Antibodies that react with predetermined sites on proteins

Peptide Antibodies: Current Status

Peptide antibodies have become one of the most important classes of reagents in molecular biology and clinical diagnostics. For this reason, methods for their production and characterization continue to be developed, including basic peptide synthesis protocols, peptide-conjugate production and characterization, conformationally restricted peptides, immunization procedures, etc. Detailed mapping of peptide antibody epitopes has yielded important information on antibody-antigen interaction in general and specifically in relation to antibody cross-reactivity and theories of molecular mimicry. This information is essential for detailed understanding of paratope-epitope dynamics, design of antibodies for research, design of peptide-based vaccines, development of therapeutic peptide antibodies, and de novo design of antibodies with predetermined specificity.

Chimeric Protein Switch Biosensors

Rapid detection of protein and small-molecule analytes is a valuable technique across multiple disciplines, but most in vitro testing of biological or environmental samples requires long, laborious processes and trained personnel in laboratory settings, leading to long wait times for results and high expenses. Fusion of recognition with reporter elements has been introduced to detection methods such as enzyme-linked immunoassays (ELISA), with enzyme-conjugated secondary antibodies removing one of the many incubation and wash steps. Chimeric protein switch biosensors go further and provide a platform for homogenous mix-and-read assays where long wash and incubation steps are eradicated from the process. Chimeric protein switch biosensors consist of an enzyme switch (the reporter) coupled to a recognition element, where binding of the analyte results in switching the activity of the reporter enzyme on or off. Several chimeric protein switch biosensors have successfully been developed for analytes ranging from small molecule drugs to large protein biomarkers. There are two main formats of chimeric protein switch biosensor developed, one-component and multi-component, and these formats exhibit unique advantages and disadvantages. Genetically fusing a recognition protein to the enzyme switch has many advantages in the production and performance of the biosensor. A range of immune and synthetic binding proteins have been developed as alternatives to antibodies, including antibody mimetics or antibody fragments. These are mainly small, easily manipulated proteins and can be genetically fused to a reporter for recombinant expression or manipulated to allow chemical fusion. Here, aspects of chimeric protein switch biosensors will be reviewed with a comparison of different classes of recognition elements and switching mechanisms.

One-Shot Generation of Epitope-Directed Monoclonal Antibodies to Multiple Nonoverlapping Targets: Peptide Selection, Antigen Preparation, and Epitope Mapping

This chapter describes an epitope-directed approach to generate antipeptide monoclonal antibodies to multiple nonoverlapping protein sites using a cocktail of fusion peptides as immunogen. It provides a step-by-step protocol on how antigenic peptides on a target protein can be identified by in silico prediction and discusses considerations for final peptide selection. Each antigenic peptide (10-20 amino acids long) is displayed as three-copy inserts on the surface exposed loop of a thioredoxin scaffold protein. The corresponding DNA coding sequence specifying the tripeptide insert flanked by Gly-Ser-Gly-Ser-Gly linkers is cloned in-frame into the Rsr II site of the thioredoxin gene in the pET-32a vector. The presence of a C-terminal polyhistidine tag (His₆-tag) allows the soluble fusion proteins to be purified by one-step native immobilized metal affinity chromatography (IMAC) to greater than 95% purity. Multiple thioredoxin fusion proteins are mixed in equimolar concentrations and used as an immunogen cocktail for animal immunization. The use of short antigenic peptides of known sequence facilitates direct epitope mapping requiring only small mutagenesis scan peptide libraries in the multipin peptide format.

Epitope-directed monoclonal antibody production using a mixed antigen cocktail facilitates antibody characterization and validation

High quality, well-validated antibodies are needed to mitigate irreproducibility and clarify conflicting data in science. We describe an epitope-directed monoclonal antibody (mAb) production method that addresses issues of antibody quality, validation and utility. The workflow is illustrated by generating mAbs against multiple in silico-predicted epitopes on human ankyrin repeat domain 1 (hANKRD1) in a single hybridoma production cycle. Antigenic peptides (13-24 residues long) presented as three-copy inserts on the surface exposed loop of a thioredoxin carrier produced high affinity mAbs that are reactive to native and denatured hANKRD1. ELISA assay miniaturization afforded by novel DEXT microplates allowed rapid hybridoma screening with concomitant epitope identification. Antibodies against spatially distant sites on hANKRD1 facilitated validation schemes applicable to two-site ELISA, western blotting and immunocytochemistry. The use of short antigenic peptides of known sequence facilitated direct epitope mapping crucial for antibody characterization. This robust method motivates its ready adoption for other protein targets.

Antibodies to influenza nucleoprotein cross-react with human hypocretin receptor 2

The sleep disorder narcolepsy is linked to the HLA-DQB1*0602 haplotype and dysregulation of the hypocretin ligand-hypocretin receptor pathway. Narcolepsy was associated with Pandemrix vaccination (an adjuvanted, influenza pandemic vaccine) and also with infection by influenza virus during the 2009 A(H1N1) influenza pandemic. In contrast, very few cases were reported after Focetria vaccination (a differently manufactured adjuvanted influenza pandemic vaccine). We hypothesized that differences between these vaccines (which are derived from inactivated influenza viral proteins) explain the association of narcolepsy with Pandemrix-vaccinated subjects. A mimic peptide was identified from a surface-exposed region of influenza nucleoprotein A that shared protein residues in common with a fragment of the first extracellular domain of hypocretin receptor 2. A significant proportion of sera from HLA-DQB1*0602 haplotype-positive narcoleptic Finnish patients with a history of Pandemrix vaccination (vaccine-associated narcolepsy) contained antibodies to hypocretin receptor 2 compared to sera from nonnarcoleptic individuals with either 2009 A(H1N1) pandemic influenza infection or history of Focetria vaccination. Antibodies from vaccine-associated narcolepsy sera cross-reacted with both influenza nucleoprotein and hypocretin receptor 2, which was demonstrated by competitive binding using 21-mer peptide (containing the identified nucleoprotein mimic) and 55-mer recombinant peptide (first extracellular domain of hypocretin receptor 2) on cell lines expressing human hypocretin receptor 2. Mass spectrometry indicated that relative to Pandemrix, Focetria contained 72.7% less influenza nucleoprotein. In accord, no durable antibody responses to nucleoprotein were detected in sera from Focetria-vaccinated nonnarcoleptic subjects. Thus, differences in vaccine nucleoprotein content and respective immune response may explain the narcolepsy association with Pandemrix.

