Application of an in vitro endopeptidase assay for detection of residual toxin activity in tetanus toxoids

Tetanus vaccine is composed of chemically denatured tetanus toxin (TeNT), thus safety testing requires confirmation of freedom from residual and reversible toxicity. Currently, TeNT activity is estimated using in vivo assay models. Information that TeNT acts by selectively inactivating protein leading to the blocking of release of neurotransmitters has provided the opportunity to develop in vitro biochemical assay for toxin activity. In this study we describe development and use of an in vitro endopeptidase assay for detection of TeNT activity in toxoid vaccine formulations.

Bacterial spores as vaccine vehicles

For the first time, bacterial spores have been evaluated as vaccine vehicles. Bacillus subtilis spores displaying the tetanus toxin fragment C (TTFC) antigen were used for oral and intranasal immunization and were shown to generate mucosal and systemic responses in a murine model. TTFC-specific immunoglobulin G titers in serum (determined by enzyme-linked immunosorbent assay) reached significant levels 33 days after oral dosing, while responses against the spore coat proteins were relatively low. Tetanus antitoxin levels were sufficient to protect against an otherwise lethal challenge of tetanus toxin (20 50% lethal doses). The robustness and long-term storage properties of bacterial spores, coupled with simplified genetic manipulation and cost-effective manufacturing, make them particularly attractive vehicles for oral and intranasal vaccination.

Zonula occludens toxin acts as an adjuvant through different mucosal routes and induces protective immune responses

Zonula occludens toxin (Zot) is produced by Vibrio cholerae and has the ability to increase mucosal permeability by reversibly affecting the structure of tight junctions. Because of this property, Zot is a promising tool for mucosal drug and antigen (Ag) delivery. Here we show that Zot acts as a mucosal adjuvant to induce long-lasting and protective immune responses upon mucosal immunization of mice. Indeed, the intranasal delivery of ovalbumin with two different recombinant forms of Zot in BALB/c mice resulted in high Ag-specific serum immunoglobulin G titers that were maintained over the course of a year. Moreover, His-Zot induced humoral and cell-mediated responses to tetanus toxoid in C57BL/6 mice and protected the mice against a systemic challenge with tetanus toxin. In addition, we found that Zot also acts as an adjuvant through the intrarectal route and that it has very low immunogenicity compared to the adjuvant Escherichia coli heat-labile enterotoxin. Finally, by using an octapeptide representing the putative binding site of Zot and of its endogenous analogue zonulin, we provide evidence that Zot may bind a mucosal receptor on nasal mucosa and may mimic an endogenous regulator of tight junctions to deliver Ags in the submucosa. In conclusion, Zot is a novel and effective mucosal adjuvant that may be useful for the development of mucosal vaccines.

Two carbohydrate binding sites in the H(CC)-domain of tetanus neurotoxin are required for toxicity

Tetanus neurotoxin binds via its carboxyl-terminal H(C)-fragment selectively to neurons mediated by complex gangliosides. We investigated the lactose and sialic acid binding pockets of four recently discovered potential binding sites employing site-directed mutagenesis. Substitution of residues in the lactose binding pocket drastically decreased the binding of the H(C)-fragment to immobilized gangliosides and to rat brain synaptosomes as well as the inhibitory action of recombinant full length tetanus neurotoxin on exocytosis at peripheral nerves. The conserved motif of S(1287)XWY(1290) em leader G(1300) assisted by N1219, D1222, and H1271 within the lactose binding site comprises a typical sugar binding pocket, as also present, for example, in cholera toxin. Replacement of the main residue of the sialic acid binding site, R1226, again caused a dramatic decline in binding affinity and neurotoxicity. Since the structural integrity of the H(C)-fragment mutants was verified by circular dichroism and fluorescence spectroscopy, these data provide the first biochemical evidence that two carbohydrate interaction sites participate in the binding and uptake process of tetanus neurotoxin. The simultaneous binding of one ganglioside molecule to each of the two binding sites was demonstrated by mass spectroscopy studies, whereas ganglioside-mediated linkage of native tetanus neurotoxin molecules was ruled out by size exclusion chromatography. Hence, a subsequent displacement of one ganglioside by a glycoprotein receptor is discussed.

