Protection against Salmonella typhi infection in mice after immunization with outer membrane proteins isolated from Salmonella typhi 9,12,d, Vi

Development of recombinant subunit vaccine targeting InvH protein of Salmonella Typhimurium and evaluation of its immunoprotective efficacy against salmonellosis

Salmonella Typhimurium is the most prevalent non-host specific Salmonella serovars and a major concern for both human and animal health systems worldwide contributing to significant economic loss. Type 3 secretion system (T3SS) of Salmonella plays an important role in bacterial adherence and entry into the host epithelial cells. The product of invH gene of Salmonella is an important component of the needle complex of the type 3 secretion system. Hence, the present study was undertaken to clone and express the 15 kDa InvH surface protein of Salmonella Typhimurium in an E. coli host and to evaluate its immune potency in mice. The purified recombinant InvH (r-InvH) protein provoked a significant (p < 0.01) rise in IgG in the inoculated mice. The immunized mice were completely (100%) protected against the challenge dose of 107.5 LD50, while protection against challenge with the same dose of heterologous serovars was 90%. The bacterin-vaccinated group showed homologous protection of 60% against all three serovars. Findings in this study suggest the potential of the r-InvH protein of S. Typhimurium as an effective vaccine candidate against Salmonella infections.

Immune response of S. Typhi-derived Vi polysaccharide and outer membrane protein a conjugate in mice

Typhoid fever is a serious concern precisely in developing nations. Still investigators are exploring a better conjugate partner for Vi-polysaccharide to develop a more effective vaccine for typhoid fever. Here, we cloned and expressed S. Typhi outer membrane protein A (OmpA). The conjugation of Vi-polysaccharide with OmpA was carried out by the carbodiimide (EDAC) method employing ADH as a linker. Total Ig and IgG generated against OmpA, and Vi polysaccharide was quantified by ELISA. Vi polysaccharide alone induced very low levels of Vi polysaccharide antibody. Vi-OmpA conjugate (Vi-conjugate) elicited a robust immune response compared to Vi polysaccharide alone and showed booster response. Further, IgG was only evoked by Vi-OmpA conjugate, not with Vi polysaccharide alone. OmpA antibody induction in both the Vi-OmpA conjugate and OmpA were similar level. Taken together, we show that OmpA as a carrier protein conjugated to Vi polysaccharide is immunogenic. We predict OmpA antibodies will contribute protection along with antibodies generated by Vi-polysaccharide. Past and current literature supports that OmpA is highly conserved protein not only among Salmonellae but entire Enterobacteriacea family with 96-100% identity.

Design and in silico analysis of mRNA vaccine construct against Salmonella

Salmonella infections are continuously growing. Causative serovars have gained enhanced drug resistance and virulence. Current vaccines have fallen short of providing sufficient protection. mRNA vaccines have come up with huge success against SARS-CoV-2; Pfizer-BioNTech and Moderna vaccines have resulted in >90% efficacy with efficient translocation, expression, and presentation of antigen to the host immune system. Herein, based on the same approach a mRNA vaccine construct has been designed and analyzed against Salmonella by joining regions of genes of outer membrane proteins C and F of S. Typhi through a flexible linker. Construct was flanked by regulatory regions that have previously shown better expression and translocation of encoded protein. GC content of the construct was improved to attain structural and thermodynamic stability and smooth translation. Sites of strong binding miRNAs were removed through codon optimization. Protein encoded by this construct is structurally plausible, highly antigenic, non-allergen to humans, and does not cross-react to the human proteome. It is enriched in potent, highly antigenic, and conserved linear and conformational epitopes. Most conserved conformational epitopes of core protein lie on extended beta hairpins exposed to the cellular exterior. Stability and thermodynamic attributes of the final construct were found highly comparable to the Pfizer-BioNTech vaccine construct. Both contain a stable stem-loop structure downstream of the start codon and do not offer destabilizing secondary structures upstream of the start codon. Given structural and thermodynamic stability, effective immune response, and epitope composition the construct is expected to provide broad-spectrum protection against clinically important Salmonella serovars.Communicated by Ramaswamy H. Sarma.

An integrated in silico based subtractive genomics and reverse vaccinology approach for the identification of novel vaccine candidate and chimeric vaccine against XDR Salmonella typhi H58

Salmonella typhi is notorious for causing enteric fever which is also known as typhoid fever. It emerged as an extreme drug resistant strain that requires urgent attention to prevent its global spread. Statistically, about 11-17 million typhoid illnesses are reported worldwide annually. The only alternative approach for the control of this illness is proper vaccination. However, available typhoid vaccine has certain limitations such as poor long-term efficacy, and non-recommendation for below 6 years children, which opens the avenues for designing new vaccines to overcome such limitations. Computational-based reverse vaccinology along with subtractive genomics analysis is one of the robust approaches used for the prioritization of vaccine candidates through direct screening of genome sequence assemblies. In the current study, we have successfully designed a peptide-based novel antigen chimeric vaccine candidate against the XDR strain of S. typhi H58. The pipeline revealed four peptides from WP_001176621.1 i.e., peptidoglycan-associated lipoprotein Pal and two peptides from WP_000747548.1 i.e., OmpA family lipoprotein as promising target for the induction of immune response against S. typhi. The six epitopes from both proteins were found as immunogenic, antigenic, virulent, highly conserved, nontoxic, and non-allergenic among whole Salmonella H58 proteome. Furthermore, the binding interaction between a chimeric vaccine and human population alleles was unveiled through structure-based studies. So far, these proteins have never been characterized as vaccine targets against S. typhi. The current study proposed that construct V2 could be a significant vaccine candidate against S. typhi H58. However, to ascertain this, future experimental holistic studies are recommended as follow-up.

Robust immunity induced by multi-epitope DnaK peptides, potential vaccine candidates against Salmonella: An in vitro study

Enteric fever is a common yet serious issue, most troublesome in underdeveloped and developing nations affecting all age group primarily children. Pitfalls of existing vaccines along with rapidly rising Multi-Drug-Resistant Salmonella strains necessitate the need for the development of new vaccine candidates having potential to provide complete protection. Several vaccine strategies are being pursued to stimulate protective immunity against typhoid, including conjugate vaccines for the elicitation of cellular and humoral responses as both arms of immunity are essential for complete protection. Bacterial HSPs are highly immunogenic to produce humoral and cellular immune responses. In this study, we are reporting in vitro immunostimulatory activity of immunodominant multi-epitope protective antigenic DnaK peptides identified earlier by immunoinformatics approach. Remarkable increase in antibody titer, lymphocyte proliferation, cytokines and NO level with individual /mixture of DnaK peptides as compared to control demonstrate immunogenic potential of these peptides that effectively augments both humoral and cellular immune responses. None of the peptides cause any hemolysis in human RBCs. Overall; our findings strongly elucidate the immune-stimulatory potential of DnaK peptides to be explored as potent vaccine candidates against multiple pathogens.

