Influence of codon usage on the immunogenicity of a DNA vaccine against tetanus

Two related DNA vaccine vector plasmids, harbouring either wild-type (pcDNA3/ntetC) or synthetic codon optimised (pcDNA3/stetC) DNA encoding fragment C (TetC) of tetanus toxin were constructed. COS-7 cells transformed with pcDNA3/stetC reproducibly expressed higher levels of TetC than similar cells transformed with pcDNA3/ntetC. BALB/c mice immunised intramuscularly with pcDNA3/stetC produced significantly higher levels of anti-TetC antibodies in their serum in the weeks following vaccination compared to mice immunised with pcDNA3/ntetC, even when differences in the CpG content between the two sequences were controlled for using non-expressing DNA.

Safety and immune responses to attenuated Salmonella enterica serovar typhi oral live vector vaccines expressing tetanus toxin fragment C

Attenuated Salmonella enterica serovar Typhi vaccine strain CVD 908-htrA was used as a vector to deliver fragment C of tetanus toxin as a single-dose oral tetanus vaccine candidate to elicit protective levels of serum tetanus antitoxin. Twenty-one healthy adult volunteers received doses of 1.6 x 10(7) to 8.2 x 10(9) CFU of one of two strains, CVD 908-htrA(pTETnir15) or CVD 908-htrA(pTETlpp), which contained plasmid-encoded fragment C, with sodium bicarbonate, and the safety and immune responses to serovar Typhi antigens and tetanus toxin were assessed. No volunteer had fever or positive blood cultures after vaccination, although diarrhea occurred in 3 volunteers and vomiting in 2 volunteers within 3 weeks after vaccination. Most volunteers excreted the vaccine strain in the first 72 h after vaccination. Three of nine volunteers who received 10(8) CFU or higher doses of the CVD 908-htrA(pTETlpp) construct developed rises in serum antitoxin antibodies. The serum and cellular immune responses to serovar Typhi antigens were less frequent than those previously observed in volunteers who ingested the parent strain CVD 908-htrA. This study demonstrates that fragment C of tetanus toxin delivered orally to volunteers in an S. Typhi vector can elicit protective levels of serum antitoxin.

Interaction of tetanus toxin derived hybrid proteins with neuronal cells

The non-toxic ganglioside binding domain of tetanus toxin (Hc fragment C or TTC) has been studied as a vector for delivering therapeutic proteins to neurons. There is little information on the cellular processing of proteins delivered by linkage to TTC. We have evaluated the cellular handling of a multi-domain hybrid protein containing TTC and both the human enzyme superoxide dismutase and the maltose binding protein from E. coli. Binding, internalization, and cleavage of this protein during prolonged incubation with fetal cortical neurons or cells of the N18-RE-105 line was evaluated by immunoblot analysis, ELISA, and immunocytochemistry. Hybrid proteins were bound and internalized in a manner very similar to TTC. Internalized proteins showed long-term stability within cells, and were degraded into predictable large protein fragments in both cell types. Fragments that were cleaved away from the TTC domain were released into extracellular fluid after internalization. Proteins coupled to TTC share its long-term stability after cellular internalization. After internalization, dissociation of proteins linked to TTC facilitates their release from the cell, but not into other cellular compartments such as the cytosol. TTC linked proteins are probably enclosed within a stable endosomal compartment throughout their cellular lifetime.

Salmonella typhimurium as a basis for a live oral Echinococcus granulosus vaccine

A live attenuated Salmonella typhimurium vaccine candidate, LVR01, was constructed by introducing a null deletion into the aroC gene of the parental canine S. typhimurium isolate, P228067. LVR01 was used to orally deliver to the canine immune system a fatty acid binding protein (FABP) from Echinococcus granulosus (EgDf1), as a fusion protein with fragment C (TetC) of tetanus toxin. Immunization studies demonstrated that live LVR01 is well tolerated by orally vaccinated dogs. There was no detectable shedding of the vaccine strain in the faeces 2 days after immunization. Humoral antibody responses were observed against Salmonella, TetC and EgDf1. Cellular responses were consistently detected against Salmonella and TetC. A cellular response against EgDf1 was also seen in a proportion of the LVR01 vaccinated dogs. We propose S. typhimurium LVR01 as a carrier for recombinant antigens and a vector for the construction of multivalent oral vaccines for dogs.

