Protective antigens in brucellosis

Expression of MPB83 from Mycobacterium bovis in Brucella abortus S19 induces specific cellular immune response against the recombinant antigen in BALB/c mice

Immunodominant MPB83 antigen from Mycobacterium bovis was expressed as a chimeric protein fused to either β-galactosidase, outer membrane lipoprotein OMP19 or periplasmic protein BP26 in gram-negative Brucella abortus S19, in all cases driven by each gene's own promoter. All fusion proteins were successfully expressed and localized in the expected subcellular fraction. Moreover, OMP19-MPB83 was processed as a lipoprotein when expressed in B. abortus. Splenocytes from BALB/c mice immunized with the recombinant S19 strains carrying the genes coding for the heterologous antigens in replicative plasmids, showed equally specific INF-γ production in response to MPB83 stimulation. Association to the lipid moiety of OMP19 presented no advantage in terms of immunogenicity for MPB83. In contrast, fusion to BP26, which was encoded by an integrative plasmid, resulted in a weaker immune response. None of the constructions affected the survival rate or the infection pattern of Brucella. We concluded that B. abortus S19 is an appropriate candidate for the expression of M. bovis antigens both associated to the membrane or cytosolic fraction and may provide the basis for a future combined vaccine for bovine brucellosis and tuberculosis.

Expression of Babesia bovis rhoptry-associated protein 1 (RAP1) in Brucella abortus S19

Brucella abortus strain 19 (live vaccine) induces a strong humoral and cellular immune response and therefore, it is an attractive vector for the delivery of heterologous antigens. The objective of the present study was to express the rhoptry-associated protein (RAP1) of Babesia bovis in B. abortus S19, as a model for heterologous expression of immunostimulatory antigens from veterinary pathogens. A plasmid for the expression of recombinant proteins fused to the aminoterminal of the outer membrane lipoprotein OMP19 was created, pursuing the objective of increasing the immunogenicity of the recombinant antigen being expressed by its association to a lipid moiety. Recombinant strains of B. abortus S19 expressing RAP1 as a fusion protein either with the first amino acids of beta-galactosidase (S19pBB-RAP1) or B. abortus OMP19 (S19pBB19-RAP1) were generated. Plasmid stability and the immunogenicity of the heterologous proteins were analyzed. Mice immunized with S19pBB-RAP1 or S19pBB19-RAP1 developed specific humoral immune response to RAP1, IgG2a being the predominant antibody isotype. Furthermore, a specific cellular immune response to recombinant RAP1 was elicited in vitro by lymphocytes from mice immunized with both strains. Therefore, we concluded that B. abortus S19 expressing RAP1 is immunostimulatory and may provide the basis for combined heterologous vaccines for babesiosis and brucellosis.

Identification of novel genes in the memory response to Brucella infection by cDNA arrays

This study investigated memory responses in immune mice spleen cells to brucellosis by gene expression utilizing cDNA micro arrays. Out of a total of 1176 cDNA's 21 genes were differentially regulated in three independent experiments, and generally supported a Th1 type immune response. 10 genes were validated by real time PCR, and 3 genes (CD 86, CD 40 L and CD 132) were also analyzed by Flow Cytometry for surface protein expression. We extended these findings by studying the expression of five selected genes (IRF 1, SOCS 1, IL 2 R, IRF 7, and CXCR 4) in two independent groups of Brucella immunized mice. In this study we show the potential application of utilizing gene arrays to identify and establish new correlates of protection against a cell mediated immune response.

Major outer membrane proteins of Brucella spp.: past, present and future

The major outer membrane proteins (OMPs) of Brucella spp. were initially identified in the early 1980s and characterised as potential immunogenic and protective antigens. They were classified according to their apparent molecular mass as 36-38 kDa OMPs or group 2 porin proteins and 31-34 and 25-27 kDa OMPs which belong to the group 3 proteins. The genes encoding the group 2 porin proteins were identified in the late 1980s and consist of two genes, omp2a and omp2b, which are closely linked in the Brucella genome, and which share a great degree of identity (>85%). In the 1990s, two genes were identified coding for the group 3 proteins and were named omp25 and omp31. The predicted amino acid sequences of omp25 and omp31 share 34% identity. The recent release of the genome sequence of B. melitensis 16 M has revealed the presence of five additional gene products homologous to Omp25 and Omp31. The use of recombinant protein technology and monoclonal antibodies (MAbs) has shown that the major OMPs appear to be of little relevance as antigens in smooth (S) B. abortus or B. melitensis infections i.e. low or no protective activity in the mouse model of infection and low or no immunogenicity during host infection. However, group 3 proteins, in particular Omp31, appear as immunodominant antigen in the course of rough (R) B. ovis infection in rams and as important protective antigen in the B. ovis mouse model of infection. The major OMP genes display diversity and specific markers have been identified for Brucella species, biovars, and strains, including the recent marine mammal Brucella isolates for which new species names have been proposed. Recently, Omp25 has been shown to be involved in virulence of B. melitensis, B. abortus and B. ovis. Mutants lacking Omp25 are indeed attenuated in animal models of infection, and moreover provide levels of protection similar or better than currently used attenuated vaccine strain B. melitensis Rev.1. Therefore, these mutant strains appear interesting vaccine candidates for the future. The other group 3 proteins identified in the genome merit also further investigation related to the development of new vaccines.