Overview of the purification of recombinant proteins

When the first version of this unit was written in 1995, protein purification of recombinant proteins was based on a variety of standard chromatographic methods and approaches, many of which were described and mentioned throughout Current Protocols in Protein Science. In the interim, there has been a shift toward an almost universal usage of the affinity or fusion tag. This may not be the case for biotechnology manufacture where affinity tags can complicate producing proteins under regulatory conditions. Regardless of the protein expression system, questions are asked as to which and how many affinity tags to use, where to attach them in the protein, and whether to engineer a self-cleavage system or simply leave them on. We will briefly address some of these issues. Also, although this overview focuses on E.coli, protein expression and purification, other commonly used expression systems are mentioned and, apart from cell-breakage methods, protein purification methods and strategies are essentially the same.

EBV-Associated Cancer and Autoimmunity: Searching for Therapies

Epstein-Barr virus (EBV) infects B-, T-, and NK cells and has been associated not only with a wide range of lymphoid malignancies but also with autoimmune diseases such as lupus erythematosus, rheumatoid arthritis and, in particular, multiple sclerosis. Hence, effective immunotherapeutic approaches to eradicate EBV infection might overthrow cancer and autoimmunity incidence. However, currently no effective anti-EBV immunotherapy is available. Here we use the concept that protein immunogenicity is allocated in rare peptide sequences and search the Epstein-Barr nuclear antigen 1 (EBNA1) sequence for peptides unique to the viral protein and absent in the human host. We report on a set of unique EBV EBNA1 peptides that might be used in designing peptide-based therapies able to specifically hitting the virus or neutralizing pathogenic autoantibodies.

Peptide Antibodies: Past, Present, and Future

Peptide antibodies recognize epitopes with amino acid residues adjacent in sequence ("linear" epitopes). Such antibodies can be made to virtually any sequence and have been immensely important in all areas of molecular biology and diagnostics due to their versatility and to the rapid growth in protein sequence information. Today, peptide antibodies can be routinely and rapidly made to large numbers of peptides, including peptides with posttranslationally modified residues, and are used for immunoblotting, immunocytochemistry, immunohistochemistry, and immunoassays. In the future, peptide antibodies will continue to be immensely important for molecular biology, TCR- and MHC-like peptide antibodies may be produced routinely, peptide antibodies with predetermined conformational specificities may be designed, and peptide-based vaccines may become part of vaccination programs.

Techniques for studying protein heterogeneity and post-translational modifications

Proteins often undergo several post-translational modification steps in parallel to protein folding. These modifications can be transient or of a more permanent nature. Most modifications are, however, susceptible to alteration during the lifespan of proteins. Post-translational modifications thus generate variability in proteins that are far beyond that provided by the genetic code. Co- and post-translational modifications can convert the 20 specific codon-encoded amino acids into more than 100 variant amino acids with new properties. These, and a number of other modifications, can considerably increase the information content and functional repertoire of proteins, thus making their analysis of paramount importance for diagnostic and basic research purposes. Various methods used in proteomics, such as 2D gel electrophoresis, 2D liquid chromatography, mass spectrometry, affinity-based analytical methods, interaction analyses, ligand blotting techniques, protein crystallography and structure-function predictions, are all applicable for the analysis of these numerous secondary modifications. In this review, examples of some of these techniques in studying the heterogeneity of proteins are highlighted. In the future, these methods will become increasingly useful in biomarker searches and in clinical diagnostics.

A vaccine for hypertension based on peptide AngI-R: a pilot study

AIMS

We aim to modulate the renin-angiotensin system (RAS) by active immunization against angiotensin I/II, potentially by a novel type of peptide--'AngI-R' for the treatment of hypertension.

METHOD

27 spontaneous hypertensive rats (SHRs) were randomly divided into 3 groups (n=9). Effect of AngI-R on systolic blood pressure of SHRs was determined by its subcutaneous injection into SHRs with anti-angiotensin peptide AngI-R, captopril, physiological salt solution in the same schedule. Systolic blood pressure was monitored by tail-cuff arterial blood pressure measurement method and then calculated from the average of three measurements in each animal at a desired time (0, 4, 8, 16W). AngI, AngII and anti-AngI antibody were detected by ELISA and western blotting method. At the end, the pathologic changes in different organs of SHRs were observed.

RESULT

The results exhibited a marked effect to lower the systolic blood pressure (-15 mmHg) of SHRs after subcutaneous injection with peptide AngI-R. The anti-hypertensive effect lasted for over 1 month. The level of AngI and AngII in the vaccinated group, after administration of AngI-R was lower than the one in the control group and the pre-administered group. The anti-AngI/II antibody titre in the experiment group significantly increased.

CONCLUSION

The peptide AngI-R was able to decrease the blood pressure of SHRs. The peptide AngI-R induced an immune response to inhibit AngI and AngII, resulting in the decrease in blood pressure in SHRs.

Libraries against libraries for combinatorial selection of replicating antigen-antibody pairs

Antibodies are among the most highly selective tight-binding ligands for proteins. Because the human genome project has deciphered the proteome, there is an opportunity to use combinatorial antibody libraries to select high-affinity antibodies to every protein encoded by the genome. However, this is a large task because the selection formats used today for combinatorial antibody libraries are geared toward generating antibodies to one antigen at a time. Here, we describe a method that accelerates the identification of antibodies to a multitude of antigens simultaneously by matching combinatorial antibody libraries against eukaryotic antigen libraries so that replication-competent cognate antigen-antibody pairs can be directly selected. Phage and yeast display systems are used because they each link genotype to phenotype and can be replicated individually. When combined with cell sorting, the two libraries can be selected against each other for recovery of cognate antigen-antibody clones in a single experiment.

Identification of the 30K protein of TMV by immunoprecipitation with antibodies directed against a synthetic peptide

A synthetic hexadecapeptide corresponding to the predicted C-terminal sequence of the 30K protein of TMV has been coupled to bovine serum albumin and used to raise antibodies in rabbits. The resulting antiserum reacted with the 30K protein translated in vitro. We report the use of this antiserum in the first detection of the 30K protein in vivo, in TMV-infected tobacco protoplasts. Several proteins, the so called family of 30K-related peptides, were immunoprecipitated among in vitro translation products, but only the 30K protein was immunoprecipitated from TMV-infected protoplasts.

