CD8+ type 1 CD44hi CD45 RBlo T lymphocytes control intracellular Brucella abortus infection as demonstrated in major histocompatibility complex class I- and class II-deficient mice

Effects of vaccination with Brucella melitensis, strains Rev 1 ΔeryCD and Rev 1, on the reproductive system of young male goats

The present study evaluates the effects of vaccination with Brucella melitensis strains Rev 1 ΔeryCD and Rev 1 on the reproductive system of male goats. Three groups, each of them consisting of 15 six-month-old brucellosis-free male goats, were studied. The first group was vaccinated with the Rev 1 ΔeryCD strain, the second group received Rev 1 and the third group was inoculated with sterile physiological saline solution. The dose of both strains was of 1×109CFU/ml. Over the course of the five months of this study, three males from each group were euthanized every month. Their reproductive tracts, spleens, and lymph nodes were collected to analyze serology, bacteriology PCR, histology, and immunohistochemistry. Results show that vaccination with B. melitensis strains Rev 1 ΔeryCD and Rev 1 does not harm the reproductive system of male goats. Strain B. melitensis Rev 1 ΔeryCD displayed a lower capacity to colonize the reproductive tract than strain Rev 1, which was attributed to its limited catabolic action toward erythritol.

Helicobacter pylori induces urease subunit B-specific CD8+ T cell responses in infected individuals via cytosolic pathway of cross-presentation

BACKGROUND

Urease subunit B (UreB), a conserved and key virulence factor of Helicobacter pylori (H. pylori), can induce the host CD4+ T cell immune responses to provide protection, but less is known regarding CD8+ T cell responses. The characteristics of H. pylori-specific CD8+ T cell responses and the mechanism underlying antigen processing and presentation pathways remain unclear. This study was focus on protective antigen recombinant UreB (rUreb) to detect specific CD8+ T cell responses in vitro and elucidate the mechanism of UreB antigen processing and presentation.

METHODS

The peripheral blood mononuclear cells (PBMCs) collected from H. pylori-infected individuals were stimulated with rUreB in vitro to detect specific CD8+ T cell responses after co-culture with rUreB-pulsed autologous hMDCs. Through blocking assay, we investigated the potential pathway of UreB antigen processing and presentation via the cytosolic pathway or vacuolar pathway. The cytokines production of UreB specific CD8+ T cell were evaluated as well.

RESULTS

We demonstrated UreB can induce specific CD8+ T cell immune responses in H. pylori infected individuals. Importantly, we characterized that UreB were mainly processed by proteasome instead of lysosomal proteases and presented through cytosolic pathway of cross-presentation, which requires endoplasmic reticulum-Golgi transport and newly synthesized MHC-I molecules, to induce functional-specific CD8+ T cell (IFN-γ + TNF-α + Grz A+ Grz B+) responses.

CONCLUSIONS

These results suggest that H. pylori UreB induces specific CD8+ T cell responses through cytosolic pathway of cross-presentation in infected individuals.

A Single Nasal Dose Vaccination with a Brucella abortus Mutant Potently Protects against Pulmonary Infection

The Brucella abortus double-mutant (ΔznuA ΔnorD Brucella abortus-lacZ [znBAZ]) was assessed for its protective efficacy after vaccination with a single nasal dose. Superior protection was achieved in znBAZ-vaccinated mice against pulmonary, wild-type B. abortus 2308 challenge when compared with conventional livestock Brucella abortus vaccines, the smooth S19 (smooth B. abortus strain 19 vaccine) and rough RB51 (rough mutant vaccine strain of B. abortus) strains. Nasal znBAZ vaccination reduced splenic and lung colonization by wild-type brucellae by >3-4 logs. In contrast, S19 reduced lung colonization by only 32-fold, and RB51 failed to reduce colonization. One profound attribute of znBAZ vaccination was the >3-fold increase in pulmonary CD8+ T cells when compared with other vaccinated groups. S19 vaccination increased only CD4+ T cells. All vaccines induced IFN-γ and TNF-α production by CD4+ T cells, but only znBAZ vaccination enhanced the recruitment of polyfunctional CD8+ T cells, by >100-fold. IL-17 by both CD4+ and CD8+ T cells was also induced by subsequent znBAZ vaccination. These results demonstrate that, in addition to achieving protective immunity by CD4+ T cells, CD8+ T cells, specifically resident memory T cells, also confer protection against brucellosis. The protection obtained by znBAZ vaccination was attributed to IFN-γ-producing CD8+ T cells, because depletion of CD8+ T cells throughout vaccination and challenge phases abrogated protection. The stimulation of only CD4+ T cells by RB51- and S19-vaccinated mice proved insufficient in protecting against pulmonary B. abortus 2308 challenge. Thus, nasal znBAZ vaccination offers an alternative means to elicit protection against brucellosis.

Identification of potential antigenic peptides of Brucella through proteome and peptidome

BACKGROUND

Brucellosis, caused by Brucella spp., is a major zoonotic public health threat. Although several Brucella vaccines have been demonstrated for use in animals, Brucella spp. can cause human infection and to date, there are no human-use vaccines licensed by any agency. Recently, methods in vaccine informatics have made major breakthroughs in peptide-based epitopes, opening up a new avenue of vaccine development.

OBJECTIVES

The purpose of this article was to identify potential antigenic peptides in Brucella by proteome and peptidome analyses.

METHODS

Mouse infection models were first established by injection with Brucella and spleen protein profiles were then analysed. Subsequently, the major histocompatibility complex class I or II (major histocompatibility complex [MHC]-I/II)-binding peptides in blood samples were collected by immunoprecipitation and peptides derived from Brucella proteins were identified through liquid chromatography-mass spectrometry (LC-MS/MS). These peptides were then evaluated in a variety of ways, such as in terms of conservation in Brucella and synchronicity in predicted peptides (similarity and coverage), which allowed us to more effectively measure their antigenic potential.

RESULTS

The expression of the inflammatory cytokines IL1B and IFN-γ was significantly altered in the spleen of infected mice and some Brucella proteins, such as Muri, AcpP and GroES, were also detected. Meanwhile, in blood, 35 peptides were identified and most showed high conservation, highlighting their potential as antigen epitopes for vaccine development. In particular, we identified four proteins containing both MHC-I- and MHC-II-binding peptides including AtpA, AtpD, DnaK and BAbS19_II02030. They were also compared with the predicted peptides to estimate their reliability.

CONCLUSIONS

The peptides we screened could bind to MHC molecules. After being stimulated with antigen T epitopes, Memory T cells can stimulate T cell activation and promote immune responses. Our results indicated that the peptides we identified may be good candidate targets for the design of subunit vaccines and these results pave the way for the study of safer vaccines against Brucella.

Live mucosal vaccination stimulates potent protection via varied CD4+ and CD8+ T cell subsets against wild-type Brucella melitensis 16M challenge

Re-emerging zoonotic pathogen Brucella spp. continues to impact developing countries and persists in expanding populations of wildlife species in the US, constantly threatening infection of our domestic herds. The development of improved animal and human vaccines remains a priority. In this study, immunity to a novel live attenuated B. melitensis strain, termed znBM-mC, was characterized. An oral prime, intranasal (IN) boost strategy conferred exquisite protection against pulmonary challenge, with wild-type (wt) B. melitensis providing nearly complete protection in the lungs and spleens from brucellae colonization. Vaccination with znBM-mC showed an IFN-γ⁺ CD8⁺ T-cell bias in the lungs as opposed to Rev 1-vaccinated mice showing IFN-γ⁺ CD4⁺ T-cell inclination. Lung CD4⁺ and CD8⁺ effector memory T cells (TEMs) increased over 200-fold; and lung CD4⁺ and CD8⁺ resident memory T cells (TRMs) increased more than 250- and 150-fold, respectively. These T cells served as the primary producers of IFN-γ in the lungs, which was essential for vaccine clearance and the predominant cytokine generated pre-and post-challenge with wt B. melitensis 16M; znBM-mC growth could not be arrested in IFN-γ^−/− mice. Increases in lung TNF-α and IL-17 were also induced, with IL-17 being mostly derived from CD4⁺ T cells. Vaccination of CD4^−/−, CD8^−/−, and B6 mice with znBM-mC conferred full protection in the lungs and spleens post-pulmonary challenge with virulent B. melitensis; vaccination of IL-17^−/− mice resulted in the protection of the lungs, but not the spleen. These data demonstrate the efficacy of mucosal vaccine administration for the generation of protective memory T cells against wt B. melitensis.

