Protective immunity elicited by a divalent DNA vaccine encoding both the L7/L12 and Omp16 genes of Brucella abortus in BALB/c mice

Influenza viral vectors expressing the Brucella OMP16 or L7/L12 proteins as vaccines against B. abortus infection

BACKGROUND

We generated novel, effective candidate vaccine against Brucella abortus based on recombinant influenza viruses expressing the Brucella ribosomal protein L7/L12 or outer membrane protein (Omp)-16 from the NS1 open reading frame. The main purpose of this work was to evaluate the safety, immunogenicity and protectiveness of vaccine candidate in laboratory animals.

METHODS AND RESULTS

Four recombinant influenza A viral constructs of the subtypes Н5N1 or H1N1 expressing the Brucella proteins L7/L12 or Omp16 were obtained by a reverse genetics method: Flu-NS1-124-L7/L12-H5N1, Flu-NS1-124-Omp16-H5N1, Flu-NS1-124-L7/L12-H1N1 and Flu-NS1-124-Omp16-H1N1. Despite of substantial modification of NS1 gene, all constructs replicated well and were retain their Brucella inserts over five passages in embryonated chicken eggs (CE). Administration of the mono- or bivalent vaccine formulation via prime-boost intranasal (i.n.), conjunctival (c.) or subcutaneous (s.c.) immunization was safe in mice; no deaths, body weight loss or pathomorphological changes were observed over 56 days. Moreover, guinea pigs vaccinated i.n. with vaccine vectors did not shed the vaccine viruses through their upper respiratory tract after the prime and booster vaccination. These findings confirmed the replication-deficient phenotype of viral vectors. The highest antibody response to Brucella antigen was obtained with constructs expressing L7/L12 (ELISA, GMT 242.5-735.0); whereas the highest T-cell immune response- with construct expressing Omp16 (ELISPOT, 337 ± 52-651 ± 45 spots/4×105cells), which was comparable (P > 0.05) to the response induced by the commercial vaccine B. abortus 19. Interestingly, c. immunization appeared to be optimal for eliciting T-cell immune response. In guinea pigs, the highest protective efficacy after challenge with B. abortus 544 was achieved with Omp16 expressing constructs in both monovalent or bivalent vaccine formulations; protective efficacy was comparable to those induced by a commercial live B. abortus 19 vaccine.

CONCLUSION

Thus, influenza vectors expressing Brucella protective antigens can be developed as novel influenza vectored vaccine against B. abortus infection.

Novel influenza virus vectors expressing Brucella L7/L12 or Omp16 proteins in cattle induced a strong T-cell immune response, as well as high protectiveness against B. abortus infection

This paper presents the results of a study of the immunogenicity and protectiveness of new candidate vector vaccine against Brucella abortus - a bivalent vaccine formulation consisting of a mixture of recombinant influenza A subtype H5N1 or H1N1 (viral constructs vaccine formulation) viruses expressing Brucella ribosomal protein L7/L12 and Omp16, in cattle. To increase the effectiveness of the candidate vaccine, adjuvants such as Montanide Gel01 or chitosan were included in its composition. Immunization of cattle (heifers aged 1-1.5 years, 5 animals per group) with the viral constructs vaccine formulation only, or its combination with adjuvants Montanide Gel01 or chitosan, was conducted via the conjunctival method using cross prime (influenza virus subtype H5N1) and booster (influenza virus subtype H1N1) vaccination schedules at an interval of 28 days. Vaccine candidates were evaluated in comparison with the positive (B. abortus S19) and negative (PBS) controls. The viral constructs vaccine formulations, particularly in combination with Montanide Gel01 adjuvant promoted formation of IgG antibodies (with a predominance of antibodies of isotype IgG2a) against Brucella L7/L12 and Omp16 proteins in ELISA. Moreover, these vaccines in cattle induced a strong antigen-specific T-cell immune response, as indicated by a high number of CD4(+) and CD8(+) cells, as well as the concentration of IFN-γ, and most importantly provided a high level of protectiveness comparable to the commercial B. abortus S19 vaccine and superior to the B. abortus S19 vaccine in combination with Montanide Gel01 adjuvant. Based on these findings, we recommended the bivalent vaccine formulation containing the adjuvant Montanide Gel01 for practical use in cattle.