Functional characterization of a broad and potent neutralizing monoclonal antibody directed against outer membrane protein (OMP) of Salmonella typhimurium

In the present study, we have generated a murine monoclonal antibody (mAb) named Sal-06 by using the crude outer membrane protein preparation of Salmonella enteric subsp. enterica serovar Typhimurium ATCC 14028 strain as antigen. Sal-06mAb belonging to IgG1 isotype demonstrated broad cross-reactivity to standard and isolated strains of genus Salmonella and others such as Escherichia coli, Klebsiella pneumonia, and Proteus mirabilis. Cross-reactivity across several bacterial genera indicated that the epitopes reactive to Sal-06mAb are conserved among these members. Neutralizing effects of Sal-06mAb on Salmonella growth and survival was evaluated in vitro using bacteriostatic and bactericidal activity with and without complement and bacterial invasion inhibition assay. Sal-06mAb demonstrated a bacteriostatic effect on the growth of S. typhimurium ATCC 14028 strain which is both time and concentration (of mAb) dependent. It was also found that the bacterial growth inhibition was complement independent. When the bacterial cells were preincubated with Sal-06mAb, it reduced the adherence and invasion of bacterial cells into A549 epithelial cell line. This was confirmed by CFU count analysis, phase contrast, and fluorescence microscopy. Scanning electron microscope (SEM) imaging confirmed the antimicrobial effects of Sal-06mAb on S. typhimurium ATCC 14028. The development of broadly reactive and cross protective Sal-06mAb opens new possibilities for immunotherapy of sepsis caused by Gram-negative Enterobacteriaceae members.

Conservation of the OmpC Porin Among Typhoidal and Non-Typhoidal Salmonella Serovars

Salmonella enterica infections remain a challenging health issue, causing significant morbidity and mortality worldwide. Current vaccines against typhoid fever display moderate efficacy whilst no licensed vaccines are available for paratyphoid fever or invasive non-typhoidal salmonellosis. Therefore, there is an urgent need to develop high efficacy broad-spectrum vaccines that can protect against typhoidal and non-typhoidal Salmonella. The Salmonella outer membrane porins OmpC and OmpF, have been shown to be highly immunogenic antigens, efficiently eliciting protective antibody, and cellular immunity. Furthermore, enterobacterial porins, particularly the OmpC, have a high degree of homology in terms of sequence and structure, thus making them a suitable vaccine candidate. However, the degree of the amino acid conservation of OmpC among typhoidal and non-typhoidal Salmonella serovars is currently unknown. Here we used a bioinformatical analysis to classify the typhoidal and non-typhoidal Salmonella OmpC amino acid sequences into different clades independently of their serological classification. Further, our analysis determined that the porin OmpC contains various amino acid sequences that are highly conserved among both typhoidal and non-typhoidal Salmonella serovars. Critically, some of these highly conserved sequences were located in the transmembrane β-sheet within the porin β-barrel and have immunogenic potential for binding to MHC-II molecules, making them suitable candidates for a broad-spectrum Salmonella vaccine. Collectively, these findings suggest that these highly conserved sequences may be used for the rational design of an effective broad-spectrum vaccine against Salmonella.

In Silico Characterization of B Cell and T Cell Epitopes for Subunit Vaccine Design of Salmonella typhi PgtE: A Molecular Dynamics Simulation Approach

Typhoid fever is an acute illness in humans, caused by Salmonella typhi, a gram-negative bacterium. Outer membrane proteins of S. typhi have strong potential for its use in the development of subunit vaccine against typhoid. In the current study, peptide-based subunit vaccine was constructed from outer membrane protease E (PgtE) against S. typhi. B cell and T cell epitopes were identified at fold level with a validated three-dimensional modeled structure. T cell epitopes from PgtE (IHPDTSANY) have 99.5% binding to a maximum number of major histocompatibility complex class I and class II alleles. They also bind to the typhoid-resistant human leukocyte antigen (HLA) alleles DRB1*0401. PgtE epitopes were docked with HLA-DR4 (PDB ID: 1D5M) and a contact map was constructed. A simulation search for the binding site for full flexibility of the peptide from CABS- (C_α, C_β, side-chain)-dock shows stable interactions. Molecular dynamics simulation studies revealed that the PgtE-epitope complex structure was more stable throughout the simulation (20 ns) and interaction did not change the radius of gyration. In conclusion, computational analysis, molecular docking, and molecular dynamics (MD) simulation of PgtE-epitope complex were used to elucidate the binding mode, and the dynamical changes of epitopes were more suitable for vaccine development against typhoid.

Salmonella Typhi Porins OmpC and OmpF Are Potent Adjuvants for T-Dependent and T-Independent Antigens

Several microbial components, such as bacterial DNA and flagellin, have been used as experimental vaccine adjuvants because of their inherent capacity to efficiently activate innate immune responses. Likewise, our previous work has shown that the major Salmonella Typhi (S. Typhi) outer membrane proteins OmpC and OmpF (porins) are highly immunogenic protective antigens that efficiently stimulate innate and adaptive immune responses in the absence of exogenous adjuvants. Moreover, S. Typhi porins induce the expression of costimulatory molecules on antigen-presenting cells through toll-like receptor canonical signaling pathways. However, the potential of major S. Typhi porins to be used as vaccine adjuvants remains unknown. Here, we evaluated the adjuvant properties of S. Typhi porins against a range of experimental and clinically relevant antigens. Co-immunization of S. Typhi porins with ovalbumin (OVA), an otherwise poorly immunogenic antigen, enhanced anti-OVA IgG titers, antibody class switching, and affinity maturation. This adjuvant effect was dependent on CD4⁺ T-cell cooperation and was associated with an increase in IFN-γ, IL-17A, and IL-2 production by OVA-specific CD4⁺ T cells. Furthermore, co-immunization of S. Typhi porins with an inactivated H1N1 2009 pandemic influenza virus experimental vaccine elicited higher hemagglutinating anti-influenza IgG titers, antibody class switching, and affinity maturation. Unexpectedly, co-administration of S. Typhi porins with purified, unconjugated Vi capsular polysaccharide vaccine (Vi CPS)—a T-independent antigen—induced higher IgG antibody titers and class switching. Together, our results suggest that S. Typhi porins OmpC and OmpF are versatile vaccine adjuvants, which could be used to enhance T-cell immune responses toward a Th1/Th17 profile, while improving antibody responses to otherwise poorly immunogenic T-dependent and T-independent antigens.