Immunosuppressive Mechanisms in Brucellosis in Light of Chronic Bacterial Diseases

Brucellosis is considered one of the major zoonoses worldwide, constituting a critical livestock and human health concern with a huge socio-economic burden. Brucella genus, its etiologic agent, is composed of intracellular bacteria that have evolved a prodigious ability to elude and shape host immunity to establish chronic infection. Brucella’s intracellular lifestyle and pathogen-associated molecular patterns, such as its specific lipopolysaccharide (LPS), are key factors for hiding and hampering recognition by the immune system. Here, we will review the current knowledge of evading and immunosuppressive mechanisms elicited by Brucella species to persist stealthily in their hosts, such as those triggered by their LPS and cyclic β-1,2-d-glucan or involved in neutrophil and monocyte avoidance, antigen presentation impairment, the modulation of T cell responses and immunometabolism. Attractive strategies exploited by other successful chronic pathogenic bacteria, including Mycobacteria, Salmonella, and Chlamydia, will be also discussed, with a special emphasis on the mechanisms operating in brucellosis, such as granuloma formation, pyroptosis, and manipulation of type I and III IFNs, B cells, innate lymphoid cells, and host lipids. A better understanding of these stratagems is essential to fighting bacterial chronic infections and designing innovative treatments and vaccines.

Immunometabolism in human brucellosis: An emerging field of investigation

In recent years, extreme attention has been focused on the role of immunometabolism in the regulation of immune cell responses in healthy individuals during infection, autoimmunity, and cancer. In the infection biology area, it has been shown that there is a close relationship between the immune system and the host metabolic changes. Brucella species is an intracellular coccobacillus that infects humans and mammals, which led to brucellosis. Brucella species with host-specific evolutionary mechanisms allow it to hide from or manipulate cellular immunity and achieve intracellular persistence. Intracellular bacterial pathogens such as Brucella species also employ host cell resources to replicate and persist inside the host. Targeting these host systems is one promising strategy for developing novel antimicrobials to tackle intracellular infections. This study will summarize the role of metabolic reprogramming in immune cells and their relationship to brucellosis.

Comparison of Immune Effects Between Brucella Recombinant Omp10-Omp28-L7/L12 Proteins Expressed in Eukaryotic and Prokaryotic Systems

Brucella, a genus of bacteria that causes brucellosis, infects and threatens domestic animals, and humans in endemic areas. Presently, some live attenuated vaccines of Brucella are used to immunize livestock; however, these vaccines are pathogenic to humans, can provoke abortion when administered to pregnant livestock, and induce antibodies in vaccinated livestock that affect the diagnosis of field infection. It is, therefore, very important for improving the safety and immune protection effects of Brucella vaccine. Currently, recombinant protein-based subunit vaccines are considered promising safe and effective alternatives against brucellosis. Here, we separately expressed the recombinant Omp10-Omp28-L7/L12 proteins of Brucella using eukaryotic and prokaryotic expression systems, which were then used as immunogens for evaluating their immune responses. Taishan Pinus massoniana pollen polysaccharides (TPPPS), an already verified natural adjuvant, was utilized to evaluate the immune conditioning effect on the recombinant proteins. Antibody levels, spleen lymphocyte proliferation, percentages of CD4⁺ and CD8⁺ T cells, and cytokine secretion in mice were examined after three successive immunizations. The protective effects against Brucella challenge were also evaluated in mice, and used a live vaccine as a positive control. The results indicated that the immune responses of the recombinant Omp10-Omp28-L7/L12 protein groups were significantly higher than those of the PBS control group. The recombinant Omp10-Omp28-L7/L12 protein expressed in Pichia pastoris (P. pastoris) exhibited a slightly higher expression level and immunogenicity than that expressed in Escherichia coli (E. coli), and the Omp10-Omp28-L7/L12 (P. pastoris) + TPPPS group provided the most pronounced immune effect. The protective results showed that the recombinant Omp10-Omp28-L7/L12 proteins expressed in the two expression systems had significantly better protective effects against Brucella melitensis challenge compared with the negative control, and the addition of TPPPS adjuvant could significantly improve the protective effects of subunit vaccines. However, we also noticed that all of the evaluated subunit vaccines induced less protection than the B. melitensis M5 live vaccine. These results indicate that the combination of recombinant Omp10-Omp28-L7/L12 antigen and TPPPS adjuvant shows potential as an effective brucellosis subunit vaccine, and P. pastoris is a preferred expression system to prepare this recombinant subunit antigen.

Evaluation of transgenic Leishmania infantum expressing mLLO-BAX-SMAC in the apoptosis of the infected macrophages in vitro and in vivo

BACKGROUND

Leishmaniasis is an important infectious disease that develops because of escaping parasite from the host immune system or preventing host macrophages apoptosis. Recently, the development of transgenic methods and the manipulation of the parasite genome has provided many advantages. So, in this study, the effect of the transgenic Leishmania infantum expressing mLLO-BAX-SMAC proteins was examined in accelerating host cell apoptosis.

METHOD

The entire coding sequence of designed codon-optimized mLLO-Bax-Smac was cloned in the pLexyNeo2 vector and integrated downstream of the 18srRNA locus of L infantum genome by homologous recombination. Next, the expression of mLLO-BAX-SMAC fusion protein was evaluated by the Western blotting technique and the pathogenesis of transgenic parasite was surveyed in vitro and in vivo.

RESULTS

The results of PCR and Western blot confirmed proper integration and expression of mLLO-Bax-Smac sequence into the 18srRNA locus of L infantum. Flow cytometry showed accelerating apoptosis of transgenic Leishmania-infected macrophages compared to wild-type parasite. Also, transgenic parasites were less virulent as a fewer parasitic burden was found in the spleen and liver of transgenic-infected mice compared to the control.

CONCLUSION

The data suggested that the transgenic L infantum expressing BAX-SMAC can be used as an experimental model for developing vaccination against leishmaniasis.

B Cells Inhibit CD4+ T Cell-Mediated Immunity to Brucella Infection in a Major Histocompatibility Complex Class II-Dependent Manner

Brucella spp. are facultative intracellular bacteria notorious for their ability to induce a chronic, and often lifelong, infection known as brucellosis. To date, no licensed vaccine exists for prevention of human disease, and mechanisms underlying chronic illness and immune evasion remain elusive. We and others have observed that B cell-deficient mice challenged with Brucella display reduced bacterial burden following infection, but the underlying mechanism has not been clearly defined. Here, we show that at 1 month postinfection, B cell deficiency alone enhanced resistance to splenic infection ∼100-fold; however, combined B and T cell deficiency did not impact bacterial burden, indicating that B cells only enhance susceptibility to infection when T cells are present. Therefore, we investigated whether B cells inhibit T cell-mediated protection against Brucella Using B and T cell-deficient Rag1^-/- animals as recipients, we demonstrate that adoptive transfer of CD4⁺ T cells alone confers marked protection against Brucella melitensis that is abrogated by cotransfer of B cells. Interestingly, depletion of CD4⁺ T cells from B cell-deficient, but not wild-type, mice enhanced susceptibility to infection, further confirming that CD4⁺ T cell-mediated immunity against Brucella is inhibited by B cells. In addition, we found that the ability of B cells to suppress CD4⁺ T cell-mediated immunity and modulate CD4⁺ T cell effector responses during infection was major histocompatibility complex class II (MHCII)-dependent. Collectively, these findings indicate that B cells modulate CD4⁺ T cell function through an MHCII-dependent mechanism which enhances susceptibility to Brucella infection.

