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PubMed1991

Minimal requirements for growth of Brucella suis and other Brucella species.

Minimal nutritional requirements and temperature limits of growth were studied in Brucella suis and, comparatively, in a few other Brucella species. In a saline basic medium including thiosulphate, ammonium sulphate and glucose with addition of 2 or 4 vitamins (nicotinic acid, thiamin and panthotenic acid, biotin), 24 out of 25 B. suis, 4/6 B. melitensis and 1/6 B. abortus strains were able to grow. Some strains, however, needed to be initially induced to grow by other ingredients, CO2, other vitamins, or amino acids, or by a prolonged incubation. In the saline basic medium without ammonium, glutamic acid and/or alanine and arginine, with or without glucose, supported the growth of all the B. suis and B. melitensis strains, except 2 which required a sulphur amino acid. Five out of 6 B. abortus strains did not grow in either medium without addition of one or several aromatic amino acids or, for one strain, aspartic acid, or valine. One strain could also be induced to grow in ammonium medium by other amino acids. In a rich medium with yeast extract, all Brucella species grew at 18 degrees C and 42.5 degrees (except one) while most B. suis (14/17) grew also at 15 degrees C and 44 degrees C, in contrast to other brucellae of which a few strains only grew at these temperatures. In saline ammonium glucose medium, yeast extract at 0.1 g/l provided all the required vitamins and amino acids for all brucellae and at 1 g/l, it even provided enough nitrogen to support growth without ammonium. Such basic saline medium with yeast extract may be advantageously used in routine Brucella culture, instead of the classic undefined peptone mediums. B. suis biovar 1 strains did not differ significantly in their minimal nutritional requirements, precluding the use of these requirements to differentiate the strains, in particular the Chinese vaccine strain S2 from the reference strain 1330 or from other strains from different parts of the world. Finally, B. suis which is endowed with a nearly complete synthetic potential may represent the parental Brucella species from which the melitensis and abortus species may have evolved.

Amino Acids↗

PubMed2002

Major histocompatibility complex class I and II expression on macrophages containing a virulent strain of Brucella abortus measured using green fluorescent protein-expressing brucellae and flow cytometry.

Immune responses appropriate for control of an intracellular pathogen are generated in mice infected with Brucella abortus, shown by the ability of T cells to adoptively transfer resistance to naive mice. The infection nevertheless persists for months. It was hypothesized that one factor in maintaining the infection despite the presence of immune T cells was suboptimal expression of major histocompatibility complex (MHC) molecules on macrophages containing brucellae. This would allow B. abortus to elude detection by the host's immune system. To test this, B. abortus organisms expressing green fluorescent protein (GFP-Brucella) were constructed and three-color flow cytometry used to evaluate MHC expression on macrophages following in vitro or in vivo infection. When infected in vitro, the levels of MHC class I and class II expression on J774 macrophages containing GFP-Brucella were the same or higher than on macrophages without GFP-Brucella in the same cultures. Similarly, the MHC expression was higher on GFP(+) peritoneal exudate cells following infection or phagocytosis of heat-killed GFP-Brucella than it was on uninfected peritoneal exudate cells. Following in vivo infection of mice the level of MHC class I and II expression on GFP(+) cells in their spleens (the main site of infection) also tended to be as high as or higher than that on the GFP-negative cells. The only in vivo GFP(+) cells that showed a decreased MHC expression was a population of splenic Mac1(+) cells recovered from interferon-gamma gene-disrupted mice at the time of their death due to an overwhelming number of bacteria per spleen. Overall, it was concluded that decreased MHC expression is not a general principle associated with brucella infection of macrophages and thus not likely to contribute to maintenance of the chronic infection.

Animals↗

PubMed2001

Deletion of wboA enhances activation of the lectin pathway of complement in Brucella abortus and Brucella melitensis.