Expression, purification and evaluation of recombinant lipoprotein of Salmonella typhi as a vaccine candidate

Lipoprotein has been reported as a vaccine candidate against many pathogenic bacteria, it plays direct role as a virulence-associated function. Here the approach is toward the expression of recombinant lipoprotein of Salmonella typhi in prokaryotic host and its evaluation as a vaccine candidate. Lipoprotein gene (lp1) was cloned in pET32a expression vector in addition to Bam HI and Hind III restriction sites, and BL21(pLysS) was used as prokaryotic expression host for transformation. Lipoprotein induction was performed by IPTG and 55 kDa (31 kDa of Gene +24 kDa of vector additional protein with His-tag) was analyzed by 12% SDS-PAGE. The recombinant lipoprotein was purified by Ni-NTA affinity chromatography due to the addition of 6X His-tag in recombinant lipoprotein. Western blot analysis using anti-His tag polyclonal antibodies confirmed the specificity of recombinant lipoprotein. Immunogenicity and protection study of recombinant lipoprotein against S. Typhi was performed in BALB/c mice. Adjuvants IFA and alum salts were used to enhance the immune response. ELISA results proved that biologically active truncated recombinant lipoprotein (31 kDa) is a suitable immunogen. Alum salts used as adjuvant was effective for long-lasting immunity.

Outer membrane vesicles derived from Salmonella Typhimurium mutants with truncated LPS induce cross-protective immune responses against infection of Salmonella enterica serovars in the mouse model

Salmonella enterica cause diarrheal and systemic diseases and are of considerable concern worldwide. Vaccines that are cross-protective against multiple serovars could provide effective control of Salmonella-mediated diseases. Bacteria-derived outer membrane vesicles (OMVs) are highly immunogenic and are capable of eliciting protective immune responses. Alterations in lipopolysaccharide (LPS) length can result in outer membrane remodeling and composition of outer membrane proteins (OMPs) changing. In this study, we investigated the impact of truncated LPS on both the production and immunogenicity of Salmonella OMVs, including the ability of OMVs to elicit cross-protection against challenge by heterologous Salmonella strains. We found that mutations in waaJ and rfbP enhanced vesiculation, while mutations in waaC, waaF and waaG inhibited this process. Animal experiments indicated that OMVs from waaC, rfaH and rfbP mutants induced stronger serum immune responses compared to OMVs from the parent strain, while all elicited protective responses against the wild-type S. Typhimurium challenge. Furthermore, intranasal or intraperitoneal immunization with OMVs derived from the waaC and rfbP mutants elicited significantly higher cross-reactive IgG responses and provided enhanced cross-protection against S. Choleraesuis and S. Enteritidis challenge than the wild-type OMVs. These results indicate that truncated-LPS OMVs are capable of conferring cross protection against multiple serotypes of Salmonella infection.

Immunogenicity and Cross-Protective Efficacy Induced by Outer Membrane Proteins from Salmonella Typhimurium Mutants with Truncated LPS in Mice

Lipopolysaccharide (LPS) is a major virulence factor present in the outer membrane of Salmonella enterica serovar Typhimurium (S. Typhimurium). Outer membrane proteins (OMPs) from Salmonella show high immunogenicity and provide protection against Salmonella infection, and truncated LPS alters the outer membrane composition of the cell wall. In our previous study, we demonstrated that Salmonella mutants carrying truncated LPS failed to induce strong immune responses and cross-reaction to other enteric bacteria, due to their high attenuation and low colonization in the host. Therefore, we plan to investigate whether outer membrane proteins from Salmonella mutants with truncated LPS resulting from a series of nonpolar mutations, including ∆waaC12, ∆waaF15, ∆waaG42, ∆rfaH49, ∆waaI43, ∆waaJ44, ∆waaL46, ∆wbaP45 and ∆wzy-48, affect immunogenicity and provide protection against diverse Salmonella challenge. In this study, the immunogenicity and cross-protection efficiency of purified OMPs from all mutants were investigated to explore a potential OMP vaccine to protect against homologous or heterologous serotype Salmonella challenge. The results demonstrated that OMPs from three Salmonella mutants (∆waaC12, ∆waaJ44 and ∆waaL46) induced higher immune responses and provided good protection against homologous S. Typhimurium. The OMPs from these three mutants were also selected to determine the cross-protective efficacy against homologous and heterologous serotype Salmonella. Our results indicated that the mutant ∆waaC12 can elicit higher cross-reactivity and can provide good protection against S. Choleraesuis and S. Enteritidis infection and that the cross-reactivity may be ascribed to an antigen of approximately 18.4–30 kDa.

Overexpression, purification and validation of antigenic Salmonella enterica serovar Typhi proteins identified from LC-MS/MS

In our earlier study, an immunoblot analysis using sera from febrile patients revealed that a 50-kDa band from an outer membrane protein fraction of Salmonella enterica serovar Typhi was specifically recognized only by typhoid sera and not sera from other febrile illnesses. Here, we investigated the identities of the proteins contained in the immunogenic 50-kDa band to pinpoint antigens responsible for its immunogenicity. We first used LC-MS/MS for protein identification, then used the online tool ANTIGENpro for antigenicity prediction and produced recombinant proteins of the lead antigens for validation in an enzyme-linked immunosorbent assay (ELISA). We found that proteins TolC, GlpK and SucB were specific to typhoid sera but react to antibodies differently under native and denatured conditions. This difference suggests the presence of linear and conformational epitopes on these proteins.

Temperature-regulated expression of outer membrane proteins in Shigella flexneri

BACKGROUND

Bacteria exist widely in a diversity of natural environments. In order to survive adverse conditions such as nutrient depletion, biochemical and biological disturbances, and high temperature, bacteria have developed a wide variety of coping mechanisms. Temperature is one of the most important factors that can enhance the expression of microbial proteins. This study was conducted to investigate how outer membrane proteins (OMPs) of the bacterium Shigella flexneri respond to stress, especially during fever when the host's body temperature is elevated.

METHODS

OMPs of S. flexneri ATCC 12022 and clinical isolate SH057 were extracted from an overnight culture grown at 37, 38.5, and 40°C. Comparisons of the expressed proteins under the different growth conditions were based on equal numbers of bacterial cells loaded in the SDS-PAGE gels. Separated proteins were stained with Coomassie brilliant blue. Selected proteins showing increased expression at 38.5 and 40°C were characterized by performing MALDI-ToF-ToF.

RESULTS

Different degrees of expression were demonstrated for different proteins expressed at 37°C compared to 38.5 and 40°C. The proteins with molecular sizes of 18.4, 25.6, and 57.0 kDa showed increased expression level at increasing temperature and were identified as Dps, WrbA, and PepA, respectively.

CONCLUSION

This study revealed that strains of S. flexneri respond at the proteomic level during stress caused by elevated temperature by decreasing the expression of proteins, maintaining the level of important proteins, or enhancing the levels of proteins presumably involved in survival and virulence.

