Immunization with Brucella VirB proteins reduces organ colonization in mice through a Th1-type immune response and elicits a similar immune response in dogs

The development of a human Brucella mucosal vaccine: What should be considered?

Brucellosis is a chronic infectious disease that is zoonotic in nature. Brucella can infect humans through interactions with livestock, primarily via the digestive tract, respiratory tract, and oral cavity. This bacterium has the potential to be utilized as a biological weapon and is classified as a Category B pathogen by the Centers for Disease Control and Prevention. Currently, there is no approved vaccine for humans against Brucella, highlighting an urgent need for the development of a vaccine to mitigate the risks posed by this pathogen. Brucella primarily infects its host by adhering to and penetrating mucosal surfaces. Mucosal immunity plays a vital role in preventing local infections, clearing microorganisms from mucosal surfaces, and inhibiting the spread of pathogens. As mucosal vaccine strategies continue to evolve, the development of a safe and effective mucosal vaccine against Brucella appears promising.This paper reviews the immune mechanism of mucosal vaccines, the infection mechanism of Brucella, successful Brucella mucosal vaccines in animals, and mucosal adjuvants. Additionally, it elucidates targeting and optimization strategies for mucosal vaccines to facilitate the development of human vaccines against Brucella.

Key immunity characteristics of diverse stages of brucellosis in rural population from Inner Mongolia, China

Background

Brucellosis poses a serious threat to human and animal health, particularly in developing countries such as China. The Inner Mongolia Autonomous Region is one of the most severely brucellosis-endemic provinces in China. Currently, the host immune responses functioning to control Brucella infection and development remain poorly understood. The aim of this study is to further clarify the key immunity characteristics of diverse stages of brucellosis in Inner Mongolia.

Methods

We collected a total of 733 blood samples from acute (n = 137), chronic (n = 316), inapparent (n = 35), recovery (n = 99), and healthy (n = 146) groups from the rural community of Inner Mongolia between 2014 and 2015. The proportions of CD4⁺, CD8⁺, Th1, Th2, and Th17 T cells in peripheral blood and the expression of TLR2 and TLR4 in lymphocytes, monocytes and granulocytes were examined using flow cytometry analysis. The differences among the five groups were compared using one-way ANOVA and the Kruskal–Wallis method, respectively.

Results

Our results revealed that the proportions of CD4⁺ and CD8⁺ T cells were significantly different among the acute, chronic, recovery, and healthy control groups (P < 0.05), with lower proportions of CD4⁺ T cells and a higher proportion of CD8⁺ T cells in the acute, chronic, and recovery groups. The proportion of Th1 cells in the acute, chronic, and inapparent groups was higher than that in the healthy and recovery groups; however, there was no significant difference between patients and healthy individuals (P > 0.05). The proportion of Th2 lymphocytes was significantly higher in the acute and healthy groups than in the inapparent group (P < 0.05). The proportion of Th17 cells in the acute group was significantly higher than that in the healthy control, chronic, and inapparent groups (P < 0.05). Finally, the highest expression of TLR4 in lymphocytes, monocytes and granulocytes was observed in the recovery group, and this was followed by the acute, chronic, healthy control, and inapparent groups. There was a significant difference between the recovery group and the other groups, except for the acute group (P < 0.05). Moreover, a correlation in TLR4 expression was observed in lymphocytes, monocytes and granulocytes among the five groups (r > 0.5), except for the inapparent group between lymphocytes and granulocytes (r = 0.34).

Conclusions

Two key factors (CD8⁺ T cells and TLR4) in human immune profiles may closely correlate with the progression of brucellosis. The detailed function of TLR4 in the context of a greater number of cell types or tissues in human or animal brucellosis and in larger samples should be further explored in the future.

Graphical Abstract

Protection against virulent Brucella spp. by gamma-irradiated B. ovis in BALB/c mice model

Purpose

Brucella spp. is a zoonosis that causes undulant fever in humans and abortion in livestock worldwide. Lately, it was conveyed that vaccines developed by irradiation have induced a strong cellular and humoral immune response which have made these types of vaccines highly effective.

Materials and Methods

In this study, we aimed to use the gamma-irradiated B. ovis as a vaccine and to study the humoral immune response and cytokines production in order to evaluate it for protecting mice against B. abortus 544, B. melitensis 16M, and B. ovis.

