Strategies for epitope analysis using peptide synthesis

Juvenile hormone binding protein and transferrin from Galleria mellonella share a similar structural motif

It has been previously suggested that juvenile hormone binding protein(s) (JHBP) belongs to a new class of proteins. In the search for other protein(s) that may contain structural motifs similar to those found in JHBP, hemolymph from Galleria mellonella (Lepidoptera) was chromatographed over a Sephadex G-200 column and resulting fractions were subjected to SDS-PAGE, transferred onto nitrocellulose membrane and scanned with a monoclonal antibody, mAb 104, against hemolymph JHBP. Two proteins yielded a positive reaction with mAb 104, one corresponding to JHBP and the second corresponding to a transferrin, as judged from N-terminal amino acid sequencing staining. Transferrin was purified to about 80% homogeneity using a two-step procedure including Sephadex G-200 gel filtration and HPLC MonoQ column chromatography. Panning of a random peptide display library and analysis with immobilized synthetic peptides were applied for finding a common epitope present in JHBP and the transferrin molecule. The postulated epitope motif recognized by mAb 104 in the JHBP sequence is RDTKAVN, and is localized at position 82-88.

Phage displayed peptides and anti-idiotype antibodies recognised by a monoclonal antibody directed against a diagnostic antigen of Mycoplasma capricolum subsp. capripneumoniae

A monoclonal antibody (Mab 4.52) raised against Mycoplasma capricolum subsp. capripneumoniae (Mccp) cell lysate was used as a template to obtain substitute antigens recognised by its paratope. Two approaches were investigated: a 17-mer random peptide library displayed on the surface of a filamentous phage was screened by panning on the immobilised Mab 4.52 and anti-idiotype antibodies were generated by immunising a chicken with the F(ab')(2) fragments of the antibody. Analysis of the peptide sequences displayed by the isolated phages identified two peptides. Both contained two cysteine residues and had identical or similar amino acids in positions 5 (P), 8 (I/L) and 13 (L). The fusion phages were also recognised by Mab 4.52 in enzyme-linked immunosorbent assay (ELISA) and binding was shown by surface plasmon resonance. One of the peptides was a markedly better inhibitor (67%) of the binding of Mab 4.52 to its original antigen than the other (20%) at 1mg/ml. After absorption, to remove isotypic and allotypic reactivities, the anti-idiotype IgY was specifically recognised by Mab 4.52 in ELISA and was able to inhibit its binding to the original antigen, whereas anti-idiotype antibodies raised against a bluetongue virus-specific antibody had no effect. In spite of unequivocal binding of the anti-idiotype antibodies and the fusion phages to the paratope of Mab 4.52, goat antisera appeared not to react with either of the surrogate antigens. In contrast, the test sera bound to the original antigen suggesting that Mab 4.52 does not recognise exactly the same antigenic site as antibodies in the goat antisera.

Binding of synthetic peptides by a human monoclonal IgM with an unusual combining site structure

Using X-ray crystallography, a human monoclonal IgM cryoglobulin (Mez) was found to have an unusual combining site topography. Analysis of the unliganded Fv at 2.6 A resolution revealed that the HCDR3 had partitioned the active site into two compartments [Ramsland PA et al. 2000. Mol. Immunol. 37: 295-310]. The two cavities had dimensions and chemical properties that were compatible with the binding of peptides. In this study, libraries of peptides were prepared using solid-phase synthesis. Binding of the intact Mez IgM to these peptides was tested by enzyme-linked immunoassays. Screening of 400 dipeptides revealed that binding was markedly skewed toward amino acids with aromatic side-chains (Phe and Trp), especially when located in the second position. Preferential recognition of aromatic side-chains by Mez IgM was confirmed with larger peptides of three to five residues, but C-terminal positioning was not favored in these peptides. Mez IgM also showed binding propensities for acidic residues (Asp and Glu) as well as several other side-chains with different chemical properties, including His, Pro, Asn and Gln. Mez IgM recognized sets of overlapping octapeptides representing the sequences of the constant domains of human IgG1 heavy chains. These peptides represented similar stretches of polypeptide on the three-dimensional structures of all three constant domains (CH1, CH2 and CH3). Thus, Mez IgM may recognize structurally homologous regions of immunoglobulin domains, which were conserved during the evolution of the immune system.

Bioanalytical characterization of proteins

Allergens from the view of a protein chemist are quite normal proteins, not to distinguish from non allergenic proteins. The first task is therefore to recognize and identify the proteins responsible for the allergenic reaction. This is usually only possible if the allergenic structure is conserved during the purification procedures. For a detailed analysis of the allergenic protein modern protein chemical methods for characterization, identification, determination of posttranslational modifications and epitope characterization have to be applied. Such techniques are briefly described in this article.

Docking of combinatorial peptide libraries into a broadly cross-reactive human IgM

A monoclonal IgM cryoglobulin with diverse binding behavior was isolated from a patient (Mez) with Waldenström's macroglobulinemia. It gave very high titers in the binding of combinatorially synthesized libraries of peptides ranging in size from two to eight residues. The crystal structure of Mez Fv revealed that the binding site was divided into two cavities of unequal volumes with dimensions and chemical properties that were compatible with the binding of peptides. Access to this unique combination of structural information and peptide binding data led us to carry out Mez-peptide docking simulations to gain insight into the Mez binding propensities. In the present article, the results for docking of five peptide libraries are combined with discussions of the methods and approximations involved in the docking process. We analyze the origins of peptide binding affinity for Mez IgM in terms of its cross-reactivity and its structural preferences.

Direct evidence for the existence of Miltenberger antigen

The Miltenberger (Mi) subsystem, which originally consisted of four phenotypes, now has 11 phenotypes. The antigens of this subsystem belong to the MNS blood group system. The Mia antigen has been reported to be present on red blood cells with several Miltenberger phenotypes, namely: Mi.I, Mi.II, Mi.III, Mi.IV, Mi.VI and Mi.X. However, the existence of the Mia antigen as a separate entity has been in question and difficult to prove with polyclonal reagents. We report the first monoclonal anti-Mia (GAMA210), whose epitope is TNDKHKRD or QTNDMHKR, and thereby confirm the existence of the Mia antigen.

Cognate T cell help is sufficient to trigger anti-nuclear autoantibodies in naive mice

The mechanisms involved in the initiation of anti-nuclear autoantibodies are unknown. In this study, we show that one factor allowing anti-nuclear autoantibodies to develop is the incomplete nature of immune tolerance to many of these proteins. Immune responses in mice toward the ubiquitous nuclear autoantigen La/SS-B are much weaker than responses to the xenoantigen, human La (hLa; 74% identical). However, in transgenic (Tg) mice expressing hLa, the Ab response to this neo-autoantigen was reduced to a level resembling the weak autoimmune response to mouse LA: Partial tolerance to endogenous La autoantigen was restricted to the T compartment because transfer of CD4(+) T cells specific for one or more hLa determinants into mice bearing the hLa transgene was sufficient to elicit production of anti-hLa autoantibodies. Notably, only hLa- specific T cells from non-Tg mice, and not T cells from hLa Tg mice, induced autoantibody production in hLa Tg mice. These findings confirm partial Th tolerance to endogenous La and indicate the existence in normal animals of autoreactive B cells continuously presenting La nuclear AG: Therefore, the B cell compartment is constitutively set to respond to particular nuclear autoantigens, implicating limiting Th responses as a critical checkpoint in the development of anti-nuclear autoantibodies in normal individuals.

Synthesis of multiple peptides on plastic pins

This unit covers the strategy of the multiple peptide approach to biological scanning, the synthetic protocols, and the handling of peptides after synthesis: cleavage, preliminary purification, storage, and analysis. It is specific for the multipin technique using equipment obtained from Chiron Technologies, although some of the approaches are applicable to other multiple synthesis techniques. This unit also includes protocols for preparing Fmoc-amino acid solutions and for acetylating or biotinylating synthesized peptides.

