlated with antigen-specific CD4⁺ T cells and IgG, IgA, and mucosal sIgA antibody responses. This CTB-UE vaccine may be a promising vaccine candidate for the control of H. pylori infection.