Epitope mapping

Plasmid DNA Prime/Protein Boost Vaccination against Campylobacter jejuni in Broilers: Impact of Vaccine Candidates on Immune Responses and Gut Microbiota

Campylobacter infections, traced to poultry products, are major bacterial foodborne zoonoses, and vaccination is a potential solution to reduce these infections. In a previous experimental trial using a plasmid DNA prime/recombinant protein boost vaccine regimen, two vaccine candidates (YP437 and YP9817) induced a partially protective immune response against Campylobacter in broilers, and an impact of the protein batch on vaccine efficacy was suspected. This new study was designed to evaluate different batches of the previously studied recombinant proteins (called YP437A, YP437P and YP9817P) and to enhance the immune responses and gut microbiota studies after a C. jejuni challenge. Throughout the 42-day trial in broilers, caecal Campylobacter load, specific antibodies in serum and bile, the relative expression of cytokines and β-defensins, and caecal microbiota were assessed. Despite there being no significant reduction in Campylobacter in the caecum of vaccinated groups, specific antibodies were detected in serum and bile, particularly for YP437A and YP9817P, whereas the production of cytokines and β-defensins was not significant. The immune responses differed according to the batch. A slight change in microbiota was demonstrated in response to vaccination against Campylobacter. The vaccine composition and/or regimen must be further optimised.

S. Typhi derived vaccines and a proposal for outer membrane vesicles (OMVs) as potential vaccine for typhoid fever

Typhoid fever is a serious systemic infection caused by Salmonella Typhi (S. Typhi), spread by the feco-oral route and closely associated with poor food hygiene and inadequate sanitation. Nearly 93% of S. Typhi strains have acquired antibiotic resistance against most antibiotics. Vaccination is the only promising way to prevent typhoid fever. This review covers the nature and composition of S. Typhi, pathogenecity and mode of infection, epidemiology, and nature of drug resistance. Several components (Vi-polysaccharides, O-antigens, flagellar antigens, full length OMPs, and short peptides from OMPs) of S. Typhi have been utilized for vaccine design for protection against typhoid fever. Vaccine delivery systems also contribute to efficacy of the vaccines. In this study, we propose to develop S. Typhi derived OMVs as vaccine for protection against typhoid fevers.

Epitope determination of immunogenic proteins of Neisseria gonorrhoeae

Neisseria gonorrhoeae is the causative organism of gonorrhoea, a sexually transmitted disease that globally accounts for an estimated 80 to 100 million new infections per year. Increasing resistances to all common antibiotics used for N. gonorrhoeae treatment pose the risk of an untreatable disease. Further knowledge of ways of infection and host immune response are needed to understand the pathogen-host interaction and to discover new treatment alternatives against this disease. Therefore, detailed information about immunogenic proteins and their properties like epitope sites could advance further research in this area. In this work, we investigated immunogenic proteins of N. gonorrhoeae for linear epitopes by microarrays. Dominant linear epitopes were identified for eleven of the nineteen investigated proteins with three polyclonal rabbit antibodies from different immunisations. Identified linear epitopes were further examined for non-specific binding with antibodies to Escherichia coli and the closely related pathogen Neisseria meningitidis. On top of that, amino acids crucial for the antibody epitope binding were detected by microarray based alanine scans.

Rapid identification of novel immunodominant proteins and characterization of a specific linear epitope of Campylobacter jejuni