In silico analysis of chimeric TF, Omp31 and BP26 fragments of Brucella melitensis for development of a multi subunit vaccine candidate

OBJECTIVE(S)

Brucellosis, especially caused by Brucella melitensis, remains one of the most common zoonotic diseases worldwide with more than 500,000 human cases reported annually. The commonly used live attenuated vaccine in ovine brucellosis prophylaxis is B. melitensis Rev1. But due to different problems caused by the administration of this vaccine, a protective subunit vaccine against B. melitensis is strongly demanded. Brucella BP26, Omp31 and TF proteins have shown a considerable potential as protective antigens for brucellosis. Chimeric proteins carrying epitopes or adjuvant sequences increase the possibility of eliciting a broad cellular or humoral immune response. In silico tools are highly suited to study, design and evaluate vaccine strategies.

MATERIALS AND METHODS

In this study, a synthetic chimeric gene, encoding TF, BP26 (93-111) and Omp31(48-74) was designed. In order to predict the 3D structure of protein, modeling was carried out.

RESULTS

Validation results showed that 91.1% of residues lie in favored or additional allowed region of Ramachandran plot. The epitopes in the chimeric protein are likely to induce both the B-cell and T-cell mediated immune responses. Conclusion : The chimeric protein may be used as multi subunit for development of Brucella vaccine candidates.

Protective effect of a DNA vaccine containing an open reading frame with homology to an ABC-type transporter present in the genomic island 3 of Brucella abortus in BALB/c mice

The immunogenicity of a DNA vaccine containing an open reading frame (ORF) of genomic island 3 (GI-3), specific for Brucella abortus and Brucella melitensis, has been examined. Intramuscular injection of plasmid DNA carrying the open reading frame with homology to an ABC-type transporter (pV278a) into BALB/c mice elicited both humoral and cellular immune responses. Mice injected with pV278a had a dominant immunoglobulin G2a (IgG2a) response. This DNA vaccine elicited a T-cell-proliferative response and induced significant levels of interferon gamma (INF-γ) upon restimulation with recombinant 278a protein. Upon stimulation with an appropriate recombinant protein or crude Brucella protein, the vaccine did not induce IL-4, suggesting a typical T-helper (TH1) response. Furthermore, the vaccine induced protection in BALB/c mice when challenged with the virulent strain Brucella abortus 2308. Taken together, these data suggest that DNA vaccination offers an improved delivery of the homologous of an ABC-type transporter antigen, and provides the first evidence of a protective effect of this antigen in the construction of vaccines against B. abortus.

A history of the development of Brucella vaccines

Brucellosis is a worldwide zoonosis affecting animal and human health. In the last several decades, much research has been performed to develop safer Brucella vaccines to control the disease mainly in animals. Till now, no effective human vaccine is available. The aim of this paper is to review and discuss the importance of methodologies used to develop Brucella vaccines in pursuing this challenge.

Evaluation of protective effect of DNA vaccines encoding the BAB1_0263 and BAB1_0278 open reading frames of Brucella abortus in BALB/c mice

The immunogenicity of two DNA vaccines encoding open reading frames (ORFs) of genomic island 3 (GI-3), specific for Brucella abortus and Brucella melitensis, has been examined. Intramuscular injection of plasmid DNA carrying the BAB1_0263 and BAB1_0278 genes (pVF263 and pVF278, respectively) into BALB/c mice elicited both humoral and cellular immune responses. Mice injected with pVF263 or pVF278 had a dominant immunoglobulin G2a (IgG2a) response. In addition, both DNA vaccines elicited a T-cell-proliferative response, but only pVF263 induced significant levels of interferon gamma (INF-γ) upon restimulation with recombinant 263 protein. Neither DNA vaccine induced interleukin (IL)-10, nor IL-4, upon stimulation with an appropriate recombinant protein or crude Brucella protein, suggesting the induction of a typical T-helper 1 (Th1)-dominated immune response. Furthermore, the pVF278 DNA vaccines induced protection in BALB/c mice against challenge with the virulent strain B. abortus 2308. Taken together, these data suggest that DNA vaccination offers an improved delivery strategy for the BAB1_0278 antigen, and provide the first evidence of a protective effect of this antigen.