Enterohaemorrhagic Escherichia coli O157:H7 target Peyer's patches in humans and cause attaching/effacing lesions in both human and bovine intestine

BACKGROUND

Enterohaemorrhagic Escherichia coli (EHEC) constitute a significant risk to human health worldwide, and infections, particularly with serogroup O157:H7, are associated with consumption of a variety of food and water vehicles, particularly food of bovine origin. EHEC cause acute gastroenteritis, bloody diarrhoea, and haemorrhagic colitis; up to 10% of cases develop severe complications, including the haemolytic uraemic syndrome, with a 5% case fatality. A virulence characteristic of enteropathogenic E coli, the attaching/effacing lesion, is considered to be important in EHEC. However, although EHEC produce this lesion on cultured human cells, this has not been demonstrated on human intestinal mucosal surfaces. In addition, the initial site(s) of colonisation of EHEC in humans is not known.

AIMS

To assess the association of EHEC O157:H7 with paediatric and bovine intestine using in vitro organ culture and determine if attaching/effacing lesions occur.

METHODS

Ultrastructural analysis of in vitro intestinal organ cultures of human small and large intestine was used to investigate adhesion of O157:H7 EHEC to intestinal surfaces. Bovine intestinal organ culture was used to examine the pathology produced by the same EHEC strain in cattle.

RESULTS

The study showed that EHEC O157:H7 adhered to human intestinal mucosa. Binding and attaching/effacing lesion formation of O157:H7 in humans was restricted to follicle associated epithelium of Peyer's patches. The same strain caused attaching/effacing lesions on bovine mucosa.

CONCLUSIONS

O157:H7 targets follicle associated epithelium in humans where it causes attaching/effacing lesions. The same human isolate can cause attaching/effacing lesions in cattle, indicating that similar pathogenic mechanisms operate across human and bovine species

Expression of intimin gamma from enterohemorrhagic Escherichia coli in Citrobacter rodentium

The carboxy-terminal 280 amino acids (Int280) of the bacterial adhesion molecule intimin include the receptor-binding domain. At least five different types of Int280, designated alpha, beta, gamma, delta, and epsilon, have been described based on sequence variation in this region. Importantly, the intimin types are associated with different evolutionary branches and contribute to distinct tissue tropism of intimin-positive bacterial pathogens. In this study we engineered a strain of Citrobacter rodentium, which normally displays intimin beta, to express intimin gamma from enterohemorrhagic Escherichia coli. We show that intimin gamma binds to the translocated intimin receptor (Tir) from C. rodentium and has the ability to produce attaching and effacing lesions on HEp-2 cells. However, C. rodentium expressing intimin gamma could not colonize orally infected mice or induce mouse colonic hyperplasia. These results suggest that intimin may contribute to host specificity, possibly through its interaction with a receptor on the host cell surface.

Interaction of Bordetella pertussis with human respiratory mucosa in vitro

The human respiratory tract pathogen Bordetella pertussis is the major cause of whooping cough in infants and young children, and also causes chronic cough in adults. B. pertussis infection damages ciliated epithelium in the respiratory tract. However, the interaction of the bacterium with the respiratory mucosa is poorly understood, and previous studies have either utilized animal tissue which may not be appropriate, or isolated cell systems which lack the complexity of the respiratory mucosa. We have studied the interaction of B. pertussis strain BP536 with human nasal turbinate tissue in an air-interface organ culture over 5 days. We have also compared infection by BP536 with two other strains, Tohama I and CN2992, to determine whether the interactions observed with BP536 are consistent, and, in both nasal turbinate and adenoid organ cultures at 24 h, to determine whether there were differences between tissue from different parts of the respiratory tract. BP536 adhered to cilia, most commonly at their base, and disorganized their spatial arrangement, they also adhered to damaged tissue and mucus, but very rarely to unciliated cells. Within the first 24 h there was a five-fold increase in bacterial density on ciliated cells, and the total number of adherent bacteria increased up to 96 h. Infection caused increased mucus at 24h and an increase in damaged epithelium from 72 h which involved both ciliated and unciliated cells. The number of residual ciliated cells did not decrease after 72 h. The three different strains of B. pertussis exhibited similar interactions with the mucosa, and there was no tissue specificity for adenoid or turbinate tissue. We conclude that B. pertussis adhered to multiple sites on the mucosa and caused hypersecretion and epithelial damage which are the pathological changes described in vivo.