Identification of continuous B-cell epitopes on the protein moiety of the 58-kiloDalton cell wall mannoprotein of Candida albicans belonging to a family of immunodominant fungal antigens

The 58-kiloDalton mannoprotein (mp58) on the surface of Candida albicans is highly immunogenic, is expressed by all C. albicans isolates tested, and elicits strong antibody responses during candidiasis. It belongs to a family of immunodominant fungal antigens with representatives also in different species of Aspergillus. The amino acid sequence of the protein portion of mp58 as deduced from the DNA sequence of its encoding gene (FBP1/PRA1) was used to synthesize a complete set of overlapping dodecapeptides (overlap, 7; offset, 5) covalently attached to the surface of derivatized polyethylene pins. The pin-coupled peptides were used in a modified enzyme-linked immunosorbent assay (ELISA) to identify continuous epitopes recognized by a number of antiserum preparations containing anti-mp58 antibodies. This comprehensive epitope-scanning study revealed the presence of multiple immunoreactive continuous B-cell epitopes within the protein sequence. Regions of increased reactivity included both the amino and carboxy termini of the mature protein (encompassing amino acid residues 16 to 50 and 286 to 299, respectively) and four internal regions spanning amino acids at positions 66 to 92, 121 to 142, 148 to 192, and 211 to 232. Further delineation of epitopic regions and identification of the boundaries of the antigenic sites was performed upon ELISA testing with a second Pepset consisting of completely overlapping 8-mer peptides spanning these reactive regions in the protein moiety of mp58. The highly reactive epitopic region at the C terminus of the protein was further evaluated using both window net and replacement net analyses. A synthetic peptide corresponding to the last 10 amino acid residues at the C terminus of the protein was immunogenic when injected into mice after being coupled to a carrier protein. Moreover, antibodies in the resulting sera specifically recognized the homologous mp58 in ELISAs and immunoblot assays. Delineation of the antibody responses to mp58 could provide the basis for the development of novel immunity-based prophylactic, therapeutic, and diagnostic techniques for the management of candidiasis.

Identification and characterization of B-cell epitopes of a 53-kDa outer membrane protein from Porphyromonas gingivalis

We have previously reported that Porphyromonas gingivalis FDC 381 possesses a 53-kDa protein antigen (Ag53) on its outer membrane that evokes a strong humoral immune response in many patients with periodontal disease and that the humoral immune responses to Ag53 differ greatly among patients. To understand how the individual humoral immune system against Ag53 was determined, the regions of Ag53 recognized by specific antibody (B-cell epitopes) and dominant subclasses of serum immunoglobulin G (IgG) against major B-cell epitopes were examined by enzyme-linked immunosorbent assay. This study used sera from six patients with periodontitis, which all reacted strongly with sonic extracts of P. gingivalis 381 and with purified Ag53, and sera from six periodontally healthy children, which did not react with either sonic extracts of P. gingivalis 381 or Ag53. The epitopes were identified using synthetic 5-residue overlapping decapeptides covering the entire Ag53. Thirteen of 89 synthetic decapeptides showed a strong reaction with sera from the periodontal patients, but no reaction with those from the healthy children. Four peptides of 13 exerted different immune responses among patients. Furthermore, restriction analyses of the highly antigenic regions revealed that three sequences, RAAIRAS, YYLQ and MSPARR, were identified as major B-cell epitopes. Additionally, these epitopes were recognized mainly by the IgG2 isotype. These data suggest that the difference of B-cell epitopes might influence individual differences in antibody titer against Ag53 and also that the epitopes recognized commonly by multiple antibodies are quite valuable for peptide vaccine development against P. gingivalis infection.

Synthetic antigenic decapeptides of human brain acetylcholinesterase cross-immunoreact with peptide-specific antibodies against Torpediniformes narcine timlei acetylcholinesterase

Antigenic decapeptides of human brain acetylcholinesterase (AChE) were investigated for immunoreactivity with the rabbit anti-Torpediniformes narcine timlei AChE polyclonal antibody (anti-narcine AChE polyclonal antibody). The decapeptides were synthesized using the multipin combinatorial chemical synthesis technique and biotinylated at N-terminals. Rabbit anti-narcine AChE polyclonal antibodies were purified by Protein A-Sepharose CL 4B column chromatography. Enzyme-linked immunosorbent assay (ELISA) was used for the assay of the reaction between the antigen and the antibody. Seven of 11 antigenic synthetic decapeptides of human brain AChE showed obvious immunoreactivity with the rabbit anti-narcine AChE polyclonal antibodies. The similarity of the AChE sequences of humans and Torpedo species were compared thereby with the epitopes indicated. The results indicate that the epitopes of human brain AChE and Torpedo AChEs have been highly conserved during evolution. In view of this, no N-glycosylation site was found in the antigenic decapeptides tested, they all belong to oligopeptide epitopes.

Chimeric synthetic peptides from the nucleocapsid p24 protein of human immunodeficiency virus type-1

Two chimeric synthetic peptides incorporating antigenic sequences from N-terminal (peptide C14) (134-163) and C-terminal (peptide C15) (335-364) of the p24 protein of human immunodefiency virus (HIV- 1), were synthesized. Peptides C14-GG-C15 and C15-GG-C14 represented sequences from the p24 protein in both possible orders, separated by two glycine residues as arm spacers. These peptides were evaluated as antigen in an Ultramicroenzyme-linked immunosorbent assay (UMELISA) using sera of HIV-1-infected individuals (n = 16) with different titers of antibodies and the specificity was evaluated with healthy blood donors (n = 20). The results were compared to plates coated with monomeric peptides C14 and C15. The chimeric peptide C14-GG-C15 was the most antigenic. Those results may be related to the peptide structure, the sequence order in the chimeric peptide, and epitope accessibility to the antibodies. This chimeric peptide would be very useful for HIV-1 diagnostics.

Grafted supports in solid-phase synthesis

Solid-phase synthesis is greatly dependent on the solid phase. We are interested in the development of a "pellicular" type of solid support where a more mobile polymer is grafted to rigid plastics. Compared to low cross-linked microporous beads that dominate the field, this approach allows great flexibility of design, as plastics are available as sheets, films, or threads, or can be molded into any shape, as required. Many different polymers or copolymers can be grafted onto any particular shape to give a wide choice of options in the physicochemical characteristics of the actual solid support. As an example of such a solid support, we report on polystyrene-grafted polypropylene in a particular shape that we have called "Lanterns." Its synthesis characteristics are compared to the commonly available low cross-linked polystyrene resins. As well, the handling advantages of these types of supports in multiple synthesis are highlighted.