Overview of the purification of recombinant proteins produced in Escherichia coli

The updated version of this unit presents an overview of recombinant protein purification with special emphasis on proteins expressed in E. coli. The first section deals with information pertinent to protein purification that can be derived from translation of the cDNA sequence. This is followed by a discussion of common problems associated with bacterial protein expression. A flow chart summarizes approaches for establishing solubility and localization of bacterially produced proteins. Purification strategies for both soluble and insoluble proteins are also reviewed. A section on glycoproteins produced in bacteria in the nonglycosylated state is included to emphasize that, although they may not be useful for in vivo studies, such proteins are well suited for structural studies. Finally, protein handling, scale and aims of purification, and specialized equipment needed for recombinant protein purification and characterization are discussed. The methodologies and approaches described here are essentially suitable for laboratory-scale operations.

Delivery of vaccine peptides by rapid conjugation to baculovirus particles

Baculoviruses deliver strong activation signals to dendritic cells and can promote potent immune responses. These properties can be harnessed to use baculovirus as an adjuvant and carrier particle for immunogenic peptides. In this study we use a chemical linker to couple peptides to the baculovirus Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). Intranasal delivery of baculovirus coupled with immunogenic peptides to mice elicited antigen-specific IgG1 and IgG2a antibody. Furthermore, antigen-specific IgA was detected in the lung, and an IFN-gamma response was observed upon re-stimulation with antigen. We show that chemical coupling enables the rapid modification of AcMNPV, allowing multiple epitopes to be delivered simultaneously on a self-adjuvanting carrier particle.

Evaluation of two carrier protein-angiotensin I conjugate vaccines to assess their future potential to control high blood pressure (hypertension) in man

AIMS

We aim to modulate the renin-angiotensin system (RAS) by active immunization against angiotensin I hormone (AI), potentially providing a novel conjugate vaccine treatment for hypertension in man.

METHODS

Immunization studies in rat and human subjects compare the effectiveness of tetanus toxoid (TT) and keyhole limpet haemocyanin (KLH) vaccines for immunotherapy following conjugation with an AI peptide analogue (AI). Cardiovascular responses were assessed in immunized rats and human subjects (two-dose trial only), following increasing i.v. infusions of either AI or angiotensin II hormone (AII).

RESULTS

The AI-TT and AI-KLH conjugate vaccines induced an equivalent immune response, and inhibition of the pressor effects to exogenous AI in rats. Single-dose clinical trials with both conjugate vaccines only resulted in an immune response to the KLH carrier protein. A two-dose clinical trial of AI-KLH conjugate vaccine resulted in a significant immune response to AI. A shift in diastolic blood pressure (DBP) dose-response was demonstrated following challenge with AI and AII for the study volunteer showing the largest anti-AI IgG induction.

CONCLUSION

KLH was shown to be a suitable alternative to TT as a carrier protein for AI, thus supporting continued evaluation of our AI-KLH conjugate vaccine for treatment of hypertension in man.

Rapid monoclonal antibody generation via dendritic cell targeting in vivo

Dendritic cells (DC) are the professional antigen-presenting cells of the immune system. Previous studies have demonstrated that targeting foreign antigens to DC leads to enhanced antigen (Ag)-specific responses in vivo. However, the utility of this strategy for the generation of MAbs has not been investigated. To address this question we immunized mice with IgG-peptide conjugates prepared with the hamster anti-murine CD11c MAb N418. Synthetic peptides corresponding to two different exposed regions of DC-specific ICAM-3 grabbing nonintegrin (DC-SIGN), a human C-type lectin, were conjugated to N418 using thiol-based chemistry. The N418 MAb served as the targeting molecule and synthetic peptides as the Ag (MAb-Ag). A rapid and peptide specific serum IgG response was produced by Day 7 when the synthetic peptides were linked to the N418 MAb, compared to peptide co-delivered with the N418 without linkage. Spleen cells from N418-peptide immunized mice were fused on Day 10, and three IgG1/k monoclonal antibodies (MAbs) were selected to one of the peptide epitopes (MID-peptide). One of the MAbs, Novik 2, bound to two forms of recombinant DC-SIGN protein in enzyme-linked immunosorbent assay (ELISA), and was specifically inhibited by the MID-peptide in solution. Two of these MAbs show specific binding to DC-SIGN expressed by cultured human primary DC. We conclude that in vivo DC targeting enhances the immunogenicity of synthetic peptides and is an effective method for the rapid generation of MAbs to predetermined epitopes.

The production of anti-hexapeptide antibodies which recognize the S7, L6 and L13 ribosomal proteins of Escherichia coli

Here we report the synthesis of the N-terminal hexapeptide H-Pro-Arg-Arg-Arg-Val-Ile-OH of the E. coli ribosomal protein S7. the C-terminal hexapeptide H-Lys-Glu-Ala-Lys-Lys-Lys-OH of L6 and the C-terminal hexapeptide H-Pro-Gln-Val-Leu-Asp-Ile-OH of L13. All peptides were prepared by SPPS following the Fmoc-strategy, using DIC/HOBt and/or HBTU as coupling reagents and 2-chlorotrityl chloride resin as the solid support. The carrier linked synthetic peptides were injected into rabbits and elicited an anti-peptide response. These anti-hexapeptide antibodies were found to recognize the corresponding peptides and proteins.

Computer-assisted analysis of molecular mimicry between human papillomavirus 16 E7 oncoprotein and human protein sequences

The immunology of human papillomavirus (HPV) infections has peculiar characteristics. The long latency for cervical cancer development after primary viral infection suggests mechanisms that may aid the virus in avoiding the host immunosurveillance and establishing persistent infections. In order to understand whether molecular mimicry phenomena might explain the ability of HPV to avoid a protective immune response by the host cell, sequence similarity between HPV16 E7 oncoprotein and human self-proteins was examined by computer-assisted analysis. Data were obtained showing that the HPV16 E7 protein has high and widespread similarity to several human proteins involved in a number of critical regulatory processes. In addition, multiple identical and different E7 peptide motifs are present in the same human protein. Thus, sharing of common motifs between viral oncoproteins and molecules of normal cells may be one cause underlying the scarce immunogenicity of HPV infections. The hypothesis is advanced that synthetic peptides harbouring viral motifs not and/or scarcely represented in the host's cellular proteins may represent a valuable immunotherapeutic approach for cervical cancer treatment.

Native-like cyclic peptide models of a viral antigenic site: finding a balance between rigidity and flexibility

Antigenic site A of foot-and-mouth disease virus (serotype C) has been reproduced by means of cyclic versions of peptide A15, YTASARGDLAHLTTT, corresponding to residues 136-150 of envelope protein VP1. A structural basis for the design of the cyclic peptides is provided by crystallographic data from complexes between the Fab fragments of anti-site A monoclonal antibodies and A15, in which the bound peptide is folded into a quasi-cyclic pattern. Head-to-tail cyclizations of A15 do not provide peptides of superior antigenicity. Internal disulfide cyclization, however, leads to analogs which are recognized as one to two orders of magnitude better than linear A15 in both ELISA and biosensor experiments. CD and NMR studies show that the best antigen, CTASARGDLAHLTT-Ahx-C (disulfide), is very insensitive to environment-induced conformational change, suggesting that cyclization helps to stabilize a bioactive-like structure.