Evaluation of Duration of Immunogenicity and Protective Efficacy of Improved Influenza Viral Vector-Based Brucella abortus Vaccine Against Brucella melitensis Infection in Sheep and Goats

In this study, we first evaluated the duration of a protective immune response against Brucella melitensis infection in non-pregnant sheep and goats immunized with an improved (by vaccine formulation and route of administration) commercial Brucella abortus vaccine based on influenza viral vectors expressing Brucella immunodominant Omp16, L7/L12, Omp19, or Cu-Zn superoxide dismutase (SOD) proteins (Flu-BA_Omp19-SOD). Sheep and goats in the vaccinated group were immunized thrice concurrently via the subcutaneous and conjunctival routes of administration at an interval of 21 days. Animals in the control group were administered with 20% Montanide Gel01 adjuvant in phosphate-buffered saline in the same way. We showed that the Flu-BA_Omp19-SOD vaccine in sheep and goats induces antigen-specific Th1-biased [immunoglobulin G2a (IgG2a) over IgG1] antibody response and T-cell and interferon γ responses lasting over a period of 1 month post–last vaccination (PLV). The levels of protection against B. melitensis 16M infection (vaccination efficacy) in vaccinated sheep for a period of 6 months were 0–20% and in goats 20–40% compared to control challenge group. But the severity of B. melitensis 16M infection in the Flu-BA_Omp19-SOD–vaccinated sheep and goats during the entire period of observation revealed the infection index (P = 0.001–P < 0.0001) and Brucella colonization in lymph nodes and organs (P = 0.04–P < 0.0001) were significantly lower than those in the control group. To conclude, the Flu-BA_Omp19-SOD vaccine using improved formulation and administration method in sheep and goats provides augmented antigen specific humoral and T-cell immune response lasting only for 1 month PLV and partial protection for 6 months against B. melitensis 16M infection.

Transcriptome analysis of Brucella abortus S19∆per immunized mouse spleen revealed activation of MHC-I and MHC-II pathways

The mouse (Mus musculus) has been extensively used for studying brucellosis, regarding pathogenesis, immunity and the evaluation of vaccines and therapeutics. In this work, RNA-seq was applied to explore the immunological potential of a live Brucella abortus S19∆per, a perosamine synthetase gene mutant of B. abortus S19. Comparison of transcriptome data was carried out for identifying differentially expressed genes among PBS (control) and B. abortus S19∆per immunized mice at 15 days post-immunization. Functional analysis revealed 545 significant differentially expressed genes related to mouse immunity. Specific activation of MHC-I and MHC-II antigen-processing pathways were identified as the highly enriched pathways based on Kyoto Encyclopedia of Genes and Genomes annotation. Other major immune response pathways regulated within the host were NF-kappa B signalling, chemokine signalling, T-cell receptor pathway, apoptosis, TNF signalling and nucleotide-binding oligomerization domain-like receptor signalling. These data provided new insights into the molecular mechanisms of B. abortus S19∆per-induced immune response in mice spleen that might facilitate the development of a highly immunogenic vaccine against brucellosis.

The BtaF Adhesin Is Necessary for Full Virulence During Respiratory Infection by Brucella suis and Is a Novel Immunogen for Nasal Vaccination Against Brucella Infection

Brucella enters their hosts mostly through mucosae from where it spreads systemically. Adhesion to extracellular matrix (ECM) components or to host cells is important for the infectious process, and is mediated by several adhesins, including the BtaF trimeric autotransporter. Although Th1 responses and gamma interferon (IFN-γ) are important for protection, antibodies able to block adhesions might also contribute to prevent Brucella infection. We evaluated the importance of BtaF for respiratory Brucella infection, and characterized the immune response and protection from mucosal challenge induced by nasal vaccination with recombinant BtaF. While lung CFU numbers did not differ at day 1 p.i. between mice intratracheally inoculated with B. suis M1330 (wild type) and those receiving a ΔbtaF mutant, they were reduced in the latter group at 7 and 30 days p.i. For vaccination studies the BtaF passenger domain was engineered and expressed as a soluble trimeric protein. Mice were immunized by the nasal route with BtaF or saline (control group) plus the mucosal adjuvant c-di-AMP. Specific anti-BtaF antibodies (IgG and IgA) were increased in serum, including a mixed IgG2a/IgG1 response. In vitro, these antibodies reduced bacterial adhesion to A549 alveolar epithelial cells. Specific IgA antibodies were also increased in several mucosae. Spleen cells from BtaF immunized mice significantly increased their IL-2, IL-5, IL-17, and IFN-γ secretion upon antigen stimulation. In cervical draining lymph nodes, antigen-experienced CD4+ T cells were maintained mainly as central memory cells. A BtaF-specific delayed-type hypersensitivity response was detected in BtaF immunized mice. Lung cells from the latter produced high levels of IFN-γ upon antigen stimulation. Although nasal immunization with BtaF did not protect mice against B. suis respiratory challenge, it conferred significant protection from intragastric challenge; the splenic load of B. suis was reduced by 3.28 log CFU in immunized mice. This study shows that nasal vaccination with BtaF+c-di-AMP protects against intragastric challenge with B. suis by inducing local and systemic antibody responses, central memory CD4+ T cells and strong Th1 responses. Therefore, although BtaF vaccination did not protect from B. suis respiratory infection, this adhesin constitutes a promising immunogen against mucosal B. suis infection.

Inhibition of antigen presentation by Brucella: many more than many ways

Brucella infection activates the immune system and favors the differentiation of CD4⁺ and CD8⁺ T cells. To persist during a long time inside macrophages evading immune surveillance of these T cells the pathogen must exploit different evasion strategies. We review the mechanisms whereby Brucella, through TLR signaling, inhibits MHC class I and II antigen presentation, allowing infected macrophages to become effective niches for Brucella survival.

Development of new generation of vaccines for Brucella abortus

Brucella abortus is a Gram-negative facultative and intracellular bacteria, it causes bovine brucellosis, a zoonotic disease that is responsible for considerable economic loss to owners of domesticated animals and can cause problems in otherwise healthy humans. There are a few available live attenuated vaccines for animal immunization against brucellosis; however, these have significant side effects and offer insufficient protective efficacy. Thus, the need for more research into the Molecular pathobiology and immunological properties of B. abortus that would lead to the development of better and safer vaccines. In this paper we have reviewed the main aspects of the pathology and the responsive immunological mechanisms, we have also covered current and new prospective vaccines against B. abortus.

Evaluation of DNA vaccine encoding BCSP31 surface protein of Brucella abortus for protective immunity

Brucellosis is a highly contagious and zoonotic disease and has a considerable impact on animal health and economy of a country, principally in Pakistan, where rural income largely depends upon livestock farming and dairy products. The disease burden is more in underdeveloped/developing countries due to the low economy and limited access to the diagnostic facilities. In Pakistan, the prevalence of Brucella abortus is very high, so it is the need of the hour to control this disease through more advanced methods. This study was designed with the aim to construct the DNA based vaccine of gene encoding antigenic surface protein (BCSP₃₁). For this purpose, the BCSP₃₁ gene was amplified, purified and ligated in pTZ57 R/T (cloning vector). Dubbed BCSP₃₁-pTZ57 R/T vector was transformed into competent cells (DH5α). After plasmid extraction, the plasmid and pET-28a vector was restricted with EcoRI and BamHI. Again, ligation was done and dubbed pET-28a-BCSP₃₁ transformed into E. coli (BL21). After expression, the protein was purified and used for evaluation of immunogenic response. The protective and immunogenic efficacy of the vaccine was evaluated in rabbits (n = 20). The rabbits were divided into four equal groups. Groups A-C were given purified protein diluted in normal saline @ 750, 1500 and 3000 μg/0.2 mL, respectively through intraconjunctival route. Group D was given 0.2 mL normal saline through intraconjunctival route. Specific immunoglobulin G (IgG) responses were measured through indirect ELISA on a weekly basis. The titer of IgG against the antigen was significantly (p < 0.05) higher in vaccinated groups A-C as compared to group D (control group) in a dose dependent manner. Moreover, log units of protection produced by DNA based vaccine in the rabbits (3.02) also indicated the protective efficacy of the DNA vaccine against B. abortus challenge. The response of this vaccine in rabbit suggested its potential effectiveness against Brucella abortus in large animals.