Brucella spp. are gram-negative intracellular pathogens that survive and multiply within phagocytic cells of their hosts. Smooth organisms present O polysaccharides (OPS) on their surface. These OPS help the bacteria avoid the bactericidal action of serum. The wboA gene, coding for the enzyme glycosyltransferase, is essential for the synthesis of O chain in Brucella. In this study, the sensitivity to serum of smooth, virulent Brucella melitensis 16M and B. abortus 2308, rough wboA mutants VTRM1, RA1, and WRR51 derived from these two Brucella species, and the B. abortus vaccine strain RB51 was assayed using normal nonimmune human serum (NHS). The deposition of complement components and mannose-binding lectin (MBL) on the bacterial surface was detected by flow cytometry. Rough B. abortus mutants were more sensitive to the bactericidal action of NHS than were rough B. melitensis mutants. Complement components were deposited on smooth strains at a slower rate compared to rough strains. Deposition of iC3b and C5b-9 and bacterial killing occurred when bacteria were treated with C1q-depleted, but not with C2-depleted serum or NHS in the presence of Mg-EGTA. These results indicate that (i) OPS-deficient strains derived from B. melitensis 16M are more resistant to the bactericidal action of NHS than OPS-deficient strains derived from B. abortus 2308, (ii) both the classical and the MBL-mediated pathways are involved in complement deposition and complement-mediated killing of Brucella, and (iii) the alternative pathway is not activated by smooth or rough brucellae.

Brucella abortus↗

PubMed1993

Successful therapeutic regimens for treating Brucella melitensis and Brucella abortus infections in cows.

Three therapeutic regimens were evaluated in 121 cows naturally infected with Brucella melitensis or Brucella abortus, using a combination of long-acting oxytetracycline (LA-OTC), streptomycin (ST) and OTC-intramammary infusion (IMI). Cessation of shedding of Brucella in udder secretions and absence of Brucella in selected tissues were considered criteria for successful treatment. Regimen A (tested on 35 cows) consisted of LA-OTC 25 mg/kg administered intramuscularly (i.m.) every 3 days for 42 days, ST 25 mg/kg i.m. daily for 8 days, and OTC-IMI 20 ml/teat daily for 4 days. Regimen B (tested on 53 cows) was similar to regimen A, except that ST was administered every 2 days for 16 days and OTC-IMI every 2 days for 8 days. Both regimens were equally effective in eliminating Brucella organisms from all cows involved in the tests and no relapses were recorded. However, regimen C, which was similar to regimen A, except that ST was administered every 3 days for 24 days and OTC-IMI every 3 days for 12 days, resulted in the elimination of Brucella organisms from only 30 (91%) of 33 cows. Before commencement of the therapeutic regimens, B. melitensis biovar 1 or 2 had been repeatedly isolated from udder secretions of 103 cows and B. abortus biovar 1 from mammary secretions of 18 cows.

Abortion, Veterinary↗

PubMed2001

Use of polymerase chain reaction to identify Brucella abortus strain RB51 among Brucella field isolates from cattle in Italy.

Brucella abortus strain RB51, a rough mutant of the B. abortus 2308 virulent strain, was recently approved in the United States as the official vaccine for brucellosis in cattle. Following recent evidence of unauthorized use of RB51 vaccine in Italy, where the use of vaccines for brucellosis is no longer allowed, the suitability of an RB51-specific polymerase chain reaction assay for identifying the RB51 strain among Brucella field isolates from cattle in Italy was investigated. The oligonucleotide primers used in this study, belonging to a six-primer cocktail for Brucella species previously described by other authors, allowed the amplification of a 364-base pair (bp) fragment specific for RB51 and its parent strain 2308, and a 498-bp product specific for B. abortus. In addition, unresolved bands ranging from 600 to 700 bp were observed from RB51 strain. Brucella abortus biovars 1, 2 and 4 have only one specific sensitive 498-bp band. The B. abortus biovars 3, 5 and 6 did not give any signal. The 498-bp product from a reference Brucella strain was sequenced and submitted to EMBL with the accession number AJ271969 while the 364-bp fragment from RB51 strain was submitted to EMBL database with accession number AJ271968. The sequence studies confirmed the specificity of the detected fragments. No amplification was obtained by testing DNA from strains antigenically related to Brucella, such as Yersinia enterocolitica O:9, Escherichia coli O:157, Salmonella urbana and Pasteurella multocida. The results of this study indicate that this technique, in combination with specific serological tests, could be a useful diagnostic method to verify the use of RB51 vaccine and can contribute to the creation of a databank of circulating strains.

