Identification of proteins of Francisella tularensis induced during growth in macrophages and cloning of the gene encoding a prominently induced 23-kilodalton protein

The adaptation of facultative intracellular bacteria to host macrophages involves regulation of the synthesis of bacterial proteins. We analyzed the protein synthesis of Francisella tularensis LVS growing intracellularly in the macrophage-like murine cell line J774 and extracellularly in culture medium. After pulse-labeling with [35S] methionine and separation by one- and two-dimensional polyacrylamide gel electrophoresis, induction of a few proteins during intracellular growth was demonstrated. One of them, a 23-kDa protein, was prominently induced in the macrophages and also when extracellularly growing F. tularensis was exposed to hydrogen peroxide. After isolation of the 23-kDa protein from a preparative two-dimensional gel, a 22-amino-acid N-terminal peptide and two peptides obtained by trypsin digestion were sequenced. Based on the sequences, degenerate oligonucleotides were constructed for use as primers in a PCR. Hybridization of amplified DNA to XbaI-digested LVS DNA identified the gene of the 23-kDa protein in a 1.3-kb DNA fragment. Nucleotide sequence analysis revealed an open reading frame encoding a putative protein of a calculated molecular mass of 22.2 kDa. The open reading frame was preceded by a sequence typical of ribosome-binding sites in Escherichia coli. The amplified gene was successfully expressed by the pTrc99A vector in E. coli under control of the trc promoter. The gene product showed the same mobility and immunoreactivity as the 23-kDa protein of F. tularensis. The deduced amino acid sequence showed no significant homology with protein sequences in current data banks. Thus, intracellular growth of F. tularensis in macrophages was associated with prominent upregulation of a novel 23-kDa protein.

Characterization of the nucleotide sequence of the groE operon encoding heat shock proteins chaperone-60 and -10 of Francisella tularensis and determination of the T-cell response to the proteins in individuals vaccinated with F. tularensis

The groE operon of Francisella tularensis LVS, encoding the heat shock proteins chaperone-10 (Cpn10) and Cpn60, was sequenced and characterized, and the T-cell response of LVS-vaccinated individuals to the two proteins and the third major chaperone, Ft-DnaK, was assayed. The cpn10 and cpn60 genes were amplified by PCR with degenerate oligonucleotides derived from the N-terminal sequence of the two proteins. The sequence analysis revealed the expected two open reading frames, encoding proteins with estimated Mrs of 10,300 and 57,400. The deduced amino acid sequences closely resembled Cpn10 and Cpn60 proteins of other prokaryotes. The genes constituted a bicistronic operon, the cpn10 gene preceding the cpn60 gene. Upstream of the cpn10 gene, an inverted repeat and motifs similar to -35 and -10 sequences of sigma70-dependent but not of sigma32-dependent promoters of Escherichia coli were found. The inverted repeat of the operon resembled so-called hairpin loops identified in other characterized prokaryotic groE operons lacking sigma32-dependent promoters. Primer extension analysis disclosed one and the same transcription start, irrespective of the presence or absence of heat or oxidative stress. After separation of lysates of the F. tularensis LVS organism by two-dimensional gel electrophoresis, DnaK, Cpn60, and Cpn10 were extracted and used as antigens in T-cell tests. When compared to those from nonvaccinated individuals, T cells from individuals previously vaccinated with live F. tularensis LVS showed an increased proliferative response to DnaK and Cpn60 but not to Cpn10. The present data will facilitate further studies of the involvement of the heat shock proteins in protective immunity to tularemia.