Protective efficacy of a canine brucellosis vaccine candidate based on live attenuated Salmonella expressing recombinant Brucella BCSP31, Omp3b and SOD proteins in Beagles

The aim of this study was to establish a proof-of-concept of protective efficacy of Salmonella-based B. abortus vaccine candidate in Beagles. Group A Beagles (n=10) were subcutaneously (SC) inoculated with S. Typhimurium delivery strain containing pMMP65 (vector to deliver antigens) only as vector control. Group B Beagles (n=10) were SC vaccinated with the mixture of the three Salmonella delivery strains expressing the recombinant B. abortus BCSP31, Outer membrane protein 3b (Omp3b), and superoxide dismutase (SOD) proteins, respectively. No Salmonella delivery strains were isolated from all tissues tested. Serum IgG, interleukin-4, tumor necrosis factor-alpha, and interferon-gamma concentrations were significantly higher in group B than in group A. Following intraconjunctival challenge with B. abortus 544, among 5 group B Beagles, the challenge strain was isolated from mandibular, and retropharyngeal lymph nodes of three Beagles, and no isolates were observed from all tissues of two Beagle. However, the challenge strains were detected from spleen, uterus (except two Beagles), and mandibular, prescapular, retropharyngeal, and superficial inguinal lymph nodes of all group A Beagles. These results suggest that the mixture of three S. Typhimurium delivery strains be a good vaccine candidate against brucellosis by B. abortus in dogs. Further investigations are needed to improve the protective efficacy of the Salmonella-based B. abortus vaccine candidate and explore its practical application in dogs.

Brucella Peptide Cross-Reactive Major Histocompatibility Complex Class I Presentation Activates SIINFEKL-Specific T Cell Receptor-Expressing T Cells

Brucella spp. are intracellular pathogenic bacteria remarkable in their ability to escape immune surveillance and therefore inflict a state of chronic disease within the host. To enable further immune response studies, Brucella was engineered to express the well-characterized chicken ovalbumin (OVA). Surprisingly, we found that CD8 T cells bearing T cell receptors (TCR) nominally specific for the OVA peptide SIINFEKL (OT-1) reacted to parental Brucella-infected targets as well as OVA-expressing Brucella variants in cytotoxicity assays. Furthermore, splenocytes from Brucella-immunized mice produced gamma interferon (IFN-γ) and exhibited cytotoxicity in response to SIINFEKL-pulsed target cells.To determine if the SIINFEKL-reactive OT-1 TCR could be cross-reacting to Brucella peptides, we searched the Brucella proteome using an algorithm to generate a list of near-neighbor nonamer peptides that would bind to H2K^b. Selecting five Brucella peptide candidates, along with controls, we verified that several of these peptides mimicked SIINFEKL, resulting in T cell activation through the “SIINFEKL-specific” TCR. Activation was dependent on peptide concentration as well as sequence. Our results underscore the complexity and ubiquity of cross-reactivity in T cell recognition. This cross-reactivity may enable microbes such as Brucella to escape immune surveillance by presenting peptides similar to those of the host and may also lead to the activation of autoreactive T cells.

Meta-Analysis of the Changes of Peripheral Blood T Cell Subsets in Patients with Brucellosis

Brucellosis is one of the most prevalent zoonotic diseases in the world, but its pathogenesis is not very clear. At present, it is thought that it may be related to the immunity of T cells. The conclusions of related studies are inconsistent, and its clinical significance is not explicit. We searched published articles in electronic databases up to December 2017 identified as relating to the clinical features of human brucellosis in China. Only eight studies had sufficient quality for data extraction. Meta-analysis showed a significantly decreased proportion of CD4+ T cells in human brucellosis patients compared to healthy subject individuals. The frequency of CD8+ T cells was significantly higher in human brucellosis patients than that in the healthy control group. The pooled analysis presented a significant decrease of the CD4+/CD8+ ratio in human brucellosis patients compared to healthy subjects. There is immunologic dysfunction of T lymphocyte in patients with human brucellosis, the CD4+ and CD8+ T cells might be the important factors affecting the progress of brucellosis.

Regulation of the Cell Biology of Antigen Cross-Presentation

Antigen cross-presentation is an adaptation of the cellular process of loading MHC-I molecules with endogenous peptides during their biosynthesis within the endoplasmic reticulum. Cross-presented peptides derive from internalized proteins, microbial pathogens, and transformed or dying cells. The physical separation of internalized cargo from the endoplasmic reticulum, where the machinery for assembling peptide-MHC-I complexes resides, poses a challenge. To solve this problem, deliberate rewiring of organelle communication within cells is necessary to prepare for cross-presentation, and different endocytic receptors and vesicular traffic patterns customize the emergent cross-presentation compartment to the nature of the peptide source. Three distinct pathways of vesicular traffic converge to form the ideal cross-presentation compartment, each regulated differently to supply a unique component that enables cross-presentation of a diverse repertoire of peptides. Delivery of centerpiece MHC-I molecules is the critical step regulated by microbe-sensitive Toll-like receptors. Defining the subcellular sources of MHC-I and identifying sites of peptide loading during cross-presentation remain key challenges.

Immunoproteasome Subunits Are Required for CD8+ T Cell Function and Host Resistance to Brucella abortus Infection in Mice

The immunoproteasome is a specific proteasome isoform composed of three subunits, termed β1i, β2i, and β5i. Its proteolytic activity enhances the quantity and quality of peptides to be presented by major histocompatibility complex class I (MHC-I) molecules to CD8⁺ T cells. However, the role of the combined deficiency of the three immunoproteasome subunits in protective immunity against bacterial pathogens has not been investigated. In this study, we addressed the role of the immunoproteasome during infection by Brucella abortus, an intracellular bacterium that requires CD8⁺ T cell responses for the control of infection. Here, we demonstrate that immunoproteasome triple-knockout (TKO) mice were more susceptible to Brucella infection. This observed susceptibility was accompanied by reduced interferon gamma (IFN-γ) production by mouse CD4⁺ and CD8⁺ T lymphocytes. Moreover, the absence of the immunoproteasome had an impact on MHC-I surface expression and antigen presentation by dendritic cells. CD8⁺ T cell function, which plays a pivotal role in B. abortus immunity, also presented a partial impairment of granzyme B expression and, consequently, reduced cytotoxic activity. In conclusion, these results strongly suggest that immunoproteasome subunits are important components in host resistance to B. abortus infection by impacting both the magnitude and quality of CD8⁺ T cell responses.

Immuno-profiles of BALB/c mice inoculated with Salmonella vector delivering B-cell mitogen hydroxyproline epimerase

The enzyme 4-hydroxyproline 2-epimerase (PrpA) involves in modulation of host immunity and is also reported as a potent B-cell mitogen. Live attenuated Salmonella Typhimurium (ST) vector constitutively expressing heterologous Brucella abortus PrpA protein (ST-PrpA) was inoculated in BALB/c mice in order to investigate the influence of the enzyme, on safety aspects, humoral and cellular immunity as well as protective efficacies against wild type challenges. No aggravation of morbidity was observed upon mice inoculation of ST-PrpA. Immunized mice showed significantly quicker anti-Salmonella IgG responses as compared to ST only immunization. This finding is in congruency with the increase IL-4 production evident in in vitro pulsed mice splenocytes. Increase protection against Salmonella challenge was also observed. These findings suggest that PrpA can be used as a protein adjuvant in a live Salmonella delivery system, in order to increase humoral responses effectively without major interference on the cell mediated immunity.