Animals↗

PubMed1995

In vitro efficacy of several antimicrobial combinations against Brucella canis and Brucella melitensis strains isolated from dogs.

In vitro efficacy of tetracyclines, aminoglycosides, fluoroquinolones, rifampin and macrolides and their combinations against four Brucella canis and two B. melitensis strains isolated from dogs was evaluated by means of inhibition tests: minimal inhibitory concentration (MIC) and fractional inhibitory concentrations (FIC) and by bactericidal tests: minimal bactericidal concentrations (MBC) and kill-time experiments. In inhibition studies, tetracyclines showed the lowest MICs of all compounds tested (0.06-0.50 mg/l). However, doxycycline did not inhibit growth of B. canis D-519 strain at concentrations lesser than 1 mg/l. Most strains were resistant to macrolides. Chequerboard MIC titrations showed synergy between enrofloxacin and aminoglycosides against B. canis RM 6/66 reference strain and between doxycycline and streptomycin against B. canis D-519 strain. Combinations of tetracyclines and aminoglycosides were at the limit of synergy for B. canis RM 6/66 strain (FIC = 0.56). Combination of doxycycline and rifampin seemed to be antagonistic against B. canis M-strain (FIC = 3). Other combinations studied were indifferent or additive against all other strains. In bactericidal studies, aminoglycosides, fluoroquinolones and rifampin showed bactericidal activity at 1-4 x MIC but tetracyclines or macrolides did not kill brucellae below 8 x MIC. Results of kill-time experiments indicated that streptomycin was the antimicrobial agent tested which more rapid killed brucellae. In most cases, doxycycline did not kill brucellae in 96 h of incubation. Which using rifampin alone, some inocula of B. canis strains RM 6/66, D-519 and M- showed regrowth after 24 h of incubation. Retesting of these regrowing brucellae showed an increased MIC indicating development of phenotypic resistance. Testing of antimicrobial combinations in kill-time experiments indicated synergy between enrofloxacin and streptomycin and antagonism between rifampin and doxycycline both for B. canis RM 6/66 strain.

Animals↗

PubMed2002

The myth of Brucella L-forms and possible involvement of Brucella penicillin binding proteins (PBPs) in pathogenicity.

Brucella spp. L-forms have been proposed to be stationary phase organisms in the evolution of new variants and enduring entities in the host in complicated cases of brucellosis and during latent brucellosis. In vitro formation of Brucella L-forms has been achieved by treating the cells with sub-lethal doses of penicillin. Interestingly, Brucella spp. have classified during the evolution into two groups, penicillin susceptible or penicillin resistant, yet both types grow on 20 microg/ml of methicillin. Strains proven susceptible to penicillin grew in the presence of methicillin as L-forms as demonstrated by light and electron microscopy. In addition, the B. melitensis vaccine strain Rev.1, a penicillin susceptible organism, responded to sheep serum by development of L-form-like structures unlike wild type, strain 16M. The two strains grew normally in sheep macrophages. We propose, for the first time, a model that associates Brucella pathogenicity with the structure and activity of two of their penicillin binding proteins (PBPs). According to the model, PBP1 has evolved as the major cell wall synthesizing enzyme of the genus, capable of responding to host serum growth factor(s) necessary for Brucella survival in the host. This property is associated with high avidity to beta-lactam antibiotics. PBP2 complements the activity of PBP1. New beta-lactam antibiotics and improved vaccines might be developed based on this property.