Rational evolutionary design: the theory of in vitro protein evolution

Directed evolution uses a combination of powerful search techniques to generate proteins with improved properties. Part of the success is due to the stochastic element of random mutagenesis; improvements can be made without a detailed description of the complex interactions that constitute function or stability. However, optimization is not a conglomeration of random processes. Rather, it requires both knowledge of the system that is being optimized and a logical series of techniques that best explores the pathways of evolution (Eigen et al., 1988). The weighing of parameters associated with mutation, recombination, and screening to achieve the maximum fitness improvement is the beginning of rational evolutionary design. The optimal mutation rate is strongly influenced by the finite number of mutants that can be screened. A smooth fitness landscape implies that many mutations can be accumulated without disrupting the fitness. This has the effect of lowering the required library size to sample a higher mutation rate. As the sequence ascends the fitness landscape, the optimal mutation rate decreases as the probability of discovering improved mutations also decreases. Highly coupled regions require that many mutations be simultaneously made to generate a positive mutant. Therefore, positive mutations are discovered at uncoupled positions as the fitness of the parent increases. The benefit of recombination is twofold: it combines good mutations and searches more sequence space in a meaningful way. Recombination is most beneficial when the number of mutants that can be screened is limited and the landscape is of an intermediate ruggedness. The structure of schema in proteins leads to the conclusion that many cut points are required. The number of parents and their sequence identity are determined by the balance between exploration and exploitation. Many disparate parents can explore more space, but at the risk of losing information. The required screening effort is related to the number of uphill paths, which decreases more rapidly for rugged landscapes. Noise in the fitness measurements causes a dramatic increase in the required mutant library size, thus implying a smaller optimal mutation rate. Because of strict limitations on the number of mutants that can be screened, there is motivation to optimize the content of the mutant library. By restricting mutations to regions of the gene that are expected to show improvement, a greater return can be made with the same number of mutants. Initial studies with subtilisin E have shown that structurally tolerant positions tend to be where positive activity mutants are made during directed evolution. Mutant fitness information is produced by the screening step that has the potential to provide insight into the structure of the fitness landscape, thus aiding the setting of experimental parameters. By analyzing the mutant fitness distribution and targeting specific regions of the sequence, in vitro evolution can be accelerated. However, when expediting the search, there is a trade-off between rapid improvement and the quality of the long-term solution. The benefit of neutrality has yet to be captured with in vitro protein evolution. Neutral theory predicts the punctuated emergence of novel structure and function, however, with current methods, the required time scale is not feasible. Utilizing neutral evolution to accelerate the discovery of new functional and structural solutions requires a theory that predicts the behavior of mutational pathways between networks. Because the transition from neutral to adaptive evolution requires a multi-mutational switch, increasing the mutation rate decreases the time required for a punctuated change to occur. By limiting the search to the less coupled region of the sequence (smooth portion of the fitness landscape), the required larger mutation rate can be tolerated. Advances in directed evolution will be achieved when the driving forces behind such proce

Coherent membrane supports for parallel microsynthesis and screening of bioactive peptides

Since its invention the SPOT-synthesis methodology has become one of the most efficient strategies for the miniaturized assembly of large numbers of peptides. The combination of a facile synthetic method with high throughput solid- and solution-phase screening assays qualifies the SPOT-technique as a valuable tool in biomedical research. Recent developments such as the introduction of novel polymeric surfaces, new linker and cleavage strategies as well as automated robot systems extended the scope of practical chemical reactions that can be accommodated as well as the numbers of compounds obtainable by this technique. Thus, highly complex spatially addressed compound arrays have become accessible. Together with the introduction of novel screening assays, the method is excellently suited to elucidate recognition events on the molecular level.

Phage-displayed peptides that mimic aflatoxin B1 in serological reactivity

AIMS

To test phage-displayed random peptide libraries as sources of peptides that mimic the binding of aflatoxin B1 to monoclonal antibodies raised against the toxin.

METHODS AND RESULTS

For two of the three MAbs tested, clones were obtained by panning, producing phage that bound specifically to MAb 13D1-1D9 (MAb 24; specific for aflatoxins B1 and G1) and MAb 6E12-1E9 (MAb 13; specific for aflatoxins B1, G1 and B2) in ELISA. The amino acid sequences of the binding peptides varied. Those binding to MAb 24 contained the sequence of '...YMD...', and those that bound to MAb 13 contained the dipeptide 'PW'. Mimotope phage was used in a competition ELISA format for assaying aflatoxin concentrations.

CONCLUSION

The results show that mimotope preparations are effective substitutes for pure toxin in these ELISA procedures.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results should contribute significantly to enhancing the safety and diminishing the costs of aflatoxin assays.

Mapping of monoclonal antibodies specific to P64k: A common antigen of several isolates of Neisseria meningitidis

P64k is a minor outer membrane protein from Neisseria meningitidis. This protein has been produced at high levels in Escherichia coli. We generated a group of monoclonal antibodies (mAbs) against recombinant P64k, which recognise four non-overlapping epitopes, as shown using competition assays with biotinylated mAbs. The P64k sequences involved in mAbs binding were mapped with synthetic overlapping peptides derived from the P64k protein, and located in the previously determined three-dimensional structure of the protein. These antibodies were also characterised by whole-cell ELISA and bactericidal tests against N. meningitidis. Only two of the recognised epitopes were exposed on the bacterial surface, and none of the mAbs showed bactericidal activity. The relationship between these results and the structural data on the epitopes bound by the mAbs is discussed.Key words: Neisseria meningitidis, P64k, monoclonal antibodies, epitope mapping.

Identification of IgE- and IgG-binding epitopes on alpha(s1)-casein: differences in patients with persistent and transient cow's milk allergy

BACKGROUND

Cow's milk allergy (CMA) affects 2.5% of children less than 2 years of age, but about 80% become clinically tolerant within the first 3 years of life. Casein is one of the major allergens responsible for CMA and seems to play an important role in persistent allergy. Previous studies on egg allergy suggested that linear epitopes are associated with long-lasting food allergy.

OBJECTIVE

The aim of the study was to identify IgE- and IgG-binding epitopes on alpha(s1)-casein and to determine whether the patterns of epitope recognition are associated with the natural history of CMA.

METHODS

According to the known amino acid (AA) sequence, 96 overlapping decapeptides representing the entire length of alpha(s1)-casein were synthesized on a cellulose-derived membrane. Sera from 24 children with milk allergy were used to identify IgE- and IgG-binding epitopes.

RESULTS

Six major and 3 minor IgE-binding, as well as 5 major and 1 minor IgG-binding, regions on alpha(s1)-casein were identified. Two IgE-binding regions (AA 69-78 and AA 173-194) were recognized by the majority of patients over 9 years of age with persistent allergy (67% and 100%, respectively) but by none of the children less than 3 years of age who are likely to outgrow CMA. No differences in IgG binding between the groups were observed.

CONCLUSION

There appears to be a difference in epitope recognition between patients with different natural histories of CMA. Screening for IgE antibodies to these epitopes may be useful in identifying children who will have persistent milk hypersensitivity.

Quantitative and qualitative influences of tapasin on the class I peptide repertoire

Tapasin is critical for efficient loading and surface expression of most HLA class I molecules. The high level surface expression of HLA-B*2705 on tapasin-deficient 721.220 cells allowed the influence of this chaperone on peptide repertoire to be examined. Comparison of peptides bound to HLA-B*2705 expressed on tapasin-deficient and -proficient cells by mass spectrometry revealed an overall reduction in the recovery of B*2705-bound peptides isolated from tapasin-deficient cells despite similar yields of B27 heavy chain and beta(2)-microglobulin. This indicated that a proportion of suboptimal ligands were associated with B27, and they were lost during the purification process. Notwithstanding this failure to recover these suboptimal peptides, there was substantial overlap in the repertoire and biochemical properties of peptides recovered from B27 complexes derived from tapasin-positive and -negative cells. Although many peptides were preferentially or uniquely isolated from B*2705 in tapasin-positive cells, a number of species were preferentially recovered in the absence of tapasin, and some of these peptide ligands have been sequenced. In general, these ligands did not exhibit exceptional binding affinity, and we invoke an argument based on lumenal availability and affinity to explain their tapasin independence. The differential display of peptides in tapasin-negative and -positive cells was also apparent in the reactivity of peptide-sensitive alloreactive CTL raised against tapasin-positive and -negative targets, demonstrating the functional relevance of the biochemical observation of changes in peptide repertoire in the tapasin-deficient APC. Overall, the data reveal that tapasin quantitatively and qualitatively influences ligand selection by class I molecules.