Perspectives and Outcomes of the Activity of a Reference Laboratory for Brucellosis

One health is an emerging conceptual approach geared to harmonize the activities of the public health, veterinary services, and extension services within a single operative structure. Brucellosis is an important zoonosis worldwide, mostly involving nomadic populations but may often affect transboundary animal management and exotic domesticated animal farming such as camels and buffalo. Here, we provide contemporary knowledge on the disease and its causative agent, a Gram-negative bacteria belonging to the genus Brucella. Further, because of the zoonotic importance, we emphasize the need to assign a national reference laboratory for the disease and discuss how this would integrate into a "One Health" system. Brucella vaccines are live attenuated strains possessing the smooth phenotype, and vaccination, therefore, hampers the ability to maintain a national surveillance program due to concerns regarding the false positive vaccine-induced responses. In order to overcome these failings, we developed a combined approach based on rapid screening of mass numbers of serum samples by the fluorescence polarization assay, a cost-effective and accurate method, and confirmation of the true positive reactors by the complement fixation test, a highly specific method that is less sensitive to vaccine-induced antibodies. We demonstrate how, despite the high vaccination coverage of the small ruminant population in Israel, our results proved to be effective in discriminating between vaccinated and infected animals. The speed and accuracy of the method further justified immediate declaration of 37% of flocks as cleansed from brucellosis, thus reducing the burden of repeated tests among this population.

Evaluation of immune responses induced by polymeric OMP25-BLS Brucella antigen

Brucellosis is one the serious infectious diseases caused deleterious health and economic losses. Vaccination with subunit vaccines is the efficient alternative way than live attenuated vaccines against infectious diseases. Herein a new chimeric OMP25-BLS antigen emulsified in Chitosan Nanoparticles was designed and its immune responses were compared with control groups. Also, the role of heat shock protein 60 kDa in combination with OMP25-BLS antigen was assessed. Structural and antigenic features of chimeric antigen were predicted using bioinformatics tools. Moreover, the humoral and cellular immune responses were measured by ELISA in seven different groups. Observations showed rOMP25-BLS structure was highly stable and antigenic. Cytokines analysis showed rOMP25 and rOMP25-BLS + rHSP60 induced higher titer of INF-γ than rHSP60 and rOMP25-BLS. There was no statistically significant difference between positive control group and rOMP25-BLS + rHSP60 in inducing TNF-α (p < .05). Additionally, the highest titer of IL-4 was dedicated to rOMP25 among other immunized treatments, while there were no significant differences between positive control group and other immunized groups with recombinant proteins (p < .05). In addition, rOMP25-BLS and rHSP60 induced higher titer of total antibody compared to other groups. Also, rHSP60 could improve IgG2a to IgG1 ratio when it used in combination with chimeric antigen. Moreover, the lymphocyte proliferation index was higher in chimeric rOMP25-BLS + HSP60 antigen. In conclusion, while rOMP25-BLS chimeric antigen unable to induce efficient cellular response than individual injection of rOMP25, its injection in combination with rHSP60 could improve cellular immunity.

Improved influenza viral vector based Brucella abortus vaccine induces robust B and T-cell responses and protection against Brucella melitensis infection in pregnant sheep and goats

We previously developed a potent candidate vaccine against bovine brucellosis caused by Brucella abortus using the influenza viral vector expressing Brucella Omp16 and L7/L12 proteins (Flu-BA). Our success in the Flu-BA vaccine trial in cattle and results of a pilot study in non-pregnant small ruminants prompted us in the current study to test its efficacy against B. melitensis infection in pregnant sheep and goats. In this study, we improved the Flu-BA vaccine formulation and immunization method to achieve maximum efficacy and safety. The Flu-BA vaccine formulation had two additional proteins Omp19 and SOD, and administered thrice with 20% Montanide Gel01 adjuvant, simultaneously by both subcutaneous and conjunctival routes at 21 days intervals in pregnant sheep and goats. At 42 days post-vaccination (DPV) we detected antigen-specific IgG antibodies predominantly of IgG2a isotype but also IgG1, and also detected a strong lymphocyte recall response with IFN-γ production. Importantly, our candidate vaccine prevented abortion in 66.7% and 77.8% of pregnant sheep and goats, respectively. Furthermore, complete protection (absence of live B. melitensis 16M) was observed in 55.6% and 66.7% of challenged sheep and goats, and 72.7% and 90.0% of their fetuses (lambs/yeanlings), respectively. The severity of B. melitensis 16M infection in vaccinated sheep and goats and their fetuses (index of infection and rates of Brucella colonization in tissues) was significantly lower than in control groups. None of the protection parameters after vaccination with Flu-BA vaccine were statistically inferior to protection seen with the commercial B. melitensis Rev.1 vaccine (protection against abortion and vaccination efficacy, alpha = 0.18–0.34, infection index, P = 0.37–0.77, Brucella colonization, P = 0.16 to P > 0.99). In conclusion, our improved Flu-BA vaccine formulation and delivery method were found safe and effective in protecting pregnant sheep and goats against adverse consequences of B. melitensis infection.

B. abortus RNA is the component involved in the down-modulation of MHC-I expression on human monocytes via TLR8 and the EGFR pathway

Despite eliciting a potent CD8⁺ T cell response, Brucella abortus is able to persist and establish a chronic infection inside its host. We have previously reported that the infection of human monocytes/macrophages with B. abortus inhibits the IFN-γ-induced MHC-I cell surface expression down-modulating cytotoxic CD8⁺ T cell responses. MHC-I down-modulation depends on bacterial viability and results from the capacity of B. abortus to retain the MHC-I molecules within the Golgi apparatus. Furthermore, we recently demonstrated that epidermal growth factor receptor (EGFR) pathway is involved in this phenomenon and that this is an early event during infection. However, the components and mechanisms whereby B. abortus is able to down-modulate MHC-I remained to be elucidated. In this study we demonstrated that the down-modulation of MHC-I expression is not mediated by well-known Brucella virulence factors but instead by B. abortus RNA, a PAMP associated to viability (vita-PAMP). Surprisingly, completely degraded RNA was also able to inhibit MHC-I expression to the same extent as intact RNA. Accordingly, B. abortus RNA and its degradation products were able to mimic the MHC-I intracellular retention within the Golgi apparatus observed upon infection. We further demonstrated that TLR8, a single-stranded RNA and RNA degradation products sensor, was involved in MHC-I inhibition. On the other hand, neutralization of the EGFR reversed the MHC-I inhibition, suggesting a connection between the TLR8 and EGFR pathways. Finally, B. abortus RNA-treated macrophages display diminished capacity of antigen presentation to CD8⁺ T cells. Overall, our results indicate that the vita-PAMP RNA as well as its degradation products constitute novel virulence factors whereby B. abortus, by a TLR8-dependent mechanism and through the EGFR pathway, inhibits the IFN-γ-induced MHC-I surface expression on human monocytes/macrophages. Thus, bacteria can hide within infected cells and avoid the immunological surveillance of cytotoxic CD8⁺ T cells.

Brucella abortus is one of the intracellular bacterial species that cause brucellosis, a zoonotic worldwide disease. An intricate enigma of Brucella immunity is its long-term persistence inside host despite a vigorous and specific immune response. Our study describes a novel immune evasion strategy exploited by B. abortus: the down-modulation of the IFN-γ-induced expression of the molecules responsible for antigen presentation to CD8⁺ T cells on the surface of monocytes, Major Histocompatibility Complex Class I (MHC-I) molecules. We found that the bacterial component responsible for this phenomenon is its RNA, a component associated with bacterial viability itself. Specifically, we demonstrated that not only does intact RNA down-modulate MHC-I but also the RNA degradation products. Bacterial RNA is sensed by pattern recognition receptors (PRRs), among which TLRs family has gained more attention. In this study, we demonstrated that the receptor involved in this phenomenon is TLR8, a single-stranded RNA and RNA degradation products sensor. By means of this mechanism, Brucella impairs antigen presentation to CD8⁺ T cells, hiding within infected cells and avoiding the immunological surveillance of cytotoxic cells. On balance, these results provide new evidence to understand how B. abortus can survive inside the host and persist chronically.

