Comparison of lipopolysaccharide and outer membrane protein-lipopolysaccharide extracts in an enzyme-linked immunosorbent assay for the diagnosis of Brucella ovis infection

Enhancing Antitumor Efficacy of Heavily Vascularized Tumors by RAMBO Virus through Decreased Tumor Endothelial Cell Activation

Vascularization is a common pathology for many solid tumors, and therefore anti-angiogenic strategies are being investigated as a therapeutic target for treatment. Numerous studies are also being conducted regarding the effects of oncolytic viruses, including Imlygic^TM, an FDA approved oncolytic herpes simplex virus-1 (oHSV) for the treatment of highly vascularized tumors such as Kaposi sarcoma (NCT04065152), and brain tumors. To our knowledge, the effects of combining oncolytic HSV with angiogenesis inhibition on endothelial cell activation has not been previously described. Here, we tested the effects of Rapid Antiangiogenesis Mediated By Oncolytic Virus (RAMBO), an oHSV which expresses a potent anti-angiogenic gene Vasculostatin on endothelial cell activation in heavily vascularized solid tumors. oHSV treatment induces endothelial cell activation, which inhibits virus propagation and oncolysis in adjacent tumor cells in vitro. Consistently, this was also observed in intravital imaging of intracranial tumor-bearing mice in vivo where infected tumor endothelial cells could efficiently clear the virus without cell lysis. Quantitative real-time PCR (Q-PCR), leukocyte adhesion assay, and fluorescent microscopy imaging data, however, revealed that RAMBO virus significantly decreased expression of endothelial cell activation markers and leukocyte adhesion, which in turn increased virus replication and cytotoxicity in endothelial cells. In vivo RAMBO treatment of subcutaneously implanted sarcoma tumors significantly reduced tumor growth in mice bearing sarcoma compared to rHSVQ. In addition, histological analysis of RAMBO-treated tumor tissues revealed large areas of necrosis and a statistically significant reduction in microvessel density (MVD). This study provides strong preclinical evidence of the therapeutic benefit for the use of RAMBO virus as a treatment option for highly vascularized tumors.

The CO2-dependence of Brucella ovis and Brucella abortus biovars is caused by defective carbonic anhydrases

Brucella bacteria cause brucellosis, a major zoonosis whose control requires efficient diagnosis and vaccines. Identification of classical Brucella spp. has traditionally relied on phenotypic characterization, including surface antigens and 5–10% CO₂ necessity for growth (CO₂-dependence), a trait of Brucella ovis and most Brucella abortus biovars 1–4 strains. Although molecular tests are replacing phenotypic methods, CO₂-dependence remains of interest as it conditions isolation and propagation and reflects Brucella metabolism, an area of active research. Here, we investigated the connection of CO₂-dependence and carbonic anhydrases (CA), the enzymes catalyzing the hydration of CO₂ to the bicarbonate used by anaplerotic and biosynthetic carboxylases. Based on the previous demonstration that B. suis carries two functional CAs (CAI and CAII), we analyzed the CA sequences of CO₂-dependent and -independent brucellae and spontaneous mutants. The comparisons strongly suggested that CAII is not functional in CO₂-dependent B. abortus and B. ovis, and that a modified CAII sequence explains the CO₂-independent phenotype of spontaneous mutants. Then, by mutagenesis and heterologous plasmid complementation and chromosomal insertion we proved that CAI alone is enough to support CO₂-independent growth of B. suis in rich media but not of B. abortus in rich media or B. suis in minimal media. Finally, we also found that insertion of a heterologous active CAII into B. ovis reverted the CO₂-dependence but did not alter its virulence in the mouse model. These results allow a better understanding of central aspects of Brucella metabolism and, in the case of B. ovis, provide tools for large-scale production of diagnostic antigens and vaccines.

Comparison of Serological Tests Based on Outer Membrane or Internal Antigens for Detecting Antibodies to Brucella Ovis in Infected Flocks

The aim of this work was to compare the performance of 6 serological tests using outer or internal antigens from Brucella for the diagnosis of Brucella ovis infection in sheep in an endemic area. Outer membrane antigens included a hot saline extract (HS) and the rough lipopolysaccharide (R-LPS) from B. ovis. Internal antigens were LPS-free total cytosolic proteins (CP) and an 18-kDa cytosolic protein (p18) from Brucella spp. Sera from 200 sheep from naturally infected flocks were assayed by agar gel immunodiffusion test (AGID) and by complement fixation test (CFT), both using HS, and by 4 ELISA using HS, R-LPS, CP, and p18, respectively. The percentage of positive results was 45.5% for ELISA with HS, 42.0% for ELISA with p18, 39.5% for CFT, 33.5% for ELISA with R-LPS, 29.0% for ELISA with CP, and 18.0% for AGID. Taking CFT as the reference test for calculating relative test parameters, the ELISA with HS had the best sensitivity (96.2%), while AGID and the ELISA with R-LPS had the best specificity (96.6%). The ELISA with CP was not more sensitive than the ELISA with p18 (67.1% vs. 79.7%) in spite of the higher number of antigens in CP. The lower relative sensitivity of tests using internal antigens might reflect a lack of antibodies to cytosolic proteins in some infected animals or a shorter persistence of these antibodies relative to antibodies to outer membrane components after recovery from infection.

