Immunological properties of ribosomal proteins from Mycobacterium bovis BCG

Genomic expression catalogue of a global collection of BCG vaccine strains show evidence for highly diverged metabolic and cell-wall adaptations

Although Bacillus Calmette-Guérin (BCG) vaccines against tuberculosis have been available for more than 90 years, their effectiveness has been hindered by variable protective efficacy and a lack of lasting memory responses. One factor contributing to this variability may be the diversity of the BCG strains that are used around the world, in part from genomic changes accumulated during vaccine production and their resulting differences in gene expression. We have compared the genomes and transcriptomes of a global collection of fourteen of the most widely used BCG strains at single base-pair resolution. We have also used quantitative proteomics to identify key differences in expression of proteins across five representative BCG strains of the four tandem duplication (DU) groups. We provide a comprehensive map of single nucleotide polymorphisms (SNPs), copy number variation and insertions and deletions (indels) across fourteen BCG strains. Genome-wide SNP characterization allowed the construction of a new and robust phylogenic genealogy of BCG strains. Transcriptional and proteomic profiling revealed a metabolic remodeling in BCG strains that may be reflected by altered immunogenicity and possibly vaccine efficacy. Together, these integrated-omic data represent the most comprehensive catalogue of genetic variation across a global collection of BCG strains.

Identification and characterization of the ribosome-associated protein, HrpA, of Bacillus Calmette-Guérin

HrpA was found as a ribosome-associated protein which appeared in heat-stressed Mycobacterium bovis Bacillus Calmette-Guérin. Here, we have studied the function of HrpA in vitro. HrpA is a heat shock protein belonging to a small heat shock protein family. The putative molecular mass was 17784.86 kDa. Recombinant HrpA formed large complexes of nonamer or dodecamer. HrpA prevented the aggregation of enzymes under heat shock conditions, and it formed stable complexes with partially denatured enzymes. HrpA was induced temporarily by oxygen repletion after anaerobic condition.

Mapping and identification of Mycobacterium tuberculosis proteins by two-dimensional gel electrophoresis, microsequencing and immunodetection

Mycobacterium tuberculosis is the infectious agent giving rise to human tuberculosis. The entire genome of M. tuberculosis, comprising approximately 4000 open reading frames, has been sequenced. The huge amount of information released from this project has facilitated proteome analysis of M. tuberculosis. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to fractions derived from M. tuberculosis culture filtrate, cell wall, and cytosol, resulting in the resolution of 376, 413, and 395 spots, respectively, in silver-stained gels. By microsequencing and immunodetection, 38 culture filtrate proteins were identified and mapped, of which 12 were identified for the first time. In the same manner, 23 cell wall proteins and 19 cytosol proteins were identified and mapped, with 9 and 10, respectively, being novel proteins. One of the novel proteins was not predicted in the genome project, and for four of the identified proteins alternative start codons were suggested. Fourteen of the culture filtrate proteins were proposed to possess signal sequences. Seven of these proteins were microsequenced and the N-terminal sequences obtained confirmed the prediction. The data presented here are an important complement to the genetic information, and the established 2-D PAGE maps (also available at: www.ssi.dk/publichealth/tbimmun) provide a basis for comparative studies of protein expression.

The potential use of heat-shock proteins to vaccinate against mycobacterial infections

Over the last few years, some of our experiments in which mycobacterial heat-shock protein (HSP) antigens were presented to the immune system as if they were viral antigens have had a significant impact on our understanding of protective immunity against tuberculosis. They have also markedly enhanced the prospects for new vaccines. We now know that the mycobacterial HSP65 antigen can confer protection equal to that from live BCG vaccine in mice.

Host immune responses to ribosome, ribosomal proteins, and RNA from Mycobacterium bovis bacille de Calmette-Gúerin

The ribosomes from BCG strongly induced delayed type hypersensitivity (DTH) skin reactions in guinea pigs immunized with live BCG or heat killed Mycobacterium tuberculosis H37Rv, and also induced lymphocyte proliferative response in mice immunized with ribosomes. In contrast, neither ribosomal proteins nor RNA alone induced both DTH skin reactions and lymphocyte proliferative responses. Particle form consisted of ribosomal proteins and RNAs might be absolutely required for the activation of immune responses.

The 16-kDa alpha-crystallin-like protein of Mycobacterium bovis BCG is produced under conditions of oxygen deficiency and is associated with ribosomes

A 16-kDa protein, identical to the alpha-crystallin-like stress protein, was induced under O2-deficient culture conditions and bound principally to the 30S ribosomal subunits of Mycobacterium bovis BCG substrain Tokyo (BCG). The 16-kDa protein was shown to be tightly associated with the ribosome.