Immunogenicity and protective potential of a bacterially expressed recombinant dihydrolipoamide succinyltransferase (rE2o) of Brucella abortus in BALB/c mice

Brucellosis is one of the world's major zoonoses. No vaccine is available for the prevention of brucellosis in human. Efforts are needed to develop an effective, safe, stable, vaccine with long lasting immunity against human brucellosis. Here, we cloned and expressed recombinant dihydrolipoamide succinyltransferase (rE2o) of Brucella abortus in Escherichia coli and purified up to homogeneity by metal affinity chromatography. The purified rE2o is immunoreactive with brucellosis positive cattle sera. The immunogenicity and the protective potential of recombinant dihydrolipoamide succinyltransferase (rE2o) were evaluated in BALB/c mice with two different adjuvants i.e., Freund's and aluminium hydroxide gel. Mice were tested for humoral immune response by ELISA. Cell mediated immune response was tested by lymphocyte proliferation assay and cytokine profiling. The recombinant E2o (rE2o) generated high IgG antibody and its isotypes IgG1, and induced significant production of INF-γ, IL-10 and IL-4 cytokines. The rE2o protein induced significant lymphoproliferation of splenocytes. Altogether, these results suggest that rE2o induces a mixed but a predominant Th2 type of immune response in BALB/c mice and provides partial protection against challenge with pathogenic Brucella abortus.

Cloning, expression, and characterization of TonB2 from Actinobacillus pleuropneumoniae and potential use as an antigenic vaccine candidate and diagnostic marker

In this study the tonB2 gene was cloned from Actinobacillus pleuropneumoniae JL01 (serovar 1) and expressed as a glutathione-S-transferase (GST) fusion protein in Escherichia coli BL21(DE3). The GST fusion protein was recognized by antibodies in serum positive for A. pleuropneumoniae by Western blot analysis. Purified soluble GST-TonB2 was assessed for its ability to protect BALB/c mice against A. pleuropneumoniae infection. Mice were vaccinated with GST-TonB2 subcutaneously and challenged intraperitoneally with either ~4.0 × 10(5) colony-forming units (CFU) or ~1.0 × 10(6) CFU of A. pleuropneumoniae 4074. They were examined daily for 7 d after challenge. The survival rate of the TonB2-vaccinated mice was significant higher than that of the mice given recombinant GST or adjuvant alone. These results demonstrate that A. pleuropneumoniae TonB2 is immunogenic in mice and should be further assessed as a potential candidate for a vaccine against A. pleuropneumoniae infection. In addition, an indirect enzyme-linked immunosorbent assay (ELISA) based on the GST-TonB2 recombinant protein was developed. Compared with the ApxIVA ELISA, the TonB2 ELISA provided earlier detection of antibodies in pigs at various times after vaccination with A. pleuropneumoniae live attenuated vaccine. When compared with an indirect hemagglutination test, the sensitivity and specificity of the TonB2 ELISA were 95% and 88%, respectively. The TonB2 ELISA provides an alternative method for rapid serologic diagnosis of A. pleuropneumoniae infection through antibody screening, which would be especially useful when the infection status or serovar is unknown.

Over-expression of homologous antigens in a leucine auxotroph of Brucella abortus strain RB51 protects mice against a virulent B. suis challenge

Infection by members of the Gram-negative bacterial genus Brucella causes brucellosis in a variety of mammals. Brucellosis in swine remains a challenge, as there is no vaccine in the USA approved for use in swine against brucellosis. Here, we developed an improved recombinant Brucella abortus vaccine strain RB51 that could afford protection against Brucella suis infection by over-expressing genes encoding homologous proteins: L7/L12 ribosomal protein, Cu/Zn superoxide dismutase [SOD] and glycosyl-transferase [WboA]. Using strain RB51leuB as a platform and an antibiotic-resistance marker free plasmid, strains RB51leuB/SOD, RB51leuB/SOD/L7/L12 and RB51leuB/SOD/WboA were constructed to over-express the antigens: SOD alone, SOD and ribosomal protein L7/L12 or SOD and glycosyl-transferase, respectively. The ability of these vaccine candidates to protect against a virulent B. suis challenge were evaluated in a mouse model. All vaccine groups protected mice significantly (P<0.05) when compared to the control group. Within the vaccine groups, the mice vaccinated with strain RB51leuB/SOD/WboA were significantly better protected than those that were vaccinated with either strain RB51leuB/SOD or RB51leuB/SOD/L7/L12. These results suggest that Brucella antigens can be over-expressed in strain RB51leuB and elicit protective immune responses against brucellosis. Since the plasmid over-expressing homologous antigens does not carry an antibiotic resistance gene, it complies with federal regulations and therefore could be used to develop safer multi-species vaccines for prevention of brucellosis caused by other species of Brucella.