Antimicrobial actions of the NADPH phagocyte oxidase and inducible nitric oxide synthase in experimental salmonellosis. II. Effects on microbial proliferation and host survival in vivo

The roles of the NADPH phagocyte oxidase (phox) and inducible nitric oxide synthase (iNOS) in host resistance to virulent Salmonella typhimurium were investigated in gp91phox(-/)-, iNOS(-/)-, and congenic wild-type mice. Although both gp91phox(-/)- and iNOS(-/)- mice demonstrated increased susceptibility to infection with S. typhimurium compared with wild-type mice, the kinetics of bacterial replication were dramatically different in the gp91phox(-/)- and iNOS(-/)- mouse strains. Greater bacterial numbers were present in the spleens and livers of gp91phox(-/)- mice compared with C57BL/6 controls as early as day 1 of infection, and all of the gp91phox(-/)- mice succumbed to infection within 5 d. In contrast, an increased bacterial burden was detected within reticuloendothelial organs of iNOS(-/)- mice only beyond the first week of infection. Influx of inflammatory CD11b(+) cells, granuloma formation, and serum interferon gamma levels were unimpaired in iNOS(-/)- mice, but the iNOS-deficient granulomas were unable to limit bacterial replication. The NADPH phagocye oxidase and iNOS are both required for host resistance to wild-type Salmonella, but appear to operate principally at different stages of infection.

The virulence plasmid of Salmonella typhimurium contains an autoregulated gene, rlgA, that codes for a resolvase-like DNA binding protein

The virulence plasmid of Salmonella typhimurium contains a gene, rlgA, that shows strong homology to several reported resolvase-like proteins. This gene maps 5 kb upstream of spv locus, the major virulence determinant on the plasmid. Regulation of rlgA was studied using a lacZ transcriptional reporter fusion. The rlgA gene was found to be repressed at the level of transcription by its own product and to be expressed maximally in the late exponential phase of growth. The transcription start site of the rlgA gene was determined and the RlgA binding site was mapped and found to overlap with the transcription initiation signals. A derivative of the virulence plasmid was constructed with a knockout mutation in rlgA. This mutation did not alter the stability of the virulence plasmid nor did it affect the ability of S. typhimurium to cause systemic disease in mice.

Transmission of IgA and IgG monoclonal antibodies to mucosal fluids following intranasal or parenteral delivery

BACKGROUND

The efficacy by which passive antibodies can reach the lungs could be important for the outcome of immunotherapy of respiratory pulmonary infections. We examined how transmission to a number of mucosal sites is affected by the route of inoculation.

METHODS

Transmission of newly raised IgA class Mabs against mycobacterial surface antigens to saliva, lung or vaginal lavage, bile and serum of BALB/c mice was compared with existing IgG Mabs. ELISA was used for testing body fluids obtained 1-24 h after intranasal or intravenous inoculation and 1-7 days following back-pack tumour growth of hybridomas.

RESULTS

Intranasal inoculation resulted in a rapid rise and high levels of both IgA and IgG class Mabs in lung lavage. In contrast, following intravenous Mab injection or back-pack tumour growth of hybridoma cells, effective lung transmission was observed for the IgG1 and IgG2b MAbs, but not for the IgA Mabs. The secretory component was acquired by the transmitted IgA MAbs in the mucosal fluids, but not in the serum. Nevertheless, the time course of mucosal IgA antibody levels was similar to that of the tested IgG Mabs. Furthermore, the relative proportion of transmission to saliva and bile varied between individual Mabs indicating a role of tissue-specific, immunoglobulin class-unrelated mechanisms.

CONCLUSIONS

Intranasal, rather than parenteral inoculation of mice is required for the efficient delivery of IgA antibodies against respiratory pulmonary pathogens. Interestingly, IgA-secretory component complexing of intranasally applied Mabs did not significantly influence their persistence in the lungs.

