Identification of Brucella abortus genes in elk (Cervus elaphus) using in vivo-induced antigen technology (IVIAT) reveals novel markers of infection

A pseudomolecule assembly of the Rocky Mountain elk genome

Rocky Mountain elk (Cervus canadensis) populations have significant economic implications to the cattle industry, as they are a major reservoir for Brucella abortus in the Greater Yellowstone area. Vaccination attempts against intracellular bacterial diseases in elk populations have not been successful due to a negligible adaptive cellular immune response. A lack of genomic resources has impeded attempts to better understand why vaccination does not induce protective immunity. To overcome this limitation, PacBio, Illumina, and Hi-C sequencing with a total of 686-fold coverage was used to assemble the elk genome into 35 pseudomolecules. A robust gene annotation was generated resulting in 18,013 gene models and 33,422 mRNAs. The accuracy of the assembly was assessed using synteny to the red deer and cattle genomes identifying several chromosomal rearrangements, fusions and fissions. Because this genome assembly and annotation provide a foundation for genome-enabled exploration of Cervus species, we demonstrate its utility by exploring the conservation of immune system-related genes. We conclude by comparing cattle immune system-related genes to the elk genome, revealing eight putative gene losses in elk.

Genomic insights into Brucella

Brucellosis is a zoonotic disease caused by certain species of Brucella. Each species has its preferred host animal, though it can infect other animals too. For a longer period, only six classical species were recognized in the genus Brucella. No vaccine is available for human brucellosis. Therefore, human brucellosis can be controlled only by controlling brucellosis in animals. The genus is now expanding with the newly isolated atypical strains from various animals, including marine mammals. Presently, 12 species of Brucella have been recognized. The first genome of Brucella was released in 2002, and today, we have more than 1500 genomes of Brucella spp. isolated worldwide. Multiple genome sequences are available for the major zoonotic species, B. abortus, B. melitensis, and B. suis. The Brucella genome has two chromosomes with the approximate sizes of 2.1 and 1.2 Mbp. The genome of Brucella is highly conserved across all the species at the nucleotide level. One of the unanswered questions is what makes host preference in different species of Brucella. Here, I summarize the recent advancements in the Brucella genomics research.

Induction of systemic immunity through nasal-associated lymphoid tissue (NALT) of mice intranasally immunized with Brucella abortus malate dehydrogenase-loaded chitosan nanoparticles

Infection with Brucella abortus causes contagious zoonosis, brucellosis, and leads to abortion in animals and chronic illness in humans. Chitosan nanoparticles (CNs), biocompatible and nontoxic polymers, acts as a mucosal adjuvant. In our previous study, B. abortus malate dehydrogenase (Mdh) was loaded in CNs, and it induced high production of pro-inflammatory cytokines in THP-1 cells and systemic IgA in BALB/C mice. In this study, the time-series gene expression analysis of nasal-associated lymphoid tissue (NALT) was performed to identify the mechanism by which Mdh affect the target site of nasal immunization. We showed that intranasal immunization of CNs-Mdh reduced cell viability of epithelial cells and muscle cells at first 1 h, then induced cellular movement of immune cells such as granulocytes, neutrophils and lymphocytes at 6h, and activated IL-6 signaling pathway at 12h within NALT. These activation of immune cells also promoted signaling pathway for high-mobility group box 1 protein (HMGB1), followed by the maturation of DCs required for mucosal immunity. The CNs also triggered the response to other organism and inflammatory response, showing it is immune-enhancing adjuvant. The ELISA showed that significant production of specific IgA was detected in the fecal excretions and genital secretions from the CNs-Mdh-immunized group after 2 weeks-post immunization. Collectively, these results suggest that B. abortus Mdh-loaded CNs triggers activation of HMGB1, IL-6 and DCs maturation signaling within NALT and induce production of systemic IgG and IgA.