Detection of Francisella tularensis in ulcers of patients with tularemia by PCR

The diagnosis of human cases of tularemia is usually confirmed by the demonstration of an antibody response to Francisella tularensis, which occurs about 2 weeks after the onset of disease. Due to a high risk of infection in the laboratory, cultivation of the causative agent tends to be avoided. During an outbreak in Sweden, the use of PCR for diagnosing the ulceroglandular form of tularemia was evaluated. Extraction and preparation of F. tularensis DNA from swab samples from the wounds of patients with tularemia involved the use of the nuclease inhibitor guanidine thiocyanate. The DNA was detected by multiplex PCR targeting the 16S rRNA gene and a 17-kDa lipoprotein gene of F. tularensis. In 29 of 40 (73%) patients with serologically confirmed tularemia, F. tularensis DNA was successfully amplified. Considering the limitations of current diagnostic procedures, PCR may become useful for the early diagnosis of tularemia.

Specific detection of Coxiella burnetii through partial amplification of 23S rDNA

A previously published sequence of the 23S rRNA gene of Coxiella burnetii has been reported to contain an intervening sequence of 444 base pairs (bp). The sequence information on the intervening sequence and the 23S rRNA gene was exploited to develop a specific PCR-based assay for C. burnetii. A primer set was designed that amplified a 477-bp fragment encompassing part of the intervening sequence and part of the 23S rDNA. From all of nine C. burnetii strains tested, a fragment of the expected size was amplified. As predicted from the published sequence, restriction endonuclease digestion of the PCR product from the Coxiella strains with RsaI produced two distinct fragments approximately 210- and 270-bp in size. The PCR-based method showed a detection limit of 10(2) bacteria as determined by visualization of the amplicon on an agarose gel. When experimentally infected blood was analyzed, the detection limit was 10(3) bacteria. No visible amplicons were observed when 41 bacterial strains, representing 29 species other than C. burnetii, were tested. The presence of the DNA in all bacterial samples was confirmed by amplification of a 350-bp fragment of the 16S rDNA using two universal primers. The described method proved to be specific for C. burnetii and may become a rapid and sensitive diagnostic assay for C. burnetii. The results also demonstrate that the intervening sequence within the 23S rRNA gene is generally found among isolates of C. burnetii.

Maternal origin of inv dup(15) chromosomes in infantile autism

Six male patients with infantile autism and an extra inverted duplicated chromosome 15[inv dup(15)] were reported in a previous study. These patients had four copies of the chromosome region 15pter-q13, or an inv dup(15)(pter-->q13; q13-->pter). In this new study, DNA from the families of four of the patients were analysed using Southern based RFLPs and microsatellite polymorphisms from the region. In all four cases the inv dup(15) chromosome was of maternal origin. Furthermore, the data suggests that it originated in the maternal meiotic process rather than in an early mitosis in the developmental process of the embryo. The extra chromosome contained material from both of the maternally derived 15-chromosomes. Based on the molecular data presented here, a model for the origin of chromosome markers of this type is proposed.

Amplification and restriction endonuclease digestion of a large fragment of genes coding for rRNA as a rapid method for discrimination of closely related pathogenic bacteria

By use of primers specific to conserved regions of the rRNA gene cluster, a discrete amplicon of approximately 5 kb was amplified by PCR from all 21 bacterial genera investigated. Subsequent endonuclease digestion of the PCR product with HaeIII distinguished between the three species of the human pathogen Francisella spp. on the one hand and four clinically relevant genomic groups of Acinetobacter spp. on the other hand. The described technique has the potential as a rapid method for discriminating between closely related species that are of clinical importance.

Orchestration of the protective immune response to intracellular bacteria: Francisella tularensis as a model organism

Francisella tularensis is used as a model organism in studies of mechanisms behind the induction of a protective T-cell response in the mammalian host. Protective immunity is associated with a CD4 and CD8 T-cell response towards a mosaic of proteins of F. tularensis and due to HLA restriction, each individual selects her own mosaic. No single protein has so far been shown to be immunodominant. Only live F. tularensis affords effective host protection. Subcellular antigen preparations induce only a marginal protective response even when combined with potent adjuvants such as immunostimulating complexes (ISCOMs). In mice, intradermal injection of live F. tularensis but not of killed bacteria results in an early cytokine expression in the infected liver, including interleukin-12, tumor necrosis factor-alpha, and interferon-gamma. This cytokine response seems to be a prerequisite for effective priming of T cells to an array of proteins of F. tularensis to occur.