Structural basis for recognition of the translocated intimin receptor (Tir) by intimin from enteropathogenic Escherichia coli

Intimin is a bacterial adhesion molecule involved in intimate attachment of enteropathogenic and enterohaemorrhagic Escherichia coli to mammalian host cells. Intimin targets the translocated intimin receptor (Tir), which is exported by the bacteria and integrated into the host cell plasma membrane. In this study we localized the Tir-binding region of intimin to the C-terminal 190 amino acids (Int190). We have also determined the region's high-resolution solution structure, which comprises an immunoglobulin domain that is intimately coupled to a novel C-type lectin domain. This fragment, which is necessary and sufficient for Tir interaction, defines a new super domain in intimin that exhibits striking structural similarity to the integrin-binding domain of the Yersinia invasin and C-type lectin families. The extracellular portion of intimin comprises an articulated rod of immunoglobulin domains extending from the bacterium surface, conveying a highly accessible 'adhesive tip' to the target cell. The interpretation of NMR-titration and mutagenesis data has enabled us to identify, for the first time, the binding site for Tir, which is located at the extremity of the Int190 moiety.

Protective effect of supplemental superoxide dismutase on survival of neuronal cells during starvation. Requirement for cytosolic distribution

There is evidence that raising cellular levels of Cu2+/Zn2+ superoxide dismutase (SOD1) can protect neurons from oxidative injury. We compared a novel method of elevating neuronal SOD activity using a recombinant hybrid protein composed of the atoxic neuronal binding domain of tetanus toxin (C fragment or TTC) and human SOD1 (hSOD1) with increasing cellular SOD levels through overexpression. Fetal murine cortical neurons or N18-RE-105 cells were incubated with the TTC-hSOD1 hybrid protein and compared to cells constitutively expressing hSOD1 for level of SOD activity, cellular localization of hSOD1, and capacity to survive glucose and pyruvate starvation. Cells incubated with TTC-hSOD1 showed a threefold increase in cellular SOD activity over control cells. This level of increase was comparable to fetal cortical neurons from transgenic mice constitutively expressing hSOD1 and transfected N18-RE-105 cells expressing a green fluorescent protein-hSOD1 fusion protein (GFP-hSOD1). Human SOD1 was distributed diffusely throughout the cytoplasm of the transgenic murine neurons and transfected N18-RE-105 cells. In contrast, cells incubated with TTC-hSOD1 showed hSOD1 localized to the cell surface and intra-cytoplasmic vesicles. The cells expressing hSOD1 showed enhanced survival in glucose- and pyruvate-free medium. Neither cortical neurons nor N18-RE-105 cells incubated in TTC-hSOD1 showed increased survival during starvation. Access to the site where toxic superoxides are generated or their targets may be necessary for the protective function of SOD1.

DNA topology and adaptation of Salmonella typhimurium to an intracellular environment

The expression of genes coding for determinants of DNA topology in the facultative intracellular pathogen Salmonella typhimurium was studied during adaptation by the bacteria to the intracellular environment of J774A.1 macrophage-like cells. A reporter plasmid was used to monitor changes in DNA supercoiling during intracellular growth. Induction of the dps and spv genes, previously shown to be induced in the macrophage, was detected, as was expression of genes coding for DNA gyrase, integration host factor and the nucleoid-associated protein H-NS. The topA gene, coding for the DNA relaxing enzyme topoisomerase I, was not induced. Reporter plasmid data showed that bacterial DNA became relaxed following uptake of S. typhimurium cells by the macrophage. These data indicate that DNA topology in S. typhimurium undergoes significant changes during adaptation to the intracellular environment. A model describing how this process may operate is discussed.

The immune responses to bacterial antigens encountered in vivo at mucosal surfaces

Mammals have evolved a sophisticated immune system for handling antigens encountered at their mucosal surfaces. The way in which mucosally delivered antigens are handled influences our ability to design effective mucosal vaccines. Live attenuated derivatives of pathogens are one route towards the development of mucosal vaccines. However, some molecules, described as mucosal immunogens, are inherently immunogenic at mucosal surfaces. Studies on mucosal immunogens may facilitate the identification of common characteristics that contribute to mucosal immunogenicity and aid the development of novel, non-living mucosal vaccines and immunostimulators.