Mutants in the lipopolysaccharide of Brucella ovis are attenuated and protect against B. ovis infection in mice

Brucella spp. are Gram-negative bacteria that behave as facultative intracellular parasites of a variety of mammals. This genus includes smooth (S) and rough (R) species that carry S and R lipopolysaccharides (LPS), respectively. S-LPS is a virulence factor, and mutants affected in the S-LPS O-polysaccharide (R mutants), core oligosaccharide or both show attenuation. However, B. ovis is naturally R and is virulent in sheep. We studied the role of B. ovis LPS in virulence by mutating the orthologues of wadA, wadB and wadC, three genes known to encode LPS core glycosyltransferases in S brucellae. When mapped with antibodies to outer membrane proteins (Omps) and R-LPS, wadB and wadC mutants displayed defects in LPS structure and outer membrane topology but inactivation of wadA had little or no effect. Consistent with these observations, the wadB and wadC but not the wadA mutants were attenuated in mice. When tested as vaccines, the wadB and wadC mutants protected mice against B. ovis challenge. The results demonstrate that the LPS core is a structure essential for survival in vivo not only of S brucellae but also of a naturally R Brucella pathogenic species, and they confirm our previous hypothesis that the Brucella LPS core is a target for vaccine development. Since vaccine B. melitensis Rev 1 is S and thus interferes in serological testing for S brucellae, wadB mutant represents a candidate vaccine to be evaluated against B. ovis infection of sheep suitable for areas free of B. melitensis.

Optimization and efficient purification of recombinant Omp28 protein of Brucella melitensis using Triton X-100 and β-mercaptoethanol

The high level expression of recombinant proteins in Escherichia coli often leads to the formation of inclusion bodies that contain most of the expressed protein held together by non-covalent forces. The inclusion bodies are usually solubilized using strong denaturing agents like urea and guanidium hydrochloride. In this study recombinant Omp28 (rOmp28) protein of Brucella melitensis was expressed in two different vector systems and further efficient purification of the protein was done by modification in buffers to improve the yield and purity. Different concentrations of Triton X-100 and β-mercaptoethanol were optimized for the solubilization of inclusion bodies. The lysis buffer with 8M urea alone was not sufficient to solubilize the inclusion bodies. It was found that the use of 1% Triton X-100 and 20mM β-mercaptoethanol in lysis and wash buffers used at different purification steps under denaturing conditions increased the yield of purified rOmp28 protein. The final yield of purified protein obtained with modified purification protocol under denaturing conditions was 151 and 90mg/l of the culture or 11.8 and 9.37mg/g of wet weight of cells in pQE30UA and pET28a(+) vector respectively. Thus modified purification protocol yielded more than threefold increase of protein in pQE30UA as compared with purification by conventional methods.

Optimization of the entrapment of bacterial cell envelope extracts into microparticles for vaccine delivery

The encapsulation of a Brucella ovis extract (HS) in microparticles has been proved effective against experimental infections in mice. This work describes different strategies to increase the HS loading and prepare large batches as necessary to test this vaccine in ovine. The mixture of HS with beta-cyclodextrin was optimized in order to increase the HS loading in microparticles. On the other hand, TROMS ('Total Recirculation One-Machine System') led microparticles with a more homogeneous size than the laboratory or standard procedure. Moreover, the initial burst release of HS from the standard microparticles was higher than for the TROMS ones. In fact, standard microparticles displayed a higher amount of adsorbed HS. On the contrary, both preparative methods were found effective to preserve the integrity and anti-genicity of the loaded HS. In summary, beta-CD can be used to increase the loading of large hydrophobic materials and TROMS is a valid large production of antigen-loaded microparticles.

Immunological responses and protective efficacy against Brucella melitensis induced by bp26 and omp31 B. melitensis Rev.1 deletion mutants in sheep

The commonly used live attenuated vaccine in ovine brucellosis prophylaxis is Brucella melitensis Rev.1. This vaccine is known to induce antibody responses in vaccinated animals indistinguishable by the current conventional serological tests from those observed in challenged animals. Brucella BP26 and Omp31 proteins have shown an interesting potential as diagnostic antigens for ovine brucellosis. Accordingly, the bp26 gene and both bp26 and omp31 genes have been deleted from the vaccine strain Rev.1. Immunogenicity and vaccine efficacy of the parental Rev.1 strain and of both mutants in protecting sheep against B. melitensis strain H38 challenge was evaluated by clinical and bacteriological examination of ewes. They were conjunctivally or subcutaneously vaccinated when 4 months old and then challenged with B. melitensis H38 at the middle of the first pregnancy following vaccination. Deletion of bp26 and omp31 genes did not significantly affect the well recognised capacity of Rev.1 to protect sheep against B. melitensis challenge. However, the protection conferred by the CGV2631 mutant was significantly lower than that conferred by the CGV26 mutant or the Rev.1 strain. Vaccinated and challenged animals were detected positive in classical serological tests and in the IFN-gamma assay. A BP26-based ELISA was investigated to discriminate between ewes vaccinated by the mutants and ewes challenged with B. melitensis H38. The cut-off which was chosen in order to have 100% specificity resulted in a moderate sensitivity for the detection of challenged ewes. The use in the field of one of the mutants as vaccine against a B. melitensis infection, combined with classic diagnostic tests and a BP26 ELISA, could thus give an improvement in the differentiation between vaccinated and infected animals and contribute to the objective of eradication of brucellosis in small ruminants.