Recombinant Salmonella enterica serovar Typhimurium as a vaccine vector for HIV-1 Gag

The HIV/AIDS epidemic remains a global health problem, especially in Sub-Saharan Africa. An effective HIV-1 vaccine is therefore badly required to mitigate this ever-expanding problem. Since HIV-1 infects its host through the mucosal surface, a vaccine for the virus needs to trigger mucosal as well as systemic immune responses. Oral, attenuated recombinant Salmonella vaccines offer this potential of delivering HIV-1 antigens to both the mucosal and systemic compartments of the immune system. So far, a number of pre-clinical studies have been performed, in which HIV-1 Gag, a highly conserved viral antigen possessing both T- and B-cell epitopes, was successfully delivered by recombinant Salmonella vaccines and, in most cases, induced HIV-specific immune responses. In this review, the potential use of Salmonella enterica serovar Typhimurium as a live vaccine vector for HIV-1 Gag is explored.

Salmonella Typhi OmpS1 and OmpS2 porins are potent protective immunogens with adjuvant properties

Salmonella enterica serovar Typhi (S. Typhi) is the causal agent of typhoid fever, a disease that primarily affects developing countries. Various antigens from this bacterium have been reported to be targets of the immune response. Recently, the S. Typhi genome has been shown to encode two porins--OmpS1 and OmpS2--which are expressed at low levels under in vitro culture conditions. In this study, we demonstrate that immunizing mice with either OmpS1 or OmpS2 induced production of specific, long-term antibody titres and conferred protection against S. Typhi challenge; in particular, OmpS1 was more immunogenic and conferred greater protective effects than OmpS2. We also found that OmpS1 is a Toll-like receptor 4 (TLR4) agonist, whereas OmpS2 is a TLR2 and TLR4 agonist. Both porins induced the production of tumour necrosis factor and interleukin-6, and OmpS2 was also able to induce interleukin-10 production. Furthermore, OmpS1 induced the over-expression of MHC II molecules in dendritic cells and OmpS2 induced the over-expression of CD40 molecules in macrophages and dendritic cells. Co-immunization of OmpS1 or OmpS2 with ovalbumin (OVA) increased anti-OVA antibody titres, the duration and isotype diversity of the OVA-specific antibody response, and the proliferation of T lymphocytes. These porins also had adjuvant effects on the antibody response when co-immunized with either the Vi capsular antigen from S. Typhi or inactivated 2009 pandemic influenza A(H1N1) virus [A(H1N1)pdm09]. Taken together, the data indicate that OmpS1 and OmpS2, despite being expressed at low levels under in vitro culture conditions, are potent protective immunogens with intrinsic adjuvant properties.

Identification and characterization of OmpL as a potential vaccine candidate for immune-protection against salmonellosis in mice

Salmonella is gram-negative flagellated bacteria that can cause food and waterborne gastroenteritis and typhoid fever in humans. Despite the importance of Salmonella infections in human and animal health, the target antigens of Salmonella-specific immunity remain poorly defined, the effectiveness of the currently available vaccines is also limited. Outer membrane proteins (OMPs) of Salmonella have been considered possible candidates for conferring protection against salmonellosis. OMPs interface the cell with the environment, thus representing important potential vaccine candidate for pathogen infection. We showed that the outer membrane porin L (OmpL) is a transmembrane β barrel (TMBB) protein, which forms 12 transmembrane β-strands. OmpL of S. Typhimurium is highly immunogenic, OmpL could evoke humoral and cell-mediated immune responses, and confer 100% protection to immunized mice against challenge with very high doses of S. Typhimurium. Besides, very efficient clearance of bacteria from the reticuloendothelial systems of immunized mice was seen. The homology search further revealed that OmpL is widely distributed and conserved, homologous proteins were identified in S. Typhi and Paratyphi by RT-PCR and western blot. We also found that anti-rOmpL serum harber a high bactericidal activity for Salmonella serovars tested in this study. Therefore, OmpL provide a promising target for the development of a candidate vaccine against Salmonella infection.

Cloning, sequencing, and in silico characterization of Omp 28 of Salmonella Typhi (strain MTCC 733) to develop r-DNA vaccine for typhoid fever

BACKGROUND

Typhoid is one of the most important diseases of human beings caused by Salmonella Typhi. There are many vaccine reported against Salmonella Typhi, but search for new candidate vaccine antigens is still going on because presently available vaccines have several limitations such as short-term immunity, high cost, and allergic reaction. Several approaches such as subunit vaccines, Vi polysaccharide, mutant vaccines, and r-DNA vaccines have been tested. r- DNA vaccines have shown some promising potential (targeted Omp). Omp 28 had shown very promising results and suggests that it should be used in further studies of animal protection against the disease.

OBJECTIVE

Cloning, Sequencing and In silico analysis of Omp 28 gene to develop r-DNA vaccine of S. Typhi.

MATERIALS AND METHODS

Omp 28 is made up of three identical subunits of 9.6 kDa showing PCR amplicon of 330 bp which has been cloned in the pJET vector. Recombinant clones has been sequenced, and data submitted to NCBI. Secondary structure was deduced by the Chou Fasman and Garnier method. The sequence of Omp 28 was studied for antigenic indexing, epitope mapping, and MHC mapping using various bioinformatics tool.

RESULTS AND CONCLUSION

The sequence of Omp 28 has been assigned accession no GQ 907044.1 by NCBI. Secondary structure has shown it has more alpha region. Hydrophobic plot and surface probability plot shows most amino acids are surface exposed which is a requirement to develop a r-DNA vaccine. Antigenic sites are located within surface exposed regions and eight antigenic determinants are present in Omp 28. On Prosite analysis of Protein shown two motifs i.e. anaphylatoxin domain signature motif at position 219-252 and other one was iron sulphur binding region signature motif at position 36-44. On epitope analysis total six major B cell epitopes were observed which can provoke humoral immunity. On T cell epitope mapping several major epitopes has been found in case of MHC class I and MHC class II. It indicates that Omp 28 can provoke cell mediated as well as humoral immunity and can be proven a promising candidates of Salmonella Typhi.

Asymmetric pore occupancy in crystal structure of OmpF porin from Salmonella typhi

OmpF is a major general diffusion porin of Salmonella typhi, a Gram-negative bacterium, which is an obligatory human pathogen causing typhoid. The structure of S. typhi Ty21a OmpF (PDB Id: 3NSG) determined at 2.8 Å resolution by X-ray crystallography shows a 16-stranded β-barrel with three β-barrel monomers associated to form a trimer. The packing observed in S. typhi Ty21a rfOmpF crystals has not been observed earlier in other porin structures. The variations seen in the loop regions provide a starting point for using the S. typhi OmpF for structure-based multi-valent vaccine design. Along one side of the S. typhi Ty21a OmpF pore there exists a staircase arrangement of basic residues (20R, 60R, 62K, 65R, 77R, 130R and 16K), which also contribute, to the electrostatic potential in the pore. This structure suggests the presence of asymmetric electrostatics in the porin oligomer. Moreover, antibiotic translocation, permeability and reduced uptake in the case of mutants can be understood based on the structure paving the way for designing new antibiotics.

