A comparative approach to strategies for cloning, expression, and purification of Mycobacterium tuberculosis mycolyl transferase 85B and evaluation of immune responses in BALB/c mice

Efficient Immunization of BALB/c Mice against Pathogenic Brucella melitensis and B. ovis: Comparing Cell-Mediated and Protective Immune Responses Elicited by pCDNA3.1 and pVAX1 DNA Vaccines Coding for Omp31 of Brucella melitensis

Background

Brucella spp. are intracellular pathogens, therefore cell-mediated immunity is the main response to inhibit survival and growth of the bacteria in vertebrate host.

Objective

Many eukaryotic plasmid vectors are being used in setting up DNA vaccines which may show different efficiencies in same conditions. This is important in designing the vaccines and immunization strategies. We looked into the probable differences of immune responses induced by different eukaryotic DNA plasmid vectors (pcDNA3.1 and pVAX1) harboring the same Omp31 gene of B. melitensis.

Materials and Methods

Female BALB/c mice were immunized with pcDNA -omp31 and pVAX-omp31 and further boosted with recombinant Omp31. Subclasses of specific serum IgG against the rOmp31 were measured by ELISA. Cytokines responses to rOmp31 in Splenocyte cultures of the immunized mice were evaluated by measuring the production of IL-4, IL-10, IL-12 and IFN-γ. Protective responses of the immunized mice were evaluated by intraperitoneal challenge with pathogenic Brucella melitensis 16M and Brucella ovis PA76250.

Results

Both DNA vaccine candidates conferred potent Th1-type responses with higher levels of cytokines and immunoglobulins observed in mice immunized with pVAX-omp31. Although pcDNA-omp31 and pVAX-omp31 both elicited protective immunity, mice immunized with the latter showed a higher protection against both B. melitensis and B. ovis PA76250.

Conclusion

The results of this study highlight the significant differences between efficiency of diverse plasmid backbones in DNA vaccines which code for an identical antigen. Comparing various plasmid vectors should be considered as an essential part of the studies aiming construction of DNA vaccines for intracellular pathogens.

Investigating the role of L. pnuemophila LPS derivatives in formation of specific cell-mediated immune responses against the pathogen

Legionella pneumophila is a Gram-negative intracellular bacterium and causes legionnaire's disease an -atypical pneumonia in humans. Lipopolysaccharide (LPS) is the main antigen of Gram-negative bacteria but is less studied because of its carbohydrate nature. Here, we immunized mice with detoxified LPS and O-antigen polysaccharide in combination with bovine serum albumin (BSA) and explored the immunological responses of mice to the bacterial infection. LPS of L. pneumophila was extracted by hot phenol-water method. Purified LPS was detoxified by sodium hydroxide alkaline procedure. O-polysaccharide antigen (OPS) obtained by acetic acid treatment of LPS. BALB/c mice were immunized mainly with non-covalent combination of detoxified LPS (dLPS) or OPS with BSA separately. Pure polysaccharide antigens did not elicit significant serum IgG against LPS. Combination of the dLPS and OPS with BSA resulted in risen IgG and its subclasses (IgG1 and IgG2a) against lipopolysaccharide. Mice were challenged intravenously with sublethal dose of L. pneumpphila. Then, splenocytes were cultured and cytokine responses of splenocytes to pathogenic Legionella was studied by ELISA. Mice immunized with combination of the dLPS or OPS and BSA showed significant elevation of cytokine responses to pathogenic L. pneumophila. Our results suggest that combination of the polysaccharide antigen derived from Legionella LPS may confer raised cell-mediated responses against the pathogen when combined with a protein antigen which is capable of eliciting cell-mediated responses. Although not covalently bond, Legionella polysaccharides combined with BSA effectively elicited Th-1 type cytokines and humoral responses against L. pneumophila in BALB/c mice.