Campylobacter jejuni remains one of the major gut pathogens of our time. Its zoonotic nature and wide-spread distribution in industrialized countries calls for a quick and reliable diagnostic tool. Antibody-based detection presents a suitable means to identify pathogenic bacteria. However, the knowledge about immunodominant targets is limited. Thus, an approach is presented, which allows for the rapid screening of numerous cDNA derived expression clones to identify novel antigens. The deeper understanding of immunodominant proteins assists in the design of diagnostic tools and furthers the insight into the bacterium's pathogenicity as well as revealing potential candidates for vaccination. We have successfully screened 1536 clones of an expression library to identify 22 proteins that have not been described as immunodominant before. After subcloning the corresponding 22 genes and expression of full-length proteins, we investigated the immunodominant character by microarrays and ELISA. Subsequently, seven proteins were selected for epitope mapping. For cj0669 and cj0920c linear epitopes were identified. For cj0669, specificity assays revealed a specific linear epitope site. Consequently, an eleven amino acid residue sequence TLIKELKRLGI was analyzed via alanine scan, which revealed the glycine residue to be significant for binding of the antibody. The innovative approach presented herein of generating cDNAs of prokaryotes in combination with a microarray platform rendering time-consuming purification steps obsolete has helped to illuminate novel immunodominant proteins of C.jejuni. The findings of a specific linear epitope pave the way for a plethora of future research and the potential use in diagnostic applications such as serological screenings. Moreover, the current approach is easily adaptable to other highly relevant bacteria making it a formidable tool for the future discovery of antigens and potential biomarkers. Consequently, it is desirable to simplify the identification of structural epitopes, as this would extend the spectrum of novel epitopes to be detected.

Catalytic domain of PDC-E2 contains epitopes recognized by antimitochondrial antibodies in primary biliary cirrhosis

AIM: To search for further immunodominant peptides of the pyruvate dehydrogenase complex E2-component (PDC-E2) recognized by antimitochondrial antibodies (AMA) in primary biliary cirrhosis (PBC).

METHODS: Sera from 95 patients with PBC were tested by enzyme-linked immunosorbent assay against 33 synthetic overlapping peptides (25 amino acids; aa) covering the entire length of the E2-subunit of PDC-E2. Furthermore, the inner lipoyl peptide 167-184 was used in an unlipoylated and a lipoylated form as well as coupled to ovalbumin. Sera from 11 AMA negative/ANA positive PBC patients, 63 patients with other liver disorders and 22 healthy blood donors served as controls.

RESULTS: Of the 95 PBC-sera, 74% reacted with the peptide 475-499 and 58% with the peptide 407-431 located within the catalytic domain of PDC-E2. Patients with other disorders or healthy controls were positive in only up to 18%. Antibodies to the unlipoylated and lipoylated peptide 167-184 within the inner lipoyl domain were found in only 5% and 11% of the PBC sera, respectively; using ovalbumin-coupled peptides, the incidence increased up to 57% (unlipoylated form).

CONCLUSION: Peptides within the catalytic site of PDC-E2 rather than the previously reported lipoyl binding peptide 167-184 may represent major immunodominant epitopes recognized by AMA in PBC.

Identification of discontinuous antigenic determinants on proteins based on shape complementarities

Diverse procedures for identifying antigenic determinants on proteins have been developed, including experimental as well as computational approaches. However, most of these techniques focus on continuous epitopes, whereas fast and reliable identification and verification of discontinuous epitopes remains barely amenable. In this paper, we describe a computational workflow for the detection of discontinuous epitopes on proteins. The workflow uses a given protein 3D structure as input, and combines a per residue solvent accessibility constraint with epitope to paratope shape complementarity measures and binding energies for assigning antigenic determinants in the conformational context. We have developed the procedure on a given set of 26 antigen-antibody complexes with a known structure, and have further expanded the available paratope shapes by generating a virtual paratope library in order to improve the screening for candidate residues constituting discontinuous epitopes. Applying the workflow on the 26 given antigens with known discontinuous epitopes resulted in the correct identification of the spatial proximity of 12 antigen-antibody interaction sites. Combining solvent accessibility, shape complementarity and binding energies towards the identification of discontinuous epitopes clearly outperforms approaches solely considering accessibility and residue distance constraints.