Live oral typhoid vaccine Ty21a induces cross-reactive humoral immune responses against Salmonella enterica serovar Paratyphi A and S. Paratyphi B in humans

Enteric fever caused by Salmonella enterica serovar Paratyphi A infection has emerged as an important public health problem. Recognizing that in randomized controlled field trials oral immunization with attenuated S. enterica serovar Typhi live vaccine Ty21a conferred significant cross-protection against S. Paratyphi B but not S. Paratyphi A disease, we undertook a clinical study to ascertain whether humoral immune responses could explain the field trial results. Ty21a immunization of adult residents of Maryland elicited predominantly IgA antibody-secreting cells (ASC) that recognize S. Typhi lipopolysaccharide (LPS). Cross-reactivity to S. Paratyphi A LPS was significantly lower than that to S. Paratyphi B LPS. ASC producing IgG and IgA that bind LPS from each of these Salmonella serovars expressed CD27 and integrin α4β7 (gut homing), with a significant proportion coexpressing CD62L (secondary lymphoid tissue homing). No significant differences were observed in serum antibody against LPS of the different serovars. Levels of IgA B memory (B(M)) cells to S. Typhi LPS were significantly higher than those against S. Paratyphi A or B LPS, with no differences observed between S. Paratyphi A and B. The response of IgA B(M) to outer membrane proteins (OMP) from S. Typhi was significantly stronger than that to OMP of S. Paratyphi A but similar to that to OMP of S. Paratyphi B. The percentages of IgG or IgA B(M) responders to LPS or OMP from these Salmonella strains were similar. Whereas cross-reactive humoral immune responses to S. Paratyphi A or B antigens are demonstrable following Ty21a immunization, they cannot explain the efficacy data gleaned from controlled field trials.

Cloning, sequencing and in silico analysis of omp C of salmonella typhimurium

Salmonella Typhimurium is an important pathogen having a broad host range. In human population it causes mostly gastroenteritis but there are reports in which it was found to be responsible to cause several lethal diseases like endocarditis and meningitis. Poultry products are the major sources of this organism in India as these are consumed at various stages of cooking. The available vaccines have their own limitations such as short-term immunity. Outer membrane proteins have shown some promising potential, so in the present study Omp C of Salmonella Typhimurium was cloned and sequenced to explore the possibility of development of r-DNA vaccine against Salmonella Typhimurium for poultry. The sequence of Omp C was studied for antigenic indexing, epitope mapping, and MHC mapping using various bioinformatic tools. The ORF analysis revealed a complete coding region of approximately 1000 bp. Five major and 13 minor B-cell epitopes were identified having an antigenic index of 1.7. The sequences also showed major histocompatibility complex (MHC) class I and class II binding region indicating a potential of eliciting cell-mediated immune response. The findings indicate that Omp C may be proven as promising candidate for development of r-DNA vaccine against Salmonella Typhimurium.

Development of recombinant vaccines in lactobacilli for elimination of salmonella

Many Lactobacillus and Lactococcus strains are generally regarded as safe for consumption because they are utilized for food fermentation or inhabit the intestinal mucosa as commensals. Recently, vaccine delivery systems using lactic acid bacteria (LAB) have been under development. Our research group has been investigating the development of oral mucosal vaccines against Salmonella enterica serovar Enteritidis (SE) using Lactobacillus casei IGM393 as an antigen delivery vehicle. Recombinant lactobacilli expressing SE antigens, FliC, SipC, and OmpC, have been constructed and orally administered to mice. Antigen specific immune responses and protective immunity were elicited after the immunization. For adjuvant-delivery, IL-1β-secreting L. casei was also engineered and its effects evaluated in vitro and in vivo. This article reviews a novel approach to the elimination of Salmonella via the development of a vaccine in lactobacilli.

Development and evaluation of gamma irradiated toxoid vaccine of Salmonella enterica var Typhimurium

Development of a single effective vaccine against non-typhoidal salmonellosis is very challenging due to the presence of hundreds of serovars of Salmonella which are antigenically different from each other. The Salmonella enterotoxin (Stn), a common virulence factor occurring amongst a wide range of serovars, used as a formalized toxoid vaccine has been found to be effective against homologous and heterologous serovars. However, the process of formalization has its own drawbacks. Gamma radiation (γ) on the other hand is widely used as a safe and convenient method of sterilization worldwide. In this experiment we used gamma rays to inactivate the partially purified Stn of Salmonella enterica serovar Typhimurium (DT 193). The toxoid obtained was tested for its immunogenicity and loss of toxicity and then used to formulate a gamma irradiated toxoid vaccine (ITST). The efficacy of the developed ITST was tested in Kuroiler, a Broiler breed, against homologous and heterologous challenges (S. Typhimurium and S. Gallinarum) administered intra-peritoneally and orally. Birds in groups challenged with S. Typhimurium by both routes recorded protective indices (PI) of 100% while birds in groups challenged intra-peritoneally with S. Gallinarum recorded PI of 83.33% and those challenged orally scored 100%. The overall protective index (PI) being 95.83%. The antibody titres calculated as geometric mean with standard error at 1:10(-4) dilutions showed a steep rise after the first dose and peaked at week 6 post primary vaccinations. Thus the ITST was found very effective in protecting poultry against both the challenge organisms tested.

Characterization of surface proteins of Cronobacter muytjensii using monoclonal antibodies and MALDI-TOF Mass spectrometry

BACKGROUND

Cronobacter spp. is a newly emerging pathogen that causes meningitis in infants and other diseases in elderly and immunocompromised individuals. This study was undertaken to investigate surface antigenic determinants in Cronobacter spp. using monoclonal antibodies (MAbs) and MALDI-TOF Mass spectrometry.

RESULTS

Spleenocytes from mice that were immunized with heat-killed (20 min, 80°C) Cronobacter cells were fused with SP2 myeloma cells. Five desirable MAbs (A1, B5, 2C2, C5 and A4) were selected. MAbs A1, B5, 2C2 and C5 were of IgG2a isotype while A4 was an IgM. Specificity of the MAbs was determined by using immunoblotting with outer membrane protein preparations (OMPs) extracted from 12 Cronobacter and 6 non-Cronobacter bacteria. All MAbs recognized proteins with molecular weight ranging between 36 and 49 kDa except for one isolate (44) in which no OMPs were detected. In addition, MAbs recognized two bands (38-41 kDa) in four of the non-Cronobacter bacteria. Most of the proteins recognized by the MAbs were identified by MALDI-TOF peptide sequencing and appeared to be heterogeneous with the identities of some of them are still unknown. All MAbs recognized the same epitope as determined by an additive Index ELISA with their epitopes appeared to be conformational rather than sequential. Further, none of the MAbs recognized purified LPS from Cronobacter spp. Specificity of the MAbs toward OMPs was further confirmed by transmission electron microscopy.