Dengue virus structural differences that correlate with pathogenesis

The understanding of dengue virus pathogenesis has been hampered by the lack of in vitro and in vivo models of disease. The study of viral factors involved in the production of severe dengue, dengue hemorrhagic fever (DHF), versus the more common dengue fever (DF), have been limited to indirect clinical and epidemiologic associations. In an effort to identify viral determinants of DHF, we have developed a method for comparing dengue type 2 genomes (reverse transcriptase PCR in six fragments) directly from patient plasma. Samples for comparison were selected from two previously described dengue type 2 genotypes which had been shown to be the cause of DF or DHF. When full genome sequences of 11 dengue viruses were analyzed, several structural differences were seen consistently between those associated with DF only and those with the potential to cause DHF: a total of six encoded amino acid charge differences were seen in the prM, E, NS4b, and NS5 genes, while sequence differences observed within the 5' nontranslated region (NTR) and 3' NTR were predicted to change RNA secondary structures. We hypothesize that the primary determinants of DHF reside in (i) amino acid 390 of the E protein, which purportedly alters virion binding to host cells; (ii) in the downstream loop (nucleotides 68 to 80) of the 5' NTR, which may be involved in translation initiation; and (iii) in the upstream 300 nucleotides of the 3' NTR, which may regulate viral replication via the formation of replicative intermediates. The significance of four amino acid differences in the nonstructural proteins NS4b and NS5, a presumed transport protein and the viral RNA polymerase, respectively, remains unknown. This new approach to the study of dengue virus genome differences should better reflect the true composition of viral RNA populations in the natural host and permit their association with pathogenesis.

Generation of polyclonal antibodies of predetermined specificity against pediocin PA-1

Polyclonal antibodies of predetermined specificity for pediocin PA-1 (pedA1) have been generated by immunization of rabbits with a chemically synthesized C-terminal fragment of this bacteriocin (PH2) conjugated to the carrier protein keyhole limpet hemocyanin (KLH). The sensitivity and specificity of the PH2-KLH-generated antibodies were evaluated by the development of various enzyme-linked immunosorbent assays (ELISAs)-a noncompetitive indirect ELISA (NCI-ELISA), a competitive indirect ELISA (CI-ELISA), and a competitive direct ELISA (CD-ELISA)-and by immunodotting. All immunoassays indicated the existence of pedA1-specific antibodies with high relative affinities and adequate sensitivities in the sera of immunized animals. The limits of detection of pedA1 in MRS medium (Oxoid Ltd., Basingstoke, United Kingdom) were found to be 2.5 microg/ml by immunodotting and 1 microg/ml in the NCI-ELISA. However, the CI-ELISA enhanced the limit of detection of pedA1 to 0.025 microg/ml, while the amount of free pedA1 required for 50% binding inhibition was 10 microg/ml. Moreover, the CD-ELISA increased the affinity of the PH2-KLH-generated antibodies for pedA1; the limit of detection of pedA1 was less than 0.025 microg/ml, and the 50% binding inhibition value was reduced to 0.5 microg of pedA1/ml. All immunoassays and the slot dot assay detected the presence of pedA1 in the supernatant of the producing strain Pediococcus acidilactici 347, with no reactivity or negligible immunoreactivity with the supernatants of other lactic acid bacteria producing or not producing different bacteriocins. The approaches taken for the generation of antibodies and the development of immunoassays could prove useful for the generation and evaluation of antibodies of predetermined specificity for other bacteriocins of interest in the food industry.

Characterization of humoral immune responses induced by immunization with plasmid DNA expressing HIV-1 Nef accessory protein

Mice immunized with plasmid DNA encoding Nef accessory protein of human immunodeficiency virus type 1 developed high levels of anti-Nef antibodies which were maintained for at least 16 months. These antibodies produced in response to Nef-expressing plasmid DNA did not recognize the linear peptides except the long C-terminal peptide for three of the ten sera. With anti-Nef antibodies produced in mice immunized with the protein Nef without any adjuvant, the same restraint epitope binding was found. On the contrary, anti-Nef antibodies from mice immunized with the protein in Freund's adjuvant showed a broader epitope reactivity pattern. Interestingly, the analysis of immunoglobulin isotype profiles of antibodies generated by the different protocols of immunization showed that plasmid DNA immunization induced predominantly IgG2a, whereas immunization with Nef protein, with or without adjuvant, yielded a preponderance of IgG1 antibodies.

Production and characterization of monoclonal antibodies to simian immunodeficiency virus envelope glycoproteins

Twelve monoclonal antibodies (MAbs), TB1 to TB12, were produced against a soluble vaccinia recombinant envelope glycoprotein (gp140) from simian immunodeficiency virus SIVmac251. These MAbs recognized SIV gp140 with a relatively high affinity (K0.5 from 6.7 x 10(-8) to 4 x 10(-9) M). All the MAbs except TB9, TB11, and TB12 cross-reacted with HIV-2 envelope glycoproteins, but none of the 12 MAbs recognized those from HIV-1. Using a panel of 87 overlapping synthetic peptides containing 20 amino acid residues, with an overlap of 10 amino acids and spanning the entire primary sequence of gp140, 3 linear epitopes were identified. The first mapped with a neutralizing MAb, TB12, which recognized a linear sequence around amino acids 28-31 within the N-terminal end of the external envelope glycoprotein. The two other new nonneutralizing MAbs recognized linear epitopes around amino acid sequence 380-381 by MAbs TB1, TB2, and TB3, and at the transmembrane glycoprotein amino acids 581-600 by MAb TB6. Seven of the 12 MAbs, TB4, TB5, TB7-9, TB10, and TB11, failed to bind the linear synthetic peptides in ELISA. Moreover, among these seven MAbs only MAbs TB4, TB5, TB9, and TB10 failed to recognize SIV envelope glycoproteins in Western blot (WB) or ELISA after reduction of disulfide bridges by dithiothreitol (DTT), suggesting that they are directed against conformational or discontinuous epitopes. It is of interest to note that MAb TB10 can block the binding of gp140 to the CD4 receptor when the MAb is previously incubated with gp140. Consistent with this result, MAb TB10 cannot bind to gp140 that has been previously complexed with the CD4 receptor. All these results suggest that MAb TB10 recognizes a conformational or discontinuous epitope overlapping or close to the CD4-binding site. These properties are probably implicated in the neutralizing activity observed with this MAb.