Genetic vaccination against tuberculosis

New weapons are needed in the fight against tuberculosis. Recent research indicates that a vaccine better than BCG may be within reach. A diverse range of protein antigens can give encouragingly high levels of protective immunity in animal models when administered with adjuvants or as DNA vaccines. Accelerated arrest of bacterial multiplication followed by sustained decline in bacterial numbers are key parameters of protection and so the vaccine must target antigens produced by both actively multiplying and growth-inhibited bacteria. Consistent with this, the protective antigens have been found among secreted and stress proteins (e.g. Ag85, ESAT-6, hsp65, hsp70). Species-specific antigens are not needed, hence these remain available for diagnostic tests. Adoptive transfer of protection from vaccinated or infected mice into naive mice by transfer of purified T cells and clones shows that protection is expressed by antigen-specific cytotoxic T cells that produce interferon-gamma and lyse infected macrophages. These cells are produced in response to endogenous antigen. DNA vaccination appears to be an excellent way of generating these cells and may be able to give long-lasting protection.

HrpA, a new ribosome-associated protein which appears in heat-stressed Mycobacterium bovis bacillus Calmette-Guérin

A novel 18-kDa heat shock protein, HrpA, has been identified from Mycobacterium bovis BCG. HrpA was rapidly synthesized in membrane and ribosome fractions but not in the cytoplasmic fraction under heat shock stress. HrpA bound tightly to 70S ribosomes, mainly in 30S subunits. HrpA might be involved in the initiation step of translation at high temperature.

Delayed-type hypersensitivity activity of the Brucella L7/L12 ribosomal protein depends on posttranslational modification

The ribosomal protein L7/L12 isolated from Brucella melitensis induces a delayed-type hypersensitivity (DTH) reaction in brucella-sensitized guinea pigs. Surprisingly, the recombinant brucella L7/L12 protein expressed in Escherichia coli as a fusion protein with a six-histidine tag cannot elicit such a reaction. The six histidines tagged to the recombinant L7/L12 protein were removed enzymatically, but the resulting protein did not induce a DTH reaction in sensitized animals. Incubation of the recombinant L7/L12 fusion protein in a B. melitensis lysate endowed the recombinant protein with a DTH activity, suggesting that the recombinant protein was modified by this treatment. Glycosylation or phosphorylation of the recombinant L7/L12 protein could not be detected. On the other hand, radiolabeled palmitic acid was found to be incorporated to the recombinant protein during its incubation in the brucella lysate. This incorporation was specific for the brucella L7/L12 protein and was inhibited when the brucella lysate was frozen and thawed before the incubation. The data reported here indicate that posttranslational modification of L7/L12 protein comprising at least an acylation step is required for the brucella L7/L12 DTH activity.

Monoclonal antibodies against Streptococcus pneumoniae detect epitopes on eubacterial ribosomal proteins L7/L12 and on streptococcal elongation factor Ts

Two monoclonal antibodies (mAbs) designated 144,H-3 (IgG2a) and 218,C-5 (IgM) were produced after immunization of mice with two different heat-treated and sonicated pneumococcal strains. Western blotting, with solubilized proteins from different bacterial genera and from mammalian lymphocytes, showed that both mAbs reacted with a protein of approximately 12 kDa in all 66 strains of eubacteria examined, representing 27 different species. The 12 kDa protein was isolated by immunoaffinity chromatography. Subsequent preparative Western blotting enabled N-terminal amino acid sequence analysis by microsequencing. A high degree of amino acid sequence similarity with eubacterial ribosomal proteins L7/L12 was demonstrated. One of the mAbs (144,H-3) also cross-reacted in Western blotting with a 43 kDa protein, but only from streptococci. The 43 kDa protein carrying the common streptococcal epitope was isolated and sequenced in the N-terminal region. A high degree of amino acid sequence identity was found to elongation factor Ts from Escherichia coli.

T lymphocyte mediated protection against facultative intracellular bacteria

Acquired immunity against intracellular bacteria is T cell dependent. T cells play a major role in protection against intracellular bacteria, but bacterial antigens recognized by T cells have been studied less extensively than bacterial antigens recognized by B cells. Using T lymphocytes from animals immunized against Brucella abortus, we have screened a bacterial genomic library for genes encoding antigens recognized by T cells. Lymphocytes that proliferated to B. abortus proteins were characterized for phenotype and cytokine activity. Bovine and murine lymphocytes recognized common bacterial antigens and possessed similar cytokine profiles, suggesting an analogous immune response in these two animal species. In vivo protection afforded by a particular cell type is dependent on the bacterial antigens presented and mechanisms of antigen presentation. MHC class I and class II gene knockout animals infected with B. abortus have demonstrated that protection to B. abortus is especially dependent on CD8+ T cells. Knowing the cells required for protection, vaccines can be designed to elicit the protective subset of lymphocytes. Currently, we are testing several recombinant B. abortus proteins using different immunization strategies. Finally, bacterial genes activated following intracellular phagocytosis are being examined using a novel, reporter system adapted to B. abortus.