CONCLUSIONS

Results obtained in this study highlight the immunological cross-reactivity among Cronobacter OMPs and their Enterobacteriaceae counterparts. Nevertheless, the identity of the identified proteins appeared to be different as inferred from the MALDI-TOF sequencing and identification.

Outer membrane protein a of Salmonella enterica serovar Typhimurium activates dendritic cells and enhances Th1 polarization

Background

Typhoid, which is caused by Salmonella enterica serovar Typhimurium, remains a major health concern worldwide. Multidrug-resistant strains of Salmonella have emerged which exhibit increased survivability and virulence, thus leading to increased morbidity. However, little is known about the protective immune response against this microorganism. The outer membrane protein (Omp)A of bacteria plays an important role in pathogenesis.

Results

We purified OmpA from S. enterica serovar Typhimurium (OmpA-sal) and characterized the role of OmpA-sal in promoting adaptive and innate immune responses. OmpA-sal functionally activated bone marrow-derived dendritic cells by augmenting expression of CD80, CD86, and major histocompatibility complex classes I and II. Interestingly, OmpA-sal induced production of interferon-γ from T cells in mixed lymphocyte reactions, thus indicating Th1-polarizing capacity. The expression of surface markers and cytokine production in dendritic cells was mediated by the TLR4 signaling pathway in a TLR4 Knock-out system.

Conclusions

Our findings suggest that OmpA-sal modulates the adaptive immune responses to S. enterica serovar Typhimurium by activating dendritic cells and driving Th1 polarization, which are important properties to consider in the development of effective S. enterica serovar Typhimurium vaccines and immunotherapy adjuvant.

Reduction of tumor necrosis factor alpha-inducing capacity of recombinant Lactobacillus casei via expression of Salmonella OmpC

The insertion of a heterologous gene into commensal bacteria is a common technique to develop a delivery agent for vaccination and therapies, but the pleiotropic effects of genetic modifications need to be investigated before its use in practical applications. Although supplemental properties provided by the expression of heterologous antigens have been reported, the negative or side effects on the immune-modulating properties caused by recombination are barely understood. In the present study, we fortuitously found that the secretion of tumor necrosis factor alpha (TNF-alpha) from murine macrophages was reduced by recombinant Lactobacillus casei expressing Salmonella OmpC compared to the stimulation of TNF-alpha secretion by nonexpressing L. casei. This reduction could not be attributed to OmpC as a purified protein. The main component of the OmpC-expressing strain included in the attenuation of TNF-alpha release seemed to be the cell wall, which exhibited higher sensitivity against N-acetylmuramidase than that of nonexpressing strains. These results suggest that the recombinant strain expressing a specific heterologous antigen might be digested rapidly in macrophages and lose immune-stimulating capability at an early time point.

TLR2 and TLR4 signaling shapes specific antibody responses to Salmonella typhi antigens

TLR directly induce innate immune responses by sensing a variety of microbial components and are critical for the fine-tuning of subsequent adaptive immune responses. However, their impact and mechanism of action on antibody responses against bacterial antigens are not yet fully understood. Salmonella enterica serovar Typhi (S. typhi) porins have been characterized as inducers of long-lasting specific antibody responses in mice. In this report, we show that immunization of TLR4-deficient (TLR4(-/-)), myeloid differentiating gene 88-deficient and Toll/IL-R domain-containing adaptor-inducing IFN-beta-deficient mice with S. typhi porins led to significantly reduced B-cell responses. TLR2(-/-) mice, as well, showed reduced IgG titers with a more pronounced impairment in the production of IgG3 anti-porins antibodies. Adoptive transfer of TLR2(-/-)- or TLR4(-/-)-B cells into B-cell-deficient mice revealed a direct effect of TLR4 on B cells for the primary IgM response, whereas stimulation of B cells via TLR2 was important for IgG production. Furthermore, S. typhi porins were found to efficiently elicit maturation of CD11c(+) conventional DC. Taken together, S. typhi porins represent not only a suitable B-cell antigen for vaccination, but exhibit potent TLR-dependent stimulatory functions on B cells and DC, which help to further enhance and shape the antibody response.

"Gently rough": the vaccine potential of a Salmonella enterica regulatory lipopolysaccharide mutant

BACKGROUND

An alternative to multivalent vaccines could be to construct strains capable of conferring broad protection through shared antigens. Down-regulation of immunodominant major antigens has been proposed to enhance the immunogenicity of conserved antigens.

METHODS

The protection provided by an aroA as well as structural and regulatory lipopolysaccharide (LPS) mutants of Salmonella enterica serovar Typhimurium against homologous and heterologous challenges was assessed in the murine model of typhoid. The reactivity and cross-reactivity of the immune sera raised was tested by enzyme-linked immunospot assay and immunoblots. Conserved outer membrane proteins were identified by mass spectrometry.

RESULTS

Unlike any structural LPS mutants, the regulatory mutant lacking RfaH was finely balanced between safety and immunogenicity, and its vaccine potential was comparable to that of the well-characterized DeltaaroA mutant. Loss of the transcriptional antiterminator RfaH resulted in a heterogeneous length of LPS chains, designated here as the "gently rough" phenotype. Our study also provides evidence that the rough phenotype enhances the immunogenicity of minor antigens, which may improve cross-protection against heterologous bacteria. A panel of conserved antigens shared by members of the Enterobacteriaceae family was identified as abundant porins and lipoprotein antigens.

CONCLUSIONS

Fine-tuned down-regulation of immunodominant epitopes can create live vaccine strains that are not only desirably attenuated but that also exhibit an improved cross-protective potential.