Immunogenicity of a contiguous T-B synthetic epitope of the A/PR/8/34 influenza virus

A contiguously linked T-B synthetic viral epitope (110HA120-150HA159,T-B) was investigated for its potency in inducing humoral and cellular immune responses in vivo. The T-cell epitope 110HA120 corresponds to the site 1 hemagglutinin (HA) of the A/PR/8/34 (PR8) influenza virus and is recognized by CD4 T cells in association with I-Ed class II major histocompatibility complex molecules. The 150HA159 represents a major B-cell epitope of the HA protein. T-B dipeptide emulsified in Freund's complete adjuvant was able to induce strong antiviral antibody titers and a high frequency of specific T-cell precursors after a single inoculation in BALB/c mice. In contrast, immunization under identical conditions with equimolar mixtures of T and B peptides did not elicit antibody titers or a cellular immune response. As indicated by the isotypes of antiviral antibodies, the T-B dipeptide preferentially induced a Th1-like immune response. Challenge with T-B dipeptide, but not with T or B peptide alone, stimulated peptide-specific T memory cells in mice previously primed with PR8 virus or with T-B dipeptide. As a consequence, 71 and 57% of these mice, respectively, survived infection with two 100% lethal doses of PR8 virus. Our results suggest that, inasmuch as contiguity between T- and B-cell epitopes provides enough signaling capacity to trigger the mechanisms of T-B-cell cooperation in vivo, a T-B contiguous epitope may well represent a minimal built-in subunit vaccine. Aside from their potential bioavailability, the T-B contiguous epitopes may also represent attractive tools for investigating the molecular mechanisms of T-B-cell cooperation responsible for antiviral protection.

Conformation of surface exposed N-terminus part of bacteriorhodopsin studied by transferred NOE technique

Interaction of the monoclonal antibody A5 raised against native bacteriorhodopsin (BR) with the synthetic peptide pGlu1-Ala-Gln-Ile-Thr-Gly-Arg7-NH2, corresponding to the amino acid sequence 1-7 was studied by transferred nuclear Overhauser effect (TRNOE) spectroscopy. The denaturing reagents and the specially designed pulse sequences which eliminate broad signals from the TRNOE spectra were used to favour evaluation of the TRNOE peaks. On the basis of the data obtained, the conformation of peptide bound with A5 was calculated. A model of the mutual arrangement of bacteriorhodopsin N-terminus and the first transmembrane alpha-helical segment 8-32 was proposed.

Short synthetic peptides exploited for reliable and specific targeting of antibodies to the C-termini of cytochrome P450 enzymes

An antibody was raised against a synthetic peptide (Ser-Glu-Asn-Tyr-Lys-Asp-Asn) corresponding to residues 290-296 of the cytochrome P450 enzyme, CYP1A2, of both rat and mouse. A cysteine residue attached to the N-terminus of the peptide during synthesis allowed coupling in a specific orientation via the thiol group to the carrier protein, keyhole limpet haemocyanin. Antiserum raised in rabbits bound specifically to CYP1A2 in the rat and mouse. To determine those amino acid residues involved in binding of the antibody, related peptides of various lengths were synthesised and the binding of the antibody was determined by an enzyme-linked immunosorbent assay. These studies show that the minimum epitope is the C-terminal tripeptide sequence, Lys-Asp-Asn. Other than in rat and mouse CYP1A2, this tripeptide is found as an internal sequence in a large number of proteins including bovine fibronectin, chicken gizzard myosin heavy chain, and the P450 enzymes, rabbit CYP3A6 and human CYP3A4, but the antibody did not bind to any of these proteins. However, the antibody did bind to yeast glucose-6-phosphate dehydrogenase in which the tripeptide sequence is the C-terminus. Antibodies raised against a truncated peptide (Tyr-Lys-Asp-Asn), representing the C-terminal half of the peptide, also bound to glucose-6-phosphate dehydrogenase, but failed to bind to CYP1A2; thus although the C-terminal region of the peptide 290-296 is strongly immunogenic, it appears that it is not this population of antibodies that binds to CYP1A2. As antibodies were found to bind strongly to the C-terminus of glucose-6-phosphate dehydrogenase, the C-termini of proteins as targets for anti-peptide antibodies were investigated further by immunising rabbits with four 5-residue peptides which represent the C-termini of the P450 enzymes, CYP1A1, CYP1A2, CYP2E1 and CYP2A6. The peptides were coupled to keyhole limpet haemocyanin through their N-termini via cysteine residues added to the sequences. All four antisera bound specifically to their respective target proteins, as demonstrated by immunoblotting using hepatic microsomal fractions from rat, rabbit and human. It is suggested that this method of antibody production could be of general use for the reliable production of antisera against proteins where their sequence at the C-terminus is known, and such antibodies can be highly specific as they do not bind to internal sequences.

Peptides as active probes

The use of peptides as probes of peptide binding sites of neuropeptide receptors, and of peptidases and proteases is discussed. The rapidly expanding use of peptide antigens as probes of protein structure and valuable diagnostics and vaccines is described. We also discuss the use of synthetic peptide motifs in studies on the molecular details of protein-protein and protein-nucleic acid interactions. Covalently modified peptides such as phosphopeptides exemplifies the use of synthetic peptides in the study of posttranslational modifications of proteins.

Polyclonal antibodies with predetermined specificity against bovine alpha s1-casein: application to the detection of bovine milk in ovine milk and cheese

Comparing the primary sequences of bovine and ovine milk proteins, some short peptide fragments are cow-specific, in particular the 141-148 fragment of bovine alpha s1-casein, which is deleted in its ovine counterpart. The 140-149 peptide was chemically synthesized on a solid phase matrix and directly used as an immunogen to produce polyclonal monospecific antibodies in rabbits. These antibodies recognized this fragment both on the peptidyl resin and in the native protein. They appeared to be monospecific, since no antigen-antibody complex was formed with homologous ovine or caprine proteins. Subsequently, a competitive enzyme-linked immunosorbent assay was successfully developed for the detection of defined amounts of cows' milk in sheep's milk from 0.125 to 64% (v/v) and in cheese from 0.5 to 25% (v/v) that was not influenced by heat treatment of milk or the degree of ripening of cheese.