Cytokine expression in the liver of mice infected with a highly virulent strain of Francisella tularensis

Cytokine mRNA expression was determined in the liver of mice subcutaneously inoculated with a lethal dose of the highly virulent strain FSC 041 of Francisella tularensis subvar, tularensis or a sublethal dose of the live vaccine strain of F. tularensis subvar. palaearctica. Expression of mRNA for TNF-alpha, IL-12, IFN-gamma, and IL-10 was demonstrated within 48 h of inoculation, the kinetics being similar irrespective of bacterial strain used. Thus, the expression of a cytokine response believed to be important in the early host defence against live vaccine strain seemed insufficient to prevent the lethality of a more virulent strain.

Fixation of femoral neck fracture. A randomized 2-year follow-up study of hook pins and sliding screw plate in 222 patients

We compared fixation with hook pins or sliding screw plate in a prospective randomized study of 222 patients with a cervical hip fracture. Radiographic evidence of early redisplacement, nonunion, or late segmental collapse was found in 43 of 122 patients operated on with two hook pins and in 40 of 100 patients operated on with the sliding screw plate. According to the actuarial method, the failure rate after 2 years was 38% with hook pins and 46% with screw plates, which not is a significant difference. Due to early redisplacement, reoperation with an endoprosthesis was performed within 0.5 (2) years in 11 (22) patients in the hook-pin group and in 4 (17) patients in the sliding-screw plate group.

Adjuvanticity of ISCOMs incorporating a T cell-reactive lipoprotein of the facultative intracellular pathogen Francisella tularensis

Immunostimulating complexes (ISCOMs) are known to be highly effective adjuvants for envelope antigens of viral agents, but have not been evaluated for use with antigens of intracellular bacteria. Balb/c mice were subcutaneously immunized with ISCOMs into which the T cell-reactive membrane protein TUL4 of Francisella tularensis had been incorporated. Spleen cells from the immunized mice responded in vitro to TUL4 and to heat-killed F. tularensis live vaccine strain (LVS) with proliferation and production of gamma-interferon, whereas spleen cells from control mice immunized with TUL4 only did not respond to the antigens. When mice immunized with TUL4 ISCOMs were challenged with F. tularensis LVS, bacterial counts in spleen and liver were lower than in non-immunized mice. Again, TUL4 had no effect when used without ISCOMs. When proteins of a total membrane preparation of F. tularensis LVS were incorporated in ISCOMs and used for immunization, a decrease in bacterial counts was obtained which was similar in magnitude to that of TUL4 ISCOMs. Generally, the adjuvant effects demonstrated did not compare with the excellent protective effect of live tularaemia vaccine. Nonetheless, ISCOMs provide a means whereby protective antigens of F. tularensis can be tested.

Cytokine expression in the liver during the early phase of murine tularemia

Cytokine expression was determined in the livers of mice inoculated subcutaneously with Francisella tularensis LVS. During the first 48 h of infection, there was a logarithmic increase of bacteria in the liver, with a doubling time of 2.5 h. Within 48 h, tumor necrosis factor alpha (TNF-alpha), interleukin 10 (IL-10), IL-12, and gamma interferon (IFN-gamma) mRNAs were expressed, and production of TNF-alpha and IFN-gamma was demonstrated. There was no expression within 96 h of mRNA from IL-2, IL-3, or IL-4. After subcutaneous inoculation of heat-killed LVS, no expression of any of the cytokine mRNAs and no increase in the levels of TNF-alpha or IFN-gamma occurred. The expression of TNF-alpha, IL-12, and IFN-gamma is held to be important to evoke an early T-cell-independent host defense against F. tularensis as well as to drive the expansion of a protective Th1 cell response.