Investigation of the functional characteristics of antibodies to therapeutic anti-human tumor necrosis factor alpha monoclonal antibody

Humanized antibody-based treatment modalities represent an active area of investigation. Included in these strategies are passive administrations of monoclonal antibodies, which recognize tumor necrosis factor alpha (TNF-alpha). However, several problems associated with these types of treatment strategies have been reported in the literature. We attempted to address the issue related to unresponsiveness to infliximab that might be induced by anti-idiotype response to the passively administered humanized monoclonal antibody. The characteristics and functional importance of antibodies to infliximab (ATI) were investigated in human sera. We studied the binding characteristics of ATI to infliximab, TNF-alpha Receptor-I (RI, p55) and Receptor-II (RII, p75). In addition, cytotoxicity effect on L929 cells and blocking effects on the binding of TNF-alpha with infliximab and etanercept were also analyzed. On the basis of the results obtained from the experiments, it seems that the target epitope for ATI is related with somewhere else not residing in the region capable of generating "mirror image". The results presented indicate that ATI does not mimic the functional characteristics of TNF-alpha. However, ATI inhibited the binding properties of infliximab to TNF-alpha.

CED: a conformational epitope database

Background

Antigen epitopes provide valuable information useful for disease prevention, diagnosis, and treatment. Recently, more and more databases focusing on different types of epitopes have become available. Conformational epitopes are an important form of epitope formed by residues that are sequentially discontinuous but close together in three-dimensional space. These epitopes have implicit structural information, making them attractive for both theoretical and applied biomedical research. However, most existing databases focus on linear rather than conformational epitopes.

Description

We describe CED, a special database of well defined conformational epitopes. CED provides a collection of conformational epitopes and related information including the residue make up and location of the epitope, the immunological property of the epitope, the source antigen and corresponding antibody of the epitope. All entries in this database are manually curated from articles published in peer review journals. The database can be browsed or searched through a user-friendly web interface. Most epitopes in CED can also be viewed interactively in the context of their 3D structures. In addition, the entries are also hyperlinked to various databases such as Swiss-Prot, PDB, KEGG and PubMed, providing wide background information.

Conclusion

A conformational epitope database called CED has been developed as an information resource for investigators involved in both theoretical and applied immunology research. It complements other existing specialised epitope databases. The database is freely available at

Identification of the immunogenic domains in HBsAg preS1 region using overlapping preS1 fragment fusion proteins

AIM: The incorporation of hepatitis B virus (HBV) preS1 region into epitope-based vaccines against HBV has been accepted widely, but the incorporate site and size of preS1 sequence is controversial. Therefore our purpose was to further investigate its immunogenic domains for the epitope-based hepatitis B vaccine design.

METHODS: Eight GST fusion proteins containing overlapping preS1 fragments in preS1 (21-119) region were expressed in E.coli. Using these purified fusion proteins, the immunogenic domains in preS1 region were identified in detail in mice and humans by Western blot analysis and ELISA.

RESULTS: The results in mice showed that the immu-nogenic domains mainly existed in preS1 (21-59) and preS1 (95-109). Similarly, these fragments had strong immunogenicity in humans; whereas the other parts except for preS1 (60-70) also had some immunogenicity. More importantly, a major immunogenic domain, preS1 (34-59), which has much stronger immunogenicity, was identified. Additionally, the antibodies against some preS1 fragments, especially preS1 (34-59), were speculated to be virus-neutralizing.

CONCLUSION: Eight GST fusion proteins containing overlapping preS1 fragments were prepared successfully. They were used for the study on the immunogenic dom-ains in preS1 (21-119) region. The preS1 (34-59) fragm-ents were the major immunogenic domains in the preS1 region, and the antibodies against these fragments were speculated to be virus-neutralizing. Therefore, the incorporation of preS1 (34-59) fragments into epitope-based HBV vaccines may be efficient for enhancement of immune response. Additionally, the results also imply that there are more complex immune responses to preS1 region and more abundant immunogenic domains in humans.

