Expression of Shiga toxin epitopes in E. coli immunological characterization

Synthetic oligodeoxynucleotides encoding for two peptides corresponding to residues 9-21 and 19-31 in the amino acid sequence of the B subunit of Shiga toxin were prepared and inserted into pTOZ plasmid, in phase with the lacZ gene. The resultant vectors were used for transfection of E. coli. The bacteria containing the recombinant DNA expressed the respective peptides in the form of fusion proteins with beta-galactosidase. The N-terminal region of the Shiga toxin B subunit, containing the two peptides, was previously identified as a relevant epitope of the toxin, leading to the induction of neutralizing antibodies. The present study demonstrates that the bacterial extracts containing the fusion proteins as the products of the recombinant vectors, when used for immunization of rabbits, elicited a humoral immune response which was specific toward the respective peptides. Furthermore, the antibodies cross-reacted with the intact Shiga toxin.     

Identification of two promiscuous T cell epitopes from tetanus toxin.

Tetanus toxoid-specific T cell clones were isolated from a human donor. To determine the T cell epitopes recognized by the clones, 30 peptides representing amphipathic alpha helical regions of the tetanus toxin were screened for ability to induce proliferation of the clones. Two T epitopes were identified. These occurred within peptides 12 and 21, and had the amino acid sequences NSVDDALINSTKIYSYFPSV and PGINGKAIHLVNNESSE, respectively. An unusual feature was that both peptides could be presented to their respective T cell clones by antigen-presenting cells of many HLA specificities. Further investigation of peptide 12 showed that the epitope was only seven amino acids in length and had a very hydrophobic sequence, namely YSYFPSV. The ability of the T cell epitope-containing peptides 12 and 21 to interact with many different HLA alleles means they may potentially be very useful as "universal carrier molecules" in synthetic vaccines.     

Neutralization of tetanus toxin by distinct monoclonal antibodies binding to multiple epitopes on the toxin molecule.

Fifty-seven hybridomas producing antibodies to tetanus toxoid or to the Ibc or B-IIb fragment of the toxin were isolated independently. Competitive inhibition studies demonstrated that monoclonal antibodies from mice immunized with the toxoid bound to at least 20 different epitopes on the toxoid molecule. Similar competitive binding studies revealed eight distinct epitopes on the B-IIb fragment and three to five epitopes on the Ibc fragment of the toxin. Neutralization of toxicity was effected by nine distinct monoclonal antibodies from hybridomas of toxoid-immunized mice and by one monoclonal antibody from B-IIb-immunized mice. Mixtures of two, three, and four different monoclonal antibodies in a variety of combinations exerted a synergistic effect of ca. 200-fold over that observed with individual monoclonal antibodies, indicating that efficient neutralization may involve the simultaneous binding of at least two antibody molecules to different specific regions of the toxin molecule. Only one toxoid-induced monoclonal antibody failed to bind to tetanus toxin. All neutralizing antibodies bound to epitopes on the heavy chain of tetanus toxin. Six of these were directed toward epitopes on the NH2-terminal half, whereas four bound to epitopes on the carboxy-terminal half of the heavy chain. Only one monoclonal antibody bound preferentially to the light chain, but two other monoclonal antibodies appeared to bind to both chains, indicating some homology between these two chains.     

Production and characterization of monoclonal antibodies to tetanus toxin

Monoclonal antibodies against tetanus toxin were produced to obtain highly specific antisera. Ten hybridoma cell lines producing monoclonal antibodies were derived from the fusion of rat myeloma cells and spleen cells from rats immunized with tetanus toxoid. Eight produced monoclonal antibodies specific for determinants on toxin and toxoid, whereas two were specific only for determinants on the toxoid. The antibodies produced by hybridomas were characterized by determination of the class of light and heavy chain components, epitope specificity, toxin neutralization, and subunit specificity. All of the antibodies contained kappa light chain, eight contained the gamma 1 heavy chain, and the remaining two contained the gamma 2a heavy chain. Five distinct epitopes were indicated by competition assay of paired monoclonal antibodies, and 4 of the 10 monoclonal antibodies neutralized the in vivo activity of tetanus toxin. The four neutralizing monoclonal antibodies and one other were specific for the C fragment of the heavy chain of the toxin molecule.     

