Virulence factors in brucellosis: implications for aetiopathogenesis and treatment

Deletion of the alr gene in Brucella suis S2 attenuates virulence by enhancing TLR4-NF-κB-NLRP3- mediated host inflammatory responses

Brucella is an intracellular parasitic bacterium lacking typical virulence factors, and its pathogenicity primarily relies on replication within host cells. In this study, we observed a significant increase in spleen weight in mice immunized with a Brucella strain deleted of the gene for alanine racemase (Alr), the enzyme responsible for alanine racemization (Δalr). However, the bacterial load in the spleen markedly decreased in the mutant strain. Concurrently, the ratio of white pulp to red pulp in the spleen was increased, serum IgG levels were elevated, but no significant damage to other organs was observed. In addition, the inflammatory response was potentiated and the NF-κB-NLRP3 signaling pathway was activated in macrophages (RAW264.7 Cells and Bone Marrow-Derived Cells) infect ed with the Δalr mutant. Further investigation revealed that the Δalr mutant released substantial amounts of protein in a simulated intracellular environment which resulted in heightened inflammation and activation of the TLR4-NF-κB-NLRP3 pathway in macrophages. The consequent cytoplasmic exocytosis reduced intracellular Brucella survival. In summary, cytoplasmic exocytosis products resulting from infection with a Brucella strain deleted of the alr gene effectively activated the TLR4-NFκB-NLRP3 pathway, triggered a robust inflammatory response, and reduced bacterial survival within host cells. Moreover, the Δalr strain exhibits lower toxicity and stronger immunogenicity in mice.

Bovine Brucellosis: Epidemiology, Public Health Implications, and Status of Brucellosis in Ethiopia

Brucellosis is a globally distributed zoonotic disease that causes serious problems in developing countries such as Ethiopia. Brucella abortus is the primary cause of brucellosis in cattle, and Brucella melitensis and Brucella suis also occasionally cause Brucella infection in cattle. Abortion and the retained fetal membrane are typical signs in females, whereas orchitis and bursitis are the known signs in male cattle. Brucellosis is typically transmitted to healthy cattle by direct or indirect contact with diseased cattle or their discharges. Humans can acquire brucellosis through the consumption of unpasteurized milk or milk products, and through contact with diseased cattle or their discharges. The occurrence of bovine brucellosis is affected by different factors related to the management system, host, and environmental factors. In Ethiopia, the occurrence of brucellosis is high in pastoral and mixed cattle management systems, wherever humans live closely with cattle and so have a higher probability of picking up the Brucella organism. The most suitable technique in the management of Brucella infection is the vaccination of young female cattle. Brucella abortus can also be eradicated by the isolation of diseased cattle, administration of immunizing agents, and test-and-slaughter methods. Therefore, it is important to implement applicable management techniques and to increase public awareness about the transmission of brucellosis, and further research should be conducted on brucellosis in high-risk groups.

The current therapeutical strategies in human brucellosis

Prompt and adequate treatment of human brucellosis continues to be the most important strategy in its management, as eradication of animal brucellosis is not possible so far, and there is no adequate vaccine for humans. The goal of antibrucellar treatment is to alleviate and shorten the symptomatic period and reduce complications, relapses, and chronicity. Contemporary trends in the treatment of human brucellosis are postulated on the ability of Brucellae to persist in host macrophages through the inhibition of phagolysosome fusion and to survive for prolonged periods intracellularly without restricting basic cellular functions. As a result of this and despite satisfactory antibiotic treatment, relapses and therapeutical failures are inevitable to a certain degree. The current principles for the treatment of brucellosis advocate for a long enough treatment duration combined with antimicrobial regimens that possess activity in the intracellular acidic environment. In the future, other antimicrobial agents, immunomodulation, decrease in the intracellular acidic environment, or development of agents that would act on well-defined molecular bacterial targets, might be incorporated to improve the therapeutical effects.