Development and evaluation as vaccines in mice of Brucella melitensis Rev.1 single and double deletion mutants of the bp26 and omp31 genes coding for antigens of diagnostic significance in ovine brucellosis

The live attenuated Brucella melitensis Rev.1 strain is considered the best vaccine available for the prophylaxis of brucellosis in sheep caused by either B. melitensis or Brucella ovis. However, its application stimulates antibody responses in vaccinated animals indistinguishable by the current conventional serological tests from those observed in infected animals. The periplasmic protein BP26 and the outer membrane protein (OMP) Omp31 are immunodominant antigens in the serological responses of B. melitensis and B. ovis infected sheep, respectively. Accordingly, vaccine strain Rev.1 single and double deletion mutants of the bp26 and omp31 genes were developed, based on the principle that the use of such mutants as vaccines in association with diagnostic tests based on BP26 and Omp31 antigens would allow the serological differentiation between infected and vaccinated animals. The deletion mutants obtained were indistinguishable from the parental Rev.1 strain by conventional bacteriological and typing tests. The expression of their major surface antigens, as determined by reactivity with specific monoclonal antibodies (MAbs), remained unaffected, i.e. smooth-lipopolysaccharide (S-LPS) and OMPs besides in the expression of the antigens whose respective genes were deleted. The bp26 and omp31 deletions did not modify the kinetics of splenic infection nor the residual virulence of Rev.1 in the BALB/c mouse model. Vaccination of BALB/c mice with the deletion mutants conferred significant protective immunity against B. melitensis strain H38 or B. ovis strain PA challenges, to the same extent as that induced by parental Rev.1 strain. Thus, these Rev.1 bp26 or omp31 deletion mutants are promising vaccine candidates against B. melitensis and B. ovis infections and will be further evaluated in sheep.

Influence of the co-encapsulation of different excipients on the properties of polyester microparticle-based vaccine against brucellosis

This work evaluates the influence of different pharmaceutical auxiliaries (Pluronic F68, polyvinylpyrrolidone [PVP] or Tween 20), when mixed with an antigenic extract from Brucella ovis (hot saline; HS), on the characteristics of the resulting poly(epsilon-caprolactone) (PEC) and poly(lactide-co-glycolide) (PLGA) microparticles. In all cases, PEC microparticles were smaller than PLGA ones. Concerning the HS loading, PLGA microparticles were highly dependent on the type of the excipient used, whereas all the PEC formulations displayed similar encapsulation efficiencies. For both types of microparticles, the presence of PVP induced a burst release effect. On the contrary, the use of Tween 20 or Pluronic F68 dramatically modified this profile. For PLGA-Tween 20 and PEC-Pluronic F68 microparticles, the HS was released in a pulsatil way during the first 7 days followed by a continuous release for at least 3 weeks. The antigenicity of the HS components was kept in all cases. Phagocytosis by murine monocytes showed a clear difference based just on the hydrophobicity of the polymer, being PEC microparticles better engulfed. Cell activation quantified by the release of H2O2 did not showed major differences between batches, however, microparticles of PEC and Pluronic F68 induced the highest nitric oxide production. Together, these results confirm the advantageous qualities of the "HS-PEC-Pluronic F68 microparticles" as favorable candidate for vaccine purposes against brucellosis.

Rough Lipopolysaccharide ofBrucella abortusRB51 as a Common Antigen for Serological Detection ofB. ovis,B. canis, andB. abortusRB51 Exposure Using Indirect Enzyme Immunoassay and Fluorescence Polarization Assay

Rough lipopolysaccharide (RLPS) antigens were prepared from cultures of Brucella abortus RB51, B. ovis, and B. canis. The preparations were standardized by weight and tested with sera from cattle immunized with B. abortus RB51, sheep infected with B. ovis, and dogs infected with B. canis. Populations of unexposed animals of each species were also tested. The tests used were the indirect enzyme immunoassay (IELISA) using RLPS and the fluorescence polarization assay (FPA) using RLPS core fractions, labeled with fluorescein isothiocyanate. The IELISA using B. abortus RB51 RLPS antigen resulted in sensitivity and specificity values of 94.8% and 97.3%, respectively, when testing bovine sera, 98.5% and 97.8% when testing ovine sera, and 95.8% and 100% when testing dog sera. The IELISA using B. ovis RLPS antigen gave sensitivity and specificity values of 80.5% and 91.7%, respectively with bovine sera, 98.9% and 93.8% with sheep sera, and 70.8% and 79.8% with dog sera. The IELISA using B. canis RLPS antigen resulted in sensitivity and specificity values of 97.0% and 97.4%, respectively, with bovine sera, 96.2% and 96.3% with sheep sera, and 95.8% and 98.8% with dog sera. Labeling RLPS core from B. ovis and B. canis with fluorescein was not successful. B. abortus RB51 core labeled with fluorescein resulted in sensitivity and specificity values of 93.5% and 99.8%, respectively, with bovine sera and 78.1% and 99.0% with sheep sera. It was not possible to test the dog sera in the FPA.

Single-step purification and evaluation of recombinant BP26 protein for serological diagnosis of Brucella ovis infection in rams

To investigate the value of the BP26 protein in the serological diagnosis of ovine brucellosis caused by Brucella ovis, recombinant BP26 protein was produced in Echerichia coli and purified for use in an indirect enzyme-linked immunosorbent assay (I-ELISA). The majority of the recombinant protein was recovered from the supernatant of sonicated recombinant E. coli cells in a soluble form. This facilitated the purification of the recombinant BP26 protein which was achieved by using ion-exchange chromatography. After one step of purification, the purity of the recombinant BP26 protein was analyzed by using SDS-PAGE, Coomassie blue staining, and Western blot with a monoclonal antibody (MAb) directed against the BP26 protein. The degree of purity appeared satisfactory so that it could be directly used in I-ELISA. Although the recombinant BP26-ELISA appeared less useful than I-ELISA using the B. ovis hot saline (HS) extract as antigen, the high number of sera from B. ovis infected rams found positive (90%) in the recombinant BP26-I-ELISA indicated that the BP26 protein may be an additional suitable antigen for serological diagnosis of B. ovis infection in rams.