Induction of Th2 response through TLR2-mediated MyD88-dependent pathway in human microfold cells stimulated with chitosan nanoparticles loaded with Brucella abortus Mdh

Drug delivery by the nasal or oral route is considered the preferred route of administration because it can induce systemic mucosal immunity. However, few studies have examined the immunogenicity and transport of antigen at the level of the microfold (M) cell, the epithelial cell that specializes in antigen sampling at mucosal surfaces. In our previous study, Brucella abortus malate dehydrogenase (Mdh) was loaded in chitosan nanoparticles (CNs), and it induced high production of proinflammatory cytokines in THP-1 cells and systemic IgA in BALB/C mice. In the present study, an in vitro M cell model was used in which Caco-2 cells and Raji B cells were co-cultured to investigate the impact of the uptake and immunogenicity of B. abortus Mdh on nanoparticle transport in human M cells. Our results showed that loaded CNs induced enhanced transport of Mdh in the M cell model. ELISAs showed significantly higher production of IL-1β and IL-6 in the CN-Mdh stimulation group than that seen in the Mdh stimulation group. The observed increase of gene expression of TLR2, MyD88, TRAF6, IRF4 and CD14 implied that MyD88-dependent TLR2 signaling was activated by stimulation with CNs-Mdh. These results suggest that Mdh and CNs may function synergistically to enhance Th2-related responses triggered by the MyD88-dependent TLR2 signaling pathway and could induce an inflammatory response in M cells as an M cell-targeted delivery system. This study will contribute to the development of not only effective antigens for intracellular bacteria, including B. abortus, but also vaccine delivery systems that target M cells.

Th2-related immune responses by the Brucella abortus cellular antigens, malate dehydrogenase, elongation factor, and arginase

Brucellosis is an important zoonotic disease caused by Brucella species. The disease is difficult to control due to the intracellular survival of the bacterium and the lack of precise understanding of pathogenesis. Despite of continuous researches on the pathogenesis of Brucella spp. infection, there is still question on the pathogenesis, especially earlier immune response in the bacterial infection. Malate dehydrogenase (MDH), elongation factor (Tsf), and arginase (RocF), which showed serological reactivity, were purified after gene cloning, and their immune modulating activities were then analyzed in a murine model. Cytokine production profiles were investigated by stimulating RAW 264.7 cells and naïve splenocytes with the three recombinant proteins. Also, immune responses were analyzed by ELISA and an ELIspot assay after immunizing mice with the three proteins. Only TNF-α was produced in stimulated RAW 264.7 cells, whereas Th1-related cytokines, IFN-γ and IL-2, were induced in naïve splenocytes. In contrast, Th2-type immune response was more strongly induced in antigen-secreting cells in the splenocytes obtained 28 days after immunizing mice with the three proteins, as were IgM and IgG. The induction of Th2-related antibody, IgG1, was higher than the Th1-related antibody, IgG2a, in immunized mice. These results suggest that the three proteins strongly induce Th2-type immune response in vivo, even though Th1-related cytokines were produced in vitro.

Molecular cloning, purification and immunogenicity of recombinant Brucella abortus 544 malate dehydrogenase protein

The Brucella mdh gene was successfully cloned and expressed in E. coli. The purified recombinant malate dehydrogenase protein (rMDH) was reactive to Brucella-positive bovine serum in the early stage, but not reactive in the middle or late stage, and was reactive to Brucella-positive mouse serum in the late stage, but not in the early or middle stage of infection. In addition, rMDH did not react with Brucella-negative bovine or mouse sera. These results suggest that rMDH has the potential for use as a specific antigen in serological diagnosis for early detection of bovine brucellosis.