Antineutrophil cytoplasmic antibodies to proteinase 3 in Wegener's granulomatosis: epitope analysis using synthetic peptides

BACKGROUND

Antineutrophil cytoplasmic antibodies (ANCA) to proteinase 3 (PR3) are strongly associated with Wegener's granulomatosis (WG) and are thought to be involved in its pathogenesis. Levels of PR3-ANCA do not always correspond to clinical disease activity nor to functional effects of these antibodies in vitro, suggesting differences in epitope specificity. To define relevant epitopes for PR3-ANCA, sera of WG patients were analyzed on their reactivity to linear peptides of PR3.

METHODS

Fifty linear peptides of 15 amino acids in length with an overlap of 10 aa spanning the entire PR3 sequence were synthesized. Sera of 27 WG patients with active disease and 27 age- and sex-matched healthy controls, eight anti-PR3 monoclonal antibodies (mAbs), and a rabbit anti-PR3 serum were tested by enzyme-linked immunosorbent assay for reactivity to PR3 peptides.

RESULTS

Rabbit anti-PR3 serum recognized three distinct peptide areas, whereas none of the anti-PR3 mAbs bound PR3 peptides. Sera of both WG patients and healthy controls recognized a restricted number of PR3 peptides. Four of these peptide areas were recognized significantly more strongly by WG sera than by control sera. Sera drawn at the initial presentation of WG mainly recognized these peptides. Two of the recognized peptide areas were located near the active center of PR3.

CONCLUSION

A restricted number of epitope areas of PR3 are recognized both by WG patient sera and control sera. Four peptide areas were bound stronger by sera of WG patients at initial presentation than by healthy controls.

T-helper and humoral responses to Puumala hantavirus nucleocapsid protein: identification of T-helper epitopes in a mouse model

Puumala hantavirus (PUUV) is a rodent-borne agent causing nephropathia epidemica in humans, a milder form of haemorrhagic fever with renal syndrome occurring in Fennoscandia, central Europe and western Russia. In this study we characterized the immunogenicity of an E. coli-expressed nucleocapsid (N) protein of PUUV (strain Kazan-E6) in inbred mice (BALB/c, CBA and C57/BL6). The recombinant N (rN) protein raised PUUV-specific antibodies in all three tested murine haplotypes, and all IgG subclasses were detected. Epitope mapping using peptides spanning the N protein revealed that the B-cell recognition sites were mainly located at the amino-terminal part of the protein. Proliferative T-helper (Th) lymphocyte responses were detected in all haplotypes after a single immunization with rN. Several Th-recognition sites, spanning amino acids 6-27, 96-117, 211-232 and 256-277, were identified using overlapping peptides. Peptides representing the identified sites could also prime Th-lymphocytes to proliferate in response to recall with rN protein, thereby confirming the authenticity of the identified sites. The rN-primed Th-lymphocytes produced predominantly interleukin (IL)-2 and gamma interferon, together with lower levels of IL-4 and IL-6, indicating a mixed Th1/Th2 response.

Antigenic Properties of Human Glycophorins - An Update

Glycophorins are complex heavily glycosylated antigens carrying peptidic and glycopeptidic epitopes. Detailed immunochemical studies showed that GPA/GPB and GPC/GPD molecules have defined sites which are particularly immunogenic. These sites include N-terminal portions of all glycophorins, internal fragments of their extracellular domains, and cytoplasmic tails. The extracellular epitopes involve directly oligosaccharide chains (e.g. blood group M- and N-related epitopes, or N-terminal epitopes of GPC) or have peptidic character, shown by the reaction of respective antibodies with synthetic peptides. Peptidic eitopes are independent of glycosylation, or are variably affected by adjacent O-glycans which may mask the epitopes or may be required for a proper exposure of an antibody binding site. Several low incidence epitopes are present on variant glycophorin molecules. Among anti-glycophorin antibodies there are the 'bispecific' ones, or antibodies recognizing an epitope formed by an interaction of two proteins (Wr(b)). Alltogether, the glycophorins serve as convenient model antigens for studying Ag-Ab interaction and a role of O-glycosylation in protein antigenic properties. Moreover, well defined specificty of monoclonal anti-glycophorin antibodies makes them more precise tools in serological investigation and identification of normal and variant antigens. Last but not least, elucidation of antigenic properties of glycophorins is important for identification and characterization of human anti-glycophorin antibodies, which in some cases create medical problems at transfusion or pregnancy.

Control of antibody-antigen interaction using anion-induced conformational change in antigen peptide

The binding of a monoclonal antibody to an epitope peptide was controlled by the conformational change of the epitope peptide induced by anions. We synthesized peptides in which the epitope sequence DTYRYI for the monoclonal antibody AU1 is located between amphiphilic peptides (KKLL)n and (LLKK)n. In the absence of an appropriate anion, the peptide was in a random coil state and the epitope was linear. In contrast, in the presence of an appropriate anion, the peptide exhibited an anti-parallel alpha-helical structure and the epitope was subsequently 'bent'. In the presence of 41 microM triphosphate, the association constant between the antibody and the peptide was decreased by one order of magnitude in the case of n = 3 and at least three orders of magnitude in the case of n = 4 or 5. Oligo-DNAs, as anions, dissociated the antibody-peptide complex, whereas triphosphate did not. The DNA concentrations required for 50% dissociation of the antibody-peptide complex at pH 7.5 were 4x10(-8), 1x10(-7) and 6x10(-6) M for decamer, octamer and hexamer DNA, respectively.

Study of antibody and T cell responses in rabbits immunized with synthetic human B cell epitope analogues of La (SSB) autoantigen

The aim of this study was to investigate the immunogenicity of four synthetic peptides, representing linear B cell epitopes of the human La/SSB autoantigen: 145-164 aa (p1), 289-308 aa (p2), 301-318 aa (p3) and 349-364 aa (p4), in rabbits. New Zealand White rabbits were immunized with each of the above peptides attached in four copies on tetrameric sequential oligopeptide carriers (SOC) in duplicate. Control immunizations were also performed (one rabbit each, immunized with Freud's complete adjuvant alone or with the SOC carrier alone). Animals were bled at regular intervals and sera were analysed for anti-La/SSB activity by ELISA assays using as antigen the various synthetic peptides, as well as the whole La/SSB protein. Four months after the last immunization, the animals were killed and peripheral blood mononuclear and spleen cells were co-cultured with either the peptides, the SOC carrier, or 27 peptides, covering the entire length of the human La/SSB molecule (23 amino acids long, overlapping by eight residues to each other). A specific, IgG, anti-peptide antibody response was detected, initially directed against the priming peptide, and subsequently expanded to the other La/SSB synthetic peptides. The antibody titres remained high, even 4 months after the last immunization. Sera from rabbits immunized with either p2 or p3 reacted also with the whole La/SSB protein, as was demonstrated by ELISA and immunoblot assays. No reactivities against either Ro60 or Ro52 autoantigen were found. Rabbit spleen cell reacted not only with the epitope used for the immunization but also with other La/SSB peptides. Immunization of rabbits with the major human La/SSB B cell antigenic determinants, linked to SOC carrier, induces strong and sustained antibody and T cell responses against multiple epitopes of the human La/SSB protein. Thus, La/SSB B cell linear epitopes are probably capable also of functioning as T cell epitopes, in this experimental animal.