Simultaneous Immunization with Omp25 and L7/L12 Provides Protection against Brucellosis in Mice

Currently used Brucella vaccines, Brucella abortus strain 19 and RB51, comprises of live attenuated Brucella strains and prevent infection in animals. However, these vaccines pose potential risks to recipient animals such as attenuation reversal and virulence in susceptible hosts on administration. In this context, recombinant subunit vaccines emerge as a safe and competent alternative in combating the disease. In this study, we formulated a divalent recombinant vaccine consisting of Omp25 and L7/L12 of B. abortus and evaluated vaccine potential individually as well as in combination. Sera obtained from divalent vaccine (Omp25+L7/L12) immunized mice group exhibited enhanced IgG titers against both components and indicated specificity upon immunoblotting reiterating its authenticity. Further, the IgG1/IgG2a ratio obtained against each antigen predicted a predominant Th2 immune response in the Omp25+L7/L12 immunized mice group. Upon infection with virulent B. abortus 544, Omp25+L7/L12 infected mice exhibited superior Log10 protection compared to individual vaccines. Consequently, this study recommends that simultaneous immunization of Omp25 and L7/L12 as a divalent vaccine complements and triggers a Th2 mediated immune response in mice competent of providing protection against brucellosis.

Prediction of Structure and Molecular Interaction with DNA of BvrR, a Virulence-Associated Regulatory Protein of Brucella

Brucellosis, also known as "undulant fever" is a zoonotic disease caused by Brucella, which is a facultative intracellular bacterium. Despite efforts to eradicate this disease, infection in uncontrolled domestic animals persists in several countries and therefore transmission to humans is common. Brucella evasion of the innate immune system depends on its ability to evade the mechanisms of intracellular death in phagocytic cells. The BvrR-BvrS two-component system allows the bacterium to detect adverse conditions in the environment. The BvrS protein has been associated with genes of virulence factors, metabolism, and membrane transport. In this study, we predicted the DNA sequence recognized by BvrR with Gibbs Recursive Sampling and identified the three-dimensional structure of BvrR using I-TASSER suite, and the interaction mechanism between BvrR and DNA with Protein-DNA docking and molecular dynamics (MD) simulation. Based on the Gibbs recursive Sampling analysis, we found the motif AAHTGC (H represents A, C, and T nucleotides) as a possible sequence recognized by BvrR. The docking and EMD simulation results showed that C-terminal effector domain of BvrR protein is likely to interact with AAHTGC sequence. In conclusion, we predicted the structure, recognition motif, and interaction of BvrR with DNA.

Comparison of a New and Rapid Method: Brucella Coombs Gel Test With Other Diagnostic Tests

BACKGROUND

The aim of this study was to detect reliability of Brucella Coombs gel test (BCGT) by comparing with with ELISA (IgG + IgM), Standard agglutination test, and Brucella immunocapture agglutination methods in serological diagnosis of brucellosis.

METHODS

Brucella Coombs gel test (BCGT), Brucella ELISA (IgG + IgM), Standard agglutination test, and Brucella immunocapture agglutination tests of 78 patients with presumptive diagnosis of brucellosis which were sent to Microbiology Laboratory of Konya Numune Hospital from various regions of Konya were studied.

RESULTS

RESULTS

Of 78 patients with ELISA IgG and IgM, STA, BICA and BCGT; 26, 21, 10, 12 and 12 were positive. When compared with BICA, the sensitivity and specifity of BCGT were 100% and 100%, respectively.

CONCLUSION

According to results BCGT can be used as a diagnostic test in routine laboratories after more comprehensive studies in control groups and patients.

Brucella spp. Virulence Factors and Immunity

Brucellosis, caused by bacteria of the genus Brucella, is an important zoonotic infection that causes reproductive disease in domestic animals and chronic debilitating disease in humans. An intriguing aspect of Brucella infection is the ability of these bacteria to evade the host immune response, leading to pathogen persistence. Conversely, in the reproductive tract of infected animals, this stealthy pathogen is able to cause an acute severe inflammatory response. In this review, we discuss the different mechanisms used by Brucella to cause disease, with emphasis on its virulence factors and the dichotomy between chronic persistence and reproductive disease.

Type IV secretion system of Brucella spp. and its effectors

Brucella spp. are intracellular bacterial pathogens that cause infection in domestic and wild animals. They are often used as model organisms to study intracellular bacterial infections. Brucella VirB T4SS is a key virulence factor that plays important roles in mediating intracellular survival and manipulating host immune response to infection. In this review, we discuss the roles of Brucella VirB T4SS and 15 effectors that are proposed to be crucial for Brucella pathogenesis. VirB T4SS regulates the inflammation response and manipulates vesicle trafficking inside host cells. VirB T4SS also plays crucial roles in the inhibition of the host immune response and intracellular survival during infection. Here, we list the key molecular events in the intracellular life cycle of Brucella that are potentially targeted by the VirB T4SS effectors. Elucidating the functions of these effectors will help clarify the molecular role of T4SS during infection. Furthermore, studying the effectors secreted by Brucella spp. might provide insights into the mechanisms used by the bacteria to hijack the host signaling pathways and aid in the development of better vaccines and therapies against brucellosis.