The comparison of antibody response to different hepatitis b vaccines with and without pre-S2 antigen in children with cancer

Children with cancer are at an increased risk of hepatitis B infection and chronic liver disease. Since hepatitis B vaccines containing pre-S2 antigen has been recently reported as being more efficient in providing immunization in healthy individuals, the authors compared antibody response to pre-S2-containing vaccine with no-pre-S2-containing hepatitis B vaccine, when given in double doses to 100 children receiving chemotherapy. Patients, aged 1 to 16 years with negative HBV serology, were vaccinated with 2 different types of HBV vaccines between 1997 and 1999. Group 1 received Gen Hevac B containing pre-S2 (n = 41) in a dose of 20 microg for patients younger than 10 years old and 40 microg for older patients. Group 2 was vaccinated at the same dose with hepatitis B vaccines not containing pre-S2 antigen. All vaccinations were repeated at 0, 1, and 6 months. Serum samples were drawn for determination of anti-HBs titers at 1, 3, 6, and 8 months. After the third dose of vaccine, the seroconversion rate was 72% in group 1 and 62% in group 2. The anti-HBs levels were higher in the group receiving pre-S2-containing hepatitis B vaccine. However, the difference between groups was not statistically significant (p > .05). The administration of pre-S2-containing hepatitis B vaccines may give a better seroconversion and higher antibody response to vaccination in children with cancer. But a further large-scale study is needed to confirm this finding.

Localization of a T-cell epitope of superantigen toxic shock syndrome toxin 1 to residues 125 to 158

Toxic shock syndrome toxin 1 (TSST-1) is a member of the staphylococcal enterotoxin superantigen family. So far, little is known about T-cell epitopes on superantigens. In this study, we developed an improved method for localizing T-cell epitopes on superantigens that involved synthetic peptides plus costimulation by CD28 or phorbol myristate acetate. Using this method, we localized a T-cell epitope to a 34-residue region, TSST-1 (residues 125 to 158), which possessed only two of four TSST-1-targeted beta-chain variable element (Vbeta) specificities of T-cell receptors in humans and mice, human Vbeta2 and murine Vbeta15.

A neutralizing epitope of human papillomavirus type 11 is principally described by a continuous set of residues which overlap a distinct linear, surface-exposed epitope

A panel of monoclonal antibodies (MAbs) which neutralize human papillomavirus type 11 (HPV11) in the athymic mouse xenograph neutralization assay and bind HPV11 virus-like particles (VLPs) has been described. We recently presented evidence that the Gly131-Tyr132 residues of the major capsid protein L1 confer type 11-specific binding. However, residues distally located on the primary L1 sequence also were shown to affect binding. This poses the question whether the epitope is principally centered in the region of Gly131-Tyr132 or, alternatively, is comprised of diversely located residues which come into proximity only upon proper assembly. We analyzed the result of numerous substitutions located between Tyr123 and Val142 of the HPV11 L1 sequence. We show that substitutions at five positions result in loss of binding for one or more of these MAbs by an enzyme-linked immunosorbent assay which measures antibody binding to VLPs. We demonstrate that binding of these MAbs is redirected to HPV16 VLPs which harbor eight type 11-like substitutions within the homologous region. Three of these substitutions did not affect binding when individually substituted in HPV11 but yet were still required to transfer binding to substituted HPV16 VLPs. The results demonstrate that the epitope for this class of neutralizing MAbs, although conformational and requiring VLP assembly for presentation, principally lies along a 20-residue stretch of the L1 major capsid protein. This targets the region for evaluation of the possibility of receptor binding and suggests possibilities for the design of peptide inhibitors of virus infectivity.

Immunochemical approach to the mapping of an assembled epitope of human chorionic gonadotropin: proximity of CTP-alpha to the receptor binding region of the beta-subunit

A single-step solid-phase RIA (SS-SPRIA) developed in our laboratory using hybridoma culture supernatants has been utilised for the quantitation of epitope-paratope interactions. Using SS-SPRIA as a quantitative tool for the assessment of epitope stability, it was found that several assembled epitopes of human chorionic gonadotropin (hCG) are differentially stable to proteolysis and chemical modification. Based on these observations an approach has been developed for identifying the amino acid residues constituting an epitopic region. This approach has now been used to map an assembled epitope at/near the receptor binding region of the hormone. The mapped site forms a part of the seat belt region and the cystine knot region (C34-C38-C88-C90-H106). The carboxy terminal region of the alpha-subunit forms a part of the epitope indicating its proximity to the receptor binding region. These results are in agreement with the reported receptor binding region identified through other approaches and the X-ray crystal structure of hCG.