Major outer membrane protein Omp25 of Brucella suis is involved in inhibition of tumor necrosis factor alpha production during infection of human macrophages

Brucella spp. can establish themselves and cause disease in humans and animals. The mechanisms by which Brucella spp. evade the antibacterial defenses of their host, however, remain largely unknown. We have previously reported that live brucellae failed to induce tumor necrosis factor alpha (TNF-alpha) production upon human macrophage infection. This inhibition is associated with a nonidentified protein that is released into culture medium. Outer membrane proteins (OMPs) of gram-negative bacteria have been shown to modulate macrophage functions, including cytokine production. Thus, we have analyzed the effects of two major OMPs (Omp25 and Omp31) of Brucella suis 1330 (wild-type [WT] B. suis) on TNF-alpha production. For this purpose, omp25 and omp31 null mutants of B. suis (Deltaomp25 B. suis and Deltaomp31 B. suis, respectively) were constructed and analyzed for the ability to activate human macrophages to secrete TNF-alpha. We showed that, in contrast to WT B. suis or Deltaomp31 B. suis, Deltaomp25 B. suis induced TNF-alpha production when phagocytosed by human macrophages. The complementation of Deltaomp25 B. suis with WT omp25 (Deltaomp25-omp25 B. suis mutant) significantly reversed this effect: Deltaomp25-omp25 B. suis-infected macrophages secreted significantly less TNF-alpha than did macrophages infected with the Deltaomp25 B. suis mutant. Furthermore, pretreatment of WT B. suis with an anti-Omp25 monoclonal antibody directed against an epitope exposed at the surface of the bacteria resulted in substancial TNF-alpha production during macrophage infection. These observations demonstrated that Omp25 of B. suis is involved in the negative regulation of TNF-alpha production upon infection of human macrophages.

Identification of protective outer membrane antigens of Brucella ovis by passive immunization of mice with monoclonal antibodies

Outer membrane proteins (OMPs) and rough lipopolysaccharide (R-LPS), the main surface antigens of Brucella ovis, display surface-exposed epitopes. Mixtures of monoclonal antibodies (mAbs) to both antigens were previously shown to protect mice against a B. ovis challenge. To further identify the antigens involved, seven mAbs against Brucella OMPs (Omp10, Omp16, Omp19, Omp25, Omp31, Omp2b and Omp1) and three to R-LPS were tested for protection either individually or in combinations. Significant reduction in spleen infection in challenged mice, relative to controls, was used as the protection criteri. Controls included nonimmunized mice and mice given an irrelevant, anti-O-polysaccharide (OPS), mAb. For comparison, a group received a mouse serum containing antibodies to both OMPs and R-LPS; this serum was prepared by immunization with a B. ovis hot-saline extract which, as described previously, induces protective immunity in mice and rams. Significant protection was observed with both mAbs to OMPs and R-LPS. mAbs to Omp16, Omp19 and Omp31 afforded the highest protection and prevented the development of splenomegaly. The protective effect of mAb to Omp31 was not interfered with by nonprotective mAbs in different mixtures. The data presented confirm the protective role of antibodies to OMPs and R-LPS against B. ovis, and identify several OMPs, especially Omp31, which are promising candidates for a subunit vaccine against ram epididymitis.

Brucella melitensis 16M: characterisation of the galE gene and mouse immunisation studies with a galE deficient mutant

The galE gene of Streptomyces lividans was used to probe a cosmid library harbouring Brucella melitensis 16M DNA and the nucleotide sequence of a 2.5 kb ClaI fragment which hybridised was determined. An open reading frame encoding a predicted polypeptide with significant homology to UDP-galactose-4-epimerases of Brucella arbortus strain 2308 and other bacterial species was identified. DNA sequences flanking the B. melitensis galE gene shared no identity with other gal genes and, as for B. abortus, were located adjacent to a mazG homologue. A plasmid which encoded the B. melitensis galE open reading frame complemented a galE mutation in Salmonella typhimurium LB5010, as shown by the restoration of smooth lipopolysaccharide (LPS) biosynthesis, sensitivity to phage P22 infection and restoration of UDP-galactose-4-epimerase activity. The galE gene on the B. melitensis 16M chromosome was disrupted by insertional inactivation and these mutants lacked UDP-galactose-4-epimerase activity but no discernible differences in LPS structure between parent and the mutants were observed. One B. melitensis 16M galE mutant, Bm92, was assessed for virulence in CD-1 and BALB/c mice and displayed similar kinetics of invasion and persistence in tissues compared with the parent bacterial strain. CD-1 mice immunised with B. melitensis 16M galE were protected against B. melitensis 16M challenge.