CD4+ and CD8+ T-cell-dependent and -independent host defense mechanisms can operate to control and resolve primary and secondary Francisella tularensis LVS infection in mice

Immunity to experimental infection with the facultative intracellular bacterium Francisella tularensis is generally considered an example of T-cell-mediated, macrophage-expressed immunity. However, the results of the present study indicate that T-cell-independent mechanisms are also important in anti-Francisella defense. They show that mice selectively depleted of CD4+, CD8+, or both T-cell populations by treatment with T-cell subset-specific monoclonal antibodies remained capable of controlling and partly resolving a primary sublethal Francisella infection. Similarly, it was found that Francisella-immune mice depleted of either or both subsets of T cells retain a high degree of acquired immunity to reinfection. Together, these findings imply that resistance to primary and secondary tularemia can be mediated by cells other than CD4+ and CD8+ T cells.

Persistence of cell-mediated immunity and decline of humoral immunity to the intracellular bacterium Francisella tularensis 25 years after natural infection

The humoral and cell-mediated immune responses to the facultative intracellular pathogen Francisella tularensis were studied in subjects who had tularemia 25 years earlier. Serum agglutinin titers were low. Of 53 subjects, only 2 had a titer > 40. The F. tularensis-induced T cell response, on the other hand, was vigorous and in fact similar in magnitude to the response to purified protein derivative (PPD) of Mycobacterium tuberculosis. T cells from 44 of 52 subjects showed a significant (P < .05) proliferative response in vitro to each of four membrane proteins of F. tularensis. Only 2 subjects did not respond to any of the proteins. In most cultures from 18 subjects tested, interferon-gamma was produced in response to the proteins. During the last 25 years, tularemia has been reported only rarely in the region where the subjects lived, suggesting that an antigen-specific T cell response may persist after tularemia independently of reexposure to F. tularensis.

Neutrophils are critical for host defense against primary infection with the facultative intracellular bacterium Francisella tularensis in mice and participate in defense against reinfection

It is generally believed that immunity to experimental infection with the facultative intracellular bacterium Francisella tularensis is an example of T-cell-mediated immunity that is expressed by activated macrophages and mediated by Francisella-specific T cells. According to the results presented herein, neutrophils are also essential for defense against primary infection with this organism. It is shown that mice depleted of neutrophils by treatment with the granulocyte-specific monoclonal antibody RB6-8C5 are rendered defenseless against otherwise sublethal doses of F. tularensis LVS inoculated intravenously or intradermally. In neutrophil-depleted mice, the organism grew progressively in the livers, spleens, and lungs to reach lethal numbers, whereas infection was resolved in normal mice. Although neutrophils were found to resistance to reinfection, their participation was less important. The results suggest that neutrophils are needed for defense against primary infection because they serve to restrict the growth of F. tularensis before it reaches numbers capable of overwhelming a developing specific immune response. The exact way that neutrophils achieve this is not clear at this time, although it is probable that they contribute in ways other than by ingesting and killing the bacterium.

Bone mineral content and fixation strength of femoral neck fractures. A cadaver study

We measured the bone mineral content (BMC) of 21 human femoral autopsy specimens using Radiographic Attenuation Technique (RAT). The specimens were then tested for stiffness in a material-testing machine. Osteosynthesis was performed after medial femoral neck osteotomy, using 1 of 3 different pinning methods: 2 hook pins (LIH), 2 cannulated screws (Uppsala), and 3 cannulated screws (CHP). The specimens were allocated to each method by grouping them in triplets with similar BMC. Cyclic loading at 500-1000 N and 1 Hz was performed during 50 minutes. The amount of axial compression during loading was measured. Finally, loading to failure was done and post-fixation stiffness and ultimate compression strength recorded. With one exception, all cases failed where the BMC was less than 0.4 g/cm2. No differences between the methods of osteosynthesis were found. The fixation strength was mostly dependent on the strength of the bone, i.e., the degree of osteoporosis.