Expression of cytokine and apoptosis-related genes in bovine peripheral blood mononuclear cells stimulated with Brucella abortus recombinant proteins

Brucellosis is a clinically and economically important disease. Therefore, eradication programs of the disease have been implemented in several countries. One hurdle in these programs is the detection of infected animals at the early stage. Although the protein antigens as diagnostic antigens have recently received attention, the exact mechanisms at the beginning of immune responses are not yet known. Therefore, genes encoding five B. abortus cellular proteins were cloned and the expressed recombinant proteins were purified. The expression of several cytokine genes (IL-1β, IL-4, IL-6, IL-12p40, IFN-γ, TNF-α, and iNOS) was analyzed in bovine peripheral blood mononuclear cells (bPBMC) after stimulation with the recombinant proteins. Three apoptosis-related genes, Bax, Bcl-2, and TLR4, were also included in the analysis to find out the adverse effects of the proteins to the cells. Each protein induced different patterns of cytokine expression depending on the stimulation time and antigen dose. Expression of IL-6, IL-12p40, and IFN-γ was induced with all of the proteins while IL-1β, IL-4, TNF-α, and iNOS gene expression was not. Expression of apoptosis-related genes was not altered except TLR4. These results suggest that the cellular antigens of B. abortus induce both humoral and cellular immunity via the production of IL-6, IL-12p40, and IFN-γ in bPBMC without exerting any adverse effects on the cells.

Use of active extracts of poplar buds against Penicillium italicum and possible modes of action

Antifungal components, from poplar buds active fraction (PBAF) against Penicillium italicum, the causal agent of blue mold in citrus fruits, were identified and possible action modes were investigated. Pinocembrin, chrysin and galangin were determined as active components in PBAF, using HPLC and HPLC-MS analysis. The antifungal activity is stable at temperatures ranging from 4 °C to 100 °C and pH levels ranging from 4 to 8. In the presence of PBAF, the hyphae become shriveled, wrinkled and the cell membrane became seriously disrupted. Further investigation on cell permeability, nucleic acid content and alkaline phosphatase suggest that the cell membrane might be the target. Mycelial oxygen consumption and the respiration-related enzymatic activity of succinate dehydrogenase, malate dehydrogenase and ATPase were all inhibited by PBAF. We propose that PBAF is a potentially useful alternative for blue mold control and may act against P. italicum by interfering with respiration and disrupting the cell membrane.

Enzymatic activity analysis and catalytic essential residues identification of Brucella abortus malate dehydrogenase

Malate dehydrogenase (MDH) plays important metabolic roles in bacteria. In this study, the recombinant MDH protein (His-MDH) of Brucella abortus was purified and its ability to catalyze the conversion of oxaloacetate (OAA) to L-malate (hereon referred to as MDH activity) was analyzed. Michaelis Constant (K_m) and Maximum Reaction Velocity (V_max) of the reaction were determined to be 6.45 × 10⁻³ M and 0.87 mM L⁻¹min⁻¹, respectively. In vitro studies showed that His-MDH exhibited maximal MDH activity in pH 6.0 reaction buffer at 40°C. The enzymatic activity was 100%, 60%, and 40% inhibited by Cu²⁺, Zn²⁺, and Pb²⁺, respectively. In addition, six amino acids in the MDH were mutated to investigate their roles in the enzymatic activity. The results showed that the substitutions of amino acids Arg 89, Asp 149, Arg 152, His 176, or Thr 231 almost abolished the activity of His-MDH. The present study will help to understand MDH's roles in B. abortus metabolism.

Characterization of the immunogenicity and pathogenicity of malate dehydrogenase in Brucella abortus

Brucella abortus is a gram-negative, facultative intracellular pathogen that causes brucellosis, a chronic zoonotic disease resulting in abortion in pregnant cattle and undulant fever in humans. Malate dehydrogenase (MDH), a key enzyme in the tricarboxylic acid cycle, plays important metabolic roles in aerobic energy producing pathways and in malate shuttle. In this study, the MDH-encoding gene for malate dehydrogenase mdh of B. abortus S2308 was cloned, sequenced and expressed. Western blot analysis demonstrated that MDH is an immunogenic membrane-associated protein. In addition, recombinant MDH showed sero-reactivity with 30 individual bovine B. abortus-positive sera by enzyme-linked immunosorbent assay, indicates that MDH may be used as a candidate marker for sero-diagnosis of brucellosis. Furthermore, MDH exhibits fibronectin and plasminogen-binding ability in immunoblotting assay. Inhibition assays on HeLa cells demonstrated that rabbit anti-serum against MDH significantly reduced both bacterial adherence and invasion abilities (p < 0.05), suggesting that MDH play a role in B. abortus colonization. Our results indicated that MDH is not only an immunogenic protein, but is also related to bacterial pathogenesis and may act as a new virulent factor, which will benefit for further understanding the MDH's roles in B. abortus metabolism, pathogenesis and immunity.