A Brucella ovis antigenic complex bearing poly-epsilon-caprolactone microparticles confer protection against experimental brucellosis in mice

A hot saline antigenic extract (HS) from Brucella ovis was encapsulated in poly-epsilon-caprolactone microparticles (PEC), and tested as a vaccine against B. ovis and B. abortus infections in mice. Subcutaneous but not oral administration in BALB/c mice of the HS-PEC induced high amounts of IFN-gamma and IL-2 but low quantities of IL-4 suggesting a combined Th1/Th2 cellular immune response. The vaccine administered either subcutaneously or orally protected mice against B. ovis infection. Such protection was similar to that provided by the reference living attenuated B. melitensis Rev. 1 vaccine. By contrast, only the subcutaneous vaccination with HS-PEC was as effective as Rev. 1 in conferring protection against B. abortus infection. The use of free HS or empty PEC microparticles did not produce any protective effect.

Comparison of polyclonal, monoclonal and protein G peroxidase conjugates in an enzyme-linked immunosorbent assay for the diagnosis of Brucella ovis in sheep

The sensitivities of three commercial peroxidase conjugates (polyclonal anti-sheep IgG, recombinant protein G and a monoclonal anti-ruminant IgG1) in an enzyme-linked immunosorbent assay for Brucella ovis were evaluated. The monoclonal and protein G conjugates reduced, but did not totally remove, the characteristic background reactivity observed with the sera from brucella-free sheep. The protein G conjugate provided the best sensitivity, similar to that obtained with the classical gel diffusion test. Both tests were highly specific when testing sera from brucella-free animals but detected as positive a large proportion of sera from both Brucella melitensis-infected and B melitensis Rev 1-vaccinated sheep.

Characterization of an immuno-dominant antigen in Brucella ovis and evaluation of its use in an enzyme-linked immunosorbent assay

A panel of 45 Brucella ovis serologically positive sera were tested in immunoblots against B. ovis outer membrane proteins Omp31 and Omp25, purified by preparative SDS-gel electrophoresis. Forty-three sera reacted with Omp31, while only 11 reacted with Omp25, suggesting that Omp31 is identical to the previously reported immuno-dominant 29-kDa protein. Attempts to purify Omp31 on a larger scale by using procedures such as ion exchange-, reversed phase-, affinity- and gel filtration chromatography suggested that the outer membrane proteins were aggregated with rough lipopolysaccharide. Only denaturing SDS-gel filtration chromatography was able to separate proteins of about 29 kDa from rough lipopolysaccharide but did not separate Omp31 from Omp25 in B. ovis preparations. When used in an enzyme-linked immunosorbent assay, this 29-kDa protein preparation was less sensitive and less specific than the routinely used heat-extracted B. ovis antigen. A readily available recombinant E. coli, expressing the gene for Omp31 from Brucella melitensis 16 M, was used to extract and enrich recombinant Omp31 by a temperature-dependent Triton X-114-based technique. When this material was used in immunoblots with the 45 sera from B. ovis-infected sheep and with 10 monoclonal antibodies, raised against B. ovis Omp31, major differences in the antibody reactivity between the recombinant B. melitensis Omp31 and the B. ovis Omp31 were found. Such differences were unexpected because of the known structural and immunological relatedness of outer membrane proteins from various Brucella species. These results indicated that the antibody-response in B. ovis naturally-infected sheep against the immuno-dominant Omp31 was directed against epitopes which were only accessible when the protein was aggregated with rough lipopolysaccharides, or which were formed after aggregation but were not present in the recombinant protein.

Identification and characterization of Brucella ovis immunogenic proteins using two-dimensional electrophoresis and immunoblotting

In a previous report, proteins from Brucella melitensis were characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and N-terminal microsequencing. In the present report, we have extended this study to the second etiologic agent in ovine brucellosis, B. ovis, responsible for ram epididymitis and infertility. The combination of 2-D gel electrophoresis and protein microsequencing facilitated the location and identification of the major proteins of B. ovis on the 2-D pattern. These proteins comprised cytoplasmic, periplasmic, and some membrane proteins except the major outer membrane proteins. By comparing 2-D gel profiles of B. ovis with that of B. melitensis described previously, a few proteins with different expression levels were readily identified. Serum from a ram naturally infected with B. ovis was used in immunoblotting studies to identify immunogenic proteins recognized during the course of infection. This serum showed antibody reactivity against approximately 82 protein spots. Twenty-one of these proteins were identified either by use of monoclonal antibodies or by N-terminal microsequencing. Several proteins previously described in earlier Brucella works were identified: the 89 kDa outer membrane protein, DnaK, GroEL, BP26, and Cu-Zn superoxide dismutase. Eight proteins had amino acid sequences homologous to those of various proteins from other bacteria found in protein databases; NikA, dihydrolipoamide succinyltransferase, a hypothetical 31 kDa protein, malate dehydrogenase, succinyl-CoA synthetase alpha subunit, an amino acid ABC type transporter, Leu/Ile/Val-binding protein precursor, and ClpP. The remaining eight proteins had N-terminal sequences lacking similarity to existing databases entries. Thus, the 2-D PAGE analysis provided a convenient first approach in the characterization of immunogenic proteins.