Toll-Like Receptors 2 and 4 Cooperate in the Control of the Emerging Pathogen Brucella microti

Toll-like receptors (TLRs) recognize pathogen-derived molecules and play a critical role during the host innate and adaptive immune response. Brucella spp. are intracellular gram-negative bacteria including several virulent species, which cause a chronic zoonotic infection in a wide range of mammalian hosts known as brucellosis. A new Brucella species, Brucella microti, was recently isolated from wild rodents and found to be highly pathogenic in mice. Using this species-specific model, it was previously found that CD8⁺ T cells are required to control this infection. In order to find out the role of TLR-mediated responses in the control of this pathogen, the course of infection of B. microti was analyzed over 3 weeks in wild-type (WT) and TLR knock out (KO) mice including TLR2^-/-, TLR4^-/-, TLR9^-/-, TLR2×4^-/- and TLR2×4×9^-/-. WT and single TLR2, TLR4 and TLR9 KO mice similarly control infection in liver and spleen. In contrast, bacterial clearance was delayed in TLR2×4^-/- and TLR2×4×9^-/- mice at 7 and 14 days post-infection. This defect correlated with impaired maturation and pro-inflammatory cytokine production in B. microti-infected dendritic cells from TLR2×4^-/- and TLR2×4×9^-/- mice. Finally, it was found that Tc cells from TLR2×4^-/- and TLR2×4×9^-/- mice showed reduced ability to inhibit growth of B. microti in macrophages, suggesting the involvement of TLR2 and 4 in the generation of specific Tc cells. Our findings indicate that TLR2 and TLR4 are required to control B. microti infection in mice and that this effect could be related to its participation in the maturation of dendritic cells and the generation of specific CD8⁺ Tc cells.

Immunotoxic effect of thiamethoxam in immunized mice with Brucella abortus cultural filtrate antigen

Aim:

This study was planned for determination the toxic effect of thiamethoxam (TMX) in immunized mice with Brucella abortus culture filtrate antigen (CFBAgs) (as a vaccine) and its role of TMX on decrease activity of B. abortus antigen on eliciting of humoral and cellular immunity.

Materials and Methods:

To achieve these goals 60 female mice were used, 7-8 weeks age, they were divided equally into three groups (20 in each group) and treated as follows: 1^st group: Mice were immunized with CFBAgs intraperitoneally in two doses, 2 weeks intervals with (protein concentration 2 mg\ml), 2^nd group: Mice immunized as in the 1^st group and was administrated orally with 1/10 lethal dose 50% of TMX (83.7 mg/kg B.W.) for 4 weeks daily, 3^rd group was administrated orally with 0.3 ml normal saline served as a control group. At day 28 post immunization (PI) delayed type hypersensitivity (skin test) was done, and serum samples were collected at day 30 (PI) for detection of passive hemagglutination test (PHA); interferon gamma (IFN-γ) which was done by enzyme-linked immunosorbent assay test in addition to phagocytes assay.

Results:

The results of skin test post injection with soluble antigen of B. abortus intradermally showed a high significantly mean values at p≤0.05 of footpad skin thickness in the 1^st group of mice which recorded (0.51±0.002 mm) as compared with the 2^nd group of mice which showed (0.08±0.002 mm) after 24 h; the mean values of skin thickness were declined in the 1^st mice (0.46±0.002) and 2^nd mice (0.070±0.001) at 48 h; control group showed a negative results. These results were agreed with results of serum levels of IFN-γ (pg/ml) that showed that a significant increase the vaccinated 1^st group (406.36±1.52), than those values in the 2^nd group (151.61±0.89) and negative result in 3^rd group (46.47±0.60), in addition to results of PHA test which showed a significant increase in antibody titer in the 1^st group (139±12.16) with low level of serum antibody in the 2^nd group (7.66±0.33). Phagocytic ratio results in the 1^st group showed an increase to reach (18.55±0.44) than a ratio in the 2^nd group (13.24±0.32) and the control group (5.46±0.25).

Conclusion:

It was concluded that TMX induced suppression of humoral and cellular immune responses in immunized mice with CFBAgs.

Inhibition of MHC-I by Brucella abortus is an early event during infection and involves EGFR pathway

Brucella abortus is able to persist inside the host despite the development of potent CD8⁺ T-cell responses. We have recently reported the ability of B. abortus to inhibit the interferon-γ-induced major histocompatibility complex (MHC)-I cell surface expression on human monocytes. This phenomenon was due to the B. abortus-mediated retention of MHC-I molecules within the Golgi apparatus and was dependent on bacterial viability. However, the implications of bacterial virulence or replicative capacity and the signaling pathways remained unknown. Here we demonstrated that the B. abortus mutant strains RB51 and virB10^- are able to inhibit MHC-I expression in the same manner as wild-type B. abortus, even though they are unable to persist inside human monocytes for a long period of time. Consistent with this, the phenomenon was triggered early in time and could be observed at 8 h postinfection. At 24 and 48 h, it was even stronger. Regarding the signaling pathway, targeting epidermal growth factor (EGF) receptor (EGFR), ErbB2 (HER2) or inhibition of tumor necrosis factor-α-converting enzyme, one of the enzymes which generates soluble EGF-like ligands, resulted in partial recovery of MHC-I surface expression. Moreover, recombinant EGF and transforming growth factor-α as well as the combination of both were also able to reproduce the B. abortus-induced MHC-I downmodulation. Finally, when infection was performed in the presence of an extracellular signal-regulated kinase 1/2 (Erk1/2) inhibitor, MHC-I surface expression was significantly recovered. Overall, these results describe how B. abortus evades CD8⁺ T-cell responses early during infection and exploits the EGFR-ERK signaling pathway to escape from the immune system and favor chronicity.

MicroRNA Expression Patterns of CD8+ T Cells in Acute and Chronic Brucellosis

Although our knowledge about Brucella virulence factors and the host response increase rapidly, the mechanisms of immune evasion by the pathogen and causes of chronic disease are still unknown. Here, we aimed to investigate the immunological factors which belong to CD8+ T cells and their roles in the transition of brucellosis from acute to chronic infection. Using miRNA microarray, more than 2000 miRNAs were screened in CD8+ T cells of patients with acute or chronic brucellosis and healthy controls that were sorted from peripheral blood with flow cytometry and validated through qRT-PCR. Findings were evaluated using GeneSpring GX (Agilent) 13.0 software and KEGG pathway analysis. Expression of two miRNAs were determined to display a significant fold change in chronic group when compared with acute or control groups. Both miRNAs (miR-126-5p and miR-4753-3p) were decreased (p <0.05 or fold change > 2). These miRNAs have the potential to be the regulators of CD8+ T cell-related marker genes for chronic brucellosis infections. The differentially expressed miRNAs and their predicted target genes are involved in MAPK signaling pathway, cytokine-cytokine receptor interactions, endocytosis, regulation of actin cytoskeleton, and focal adhesion indicating their potential roles in chronic brucellosis and its progression. It is the first study of miRNA expression analysis of human CD8+ T cells to clarify the mechanism of inveteracy in brucellosis.

First evaluation of an influenza viral vector based Brucella abortus vaccine in sheep and goats: Assessment of safety, immunogenicity and protective efficacy against Brucella melitensis infection

Previously we developed and evaluated a candidate influenza viral vector based Brucella abortus vaccine (Flu-BA) administered with a potent adjuvant Montanide Gel01 in cattle, which was found safe and highly effective. This study was aimed to establish a proof-of-concept of the efficacy of Flu-BA vaccine formulation in sheep and goats. We vaccinated sheep and goats with Flu-BA vaccine and as a positive control vaccinated a group of animals with a commercial B. melitensis Rev.1 vaccine. Clinically, both Flu-BA and Rev.1 vaccines were found safe. Serological analysis showed the animals received Flu-BA vaccine did not induce antibody response against Brucella Omp16 and L7/L12 proteins during the period of our study (56days post-initial vaccination, PIV). But observed significant antigen-specific T cell response indicated by increased lymphocyte stimulation index and enhanced secretion of IFN-γ at day 56 PIV in Flu-BA group. The Flu-BA vaccinated animals completely protected 57.1% of sheep and 42.9% of goats against B. melitensis 16M challenge. The severity of brucellosis in terms of infection index and colonization of Brucella in tissues was significantly lower in the Flu-BA group compared to negative control animals group. Nevertheless, positive control commercial Rev.1 vaccine provided strong antigen-specific T cell immunity and protection against B. melitensis 16M infection. We conclude that the Flu-BA vaccine induces a significant antigen-specific T-cell response and provides complete protection in approximately 50% of sheep and goats against B. melitensis 16M infection. Further investigations are needed to improve the efficacy of Flu-BA and explore its practical application in small ruminants.