Animals↗

PubMed2001

Minor nucleotide substitutions in the omp31 gene of Brucella ovis result in antigenic differences in the major outer membrane protein that it encodes compared to those of the other Brucella species.

The gene coding for the major outer membrane protein Omp31 was sequenced in five Brucella species and their biovars. Although the omp31 genes appeared to be highly conserved in the genus Brucella, nine nucleotide substitutions were detected in the gene of Brucella ovis compared to that of Brucella melitensis. As shown by differential binding properties of monoclonal antibodies (MAbs) to the two Brucella species, these nucleotide substitutions result in different antigenic properties of Omp31. The antigenic differences were also evidenced when sera from B. ovis-infected rams were tested by Western blotting with the recombinant B. melitensis or B. ovis Omp31 proteins. Twelve available sera reacted with recombinant B. ovis Omp31, but only four of them reacted with recombinant B. melitensis Omp31. These results validate previous evidence for the potential of Omp31 as a diagnostic antigen for B. ovis infection in rams and demonstrate that B. ovis Omp31, instead of B. melitensis Omp31, should be used to evaluate this point. The antigenic differences between the B. melitensis and B. ovis Omp31 proteins should also be taken into account when Omp31 is evaluated as a candidate for the development of subcellular vaccines against B. ovis infection. No reactivity against recombinant B. melitensis Omp31 was detected, by Western blotting, with sera from B. melitensis-infected sheep. Accordingly, Omp31 does not seem to be a good diagnostic antigen for B. melitensis infections in sheep. Two immunodominant regions were identified on the B. ovis Omp31 protein by using recombinant DNA techniques and specific MAbs. Sera from B. ovis-infected rams that reacted with the recombinant protein were tested by Western blotting against one of these immunodominant regions shown to be exposed at the bacterial surface. Only 4 of the 12 sera reacted, but with strong intensity.

Amino Acid Sequence↗

PubMed2002

Comparison of the Brucella Standard Agglutination Test with the ELISA IgG and IgM in patients with Brucella bacteremia.

The presumptive diagnosis of Brucellosis is based on a high or rising antibody titer measured by the Brucella Standard Agglutination Test (SAT). This tests does not discriminate between the immunoglobulin classes (IgG and IgM). The purpose of this study was to compare the diagnostic value of SAT with Brucella Enzyme Linked Immunosorbent Assay (ELISA) IgG and IgM tests in patients with Brucella bacteremia. Over a one-year period, we had 68 patients with clinical features suggestive of Brucellosis who had positive blood cultures for Brucella species. Sera were obtained from all of the patients as well as a control group of 70 healthy military personnel who were blood donors and had no symptoms of Brucellosis. Patients and blood donors originated from the same referral population. All the sera were tested by SAT and ELISA. All the 70 controls had a negative SAT. The sensitivity and specificity of the SAT test for the bacteremic patients were 95.6% and 100.0% respectively, while that of the ELISA IgG were 45.6% and 97.1%, and that of the ELISA IgM were 79.1% and 100.0% respectively. The sensitivity and specificity of either IgG or IgM positivity were 94.1% and 97.1% respectively. Assuming that the population prevalence of active Brucellosis in Saudi Arabia (SAT >or=1:320) is 5%, the positive and negative predictive values of SAT were 100% and 99.7% respectively; of ELISA IgG they were 45.2% and 97.1%; and of ELISA IgM they were 100% and 98.9%. When both the ELISA IgG and IgM were combined, the positive and negative predictive values were 63% and 99.6% respectively. In patients with Brucella bactremia, the sensitivity of either ELISA IgM or IgG were lower than SAT, however, combining IgM and IgG had similar sensitivity and specificity to SAT. The positive predictive value of SAT and IgM is satisfactory.

Agglutination Tests↗

PubMed2002

Detection of Brucella melitensis by the BacT/Alert automated system and Brucella broth culture.