Evaluation of an enzyme-linked immunosorbent assay for the detection of sheep infected and vaccinated with Brucella melitensis

An indirect enzyme-linked immunosorbent assay (ELISA), using the lipopolysaccharide of the cell wall as an antigen, was used to detect Brucella melitensis antibodies in ovine serum. The test was carried out on 703 samples of field serums, which were also analyzed by the complement fixation (CF) test and the rose Bengal (RB) test. The ELISA results were more similar to those of the CF test (kappa = 0.89) than to the results of the RB test (kappa = 0.73). The ELISA also had high sensitivity (94.7%) and a somewhat lower specificity (90.4%). One group of 139 young brucellosis-free animals 3-6 months of age were vaccinated with B. melitensis rev. 1 at a dose of 1.2 x 10(9) live organisms. The ELISA detected a significantly lower number of reactors than the CF and RB tests (P < 0.001). The ELISA values remained below the cutoff level during the 9 months following vaccination.

Identification and characterization of immunodominant antigens during the course of infection with Brucella ovis

The seroresponse against Brucella ovis of 8 intrapreputially and 6 intravenously infected rams and 9 ewes infected through mating was analyzed by electrophoretic immunoblotting. Additionally, 87 sera from chronically infected rams that were shedding B. ovis in their semen, 226 sera from rams belonging to infected flocks, and 324 sera from false-positive complement fixation test (CFT) reactors were examined. In all infected animals, antibody reactivity was predominantly found against 5 B. ovis components of 8-12, 17, 19, 29, and 63 kD, of which the 29-kD antigen was most dominant in the seroresponse. Antibodies to the 29-kD component were present in 93-100% of the infected sheep in each infected group, whereas the frequency of antibodies to the 4 other components varied considerably among and within the different groups. No reactivity against the 29-kD antigen was found in the false-positive CFT reactors. By using monoclonal antibodies against known bacterial macromolecules, the immunodominant antigens were identified as rough lipopolysaccharide (8-12 kD), outer membrane proteins (17, 19, 29 kD), and a heat-shock protein (63 kD).

Vaccination with Brucella abortus rough mutant RB51 protects BALB/c mice against virulent strains of Brucella abortus, Brucella melitensis, and Brucella ovis

Vaccination of BALB/c mice with live Brucella abortus RB51, a stable rough mutant, produced protection against challenge with virulent strains of Brucella abortus, Brucella melitensis, and Brucella ovis. Passive-transfer experiments indicated that vaccinated mice were protected against B. abortus 2308 through cell-mediated immunity, against B. ovis PA through humoral immunity, and against B. melitensis 16M through both forms of immunity. Live bacteria were required for the induction of protective cell-mediated immunity; vaccination with whole killed cells of strain RB51 failed to protect mice against B. abortus 2308 despite development of good delayed-type hypersensitivity reactions. Protective antibodies against the heterologous species were generated in vaccinated mice primarily through anamnestic responses following challenge infections. Growth of the antigenically unrelated bacterium Listeria monocytogenes in the spleens of vaccinated mice indicated that nonspecific killing by residual activated macrophages contributed minimally to protection. These results encourage the continued investigation of strain RB51 as an alternative vaccine against heterologous Brucella species. However, its usefulness against B. ovis would be limited if, as suggested here, epitopes critical for protective cell-mediated immunity are not shared between B. abortus and B. ovis.

Brucella melitensis cell envelope protein and lipopolysaccharide epitopes involved in humoral immune responses of naturally and experimentally infected sheep

Cell envelope fraction (CEF) of Brucella melitensis B115 was used to investigate antibody responses of B. melitensis naturally and strain H38 experimentally infected sheep by immunoblotting, indirect enzyme-linked immunosorbent assay (ELISA) (I-ELISA), and competitive ELISA (C-ELISA) with monoclonal antibodies (MAbs). MAbs used were directed to outer membrane proteins with molecular masses of 10, 16.5, 19, 25 to 27, 31 to 34, 36 to 38, and 89 kDa; to the heat shock protein DnaK, to O-polysaccharide (O-PS) common (C) and M epitopes; and to rough lipopolysaccharide (R-LPS) epitopes. In immunoblotting, all infected sheep sera tested recognized a large number of protein bands, including the above-cited proteins and other proteins for which MAbs have not been defined. The antibody response pattern was different from one animal to another, even within the experimentally infected sheep which were infected under the same experimental conditions. A number of protein bands were recognized by the sheep sera prior to experimental infection and by other uninfected sheep sera. The antibody reactivity to these antigens and others might explain the nonspecific antibody reactivity of sera in I-ELISA with CEF. C-ELISA confirmed also the individual variability of the antibody responses of infected sheep to protein antigens. Antibody responses to O-PS C and M epitopes were detected in all experimentally infected sheep and in half of the naturally infected sheep, but these responses were also heterogeneous in relation to their intensities. Antibody responses to R-LPS epitopes detected by use of C-ELISA with the anti-R-LPS MAbs were low or negative in most of the infected animals. Despite antibody response heterogeneity for CEF antigens, immunoblot and C-ELISA results indicated that, among the CEF antigens, the O-PS epitopes (C and M epitopes) and epitopes of the major 25- to 27- and 31- to 34-kDa outer membrane proteins seem to be the most promising for detecting B. melitensis infection in sheep.

A sensitive immunoblotting technique for the serodiagnosis of Brucella ovis infections

A simplified electrophoretic immunoblotting technique based on antigen extracted from Brucella ovis cells with sodium dodecyl sulfate/mercaptoethanol was compared with the complement fixation test (CFT), the enzyme-linked immunosorbent assay, and the gel diffusion test. Sera from 89 chronically infected, semen culture-positive rams, 378 sera from B. ovis-infected flocks, 300 sera from accredited disease-free flocks, and 29 sera from specific-pathogen-free sheep were used. The immunoblotting technique had sensitivity and specificity comparable to those of the standard tests and was able to identify several CFT-negative or -borderline sera as positive. The major immunoreactive antigens of B. ovis had molecular masses of 63, 29, 19 kD (proteins) and 8-12 kD (rough lipopolysaccharide). Antibodies against these antigens were present in 96% of CFT-positive sera from infected flocks and in 100% of sera from semen culture-positive rams. However, immunoblotting also identified antibodies to components other than the major antigens in 1% of CFT-negative sera from infected flocks and in 7.7% of the sera from flocks with a history of freedom from the disease. These reactions probably represent cross-reactivities with other microorganisms and were distinguishable from truly positive reactions.