Human immune responses to Burkholderia pseudomallei characterized by protein microarray analysis

BACKGROUND

We aimed to determine the antibody and T cell responses to Burkholderia pseudomallei of humans to select candidate vaccine antigens.

METHODS

For antibody profiling, a protein microarray of 154 B. pseudomallei proteins was probed with plasma from 108 healthy individuals and 72 recovered patients. Blood from 20 of the healthy and 30 of the recovered individuals was also obtained for T cell assays.

RESULTS

Twenty-seven proteins distinctively reacted with human plasma following environmental exposure or clinical melioidosis. We compared the responses according to the patient's history of subsequent relapse, and antibody response to BPSL2765 was higher in plasma from individuals who had only 1 episode of disease than in those with recurrent melioidosis. A comparison of antibody and T cell responses to 5 B. pseudomallei proteins revealed that BimA and flagellin-induced responses were similar but that BPSS0530 could induce T cell responses in healthy controls more than in recovered patients.

CONCLUSIONS

By combining large-scale antibody microarrays and assays of T cell-mediated immunity, we identified a panel of novel B. pseudomallei proteins that show distinct patterns of reactivity in different stages of human melioidosis. These proteins may be useful candidates for development of subunit-based vaccines and in monitoring the risks of treatment failure and relapse.

Protective efficacy of DNA vaccines encoding outer membrane protein A and OmpK36 of Klebsiella pneumoniae in mice

The immunogenicity of DNA vaccines expressing outer membrane proteins as antigens was evaluated in this study. DNA vaccines consisting of vector pVAX1 expressing either outer membrane protein A or OmpK36 were injected into mice by either the intradermal or the intramuscular route. Antibodies elicited were shown to be specifically reactive to OmpA and OmpK36 by immunoblotting. The immunoglobulin G (IgG) antibodies elicited by both vaccines included IgG1, IgG2a, IgG2b, and IgG3. Immunized mice exhibited a predominance of IgG1 over IgG2a, therefore indicating a stronger humoral response. Mice receiving either of the DNA vaccines produced high levels of interleukin-12 (IL-12) and IL-10 and low levels of gamma interferon, suggesting the induction of a mixed Th1 and Th2 response. Sera from DNA vaccine-immunized mice had significantly higher opsonic activity in opsonophagocytic assays than did sera from the control mice. The level of protection afforded by pOmpK36 DNA injected intradermally into mice was the highest. These results suggest that both OmpA and OmpK36 are excellent candidates for use in future studies of vaccination against infections caused by Klebsiella pneumoniae. This is the first study which established the efficacy of protection afforded by DNA vaccines based on outer membrane proteins against K. pneumoniae infections.

The protein moiety of Brucella abortus outer membrane protein 16 is a new bacterial pathogen-associated molecular pattern that activates dendritic cells in vivo, induces a Th1 immune response, and is a promising self-adjuvanting vaccine against systemic and oral acquired brucellosis

Knowing the inherent stimulatory properties of the lipid moiety of bacterial lipoproteins, we first hypothesized that Brucella abortus outer membrane protein (Omp)16 lipoprotein would be able to elicit a protective immune response without the need of external adjuvants. In this study, we demonstrate that Omp16 administered by the i.p. route confers significant protection against B. abortus infection and that the protective response evoked is independent of the protein lipidation. To date, Omp16 is the first Brucella protein that without the requirement of external adjuvants is able to induce similar protection levels to the control live vaccine S19. Moreover, the protein portion of Omp16 (unlipidated Omp16 [U-Omp16]) elicits a protective response when administered by the oral route. Either systemic or oral immunization with U-Omp16 elicits a Th1-specific response. These abilities of U-Omp16 indicate that it is endowed with self-adjuvanting properties. The adjuvanticity of U-Omp16 could be explained, at least in part, by its capacity to activate dendritic cells in vivo. U-Omp16 is also able to stimulate dendritic cells and macrophages in vitro. The latter property and its ability to induce a protective Th1 immune response against B. abortus infection have been found to be TLR4 dependent. The facts that U-Omp16 is an oral protective Ag and possesses a mucosal self-adjuvanting property led us to develop a plant-made vaccine expressing U-Omp16. Our results indicate that plant-expressed recombinant U-Omp16 is able to confer protective immunity, when given orally, indicating that a plant-based oral vaccine expressing U-Omp16 could be a valuable approach to controlling this disease.