Characterization of an isogenic mutant of Streptococcus pyogenes Manfredo lacking the ability to make streptococcal acid glycoprotein

An isogenic mutant of Streptococcus pyogenes Manfredo that lacks the ability to make streptococcal acid glycoprotein (SAGP) has been constructed by inserting a deletion in the sagp gene using the method of allelic exchange. An assay of cell extracts (CE) prepared from the wild-type and mutant Manfredo strains for the enzyme arginine deiminase (AD) showed that significant activity was present in wild-type CE but none could be detected in mutant CE. These findings confirm our earlier conclusion that SAGP has AD activity (B. A. Degnan, J. M. Palmer, T. Robson, C. E. D. Jones, M. Fischer, M. Glanville, G. D. Mellor, A. G. Diamond, M. A. Kehoe, and J. A. Goodacre, Infect. Immun. 66:3050-3058, 1998). Wild-type CE but not mutant CE potently inhibited human peripheral blood mononuclear cell proliferation in response to phytohemagglutinin, and this inhibition was overcome by the addition of L-arginine to proliferation assay mixtures. Invasion assays showed that the isogenic mutant organisms lacking SAGP, and thus AD activity, were between three and five times less able to enter epithelial cells (Hep-2C and A549) than were the wild-type streptococci. Both wild-type and mutant S. pyogenes bacteria were extremely sensitive to low pH. However, L-arginine (1 mM or above) significantly increased the viability of the wild type but not the isogenic mutant organisms under acidic conditions. The difference in acid susceptibility between wild-type and mutant bacteria may explain the reduced capacity of the isogenic mutant bacteria to invade and survive intracellularly.

Kinetics of the mucosal antibody secreting cell response and evidence of specific lymphocyte migration to the lung after oral immunisation with attenuated S. enterica var. typhimurium

The kinetic of mucosal secretory responses elicited by the vaccine vector Salmonella enterica var. typhimurium (S. typhimurium) was examined by enzyme linked immunospot (ELISPOT) and compared with serum responses. Mice immunised orally with BRD509, the aroA, aroD mutant of virulent S. typhimurium SL1344 expressing the C Fragment of tetanus toxin (TT), simultaneously developed an IgA antibody secreting cells (ASC) response in the gastrointestinal lamina propria, the spleen and the lung, against both S. typhimurium lipopolysaccharide (LPS) and TT. The magnitude of the ASC response was greatest in the gut, was boosted by a secondary immunisation at day 25, and the kinetic of the response did not correlate with the appearance of serum antibodies. This study suggests that S. typhimurium can engage the common mucosal immune system to effect mucosal secretory responses at distal sites, however, the magnitude of the responses is both greatest in the gut and antigen-specific. The ASC origin of the serum antibodies specific for S. typhimurium and antigens expressed by the bacterium is yet to be elucidated.

Salmonella enterica serovar typhimurium surA mutants are attenuated and effective live oral vaccines

A previously described attenuated TnphoA mutant (BRD441) of Salmonella enterica serovar Typhimurium C5 (I. Miller, D. Maskell, C. Hormaeche, K. Johnson, D. Pickard, and G. Dougan, Infect. Immun. 57:2758-2763, 1989) was characterized, and the transposon was shown to be inserted in surA, a gene which encodes a peptidylprolyl-cis, trans-isomerase. A defined surA deletion mutation was introduced into S. enterica serovar Typhimurium C5 and the mutant strain, named S. enterica serovar Typhimurium BRD1115, was extensively characterized both in vitro and in vivo. S. enterica serovar Typhimurium BRD1115 was found to be defective in the ability to adhere to and invade eukaryotic cells. Furthermore, S. enterica serovar Typhimurium BRD1115 was attenuated by at least 3 log units when administered orally or intravenously to BALB/c mice. Complementation of the mutation with a plasmid carrying the intact surA gene almost completely restored the virulence of BRD1115. In addition, S. enterica serovar Typhimurium BRD1115 demonstrated potential as a vaccine candidate, since mice immunized with BRD1115 were protected against subsequent challenge with S. enterica serovar Typhimurium C5. S. enterica serovar Typhimurium BRD1115 also showed potential as a vehicle for the effective delivery of heterologous antigens, such as the nontoxic, protective fragment C domain of tetanus toxin, to the murine immune system.