Quantification of self-recognition in multiple sclerosis by single-cell analysis of cytokine production

Identifying and quantifying autoaggressive responses in multiple sclerosis (MS) has been difficult in the past due to the low frequency of autoantigen-specific T cells, the high number of putative determinants on the autoantigens, and the different cytokine signatures of the autoreactive T cells. We used single-cell resolution enzyme-linked immunospot (ELISPOT) assays to study, directly ex vivo, proteolipid protein (PLP)-specific memory cell reactivity from MS patients and controls. Overlapping 9-aa-long peptides, spanning the entire PLP molecule in single amino acid steps, were used to determine the frequency and fine specificity of PLP-specific lymphocytes as measured by their IFN-gamma and IL-5 production. MS patients (n = 22) responded to 4 times as many PLP peptides as did healthy controls (n = 22). The epitopes recognized in individual patients, up to 22 peptides, were scattered throughout the PLP molecule, showing considerable heterogeneity among MS patients. Frequency measurements showed that the number of PLP peptide-specific IFN-gamma-producing cells averaged 11 times higher in MS patients than in controls. PLP peptide-induced IL-5-producing T cells occurred in very low frequencies in both MS patients and controls. This first comprehensive assessment of the anti-PLP-Th1/Th2 response in MS shows a greatly increased Th1 effector cell mass in MS patients. Moreover, the highly IFN-gamma-polarized, IL-5-negative cytokine profile of the PLP-reactive T cells suggests that these cells are committed Th1 cells. The essential absence of uncommitted Th0 cells producing both cytokines may explain why therapeutic strategies that aim at the induction of immune deviation show little efficacy in the established disease.

Analysis of the autoimmune epitopes on human testicular NASP using recombinant and synthetic peptides

The human nuclear autoantigenic sperm protein, NASP, is a testicular histone-binding protein of 787 amino acids to which most vasectomized men develop autoantibodies. In this study to define the boundaries of antigenic regions and epitope recognition pattern, recombinant deletion mutants spanning the entire protein coding sequence and a human NASP cDNA sublibrary were screened with vasectomy patients' sera. Employing panel sera from 21 vasectomy patients with anti-sperm antibodies, a heterogeneous pattern of autoantibody binding to the recombinant polypeptides was detected in ELISA and immunoblotting. The majority of sera (20/21) had antibodies to one or more of the NASP fusion proteins. Antigenic sites preferentially recognized by the individual patients' sera were located within aa 32-352 and aa 572-787. Using a patient's serum selected for its reactivity to the whole recombinant protein in Western blots, cDNA clones positive for the C-terminal domain of the molecule were identified. The number and location of linear epitopes in this region were determined by synthetic peptide mapping and inhibition studies. The epitope-containing segment was delimited to the sequence aa 619-692 and analysis of a series of 74 concurrent overlapping 9mer synthetic peptides encompassing this region revealed four linear epitopes: amino acid residues IREKIEDAK (aa 648-656), KESQRSGNV (aa 656-664), AELALKATL (aa 665-673) and GFTPGGGGS (aa 680-688). All individual patients' sera reacted with epitopes within the sequence IREellipsis.GGS (aa 648-688). The strongest reactivity was displayed by peptides corresponding to the sequence AELALKATL (aa 665-673). Thus, multiple continuous autoimmune epitopes in NASP involving sequences in the conserved C-terminal domain as well as in the less conserved testis-specific N-terminal region comprising the histone-binding sites, as predicted for an antigen-driven immune response, may be a target of autoantibodies in vasectomized men and may provide a relevant laboratory variable to describe more accurately the spectrum of autoantibody specificities associated with the clinical manifestation of vasectomy.

Synthetic peptides as putative therapeutic agents in transplantation medicine: application of PEPSCAN to the identification of functional sequences in the extracellular domain of the interleukin-2 receptor beta chain (IL-2Rbeta)

A desired treatment strategy in transplantation medicine is the selective targeting of alloreactive T cells without impairing antileukemic and antiviral activities. One approach is the synthesis of peptides that interfere with the binding of interleukin-2 (IL-2) to its high affinity receptor (IL-2R). This blocks the activation and proliferation of the antigen-activated T cells and the secretion of IL-2. The latter binds to its receptor, via the extracellular domain of the IL-2Rbeta chain, while its cytoplasmic domain is required for intracellular signal transduction. In this study, the PEPSCAN method was applied in order to identify antigenic sequences (epitopes) in the extracellular domain of the IL-2Rbeta. Based on the primary amino acid (aa) sequence of the IL-2Rbeta, a total of 239 overlapping dodecapeptides, spanning the entire sequence of IL-2Rbeta, were synthesized by PEPSCAN and their immunoreactivity was tested by ELISA using monoclonal antibodies (mAbs) specific for IL-2Rbeta such as TU11, Mikbeta1, HuMikbeta1 and TU27. TU11 recognized a linear epitope located in the region 85R-Q(96). None of the 239 synthetic peptides was recognized by TU27. Mikbeta1 (and HuMikbeta1) recognized a discontinuous epitope formed by aa located in the IL-2Rbeta domains L(106) to P(148) and E(170) to A(202). Subsequently, synthetic peptides corresponding to the identified putative epitopic sequences were prepared by solid phase synthesis and their immunogenicity in vivo was assessed by raising polyclonal antibodies. Given that Mikbeta1 and HuMikbeta1 inhibit binding of IL-2 on the IL-2Rbeta, we addressed the question of whether the identified antigenic sequences serve as putative IL-2 binding domains. Synthetic peptides corresponding to these sequences were tested for their ability to compete with IL-2 for binding and, thereby, inhibit IL-2-induced proliferation of mitogen-stimulated human peripheral blood T cells. Sequences 107M-E(118) and 178Y-Q(199) probably represent functional IL-2 binding domains on IL-2Rbeta, since these synthetic peptides significantly inhibited the proliferation of activated T cells and secretion of IL-2.

Epitopes of human brain acetylcholinesterase

The main purpose of the present work was to identify B-cell epitopes on human brain acetylcholinesterase (AChE) by the synthetic peptide approach. Five hundred and seventy-four decapeptides comprising amino acids No. n to n+9 (where n denotes the residue number of the 583 amino acids in the primary structure of human brain AChE and is an integer in the range 1-574) were synthesized, using the multipin combinatorial chemical synthesis technique, and biotinylated. Epitopes of human brain AChE were detected by enzyme-linked immunosorbent assay (ELISA) and compared with the predicted epitopes of human AChE by 'Goldkey' software. Among 574 synthetic decapeptides, 47 decapeptides at 11 antigenic regions showed immunoreactivity with mouse anti-human brain AChE polyclonal antibodies. The minimum sequence of epitope was defined at every antigenic region explored. The locations and sequences of the former ten continuous epitopes at the 11 antigenic regions of the human brain AChE had been identified as follows: TPVLVWIY (112-119), RTVLVSMNY (143-151), LLDQRLALQW (173-182), RRATQLAH (246-253), VFRFSFVPV (294 approximately 302), KDEGSYFLVY (332-341), RVYA (424-427), LMRY (476-479), KAPQWPPY (496-503), GLRAQACAFW (523-532). The rate of hits of the predicted epitopes from the software came out at 33%. In our work, the epitopes of human AChE have been mapped by purified polyclonal antibody at eleven distinct sites in the primary structure.

Immunoglobulin A responses to Puumala hantavirus

Puumala hantavirus (PUUV) causes nephropathia epidemica (NE), a form of haemorrhagic fever with renal syndrome that occurs in northern and central Europe. The immunoglobulin A (IgA) response in NE patients was studied. The levels of total serum IgA in acute-phase samples from NE patients were found to be significantly elevated when compared with the levels in healthy controls. ELISAs for detection of the IgA1 and IgA2 responses against each PUUV structural protein (N, G1 and G2) were developed and evaluated. Sequential sera from NE patients (acute, convalescent, 2-year) and 10-20 year NE-convalescent sera were examined. Most patients developed detectable levels of IgA1 against N and G2, while the G1 responses were low or undetectable. Seven of nine 10-20 year sera contained virus-specific IgA1, which may indicate the prolonged presence of viral antigens after the initial infection. PEPSCAN analysis revealed several IgA-reactive antigenic regions in the N protein. Serum IgA and IgG was purified by affinity chromatography and examined by a virus-neutralization assay. Three of five sera from acute-phase NE patients contained neutralizing IgA1. The diagnostic potential of the PUUV-specific IgA1 response was evaluated. The N and G2 assays showed specificities of 100% with sensitivities of 91 and 84%, respectively, compared with an IgM mu-capture ELISA. Several NE patients, clinically diagnosed for acute PUUV infection, with borderline or undetectable levels of PUUV-specific IgM, were found to be highly positive for the presence of PUUV N-specific serum IgA1, proving the diagnostic value of IgA analysis as a complement to detection of IgM.