RNA-seq reveals the critical role of OtpR in regulating Brucella melitensis metabolism and virulence under acidic stress

The response regulator OtpR is critical for the growth, morphology and virulence of Brucella melitensis. Compared to its wild type strain 16 M, B. melitensis 16 MΔotpR mutant has decreased tolerance to acid stress. To analyze the genes regulated by OtpR under acid stress, we performed RNA-seq whole transcriptome analysis of 16 MΔotpR and 16 M. In total, 501 differentially expressed genes were identified, including 390 down-regulated and 111 up-regulated genes. Among these genes, 209 were associated with bacterial metabolism, including 54 genes involving carbohydrate metabolism, 13 genes associated with nitrogen metabolism, and seven genes associated with iron metabolism. The 16 MΔotpR also decreased capacity to utilize different carbon sources and to tolerate iron limitation in culture experiments. Notably, OtpR regulated many Brucella virulence factors essential for B. melitensis intracellular survival. For instance, the virB operon encoding type IV secretion system was significantly down-regulated, and 36 known transcriptional regulators (e.g., vjbR and blxR) were differentially expressed in 16 MΔotpR. Selected RNA-seq results were experimentally confirmed by RT-PCR and RT-qPCR. Overall, these results deciphered differential phenomena associated with virulence, environmental stresses and cell morphology in 16 MΔotpR and 16 M, which provided important information for understanding the detailed OtpR-regulated interaction networks and Brucella pathogenesis.

[Factors associated with Brucella canis seropositivity in kennels of two regions of Antioquia, Colombia]

The objectives of this study were to determine Brucella canis seroprevalence in dogs and in humans living near kennels and to explore risk factors associated with seropositivity. Twenty kennels were included in a serological survey with RSAT-2ME, and samples were collected from 428 dogs and 91 humans. An interview was applied to determine risk factors, and the data were analyzed using logistic regression. Seroprevalence was 15% in dogs and 9% in humans. Factors associated with current canine seropositivity were: history of canine seropositivity, non-culling of seropositive dogs, history of abortion, poor hygiene and personal protection during reproductive service, and unsafe procedures during care for abortions. Protective factors included: rural location of kennels, ease of cleaning kennels, pre-mating RSAT-2ME, and safe procedures during care for delivery. Factors associated with seropositive status in humans were: kennels located in Valle de Aburrá and urban location.

Mechanism of Asp24 upregulation in Brucella abortus rough mutant with a disrupted O-antigen export system and effect of Asp24 in bacterial intracellular survival

We previously showed that Brucella abortus rough mutant strain 2308 ΔATP (called the ΔrfbE mutant in this study) exhibits reduced intracellular survival in RAW264.7 cells and attenuated persistence in BALB/c mice. In this study, we performed microarray analysis to detect genes with differential expression between the ΔrfbE mutant and wild-type strain S2308. Interestingly, acid shock protein 24 gene (asp24) expression was significantly upregulated in the ΔrfbE mutant compared to S2308, as confirmed by quantitative reverse transcription-PCR (qRT-PCR) and Western blotting. Further studies using additional strains indicated that the upregulation of asp24 occurred only in rough mutants with disrupted O-antigen export system components, including the ATP-binding protein gene rfbE (bab1_0542) and the permease gene rfbD (bab1_0543), while the ΔwboA rough mutant (which lacks an O-antigen synthesis-related glycosyltransferase) and the RB51 strain (a vaccine strain with the rough phenotype) showed no significant changes in asp24 expression compared to S2308. In addition, abolishing the intracellular O-antigen synthesis of the ΔrfbE mutant by deleting the wboA gene (thereby creating the ΔrfbE ΔwboA double-knockout strain) recovered asp24 expression. These results indicated that asp24 upregulation is associated with intracellular O-antigen synthesis and accumulation but not with the bacterial rough phenotype. Further studies indicated that asp24 upregulation in the ΔrfbE mutant was associated neither with bacterial adherence and invasion nor with cellular necrosis on RAW264.7 macrophages. However, proper expression of the asp24 gene favors intracellular survival of Brucella in RAW264.7 cells and HeLa cells during an infection. This study reveals a novel mechanism for asp24 upregulation in B. abortus mutants.