Results

The humoral immune response in immunized mice with gamma-irradiated B. ovis showed a lasting for 8 weeks after immunization. Moreover, immunoglobulin G (IgG), IgG1, IgG2a, and IgG2b isotypes antibodies against B. ovis were observed after 4 and 8 weeks of the last immunization. It was noticed that the production of tumor necrosis factor-α, interferon-γ, and interleukin (IL)-10 continued after 4 and 8 weeks by splenocytes from immunized BALB/c mice, while no production of IL-4 or IL-5 was observed.

Conclusion

Our results indicate that the protection of BALB/c mice against B. melitensis 16M, B. abortus 544, and B. ovis was induced and the developed vaccine at our laboratory could stimulate similar protection to those induced by the traditional vaccine.

Secretory System Components as Potential Prophylactic Targets for Bacterial Pathogens

Bacterial secretory systems are essential for virulence in human pathogens. The systems have become a target of alternative antibacterial strategies based on small molecules and antibodies. Strategies to use components of the systems to design prophylactics have been less publicized despite vaccines being the preferred solution to dealing with bacterial infections. In the current review, strategies to design vaccines against selected pathogens are presented and connected to the biology of the system. The examples are given for Y. pestis, S. enterica, B. anthracis, S. flexneri, and other human pathogens, and discussed in terms of effectiveness and long-term protection.

Canine Brucellosis: An Update

Canine brucellosis is an infectious and zoonotic disease caused by Brucella canis, which has been reported worldwide, and is a major public health concern due to close contact between dogs and humans. In dogs, canine brucellosis manifests with abortion outbreaks, reproductive failure, enlargement of lymph nodes, and occasionally affects the osteoarticular system, although the occurrence of asymptomatic infections in dogs are not uncommon. In humans, the disease is associated with a febrile syndrome, commonly with non-specific symptoms including splenomegaly, fatigue, and weakness. Infection of dogs occurs mostly by the oronasal route when in contact with contaminated tissues such as aborted fetuses, semen, urine, and vaginal secretions. In humans, contact with contaminated fluids from infected dogs is an important source of infection, and it is an occupational risk for veterinarians, breeders, laboratory workers, among other professionals who deal with infected animals or biological samples. The diagnosis in dogs is largely based on serologic methods. However, serologic diagnosis of canine brucellosis remains very challenging due to the low accuracy of available tests. Molecular diagnostic methods have been increasingly used in the past few years. Treatment of infected dogs is associated with a high frequency of relapse, and should be employed only in selected cases. Currently there are no commercially available vaccines for prevention of canine brucellosis. Therefore, development of novel and improved diagnostic methods as well as the development of efficacious and safe vaccination protocols are needed for an effective control of canine brucellosis and its associated zoonotic risk.

Prevalence and Genomic Characterization of Brucella canis Strains Isolated from Kennels, Household, and Stray Dogs in Chile

Canine brucellosis caused by Brucella canis is a zoonotic disease that causes reproductive alterations in dogs, such as infertility, abortion, and epididymitis. This pathogen is especially prevalent in South America, and due to the lack of official control programs and the growing trend of adopting dogs it constitutes a public health risk that must be addressed. The aim of this study was to determine the prevalence of B. canis infection in kennel, shelter, and household dogs and to characterize the genomic properties of circulating strains, including ure and virB operons and omp25/31 genes. Samples from 771 dogs were obtained, and the infection was detected by blood culture and/or serology in 7.0% of the animals. The complete ure and virB operons and the omp25/31 genes were detected. Interestingly, we found different single-nucleotide polymorphisms (SNPs) in some of the analyzed genes, which could mean a change in the fitness or virulence of these strains. This study provides further evidence about dogs as a source of B. canis strains that can infect people. This also highlights the need to implement official control programs, including the mandatory testing of dogs, especially stray dogs, before adoption.