The role of NLRP3 and AIM2 in inflammasome activation during Brucella abortus infection

The innate immune system is essential for the detection and elimination of bacterial pathogens. Upon inflammasome activation, caspase-1 cleaves pro-IL-1β and pro-IL-18 to their mature forms IL-1β and IL-18, respectively, and the cell undergoes inflammatory death termed pyroptosis. Here, we reviewed recent findings demonstrating that Brucella abortus ligands activate NLRP3 and AIM2 inflammasomes which lead to control of infection. This protective effect is due to the inflammatory response caused by IL-1β and IL-18 rather than cell death. Brucella DNA is sensed by AIM2 and bacteria-induced mitochondrial reactive oxygen species is detected by NLRP3. However, deregulation of pro-inflammatory cytokine production can lead to immunopathology. Nervous system invasion by bacteria of the genus Brucella results in an inflammatory disorder termed neurobrucellosis. Herein, we discuss the mechanism of caspase-1 activation and IL-1β secretion in glial cells infected with B. abortus. Our results demonstrate that the ASC inflammasome is indispensable for inducing the activation of caspase-1 and secretion of IL-1β upon infection of astrocytes and microglia with Brucella. Moreover, our results demonstrate that secretion of IL-1β by Brucella-infected glial cells depends on NLRP3 and AIM2 and leads to neurobrucellosis. Further, the inhibition of the host cell inflammasome as an immune evasion strategy has been described for bacterial pathogens. We discuss here that the bacterial type IV secretion system VirB is required for inflammasome activation in host cells during infection. Taken together, our results indicate that Brucella is sensed by ASC inflammasomes mainly NLRP3 and AIM2 that collectively orchestrate a robust caspase-1 activation and pro-inflammatory response.

The Brucella melitensis M5-90 phosphoglucomutase (PGM) mutant is attenuated and confers protection against wild-type challenge in BALB/c mice

Brucellae are Gram-negative intracellular bacterial pathogens that infect humans and animals, bringing great economic burdens to developing countries. Live attenuated Brucella vaccines (strain M5-90 or others) are the most efficient means for prevention and control of animal brucellosis. However, these vaccines have several drawbacks, including residual virulence in animals, and difficulties in differentiating natural infection from vaccine immunization, which limit their application. A vaccine that can differentiate infection from immunization will have extensive applications. A Brucella melitensis (B. melitensis) strain M5-90 pgm mutant (M5-90Δpgm) was constructed to overcome these drawbacks. M5-90Δpgm showed significantly reduced survival in embryonic trophoblast cells and in mice, and induced high protective immunity in BALB/c mice. Moreover, M5-90Δpgm elicited an anti-Brucella-specific immunoglobulin G response and induced the secretion of gamma interferon (IFN-γ) and interleukin-2 (IL-2). In addition, M5-90Δpgm induced the secretion of IFN-γ in immunized sheep. Serum samples from sheep inoculated with M5-90Δpgm were negative by the Rose Bengal Plate Test (RBPT) and Standard Tube Agglutination Test (STAT). Furthermore, the PGM antigen allowed serological differentiation between infected and vaccinated animals. These results suggest that M5-90Δpgm is an ideal live attenuated vaccine candidate against B. melitensis 16 M and deserves further evaluation for vaccine development.

Nasal vaccination stimulates CD8(+) T cells for potent protection against mucosal Brucella melitensis challenge

Brucellosis remains a significant zoonotic threat worldwide. Humans and animals acquire infection via their oropharynx and upper respiratory tract following oral or aerosol exposure. After mucosal infection, brucellosis develops into a systemic disease. Mucosal vaccination could offer a viable alternative to conventional injection practices to deter disease. Using a nasal vaccination approach, the ΔznuA B. melitensis was found to confer potent protection against pulmonary Brucella challenge, and reduce colonization of spleens and lungs by more than 2500-fold, with more than 50% of vaccinated mice showing no detectable brucellae. Furthermore, tenfold more brucellae-specific, IFN-γ-producing CD8⁺ T cells than CD4⁺ T cells were induced in the spleen and respiratory lymph nodes. Evaluation of pulmonary and splenic CD8⁺ T cells from mice vaccinated with ΔznuA B. melitensis revealed that these expressed an activated effector memory (CD44^hiCD62L^loCCR7^lo) T cells producing elevated levels of IFN-γ, TNF-α, perforin, and granzyme B. To assess the relative importance of these increased numbers of CD8⁺ T cells, CD8^−/− mice were challenged with virulent B. melitensis, and they showed markedly increased bacterial loads in organs in contrast to similarly challenged CD4^−/− mice. Only ΔznuA B. melitensis- and Rev-1-vaccinated CD4^−/− and wild-type mice, not CD8^−/− mice, were completely protected against Brucella challenge. Determination of cytokines responsible for conferring protection showed the relative importance of IFN-γ, but not IL-17. Unlike wild-type mice, IL-17 was greatly induced in IFN-γ^−/− mice, but IL-17 could not substitute for IFN-γ’s protection, although an increase in brucellae dissemination was observed upon in vivo IL-17 neutralization. These results show that nasal ΔznuA B. melitensis vaccination represents an attractive means to stimulate systemic and mucosal immune protection via CD8⁺ T cell engagement.

CD8+ T cell exhaustion, suppressed gamma interferon production, and delayed memory response induced by chronic Brucella melitensis infection

Brucella melitensis is a well-adapted zoonotic pathogen considered a scourge of mankind since recorded history. In some cases, initial infection leads to chronic and reactivating brucellosis, incurring significant morbidity and economic loss. The mechanism by which B. melitensis subverts adaptive immunological memory is poorly understood. Previous work has shown that Brucella-specific CD8(+) T cells express gamma interferon (IFN-γ) and can transition to long-lived memory cells but are not polyfunctional. In this study, chronic infection of mice with B. melitensis led to CD8(+) T cell exhaustion, manifested by programmed cell death 1 (PD-1) and lymphocyte activation gene 3 (LAG-3) expression and a lack of IFN-γ production. The B. melitensis-specific CD8(+) T cells that produced IFN-γ expressed less IFN-γ per cell than did CD8(+) cells from uninfected mice. Both memory precursor (CD8(+) LFA1(HI) CD127(HI) KLRG1(LO)) and long-lived memory (CD8(+) CD27(HI) CD127(HI) KLRG1(LO)) cells were identified during chronic infection. Interestingly, after adoptive transfer, mice receiving cells from chronically infected animals were able to contain infection more rapidly than recipients of cells from acutely infected or uninfected donors, although the proportions of exhausted CD8(+) T cells increased after adoptive transfer in both challenged and unchallenged recipients. CD8(+) T cells of challenged recipients initially retained the stunted IFN-γ production found prior to transfer, and cells from acutely infected mice were never seen to transition to either memory subset at all time points tested, up to 30 days post-primary infection, suggesting a delay in the generation of memory. Here we have identified defects in Brucella-responsive CD8(+) T cells that allow chronic persistence of infection.