Characterization of an outer membrane protein of Salmonella enterica serovar typhimurium that confers protection against typhoid

Typhoid caused by Salmonella enterica serovar Typhi remains a major health concern worldwide. The emergence of multidrug-resistant strains of Salmonella with increased virulence, communicability, and survivability leading to increased morbidity and mortality has further complicated its management. Currently available vaccines for typhoid have less-than-desired efficacy and certain unacceptable side effects, making it pertinent to search for new immunogens suitable for vaccine formulation. The outer membrane proteins (OMPs) of Salmonella have been considered possible candidates for conferring protection against typhoid. OMPs interface the cell with the environment, thus representing important virulence factors with a significant role in the pathobiology of gram-negative bacteria and bacterial adaptation. An OMP of Salmonella enterica serovar Typhimurium with an apparent molecular mass of 49 kDa that is highly immunogenic, evokes humoral and cell-mediated immune responses, and confers 100% protection to immunized rats against challenge with very high doses (up to 100 times the 50% lethal dose) of Salmonella enterica serovar Typhimurium has been identified. Further, very efficient clearance of bacteria from the reticuloendothelial systems of immunized animals was seen. This protein is recognized by the antibodies present in serum of typhoid patients. When sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel-eluted protein was further analyzed by high-performance liquid chromatography (HPLC) and two-dimensional electrophoresis, two polypeptides with the same molecular weight were resolved. These have different isoelectric points and gave two peaks with different retention times in reverse-phase HPLC. However, only one of the two bands interacted with patient serum. The immunogenicity studies (enzyme-linked immunosorbent assay and delayed-type hypersensitivity [DTH]) indicated that the immunoreactive protein evoked a strong immune response in rats. The N-terminal sequencing and analysis of the homology of this protein with sequences in the protein database of Salmonella resulted in a match with the N-terminal sequences of a protein in Salmonella enterica serovar Typhi (CT18 and Ty2 strains). The homology search further revealed it to be a hypothetical protein, whose gene had unidentified open reading frames in Salmonella serovar Typhi encoding 447 amino acid residues, corresponding to a molecular mass of 49 kDa. The nucleotide sequence of the encoding gene was deduced, and the gene was amplified by PCR using appropriate primers. An amplified 1.3-kb band was purified and sequenced to confirm its identity. These OMPs provide promising targets for the development of a candidate vaccine against typhoid.

Immunization with Outer Membrane Proteins of Pasteurella multocida (6:B) Provides Protection in Mice

The immunoprotective efficacy of Pasteurella multocida (6:B) outer membrane proteins (OMPs) was examined in the mouse model. Bacterial OMPs were extracted using sarkosyl method and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting. Prototype vaccines were prepared using OMPs with adjuvants including dioleoyl phosphatidyl choline-based liposome and Montanide ISA206 water-in oil-in water emulsion. Antibody response to the vaccine was monitored using indirect enzyme linked immunosorbent assay. The results of the study showed that immunized mice had high titre with both the formulations. The vaccinated mice were able to survive a live virulent bacterial challenge. Based on the findings of the study it can be inferred that OMPs are important determinants of immunoprotection hence can serve as vaccine candidates against haemorrhagic septicaemia.

Salmonella enterica serovar Typhimurium ompS1 and ompS2 mutants are attenuated for virulence in mice

Salmonella enterica serovar Typhimurium mutants with mutations in the ompS1 and ompS2 genes, which code for quiescent porins, were nevertheless highly attenuated for virulence in a mouse model, indicating a role in pathogenesis. Similarly, a strain with a mutation in the gene coding for LeuO, a positive regulator of ompS2, was also attenuated.

Salmonella porins induce a sustained, lifelong specific bactericidal antibody memory response

We examined the ability of porins from Salmonella enterica serovar typhi to induce a long-term antibody response in BALB/c mice. These porins triggered a strong lifelong production of immunoglobulin G (IgG) antibody in the absence of exogenous adjuvant. Analysis of the IgG subclasses produced during this antibody response revealed the presence of the subclasses IgG2b, IgG1, IgG2a and weak IgG3. Despite the high homology of porins, the long-lasting anti-S. typhi porin sera did not cross-react with S. typhimurium. Notably, the antiporin sera showed a sustained lifelong bactericidal-binding activity to the wild-type S. typhi strain, whereas porin-specific antibody titres measured by enzyme-linked immunosorbent assay (ELISA) decreased with time. Because our porin preparations contained the outer membrane proteins C and F (OmpC and OmpF), we evaluated the individual contribution of each porin to the long-lasting antibody response. OmpC and OmpF induced long-lasting antibody titres, measured by ELISA, which were sustained for 300 days. In contrast, although OmpC induced sustained high bactericidal antibody titres for 300 days, postimmunization, the bactericidal antibody titre induced by OmpF was not detected at day 180. These results indicate that OmpC is the main protein responsible for the antibody-mediated memory bactericidal response induced by porins. Taken together, our results show that porins are strong immunogens that confer lifelong specific bactericidal antibody responses in the absence of added adjuvant.

Cellular immune response induced by Salmonella enterica serotype Typhi iron-regulated outer-membrane proteins at peripheral and mucosal levels

The role of purified iron-regulated outer-membrane proteins (IROMPs) from Salmonella enterica serotype Typhi in modulation of specific T-cell responses was studied. The cellular immune response induced by IROMPs was measured by assessing the delayed-type hypersensitivity (DTH) response, lymphocyte proliferation, T-cell phenotyping and cytokine-producing cells using lymphocytes isolated from the spleen and Peyer's patches of IROMPs-immunized, immunized-challenged, infected and control mice. IROMPs immunization resulted in an enhanced DTH response and exhibited a significant increase in the protein-specific proliferative response of lymphocyte from the spleen as well as Peyer's patches. A significant increase was also observed in the ratio of CD4+/CD8+ cells in the immunized mice as compared to the infected mice. Results of the cytokine analysis revealed that during the initial period there was increased production of interleukin (IL)-2- and interferon (IFN)-gamma-producing cells in the spleen and Peyer's patches, indicating a Th1 type response, whereas in the later period of the study, increased production of IL-4-producing cells suggested a Th2 type response. The results of this study suggest a role for S. Typhi IROMPs in modulating the cellular immune response at peripheral and mucosal levels.

Role of Salmonella surface components in immunomodulation of inflammatory mediators

Salmonella enterica serovar Typhimurium and its surface components were assessed for their inflammatory potential by footpad oedema test using plethysmometer. Inflammation was found to be the highest when outer membrane proteins (OMPs) were used as inflammagen followed by lipid associated protein-lipopolysaccharide complex (LAP-LPS) and lipopolysaccharides (LPS). Inflammation produced by OMPs was found to be comparable to that by carrageenan (a known positive inflammagen). However, injection of L-histidine (an antioxidant) prior to administration of carrageenan or Salmonella enterica serovar Typhimurium inhibited the inflammation, which indicated the involvement of oxidants during inflammatory response. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and nitric oxide (NO) production by peritoneal macrophages from infected mice exhibited a significant increase as compared to those of the immunized mice. In contrast, glutathione production was found to be the maximum in the macrophages taken from OMPs-immunized mice followed by LAP-LPS and LPS alone. The biochemical studies correlated well with histopathological studies of intestinal tissue of animals from various groups. Based upon these parameters, inflammation seems to be modulated by OMPs and LAP-LPS, which may be because of the protein moieties present in the components. Hence, immunization with protein moieties having L-histidine or L-histidine-like structures may suggest an alternative to the potential therapeutic values of anti-inflammatory drugs. Thus the results of this study form the basis for evaluating these antigens (either alone or in combination with polysaccharides) for preventive intervention rather than therapeutic.