Towards a Brucella vaccine for humans

There is currently no licensed vaccine for brucellosis in humans. Available animal vaccines may cause disease and are considered unsuitable for use in humans. However, the causative pathogen, Brucella, is among the most common causes of laboratory-acquired infections and is a Center for Disease Control category B select agent. Thus, human vaccines for brucellosis are required. This review highlights the considerations that are needed in the journey to develop a human vaccine, including animal models, and includes an assessment of the current status of novel vaccine candidates.

Protection of mice against Brucella abortus 544 challenge by vaccination with recombinant OMP28 adjuvanted with CpG oligonucleotides

Brucella abortus, a gram negative, facultative intracellular pathogen causes brucellosis in many animal species and humans. Although live, attenuated vaccines are available against this infection, they suffer from certain limitations. Therefore, the development of an effective subunit vaccine against brucellosis is an area of intense research. The outer membrane proteins (OMPs) of Brucella species have been extensively studied for its immunogenicity and protective ability. We have investigated the potential of CpG ODN to enhance the immunogenicity and protective efficacy of recombinant 28 kDa outer membrane protein (rOMP28) of Brucella melitensis. The study demonstrated vigorous immunoglobulin G (IgG) response of OMP28. The administration of rOMP28 with CpG caused increased cell mediated immune response in terms of induced IgG2a, T-cell proliferation and up-regulation of type I cytokine expression. In contrast, the free antigen suppressed the interferon gamma (type I cytokine) production on in-vitro stimulation of spleenocytes. The result indicates the role of OMP28 in the down regulation of IFN-gamma production. Moreover, the B. abortus S-19 vaccinated mice showed highest production of IL-4 and IFN-gamma. The protective ability of the antigen was evaluated by systemic bacterial clearance after challenging the mouse with B. abortus 544 pathogen. The level of protection was significant in rOMP28+CpG treated mice but was lower than the required level. The results of the present study indicate that rOMP28 could be an immunogen capable of inducing both humoral and cellular immune response. The humoral response was biased towards Th1 type when it was co-administered with CpG.

Technical transformation of biodefense vaccines

Biodefense vaccines are developed against a diverse group of pathogens. Vaccines were developed for some of these pathogens a long time ago but they are facing new challenges to move beyond the old manufacturing technologies. New vaccines to be developed against other pathogens have to determine whether to follow traditional vaccination strategies or to seek new approaches. Advances in basic immunology and recombinant DNA technology have fundamentally transformed the process of formulating a vaccine concept, optimizing protective antigens, and selecting the most effective vaccine delivery approach for candidate biodefense vaccines.

The profile of cytokines and IgG subclasses in BALB/c mice after immunization with Brucella ribosomal gene

This study was evaluated the ability of DNA vaccine encoding L7/L12 protein of Brucella sp. to induce cellular and humoral immune responses in BALB/c mice and the profile of cytokines and IgG sub classes were determined. Intra muscular vaccination of mice using L7/L12 gene. Three vaccinations at 3 week intervals were performed. Cytokines and IgG subclasses were analyzed 3 week after the last DNA vaccination. Splenic lymphocytes from L7/L12pCDNA3-vaccinated mice produced high levels of IFNy (3100 pg mL(-1)) and low levels of IL-5 (300 pg mL(-1)), 3 weeks post-vaccination. The L7/L12pCDNA3 immunizations elicited high IgG2a isotype response in mice immunized. This antigen also induced IgG1 titers which were slightly lower than the IgG2a titers. Immunological analysis shows the appropriate immune response in BALB/c mice model after vaccination with L7/L12 gene. The high level of IFNgamma and low level of IL-5 in combination with high IgG2a/IgG1 ratio show the activation of Th1 cell response. The lower bacterial cfu from vaccinated mice in comparison with control groups show the efficiency of L7/L12 DNA vaccination in mice model.