Identification of an immunodominant ABC transporter in methicillin-resistant Staphylococcus aureus infections

Immunoblotting sera from 26 patients with septicemia due to an epidemic strain of methicillin-resistant Staphylococcus aureus (EMRSA-15), 6 of whom died, revealed an immunodominant EMRSA-15 antigen at 61 kDa. There was a statistically significant correlate (P < 0.001) between survival and immunoglobulin G to the 61-kDa band. The antigen was identified by sequencing positive clones obtained by screening a genomic expression library of EMRSA-15 with pooled sera from patients taken after the septicemic episode. Eluted antibody reacted with the 61-kDa antigen on immunoblots. The amino terminus was obtained by searching the S. aureus NCTC 8325 and MRSA strain COL databases, and the whole protein was expressed in Escherichia coli TOP 10F'. The derived amino acid sequence showed homology with ABC transporters, with paired Walker A and Walker B motifs and 73% homology to YkpA from Bacillus subtilis. Epitope mapping of the derived amino acid sequence with sera from patients who had recovered from EMRSA-15 septicemia delineated seven epitopes. Three of these epitopes, represented by peptides 1 (KIKVYVGNYDFWYQS), 2 (TVIVVSHDRHFLYNNV), and 3 (TETFLRGFLGRMLFS), were synthesized and used to isolate human recombinant antibodies from a phage antibody display library. Recombinant antibodies against peptides 1 and 2 gave logarithmic reductions in organ colony counts, compared with control groups, in a mouse model of the infection. This study suggests the potential role of an ABC transporter as a target for immunotherapy.

B cell responses to a peptide epitope. X. Epitope selection in a primary response is thermodynamically regulated

We examine the etiological basis of hierarchical immunodominance of B cell epitopes on a multideterminant Ag. A model T-dependent immunogen, containing a single immunodominant B cell epitope, was used. The primary IgM response to this peptide included Abs directed against diverse determinants presented by the peptide. Interestingly, affinity of individual monomeric IgM Abs segregated around epitope recognized and was independent of their clonal origins. Furthermore, affinity of Abs directed against the immunodominant epitope were markedly higher than that of the alternate specificities. These studies suggested that the affinity of an epitope-specific primary response, and variations therein, may be determined by the chemical composition of epitope. This inference was supported by thermodynamic analyses of monomer IgM binding to Ag, which revealed that this interaction occurs at the expense of unfavorable entropy changes. Permissible binding required compensation by net enthalpic changes. Finally, the correlation between chemical composition of an epitope, the resultant affinity of the early primary humoral response, and its eventual influence on relative immunogenicity could be experimentally verified. This was achieved by examining the effect of various amino-terminal substitutions on immunogenicity of a, hitherto cryptic, amino-terminal determinant. Such experiments permitted delineation of a hierarchy of individual amino acid residues based on their influence; which correlated well with calculated Gibbs-free energy changes that individual residue side chains were expected to contribute in a binding interaction. Thus, maturation of a T-dependent humoral response is initiated by a step that is under thermodynamic control.

Inhibition of staphylococcal enterotoxin B-induced lymphocyte proliferation and tumor necrosis factor alpha secretion by MAb5, an anti-toxic shock syndrome toxin 1 monoclonal antibody

Toxic shock syndrome (TSS) is primarily caused by toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin B (SEB). These toxins belong to a family of pyrogenic toxin superantigens (PTSAgs) produced by Staphylococcus aureus and exhibit several shared biological properties, including the induction of massive cytokine release and Vbeta-specific T-cell proliferation. The crystal structures of most PTSAgs are now published, and they demonstrate a striking similarity in conformational architecture even though their primary protein sequences are different. Despite these structural and immunobiological similarities, no cross-reactivity between TSST-1 and other PTSAgs has been demonstrated in serological or neutralization assays. Our laboratory has developed a neutralizing murine anti-TSST-1 monoclonal antibody (MAb5) which displayed cross-reactivity with SEB by enzyme-linked immunosorbent assay. The aim of the present study was to evaluate whether MAb5 can also cross-neutralize SEB-induced superantigenic activities in vitro. MAb5 was found to partially inhibit SEB-induced T-cell mitogenesis (63%) and tumor necrosis factor alpha (TNF-alpha) secretion (70%) in human peripheral blood mononuclear cells (PBMC) in a dose-dependent manner, while an isotypic anti-TSST-1 monoclonal antibody showed no effect. Epitope mapping revealed that MAb5 bound to TSST-1 residues 47 to 56 ((47)FPSPYYSPAF(56)) and to SEB residues 83 to 92 ((83)DVFGANYYYQ(92)), sequences that located in different regions of these toxins and are structurally dissimilar. SEB peptide (83)DVFGANYYYQ(92) was synthesized and found to also inhibit SEB-induced mitogenesis and TNF-alpha secretion in human PBMC. Our results demonstrate for the first time that MAb5 binds to different epitopes on TSST-1 and SEB that appear functionally important in inducing T-cell mitogenesis and TNF-alpha secretion in vitro.

B-Cell epitope mapping of DNA topoisomerase I defines epitopes strongly associated with pulmonary fibrosis in systemic sclerosis

We hypothesized that B-cell epitope mapping of DNA Topoisomerase I (type-I topoisomerase, or Topo I) may define epitopes strongly associated with pulmonary interstitial fibrosis (PIF) in systemic sclerosis (SSc). B-cell epitope mapping of Topo I was performed using 63 20-mer peptides overlapping by eight residues and spanning the entire length of the Topo I sequence. These peptides, coupled to polystyrene pins, were tested for antibody binding by enzyme-linked immunosorbent assays (ELISAs) using immunoglobulin G fractions from anti-Topo I, anticentromere, anti-U3RNP-positive, and normal sera. Four major epitopes were recognized by anti-Topo I sera, but not from the control sera: WWEEERYPEGIKWKFLEHKG (205-224, epitope I), RIANFKIEPPGLFRGRGNHP (349-368, epitope II), PGHKWKEVRHDNKVTWLVSW (397-416, epitope III), and ELDGQEYVVEFDFLGKDSIR (517-536, epitope IV). Peptide-epitopes were then synthesized in their soluble forms and ELISA systems were developed. Epitopes II to IV are localized at highly exposed sites of the Topo I tertiary structure, whereas epitope I is localized at a less accessible site. In a cohort of 81 patients with SSc with clinical data on the evolution of their disease, patients with antibodies in their sera recognizing at least three of the four epitopes had 3.1 times (P = 0.02) the hazard of developing PIF compared with patients whose sera recognized no epitopes or only one or two of the four epitopes. The discrimination was much stronger than that achieved by the simple determination of Topo I antibodies by counterimmunoelectrophoresis and immunoblot (hazard ratio 1.7, P = 0.30) in the same patients. B-cell epitope mapping of the anti-Topo I response has identified four major epitopes which cumulatively show a strong association with the development of PIF in SSc.