Antibody response to Brucella melitensis outer membrane antigens in naturally infected and Rev1 vaccinated sheep

Sera from Brucella infected and B. melitensis Rev1 vaccinated sheep were analysed by immunoblotting using the cell envelope fraction (CEF) of B. melitensis B115. The CEF of B. melitensis B115 was analysed using a bank of monoclonal antibodies. The fraction consisted mainly of S-LPS like molecules, R-LPS and outer membrane proteins (OMPs) of molecular masses of 10, 16.5, 19, 25-27, 31-34, 36-38, 73 and 89 kDa. Immunoblot analysis indicates that the antibody response in infected sheep was mainly directed against the major OMPs of 25-27, 31-34, 36-38 kDa, against 55 to 62, 70-73 and 89 to 94 kDa proteins associated with the CEF and, against S-LPS like molecules. Some infected sheep reacted with antigens of molecular mass lower than 20 kDa. Sera from vaccinated sheep reacted only with OMPs of 36-38, 60, 70-73 and 89 kDa. The major 25-27 and 31-34 kDa OMPs and proteins below 20 kDa were only detected by the sera of infected sheep. These differences may be due to the persistence of the field infection also reflected by the fact that antibody response against O-polysaccharide (O-PS), as measured by enzyme-linked immunosorbent assay (ELISA), was more intense in infected sheep than in vaccinated ones. These results also indicate that these OMPs could be useful to differentiate B. melitensis infection from B. melitensis Rev.1 vaccination in sheep.

Protective immunity to Brucella ovis in BALB/c mice following recovery from primary infection or immunization with subcellular vaccines

Experiments were performed with BALB/c mice to elucidate the roles of humoral and cell-mediated immune responses in the acquisition of protective immunity to Brucella ovis and to compare infection immunity with immunity developed through vaccination with a hot saline extract (HS) of B. ovis. Mice convalescing from a primary infection with B. ovis displayed a high level of resistance to reinfection, as evidenced by splenic bacterial counts decreased over 10,000-fold from control groups at 2 weeks after challenge. Passive transfer assays revealed that protection was mediated by both T lymphocytes and antibodies but that antibodies had a substantially greater role on the basis of log units of protection that were transferred. Antibodies specific for HS proteins in sera from convalescent mice were predominantly of the immunoglobulin G 2a and 3 isotypes. Vaccination with HS conferred good protection against B. ovis, but protection was greatly enhanced by the incorporation of QS-21 or other adjuvants. Protection provided by the HS vaccine resulted largely from immune responses to its protein moieties. A critical evaluation of the protective efficacy of the rough lipopolysaccharide component of HS was precluded by its poor immunogenicity in BALB/c mice. HS-QS-21 afforded protection against challenge infection with B. ovis as good as that which developed after a primary infection and as good as or better than that provided by attenuated Brucella melitensis vaccine strain Rev 1. Passive transfer experiments confirmed that the magnitudes of both humoral and cell-mediated forms of protective immunity were equivalent in mice vaccinated with HS-QS-21 and those recovering from a primary infection. Protective immunity to B. ovis in mice therefore resembled that to Brucella abortus, except that the relative roles of humoral and cell-mediated immunity, rather than being equivalent, were shifted toward a greater role for antibodies.

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.

Evaluation of whole cell and subcellular vaccines against Brucella ovis in rams

Five antigen preparations from Brucella ovis strain REO 198 were incorporated with the pluronic polymer L-121 and muramyl dipeptide and tested as vaccines against B. ovis infection of rams. The antigenic preparations were: (1) a fraction enriched in outer membrane proteins and rough lipopolysaccharide (hot saline extract, HS); (2) the proteins from HS substantially free of lipopolysaccharide; (3) outer membrane blebs; (4) outer membrane-peptidoglycan complexes extracted with detergent; (5) killed whole cells. The experimental vaccines were compared with two standard vaccines, rough Brucella abortus 45/20 whole killed cells in an oil based adjuvant, and live Brucella melitensis Rev 1. Immunizations with non-living vaccines were performed on two occasions, 18 weeks apart. The rams were challenged with a virulent strain of B. ovis 31 weeks after the second vaccination and slaughtered 15 weeks thereafter. Rates of infection in groups vaccinated with Rev 1 (33%), and HS (40%) were significantly lower (P < 0.005 and P < 0.025, respectively) than that in the non-vaccinated control group (87%). Strain 45/20 was the only other vaccine that conferred a significant level of protection (50%) (P < 0.05). The organ distribution of the infection and the level of colonization of infected organs did not differ significantly between infected animals in the various vaccine groups and those in the unvaccinated control group. No statistically significant relationship was detected between the magnitude of the antibody responses to the HS extract, to outer membrane proteins, or to the rough lipopolysaccharide, and freedom from infection. The results indicate that the HS extract of B. ovis may represent a useful alternative to B. melitensis Rev 1 or B. abortus 45/20 as a vaccine against B. ovis.