Mycobacterial infections: are the observed enigmas and paradoxes explained by immunosuppression and immunodeficiency?

The enigmas and paradoxes observed in tuberculous patients, in Bacille Calmette-Guérin-vaccinated people and in Bacille Calmette-Guérin-treated cancer patients have been examined, in an attempt to explain them through the mechanisms of immunodeficiency and immunosuppression. A dual effect is postulated: an immunosuppression induced by the infecting mycobacteria that adds to a pre-existing or emerging state of immunodeficiency of the infected individual. The immunological cellular and humoral anergies observed at the beginning of a tuberculous therapy are usually lifted after the first two weeks of treatment. This restoration of immune responsiveness may be attributed to the destruction or to the growth inhibition of immunosuppressive mycobacteria. The observation that drugs cytocidal in vitro do not always sterilize the patients under treatment whereas bacteriostatic drugs do, may find an explanation in the dual immunosuppression induced by cytocidal drugs and mycobacteria. The fact that Bacille Calmette-Guérin applied as an immunotherapy to residual cancer has either a favorable or an unfavorable action may be due to the immunosuppressive activity attached to some Bacille Calmette-Guérin strains and to some cancers. The variable protective activity of Bacille Calmette-Guérin vaccines may be due to the immunological status of the vaccinated people and the compositional differences between strains. The protective activity of subunit vaccines in experimental models can be attributed to the elimination of immunosuppressive factors present in whole killed mycobacteria.

Homology between the MPB70 and MPB83 proteins of Mycobacterium bovis BCG

Isolation of MPB83 from Mycobacterium bovis BCG Tokyo culture fluid is described. MPB70 and MPB83 have similar molecular mass as judged by SDS-PAGE but differ in isoelectric points. Peptides isolated after CNBr cleavage of MPB83 revealed extensive homology as well as distinct differences from corresponding parts of the amino acid sequence deduced from the mpb70 gene cloned by Terasaka et al. Antibodies produced by immunization with MPB70 and MPB83 had distinctly different fine specificity revealing cross-reactivity between the proteins. These findings indicate that two distinct, homologous genes code for these proteins. Sensitization with live BCG Tokyo also induced T cell responses to MPB83 with development of delayed type hypersensitivity in guinea pigs.

Characterization of the gene encoding the MPB51, one of the major secreted protein antigens of Mycobacterium bovis BCG, and identification of the secreted protein closely related to the fibronectin binding 85 complex

The secreted protein MPB51 is one of the major proteins in the culture filtrate of Mycobacterium bovis BCG (BCG) and is a protein immunologically cross-reacting with the fibronectin binding 85 complex secreted by this bacterium. The gene encoding MPB51 (mpb51) was cloned, sequenced, and expressed in Escherichia coli. The mpb51 gene was mapped downstream of the gene for 85A component with 179 bp spaces. The mpb51 gene encoded 299 amino acids, including 33 amino acids for the signal peptide, followed by 266 amino acids for the mature protein with a molecular mass of 27807.37 Da. This is the first complete sequence of MPB51. MPB51 showed 37-43% homology to the components of 85 complex. Two-dimensional electrophoresis of culture fluids of BCG and Western blotting indicated the existence of the other novel protein(s) which strongly cross-reacted with the alpha antigen (85B) and MPB51.

Recombinant L7/L12 ribosomal protein and gamma-irradiated Brucella abortus induce a T-helper 1 subset response from murine CD4+ T cells