Molecular characterization of P-29, a metacestode-specific component of Echinococcus granulosus which is immunologically related to, but distinct from, antigen 5

In this work the characterization of P-29, a novel 29 kDa antigen from Echinococcus granulosus is reported. E. granulosus was identified while looking for parasite antigens distinct from those present in hydatid cyst fluid. A monoclonal antibody (mAb 47H.PS) prepared against protoscolex components revealed that P-29 is localized to the tegument and rostellum of protoscoleces, and to the germinal layer of the cyst, but it is absent in hydatid cyst fluid or adult worm extracts. Several internal fragments of P-29 showed sequence identity to the amino acid sequence encoded by Eg6, a partial gene sequence reported to code for an epitope of antigen 5 (Ag5), one of the major diagnostic antigens of the parasite. We confirmed that Eg6 encodes a sub-fragment of P-29 by mapping the epitope of mAb 47H.PS, and isolating the full length P-29 cDNA. Since Eg6 had been, postulated to encode a fragment of Ag5, we specifically studied the relationship of P-29 and Ag5 by: (i) examining the cross-reactivity displayed by different mAbs; (ii) comparison of their peptide finger prints; and (iii) a comparative study of their diagnostic value. Our results prove unequivocally that P-29 and Ag5 are immunologically related, but different proteins, raising several questions on the current knowledge of Ag5.

Defining a novel domain of staphylococcal toxic shock syndrome toxin-1 critical for major histocompatibility complex class II binding, superantigenic activity, and lethality

Staphylococcal toxic shock syndrome toxin-1 (TSST-1) is implicated in the pathogenesis of superantigen-mediated shock. We previously identified TSST-1 residues G31/S32 to be important for major histocompatibility complex (MHC) class II binding, as well as superantigenic and lethal activities. However, the site-directed TSST-1 mutant toxin, G31R, could still induce mitogenesis and low-level TNFalpha secretion, suggesting that additional MHC class II binding sites other than G31/S32 may exist. In the current study, a TSST-1-neutralizing monoclonal antibody, MAb5, was found to inhibit TSST-1 binding to human peripheral blood mononuclear cells, neutralize TSST-1-induced mitogenesis and cytokine secretion, and protect against TSST-1-induced lethality in vivo. Epitope mapping revealed that MAb5 bound to TSST-1 residues 51-56 (T(51-56);51YYSPAF56). Peptide T(51-56) was synthesized and found to also inhibit TSST-1 binding to human monocytes as well as TSST-1-induced mitogenesis, cytokine secretion, and lethality in vivo. This T(51-56) epitope, located within the beta3/beta4 loop, and the previously identified G31/S32 epitope, within the beta1/beta2 loop of TSST-1, are separated within the primary sequence, but spatially juxtaposed to each other. Collectively, these findings suggest that a discontinuous epitope comprising of regions within both the beta1/beta2 and beta3/beta4 loops, are critical for MHC class II binding, and the consequent superantigenic and lethal activities of TSST-1.

Reduced immunogenicity of beta-lactoglobulin by conjugation with carboxymethyl dextran

We prepared two beta-lactoglobulin (beta-LG)-carboxymethyl dextran (CMD) conjugates (Conj. 10A and Conj. 10B) by using a water-soluble carbodiimide to decrease the immunogenicity of beta-LG. The molar ratios of beta-LG to CMD in the conjugates were 5:1 (Conj. 10A) and 2:1 (Conj. 10B). The beta-LG-CMD conjugates maintained the retinol-binding activity of native beta-LG. Intrinsic fluorescence study indicated that shielding of the surface of beta-LG by CMD occurred in each conjugate, which was eminent in Conj. 10B. A local conformational change around (125)Thr-(135)Lys (alpha-helix) in each conjugate was detected by ELISA with monoclonal antibodies. The denaturation temperature of beta-LG evaluated by differential scanning calorimetry was greatly enhanced in each conjugate. The anti-beta-LG antibody response was markedly reduced after immunization with the beta-LG-CMD conjugates in BALB/c, C57BL/6, and C3H/He mice. We determined the B cell epitopes of beta-LG and each conjugate recognized in these mice and found that the linear epitope profiles of the beta-LG-CMD conjugates were similar to those of beta-LG, while the antibody response for each epitope was dramatically reduced. The reduced immunogenicity of beta-LG was most marked in the case of Conj. 10B, which contained more CMD than Conj. 10A, and was effectively shielded by CMD. We concluded that masking of epitopes by CMD is responsible for the decreased immunogenicity of the beta-LG in these conjugates.

Cellular and subcellular immunolocalization of ClC-5 channel in mouse kidney: colocalization with H+-ATPase

To determine the immunolocalization of ClC-5 in the mouse kidney, we developed a ClC-5-specific rat monoclonal antibody. Immunoblotting demonstrated an 85-kDa band of ClC-5 in the kidney and ClC-5 transfected cells. Immunocytochemistry revealed significant labeling of ClC-5 in brush-border membrane and subapical intracellular vesicles of the proximal tubule. In addition, apical and cytoplasmic staining was observed in the type A intercalated cells in the cortical collecting duct. In contrast, the staining was minimal in the outer and inner medullary collecting ducts and the thick ascending limb. Western blotting of vesicles immunoisolated by the ClC-5 antibody showed the presence of H+-ATPase, strongly indicating that these two proteins were present in the same membranes. Double labeling with antibodies against ClC-5 and H+-ATPase and analysis by confocal images showed that ClC-5 and H+-ATPase colocalized in these ClC-5-positive cells. These findings suggest that ClC-5 might be involved in the endocytosis and/or the H+ secretion in the proximal tubule cells and the cortical collecting duct type A intercalated cells in mouse kidney.

Immunogenic and protective ability of the two developmental forms of Chlamydiae in a mouse model of infertility

To compare the ability of elementary bodies (EB) and reticulate bodies (RB) of the Chlamydia trachomatis mouse pneumonitis (MoPn) biovar to induce a protective immune response, two groups of BALB/c mice were inoculated and boosted twice, with UV-inactivated EB or RB in Freund's adjuvant. Two weeks after the last immunization mice were challenged with C. trachomatis in the ovarian bursa. Vaginal cultures collected for 6 weeks after the intrabursal challenge showed that mice inoculated with EB were significantly protected, while mice inoculated with RB were not. Six weeks after the genital challenge mice were mated. Mice immunized with EB showed significant protection as demonstrated by the number of animals which were fertile and the number of embryos present in the uterine horns. In contrast, no significant protection against infertility was observed in the mice immunized with RB.

pET-prof, a plasmid for high-level expression of recombinant peptides fused to a birch profilin-derived hexadecapeptide tag: a system for the detection and presentation of recombinant antigens

We have previously identified a birch pollen profilin hexadecapeptide (Bp36/51), which was recognized by a monoclonal antibody (moAb 4A6) with high affinity. Here, we report the construction of a T7 RNA polymerase-driven high-level plasmid expression system, pET-prof, capable of producing proteins and peptides containing the Bp36/51 birch profilin-derived peptide fused to their N-terminus. As examples, the cDNAs coding for two major timothy grass (Phleum pratense) pollen allergens, Phl p 2 and Phl p 6, as well as for an alder (Alnus glutinosa) pollen allergen, Aln g 4, were overexpressed in Escherichia coli as BP36/51-tagged proteins. All three recombinant allergens were readily detected in nitrocellulose-blotted E. coli extracts by the Bp36/51-specific moAb 4A6. We demonstrate comparable IgE recognition of Bp36/51-tagged and untagged recombinant allergens by immunoblotting. A sandwich ELISA was developed using plate-bound moAb 4A6 to immobilize and present Bp36/51-tagged recombinant allergens to IgE antibodies of allergic patients. Using immunoelectronmicroscopy, we demonstrate that even under harsh fixation conditions, tagged allergens can be localized simultaneously in situ by moAb 4A6 and allergen-specific antisera. We suggest the use of the pET-prof system for the high-level expression of Bp36/51-tagged polypeptides that can be rapidly detected in total protein extracts, immunolocalized in situ, immobilized and presented to other antigen-specific antibodies (e.g. IgE), even when they occur in minute concentrations.