Characterization of the sortase A from Lactobacillus acidophilus ATCC 4356 involved in adherence to intestinal cells

Aim: Confirmation of the enzymatic activity of Class A sortase (SrtA) in probiotic strain Lactobacillus acidophilus associated with the adhesion properties. Materials & methods: SrtA from L. acidophilus ATCC 4356 was purified and its enzymatic properties was investigated by site-directed mutagenesis approach and the sensitivity to metal ions was also detected. Results: SrtA of L. acidophilus ATCC4356 can recognize LPxTG and LPxTD sorting motifs. The active sites of SrtA include His137, Cys198 and Arg205. Furthermore, acacetin can increase the activity of SrtA, while phenyl vinyl sulfone could effectively inhibit the activity of SrtA with an IC₅₀ of 143.32 μg/ml. The adhesion ability of L. acidophilus was also decreased resulting from the inhibition of SrtA activity. Conclusion: The unique properties of SrtA of L. acidophilus can provide some insights into the development of high-adhesion Lactobacillus strains in the GI tract.

Recombinant Omp2b antigen-based ELISA is an efficient tool for specific serodiagnosis of animal brucellosis

Control of brucellosis as a worldwide zoonotic disease is based on vaccination of animals and diagnosis of infected cases to be eradicated. Accurate and rapid detection of infected animals is of critical importance for preventing the spread of disease. Current detection of brucellosis is based on whole-cell antigens and investigating serum antibodies against Brucella lipopolysaccharide (LPS). The critical disadvantage is misdiagnosis of vaccinated animals as infected ones and also cross-reactions with other Gram-negative bacteria. Recombinant outer membrane protein 2b (Omp2b) of Brucella abortus was evaluated as a novel serodiagnostic target in comparison to conventional tests which are based on LPS. Recombinant Omp2b (rOmp2b) was expressed in Escherichia coli BL21 and purified by Ni²⁺-based chromatography. rOmp2b was evaluated in an indirect enzyme-linked immunosorbent assay (ELISA) system for diagnosis of brucellosis, with sera from Brucella-infected mice along with negative sera and sera from mice which were inoculated with other Gram-negative species for assurance of specificity. Thereafter, cattle sera collected from different regions were assessed along with known negative and known positive serum samples. We found that Omp2b can discriminate between Brucella-infected animals and non-infected ones. Results for assessment of two hundred and fifty cattle sera by Omp2b-based indirect ELISA which were compared to Rose Bengal plate agglutination test (RBPT) and serum tube agglutination test (SAT) showed that our proposed procedure has the sensitivity of 88.5%, specificity of 100%, and accuracy of 90.8%. We suggest that recombinant Omp2b could be used as a protein antigen for diagnosis of brucellosis in domestic animals and can be evaluated for detection of human brucellosis.

Induction of protective immunity by recombinant peptidoglycan associated lipoprotein (rPAL) protein of Legionella pneumophila in a BALB/c mouse model

Legionella pneumophila causes a severe form of pneumonia known as Legionnaires' disease especially in patients with impaired cellular immune response. In order to prevent the disease, immunogenicity and the level of the induction of protective immunity from the recombinant peptidoglycan-associated lipoprotein (rPAL) against Legionella pneumophila in BALB/c mice was examined. Mice immunized with (rPAL) rapidly increased an antibody response in serum and also displayed a strong activation of both innate and adaptive cell-mediated immunity as determined by antigen-specific splenocyte proliferation, an early production of pro-inflammatory cytokines in the serum and in the splenocyte cultures. Infection with a primary sublethal does of Legionella pneumophila serogroup 1, strain paris, caused resistance to a lethal challenge infection in the animals with 100% survival rate. However, mice treated with rPAL survived with 60% rate in 10 days after a lethal i.v challenge with L. pneumophila. All of the control animals receiving PBS died within 24 h. The present study indicates that recombinant protein PAL of Legionella pneumophila is strongly immunogenic and capable to elicit early innate and adaptive immune responses and lasting immunity against a lethal dose of Legionella pneumophila challenge. Antigenic characterization and immune protection of recombinant protein PAL would be of considerable value in comprehension the immune-pathogenesis of the disease and in development possible vaccine against the Legionella.