Analysis of 16S ribosomal DNA sequences of Francisella strains and utilization for determination of the phylogeny of the genus and for identification of strains by PCR

The 16S ribosomal DNAs (rDNAs) of two strains of Francisella tularensis and one strain of Francisella philomiragia were sequenced. On the basis of phylogenetic analysis data, the genus Francisella was placed in the gamma subclass of the Proteobacteria. The most closely related organism was the intracellular bacterium Wolbachia persica. The sequenced 16S rDNA molecules of the Francisella species exhibited very high levels of similarity (98.5 to 99.9%). Two variable regions, comprising 390 to 450 nucleotides of the 16S rDNA molecules of 17 additional Francisella strains, including members of the species F. tularensis and F. philomiragia, were also sequenced. At most, six nucleotide differences were observed among the sequences of the F. tularensis strains. The sequence of Francisella novicida was virtually identical to the sequences of the F. tularensis strains, thereby supporting the hypothesis that these organisms are members of the same species. On the basis of the observed differences, primer pairs were designed to distinguish strains by using the PCR at the genus, species, and subspecies levels. This permitted sensitive identification of strains belonging to the genus Francisella and discrimination of the species F. tularensis and F. philomiragia.

Increased synthesis of DnaK, GroEL, and GroES homologs by Francisella tularensis LVS in response to heat and hydrogen peroxide

The response of the facultative intracellular bacterium Francisella tularensis LVS to stress was assayed by pulse-labeling with [35S]methionine followed by two-dimensional gel electrophoresis and autoradiography. A temperature increase from 37 to 42 degrees C or exposure to 5 mM hydrogen peroxide induced increased syntheses of at least 15 proteins. Among these proteins were a 75-, a 60-, and a 10-kDa protein. By N-terminal sequence analysis, these three proteins were found to be extensively homologous to the highly conserved chaperone proteins DnaK, GroEL, and GroES of Escherichia coli. Antibodies specific to the DnaK homolog of E. coli reacted with the 75-kDa protein, and antibodies to the GroEL homolog of Legionella micdadei reacted with the 60-kDa protein. A readiness to respond to hydrogen peroxide with synthesis of the chaperone components may be fundamental to the intracellular survival of pathogens such as F. tularensis, which are exposed to oxidative stress while invading the host macrophages.

Immunogenicity and toxicity of lipopolysaccharide from Francisella tularensis LVS

Lipopolysaccharide (LPS) from the live vaccine strain of Francisella tularensis (F. tularensis LVS) was isolated and purified. The LPS did not stimulate lymphocytes from previously tularaemia-vaccinated individuals or lymphocytes from non-primed individuals. However, serum antibodies from tularaemia vaccinees reacted with the LPS whereas virtually no reactivity was found with antibodies from individuals not exposed to F. tularensis LVS. Antibodies of immunoglobulin class M displayed the antibody reactivity predominantly. The LPS failed to induce the mononuclear cell-derived cytokine interleukin-1 and only low levels of tumour necrosis factor were detected. Furthermore, no LPS endotoxin properties were found in galactosamine-treated mice or in the Limulus amoebocyte lysate assay. From these results it can be concluded that F. tularensis LVS possesses a lipopolysaccharide-like molecule, which does not exhibit properties of a classical endotoxin.

The 17 kDa lipoprotein and encoding gene of Francisella tularensis LVS are conserved in strains of Francisella tularensis