Monoclonal antibodies to Brucella rough lipopolysaccharide: characterization and evaluation of their protective effect against B. abortus

We characterized 4 monoclonal antibodies (mAb) specific for rough lipopolysaccharide (R-LPS) of Brucella. mAb were selected by enzyme-linked immunosorbent assay (ELISA) on whole B. abortus 45/20 rough cells and R-LPS from B. melitensis B115 rough cells. Specificity was confirmed by immunoblot analysis using R-LPS and smooth LPS (S-LPS) preparations. Anti-R-LPS revealed the low molecular mass R-LPS molecules below 20.1 kDa in the R-LPS and S-LPS preparations as well as the typical A and M patterns in high molecular mass S-LPS molecules (between 21.5 and 66 kDa) in the S-LPS preparations. An O-polysaccharide-specific mAb revealed only high molecular mass S-LPS molecules in the S-LPS preparation. In ELISA the anti-R-LPS mAb bound better on rough than on smooth B. abortus 544 whole cells, and this was confirmed by immunoelectron microscopy. Protective activity of anti-R-LPS mAb of different isotypes was tested on mice and compared with an S-LPS-specific mAb. Only the IgG3 mAb reduced significantly the splenic infection but did not reach the level of protection conferred by the S-LPS-specific mAb.

Antibody response to Brucella outer membrane proteins in bovine brucellosis: immunoblot analysis and competitive enzyme-linked immunosorbent assay using monoclonal antibodies

Sera from Brucella-infected bovines were analyzed by immunoblotting by using sonicated cell extracts of B. melitensis or B. abortus and a competitive enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies against outer membrane proteins (OMPs) with molecular masses of 10, 16.5, 19, 25 to 27, 36 to 38, and 89 kDa. Antibody responses against OMPs were compared with antibody responses against smooth lipopolysaccharide. Immunoblot analysis indicated that the antibody response in infected animals was largely different from one animal to another. The antigens of concern were OMPs with molecular masses of 10, 16.5, 19, 25 to 27, 36 to 38, and 89 kDa and other proteins with molecular masses of between 40 and 80 kDa. According to the specificity of the competitive ELISA, OMPs useful for the detection of infected animals are the OMPs of 10, 16.5, 19, 25 to 27, and 36 to 38 kDa. A competitive ELISA with the anti-89 kDa monoclonal antibody was not specific. Results of the competitive ELISA confirmed the individual variability of the humoral immune response against OMPs. It therefore seems that a combination of several protein antigens is necessary for the development of an immunoassay with a sensitivity comparable to that of the smooth lipopolysaccharide ELISA.

Immunochemical studies on a Brucella ovis specific protein antigen

A Brucella ovis surface protein antigen (P-II), obtained by gel filtration with Sepharose 4B of a hot saline extract was characterized. The analysis of P-II over gradient sodium dodecylsulfate electrophoresis yielded an 18.5 and a 20 kDa band. In a radioimmunoprecipitation assay using P-II labeled with 125I, the antigen reacted specifically only with sera from rams experimentally infected with a naturally occurring rough strain of B. ovis and did not react with sera from rams experimentally infected with other smooth Brucella strains (B. abortus and B. melitensis).

Profiles of serological reactivity against cytosoluble antigens of Brucella ovis in experimentally infected rams

Sera from rams infected with and excreting Brucella ovis in the semen (shedders), as well as from animals which had recovered from previous experimental challenge with B. ovis, were analyzed for their serological reactivities against cytosolic antigens of the bacterium. Membrane vesicles, including outer and inner membrane components, were precluded from the analyses by subjecting French-pressed bacteria to ultracentrifugation. The resulting cytosolic supernatant was fractionated into four major antigenic fractions, fractions A, B, C, and D, by high-pressure liquid chromatography. Temporal enzyme-linked immunosorbent assays with the A antigen revealed that all shedder rams displayed a rise-and-surge response, while rams which recovered from experimental challenge showed a rise-and-fall profile. The B antigen was less discriminatory in detecting a difference between the two ram groups, while C and D antigens were serologically unreactive in the enzyme-linked immunosorbent assay. In contrast to the reactivity patterns shown by native high-pressure liquid chromatography-fractionated cytosolic supernatant antigens, immunoblotting of C and D polypeptides generated by boiling in the presence of sodium dodecyl sulfate and mercaptoethanol was particularly useful in distinguishing between sera collected at the mid-surge phase of infected rams from sera obtained at the mid-fall stage of recovered animals. It is likely that native or denatured antigens of different cytosolic fractions may provide useful serological reagents for differentiating between infected rams and those which have recovered from exposure to B. ovis.

Antibody response to Brucella ovis outer membrane proteins in ovine brucellosis

Hot saline extracts of Brucella ovis were composed of vesicles with outer membrane proteins (OMPs), lipopolysaccharide, and phospholipid as constituents. Extraction with petroleum ether-chloroform-phenol yielded a protein fraction free of detectable lipopolysaccharide, in which group 3 OMPs (28,500 apparent molecular weight [28.5K], 27.0K, and 25.5K) represented 81% of the total. Group 1 OMPs and 67.0K, 22.5K to 21.5K, and 19.5K to 18.0K proteins were also detected. Adsorption of immune sera with whole bacteria suggested that group 3 OMPs and 67.0K, 22.5K to 21.5K, and 19.5K to 18.0K proteins had antigenic determinants exposed on the surfaces of both B. ovis and rough B. melitensis cells but not on smooth B. melitensis cells. Antibodies to group 3 OMPs and the 67.0K protein in the sera of 93 and 87%, respectively, of B. ovis-infected rams were found by immunoblotting. Antibodies to other proteins were present in 67% of these animals. Compared with B. ovis-infected rams which had not developed lesions, rams with epididymo-orchitis had antibodies to a larger variety of proteins. Although ewes infected with B. melitensis also showed antibodies to OMPs, the immunoblot reactions were less intense.