Phase 2 clinical trial of attenuated Salmonella enterica serovar typhi oral live vector vaccine CVD 908-htrA in U.S. volunteers

Salmonella enterica serovar Typhi strain CVD 908-htrA is a live attenuated strain which may be useful as an improved oral typhoid vaccine and as a vector for cloned genes of other pathogens. We conducted a phase 2 trial in which 80 healthy adults received one of two dosage levels of CVD 908-htrA in a double-blind, placebo-controlled, crossover study. There were no differences in the rates of side effects among volunteers who received high-dose vaccine (4.5 x 10(8) CFU), lower-dose vaccine (5 x 10(7) CFU), or placebo in the 21 days after vaccination, although recipients of high-dose vaccine (8%) had more frequent diarrhea than placebo recipients (0%) in the first 7 days. Seventy-seven percent and 46% of recipients of high- and lower-dose vaccines, respectively, briefly excreted vaccine organisms in their stools. All blood cultures were negative. Antibody-secreting cells producing antilipopolysaccharide (LPS) immunoglobulin A (IgA) were detected in 100 and 92% of recipients of high- and lower-dose vaccines, respectively. Almost half the volunteers developed serum anti-LPS IgG. Lymphocyte proliferation and gamma interferon production against serovar Typhi antigens occurred in a significant proportion of vaccinees. This phase 2 study supports the further development of CVD 908-htrA as a single-dose vaccine against typhoid fever and as a possible live vector for oral delivery of other vaccine antigens.

Cattle immune responses to tetanus toxoid elicited by recombinant S. typhimurium vaccines or tetanus toxoid in alum or Freund's adjuvant

Cattle were immunised orally, nasally or subcutaneously with either S. typhimurium 4/74 aroA(-) aroD(-) or S. typhimurium 4/74 htrA-based live vaccines expressing Fragment C (TetC) of tetanus toxin from plasmid pTetnir15. Oral inoculation with S. typhimurium 4/74 aroA(-) aroD(-)- (pTetnir15) elicited mucosal anti-TetC IgA but no measurable systemic humoral responses to TetC. Subcutaneous inoculation with the same strain elicited both mucosal IgA and systemic anti-TetC IgG1 responses. Nasal inoculation did not elicit any detectable anti-TetC responses. Oral delivery of S. typhimurium htrA(-) proved fatal in inoculated animals. None of the animals inoculated with either mutant S. typhimurium developed detectable T cell proliferative responses to the guest antigen. Cattle were also inoculated with tetanus toxoid adsorbed in alum or emulsified in Freund's complete adjuvant. Animals inoculated subcutaneously with Ttox emulsified in FCA developed systemic IgG1 and IgG2 antibody, while animals inoculated with Ttox adsorbed in alum developed systemic IgG1 but little IgG2 to Ttox. Both of these groups of animals developed measurable TetC-specific proliferative T cell responses that were associated with the production of IFNgamma.

Epidemic typhoid in vietnam: molecular typing of multiple-antibiotic-resistant Salmonella enterica serotype typhi from four outbreaks

Multidrug-resistant Salmonella enterica serotype Typhi isolates from four outbreaks of typhoid fever in southern Vietnam between 1993 and 1997 were compared. Pulsed-field gel electrophoresis, bacteriophage and plasmid typing, and antibiotic susceptibilities showed that independent outbreaks of multidrug-resistant typhoid fever in southern Vietnam are caused by single bacterial strains. However, different outbreaks do not derive from the clonal expansion of a single multidrug-resistant serotype Typhi strain.

Characterisation of Candida albicans infections of haematogenous and mucosal origin in mice lacking the interferon gamma receptor protein

Mice harbouring a null deletion mutation in the IFNgamma receptor gene were used to study the role of IFNgamma responsiveness during experimental systemic candidiasis of mucosal or haematogenous origin. After intravenous (i.v.) or intranasal (i.n.) challenge with Candida albicans the progression of infection and concomitant cellular and antibody anti-C. albicans immune responses were analysed. During the week following i.v. challenge, the rate of C. albicans multiplication in kidneys, liver and spleen was faster in IFNgammaR (-/-) than IFNgammaR (+/+) mice. As a result, IFNgammaR (-/-) mice perished earlier than IFNgammaR (+/+) mice when challenged with equal numbers of live yeast cells. However, the overall susceptibility of the two mouse strains, in terms of survival against different C. albicans challenge doses over a 60-day period, was similar. No differences were found in the cellular anti-C. albicans response generated by i.v. challenge in both mouse strains. In contrast the kinetics and strength of the serum anti-C. albicans antibody responses were markedly different. Significantly stronger, predominantly IgG2a antibody responses accompanied the eventual control of C. albicans infection in IFNgammaR (-/-) mice. Following intranasal challenge, there was no difference in the rate of C. albicans clearance from the lungs of IFNgammaR (-/-) and IFNgammaR (+/+) mice. However, 48 h after challenge, large, conspicuous abscesses appeared in the lungs, liver, kidneys and spleen of IFNgammaR (-/-) mice. These abscesses were characterised by the presence of C. albicans and abundant neutrophilic infiltrates, but very few macrophages. No such abscesses developed in i.n. challenged IFNgammaR (+/+) mice. In both mouse strains, i.n. challenge induced strong systemic anti-C. albicans cellular responses, but relatively low titre systemic antibody responses. Mucosal anti-C. albicans antibody responses were detected in IFNgammaR (+/+), but not IFNgammaR (-/-) mice. Splenic adherent macrophages obtained from IFNgammaR (-/-) mice exhibited a significantly lower candidacidal activity than those of IFNgammaR (+/+) mice, and as expected, were not responsive to IFNgamma. In summary, these data suggest that IFNgamma has a role in limiting C. albicans multiplication during the early stages of infection, as well as in preventing the development of C. albicans-associated abscesses. Activation of macrophages by IFNgamma might be pivotal in mediating this role.

