Immunization of BALB/c mice with Brucella abortus 2308ΔwbkA confers protection against wild-type infection

Differentially expressed long noncoding RNAs in RAW264.7 macrophages during Brucella infection and functional analysis on the bacterial intracellular replication

Long noncoding RNAs (lncRNAs) are a group of functional RNA molecules without protein-coding potential and play vital roles in majority of biological processes. To date, the expression profiles of lncRNAs and their influence on Brucella replication in RAW264.7 cells are poorly understood. In this study, we performed high-throughput transcriptome analysis to investigate the differentially expressed lncRNAs associated with Brucella abortus S2308 infection. Of these, 8, 6, 130 and 94 cellular lncRNAs were differentially expressed at 4, 8, 24 and 48 h post-infection, respectively. Moreover, 1918 protein-coding genes are predicted as potential cis target genes of differentially expressed lncRNAs by searching protein-coding genes located at upstream and downstream of lncRNA loci on the chromosome DNA of Mus musculus. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated that majority of lncRNA target genes were associated with B. abortus infection. Fourteen lncRNAs from transcriptome data were selected for qRT-PCR verification, confirming 13 were differentially expressed. Animal experiments revealed three were differentially expressed in vivo by qRT-PCR analysis. Furthermore, knockdown of LNC_000428 by CRISPR/dCas9 inhibition or Locked Nucleic Acids transfection downregulated Tnfrsf8 expression at mRNA level and increased Brucella intracellular replication. Thus, we provide a novel evidence that lncRNAs induced by Brucella-infection function on Brucella intracellular replication.

Interferon-Inducible Transmembrane Protein 3-Containing Exosome as a New Carrier for the Cell-to-Cell Transmission of Anti-Brucella Activity

Exosomes are small extracellular vesicles that are released from cells and that function in intercellular communication. Recently, interferon-inducible transmembrane protein 3 (IFITM3) has been identified as a highly effective anti-intracellular pathogen protein that can inhibit the invasion of a wide range of pathogenic microorganisms. However, whether Brucella infection induces secretion of exosomes and whether these exosomes contain IFITM3 protein remain unknown. Here, we focused on the immune function of extracellular IFITM3 protein in the process of Brucella infection. This study is the first to show that Brucella melitensis strain M5 (Brucella M5) can stimulate macrophages to secrete large amounts of exosomes. Most importantly, we identified exosomes from Brucella M5-infected cells that were rich in molecules of IFITM3, and these exosomes could transmit the IFITM3 from one cell to another, thereby effectively inhibiting the intracellular survival of Brucella. Moreover, immunization with exosomes carrying IFITM3 decreased mouse spleen tissue damage and spleen colony forming unit (CFU), leading to the establishment of an anti-Brucella state in mice. In conclusion, our findings provide new insights into the anti-Brucella mechanism of IFITM3-containg exosomes, thus providing a theoretical foundation for systematic elaboration of the mechanisms of Brucella infection and host immunity. The results provide new ideas for the development of candidate vaccines for Brucella.

Small ubiquitin-related modifier 2 affects the intracellular survival of Brucella abortus 2308 by regulating activation of the NF-κB pathway

Brucella is a genus of Gram-negative intracellular pathogens that cause animal and human diseases. Brucella survival and replication inside immune cells is critical for the establishment of chronic infections. Protein modifications by small ubiquitin-related modifier proteins and the NF-κB pathway are involved in many cellular activities, playing major roles in regulating protein function that is essential for pathogenic bacteria during infection. However, the relationship between them in the intracellular survival of Brucella is still largely unknown. We demonstrated that Brucella abortus 2308 infection can activate the expression of small ubiquitin-related modifier-2 proteins in a time-dependent manner. We found the production of Th1 cytokines (IFN-γ and TNF-α) and the transcription of NF-κB/p65 were promoted by overexpression and inhibited by interference of small ubiquitin-related modifier-2. In addition, we showed that small ubiquitin-related modifier-2 can inhibit intracellular survival of Brucella abortus 2308 by regulating activation of the NF-κB pathway. Taken together, this work shows that small ubiquitin-related modifier-2 modification of NF-κB2/p65 is essential for the survival of Brucella abortus 2308 inside macrophages. This work may help to unravel the pathogenic mechanisms of Brucella infections.