Identification of novel factor VIII inhibitor epitopes using synthetic peptide arrays

OBJECTIVES

Mapping the antibody-binding sites on the factor VIII (FVIII) protein opens the prospect of studying the development of FVIII inhibitors and the alteration of inhibitor specificities over time. This paper describes a novel approach to the mapping of FVIII antibody-binding sites.

METHODS

Immobilized synthetic peptide arrays covering 80% of the complete 2351 amino acid sequence of factor VIII (FVIII) were used to determine epitope specificity of 6 alloantibodies and 3 autoantibodies inhibitory to FVIII activity. This detailed assessment was carried out using a modified enzyme-linked immunosorbent assay with plasma from normal persons or hemophilia A patients without inhibitors as negative controls.

RESULTS

Antibody-combining sites could be differentiated in both a qualitative and quantitative manner and were patient-specific. Highly reactive peptides were restricted to specific sites in the A1-A3 and C1-C2 domains and were not proximal to known proteolytic cleavage sites. Free peptides incubated in vitro with the plasmas of 3 patients significantly reduced residual inhibitor titers in a dose-dependent manner.

CONCLUSION

This technique permits the study of the development and specificity of FVIII inhibitors, can detect and differentiate between inhibitory and noninhibitory antibodies using immobilized or free peptides respectively, permits correlation of antibody-combining sites with inhibition of FVIII activity and provides a basis for the development of inhibitor adsorption or neutralization technology.

Comparison of two different methods using overlapping synthetic peptides for localizing linear B cell epitopes in the U1 snRNP-C autoantigen

We have compared the performances of two different approaches using overlapping synthetic peptides to identify the location of linear epitopes of the U1 snRNP-C autoantigen. The first method was based on the use of 15 overlapping peptides (16-30 residue-long) synthesized using conventional Fmoc chemistry, removed from the resin by a standard cleavage procedure, and tested by ELISA after direct coating to polyvinyl microtiter plates. The second approach used a commercial kit (SPOT) to synthesize 75 overlapping decapeptides on cellulose membrane which were assayed by a direct immunoenzymatic test. Both standard and SPOTscan methods were evaluated with antibodies raised in rabbits against synthetic peptides of U1C and sera from patients with autoimmune diseases. In addition to inherent problems linked to the SPOT synthesis (in particular the impossibility of checking the quality of peptides), a number of limitations in the SPOTscan method were identified (e.g. a certain lack of sensitivity and, in one case, the complete lack of peptide reactivity due to the removal of charged end groups at both extremities). However, we found no background with sera from autoimmune patients in the SPOTscan and the antigenic maps obtained using the two approaches generally agreed. This study shows that the SPOTscan approach represents a simple, relatively non expensive and rapid method for initial screening to identify candidate sequences that may be dominant linear epitopes in a protein. Subsequent analysis and controls should include the preparation of conventionally synthesized peptides for formal immunochemical investigations.

Analysis of 15 adenovirus hexon proteins reveals the location and structure of seven hypervariable regions containing serotype-specific residues

The first full-length hexon protein DNA and deduced amino acid sequences of a subgenus D adenovirus (AV) were determined from candidate AV48 (85-0844). Comprehensive comparison of this sequence with hexon protein sequences from human subgenera A, B, C, D, F, bovine AV3, and mouse AV1 revealed seven discrete hypervariable regions (HVRs) among the 250 variable residues in loops 1 and 2. These regions differed in length between serotypes, from 2 to 38 residues, and contained > 00% of hexon serotype-specific residues among human serotypes. Alignment with the published crystal structure of AV2 established the location and structure of the type-specific regions. Five HVRs were shown to be part of linear loops on the exposed surfaces of the protein, analogous to the serotype-specific loops or "puffs" in picornavirus capsid proteins. The HVRs were supported by a common framework of conserved residues, of which 68 to 75% were hydrophobic. Unique sequences were limited to the seven HVRs, so that one or more of these regions contain the type-specific neutralization epitopes. A neutralizing AV48 hexon-specific antiserum recognized linear peptides that corresponded to six HVRs by enzyme immunoassay. Affinity-purification removal of all peptide-reactive antibodies did not significantly decrease the neutralization titer. Eluted peptide-reactive antibodies did not neutralize. Human antisera that neutralized AV48 did not recognize linear peptides. Purified trimeric native hexon inhibited neutralization, but monomeric heat-denatured hexon did not. We conclude that the AV48 neutralization epitope(s) is complex and conformational.