The role of cellular secretion in autism spectrum disorders: a unifying hypothesis

This paper outlines the possibility that disruption of cell-to-cell biochemical signaling activates a cascade of events resulting in a diverse spectrum of behavioral and biological symptoms associated with autism spectrum disorders.

A mechanism of the thearubigin fraction of black tea (Camellia sinensis) extract protecting against the effect of tetanus toxin

The aim of the present study was to elucidate the mechanism of the protective effect of black tea extract's thearubigin fraction against the action of tetanus toxin. The effects of thearubigin fraction extracted from a black tea infusion were examined for neuromuscular blocking action on tetanus toxin in mouse phrenic nerve-diaphragm preparations and on the binding of this toxin to the synaptosomal membrane preparations of rat cerebral cortices. The interaction between tetanus toxin and thearubigin fraction was also investigated. Tetanus toxin (4 micrograms/ml) abolished indirect twitches in mouse phrenic nerve-diaphragm preparations within 150 min. Thearubigin fraction mixed with tetanus toxin blocked the inhibitory effect of the toxin. Mixing iodinated toxin with thearubigin fraction inhibited the specific binding of [125I]tetanus toxin to the synaptosomal membrane preparation. The effects of thearubigin fraction were dose-dependent. The elution profile of [125I]tetanus toxin on Sephadex G-50 column chromatography was different from that of toxin mixed with thearubigin fraction. These findings indicate that thearubigin fraction protects against the action of tetanus toxin by binding with the toxin.

Protection against tetanus toxin after intragastric administration of two recombinant lactic acid bacteria: impact of strain viability and in vivo persistence

Non-pathogenic lactic acid bacteria (LAB) are attractive as live carriers to deliver protective antigens to the mucosal immune system. Both persisting and non-persisting strains of lactic acid bacteria have been evaluated and seem to work equally well by the systemic and nasal routes of administration. However, it is not known if persistence and viability of the strain play a critical role when immunizing by the oral route. To address this question, recombinant LAB strains, able to persist (Lactobacillus plantarum NCIMB8826/pMEC127) or not (Lactococcus lactis MG1363/pMEC46) in the gastro-intestinal tract of mice and producing equivalent amounts of the tetanus toxin fragment C (TTFC) were compared to each other. A very strong ELISA TTFC-specific and protective humoral response was elicited by either live or UV-inactivated recombinant Lb. plantarum strains. In a similar protocol, recombinant Lc. lactis seemed to be somewhat less efficient than the former host. It is thus tempting to propose that the difference in the capacity of the bacterial vector to persist in the gastro-intestinal tract impacts on its immunogenicity and on the level of protection it may induce. Protection was slightly superior after administration of live strains.

A comparison of the efficacy of carbamazepine and the novel anti-epileptic drug levetiracetam in the tetanus toxin model of focal complex partial epilepsy

1. The tetanus toxin seizure model, which is associated with spontaneous and intermittent generalized and non-generalized seizures, is considered to reflect human complex partial epilepsy. The purpose of the present study was to investigate and compare the anticonvulsant effects of carbamazepine with that of levetiracetam, a new anti-epileptic drug in this model. 2. One microl of tetanus toxin solution (containing 12 mLD(50) microl(-1) of tetanus toxin) was placed stereotactically into the rat left hippocampus resulting in generalized and non-generalized seizures. 3. Carbamazepine (4 mg kg(-1) h(-1)) and levetiracetam (8 and 16 mg kg(-1) h(-1)) were administered during a 7 day period via an osmotic minipump which was placed in the peritoneal cavity. Carbamazepine (4 mg kg(-1) h(-1)) exhibited no significant anticonvulsant effect, compared to control, when the entire 7 day study period was evaluated but the reduction in generalized seizures was greater (35.5%) than that for non-generalized seizures (12.6%). However, during the first 2 days of carbamazepine administration a significant reduction in both generalized seizure frequency (90%) and duration (25%) was observed. Non-generalized seizures were unaffected. This time-dependent anticonvulsant effect exactly paralleled the central (CSF) and peripheral (serum) kinetics of carbamazepine in that steady-state concentrations declined over time, with the highest concentrations achieved during the first 2 days. Also there was a significant 27.3% reduction in duration of generalized seizures during the 7 day study period (P=0.0001). 4. Levetiracetam administration (8 and 16 mg kg(-1) h(-1)) was associated with a dose-dependent reduction in the frequency of both generalized (39 v 57%) and non-generalized (36 v 41%) seizures. However, seizure suppression was more substantial for generalized seizures. Also a significant dose-dependent reduction in overall generalized seizure duration was observed. 5. These data provide experimental evidence for the clinical efficacy of levetiracetam for the management of patients with complex partial seizures. Furthermore, levetiracetam probably does not act by preventing ictogenesis per se but acts to reduce seizure severity and seizure generalization.