Recombinant flagellin-PAL fusion protein of Legionella pneumophila induced cell-mediated and protective immunity against bacteremia in BALB/c mice

We report a new recombinant fusion protein composed of full-length Legionella pneumophila flagellin A and peptidoglycan-associated lipoprotein (PAL), rFLA-PAL, capable of inducing protective immunity against L. pneumophila. The recombinant protein was over expressed in Escherichia coli strain BL21 (DE3) using pET-28a (+) expression vector (pET28a-flaA-pal) and purified by Ni²⁺ exchange chromatography. Immunological properties of rFLA-PAL were assessed in a mouse model. Female BALB/c mice, immunized with rFLA-PAL, exhibited a rapid increase in serum antibody concentration against each of its protein portions. Furthermore, a strong activation of both innate and adaptive cell-mediated immunity was observed as indicated by antigen-specific splenocyte proliferation, IFN-γ and IL-12 production, and early production of TNF-α in the serum and in splenocyte cultures which were separately assessed against PAL and FLA. BALB/c mice were challenged with a lethal dose of L. pneumophila intravenously. In a 10-days follow-up after intravenous lethal challenge with L. pneumophila, a 100% survival rate was observed for mice immunized with rFLA-PAL, same as for those immunized with a sublethal dose of L. pneumophila. Based on the potent immune responses observed in mice immunized with rFLA-PAL, this recombinant fusion protein could be a potential vaccine candidate against the intracellular pathogen L. pneumophila.

Binding of the Helicobacter pylori OipA causes apoptosis of host cells via modulation of Bax/Bcl-2 levels

The H. pylori outer inflammatory protein A (OipA) is an outer membrane protein that contributes to gastric inflammation. OipA is believed to affect intra-cellular signalling and modulate the host signalling pathways. The aim of the current study was to clarify the role of OipA in H. pylori pathogenesis and its effect on host cell signalling pathways. To this end, the oipA gene was isolated and inserted into cloning and expression vectors. The recombinant plasmid was transferred into an expression host to produce OipA, which was subsequently purified by affinity chromatography and used for antibody production. A confluent monolayer of gastric cell lines was treated with various concentrations of OipA and investigated for attachment, toxicity, and apoptosis and alterations in signalling pathways. OipA bound to gastric cell lines confirming its role in the attachment of H. pylori to host cells. The ratio of Bax/Bcl-2 and caspase3, 8, FasL in the host cells were assessed and the results showed that the Bax/Bcl-2 ratio as well as the level of cleaved-caspase 3 was elevated in OipA-treated cells. These findings suggest that OipA can bind and induce toxic events as well as triggering apoptotic cascade in host gastric cells through intrinsic pathway.

Protection against Legionnaire's Disease: Recombinant Flagellin A of Can Induce Protective Immunity against Bacteremia in a BALB/c Murine Model

To investigate the immunoprotective effects of the recombinant type A flagellin (FLA), the <i>fla</i>A gene of <i>Legionella pneumophila</i> serogroup 1 strain Paris was cloned into pET28a(+). Recombinant FLA (rFLA) was overexpressed in <i>E. coli</i> BL21 (DE3) and purified by Ni²⁺ exchange chromatography. Female BALB/c aged 6-8 weeks were immunized with 20 μg of rFLA. Nonimmunized mice along with mice inoculated with a sublethal dose of live <i>L. pneumophila</i> intravenously were considered as negative and positive controls, respectively. A significant serum antibody response was observed in female BALB/c mice immunized with rFLA. Production of IFN-&#x03B3; and IL-12, and TNF-α in the serum and the splenocyte cultures, and antigen-specific splenocyte proliferation suggested a strong innate and adaptive cell-mediated immunity response in rFLA-immunized mice. Intravenous lethal challenge with <i>L. pneumophila</i> serogroup 1 (strain Paris) showed that 60% of mice immunized with rFLA survived in a 10-day follow-up survey. These results show that rFLA from <i>L. pneumophila</i> can elicit strong innate and adaptive immune responses and suggest the possibility of a long-term immunity against lethal challenge with <i>L. pneumophila</i>.