Immunization with recombinant Brucella species outer membrane protein Omp16 or Omp19 in adjuvant induces specific CD4+ and CD8+ T cells as well as systemic and oral protection against Brucella abortus infection

Available vaccines against Brucella spp. are live attenuated Brucella strains. In order to engineer a better vaccine to be used in animals and humans, our laboratory aims to develop an innocuous subunit vaccine. Particularly, we are interested in the outer membrane proteins (OMPs) of B. abortus: Omp16 and Omp19. In this study, we assessed the use of these proteins as vaccines against Brucella in BALB/c mice. Immunization with lipidated Omp16 (L-Omp16) or L-Omp19 in incomplete Freund's adjuvant (IFA) conferred significant protection against B. abortus infection. Vaccination with unlipidated Omp16 (U-Omp16) or U-Omp19 in IFA induced a higher degree of protection than the respective lipidated versions. Moreover, the level of protection induced after U-Omp16 or U-Omp19 immunization in IFA was similar to that elicited by live B. abortus S19 immunization. Flow cytometric analysis showed that immunization with U-Omp16 or U-Omp19 induced antigen-specific CD4(+) as well as CD8(+) T cells producing gamma interferon. In vivo depletion of CD4(+) or CD8(+) T cells in mice immunized with U-Omp16 or U-Omp19 plus IFA resulted in a loss of the elicited protection, indicating that both cell types are mediating immune protection. U-Omp16 or U-Omp19 vaccination induced a T helper 1 response, systemic protection in aluminum hydroxide formulation, and oral protection with cholera toxin adjuvant against B. abortus infection. Both immunization routes exhibited a similar degree of protection to attenuated Brucella vaccines (S19 and RB51, respectively). Overall these results indicate that U-Omp16 or U-Omp19 would be a useful candidate for a subunit vaccine against human and animal brucellosis.

Vaccination with Brucella recombinant DnaK and SurA proteins induces protection against Brucella abortus infection in BALB/c mice

The immunogenicity and protective efficacy of recombinant SurA (rSurA) and rDnaK from Brucella spp. were evaluated in BALB/c mice. Immunization with rSurA in adjuvant induced a vigorous immunoglobulin G (IgG) response, with higher IgG2a than IgG1 titers. In addition, after in vitro stimulation with rSurA, spleen cells from rSurA-immunized mice produced interleukin-2 (IL-2), interferon (IFN)-gamma, IL-4 and IL-5. Immunization with rDnaK plus adjuvant induced a strong humoral response resulting in similar anti-rDnaK IgG titers than immunization with rDnaK alone. IgG2a titers predominated over IgG1 in mice injected with rDnaK alone or rDnaK plus adjuvant. Spleen cells from mice immunized with rDnaK plus adjuvant secreted IFN-gamma and IL-2 upon stimulation with rDnaK and induced a specific cytotoxic response. On the contrary, mice immunized with rDnaK alone did not exhibit a specific T helper or cytotoxic response in vitro. Mice given rSurA or rDnaK with adjuvant exhibited a significant degree of protection whereas immunization with rDnaK alone induced a low but still statistically significant level of protection against B. abortus infection. All studied vaccines were less protected than mice immunized with H38 or B. abortus strain 19 control vaccines. Altogether these results suggest that rSurA or rDnaK induce partial protection against B. abortus infection and could be useful candidates for the development of subunit vaccines against brucellosis.

Partial protection against Brucella infection in mice by immunization with nonpathogenic alphaproteobacteria

Previous findings indicate that Brucella antigens and those from nonpathogenic alphaproteobacteria (NPAP) are cross-recognized by the immune system. We hypothesized that immunization with NPAP would protect mice from Brucella infection. Mice were immunized subcutaneously with heat-killed Ochrobactrum anthropi, Sinorhizobium meliloti, Mesorhizobium loti, Agrobacterium tumefaciens, or Brucella melitensis H38 (standard positive control) before intravenous challenge with Brucella abortus 2308. Cross-reacting serum antibodies against Brucella antigens were detected at the moment of challenge in all NPAP-immunized mice. Thirty days after B. abortus challenge, splenic CFU counts were significantly lower in mice immunized with O. anthropi, M. loti, and B. melitensis H38 than in the phosphate-buffered saline controls (protection levels were 0.80, 0.66, and 1.99 log units, respectively). In mice immunized intraperitoneally with cytosoluble extracts from NPAP or Brucella abortus, protection levels were 1.58 for the latter, 0.63 for O. anthropi, and 0.40 for M. loti. To test whether the use of live NPAP would increase protection further, mice were both immunized and challenged by the oral route. Immunization with NPAP induced a significant increase in serum immunoglobulin G (IgG), but not serum or fecal IgA, against Brucella antigens. After challenge, anti-Brucella IgA increased significantly in the sera and feces of mice orally immunized with O. anthropi. For all NPAP, protection levels were higher than those obtained with systemic immunizations but were lower than those obtained by oral immunization with heat-killed B. abortus. These results show that immunization with NPAP, especially O. anthropi, confers partial protection against Brucella challenge. However, such protection is lower than that conferred by immunization with whole Brucella or its cytosoluble fraction.