The effect of tetanus toxin on in vitro synaptogenesis

Cultures of spinal cord neurons and cocultures of rat embryo neurons and muscle cells have been studied in the presence of tetanus toxin (TT) at a concentration of 40 micrograms/ml of medium. TT strongly stimulated neurite outgrowth, notably branching from the cell bodies. In addition it induced a marked, overall increase in acetylcholine receptor (AChR), but inhibited focalisation of AChR and acetylcholinesterase (AChE) at the synaptic sites. TT seems to act on neurite emergence, on the neuronal factor(s) controlling AChE and AChR concentrations, and on the factor(s) modulating degradation and/or synthesis of AChR.     

Protection of mice against tetanus toxin by combination of two human monoclonal antibodies recognizing distinct epitopes on the toxin molecule

Human B-lymphocytes were fused with the human lymphoblastoid B-cell line WI-L2-729 HF2. Hybridoma frequencies were in the range of 10(-5) when the mononuclear cells were (a) prestimulated with pokeweed mitogen (PWM), (b) fused with polyethyleneglycol (PEG), and (c) selected in a hypoxanthine-azaserine (HAza) containing medium. To generate monoclonal antibodies (MAb) specific for tetanus toxin (TToxin) human spleen cells were precultured with PWM plus tetanus toxoid (TToxoid) in two separate fusions. Two hybridomas were selected based on high binding activity using an enzyme-linked immunosorbent assay (ELISA) for TToxoid. Both hybridomas, cloned twice and designated anti-TT1 and anti-TT2, exhibited a near tetraploid karyotype and showed stable production of antibody (0.15 micrograms/ml) over several months. Using ELISA for fragments of TToxin and the immunoblotting technique, the two IgG1 monoclonal antibodies were found to bind to the heavy chain portion of the B-fragment (anti-TT1) and on the C-fragment (anti-TT2) of the toxin. When tested in an ELISA with TToxin the combination of anti-TT1 and anti-TT2 showed higher binding activity than either reagent alone. In an in vivo neutralization assay mice were completely protected against TToxin by the combination of the two antibodies while either antibody alone resulted only in a delay of death of the mice. These findings demonstrate that a cocktail of appropriate human monoclonal antibodies can be far superior to a single reagent when used in a therapeutic setting.     

苦荞过敏原TBa表位区段的表达及免疫活性分析

目的:确定苦荞过敏原(TBa)的主要表位区段。方法:以TBacDNA为模板,利用PCR方法,构建TBa的4个表位区段(E12、E3、E6、E36)的重组原核表达载体,转入大肠杆菌BL21(DE3)中诱导表达。经Ni2+-NTA亲和纯化后,SDS-PAGE分析。采用间接和竞争ELISA以及点杂交技术进行免疫活性测定。结果:获得了纯度较高的TBa重组表位蛋白(E12、E3、E6、E36),与先前获得表位E1、E2的免疫活性比较表明,重组表位蛋白与荞麦过敏症患者血清均有IgE结合活性,其中E1的活性最强。结论:E1可能是苦荞过敏蛋白TBa中最重要的抗原结合区域之一。     

Immunization of mice against tetanus with fragments of tetanus toxin synthesized in Escherichia coli.

Two recombinant plasmids, pTet11 and pTet18, which express nontoxic protein fragments of tetanus toxin in Escherichia coli, were constructed. pTet11 protein (86 kilodaltons) is a fusion between part of the E. coli trpE protein and 441 amino acids of tetanus fragment C, and pTet18 (63 kilodaltons) consists of part of fragment B and all of fragment C of tetanus toxin. The synthesis of these proteins was induced in E. coli cultures, and the proteins were partially purified. Mice were immunized with these proteins, and dose-dependent titers of anti-tetanus toxoid antibodies were obtained. The proteins were able to induce neutralizing antibodies in mice, as demonstrated by the ability of mice immunized with 1 microgram or more of protein to survive challenge with 10 50% lethal doses of tetanus toxin.     