In vivo-induced argininosuccinate lyase plays a role in the replication of Brucella abortus in RAW264.7 cells

Brucellosis caused by Brucella species is a zoonotic disease with a serious impact on public health and the livestock industry. To better understand the pathogenesis of the disease, in vivo-induced antigen technology (IVIAT) was used to investigate the in vivo-induced antigens of Brucella abortus in this study. A genomic expression library of B. abortus was constructed and screened using pooled bovine B. abortus-positive sera by IVIAT. In total, 33 antigens were identified. Five antigens were further expressed and tested for their seroreactivity against 33 individual bovine B. abortus-positive sera by Western blot analysis. The results showed a highest positive rate of 32/33 for argininosuccinate lyase (ASL), indicating that ASL may be used as a candidate marker for serodiagnosis of brucellosis. Furthermore, an asl gene-deleted mutant strain S2308ΔASL was constructed, and the intracellular survival and replication of the mutant strain in RAW264.7 cells were investigated. Interestingly, the numbers of bacteria recovered from cells infected with mutant strain S2308ΔASL were similar at all time points observed from 0 h to 96 h post-infection, suggesting the asl gene plays an important role in the bacterial replication in RAW264.7 cells. Real-time quantitative PCR (qPCR) analysis showed that the mRNA levels in S2308ΔASL were decreased for BvrR, BvrS and virB5 when compared with those in S2308 (P<0.05). Our results not only expand the knowledge of Brucella intracellular replication but also expand the list of candidates for serodiagnostic markers of brucellosis.

Vaccination with Brucella abortus recombinant in vivo-induced antigens reduces bacterial load and promotes clearance in a mouse model for infection

Current vaccines used for the prevention of brucellosis are ineffective in inducing protective immunity in animals that are chronically infected with Brucella abortus, such as elk. Using a gene discovery approach, in vivo-induced antigen technology (IVIAT) on B. abortus, we previously identified ten loci that encode products up-regulated during infection in elk and consequently may play a role in virulence. In our present study, five of the loci (D15, 0187, VirJ, Mdh, AfuA) were selected for further characterization and compared with three additional antigens with virulence potential (Hia, PrpA, MltA). All eight genes were PCR-amplified from B. abortus and cloned into E. coli. The recombinant products were then expressed, purified, adjuvanted, and delivered subcutaneously to BALB/c mice. After primary immunization and two boosts, mice were challenged i.p. with 5 x 10⁴ CFU of B. abortus strain 19. Spleens from challenged animals were harvested and bacterial loads determined by colony count at various time points. While vaccination with four of the eight individual proteins appeared to have some effect on clearance kinetics, mice vaccinated with recombinant Mdh displayed the most significant reduction in bacterial colonization. Furthermore, mice immunized with Mdh maintained higher levels of IFN-γ in spleens compared to other treatment groups. Collectively, our in vivo data gathered from the S19 murine colonization model suggest that vaccination with at least three of the IVIAT antigens conferred an enhanced ability of the host to respond to infection, reinforcing the utility of this methodology for the identification of potential vaccine candidates against brucellosis. Mechanisms for immunity to one protein, Mdh, require further in vitro exploration and evaluation against wild-type B. abortus challenge in mice, as well as other hosts. Additional studies are being undertaken to clarify the role of Mdh and other IVI antigens in B. abortus virulence and induction of protective immunity.