Evaluation of the Efficacy of the Brucella canis RM6/66 ΔvjbR Vaccine Candidate for Protection against B. canis Infection in Mice

Brucella canis is a Gram-negative, facultative intracellular bacterium and the causative agent of canine brucellosis, a highly contagious disease of dogs that can be transmitted to humans. Unfortunately, no vaccine is available to prevent infection. We recently characterized the kinetics of B. canis infection in the mouse model, establishing the required dose necessary to achieve systemic infection. The objective of this study was to investigate the utility of the mouse model in assessing canine brucellosis vaccine candidates and to subsequently investigate the safety and efficacy of a live attenuated vaccine, the B. canis RM6/66 ΔvjbR strain. Mice vaccinated with a dose of 109 CFU of the vaccine strain by both intraperitoneal and subcutaneous routes were afforded significant protection against organ colonization and development of histopathologic lesions following intraperitoneal challenge. Addition of an adjuvant or a booster dose 2 weeks following initial vaccination did not alter protection levels. Vaccination also resulted in a robust humoral immune response in mice, and B. canis RM6/66 ΔvjbR was capable of activating canine dendritic cells in vitro These data demonstrate that the B. canis RM6/66 ΔvjbR strain shows promise as a vaccine for canine brucellosis and validates the mouse model for future vaccine efficacy studies.IMPORTANCE Canine brucellosis, caused by Brucella canis, is the primary cause of reproductive failure in dogs and represents a public health concern due to its zoonotic nature. Cases in dogs in the United States have been increasing due to the persistent nature of the bacterium, deficiencies in current diagnostic testing, and, most importantly, the lack of a protective vaccine. Current estimates place the seroprevalence of B. canis in the southern United States at 7% to 8%, but with the unprecedented rates of animals moving across state and international borders and the lack of federal regulations in regard to testing, the true seroprevalence of B. canis in the United States may very well be higher. Vaccination represents the most effective method of brucellosis control and, in response to the demand for a vaccine against B. canis, we have developed the live attenuated B. canis RM6/66 ΔvjbR vaccine strain capable of protecting mice against challenge.

Brucella ovis mutant in ABC transporter protects against Brucella canis infection in mice and it is safe for dogs

BACKGROUND/OBJECTIVES

Vaccination is the most important tool for controlling brucellosis, but currently there is no vaccine available for canine brucellosis, which is a zoonotic disease of worldwide distribution caused by Brucella canis. This study aimed to evaluate protection and immune response induced by Brucella ovis ΔabcBA (BoΔabcBA) encapsulated with alginate against the challenge with Brucella canis in mice and to assess the safety of this strain for dogs.

METHODS

Intracellular growth of the vaccine strain BoΔabcBA was assessed in canine and ovine macrophages. Protection induced by BoΔabcBA against virulent Brucella canis was evaluated in the mouse model. Safety of the vaccine strain BoΔabcBA was assessed in experimentally inoculated dogs.

RESULTS

Wild type B. ovis and B. canis had similar internalization and intracellular multiplication profiles in both canine and ovine macrophages. The BoΔabcBA strain had an attenuated phenotype in both canine and ovine macrophages. Immunization of BALB/c mice with alginate-encapsulated BoΔabcBA (108 CFU) induced lymphocyte proliferation, production of IL-10 and IFN-γ, and protected against experimental challenge with B. canis. Dogs immunized with alginate-encapsulated BoΔabcBA (109 CFU) seroconverted, and had no hematologic, biochemical or clinical changes. Furthermore, BoΔabcBA was not detected by isolation or PCR performed using blood, semen, urine samples or vaginal swabs at any time point over the course of this study. BoΔabcBA was isolated from lymph nodes near to the site of inoculation in two dogs at 22 weeks post immunization.

CONCLUSION

Encapsulated BoΔabcBA protected mice against experimental B. canis infection, and it is safe for dogs. Therefore, B. ovis ΔabcBA has potential as a vaccine candidate for canine brucellosis prevention.

Preliminary study on the role of novel LysR family gene kp05372 in Klebsiella pneumoniae of forest musk deer