Competition between tetanus toxoid and toxin

Experiments on albino mice showed that preliminary injection of tetanus toxoid increases the resistance of animals to tetanus toxin, as manifested by an increase in LD₅₀. The effect is enhanced by increasing the dose of toxoid or by giving it in fractional doses. The use of protagon and unpurified mitochondrial fraction, isolated from the brain, as receptor of tetanus toxin in the nerve tissue revealed competition for substrate between the tetanus toxoid and toxin. The results of these experiments confirm the writers' earlier hypothesis that the tetanus toxin molecule contains different functional groups responsible for binding the toxin with the receptor in brain tissue, for the pathogenic action of the toxin, and for the binding of the toxin with antitoxin.     

Production, characterization and applications of a tetanus toxin specific monoclonal antibody T-62

Tetanus neurotoxin (TeNT) represents a potent toxin that binds to its receptors on neurons and inhibits the release of neurotransmitters. Additionally, its fragments are used to transport pharmacological substances to neuronal cell bodies. The main objective of this study was the development of a suitable model system to study internalization of the TeNT. We have produced a monoclonal antibody (MoAb) specific for TeNT by hybridoma technology, after immunization of BALB/c mice with tetanus toxoid, and have named it T-62. The immunochemical characteristics of MoAb T-62 were tested using ELISA, PAGE and immunoblotting. Finally, we have used an immunohistochemical method to detect specific binding of MoAb T-62 to TeNT bound to PC 12 cells. Our results show that MoAb T-62 is highly specific for TeNT, even when it is bound to its receptor, and that it could be of considerable importance in studies regarding fundamental research on TeNT receptors, intracellular transport of TeNT, as well as retrograde transport of pharmaceutical substances and non-invasive delivery of polypeptides through the blood brain barrier. In addition, MoAb T-62 is an invaluable tool in TeNT vaccine production as it can be used for the detection of reverse toxicity, which could drastically reduce the need to use animals in these experiments.     

Toxin-neutralizing effect of antibody against subtilisin-digested tetanus toxin.

A form of systemic tetanus with atypical symptoms was observed in mice injected in the left thigh with a mixture of tetanus toxin and antibody produced in guinea pigs against a fragment of toxin obtained from a subtilisin digest of the crystallized toxin. The mice did not show typical symptoms of the local tetanus such as convulsions or spastic paralysis of the injected limb.     

Cloning and expression of functional fragment C of tetanus toxin.

A segment of Clostridium tetani DNA corresponding to fragment C of tetanus toxin was amplified by using the polymerase chain reaction. This fragment was cloned into expression vector pTTQ8, under the control of the tac promoter. Expression of this plasmid in Escherichia coli resulted in the production of a protein consisting of 8 amino acids of the vector fused to the C-terminal 460 amino acids of tetanus toxin. This protein (rFragment C) was recognized by an antipeptide antibody specific for fragment C in an enzyme-linked immunosorbent assay and on immunoblots. rFragment C could be purified significantly in one step by immunoaffinity chromatography. Immunization of mice with rFragment C resulted in the production of antibodies that were able to protect the mice against a challenge with tetanus toxin. rFragment C bound to ganglioside GT1b and to neuronal cells in a manner indistinguishable from that of fragment C obtained by papain cleavage of tetanus toxin. For many applications, rFragment C appears to be a suitable alternative to tetanus toxin or toxin-derived fragment C.     

破伤风毒素C片段的基因克隆、表达、纯化及免疫原性分析

目的　对破伤风毒素C片段进行基因克隆、重组表达、蛋白纯化和免疫原性分析。方法　应用PCR技术直接从破伤风梭状芽孢杆菌的质粒DNA中扩增出 1370bp的破伤风毒素C片段(简称TTC)基因 ,将此基因片段插入到表达载体pET 2 2b( )中 ,并在大肠杆菌BL2 1(DE3)中表达。用阴离子交换层析和金属离子螯合亲和层析方法进行蛋白纯化后 ,参照《中国生物制品规程 2 0 0 0年版》的免疫攻击实验方法测定其效价。结果　经SDS PAGE分析 ,重组蛋白的表达量占菌体总蛋白的15 %。免疫印迹实验证实该重组蛋白是破伤风毒素C片段抗原。纯化得到纯度为 96 .5 %的重组蛋白 ,纯化回收率达 4 0 %。免疫攻击实验测定其效价为 18.70 6IU/mg,ED50 为 2 0 μg。经加强免疫 ,1μg免疫剂量即能产生足够的抗体保护动物免受破伤风毒素的攻击。结论　所获得的重组蛋白具有良好的免疫原性 ,为开发基因工程疫苗奠定了基础     