Immune Response of Calves Vaccinated with Brucella abortus S19 or RB51 and Revaccinated with RB51

Brucella abortus S19 and RB51 strains have been successfully used to control bovine brucellosis worldwide; however, currently, most of our understanding of the protective immune response induced by vaccination comes from studies in mice. The aim of this study was to characterize and compare the immune responses induced in cattle prime-immunized with B. abortus S19 or RB51 and revaccinated with RB51. Female calves, aged 4 to 8 months, were vaccinated with either vaccine S19 (0.6-1.2 x 1011 CFU) or RB51 (1.3 x 1010 CFU) on day 0, and revaccinated with RB51 (1.3 x 1010 CFU) on day 365 of the experiment. Characterization of the immune response was performed using serum and peripheral blood mononuclear cells. Blood samples were collected on days 0, 28, 210, 365, 393 and 575 post-immunization. Results showed that S19 and RB51 vaccination induced an immune response characterized by proliferation of CD4+ and CD8+ T-cells; IFN-ɣ and IL-17A production by CD4+ T-cells; cytotoxic CD8+ T-cells; IL-6 secretion; CD4+ and CD8+ memory cells; antibodies of IgG1 class; and expression of the phenotypes of activation in T-cells. However, the immune response stimulated by S19 compared to RB51 showed higher persistency of IFN-ɣ and CD4+ memory cells, induction of CD21+ memory cells and higher secretion of IL-6. After RB51 revaccination, the immune response was chiefly characterized by increase in IFN-ɣ expression, proliferation of antigen-specific CD4+ and CD8+ T-cells, cytotoxic CD8+ T-cells and decrease of IL-6 production in both groups. Nevertheless, a different polarization of the immune response, CD4+- or CD8+-dominant, was observed after the booster with RB51 for S19 and RB51 prime-vaccinated animals, respectively. Our results indicate that after prime vaccination both vaccine strains induce a strong and complex Th1 immune response, although after RB51 revaccination the differences between immune profiles induced by prime-vaccination become accentuated.

Immune response triggered by Brucella abortus following infection or vaccination

Brucella abortus live vaccines have been used successfully to control bovine brucellosis worldwide for decades. However, due to some limitations of these live vaccines, efforts are being made for the development of new safer and more effective vaccines that could also be used in other susceptible species. In this context, understanding the protective immune responses triggered by B. abortus is critical for the development of new vaccines. Such understandings will enhance our knowledge of the host/pathogen interactions and enable to develop methods to evaluate potential vaccines and innovative treatments for animals or humans. At present, almost all the knowledge regarding B. abortus specific immunological responses comes from studies in mice. Active participation of macrophages, dendritic cells, IFN-γ producing CD4(+) T-cells and cytotoxic CD8(+) T-cells are vital to overcome the infection. In this review, we discuss the characteristics of the immune responses triggered by vaccination versus infection by B. abortus, in different hosts.

Adrenal steroids modulate the immune response during Brucella abortus infection by a mechanism that depends on the regulation of cytokine production

Human brucellosis is a protean disease with a diversity of clinical signs and symptoms resulting from infection with Brucella species. Recent reports suggest a cross-regulation between adrenal steroids (cortisol and dehydroepiandrosterone [DHEA]) and the immune system. Monocytes and macrophages are the main replication niche for Brucella. Therefore, we investigated the role of adrenal hormones on the modulation of the immune response mediated by macrophages in B. abortus infection. Cortisol treatment during B. abortus infection significantly inhibits cytokine, chemokine, and MMP-9 secretion. In contrast, DHEA treatment had no effect. However, DHEA treatment increases the expression of costimulatory molecules (CD40, CD86), the adhesion molecule CD54, and major histocompatibility complex class I (MHC-I) and MHC-II expression on the surface of B. abortus-infected monocytes. It is known that B. abortus infection inhibits MHC-I and MHC-II expression induced by gamma interferon (IFN-γ) treatment. DHEA reverses B. abortus downmodulation of the MHC-I and -II expression induced by IFN-γ. Taken together, our data indicate that DHEA immune intervention may positively affect monocyte activity during B. abortus infection.

5-Lipoxygenase negatively regulates Th1 response during Brucella abortus infection in mice

Brucella abortus is a Gram-negative bacterium that infects humans and cattle, causing a chronic inflammatory disease known as brucellosis. A Th1-mediated immune response plays a critical role in host control of this pathogen. Recent findings indicate contrasting roles for lipid mediators in host responses against infections. 5-Lipoxygenase (5-LO) is an enzyme required for the production of the lipid mediators leukotrienes and lipoxins. To determine the involvement of 5-LO in host responses to B. abortus infection, we intraperitoneally infected wild-type and 5-LO-deficient mice and evaluated the progression of infection and concomitant expression of immune mediators. Here, we demonstrate that B. abortus induced the upregulation of 5-LO mRNA in wild-type mice. Moreover, this pathogen upregulated the production of the lipid mediators leukotriene B4 and lipoxin A4 in a 5-LO-dependent manner. 5-LO-deficient mice displayed lower bacterial burdens in the spleen and liver and less severe liver pathology, demonstrating an enhanced resistance to infection. Host resistance paralleled an increased expression of the proinflammatory mediators interleukin-12 (IL-12), gamma interferon (IFN-γ), and inducible nitric oxide synthase (iNOS) during the course of infection. Moreover, we demonstrated that 5-LO downregulated the expression of IL-12 in macrophages during B. abortus infection. Our results suggest that 5-LO has a major involvement in B. abortus infection, by functioning as a negative regulator of the protective Th1 immune responses against this pathogen.

T lymphocytes subsets and cytokine pattern induced by vaccination against bovine brucellosis employing S19 calfhood vaccination and adult RB51 revaccination

The aims of this study were to address the protective immune response induced by S19 vaccination (n=10) and RB51 revaccination, in pregnant (n=9) and non-pregnant (n=10) S19 calfhood-vaccinated cattle as follows: evaluate the in vitro CD4(+) and CD8(+) T-lymphocytes specific proliferation, and in vitro expression of IFN-γ by CD4(+) and CD8(+) T-cells and IL-4 by CD4(+), CD8(+) and CD21(+) lymphocytes subset. Upon in vitro stimulation with γ-irradiated Brucella abortus 2308, blood mononuclear cells from S19 vaccinated and RB51 revaccinated cows exhibited significantly higher proliferation of CD4(+) and CD8(+) T-lymphocytes and CD4(+)IFN-γ(+) T-cells compared to non-vaccinated animals. RB51 revaccination, regardless of the pregnancy status, did not enhance the proliferation of CD4(+) or CD8(+) T-cells nor IFN-γ or IL-4 production. Data from the present study suggest that cattle's cellular immune response induced after brucellosis vaccination and revaccination is due to CD4(+) and CD8(+) T-lymphocytes, being CD4(+) T-cells the main source of IFN-γ.

Roles of major histocompatibility complex class II in inducing protective immune responses to influenza vaccination

Major histocompatibility complex class II-deficient (MHC-II KO; Aβ(-/-)) mice were used to assess the roles of MHC-II molecules in inducing protective immune responses to vaccination. After vaccination with influenza A/PR8 virus-like particle (VLP) vaccine, in vivo and in vitro vaccine antigen-specific IgG isotype antibodies were not detected in MHC-II KO mice, which is quite different from CD4 T cell-deficient mice that induced vaccine-specific IgG antibodies. The deficiency in MHC-II did not significantly affect the induction of antigen-specific IgM antibody in sera. MHC-II KO mice that were vaccinated with influenza VLP, whole inactivated influenza virus, or live attenuated influenza virus vaccines were not protected against lethal infection with influenza A/PR8 virus. Adoptive transfer of fractionated spleen cells from wild-type mice to MHC-II KO mice indicated that CD43(+) cell populations with MHC-II contributed more significantly to producing vaccine-specific IgG antibodies than CD43(-) B220(+) conventional B cell or CD4 T cell populations, as well as conferring protection against lethal infection. Bone marrow-derived dendritic cells from MHC-II KO mice showed a significant defect in producing interleukin-6 and tumor necrosis factor alpha cytokines. Thus, results indicate that MHC-II molecules play multiple roles in inducing protective immunity to influenza vaccination. Importance: Major histocompatibility complex class II (MHC-II) has been known to activate CD4 T helper immune cells. A deficiency in MHC-II was considered to be equivalent to the lack of CD4 T cells in developing host immune responses to pathogens. However, the roles of MHC-II in inducing protective immune responses to vaccination have not been well understood. In the present study, we demonstrate that MHC-II-deficient mice showed much more significant defects in inducing protective antibody responses to influenza vaccination than CD4 T cell-deficient mice. Further analysis showed that CD43 marker-positive immune cells with MHC-II, as well as an innate immunity-simulating adjuvant, could rescue some defects in inducing protective immune responses in MHC-II-deficient mice. These results have important implications for our understanding of host immunity-inducing mechanisms to vaccination, as well as in developing effective vaccines and adjuvants.

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.