Cloning, Expression, and Purification of Pseudomonas aeruginosa Flagellin, and Characterization of the Elicited Anti-Flagellin Antibody

BACKGROUND

Pseudomonas aeruginosa is an important opportunistic human pathogen that causes serious infections in immunocompromised hosts. The single polar flagellum is an important factor in both virulence and colonization.

OBJECTIVES

As flagellin is the major component of the flagellar filament, the main aims of the present study are to identify, clone, express, and purify the recombinant type B flagellin (r-B-flagellin) of P. aeruginosa, as well as to evaluate the functional activity of the rabbit polyclonal antibody raised against this r-B-flagellin.

MATERIALS AND METHODS

In the current experimental study, the r-B-flagellin gene was isolated from the P. aeruginosa PAO1 strain by PCR. It was cloned into the pET-28a vector and then transformed into the E. coli BL21 strain. Next, r-B-flagellin was overexpressed and affinity purified by Ni-NTA agarose-affinity chromatography, followed by on-column resolubilization. Polyclonal antisera against the recombinant flagellin were raised in rabbits, and the functional activity of the anti-r-B-flagellin antibody was determined by in vitro assays.

RESULTS

The polyclonal antibodies raised against this r-B-flagellin inhibited the motility of the homologous PAO1 strain of P. aeruginosa, which significantly decreased the invasion of the PAO1 strain into the A549 cells and also enhanced the opsonophagocytosis of this strain. However, our polyclonal antibody showed little effect on the heterologous PAK strain.

CONCLUSIONS

The r-B-flagellin carried antigenic epitopes just like the native flagellin, while the polyclonal antibody raised against it exhibited functional activity.

Production of specific IgY Helicobacter pylori recombinant OipA protein and assessment of its inhibitory effects towards attachment of H. pylori to AGS cell line

Purpose

The common triple therapy for Helicobacter pylori is challenged by the increasing cases of antibiotic resistant infections, raising the need to explore alternative therapies. Oral administration of egg yolk immunoglobulin Y (IgY) has been previously reported as a means of passive immunization therapy for H. pylori infections. In this work, we investigated the inhibitory effect of IgY on the attachment of H. pylori to AGS cell line.

Materials and Methods

Recombinant OipA was prepared. Hens were immunized with recombinant protein three times. IgY was purified from egg yolks of immunized hens using polyethylene glycol precipitation method. The inhibitory effect of the specific immunoglobulin was evaluated in AGS cell line infected with H. pylori.

Results

The presence of recombinant OipA (30 kD) was confirmed via sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Immunization of hens was confirmed using enzyme-linked immunosorbent assay. The purified IgY from egg yolks were assessed using SDS-PAGE and confirmed by western blot.

Conclusion

The results showed that IgY-OipA had inhibitory effect on attachment of H. pylori to AGS cell line and may be utilized as a therapeutic or prophylaxis material.

Protection of mice against Staphylococcus aureus infection by a recombinant protein ClfA-IsdB-Hlg as a vaccine candidate

Staphylococcus aureus is one of the most important causes of nosocomial infections. An effective vaccine to prevent S. aureus infections is urgently required due to the dramatic increase in the number of antibiotic-resistant strains. In this report, we evaluated a newly recombinant protein composed of selected antigenic regions of clumping factor A (ClfA), iron surface determinant B (IsdB) and gamma hemolysin B (HlgB) of S. aureus and sequence coding for hydrophobic linkers between three domains. The recombinant gene was constructed in pET-28a (+) and expressed in Escherichia coli BL21. In addition, sequence coding for a His(6)-tag was added followed by a hybrid procedure of nickel chelate protein purification. Immunization of BALB/c mice with the recombinant protein ClfA-IsdB-Hlg evoked antigen-specific antibodies that could opsonize S. aureus cells, enhancing in vitro phagocytosis by macrophages. Vaccination with the recombinant protein also reduced the bacterial load recovered from mice spleen samples and increased survival following the intraperitoneal challenge with pathogenic S. aureus compared to the control mice. Our results showed that the recombinant protein ClfA-IsdB-Hlg is a promising vaccine candidate for the prevention of S. aureus bacteremia infections.