Characteristics and potency of an acellular pertussis vaccine composed of pertussis toxin, filamentous hemagglutinin, and pertactin

In an attempt to develop a safer pertussis vaccine, we successfully purified 3 pertussis protective antigens-pertussis toxin, filamentous hemagglutinin, and a 69-kDa outer membrane protein (also named pertactin), from Bordetella pertussis strain ATCC 9340. The toxicity of pertussis toxin could be effectively reduced by the treatment with formaldehyde 0.07% while preserving of a high degree of immunogenicity. By mixing purified pertussis antigens with diphtheria and tetanus toxoids (DT), we have formulated a DT acellular pertussis (DTaP) vaccine. Toxicity studies on body-weight gain in mouse, histamine sensitization, lymphocyte promoting, and Chinese hamster ovary cell clustering tests suggested that this DTaP vaccine is safer than a whole cell vaccine produced in France (DTP[F]). The formulated vaccine elicited high levels of anti-pertussis toxin antibodies in both mice and monkeys. In mice, a 2-fold neutralization of anti-pertussis toxin antibodies was produced by DTaP compared with DTP(F) vaccine and an acellular vaccine manufactured in Japan (DTaP[J]). More importantly, in intracerebral challenge assay in mouse, this vaccine also provided a better protection than DTaP(J).

Quality control of diphtheria tetanus acellular pertussis combined (DTaP) vaccines in Japan

Diphtheria tetanus acellular pertussis combined (DTaP) vaccines have been successfully used in Japan by controlling their potencies and toxicities with animal models. In accordance with the recent practical introduction of DTaP vaccines of various formulations, a question has been raised in other nations as to the efficacy of a quality control system based on animal tests and standard preparations. The World Health Organization issued its guidelines on the production and quality control of acellular pertussis vaccines in 1998 along with the concept of quality control by ensuring that production lots were consistent with clinical trial lots, rather than by comparing them with standard preparations in traditional laboratory tests. However, because it is not feasible to evaluate the combined use of vaccines from different manufacturers in a clinical study, the alternative trend of quality control may give rise to a difficulty in rationalizing the practical immunizations to use vaccines of different brands in a mixed consequence. A standardized national regulation system to ensure the equivalence of approved products would be essential for such an immunization practice. The success of the Japanese DTaP vaccination suggests the possibility of an effective quality control of DTaP vaccines by means of standardized test systems.

Recombinant forms of tetanus toxin engineered for examining and exploiting neuronal trafficking pathways

Tetanus toxin is a fascinating, multifunctional protein that binds to peripheral neurons, undergoes retrograde transport and trans-synaptic transfer to central inhibitory neurons where it blocks transmitter release, thereby, causing spastic paralysis. As a pre-requisite for exploiting its unique trafficking properties, a novel recombinant single chain was expressed at a high level in Escherichia coli as a soluble, easily purifiable protein. It could be activated with enterokinase to produce a dichain that matched native toxin in terms of proteolytic and neuroinhibitory activities, as well as induction of spastic paralysis in mice. Importantly, nicking was not essential for protease activity. Substitution of Glu(234) by Ala created a protease-deficient atoxic form, which blocked the neuroparalytic action of tetanus toxin in vitro, with equal potency to its heavy chain; but, the mutant proved >30-fold more potent in preventing tetanus in mice. This observation unveils differences between the intoxication processes resulting from retrograde transport of toxin in vivo and its local uptake into peripheral or central nerves in vitro, dispelling a popularly held belief that the heavy chain is the sole determinant for efficient trafficking. Thus, this innocuous mutant may be a useful vehicle, superior to the heavy chain, for drug delivery to central neurons.