Immunogenic response induced by wzm and wzt gene deletion mutants from Brucella abortus S19

Brucellosis is an infectious disease affecting humans and animals worldwide. Effective methods of control include inducing immunity in animals by vaccination and elimination. Brucella abortus S19 is one of the popular vaccines for control of cattle brucellosis, as it has low virulence. In this paper, allelic exchange plasmids of wzm and wzt genes were constructed and partially knocked out to evaluate the effects on the induction of immunity to Brucella abortus S19 mutants. Cytokine secretion in vitro, INF-γ induction in vivo and antibody dynamics were evaluated. These data suggested that the immunity-eliciting ability of the wzm and wzt gene deletion mutants was similar, although reduced compared with the S19 strain. The results demonstrated that the wzt gene may be more important in the regulation of the induction of immunity than the wzm gene.

A history of the development of Brucella vaccines

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

Renal cyst infection caused by Brucella abortus

A 49-year-old man with a medical history of polycystic kidney disease was presented to the emergency department with fever and left flank pain. Abdominal examination revealed an enlarged and painful left kidney. The C-reactive protein level was significantly high and the magnetic resonance imaging revealed areas of abnormal intensity and fluid-fluid levels in renal cysts. Brucella abortus was yielded from both blood and cyst fluid culture. Standard therapy (rifampicin plus doxycycline) of brucellosis was started, but the clinical and laboratory signs subsided after the addition of ciprofloxacin. There was no need for aspiration of infected cyst fluid. Hereby, according to the medical database search, we report that the first renal cyst infection caused by B. abortus was successfully treated with triple antibiotic therapy.

Substrate-specific gene expression in Batrachochytrium dendrobatidis, the chytrid pathogen of amphibians

Determining the mechanisms of host-pathogen interaction is critical for understanding and mitigating infectious disease. Mechanisms of fungal pathogenicity are of particular interest given the recent outbreaks of fungal diseases in wildlife populations. Our study focuses on Batrachochytrium dendrobatidis (Bd), the chytrid pathogen responsible for amphibian declines around the world. Previous studies have hypothesized a role for several specific families of secreted proteases as pathogenicity factors in Bd, but the expression of these genes has only been evaluated in laboratory growth conditions. Here we conduct a genome-wide study of Bd gene expression under two different nutrient conditions. We compare Bd gene expression profiles in standard laboratory growth media and in pulverized host tissue (i.e., frog skin). A large proportion of genes in the Bd genome show increased expression when grown in host tissue, indicating the importance of studying pathogens on host substrate. A number of gene classes show particularly high levels of expression in host tissue, including three families of secreted proteases (metallo-, serine- and aspartyl-proteases), adhesion genes, lipase-3 encoding genes, and a group of phylogenetically unusual crinkler-like effectors. We discuss the roles of these different genes as putative pathogenicity factors and discuss what they can teach us about Bd’s metabolic targets, host invasion, and pathogenesis.

Exploiting the Campylobacter jejuni protein glycosylation system for glycoengineering vaccines and diagnostic tools directed against brucellosis

Background

Immune responses directed towards surface polysaccharides conjugated to proteins are effective in preventing colonization and infection of bacterial pathogens. Presently, the production of these conjugate vaccines requires intricate synthetic chemistry for obtaining, activating, and attaching the polysaccharides to protein carriers. Glycoproteins generated by engineering bacterial glycosylation machineries have been proposed to be a viable alternative to traditional conjugation methods.

Results

In this work we expressed the C. jejuni oligosaccharyltansferase (OTase) PglB, responsible for N-linked protein glycosylation together with a suitable acceptor protein (AcrA) in Yersinia enterocolitica O9 cells. MS analysis of the acceptor protein demonstrated the transfer of a polymer of N-formylperosamine to AcrA in vivo. Because Y. enterocolitica O9 and Brucella abortus share an identical O polysaccharide structure, we explored the application of the resulting glycoprotein in vaccinology and diagnostics of brucellosis, one of the most common zoonotic diseases with over half a million new cases annually. Injection of the glycoprotein into mice generated an IgG response that recognized the O antigen of Brucella, although this response was not protective against a challenge with a virulent B. abortus strain. The recombinant glycoprotein coated onto magnetic beads was efficient in differentiating between naïve and infected bovine sera.