Two Salmonella OmpC K(b)-restricted epitopes for CD8+-T-cell recognition

We report the identification of two peptides from Salmonella OmpC porin that can bind to major histocompatibility complex class I K(b) molecules and are targets of cytotoxic T lymphocytes from Salmonella-infected mice. These peptides are conserved in gram-negative bacterial porins and are the first Salmonella porin-specific epitopes described for possible CD8(+)-T-cell elimination of infected cells.

OmpR and LeuO positively regulate the Salmonella enterica serovar Typhi ompS2 porin gene

The Salmonella enterica serovar Typhi ompS2 gene codes for a 362-amino-acid outer membrane protein that contains motifs common to the porin superfamily. It is expressed at very low levels compared to the major OmpC and OmpF porins, as observed for S. enterica serovar Typhi OmpS1, Escherichia coli OmpN, and Klebsiella pneumoniae OmpK37 quiescent porins. A region of 316 bp, between nucleotides -413 and -97 upstream of the transcriptional start point, is involved in negative regulation, as its removal resulted in a 10-fold increase in ompS2 expression in an S. enterica serovar Typhi wild-type strain. This enhancement in expression was not observed in isogenic mutant strains, which had specific deletions of the regulatory ompB (ompR envZ) operon. Furthermore, ompS2 expression was substantially reduced in the presence of the OmpR D55A mutant, altered in the major phosphorylation site. Upon random mutagenesis, a mutant where the transposon had inserted into the upstream regulatory region of the gene coding for the LeuO regulator, showed an increased level of ompS2 expression. Augmented expression of ompS2 was also obtained upon addition of cloned leuO to the wild-type strain, but not in an ompR isogenic derivative, consistent with the notion that the transposon insertion had increased the cellular levels of LeuO and with the observed dependence on OmpR. Moreover, LeuO and OmpR bound in close proximity, but independently, to the 5' upstream regulatory region. Thus, the OmpR and LeuO regulators positively regulate ompS2.

Induction of cellular immune response and anti-Salmonella enterica serovar typhi bactericidal antibodies in healthy volunteers by immunization with a vaccine candidate against typhoid fever

Typhoid fever remains a serious public health problem. We have developed a vaccine from Salmonella enterica serovar typhi (S. typhi) outer-membrane proteins (OMPs) known as porins. A single subcutaneous dose of 10 microg of porins induced a five-fold (P = 0.05) seroconversion index consisting of IgM and IgG at 7 and 15 days after vaccination as well as the production of IgG1 and IgG2 isotypes. The porins-based vaccine induced a two-fold increase (P = 0.05) in bactericidal titres in volunteers, whom also developed a T-cell response characterized by the production of interferon-gamma (INF-gamma). Side effects after vaccination were mild and transient. The data showed that our S. typhi porins-based candidate vaccine is safe and immunogenic in healthy humans.

Negative osmoregulation of the Salmonella ompS1 porin gene independently of OmpR in an hns background

The ompS1 gene encodes a quiescent porin in Salmonella enterica serovars Typhi and Typhimurium. By using random mariner transposon mutagenesis, mutations that caused derepression of ompS1 expression were isolated, one in S. enterica serovar Typhi and two in S. enterica serovar Typhimurium. All of them mapped in the hns gene in the region coding for the carboxy terminus of the H-NS nucleoid protein. The derepressed ompS1 expression was subject to negative regulation at high osmolarity, both in the presence and in the absence of OmpR. This observation was possible due to the fact that there are two promoters: P1, which is OmpR dependent, and P2, which does not require OmpR for activation (rather, OmpR represses P2). The sequences upstream from position -88, a region previously shown to be involved in the negative regulation of ompS1, can form a static bend, and the integrity of this region was required for function and binding of H-NS and for osmoregulation, as determined with gene reporter fusions of different lengths and with a 31-bp deletion mutant. This is consistent with the notion that this region determines a structure required for repression. Hence, ompS1 shares negative regulation by H-NS with other loci, such as the bgl operon and the ade gene.

Chicken egg yolk antibodies as therapeutics in enteric infectious disease: a review

Passive immunization by oral administration of specific antibodies has been an attractive approach against gastrointestinal (GI) pathogens in both humans and animals. Recently, laying chickens have attracted considerable attention as an alternative source of antibodies for the prevention and treatment of infectious GI diseases. After immunization, the specific antibodies (called IgY) are transported to the egg yolk, from which the IgY then can be separated without sacrificing chickens. A chicken usually lays about 280 eggs in a year, and egg yolk contains 100-150 mg of IgY per yolk, suggesting that more than 40 g of IgY per year can be obtained from each chicken through eggs. IgY is also an alternative to antibiotics for treatment of enteric antibiotic-resistant pathogens. Oral administration of IgY has proved successful for treatment of a variety of GI infections, such as bovine and human rotaviruses, bovine coronavirus, Yersinia ruckeri, enterotoxigenic Escherichia coli, Salmonella spp., Edwardsiella tarda, Staphylococcus, and Pseudomonas. The IgY technology offers great future opportunities for designing prophylactic strategies against infectious GI diseases in humans and animals. However, there is still controversy regarding the stability of IgY through the GI tract. Finding an effective way to protect the antibodies from degradation in the GI tract would open the door for significant advances in IgY technology and nutraceutical applications.

Macrophages present exogenous antigens by class I major histocompatibility complex molecules via a secretory pathway as a consequence of interferon-gamma activation

Macrophages can process and present exogenous antigens on major histocompatibility complex (MHC) class I molecules through an alternative mechanism involving the internalization of antigens and the secretion of peptides loading MHC class I molecules at the cell surface. In this paper, we found that interferon-gamma (IFN-gamma) -activated macrophages infected with Salmonella typhimurum secreted peptides able to load empty MHC Kb molecules on co-cultured TAP-2-deficient RMA-S cells, added as targets for peptide loading. The increase in class I Kb on the RMA-S cells, resulting from the macrophage-derived peptides, exhibited a comparable stability as the direct addition of an exogenous Kb-binding peptide (OVA257-264) to the RMA-S cells. In both cases, the Kb complexes were stable for at least 3 hr after separating the RMA-S cells from the macrophages. The endosomal inhibitors, leupeptin and ammonium chloride, did not inhibit the release of peptides and the increase in Kb staining on the RMA-S cells in the co-culture systems. Brefeldin A also had no effect. P815 cells previously co-cultured with Salmonella-infected macrophages became targets for cytotoxic T lymphocytes isolated from Salmonella-infected BALB/c mice. Taken together, our data suggest that IFN-gamma-activated macrophages process exogenous antigens in an intracellular compartment where serine proteases generate peptides released to the external environment for loading empty MHC class I molecules at the cell surface. This TAP-independent mechanism for the MHC class I presentation may be involved in priming cytotoxic T lymphocytes against intracellular pathogens in vivo.