Mucosal immune responses and protection against tetanus toxin after intranasal immunization with recombinant Lactobacillus plantarum

The use of live microorganisms as an antigen delivery system is an effective means to elicit local immune responses and thus represents a promising strategy for mucosal vaccination. In this respect, lactic acid bacteria represent an original and attractive approach, as they are safe organisms that are used as food starters and probiotics. To determine whether an immune response could be elicited by intranasal delivery of recombinant lactobacilli, a Lactobacillus plantarum strain of human origin (NCIMB8826) was selected as the expression host. Cytoplasmic production of the 47-kDa fragment C of tetanus toxin (TTFC) was achieved at different levels depending on the plasmid construct. All recombinant strains proved to be immunogenic by the intranasal route in mice and able to elicit very high systemic immunoglobulin G (IgG1, IgG2b, and IgG2a) responses which correlated to the antigen dose. No significant differences in enzyme-linked immunosorbent assay IgG titers were observed when mice were immunized with live or mitomycin C-treated recombinant lactobacilli. Nevertheless, protection against the lethal effect of tetanus toxin was obtained only with the strains producing the highest dose of antigen and was greater following immunization with live bacteria. Significant TTFC-specific mucosal IgA responses were measured in bronchoalveolar lavage fluids, and antigen-specific T-cell responses were detected in cervical lymph nodes, both responses being higher in mice receiving a double dose of bacteria (at a 24-h interval) at each administration. These results demonstrate that recombinant lactobacilli can induce specific humoral (protective) and mucosal antibodies and cellular immune response against protective antigens upon nasal administration.

Immunization with recombinant Streptococcus gordonii expressing tetanus toxin fragment C confers protection from lethal challenge in mice

Tetanus toxin fragment C (TTFC) was expressed on the surface of the vaccine vector Streptococcus gordonii, a Gram-positive commensal bacterium of the human oral cavity. The immunogenicity of recombinant S. gordonii expressing TTFC was assayed in mice immunized by the parenteral and mucosal routes. High serum TTFC-specific IgG responses were induced in both BALB/c and C57BL/6 mice immunized subcutaneously. A total of 82% of vaccinated BALB/c mice were protected from the lethal challenge with 50 LD(50) of tetanus toxin (TT) and a direct correlation between the serum TTFC-specific IgG concentration and survival time of unprotected animals was observed. Intranasal immunization of BALB/c mice was also effective in inducing TTFC-specific serum IgG and local IgA in lung washes. Furthermore, 38% of animals immunized intranasally were protected from the lethal challenge with 10 LD(50) of TT while all control animals died within 24 h. Analysis of the serum IgG subclasses showed that the IgG1 subclass was predominant after parenteral immunization in BALB/c mice (IgG1/IgG2a ratio congruent with6) while following mucosal immunization a mixed IgG1 and IgG2a pattern (IgG1/IgG2a ratio congruent with1) was observed. These data show that TTFC expressed on the surface of S. gordonii is immunogenic by the subcutaneous and mucosal routes and the immune response induced is capable of conferring protection from the lethal challenge with TT.

Novel use of anaerobically induced promoter, dmsA, for controlled expression of fragment C of tetanus toxin in live attenuated Salmonella enterica serovar Typhi strain CVD 908-htrA

The anaerobically induced promoter dmsA (PdmsA) was adapted to optimize in vivo expression of foreign antigens in attenuated Salmonella enterica serovar Typhi live vector vaccines CVD 908-htrA. PdmsA from Escherichia coli and two derivatives, PdmsA2 and PdmsA3 were cloned into a plasmid driving the expression of a gene encoding tetanus toxin fragment C. Expression of fragment C varied from a low level induced by pTETdmsA, to moderate and high levels induced, respectively, by pTETdmsA2 and pTETdmsA3. Mice were immunized intranasally with CVD 908-htrA harboring pTETdmsA2 or pTETdmsA3, and the serum antitoxin response was compared to that elicited by CVD 908-htrA(pTETnir15) (Pnir15 is a benchmark anaerobically activated promoter). S. Typhi carrying pTETdmsA2 elicited modest tetanus antitoxin titers while S. Typhi harboring pTETdmsA3 generated elevated titers (GMT=55384) that were higher than elicited by pTETnir15 (GMT=4354) (P=0.007). Mice immunized with CVD 908-htrA carrying pTETdmsA3 and pTETnir15 survived tetanus toxin challenge. P(dmsA) derivatives are attractive promoters for in vivo expression of foreign genes in attenuated live vector vaccines.