LysR-type transcriptional regulators are involved in the regulation of numerous cellular metabolic processes in Klebsiella pneumoniae, leading to severe infection. Earlier, we found a novel LysR family gene, named kp05372, in a strain of K. pneumoniae (designated GPKP) isolated from forest musk deer. To study the function of this gene in relation to the biological characteristics of GPKP, we used the suicide plasmid and conjugative transfer methods to construct deletion mutant strain GPKP-Δkp05372; moreover, we also constructed the GPKP-Δkp05372+ complemented strain. The role of this gene was determined by comparing the following characteristics of three strains: growth curves, biofilm formation, drug resistance, stress resistance, median lethal dose (LD₅₀), organ colonization ability, and the histopathology of GPKP. Real-time polymerase chain reaction (RT-PCR) was used to test the expression level of seven genes upstream of kp05372. There was no significant difference in the growth rates when comparing the three bacterial strains, and no significant difference was recorded at different osmotic pressures, temperatures, salt contents, or hydrogen peroxide concentrations. The GPKP-Δkp05372 mutant formed a weak biofilm, and the other two strains formed medium biofilm. The drug resistance of the GPKP-Δkp05372 mutant toward cephalothin, cotrimoxazole, and polymyxin B was changed. The acid tolerance of the deletion strain was stronger than that of the other two strains. The LD₅₀ values of the wild-type and complemented strains were 174-fold and 77-fold higher than that of the GPKP-Δkp05372 mutant, respectively. The colonization ability of the GPKP-Δkp05372 mutant in the heart, liver, spleen, kidney, and intestine was the weakest. The three strains caused different histopathological changes in the liver and lungs. In the GPKP-Δkp05372 mutant, the relative expression levels of kp05374 and kp05379 were increased to 1.32-fold and 1.42-fold, respectively, while the level of kp05378 was decreased by 42%. Overall, the deletion of kp05372 gene leads to changes in the following: drug resistance and acid tolerance; decreases in virulence, biofilm formation, and colonization ability of GPKP; and regulation of the upstream region of adjacent genes.

Deletion of the LuxR-type regulator VjbR in Brucella canis affects expression of type IV secretion system and bacterial virulence, and the mutant strain confers protection against Brucella canis challenge in mice

Brucella spp. are facultative intracellular pathogens and zoonotic agents which pose a huge threat to human health and animal husbandry. The B. melitensis, B. abortus, and B. suis cause undulant fever and influenza-like symptoms in humans. However, the effects of B. canis have not been extensively studied. The quorum sensing-dependent transcriptional regulator VjbR influences the Brucella virulence in smooth type Brucella strains, such as B. melitensis, B. abortus and rough type Brucella ovis. However, the function of VjbR in the rough-type B. canis is unknown. In the present study, we discovered that deletion of this regulator significantly affected Brucella virulence in macrophage and mice infection models. The expression levels of virB operon and the ftcR gene were significantly altered in the vjbR mutant strain. We further investigated the protective effect of different doses of the vjbR mutant in mice and the results indicated that VjbR conferred protection against the virulent B. canis strain. This study presents the first evidence that the transcriptional regulator VjbR has important function in B. canis. In addition, according to its reduced virulence and the protective immunity it induces in mice, it can be a potential live attenuated vaccine against B. canis.

Characterization of Brucella canis infection in mice

Canine brucellosis, caused by Brucella canis, is a disease of dogs and represents a public health concern as it can be transmitted to humans. Canine brucellosis is on the rise in the United States and there is currently no vaccine for use in dogs. Mice have been extensively utilized to investigate host-pathogen interactions and vaccine candidates for smooth Brucella species and could serve a similar role for studying B. canis. However, comparatively little is known about B. canis infection in mice. The objective of this study was to characterize the kinetics of colonization and pathogenicity of B. canis in mice in order to evaluate the mouse as a model for studying this pathogen. C57BL/6 mice were inoculated intraperitoneally with 105, 107, or 109 CFU of Brucella canis RM6/66 and euthanized 1-, 2-, 4-, 6-, 9-, and 12-weeks post-inoculation. B. canis induced splenomegaly in mice infected with 109 CFU at 1- and 2 weeks post-inoculation while no gross lesions were observed in other dose groups. Infection at the two higher doses resulted in dose-dependent granulomatous hepatitis and histiocytic infiltration of the spleen and mesenteric lymph nodes by 1-2 weeks. B. canis was cultured from the liver, spleen, uterus, bone marrow, lung, and kidney in all groups with colonization declining at a slow but steady rate throughout the experiment. Clearance was achieved by 9 weeks 105 CFU group and by 12 weeks in the 107 CFU group, while B. canis persisted in the spleen until 12 weeks in the highest dose group. Although B. canis does not demonstrate significant replication in C57BL/6 mice, it has the ability to establish an infection, induce splenomegaly, and persist for several weeks in multiple organs. Moreover, 1 x 107 CFU appears to be a suitable challenge dose for investigating vaccine safety.

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.