F0 complex of the Escherichia coli ATP synthase. Not all monomers of the subunit c oligomer are involved in F1 interaction

The antigenic determinants of mAbs against subunit c of the Escherichia coli ATP synthase were mapped by ELISA using overlapping synthetic heptapeptides. All epitopes recognized are located in the hydrophilic loop region and are as follows: 31-LGGKFLE-37, 35-FLEGAAR-41, 36-LEGAAR-41 and 36-LEGAARQ-42. Binding studies with membrane vesicles of different orientation revealed that all mAbs bind to everted membrane vesicles independent of the presence or absence of the F1 part. Although the hydrophilic region of subunit c and particularly the highly conserved residues A40, R41, Q42 and P43 are known to interact with subunits gamma and epsilon of the F1 part, the mAb molecules have no effect on the function of F0. Furthermore, it could be demonstrated that the F1 part and the mAb molecule(s) are bound simultaneously to the F0 complex suggesting that not all c subunits are involved in F1 interaction. From the results obtained, it can be concluded that this interaction is fixed, which means that subunits gamma and epsilon do not switch between the c subunits during catalysis and furthermore, a complete rotation of the subunit c oligomer modified with mAb(s) along the stator of the F1F0 complex, proposed to be composed of at least subunits b and delta, seems to be unlikely.

Optimization of solid supports for combinatorial chemical synthesis

Until recently, resins were used primarily for peptide and oligonucleotide synthesis. Recent advances in combinatorial chemistry have fostered increased acceptance of resins as supports for the synthesis of small molecule libraries. The methodology for selecting a resin bead that is ideal for the solid phase synthesis of small molecules is described in this review. The process of manufacturing a typical resin, the UniSphere-200, is also explained. Furthermore, a new approach is proposed for the solid phase synthesis of analogs which are traditionally done in solution phase. This new procedure involves the use of building blocks attached to an activated resin. These building blocks are displaced by a functional group on the scaffold around which the analogs are built. Use of an excess of resin-linked building blocks drives the reaction to completion. Additionally, a newly developed, grafted surface solid support, is described. This support, the MicroTube, can be used for the synthesis of large numbers of discrete molecules by a patented directed sorting method.

Mapping of IgE binding regions in the major rat urinary protein, alpha 2u-globulin, using overlapping peptides

Exposure to laboratory animals poses a hazard for development of occupational allergy. Identification of antigenic determinants of allergenic proteins may be valuable for immunotherapeutic purposes. Overlapping peptides of the major allergen in rat urine, Rat n 1.02, corresponding to the protein alpha2u-globulin were synthesised on solid support and screened simultaneously to locate IgE binding linear epitopes using a simple modified ELISA procedure. Thirty-nine peptides were synthesised, each 8 amino acids long with 4 amino acids overlaps. Sera from fifteen rat-sensitized subjects were analyzed and as controls sera from 7 non-rat-sensitized individuals were used. In general low binding and a great individual variation between sera from rat allergic individuals were seen. Some peptides were more frequently recognized by IgE antibodies in sera from rat allergics. These peptides were mainly clustered towards the N-terminal and C-terminal parts of the protein. Taken together our data suggest the existence of linear IgE binding epitopes in the rat urine allergen, Rat n 1.02. However, the role of these sequences in the allergic reaction needs further investigation.

Deconstructing the antigenic profile of a protective epitope from measles virus fusion protein using overlapping peptides

Three different approaches of using overlapping peptides have been compared to analyse the fine specificity of the antibody response to a protective epitope from measles virus (MV) fusion protein, spanning residues 397-420. Anti-peptide antibodies raised in BALB/c, CBA and C57BL/6 mice were shown to react with the homologous peptide and the MV by ELISA. Results from indirect ELISA using 15mer peptides (overlapping by one residue) as solid phase antigens have shown that anti-peptide antibodies from CBA and C57BL/6 mice recognised the same B-cell epitope(s) located within the 398-414 region, whereas BALB/c mice predominantly recognised epitopes located within the 400-417 region. When the 15mer peptides were used as fluid phase antigens in an inhibition ELISA, peptide 405-419 was shown to be the most effective inhibitor in all three strains of mice. Analysis of serum samples by SPOTs ELISA has shown that the region 407-417 was predominantly recognised by BALB/c mice, whereas antibodies from C57BL/6 mice recognised the 408-420 region. No reactivity was observed with serum samples from CBA mice. Although the majority of the identified B-cell epitopes were shown to overlap by the three methods, the identified boundaries of these epitopes differed, suggesting that the size and the mode of peptide presentation affects their antigenicity.

B Cell Responses to a Peptide Epitope. VIII. Immune Complex-Mediated Regulation of Memory B Cell Generation Within Germinal Centers

Using an in vivo reconstitution assay, we examine here the role of immune complexes in both formation of germinal centers (GC) and processes that occur subsequently within. The presence of Ag, as immune complexes, was found not to constitute a limiting requirement for the initiation of GC formation. No detrimental effect either on numbers or sizes of the resulting GC was observed when Ag-containing immune complexes were omitted during reconstitution. Thus, both recruitment and proliferation of Ag-activated B cells within GC appear not to be limited by Ag concentrations. In contrast, the presence of immune complexes was observed to be obligatory for the generation of Ag-specific memory B cells. This optimally required immune complexes to be constituted by IgG-class Abs with epitope specificities that were homologous to those of the GC B cells. The GC reaction was also found to be characterized by an enhancement of Ab specificity for the homologous epitope. Although some improvement in specificity was noted in recall responses from immune complex-deficient GC, the presence of appropriate immune complexes served to further optimize the outcome. Here again, isotype and epitope-specificity of the Ab constituent in immune complexes proved to be important.

Regression and spreading of self-recognition during the development of autoimmune demyelinating disease

The autoimmune T cell repertoire in experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS) is characterized by CD4(+)T cells of the Th1 phenotype that recognize peptide determinants of central nervous system (CNS) myelin proteins in an MHC class II-restricted manner. Our recent studies and those performed by others have shown that progression to chronicity in EAE and MS is accompanied by a broadening of the T cell repertoire with time. This acquired neo-autoreactivity is commonly referred to as epitope spreading and is presumably the result of endogenous priming to new self-determinants during the CNS inflammation that accompanies disease onset and relapse. In the present study we extend our earlier observations by showing that disease progression in both EAE and MS is accompanied by two concurrent events, viz. (1) the spontaneous regression of the primary established autoimmune repertoire associated with disease onset, and (2) the emergence of the epitope spreading cascade associated with disease progression. Our data show that disease initiation and disease progression in both EAE and MS are typically associated with distinctly different autoimmune T cell repertoires. Our data support the view that the natural development of self-recognition during autoimmune disease may best be understood when considered in the temporal context of an 'epitope du jour' and 'moving target' perspective.

Peptide Ligands That Bind IgM Antibodies and Block Interaction with Antigen

We have selected a peptide-display phage library on IgM Abs and identified a panel of phage-expressing peptides that bind to IgM Abs in general, but not to Abs of other classes. A synthetic peptide corresponding to one of the displayed peptide sequences also binds to IgM Abs. The peptides bind to both soluble pentameric Abs and to monomeric cell-surface IgM. The phage-displayed and synthetic peptides inhibit the binding of IgM Abs to Ag. These peptides may create confounding artifacts when IgM Abs are used for epitope mapping studies. Nonetheless, the peptides may have both experimental and therapeutic utility.