Interaction between Brucella melitensis 16M and small ubiquitin-related modifier 1 and E2 conjugating enzyme 9 in mouse RAW264.7 macrophages

Brucella is an intracellular pathogen that invades a host and settles in its immune cells; however, the mechanism of its intracellular survival is unclear. Modification of small ubiquitin-related modifier (SUMO) occurs in many cellular activities. E2 conjugating enzyme 9 (Ubc9) is the only reported ubiquitin-conjugating enzyme that links the SUMO molecule with a target protein. Brucella's intracellular survival mechanism has not been studied with respect to SUMO-related proteins and Ubc9. Therefore, to investigate the relationship between Brucella melitensis 16M and SUMO, we constructed plasmids and cells lines suitable for overexpression and knockdown of SUMO1 and Ubc9 genes. Brucella 16M activated SUMO1/Ubc9 expression in a time-dependent manner, and Brucella 16M intracellular survival was inhibited by SUMO1/Ubc9 overexpression and promoted by SUMO1/Ubc9 depletion. In macrophages, Brucella 16M-dependent apoptosis and immune factors were induced by SUMO1/Ubc9 overexpression and restricted by SUMO1/Ubc9 depletion. We noted no effect on the expressions of SUMO1 and Ubc9 in B. melitensis 16M lipopolysaccharide-prestimulated mouse RAW264.7 macrophages. Additionally, intracellular survival of the 16M△VirB2 mutant was lower than that of Brucella 16M (p < 0.05). VirB2 can affect expression levels of Ubc9, thereby increasing intracellular survival of Brucella in macrophages at the late stage of infection. Collectively, our results demonstrate that B. melitensis 16M may use the VirB IV secretion system of Brucella to interact with SUMO-related proteins during infection of host cells, which interferes with SUMO function and promotes pathogen survival in host cells.

New Brucella abortus S19 Mutant to Improve Distinction Between Infected and Vaccinated Animals

Background

Using Brucella abortus Strain 19 (S19) to control bovine brucellosis is restricted due to induce antibodies to the O-side chain of the smooth lipopolysaccharide (LPS) which may be difficult to differentiate vaccinated and infected animals. Furthermore, it is virulent for humans and can induce abortion to cattle.

Objectives

The aim of this study was to employ gene knockout B. abortus S19 for the first time to eliminate diagnostic defects and obtain the attenuated mutant strain.

Material and Methods

The wbkA gene, which is one of the LPS O-chain coding genes, was knocked out in vaccinal Brucella abortus S19. The proliferative response and immunoglobulin M production were analyzed in wbkA deletion strain-infected BALB/c mice.

Results

The loss of wbkA gene function resulted in induction of the splenocyte proliferative response in mice infected by the mutant S19 strain compare to those induced by parental S19 and RB51 strains. Moreover, wbkA mutant did not induce any IgM antibody response using the enzyme-linked immunosorbent assay.

Conclusions

As a result, the new mutant S19 strain had deficiency in its LPS O-chain structure, besides cannot induce IgM response then, reduce mistakes to discriminate between vaccinated and infected animal, and also can be considered as a new vaccine candidate.

Brucellosis vaccines based on the open reading frames from genomic island 3 of Brucella abortus

Brucella abortus is the etiological agent of brucellosis, a zoonotic disease affecting cattle and humans. This disease has been partially controlled in cattle by immunization with live attenuated B. abortus S19 and RB51 strains. However, use of these vaccine strains has been associated with safety issues in animals and humans. New vaccines have since emerged in the prevention of brucellosis, particularly DNA vaccines, which have shown effectiveness and a good safety profile. Their protection efficacy in mice is associated with the induction of Th1 type and cytotoxic T cell mediated immune response against structural antigens and virulence factors expressed during B. abortus infection. Some antigenic candidate for vaccine design against brucellosis (mainly DNA vaccines) have been obtained from genomic island 3 (GI-3) of B. abortus, which encodes several open reading frames (ORFs) involved in the intracellular survival and virulence of this pathogen. The immunogenicity and protection conferred by these DNA vaccines in a murine model is reviewed in this article, suggesting that some of them could be safe and effective vaccine candidates against to prevent B. abortus infection.