Helper and cytotoxic T cell responses of HIV type 1-infected individuals to synthetic peptides of HIV type 1 Rev

In cell-mediated immunity T cells recognize peptide fragments of the antigenic protein in association with major histocompatibility complex (MHC) proteins. Synthetic 9- to 16-mer peptides have been widely used to identify the region(s) of a protein that act as T cell epitope. Here, we report antigenic peptides identified on HIV-1 regulatory protein Rev. Four synthetic peptides (amino acids 9-23, 25-39, 33-48, and 41-56) were first shown to stimulate T helper (Th) cell proliferation in peripheral blood lymphocytes (PBLs) derived from HIV-seropositive (HIV+) individuals. The same peptides induced cytotoxic T lymphocyte (CTL) activities toward the autologous target cells incubated with the peptides. Both responses were specific to the HIV infection as HIV-seronegative (HIV-) control individuals showed no significant proliferative or cytotoxic activity. The proliferating cells were CD4+ T cells, and CTL activity was mediated by CD8+ human leukocyte antigen (HLA)-restricted T cells. The identification of peptides containing epitopes that can induce both Th and CTL responses to regulatory proteins of HIV-1 in infected individuals might be important for vaccine development against AIDS. Since early regulatory proteins of HIV are expressed by the infected cells before the initiation of the synthesis of structural proteins, a CTL response against these proteins could destroy the infected cells before the release of infectious virions.

Identification of linear antigenic sites on the Porphyromonas gingivalis 43-kDa fimbrillin subunit

The fimbrillin of Porphyromonas gingivalis is thought to be an important virulence factor that mediates adherence to host surfaces. The linear immunogenic and antigenic structure of P. gingivalis fimbrillin was investigated with synthetic peptides corresponding to the amino acid sequence predicted from the cloned fimbrillin gene for P. gingivalis 2561. A series of continuous and overlapping peptides corresponding to the entire sequence of P. gingivalis fimbrillin was used to immunize Wistar rats. The resulting polyclonal antibodies were used to test the antigenicity of the 43-kDa fimbrillin protein by enzyme-linked immunosorbent assay and Western blot analysis. All the peptides elicited specific antibodies directed to the corresponding peptides but differed in their ability to elicit antisera that cross-reacted with either native or denatured fimbrillin. Antisera to various C-terminal one-third peptides were more reactive to the denatured monomeric form of fimbrillin by Western blot analysis. Antisera to peptide 99-110 was by far the most reactive against the native form of the oligomeric fimbrillin as well as the partially denatured oligomeric form of fimbrillin. The results indicate that amino acid residues 99-110 on the native fimbrillin protein are accessible to antibody binding and that the immunogen 99-110, when conjugated to thyroglobulin, is able to mimic an epitope on the 43-kDa fimbrillin.

Identification of Schistosoma mansoni antigens recognized by spleen cells of C57B1/6 mice immunized with ultraviolet-irradiated cercariae

Spleen cells of C57B1/6 mice immunized twice with Schistosoma mansoni cercariae attenuated by ultraviolet irradiation proliferated and produced interleukin-(II)-2 and/or II-4 in response to both soluble schistosomular and adult worm antigens of 72-68, 60-62, 50, 45, 29.5 and 28 kDa. All of these bands, except the 45 kDa, were also recognized by serum antibodies in Western blotting.