Research progress on the role of immune cells in Brucella infection

Brucellosis is one of the most prevalent zoonoses in the world. Incidence of the disease has increased significantly in recent years and has seriously affected the health of human beings and the development of animal husbandry. The pathogenesis of brucellosis remains unclear. Current studies suggest that this disease may be related to changes in natural killer cells, dendritic cells, and macrophages in immune cell subsets. Brucellosis may be also related to T helper (Th) 1 cell/Th2 cell imbalance in the CD4+ T cell subset, immunoregulation of regulatory T cells and Th17 cells, and the mechanism of action of CD8+ T cell. This paper aims to review the research progress on these inherent immune cells, the CD4+ T cell subset, and CD8+ T cells in Brucella infection.

Recombinant Enolase of Trypanosoma cruzi as a Novel Vaccine Candidate against Chagas Disease in a Mouse Model of Acute Infection

Trypanosoma cruzi is the protozoan parasite that causes Chagas disease, which is considered by the World Health Organization to be a neglected tropical disease. Two drugs exist for the treatment of Chagas disease, nifurtimox and benznidazole; they are only effective in the acute phase, and a vaccine is currently not available. In this study, we used the recombinant enolase from T. cruzi H8 strain (MHOM/MX/1992/H8 Yucatán) (rTcENO) and its encoding DNA (pBKTcENO) to immunize mice and evaluate their protective effects in an experimental murine model of acute phase infection. Our results showed that mice vaccinated with rTcENO or its encoding DNA were able to generate typical specific antibodies (IgG1, IgG2a, and IgG2b), suggesting that a mixed Th1/Th2 immune response was induced. The parasite burden in the blood was reduced to 69.8% and 71% in mice vaccinated with rTcENO and pBKTcENO, respectively. The group vaccinated with rTcENO achieved 75% survival, in contrast to the group vaccinated with pBKTcENO that showed no survival in comparison to the control groups. Moreover, rTcENO immunization elevated the production of IFN-γ and IL-2 after the parasite challenge, suggesting that the Th1-type immune response was polarized. These results indicated that rTcENO could be used as a vaccine against Chagas disease.

Brucella canis: An update on research and clinical management

In Canada, Brucella canis remains a potentially devastating infectious agent that is still considered uncommon, despite the increasing international movement of dogs. There may be a growing risk to the Canadian canine population due to a reliance on outdated seroprevalence studies and the lack of federal regulation. With the complex diagnostic and management challenges associated with Brucella canis, a One Health approach is necessary to address the need for ongoing research, including updating canine and human seroprevalence rates in Canada, elucidating the pathogenesis, and determining the most appropriate treatment and prevention strategies. Clinical management decisions are often complicated by currently available treatment protocols, and health risks to both canine and human populations. This article integrates recent research focusing on the pathogenesis, diagnosis, and treatment of Brucella canis, and outlines current clinical management approaches.

Polymeric antigen BLSOmp31 in aluminium hydroxide induces serum bactericidal and opsonic antibodies against Brucella canis in dogs

Polymeric antigen BLSOmp31 is an immunogenic vaccine candidate that confers protection against Brucella canis in mice. In this preliminary study, the immunogenicity and safety of BLSOmp31 adsorbed to aluminum hydroxide gel (BLSOmp31-AH) were evaluated in Beagle dogs. In addition, the potential to elicit serum antibodies with complement-dependent bactericidal activity and/or to enhance phagocytosis by neutrophils were analyzed. Dogs were immunized three times with BLSOmp31-AH by subcutaneous route, followed by an annual booster. The vaccine elicited specific antibodies 3 weeks after the first immunization. Annual booster induced comparable antibody response as the primary series. Humoral immune response stimulated by BLSOmp31-AH did not interfere with routine agglutination test for canine brucellosis. Antibodies demonstrated a high complement-dependent bactericidal activity against B. canis. Moreover, opsonization by immune serum not only stimulated binding and uptake of the bacteria by neutrophils but effectively enhanced the destruction of B. canis. Specific IgG was detected in 3/4 immunized dogs in preputial secretions. The antibody profile corresponded to a marked Th2 response, since IgG1 prevailed over IgG2 and cellular immune response was not detected in vitro or in vivo. These results require further evaluation in larger field studies to establish the full prophylactic activity of BLSOmp31 against canine brucellosis.

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.