A T-cell-stimulating 17 kDa protein of the vaccine strain Francisella tularensis LVS has previously been cloned, sequenced and shown to be a lipoprotein. In the present study, it was investigated whether the protein, denoted TUL4, and its gene are present in various strains of the genus Francisella. By Western blot analysis, it was demonstrated that a TUL4-specific monoclonal antibody bound to a protein present in each of the Francisella strains. The immunoreactive proteins had an M(r) of 17 kDa in all F. tularensis strains and in the strain Francisella novicida, whereas the M(r) in strains of Francisella philomiragia was 20 kDa. When genomic preparations were probed with a radioactive DNA fragment of F. tularensis LVS encoding TUL4, hybridization was demonstrated in all strains of Francisella, although the F. philomiragia strains did not hybridize under conditions of high stringency. The hybridizing chromosomal DNA fragment of the F. philomiragia strains was larger than that of the other Francisella strains. No hybridization or Western blot reactivity was seen when various other Gram-negative and Gram-positive bacteria were probed. In summary, the 17 kDa lipoprotein of F. tularensis LVS appears to be Francisella-specific and present in the species F. tularensis and F. novicida, whereas an immunologically related protein is present in F. philomiragia.

Various membrane proteins of Francisella tularensis induce interferon-gamma production in both CD4+ and CD8+ T cells of primed humans

Tularaemia is an intracellular infection, which is controlled by the host as a result of an immunospecific T-cell response. A crucial product of the responding T cells is interferon-gamma (IFN-gamma), which acts by enhancing the microbicidal activity of macrophages. T cells of tularaemia-vaccinated individuals respond in vitro to a multitude of protein antigens of the vaccine strain Francisella tularensis LVS. In the present study, the responses to four of these antigens were shown to be confined mostly to the CD45RO+ memory T-cell subset. To characterize further the phenotype of the responding cells, purified CD4+ and CD8+ T cells were stimulated with the antigens. CD4+ T cells, but not CD8+ T cells, proliferated and produced IFN-gamma. However, when CD8+ T cells were isolated from bulk cultures of lymphocytes, which had been stimulated with antigen for 3 days, they responded to an extent similar to that of CD4+ T cells. Purified CD8+ T cells also responded when they were supplemented with interleukin-2 (IL-2). There was a direct quantitative correlation between the proliferative response of CD4+ and CD8+ T cells and their production of IFN-gamma. IL-2 was produced in the cultures, the amounts being higher in the cultures of CD4+ than in those of CD8+ cells. IL-4 was not detected in the culture medium of any of the T-cell subsets. Seventeen human alpha beta + CD4+ CD8- CD3+ T-cell clones, specific to antigens of F. tularensis, were raised. When proliferating, these clones did invariably produce IL-2 and IFN-gamma but no IL-4. In conclusion, both CD4+ and CD8+ T cells of tularaemia-vaccinated individuals respond with proliferation to various protein antigens of F. tularensis, and the proliferative response is strictly associated with IFN-gamma production. The CD8+ T-cell response seems to depend on cytokines supplied by proliferating CD4+ T cells.

Humoral and cell-mediated immunity in mice to a 17-kilodalton lipoprotein of Francisella tularensis expressed by Salmonella typhimurium

A 17-kDa lipoprotein, TUL4, of the facultative intracellular bacterium Francisella tularensis is one of several membrane proteins that induce an in vitro response in T cells from F. tularensis-primed humans. A DNA fragment of the live vaccine strain F. tularensis LVS encoding TUL4 was cloned into Salmonella typhimurium chi 4072, an attenuated delta cya delta crp mutant. Expression of the protein by the recombinant S. typhimurium chi 4072 (pTUL4-15) was maintained after passage in BALB/cJ mice. When mice were immunized with S. typhimurium chi 4072(pTUL4-15), some animals showed an antibody response and a T-cell response to TUL4. When the immunized mice were challenged with the live vaccine strain F. tularensis LVS, bacterial counts in the liver and spleen were lower than in animals immunized with S. typhimurium chi 4072. Immunization with F. tularensis LVS caused a much stronger protection against the challenge than did immunization with S. typhimurium chi 4072(pTUL4-15). The present study demonstrated that the 17-kDa lipoprotein TUL4 of F. tularensis is involved in a protective immunity to tularemia. Possibly, several T-cell-reactive proteins of the organism have to contribute for optimal protection to be achieved.