Tetanus and botulinum neurotoxins: turning bad guys into good by research

The neuroparalytic syndromes of tetanus and botulism are caused by neurotoxins produced by bacteria of the genus Clostridium. They are 150 kDa proteins consisting of three-domains, endowed with different functions: neurospecific binding, membrane translocation and specific proteolysis of three key components of the neuroexocytosis apparatus. After binding to the presynaptic membrane of motoneurons, tetanus neurotoxin (TeNT) is internalized and transported retroaxonally to the spinal cord, where it blocks neurotransmitter release from spinal inhibitory interneurons. In contrast, the seven botulinum neurotoxins (BoNT) act at the periphery and inhibit acetylcholine release from peripheral cholinergic nerve terminals. TeNT and BoNT-B, -D, -F and -G cleave specifically at single but different peptide bonds, VAMP/synaptobrevin, a membrane protein of small synaptic vesicles. BoNT types -A, -C and -E cleave SNAP-25 at different sites within the COOH-terminus, whereas BoNT-C also cleaves syntaxin. BoNTs are increasingly used in medicine for the treatment of human diseases characterized by hyperfunction of cholinergic terminals.

Recovery from 6 weeks of repeated strain injury to rat soleus muscles

Recovery from chronic strain injury (50 strains daily, five times weekly for 6 weeks to hyperactive soleus muscles) was followed for 3 months in female rats after cessation of chronic hyperactivity induced by pretreatment of the plantar flexor muscles with tetanus toxin. After 6 weeks of repeated strains, muscle mass decreased by 62%, myofiber areas were reduced by 87%, and noncontractile tissue expanded dramatically by 222%. Collagen content increased by almost ninefold (control 40 +/- 3 microg/mg, chronic injury 392 +/- 53 microg/mg), whereas the molar ratio of collagen (pyridinoline) crosslinks to collagen remained the same (control 0.20 +/- 0.01, chronic injury 0.16 +/- 0.01). After 3 months of ambulation, muscle mass returned to normal but myofiber areas remained smaller by 21%, noncontractile tissue was still markedly elevated by 18% with increased collagen content (107 +/- 15 microg/mg), and the molar ratio of crosslinks to collagen increased by 75% during recovery. Thus, rat soleus muscles recovered very slowly and incompletely from chronic strain injuries that produced muscle fibrosis, highlighting the necessity of devising preventative strategies for repeated strain injuries.

Acid secretion of parietal cells is paralleled by a redistribution of NSF and alpha, beta-SNAPs and inhibited by tetanus toxin

Stimulation of parietal cells causes fusion of intracellular tubulovesicles with the canalicular plasma membrane thereby increasing the apical membrane area up to tenfold. The presence of the SNARE proteins synaptobrevin, syntaxin1, and SNAP25 in parietal cells and their intracellular redistribution after stimulation suggest a SNARE-mediated mechanism. Here we show that NSF and alpha, beta-SNAPs which are involved in the dissociation of the SNARE complex in neurons also occur in parietal cells exhibiting subcellular distributions similar to the ones obtained for SNARE proteins and for the H+, K(+)-ATPase. More importantly proteolytic cleavage of synaptobrevin by tetanus neurotoxin completely inhibits the cAMP-dependent increase of acid secretion further supporting the crucial role SNARE proteins play in parietal cells.