This study was conducted to evaluate the ability of the BacT/Alert automated blood culture system to detect Brucella spp. in comparison with traditional Brucella broth culture. Overall, 100 (50 bone marrow and 50 blood samples) paired cultures were obtained, and 59 were positive by at least one method. The Brucella broth culture method detected all 59 positive cultures (100%), and the BacT/Alert system detected 30 (50.8%) (P < 0.05). The mean detection times for B. melitensis were 4.5 days in the BacT/Alert system and 5 days in Brucella broth culture (P > 0.05). There is no significant difference between the two methods with respect to growth time of the microorganism, but Brucella broth culture is more sensitive than the BacT/Alert system.

Adolescent↗

PubMed1998

Evaluation of the relatedness of Brucella spp. and Ochrobactrum anthropi and description of Ochrobactrum intermedium sp. nov., a new species with a closer relationship to Brucella spp.

The relatedness of Brucella spp. and Ochrobactrum anthropi was studied by protein profiling, Western blot, immunoelectrophoresis and 16S rRNA analysis. Whole-cell and soluble proteins of brucellae and O. anthropi showed serological cross-reactivities quantitatively and qualitatively more intense than those existing with similar extracts of Agrobacterium spp. Numerical analysis of Western blot profiles of whole-cell extracts showed that O. anthropi LMG 3301 was closer to Brucella spp. than to O. anthropi LMG 3331T, a result not obtained by protein profiling. These differences were not observed by Western blot with soluble fractions, and immunoelectrophoretic analyses suggested that this was due to destruction of conformational epitopes in Western blot procedures with the subsequent simplification of antigenic profile. Analysis of the 16S rRNA sequences of strains previously used in the species definition confirmed that strain LMG 3301, and also LMG 3306, were closer to the brucellae, and that LMG 3331T was in a separate cluster. The LMG 3301 and the LMG 3331T clusters could also be separated by their different colistin sensitivity and by PCR with 16S rRNA Brucella primers, and both methods showed strains of both clusters among clinical isolates classified as O. anthropi by conventional tests. These results and those of previous DNA-DNA hybridization studies [Holmes, B., Popoff, M., Kiredjian, M. & Kersters, K. (1988). Int J Syst Bacteriol 38, 406-416] show that the LMG 3301 cluster and related clinical isolates should be given a new species status for which the name Ochrobactrum intermedium sp. nov. is proposed (type strain is LMG 3301T=NCTC 12171T = CNS 2-75T).

Animals↗

PubMed1996

Polymorphism at the dnaK locus of Brucella species and identification of a Brucella melitensis species-specific marker.

The dnaK gene and surrounding sequences from reference strains of the six Brucella species were amplified by the polymerase chain reaction (PCR) with primers chosen according to the published sequence of the B. ovis dnaK gene and studied for polymorphism with nine restriction endonucleases. The restriction patterns were identical for all species with all restriction endonucleases tested except for B. melitensis strain 16M that showed a different pattern with EcoRV, consistent with the presence of a single site instead of two for the other Brucella species. The absence of the second EcoRV site for B. melitensis 16M was confirmed by DNA sequence analysis. The second EcoRV site in other Brucella species was located in a 12-bp segment, which was missing from the published dnaK sequence of B. ovis, between the stop codon of the dnaK gene and its putative transcription terminator sequence. The difference between B. ovis strain 63/290 and B. melitensis 16M was due to an additional base-pair in B. melitensis 16M. Subsequently, 71 other field, vaccinal and reference strains of the six Brucella species and their different biovars were studied for restriction fragment length polymorphism (RFLP) of the dnaK locus with EcoRV. The presence of a unique EcoRV site was specific to B. melitensis strains. Southern blot analysis of whole genomic DNA digested with EcoRV and with the dnaK gene used as probe also detected a distinct pattern for B. melitensis. These results indicate that both PCR-RFLP and Southern blot analysis of the dnaK locus can be used to distinguish B. melitensis strains from the other Brucella species and may be useful for typing and diagnostic purposes as well.