Conclusion

Bacterial engineered glycoproteins show promising applications for the development on an array of diagnostics and immunoprotective opportunities in the future.

Deep-sequencing analysis of the mouse transcriptome response to infection with Brucella melitensis strains of differing virulence

Brucella melitensis is an important zoonotic pathogen that causes brucellosis, a disease that affects sheep, cattle and occasionally humans. B. melitensis strain M5-90, a live attenuated vaccine cultured from B. melitensis strain M28, has been used as an effective tool in the control of brucellosis in goats and sheep in China. However, the molecular changes leading to attenuated virulence and pathogenicity in B. melitensis remain poorly understood. In this study we employed the Illumina Genome Analyzer platform to perform genome-wide digital gene expression (DGE) analysis of mouse peritoneal macrophage responses to B. melitensis infection. Many parallel changes in gene expression profiles were observed in M28- and M5-90-infected macrophages, suggesting that they employ similar survival strategies, notably the induction of anti-inflammatory and antiapoptotic factors. Moreover, 1019 differentially expressed macrophage transcripts were identified 4 h after infection with the different B. melitensis strains, and these differential transcripts notably identified genes involved in the lysosome and mitogen-activated protein kinase (MAPK) pathways. Further analysis employed gene ontology (GO) analysis: high-enrichment GOs identified endocytosis, inflammatory, apoptosis, and transport pathways. Path-Net and Signal-Net analysis highlighted the MAPK pathway as the key regulatory pathway. Moreover, the key differentially expressed genes of the significant pathways were apoptosis-related. These findings demonstrate previously unrecognized changes in gene transcription that are associated with B. melitensis infection of macrophages, and the central signaling pathways identified here merit further investigation. Our data provide new insights into the molecular attenuation mechanism of strain M5-90 and will facilitate the generation of new attenuated vaccine strains with enhanced efficacy.

Host cell autophagy in immune response to zoonotic infections

Autophagy is a fundamental homeostatic process in which cytoplasmic targets are sequestered within double-membraned autophagosomes and subsequently delivered to lysosomes for degradation. Accumulating evidence supports the pivotal role of autophagy in host defense against intracellular pathogens implicating both innate and adaptive immunity. Many of these pathogens cause common zoonotic infections worldwide. The induction of the autophagic machinery by innate immune receptors signaling, such as TLRs, NOD1/2, and p62/SQSTM1 in antigen-presenting cells results in inhibition of survival and elimination of invading pathogens. Furthermore, Th1 cytokines induce the autophagic process, whereas autophagy also contributes to antigen processing and MHC class II presentation, linking innate to adaptive immunity. However, several pathogens have developed strategies to avoid autophagy or exploit autophagic machinery to their advantage. This paper focuses on the role of host cell autophagy in the regulation of immune response against intracellular pathogens, emphasizing on selected bacterial and protozoan zoonoses.

Importance of Lipopolysaccharide and Cyclic β-1,2-Glucans in Brucella-Mammalian Infections

Brucella species are the causative agents of one of the most prevalent zoonotic diseases: brucellosis. Infections by Brucella species cause major economic losses in agriculture, leading to abortions in infected animals and resulting in a severe, although rarely lethal, debilitating disease in humans. Brucella species persist as intracellular pathogens that manage to effectively evade recognition by the host's immune system. Sugar-modified components in the Brucella cell envelope play an important role in their host interaction. Brucella lipopolysaccharide (LPS), unlike Escherichia coli LPS, does not trigger the host's innate immune system. Brucella produces cyclic β-1,2-glucans, which are important for targeting them to their replicative niche in the endoplasmic reticulum within the host cell. This paper will focus on the role of LPS and cyclic β-1,2-glucans in Brucella-mammalian infections and discuss the use of mutants, within the biosynthesis pathway of these cell envelope structures, in vaccine development.