Monoclonal antibodies against tetanus toxin and toxoid

Monoclonal antibodies against tetanus toxin and its toxoid were produced by immunizing mice with toxoid or toxin. They were measured by an enzyme-linked immunosorbent assay (ELISA), by a toxin neutralization test in mice (in vivo prevention test), and by their ability to prevent binding of¹²⁵I-toxin to brain membranes or gangliosides (in vitro prevention test). Six monoclonal antibodies obtained by immunization with toxoid (anti-toxoid 1–6) were investigated in more detail. They belonged to IgG class 1. Three of them (anti-toxoid 1, 2 and 3) recognized both toxoid and toxin as well as fragment B and the light chain of toxin, but not fragment C. Two other antibodies (anti-toxoid 4 and 5) were directed against toxoid only. Neither of them prevented toxin action in vitro or in vivo. Anti-toxoid 6 recognized toxin, toxoid and fragment C, but not light chain, and prevented toxin action in vitro and in vivo. Immunization against toxin was initiated with a toxin-antitoxin complex and boosted with toxin. We studied six antibodies in more detail, all of IgG type 2. Their K_D against¹²⁵I-tetanus toxin varied from 10^–9 to 10^–10 M. Anti-toxin 2 recognized toxin, toxoid, light chain and fragment B, but not fragment C. The others reacted with toxin, toxoid and fragment C, but not with light chain or fragment B. All of them prevented toxin action in vitro and in vivo. As calculated from the maximal extinction achieved in the ELISA, tetanus toxin combined with a maximum of two different antibody molecules from our set. Gel filtration data indicate that tetanus toxin reacts with monoclonal antibodies one by one. Compared with polyclonal antiserum, monoclonal antibodies yield flatter slopes in both in vitro and in vivo prevention tests. Thus, they cannot substitute for the polyclonal antibodies in clinical situations, and cannot be calibrated in international units.This communication contains parts of the M.D. thesis of K.G. and C.V.     

Naturally acquired immunity to tetanus toxin in an isolated community.

Literature on natural immunity to tetanus is scarce. We examined antitetanus antibody levels with the enzyme-linked immunosorbent assay in 200 people living in an isolated community and clarified the influence of age and sex on immunity. In 197 subjects, antitoxin antibodies were measured. No sex differences were noted, and 30% had protective levels (above 0.01 IU/ml). The percentage of those considered protected was age dependent.     

Central nervous changes in experimental tetanus and the mode of action of the tetanus toxin

Summary Spread of the excitation along the spinal cord was studied in white rats in ascending general tetanus. The special feature of this phenomenon is that the excitation becomes generalized completely (in some cases only) on stimulating the limb into whichthe lethal dose of toxin had been injected. The clinical effect takes the form of a convulsive attack with characteristic features of spasticity. High division of the spinal cord had no appreciable effect on the phenomenon.The same effect was observed on stimulating the central ends of the cut dorsal roots on the side of the toxin injection.Synchronization of the bursts of excitation occurred in remote groups of motor neurons located in different segements of the cord.The part played by the various types of internuncial and motor neurons of the spinal cord is discussed. It is suggested that neurons functioning as dispatching stations may play a special part.Presented by Active Member of the AMN SSSR V. N. Chernigovskii     

Central nervous changes in experimental tetanus and the mode of action of the tetanus toxin

Summary Experiments were performed on white rats, affected by ascending general tetanus. The general convulsions were provoked with great ease by applying stimulation to the extremity into which a lethal dose of tetanus toxin had been introduced. This phenomenon was not connected with increased excitability of exter- ad proprioceptors and cannot be explained by the functional changes of the synapses, which have an inhibiting effect on the motor cells of the anterior horns of the spinal cord. The data which were obtained allow us to conclude that the effect of tetanus toxin is not limited to the area of motoneurons but that it, likewise, spreads to the synaptic formations of other portions of the multineuronic reflex arcs.Presented by Active Member of the Acad. Med. Sci. USSR, V. N. Chernigovsky