Protective antigen-mediated antibody response against a heterologous protein produced in vivo by Bacillus anthracis

Bacillus anthracis secretes a lethal toxin composed of two proteins, the lethal factor (LF) and the protective antigen (PA), which interact within the host or in vitro at the surfaces of eukaryotic cells. Immunization with attenuated B. anthracis strains induces an antibody response against PA and LF. The LF-specific response is potentiated by the binding of LF to PA. In this study, we investigated the capacity of PA to increase the antibody response against a foreign antigen. We constructed a chimeric gene encoding the PA-binding part of LF (LF254) fused to the C fragment of tetanus toxin (ToxC). The construct was introduced by allelic exchange into the locus encoding LF. Two recombinant B. anthracis strains secreting the hybrid protein LF254-ToxC were generated, one in a PA-producing background and the other in a PA-deficient background. Mice were immunized with spores of the strains, and the humoral response and protection against tetanus toxin were assessed. The B. anthracis strain producing both PA and LF254-ToxC induced significantly higher antibody titers and provided better protection against a lethal challenge with tetanus toxin than did its PA-deficient counterpart. Thus, PA is able to potentiate protective immunity against a heterologous antigen, demonstrating the potential of B. anthracis recombinant strains for use as live vaccine vehicles.

Tetanus toxin-mediated cleavage of cellubrevin inhibits proton secretion in the male reproductive tract

Our laboratory has previously shown that the vacuolar H(+)-ATPase, located in a subpopulation of specialized cells establishes a luminal acidic environment in the epididymis and proximal part of the vas deferens (Breton S, Smith PJS, Lui B, and Brown D. Nat Med 2: 470-472, 1996). Low luminal pH is critical for sperm maturation and maintenance of sperm in a quiescent state during storage in these organs. In the present study we examined the regulation of proton secretion in the epididymis and vas deferens. In vivo microtubule disruption by colchicine induced an almost complete loss of H(+)-ATPase apical polarity. Endocytotic vesicles, visualized by Texas red-dextran internalization, contain H(+)-ATPase, indicating active endocytosis of the pump. Cellubrevin, an analog of the vesicle soluble N-ethyl malemide-sensitive factor attachment protein (SNAP) receptor (v-SNARE) synaptobrevin, is highly enriched in H(+)-ATPase-rich cells of the epididymis and vas deferens, and tetanus toxin treatment markedly inhibited bafilomycin-sensitive proton secretion by 64.3+/-9.0% in the proximal vas deferens. Western blotting showed effective cleavage of cellubrevin by tetanus toxin in intact vas deferens, demonstrating that the toxin gained access to cellubrevin. These results suggest that H(+)-ATPase is actively endocytosed and exocytosed in proton-secreting cells of the epididymis and vas deferens and that net proton secretion requires the participation of the v-SNARE cellubrevin.

RPD3-type histone deacetylases in maize embryos

Posttranslational core histone acetylation is established and maintained by histone acetyltransferases and deacetylases. Both have been identified as important transcriptional regulators in various eukaryotic systems. In contrast to nonplant systems where only RPD3-related histone deacetylases (HD) have been characterized so far, maize embryos contain three unrelated families of deacetylases (HD1A, HD1B, and HD2). Purification, cDNA cloning, and immunological studies identified the two maize histone deacetylase HD1B forms as close homologues of the RPD3-type deacetylase HDAC1. Unlike the other maize deacetylases, HD1A and nucleolar HD2, HD1B copurified as a complex with a protein related to the retinoblastoma-associated protein, Rbap46. Two HD1B mRNA species could be detected on RNA blots, encoding proteins of 58 kDa (HD1B-I) and 51 kDa (HD1B-II). HD1B-I (zmRpd3) represents the major enzyme form as judged from RNA and immunoblots. Levels of expression of HD1B-I and -II mRNA differ during early embryo germination; HD1B-I mRNA and protein are present during the entire germination pathway, even in the quiescent embryo, whereas HD1B-II expression starts when meristematic cells enter S-phase of the cell cycle. In line with previous results, HD1B exists as soluble and chromatin-bound enzyme forms. In vivo treatment of meristematic tissue with the deacetylase inhibitor HC toxin does not affect the expression of the three maize histone deacetylases, whereas it causes downregulation of histone acetyltransferase B.