A recombinant subunit vaccine based on the insertion of 27 amino acids from Omp31 to the N-terminus of BLS induced a similar degree of protection against B. ovis than Rev.1 vaccination

The development of an effective subunit vaccine against brucellosis is a research area of intense interest. The enzyme lumazine synthase from Brucella spp. (BLS) is highly immunogenic, presumably due to its decameric arrangement and remarkable stability. In this work we decided to develop a chimera with the scaffold protein BLS decorated with 10 copies of a known protective epitope derived from an outer membrane protein of 31kDa (Omp31) from Brucella spp. Vaccination of BALB/c mice with the chimera as a recombinant protein (rBLSOmp31) provided the best protection level against Brucella ovis, which was higher than the given by the co-delivery of both recombinant proteins (rBLS + rOmp31) and similar than the control vaccine Brucella melitensis strain Rev.1. Moreover rBLSOmp31 induced protection against Brucella melitensis but to a lesser degree than Rev.1. The chimera induced a strong humoral response against the inserted peptide. It also induced peptide- and BLS-specific T helper 1 and cytotoxic T responses. In conclusion, our results indicate that BLSOmp31 could be a useful candidate for the development of subunit vaccines against brucellosis since it elicits humoral, T helper and cytotoxic immune responses and protection against smooth and rough species of Brucella.

Nasal immunization with recombinant Brucella melitensis bp26 and trigger factor with cholera toxin reduces B. melitensis colonization

bp26 and trigger factor (Tf) DNA vaccines have previously been shown to protect against Brucella infection. In this study, purified bp26 and Tf proteins were tested in BALB/c mice for immunity and protection. The results showed that intranasal (i.n.) immunization with bp26 and Tf in conjunction with cholera toxin (CT) adjuvant elicit both elevated mucosal and systemic immune responses. While nasal immunization with either bp26 or Tf elicited elevated antibody responses, co-immunization with both enhanced anti-Tf immunity, suggesting bp26 adjuvant activity. Evaluation of serum IgG subclass responses showed elevated IgG1 titers. Further analysis to discern the source of immune B cells revealed effective immunization of respiratory tissues. However, Tf stimulated a significantly higher level of cytokine-forming cells (CFC) than bp26. These results imply that co-immunization of bp26 and Tf proteins elicits synergistic cooperation to stimulate the immune system. When immunized mice were challenged with B. melitensis 16M, bp26-plus Tf-immunized mice showed no difference in splenic weights but harbored three-fold less bacterial CFU when compared to sPBS-immunized control mice.

Cloning and characterization of a ribosomal protein L23a from Haemaphysalis qinghaiensis eggs by immuno screening of a cDNA expression library

A primary cDNA library with a size of 1.34 x 10(6) PFU was constructed from Haemaphysalis qinghaiensis eggs and was immunoscreened with rabbit anti-H. qinghaiensis serum. One clone (Hq22, named following those clones obtained from adult Haemaphysalis qinghaiensis cDNA library which we constructed before) screened from the cDNA library was selected randomly for sequencing. The entire sequence of the clone was subsequently obtained using rapid amplification of the cDNA ends (RACE). A search of the cloned sequence against GenBank revealed that it related to ribosomal protein L23a (Rpl23a) and had a high percentage similarity to this protein from different species. Conserved domains for Rpl23a were also identified in the cloned sequence. Expression analysis by RT-PCR showed that this gene is expressed in salivary glands, midguts, other tissues and different developmental stages of H. qinghaiensis. Based on the H. qinghaiensis Rpl23a sequence, open reading frames (ORF) of Rpl23a of Heamaphysalis longicornis and Boophilus microplus were also cloned and were performed for comparison with Rpl23a of H. qinghaiensis and other organisms as well. Vaccine based on Rpl23a recombinant protein cannot protect sheep against H. qinghaiensis.