Anti-peptide antibodies against the human blood platelet thromboxane A2/prostaglandin H2 receptor. Production, purification and characterization

Two anti-peptide antibodies have been raised against the human blood platelet thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. Based on the published sequence of the placental TXA2/PGH2 receptor, two decapeptide segments were selected as potential antigens: one in the first extracellular loop corresponding to residue 89 through 98, and the other in the C-terminal region of the intracellular domain corresponding to residue 314 through 323. Rabbits were immunized with each peptide, and the antisera were subjected to a two-step purification procedure. The IgG fraction was purified using a DEAE Affi-Gel Blue column, and the peptide-specific IgG was further purified by affinity chromatography employing each peptide as the immobilized ligand. The combined purification factor for both procedures was approximately 60-fold. By ELISA, both antibodies displayed immunoreactivity toward their synthetic antigens, solubilized platelet membranes and affinity-purified TXA2/PGH2 receptor protein. Furthermore, Western blot analysis revealed that: (1) each antibody reacted with the purified platelet TXA2/PGH2 receptor protein (55 kDa); and (2) each antibody recognized a single band (55 kDa) in solubilized platelet membranes. These findings establish antibody specificity for the human platelet TXA2/PGH2 receptor protein. Functional analysis demonstrated that neither antibody interfered with ADP- or U46619-induced platelet aggregation of [3H]SQ29,548 binding to the solubilized receptor. These results suggest that the antibody epitopes are separate from the TXA2/PGH2 binding domain. In summary, two specific anti-peptide antibodies have been raised against the human platelet TXA2/PGH2 receptor. These antibodies should prove to be of value in the further investigation of the platelet TXA2/PGH2 receptor.

Comprehensive delineation of antigenic and immunogenic properties of peptides derived from the nef HIV-1 regulatory protein

The Human Immunodeficiency Virus (HIV-1) nef regulatory protein, a protein involved in AIDS pathology, was used as a model to investigate and analyze B- and T-cell epitopes. In this paper, we describe the potential structural basis of antigenic and immunogenic reactivity of synthetic peptides derived from the macromolecular antigen. The relationship between B- and T-cell determinants in the context of regulatory mechanisms involved in immune recognition, while integrating recent data concerning MHC presentation. As a result of the recent progress in the field of peptide recognition and presentation, the potential of the peptide approach for constructing successful synthetic vaccines needs to be continuously re-evaluated.

Specificity of anti-P25 antibodies produced against whole HIV-1 particles or soluble forms of the protein

Specificity of anti-p25 antibodies produced against either whole Human Immunodeficiency Virus type 1 (HIV-1) particles in humans and chimpanzees, or against soluble forms of the protein in chimpanzees and rabbits was analyzed by ELISA using a panel of 37 long (> or = 30 residues) or shorter (9-21 residues) overlapping peptides covering the entire p25 sequence. Antibodies elicited by intact virions presented similar reactivity patterns in HIV-1-infected humans and in HIV-1-infected or immunized chimpanzees and recognized only a limited region mostly the C-terminus of the molecule. Moreover, 8 of the human sera (36%), which nonetheless reacted with high titers and avidity with native p25, did not bind to any long or short peptide. These results suggest that the majority of antibodies elicited by viral particles are presumably directed to conformational epitopes. In contrast, antibodies raised against soluble forms of p25 could react against all long peptides but one (residues 211-245) and against some short peptides, indicating that most of p25 sequence may be immunogenic under these conditions. These results suggest that the reactivity spectrum of anti p25 antibodies is rather different if they are produced against intact HIV-1 particles or the soluble protein. They also indicate that it may be possible to manipulate the specificity of the humoral immune response by using either intact virions or purified proteins.

Characterization of the lymphocyte activation gene 3-encoded protein. A new ligand for human leukocyte antigen class II antigens

The lymphocyte activation gene 3 (LAG-3), expressed in human activated T and natural killer (NK) cells, is closely related to CD4 at the gene and protein levels. We report here the initial characterization of the LAG-3-encoded protein. We have generated two monoclonal antibodies after immunization of mice with a 30-amino acid peptide that corresponds to an exposed extra loop region present in the LAG-3 immunoglobulin-like first domain. The reactivity of these reagents is directed against LAG-3 since they recognize both membrane-expressed and soluble recombinant LAG-3 molecules produced in a baculovirus expression system. The two antibodies are likely to react with the same or closely related epitope (termed LAG-3.1) exposed on the LAG-3 first domain extra loop, as assessed in competition experiments on LAG-3-expressing activated lymphocytes. Cellular distribution analysis indicated that the LAG-3.1 epitope is expressed on activated T (both CD4+ and CD8+ subsets) and NK cells, and not on activated B cells or monocytes. In immunoprecipitation experiments performed on activated T and NK cell lysates, a 70-kD protein was detected after SDS-PAGE analysis. 45-kD protein species were also immunoprecipitated. Both the 70- and 45-kD proteins were shown to be N-glycosylated. In Western blot analysis, only the former molecule was recognized by the anti-LAG-3 antibodies, demonstrating that it is LAG-3 encoded. These anti-LAG-3 antibodies were used to investigate whether the LAG-3 protein interacts with the CD4 ligands. By using a high-level expression cellular system based on COS-7 cell transfection with recombinant CDM8 vectors and a quantitative cellular adhesion assay, we demonstrate that rosette formation between LAG-3-transfected COS-7 cells and human leukocyte antigen (HLA) class II-bearing B lymphocytes is specifically dependent on LAG-3/HLA class II interaction. In contrast to CD4, LAG-3 does not bind the human immunodeficiency virus gp120. This initial characterization will guide further studies on the functions of this molecule, which may play an important role in immune responses mediated by T and NK lymphocytes.

Mapping of a region of dengue virus type-2 glycoprotein required for binding by a neutralizing monoclonal antibody

Envelope glycoprotein E of flaviviruses is exposed at the surface of the virion, and is responsible for eliciting a neutralizing antibody (Ab) response, as well as protective immunity in the host. In this report, we describe a method for the fine mapping of a linear sequence of the E protein of dengue virus type-2 (DEN-2), recognized by a type-specific and neutralizing monoclonal Ab (mAb), 3H5. First, an Escherichia coli expression vector containing a heat-inducible lambda pL promoter was used to synthesize several truncated, and near-full length E polypeptides. Reactivities of these polypeptides with polyclonal mouse hyperimmune sera, as well as the 3H5 mAb revealed the location of the 3H5-binding site to be within a region of 166 amino acids (aa) between aa 255 and 422. For fine mapping, a series of targeted deletions were made inframe within this region using the polymerase chain reaction (PCR). The hydrophilicity pattern of this region was used as a guide to systematically delete the regions encoding the various groups of surface aa residues within the context of a near-full-length E polypeptide by using PCR. The 3H5-binding site was thus precisely mapped to a region encoding 12 aa (between aa 386 and 397). A synthetic peptide containing this sequence was able to bind to the 3H5 mAb specifically, as shown by enzyme-linked immunosorbent assay. In addition, we show that rabbit Abs raised against the synthetic peptide of 12 aa were able to bind to the authentic E protein, and to neutralize DEN-2 virus in a plaque reduction assay.