Identification and diagnostic value of a major antibody epitope on the 12 kDa antigen from Echinococcus granulosus (hydatid disease) cyst fluid

An IgG1 monoclonal antibody (MoAb), designated C9E7H8, has been produced against an epitope on the 12 kDa antigen of Echinococcus granulosus cyst fluid, believed to represent the smallest subunit of antigen B. This MoAb, raised against purified 12 kDa antigen eluted from a reducing SDS-PAGE gel, demonstrated strong binding to native sheep cyst fluid in ELISA and recognition of all three subunits of antigen B (at 12, 16, 23 kDa) by immunoblot under both reducing and non-reducing conditions. Immunoblot analysis also indicated that the complementary epitope is conserved amongst cyst fluids from different intermediate hosts of E. granulosus, including fluids from cysts of two distinct strains, and is present in cyst fluid from E. multilocularis. The monoclonal displays binding to a cDNA clone, EgPS-3, which we have previously shown expresses part of the 12 kDa molecule. EgPS-3, expressed as a glutathione-S-transferase fusion protein, was successful in positive detection of 74% of cystic hydatid patients, although cross-reactions were observed with 25% of sera from alveolar hydatid and 22% of sera from schistosomiasis japonica patients. Three peptides, based on the predicted amino acid sequence of EgPS-3, showed increased specificity but slightly reduced sensitivity in the detection of antibody from E. granulosus patients. The predominant epitope recognized by human antibody occurs in the N-terminal 27 amino acids (peptide 65) of EgPS-3 which also correlates with the location of the monoclonal antibody epitope.

Analysis of a human monoclonal antibody reactive with multiple Plasmodium falciparum antigen repeat sequences using a solid phase affinity assay

A solid-phase affinity assay was set up for the determination of the affinity of the interaction between the human monoclonal antibody (mAb) 33G2 and peptides corresponding to repeated sequences in three blood stage antigens of the malaria parasite Plasmodium falciparum. The epitope of this mAb is of interest due to the parasite blocking capacity of the mAb. Previous studies with PEPSCAN have defined the minimal epitope for the mAb as the pentapeptide VTEEI, a sequence frequently found in antigen Pf332. In the previous study, epitopes responsible for the cross-reactivity of the mAb with antigens Pf155/RESA and Pf11.1 were also identified. In the affinity assay described herein, the mAb was coated on a solid phase and binding of a labelled peptide was displaced by homologous or heterologous peptides. The affinity of peptides corresponding to Pf332 increased with increasing length, and the highest affinity was displayed by a dimer (23 amino acids) of a Pf332 repeat (K = 1.9 x 10(8) M-1). Peptide length did not influence the binding of peptides corresponding to the Pf155/RESA and Pf11.1 repeats, which had lower affinities comparable to that of the shortest Pf332 octapeptide (K = 2.2 x 10(4) M-1). Only peptides containing binding sites as defined by PEPSCAN analysis showed a measurable binding. When using peptides as inhibitors in peptide ELISA, binding correlated with the affinity of the peptides, but only the high affinity peptides were inhibitory. In contrast, a poor correlation was found when peptides were used directly for coating in ELISA.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a linear neutralization site within the third variable region of the feline immunodeficiency virus envelope

Synthetic peptides have been used to map linear B-cell epitopes of the third variable (V3) region of the feline immunodeficiency virus (FIV) external membrane glycoprotein gp120. The analysis of sera from naturally and experimentally FIV-infected cats by Pepscan and enzyme immunoassay with four partially overlapping peptides evidenced three antibody-binding domains, two of which mapped in the carboxyl-terminal half of V3. In particular, the V3.3 sequence (Gly-392-Phe-413) turned out to be important for in vitro neutralization of the virus in that the peptide inhibited the FIV-neutralizing activity of pooled immune cat sera, and on the other hand, cat sera raised against this peptide effectively neutralized FIV infectivity for Crandell feline kidney cells.