Use of the stationary phase inducible promoters, spv and dps, to drive heterologous antigen expression in Salmonella vaccine strains

We have investigated the ability of the growth phase regulated promoters dps and spv, to drive expression of heterologous antigens in Salmonella vaccine strains. Reporter plasmids were constructed which directed beta-galactosidase expression from dps (pDpslacZ) or spv (pSpvlacZ) and these were introduced independently into the Salmonella typhimurium vaccine strain SL3261 (aroA(-)). beta-galactosidase expression was induced 20-fold and 100-fold when broth cultures of SL3261 (pDpslacZ) or SL3261 (pSpvlacZ) respectively, entered the stationary phase of growth. Within macrophages, beta-galactosidase expression was induced 3.5-fold with SL3261 (pDpslacZ) and 7-fold with SL3261 (pSpvlacZ). The spv and dps promoters were used to drive independent expression of the C fragment domain of tetanus toxin (TetC) from plasmids harboured in S. typhimurium SL3261. Levels of anti-TetC antibodies were significantly higher in the sera of BALB/c mice perorally inoculated with SL3261 (pSpvtetC) or SL3261 (pDpstetC) compared to unvaccinated controls. This suggests that these promoter systems may be used to drive foreign antigen expression in live oral Salmonella vaccines.

Human colostrum and serum contain antibodies reactive to the intimin-binding region of the enteropathogenic Escherichia coli translocated intimin receptor

BACKGROUND

In Brazil, enteropathogenic Escherichia coli (EPEC) diarrhoea is endemic in young infants. A characteristic feature of EPEC adhesion to host cells is intimate attachment leading to the formation of distinctive "attaching and effacing" (A/E) lesions on mammalian cells. Two genes directly involved in intimate adhesion, eae and tir, encode the adhesion molecule intimin and its translocated receptor Tir, respectively. The intimin-binding domain of Tir was recently mapped to the middle part of the polypeptide (Tir-M), and the amino (Tir-N) and carboxy (Tir-C) termini were found to be located within infected host cells. Recently, it was shown that colostrum samples from mothers living in Sao Paulo contain IgA-class antibodies reactive with a number of proteins associated with EPEC virulence. It has also been shown that patients infected with verocytotoxin-producing E. coli O157 can produce antibodies to Tir. In the current study antibody responses to the different Tir domains were analyzed in sera and colostrum samples collected in an EPEC-endemic area of Brazil.

METHODS

Recombinant Tir, Tir-N, Tir-M, and Tir-C were expressed as His-tagged protein in E. coli BL21a and purified on nickel columns. Western blot analysis was used to investigate colostrum IgA- and serum IgG-class antibodies reactive with the Tir fragments.

RESULTS

Anti-Tir IgG antibodies were detected in the serum of children, with (63%) or without (50%) diarrhoea. Anti-Tir IgA-class antibodies were detected in all the colostrum pools tested. With the use of both serum IgG- and colostrum IgA-class antibodies, an immunodominant domain of the Tir-polypeptide, Tir M, was identified.

CONCLUSION

The intimin-binding region of Tir (Tir-M) is the immunodominant region of the polypeptide in humans. Both serum IgG-class and colostrum IgA-class antibodies reacted predominantly with the Tir-M domain.