Development and evaluation of in murine model, of an improved live-vaccine candidate against brucellosis from to Brucella melitensis vjbR deletion mutant

Brucellosis is an infectious disease that brings enormous economic burdens for developing countries. The Brucella melitensis (B. melitensis) M5-90 vaccine strain (M5-90) has been used on a large scale in China, but may cause abortions if given to pregnant goats or sheep subcutaneously during the late stages of gestation. Moreover, the vaccine M5-90 cannot differentiate natural from vaccinated infection. Therefore, a safer and more potent M5-90 vaccine is required. In this study, a vjbR mutant of M5-90 (M5-90ΔvjbR) was constructed and overcame these drawbacks. M5-90ΔvjbR strain showed reduced survival capability in murine macrophages (RAW 264.7) and BALB/c mice and induced high protective immunity in mice. In addition, M5-90ΔvjbR induced an anti-Brucella-specific immunoglobulin G (IgG) response and stimulated the expression of gamma interferon (INF-γ) and interleukin-4 (IL-4) in vaccinated mice. Furthermore, M5-90ΔvjbR induced IgG response and stimulated the secretion of IFN-γ and IL-4 in immunized sheep. Moreover, the VjbR antigen allowed serological differentiation between infected and vaccinated animals. These results suggest that M5-90ΔvjbR is an ideal live attenuated and efficacious live vaccine candidate against B. melitensis 16 M infection.

Deletion of the transcriptional regulator GntR down regulated the expression of Genes Related to Virulence and Conferred Protection against Wild-Type Brucella Challenge in BALB/c Mice

Brucellosis, which is caused by Brucella spp., is a zoonotic infectious disease that can cause great hazard to public health and safety. The virulence of Brucella is essential for survive and multiply in host macrophages. GntR is a transcriptional regulator in Brucella that is required for virulence in macrophages and mice, and involved in resistance to stress responses. To determine the expression levels of target genes of GntR, we detected the expression levels of the GntR target genes in Brucella infected BALB/c mice. The results showed that several genes related to virulence, including omp25, virB1, vjbR, dnaK, htrA and hfq, were regulated by GntR during infection in BALB/c mice. Moreover, the 2308ΔgntR mutant induced high protective immunity in BALB/c mice challenge with B. abortus 2308 (S2308), and elicited an anti-Brucella-specific immunoglobulin G (IgG) response and induced the secretion of gamma interferon (IFN-γ) and interleukin-4 (IL-4). All together, these results indicated that gntR promoted the virulence of Brucella. The 2308ΔgntR was significantly attenuated in macrophages and mice and induced protective immune response during infection, suggested that 2308ΔgntR mutant is an attractive candidate for the design of a live attenuated vaccine against Brucella.

Meta-Analysis and Advancement of Brucellosis Vaccinology

Background/Objectives

In spite of all the research effort for developing new vaccines against brucellosis, it remains unclear whether these new vaccine technologies will in fact become widely used. The goal of this study was to perform a meta-analysis to identify parameters that influence vaccine efficacy as well as a descriptive analysis on how the field of Brucella vaccinology is advancing concerning type of vaccine, improvement of protection on animal models over time, and factors that may affect protection in the mouse model.

Methods

A total of 117 publications that met the criteria were selected for inclusion in this study, with a total of 782 individual experiments analyzed.

Results

Attenuated (n = 221), inactivated (n = 66) and mutant (n = 102) vaccines provided median protection index above 2, whereas subunit (n = 287), DNA (n = 68), and vectored (n = 38) vaccines provided protection indexes lower than 2. When all categories of experimental vaccines are analyzed together, the trend line clearly demonstrates that there was no improvement of the protection indexes over the past 30 years, with a low negative and non significant linear coefficient. A meta-regression model was developed including all vaccine categories (attenuated, DNA, inactivated, mutant, subunit, and vectored) considering the protection index as a dependent variable and the other parameters (mouse strain, route of vaccination, number of vaccinations, use of adjuvant, challenge Brucella species) as independent variables. Some of these variables influenced the expected protection index of experimental vaccines against Brucella spp. in the mouse model.

Conclusion

In spite of the large number of publication over the past 30 years, our results indicate that there is not clear trend to improve the protective potential of these experimental vaccines.