Thrombotic thrombocytopenic purpura in a case of brucellosis

Thrombotic thrombocytopenic purpura (TTP) is characterized by disseminated thrombotic occlusions located in the microcirculation and a syndrome of microangiopathic hemolytic anemia, thrombocytopenia, fever, and renal and neurologic abnormalities. Thrombotic thrombocytopenic purpura is encountered in a variety of clinical situations such as viral, bacterial, and mycobacterial infections, autoimmune disorders, drug reactions, connective tissue disease, and solid tumors. In this report, we present TTP in a case of brucellosis because of rare presentation. A 7-year-old girl was admitted with the complaints of headache, fever, hematuria, malaise, jaundice, epistaxis, and purpura. Her physical examination revealed conjunctival pallor, scleral icterus, petechial-purpuric skin lesions on both legs, and confusion. Laboratory tests showed hematocrit 14%; hemoglobin 4.8 g/dL; platelet count 6000/mm(3), and reticulocytosis 6%. Peripheral blood smear revealed fragmented red blood cells and a complete absence of platelets. The clinical and laboratory findings were consistent with TTP. Serum antibrucella titration agglutination test was found to be 1/1280 positive.

Bacterial manipulation of innate immunity to promote infection

The mammalian innate immune response provides a barrier against invading pathogens. Innate immune mechanisms are used by the host to respond to a range of bacterial pathogens in an acute and conserved fashion. Host cells express pattern recognition receptors that sense pathogen-associated molecular patterns. After detection, an arsenal of antimicrobial mechanisms is deployed to kill bacteria in infected cells. Innate immunity also stimulates antigen-specific responses mediated by the adaptive immune system. In response, pathogens manipulate host defence mechanisms to survive and eventually replicate. This Review focuses on the control of host innate immune responses by pathogenic intracellular bacteria.

Evaluation of recombinant invasive, non-pathogenic Eschericia coli as a vaccine vector against the intracellular pathogen, Brucella

Background

There is no safe, effective human vaccine against brucellosis. Live attenuated Brucella strains are widely used to vaccinate animals. However these live Brucella vaccines can cause disease and are unsafe for humans. Killed Brucella or subunit vaccines are not effective in eliciting long term protection. In this study, we evaluate an approach using a live, non-pathogenic bacteria (E. coli) genetically engineered to mimic the brucellae pathway of infection and present antigens for an appropriate cytolitic T cell response.

Methods

E. coli was modified to express invasin of Yersinia and listerialysin O (LLO) of Listeria to impart the necessary infectivity and antigen releasing traits of the intracellular pathogen, Brucella. This modified E. coli was considered our vaccine delivery system and was engineered to express Green Fluorescent Protein (GFP) or Brucella antigens for in vitro and in vivo immunological studies including cytokine profiling and cytotoxicity assays.

Results

The E. coli vaccine vector was able to infect all cells tested and efficiently deliver therapeutics to the host cell. Using GFP as antigen, we demonstrate that the E. coli vaccine vector elicits a Th1 cytokine profile in both primary and secondary immune responses. Additionally, using this vector to deliver a Brucella antigen, we demonstrate the ability of the E. coli vaccine vector to induce specific Cytotoxic T Lymphocytes (CTLs).

Conclusion

Protection against most intracellular bacterial pathogens can be obtained mostly through cell mediated immunity. Data presented here suggest modified E. coli can be used as a vaccine vector for delivery of antigens and therapeutics mimicking the infection of the pathogen and inducing cell mediated immunity to that pathogen.

Brucella: a Mr "Hide" converted into Dr Jekyll

Dr David Bruce (1855-1931) first identified the causative agent of brucellosis as a small Gram-negative alpha-Proteobacterium, which was later on called Brucella melitensis in his honor by Meyer and Shaw. Nowadays, four strains exhibit pathogenicity in humans with B. melitensis being the least host specific and also the most infectious for humans. The other strains are Brucella suis and Brucella abortus and more recently human cases being infected with Brucella cetaceae have been reported. Why such a reemerging disease is so difficult to fight, evidence shows that the pathogenic bacterium has developed strategies to hide from immune recognition.

Vaccines against intracellular bacterial pathogens

There is a long history of remarkable success in developing vaccines against bacteria that are extracellular pathogens. In general, the development of vaccines against intracellular bacterial pathogens has proven to be more challenging. Typically, such vaccines need to induce a range of immune responses, including antibody, CD4(+) and CD8(+) T cell responses. These responses can be induced by live attenuated vaccines, but eliciting these responses with non-living vaccines has proven to be difficult. The difficulties appear to be related partly to the problems associated with the identification of protective antigens and partly with the difficulties associated with inducing CD8(+) T cell responses.