Production and characteristics of human tissue plasminogen-activator antibodies with region-oriented synthetic peptides

We selected six peptide sequences as belonging to potential epitopes of tissue plasminogen activator (tPA) using, as the main criterion for their choice, the location of the peptide sequences on the surface of the protein molecule. The six peptides (corresponding to amino acids 4-8, 11-16, 96-101, 272-277, 371-376 and 514-519) were synthesized, coupled to carrier proteins and injected into rabbits. All of these peptides elicited antibodies and 15-75% binding of the corresponding iodinated peptide was obtained with a 1:100 dilution of antiserum. Only two anti-(peptide) sera [anti-(tPA96-101) and anti-(tPA272-277)] reacted with intact tPA and its heavy chain in Western immunoblotting analysis. These two peptides sequences and fragment tPA11-16 appear to be involved in the structure of native antigenic epitopes of tPA, since they were recognized and antibodies present in antisera raised against native tPA. There was no interaction between anti-(tPA4-8) and anti-(tPA371-376) sera with intact one-chain or two-chain tPA. In the case of anti-(tPA4-8) cleavage of one-chain tPA to two-chain tPA and reduction of disulfide bonds exposed this epitope.

Induction of polyclonal antibodies to the S1 subunit of pertussis toxin by synthetic peptides coupled to PPD: effect of conjugation method, adjuvant, priming and animal species

Two peptides, designated L and K, covering a sequence near the NH-terminal end of the S1 subunit of pertussis toxin (PT) were conjugated to the PPD (purified protein derivative) of M. tuberculosis by either glutaraldehyde (GLUT) or succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) and N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) and injected into groups of mice and guinea pigs. Initially, the effect of priming the animals with BCG vaccine and the use of aluminium hydroxide as adjuvant for the anti-peptide antibody response was studied. The group of BCG-primed mice immunized with adsorbed peptide conjugates showed the highest anti-peptide conjugate antibody response. Based on this finding, groups of BCG-primed mice were immunized four times with either adsorbed peptide L-GLUT, peptide L-SMCC/SPDP or peptide K-SMCC/SPDP conjugates and the fine peptide specificity as well as the PT and S1 cross-reactivity was investigated in ELISA. Mice immunized with peptide L-GLUT showed a significant antibody response to the homologous conjugate, only, whereas the group injected with the peptide L-SMCC/SPDP conjugate gave a significant response to both peptide K and L conjugated by the SMCC-SPDP method. Likewise, mice immunized with the peptide K-SMCC/SPDP conjugate reacted with the homologous and peptide L-SMCC/SPDP conjugate, although only the response to the former conjugate was significantly greater than the response to PPD. All groups showed a strong anti-PPD response. The anti-PT/S1 cross-reactivity of the antisera varied considerably within each group but was found to be highest in the peptide L-GLUT-immunized animals. The results of the present study not only stress the importance of BCG priming and use of aluminium hydroxide adjuvants for the immunogenicity of the peptides in question but also point to the specificity of the conjugation methods employed as low cross-reactivity between the anti-peptide L-GLUT and L-SMCC/SPDP antisera was noted. Moreover, it appeared that the choice of conjugation method may have an effect on the ability of the peptide conjugates to induce an antibody response cross-reacting with the native protein.

Structural analysis of the human papillomavirus type 16-E2 transactivator with antipeptide antibodies reveals a high mobility region linking the transactivation and the DNA-binding domains

In order to probe the structure of the transcription factor encoded by the E2 Open Reading Frame of papillomaviruses, we raised polyclonal antibodies against a series of synthetic peptides that cover the HPV16-E2 protein. In gel shift experiments with the native form of the protein, we detected supershifts (caused by the binding of antibodies to the E2-DNA complex) with antibodies synthesized against peptides covering a central region 50 residues long in the E2 protein. On the contrary, antibodies raised against peptides from the NH2- and COOH-termini did not give any supershifted band. Western blot experiments showed that several of these non reacting antibodies did however interact with the denatured protein. These results suggest that the central region that connects the NH2-terminal domain responsible for transcriptional activation and the COOH-domain involved in DNA-binding is exposed and maintained in a conformation resembling the peptide, indicating a high mobility region. In contrast, the DNA-binding and transactivation domains were not recognized by the antipeptide antibodies, in line with secondary structure predictions and sequence comparisons indicating that the E2 protein consists of structured and conserved NH2 and COOH-terminal regions separated by a non-conserved and unstructured region. This flexible 'hinge' region may facilitate contacts between E2 dimers at distance in mechanisms of transcriptional activation steps that involve homosynergy or DNA-looping.

A nondestructive method for peptide bond conjugation of antigenic haptens to a diphtheria toxoid carrier, exemplified by two antisera specific to acetolactate synthase

A method for the preparation of an activated protein carrier is described: Protein carboxyl groups are transformed into N-hydroxysulfosuccinimide esters, a structure that will react with primary amino groups under amide bond formation. Although the activated ester is unstable under aqueous conditions, a significant amount of hapten molecules can be bound covalently to the carrier under very mild conditions. Ligands can be peptides or other molecules possessing a primary amino group. The method avoids the risk of ligand polymerization and no derivatization of the ligand prior to conjugation is needed. Residual unreacted ligand molecules can therefore be recovered in their native form by size exclusion chromatography. The method was used to conjugate two synthetic sugar beet acetolactate synthetase (E.C. 4.1.3.18) peptides to diphtheria toxoid. Antibodies were raised against both of the conjugates. The specificity of these antibodies against sugar beet acetolactate synthetase was verified using immunoblotting, ELISA, and immunoprecipitation.

A radioimmunoassay for the determination of insulins from several animal species, insulin derivatives and insulin precursors in both their native and denatured state

Antibodies were raised against the carboxy terminus of the insulin A chain in sheep, goat and rabbit using as antigen the synthetic octapeptide YQLENYCN conjugated to bovine serum albumin (BSA). All of the antisera obtained cross-reacted with molecules containing this peptide sequence. Using these antibodies, we developed a radioimmunoassay that could detect the insulin A chain itself, both denatured and natural mammalian and avian insulins, as well as proinsulins and insulin fusion proteins from microorganisms.