Base Sequence↗

PubMed1998

Identification of the perosamine synthetase gene of Brucella melitensis 16M and involvement of lipopolysaccharide O side chain in Brucella survival in mice and in macrophages.

Brucella organisms are facultative intracellular bacteria that may infect many species of animals as well as humans. The smooth lipopolysaccharide (S-LPS) has been reported to be an important virulence factor of these organisms, but the genetic basis of expression of the S-LPS O antigen has not yet been described. Likewise, the role of the O side chain of S-LPS in the survival of Brucella has not been clearly defined. A mini-Tn5 transposon mutant library of Brucella melitensis 16M was screened by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies (MAbs) directed against the O side chain of Brucella. One mutant, designated B3B2, failed to express any O side chain as confirmed by ELISA, Western blot analysis, and colony coloration with crystal violet. Nucleotide sequence analysis demonstrated that the transposon disrupted an open reading frame with significant homology to the putative perosamine synthetase genes of Vibrio cholerae O1 and Escherichia coli O157:H7. The low G+C content of this DNA region suggests that this gene may have originated from a species other than a Brucella sp. The survival of B. melitensis mutant strain B3B2 in the mouse model and in bovine macrophages was examined. The results suggested that S-LPS or, more precisely, its O side chain is essential for survival in mice but not in macrophages.

Amino Acid Sequence↗

PubMed1990

[An experimental study on preparing monoclonal antibodies of rough Brucella spp. and identification species Brucella].

A report of preparation of monoclonal antibodies of B. canis and B. ovis and the use of identification for rough species of Brucella was described. The results showed that the above two monoclonal antibodies were specific for rough Brucella Spp. The use of the above described monoclonal antibodies gave us the possibility to differentiate rough and smooth Brucella species. The results also showed that the ELISA using monoclonal antibodies of rough Brucella Spp. was more specific than the agglutination test using routine antibodies of rough Brucella.

Animals↗

PubMed1971

Sensitization and recall of anti-Brucella immunity in Guinea pig macrophages by attenuated and virulent Brucella.

Peritoneal macrophages from guinea pigs vaccinated with strain Rev I of Brucella melitensis were only moderately activated thereby to limit, in an in vitro system, the intracellular growth of Rev I bacilli. Nevertheless, the appropriate memory cells had been primed, as demonstrated by the observation that reinfection of animals with virulent B. melitensis followed by intraperitoneal inoculation of mineral oil called forth macrophages in immunized guinea pigs which inhibited strongly the intracellular growth of brucellae. These macrophages slowed the growth of brucellae in the absence of immune serum. The intensity of the recall response was related to the challenge route and to the virulence of the challenge strain. After equal doses of attenuated or virulent brucellae, resistance was highest in macrophages recalled by the virulent strain. An important basis for the attenuation of the Rev I strain may lie in its initially low degree of macrophage activation during primary infection, although still retaining the capacity to prime stem cells. This property is associated with a protein found in fraction I, because 600 mug/ml in Freund's adjuvant primed guinea pigs so that challenge by strain 6015 evoked activated macrophages. This was seen microscopically as a reduced spread of infection in and amongst the macrophage population. Immune serum further reduced this spread and limited the number of viable intracellular brucellae.

Journal Article↗

PubMed1961

METABOLIC CHARACTERIZATION OF THE GENUS BRUCELLA IV. 3: Correlation of Oxidative Metabolic Patterns and Susceptibility to Brucella Bacteriophage, Type abortus, Strain.