Chronic toxicity and reversibility of antifertility effect of immunization against gonadotropin-releasing hormone in male rats and rabbits

The chronic systemic toxicity of immunization with gonadotropin-releasing hormone, conjugated to tetanus toxoid (GnRH-TT), was investigated in male rats and rabbits in order to start Phase I clinical trials. Groups of rats and rabbits were immunized with GnRH-TT dissolved in aqueous adjuvant. The antigen was administered at weeks 0, 4, and 8, followed by boosters to maintain high antibody titers. At termination (8-9 months after first immunization), twenty rats and ten rabbits exhibiting the highest mean anti-GnRH titers and all the controls were selected for complete toxicological evaluation. In the rat study, a castrated control group was included for comparison with the immunized group. The hematological and serum chemistry parameters of immunized rats and rabbits were not affected in a significant manner. Most of the changes in serum chemistry of immunized rats were also found in castrated rats, indicating that the changes are most likely due to the withdrawal of androgenic support. The weights of the testes, epididymides, and sex accessory glands were lower in all immunized animals. There was significant atrophy of the germinal epithelium, which, however, sustained a population of Sertoli cells, spermatogonia, and pachytene spermatocytes. Other morphological changes in the prostate, seminal vesicles, pituitary, and mammary gland reflected the effect of androgen withdrawal. The decrease in the weight of liver, kidney, and heart seen in the immunized rats was also present in castrated rats and was not associated with any histopathological changes. The reversibility of immunization-induced infertility was investigated by mating the rats with normal females. Four months after the start of immunization, 9 out of 10 immunized rats were infertile whereas by nine months, all rats had regained fertility. Thus, it is concluded that immunization with GnRH-TT had no systemic toxicological effects in the adult male rats and rabbits for the period studied. The results also indicated that the GnRH-TT immunization had an antifertility effect in male rats. Fertility was restored following cessation of immunization and decline in anti-GnRH antibody titers.

Gangliosides are the binding substances in neural cells for tetanus and botulinum toxins in mice

We used the knockout mice lacking gangliosides and evaluated their response to tetanus and botulinum toxins. We found that tetanus toxin and botulinum type A or B toxin was less toxic in the knockout mice. We conclude that the toxins bind to the gangliosides on the synapses in the initial step of intoxication prior to penetration of the toxins into the neural cells.

Prior immunity to homologous and heterologous Salmonella serotypes suppresses local and systemic anti-fragment C antibody responses and protection from tetanus toxin in mice immunized with Salmonella strains expressing fragment C

We have investigated the effect of preexisting immunity to homologous (Salmonella typhimurium) or heterologous (S. dublin) serotypes of Salmonella on the ability of an attenuated S. typhimurium aroA aroD vector (BRD509) to immunize mice against the heterologous antigen fragment C (FrgC). We studied two strains, BRD847 and BRD937, expressing FrgC carried on plasmids that differ only with respect to the promoter controlling FrgC expression, the nirB promoter in the case of BRD847 and the htrA promoter in the case of BRD937. Mice were preimmunized orally with S. typhimurium BRD509, S. dublin aroA aroD (BRD620), or saline. Forty-four days later, they were immunized orally with BRD847 or BRD937. Prior immunity to S. typhimurium severely depressed the serum immunoglobulin G (IgG) and IgA anti-FrgC response in both BRD847- and BRD937-immunized mice. Mice with existing immunity to S. dublin also had lower IgG anti-FrgC geometric mean titers (GMTs) than did mice preimmunized with saline, but this difference was significant only in the case of mice immunized with BRD937. However, in nonimmune mice or in mice preimmunized with S. typhimurium or S. dublin, the anti-FrgC IgG GMTs were always higher in mice in the BRD937 groups than in the equivalent BRD847 groups. This is reflected in the effect of prior immunity on the ability of oral immunization with BRD847 or BRD937 to protect mice from challenge with a lethal dose of tetanus toxin. All of the mice preimmunized with saline and then immunized with BRD847 or BRD937 survived challenge. Only 20% of the animals immunized with BRD847 and 60% of the mice in the BRD937 group survived tetanus toxin challenge if they were preimmunized with BRD509. Preexisting immunity to S. dublin did not affect the ability of BRD937 to immunize mice against tetanus, but it did reduce the efficiency of BRD847: only 60% percent of the mice survived challenge. The intestinal secretory IgA responses to FrgC were very similar in the BRD847 and BRD937 groups. Prior immunity did depress the IgA anti-FrgC titers but only significantly so in the mice preimmunized with BRD509. These results show that preexisting Salmonella immunity, particularly to homologous serotypes, can severely compromise the ability of live Salmonella vectors to deliver heterologous antigens to the mammalian immune system. However, the results also indicate that this may be overcome by the design of more powerful in vivo expression systems.