Antibodies to the protein core of the small cell lung cancer workshop antigen cluster-w4 and to the leucocyte workshop antigen CD24 recognize the same short protein sequence leucine-alanine-proline

We recently described the identity of the small cell lung cancer (SCLC) cluster-w4 antigen and the human B cell differentiation marker CD24, a glycosylphosphatidylinositol (GPI)-anchored, highly glycosylated surface molecule of only 31-35 amino acids [15]. The specificities of three anti-cluster-w4 and of eleven anti-CD24 MoAbs have been investigated with respect to their binding capacity to the protein core of cluster-w4/CD24 antigen. Four overlapping peptides spanning this protein core were synthesized. MoAbs shown to bind to two overlapping peptides by antibody binding inhibition using the cluster-w4/CD24-positive SCLC cell line SW2 and by direct peptide binding detected in an ELISA were investigated in more detail. To determine the exact epitopes recognized by these MoAbs, an epitope mapping assay using peptides synthesized onto polyethylene pins was established. The three anti-cluster-w4 MoAbs SWA11, SWA21 and SWA22 and the anti-CD24 MoAbs OKB2 and ALB9 recognized the same short leucine-alanine-proline (LAP) sequence in an area without potential glycosylation sites close to the GPI anchor of the protein core of the cluster-w4/CD24 antigen.

Epitope mapping: synthetic approaches to the understanding of molecular recognition in the immune system

Progress in the field of immunochemistry is rapidly increasing due to very efficient methods of epitope mapping. Experimental results on the allele-specific sequence motifs of MHC-binding peptides allow the exact forecast of T-cell epitopes and, in combination with B-cell prediction methods and synthetic adjuvant systems, fully synthetic vaccines may be constructed. Methods of multiple peptide synthesis are of particular use for such constructs and for the fine mapping of monoclonal antibodies or sera of patients. Peptide libraries, containing hundred thousands of different oligopeptides are made available for novel screening procedures. These techniques and their applications in various fields are summarized and discussed with respect to efficiency and productivity.

Molecular and biotechnological approaches to fish vaccines

Global aquaculture is projected to grow from 10 million to 20 million metric tons by the year 2000. To meet this projection, the aquaculture industry must bring some of its infectious disease problems under control without relying on antibiotics and chemotherapeutics. Thus, vaccines for fish and shellfish are being sought by the industry. The very first commercial fish vaccine was a killed vibriosis bacterin which was very effective and relatively easy to produce. Vaccines for other bacterial, viral, and parasitic fish pathogens are proving more difficult to develop and researchers have begun to use molecular and biotechnological approaches to develop such vaccines. This review describes the vaccines that are now available as well as the vaccines that are being developed and includes a discussion of live, attenuated vaccines, immunoadjuvants, and subunit vaccines for fish.

Differences in the antibody response to human immunodeficiency virus-1 envelope glycoprotein (gp160) in infected laboratory workers and vaccinees

Studies of the immune response to the human immunodeficiency virus (HIV) have been hampered by the antigenic diversity of the HIV envelope protein. In an effort to predict the efficacy of vaccination we have compared the systemic anti-envelope antibody response in seronegative volunteers immunized with recombinant gp160 (either in vaccinia or as soluble protein produced in baculovirus) derived from the HTLV-IIIB strain of HIV-1 and in two laboratory workers accidentally infected with the same strain. 11 of 14 vaccinees responded to immunization by producing anti-gp160 of similar titer and the same isotype as that seen in the laboratory workers. Four vaccinees also had antibody to the principal neutralizing domain (V3 loop) that was comparable in titer with that seen in the laboratory workers, but the fine specificity of anti-V3 antibody was qualitatively different in the two groups. Antibody that can block the interaction between CD4 and gp120 was present at comparable levels in three vaccines and the lab workers. Neutralizing antibody titers were markedly lower in the vaccinees than in the laboratory workers. In seven of the vaccinees, an immunodominant epitope was at amino acid 720-740. Analyses of monoclonal antibodies to this region indicate that they do not neutralize, bind to infected cells, nor function as immunotoxins. Although the anti-gp160 antibody response was of similar magnitude in both infected and vaccinated individuals, there were important qualitative differences.

Carrier sequence selection--one key to successful vaccines

The trend towards epitopic vaccines has brought with it the problem of ensuring carrier function, a role previously filled by carrier sequences of the attenuated organism. Here, Howard Etlinger proposes the use of carrier epitopes, derived from vaccines already in use and selected for their ability to activate only helper T-cell responses, in the administration of B-cell-specific epitopic vaccines.