Meyer, Margaret E. (University of California, Davis). Metabolic characterization of the genus Brucella. IV. Correlation of oxidative metabolic patterns and susceptibility to Brucella bacteriophage, type abortus, strain 3. J. Bacteriol. 82:950-953. 1961.-A total of 212 strains of brucellae that had been identified as Brucella melitensis, B. abortus, B. suis, or B. neotomae by their oxidative metabolism were tested for their susceptibility to Brucella bacteriophage, type abortus, strain 3. It was demonstrated that only those organisms that displayed the oxidative metabolic pattern that is singular for B. abortus were susceptible to this strain of phage, irrespective of their identity by the conventional methods usually employed for differentiating members of this genus. Strains of organisms that display the features of B. melitensis by the conventional determinative methods, but display the metabolic characteristics of B. abortus, are susceptible to lysis by this phage. These organisms are in fact B. abortus. Strains of organisms that display the features of B. melitensis by the classical methods, and display the metabolic pattern of B. melitensis, are not lysed by this phage. These organisms are B. melitensis. The conclusions then were drawn that B. abortus is the only species that can serve as host for this strain of phage, that oxidative metabolic patterns accurately identify the species in this genus, and that by the conventional methods of differentiation, many strains of B. abortus are misidentified as B. melitensis.

Journal Article↗

PubMed1993

Efficacy of Brucella suis strain 2 vaccine against Brucella ovis in rams.

The protective efficacy against Brucella ovis of live vaccine Brucella suis strain 2 (S2) and Brucella melitensis strain Rev 1 has been evaluated in rams. Fourteen 4-month-old Brucella-free Aragonesa rams were vaccinated conjunctivally with 2 x 10(9) c.f.u. S2. Sixteen rams of the same breed, condition and age were conjunctivally vaccinated the same day with 1.6 x 10(9) Rev 1. Thirteen rams were unvaccinated controls. Eight months after vaccination all rams were challenged with 6 x 10(9) c.f.u. B. ovis and slaughtered 2 months thereafter for bacteriological and pathological studies. The percentage of infection in the group vaccinated with Rev 1 (43.7%) was significantly lower (p < 0.05) than that of the S2-vaccinated animals (78.6%) and unvaccinated controls (84.6%). No significant differences were found when comparing the percentages of infection corresponding to S2-vaccinated and control groups. The degree of infection (percentage of necropsy samples infected) was significantly lower in Rev 1-vaccinated (13%) than in S2-vaccinated (36.9%) or control groups (47.4%) (p < 0.001). However, no significant differences were found when comparing S2-vaccinated and control groups.

Animals↗

PubMed1995

Differential activation of Brucella-reactive CD4+ T cells by Brucella infection or immunization with antigenic extracts.

In order to induce acquired cellular resistance to facultative bacterial pathogens, infection with live organisms is required. We have previously demonstrated that spleen cells from Brucella-infected mice produced gamma interferon (IFN-gamma) and interleukin-2 (IL-2) in response to Brucella antigens in vitro, while spleen cells from mice immunized with soluble Brucella proteins (SBP) produced substantial amounts of IL-2 but no detectable amount of IFN-gamma. In this study, we further analyzed the response of T cells from Brucella-infected mice and SBP-immunized mice and demonstrated that CD4(+)-enriched cells from SBP-immunized mice also produced significant amounts of IL-4, which was not detected in bulk cultures of spleen cells from infected mice. Limiting dilution analysis showed that infection resulted in a higher precursor frequency of IFN-gamma-producing CD4+ T cells and a lower precursor frequency of IL-4-producing CD4+ T cells, while immunization with SBP resulted in a higher precursor frequency of IL-4-producing cells and a very low frequency of IFN-gamma-producing cells. The precursor frequencies of IL-2-producing cells for the two groups were similar. Furthermore, IFN-gamma-producing CD4+ T cells from infected donor mice were capable of mediating resistance against challenge infection in recipient mice, but IL-4-producing CD4+ T cells from immunized mice failed to do so. These results indicate that the form of antigen has a profound influence on the outcome of the immune response. The results are discussed in light of the supposed dichotomy between Th1 and Th2 cytokine responses.

Animals↗