Immunity to Brucella abortus crucially depends on antigen (Ag)-specific T-cell mediated activation of macrophages, which are the major effectors of cell-mediated killing of this organism. Ribosomal preparations have been used as vaccines against several pathogens, including B. abortus, conferring a high degree of protection. In the present study, we have examined the pattern of T-helper (Th) cell response from infected BALB/c mice after in vitro stimulation with recombinant (r) L7/L12 ribosomal protein or gamma-irradiated B. abortus. In addition to Ag-specific proliferation, CD4+ T cells were tested for interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma) mRNA expression and secretion. Detection of cytokine transcripts and secreted cytokines was performed using reverse transcriptase (RT)-polymerase chain reaction (PCR) and specific ELISA assays. Primed CD4+ T cells proliferated to the recombinant protein or whole B. abortus. The functional cytokine profile of the proliferating cells was typical of a Th1 cell phenotype, as we detected transcripts for IL-2 and IFN-gamma but not IL-4. Among the cytokines analysed, only IFN-gamma produced in the Th cell culture supernatants was detected by ELISA when bacteria or recombinant protein were used. Thus, rL7/L12 ribosomal protein and gamma-irradiated B. abortus preferentially stimulated IFN-gamma-producing Th1 cells after in vitro stimulation. The results of this study provide for the first time an explanation of why ribosomal vaccines may protect against intracellular infections, and an experimental basis for identifying polypeptides from a pathogen which stimulates the desired cytokine profile and Th cell response crucial for the design of genetically engineered candidate vaccines.

Brucella ribosomal protein L7/L12 is a major component in the antigenicity of brucellin INRA for delayed-type hypersensitivity in brucella-sensitized guinea pigs

A delayed-type hypersensitivity (DTH) reaction in the course of brucellosis in humans and animals can be revealed by the brucellin INRA (Brucellergen) skin test. Brucellergen is composed of more than 20 proteins of different molecular weights. A 12-kDa protein eliciting DTH in Brucella melitensis Rev1-sensitized guinea pigs was found to be a significant component for the allergenic properties of Brucellergen. Sequencing of the gene encoding this protein identified it as the L7/L12 ribosomal protein. The L7/L12 gene of B. melitensis was amplified by PCR and subcloned in the Escherichia coli pQE30 plasmid. The resulting recombinant protein did not produce a DTH reaction in sensitized animals. It was used to raise specific antibodies in a rabbit. Affinity chromatography with these antibodies was used to isolate a single protein from Brucellergen and from B. melitensis cytosol preparations which produced a DTH reaction in guinea pigs sensitized with B. melitensis Rev1. N-terminal amino acid sequencing of the protein confirmed that it was the L7/L12 ribosomal protein. This is the first complete report on the involvement of a defined bacterial ribosomal protein in the DTH response of animals infected with intracellularly multiplying bacteria.

Subcloning and expression of the Brucella abortus L7/L12 ribosomal gene and T-lymphocyte recognition of the recombinant protein

The Brucella abortus L7/L12 ribosomal gene was amplified by PCR and subcloned into the prokaryotic expression vector pMAL-c2. Escherichia coli DH5 alpha was transformed with the pMAL-L7/L12 construct, and gene expression was induced by IPTG (isopropyl-beta-D-thiogalactopyranoside). The resulting fusion protein was purified by affinity chromatography and confirmed by Western blot (immunoblot) analysis using an anti-maltose-binding protein antibody. Additionally, purified recombinant L7/L12 protein induced T-lymphocyte proliferation of B. abortus-primed bovine peripheral blood mononuclear cells. Phenotypic analysis of the proliferating cell population demonstrated an increase in the percentage of CD4+ T lymphocytes when peripheral blood mononuclear cells were cultured with recombinant L7/L12 compared with cells cultured in medium alone. Subcloning and expression of a B. abortus gene encoding a previously demonstrated immunodominant protein for bovine lymphocytes are important steps in selecting Brucella proteins that have potential as a component of a genetically engineered candidate vaccine.

Bacterial crude extracts or ribosomes are recognized similarly by peripheral and mucosal B cells

Bacterial ribosomes have been shown to induce effective humoral and cellular immunological responses to whole microorganisms. In this study, the numbers of specific antibody producing cells directed towards Klebsiella pneumoniae, Streptococcus pneumoniae, Streptococcus pyogenes and Haemophilus influenzae ribosomes or whole bacteria sonicates were compared in the peripheral blood and tonsils of 7 children, and in the tonsils, mesenteric and cervical lymph nodes of 10 sheep. No significant difference was noted between the two types of antigens, confirming that ribosomal preparations are able to mimic the immunogenicity of whole bacteria in the mucosae-associated lymphoid tissue.

Identification and nucleotide sequence of Brucella melitensis L7/L12 ribosomal protein

DNA sequencing of the gene encoding a Brucella melitensis 12-kDa protein revealed that this protein was the ribosomal protein L7/L12. The B. melitensis L7/L12 DNA sequence was identical to that of the corresponding B. abortus gene, showing the near identity of these two organisms. When comparing the sequence of this protein to that of other organisms some domains were highly conserved, especially the C-terminus, which contrasted with the lack of conservation of the sequences at the N-terminus. The finding that the ribosomal protein L7/L12 of Brucella is an immunodominant antigen provides a new rationale to explain the activity of ribosomal vaccines.