Determination by enzyme-linked immunosorbent assay of immunoglobulin G (IgG), IgM, and IgA to Brucella melitensis major outer membrane proteins and whole-cell heat-killed antigens in sera of patients with brucellosis

An enzyme-linked immunosorbent assay was used to compare Brucella melitensis major outer membrane proteins (MOMP) and whole-cell heat-killed antigens (HK) in measuring antibrucella immunoglobulin G (IgG), IgM, and IgA in sera of brucellosis patients and controls. Antibodies to MOMP were generally similar to those against HK, and the correlation coefficients between the two antigens and IgG, IgM, and IgA in patients varied between 0.73 and 0.94. Both antigens are comparably suitable in detecting antibrucella immunoglobulin isotypes for the serologic diagnosis of patients with brucellosis, with high (greater than or equal to 95%) sensitivity and specificity.

Discrimination between sheep antibodies to Brucella melitensis and to Brucella ovis

When preparations containing smooth Brucella abortus lipopolysaccharide (LPS) were used as antigen in an ELISA, strong positive reactions were obtained with sera from sheep infected with Brucella melitensis or with Brucella ovis. Oxidation of the LPS with sodium metaperiodate greatly reduced the extent of the cross-reactions with antisera to B. ovis, with little effect on the reactions with antisera to smooth B. melitensis. Periodate oxidation of hot saline extract (HSX) antigen of B. ovis markedly reduced its reactivity in ELISA with anti-B. ovis sera and eliminated cross-reactivity with anti-B. melitensis sera. The reactivity of HSX was maintained after treatment with proteinase K. A simple ELISA system, in which replicate samples from a single serum dilution were tested in parallel against both B. ovis HSX antigen and periodate-oxidised smooth phase B. abortus LPS, was evaluated. It was found to discriminate well between antibodies induced by vaccination or virulent infection with B. melitensis strains and those induced by infection with B. ovis.

Comparative analyses of proteins extracted by hot saline or released spontaneously into outer membrane blebs from field strains of Brucella ovis and Brucella melitensis

Sheep infected with Brucella ovis produce antibody responses to the rough lipopolysaccharide and to proteins present in hot saline (HS) extracts of B. ovis (J. I. Riezu-Boj, I. Moriyón, J. M. Blasco, C. M. Marín, and R. Díaz, J. Clin. Microbiol. 23:938-942, 1986). The distribution and antigenic relatedness of proteins in HS extracts and in outer membrane blebs were established by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting for 41 strains of B. ovis and 26 strains of Brucella melitensis of diverse geographic origin. Five major groups of proteins were identified in HS extracts of B. ovis that had been freed of rough lipopolysaccharide: proteins of 43 kilodaltons (kDa), group A (25.5 to 32.0 kDa), group B (21.5 to 22.5 kDa); group C (18.0 to 19.5 kDa), and group D (13.0 to 15.5 kDa). Group A, B, C, and D proteins were also present in blebs. The profiles of proteins in HS extracts or blebs from strains of both Brucella species were very similar. Cross-reactions were demonstrated among HS extracts and blebs of all strains tested in immunoblots performed with an antiserum against the HS extract of a reference strain of B. ovis. Evidence was also provided of an antigenic relationship between group 3 proteins of the outer membrane and some of the proteins in groups A, B, and C. The conservation of these antigens and their immunogenicity in infected animals provide promise that they may serve as components of an effective subcellular vaccine for ovine brucellosis.

Serological response to the outer membrane lipoprotein in animal brucellosis

The presence of antibodies to Brucella outer membrane lipoprotein was investigated in cattle and rams. Low but significant amounts of antibody were detected in sera from B. abortus-infected cattle and from B. ovis-infected rams which had developed epididymitis. Strain-19-vaccinated cattle also showed a weak albeit transient antibody response.

Isolation and antigenic reactivity of Brucella ovis outer membrane proteins

Brucella ovis cell membranes were isolated from fractured and lysozyme-treated cells by ultracentrifugation. These preparations appeared to consist largely of outer membranes, as judged from the results of ultracentrifugation experiments in sucrose density gradients under conditions that are widely used to separate inner and outer membranes of gram-negative bacteria. The sequential detergent extraction of cell membranes yielded mainly lipopolysaccharide and three groups of outer membrane proteins. In immunoblotting, lipopolysaccharide had good antigenic reactivity with all sera from rams exposed to B. ovis (vaccination or natural infection), but some outer membrane proteins reacted strongly only with sera from immune (vaccinated) rams, not from infected rams, suggesting a possible diagnostic role for such proteins in predicting immunity or infection.

Immunization with Brucella melitensis Rev 1 against Brucella ovis infection of rams

The efficacy of Brucella Melitensis Rev 1 vaccine (Rev 1) for the prophylaxis of Brucella ovis ram epididymitis was evaluated. Twenty-nine 3-month-old rams were vaccinated with 2 X 10(9) Rev 1 and 14 were revaccinated with 5 X 10(8) at 14 months of age. Six rams remained unvaccinated as a control group. All rams were challenged with 5 X 10(8) B. ovis at 21 months of age. Before being slaughtered 8 weeks later, only one vaccinated ram developed epididymitis while four of the six control rams developed testicular alterations. Genital and selected extragenital organs and lymph nodes were removed at slaughter and inoculated on selective media. B. ovis was isolated from 26.6% of the vaccinated rams, 21.4% of the revaccinated rams and 100% of control rams. Portions of epididymis, testes and vesicular glands were also used for pathological studies. More severe lesions were observed in control rams than in vaccinated ones. In conclusion, these results show that vaccination of young lambs, followed or not by revaccination, is a suitable method for the prophylaxis of B. ovis infection of rams.