The physiology of anti-idiotypic interactions: from clonal to paratopic selection

On theoretical and experimental grounds, it has been proposed that the idiotypes of immunoglobulins and of T cell receptors are composed of multiple paratopes, as opposed to a single paratope and several idiotopes. This necessitates a revision of some of the basic principles of anti-idiotypic reactions. It is also possible to infer the presence of the same or similar paratopes on different idiotypes. A paratope cannot therefore be regarded as restricted to or unique on an idiotype. For these reasons, the perception of immunological specificity in terms of clonal units is misleading. This review proposes instead that the physiological unit of immunological specificity and regulation is the paratope. This essential alteration in the perception of the immune system is referred to as paratopic selection. The approach is assessed in terms of immunological regulation and specificity, and appears to allow new insights into these areas.

Expression of a human cytomegalovirus glycoprotein multigene family

The short unique component of the human cytomegalovirus genome contains several multigene families, one of which encodes glycoproteins in the virion envelope glycoprotein complex gcII (4). The HXLF glycoprotein multigene family was subcloned into pSP6 or pGEM transcription vectors. Gene products were expressed from the six open reading frames (designated HXLF1 through HXLF6) via in vitro transcription and translation in rabbit reticulocyte lysates. The HXLF gene products were analyzed by immunoprecipitation using virus-specific monoclonal antibodies or human convalescent-phase antisera. One of the anti-gcII monoclonal antibodies, designated 9E10, specifically immunoprecipitated each of the HXLF gene products. Four of the HXLF gene products were immunoprecipitated by human convalescent-phase antisera, but not preimmune sera. Southern blot analysis of genomic DNAs purified from 12 different virus isolates indicated the HXLF multigene family is present in wild-type strains of human cytomegalovirus.

Chemically unambiguous peptide immunogen: preparation, orientation and antigenicity of purified peptide conjugated to the multiple antigen peptide system

We described a novel and simple approach to prepare chemically unambiguous peptide immunogen using the multiple antigen peptide (MAP) approach. This approach requires the conjugation of two purified components: a chloroacetylated oligomeric lysine core matrix and a synthetic peptide containing cysteine at either the carboxyl or amino terminus. The resulting MAP is structurally unambiguous and contains a quantifiable amount of peptide antigens. Furthermore, this method also provides a flexible strategy to link a peptide antigen to the core matrix at the desirable orientation to mimic the native molecule. The carboxyl fragment 43-50 of human transforming growth factor alpha (TGF alpha) was used as a test model for this approach. Antipeptide antibodies did not recognize the "reverse immunogen" in which the peptide was attached to the MAP core matrix at a reverse orientation. To determine the specificity of the antibodies, we used two series of point-substituted TGF alpha analogs containing either alanine or the corresponding D-amino acid replacement to map the antigenic site. The alanine analogs were used to determine the contribution of the side chain while the D-amino acid analogs were used to determine the importance of backbone conformation. The antigen site was found to consist of four residues (Asp47-Leu48-Leu49-Ala50) at the distal end of the peptide-MAP conjugate. The results provide a clear explanation for the specificity of the antipeptide antibodies and their failure to recognize the "reverse immunogen" since the distal and the flexible end of the peptide-MAP construct constitutes the antigenic site. Furthermore, our results also suggests a strategy of placing the antigenic portion of a short-peptide at the distal end in the MAP approach to prepare immunogen.

Antibodies raised against peptide fragments of bovine alpha s1-casein cross-react with the native protein, but recognize sites distinct from the determinants on the protein

Bovine alpha s1-casein (alpha s1-CN) and its peptides 61-110 and 91-110, which contain both T and B cell determinants on alpha s1-CN and can elicit peptide-native protein cross-reactive antibodies, were selected as model antigens to study whether or not the immune response to the peptides is similar to that to the corresponding regions of the native protein, because they both have a similar disordered conformation in solution. Both alpha s1-CN- and peptide 61-110-primed T cells responded to peptides 61-80 and 91-100, but not to peptides 76-95 and 101-110. In addition, T cells immunized with peptide 91-110 were also stimulated by peptide 91-100, but not by peptide 101-110. These results suggest that the location of the T cell determinant was almost the same in alpha s1-CN and its peptides. On the contrary, antibodies raised against alpha s1-CN bound to peptides 76-95 and 91-100, but not to peptides 61-80 nor 101-110, while anti-peptide 61-110 antibodies preferentially reacted with peptides 61-80 and 101-110, and anti-peptide 91-110 antibodies also bound to peptide 101-110 but not to peptide 91-100. These results indicate that the B cell epitopes were not similar between alpha s1-CN and its peptides. This difference may have arisen because the antigen-B cell or T-B interactions required for the development of a specific antibody response occurred in a different manner between alpha s1-CN and its peptides. These findings may be useful for basic studies on immunology, and could also be applied to the design of new peptide vaccines.

Generation and characterization of an antiserum directed against neurohypophyseal prohormones

Abstract An antiserum to neurohypophyseal prohormones was generated by immunization of rabbits with a synthetic peptide fragment bridging the prohormone cleavage site between the vasopressin (AVP) and human AVP-neurophysin sequences of pro-pressophysin. Polyclonal antibodies directed against this peptide cross-reacted with intact human pro-pressophysin (ED(50) of 260fmol), but not with either of the final products of enzymatic processing, AVP and human AVP-neurophysin. Gel electrophoresis and Western immunoblotting of pituitary or hypothalamic extracts from multiple species including mouse, cow and man identified a protein band of molecular weight consistent with intact pro-pressophysin; in hypothalamic extracts from normally-hydrated rats no protein bands were stained, but in extracts from Brattleboro rats a faint band in the area of pro-oxyphysin was identified. Immunohistochemical studies using the antiserum demonstrated the presence of only very small amounts of immunoreactive prohormone in a few widely scattered cells in the hypothalami of normally-hydrated rats. However, after 5 days of solute loading with 2% NaCl as drinking solution, staining for intact prohormone was prominent in the supraoptic and paraventricular nuclei of the hypothalamus. Combined immunoperoxidase-immunofluorescence labeling for prohormone and either AVP-neurophysin or oxytocin-neurophysin revealed prohormone staining in both types of magnocellular neurons in rat hypothalami. These studies suggest that during states of accelerated synthesis and secretion of neurohypophyseal hormones some accumulation of intact prohormone occurs in both AVP and oxytocin magnocellular neurons.