Vector development for the expression of foreign proteins in the vaccine strain Brucella abortus S19

A vector for the expression of foreign antigens in the vaccine strain Brucella abortus S19 was developed by using a DNA fragment containing the regulatory sequences and the signal peptide of the Brucella bcsp31 gene. This fragment was cloned in broad-host-range plasmid pBBR4MCS, resulting in plasmid pBEV. As a reporter protein, a repetitive antigen of Trypanosoma cruzi was used. The recombinant fusion protein is stably expressed and secreted into the Brucella periplasmic space, inducing a good antibody response against the T. cruzi antigen. The expression of the repetitive antigen in Brucella neither altered its growth pattern nor generated a toxic or lethal effect during experimental infection. The application of this strategy for the generation of live recombinant vaccines and the tagging of B. abortus S19 vaccine is discussed. This is the first time that a recombinant protein has been expressed in the periplasm of brucellae.

Molecular and immunological characterization of the major outer membrane proteins of Brucella

The major outer membrane proteins (OMPs) of Brucella spp. were initially identified in the early 1980s by selective extraction techniques and classified according to their apparent molecular mass as 36-38 kDa OMPs or group 2 porin proteins and 31-34 kDa and 25-27 kDa OMPs which belong to the group 3 proteins. Variation in apparent molecular mass is essentially due to association with peptidoglycan subunits of different sizes. Two genes, omp2a and omp2b, which are closely linked in the Brucella genome, and which share a great degree of homology (> 85%), encode the 36 kDa porin proteins, now named Omp2a and Omp2b proteins respectively. Two genes code for the group 3 OMPs and are named omp25 and omp31. The predicted amino acid sequences of omp25 and omp31 share 34% identity. Furthermore, all Brucella major OMPs share amino acid sequence homology with the major OMPs RopA or RopB of Rhizobium leguminosarum, which supports the close genetic relationship of brucellae with members of the alpha-2 subdivision of the class Proteobacteria. Another characteristic common to the major OMPs of R. leguminosarum and Brucella is that they are tightly, probably covalently, associated with the peptidoglycan. The major OMP genes display diversity among Brucella species, biovars and strains allowing their differentiation, and the polymorphic markers identified have brought new insights into the evolutionary development of the genus Brucella, antigenic variability of brucellae, and future prospects in the field of vaccine development.

Cloning, nucleotide sequence, and expression of the Brucella melitensis omp31 gene coding for an immunogenic major outer membrane protein

The gene coding for the major outer membrane protein (OMP) of 31 to 34 kDa, now designated Omp31, of Brucella melitensis 16M was cloned and sequenced. A B. melitensis 16M genomic library was constructed in lambda GEM-12 XhoI half-site arms, and recombinant phages expressing omp31 were identified by using the anti-Omp31 monoclonal antibody (MAb) A59/10F09/G10. Subcloning of insert DNA from a positive phage into pGEM-7Zf allowed the selection of a plasmid bearing a 4.4-kb EcoRI fragment that seemed to contain the entire omp31 gene under control of its own promoter. omp31 was localized within a region of the EcoRI insert of approximately 1.1 kb. Sequencing of this region revealed an open reading frame of 720 bp encoding a protein of 240 amino acids and a predicted molecular mass of 25,307 Da. Cleavage of the first 19 amino acids, showing typical features of signal peptides for protein export, leaves a mature protein of 221 amino acids with a predicted molecular mass of 23,412 Da. The predicted amino acid sequence of B. melitensis 16M Omp31 showed 35.2% identity with the RopB OMP of Rhizobium leguminosarum bv. viciae 248 and 34.3% identity with Omp25 of B. abortus 544. As in Brucella spp., Omp31 was located in the outer membrane of recombinant Escherichia coli, but its reported peptidoglycan association in Brucella cells was not detected in E. coli. The ability of Omp31 to form oligomers resistant to sodium dodecyl sulfate denaturation at low temperatures, a characteristic described for several bacterial porins, was observed in both B. melitensis and recombinant E. coli. The epitope recognized by the anti-Omp31 MAb A59/10F09/G10, for which a protective activity has been suggested, has been delimited to a region of 36 amino acids of Omp31 covering the most hydrophilic part of the protein. The availability of recombinant Omp31 and the identification of the antigenic determinant recognized by MAb A59/10F09/G10 will allow the evaluation of their potential protective activity and their potential for the development of subcellular vaccines against brucellosis.

Nucleotide sequence and expression of the gene encoding the major 25-kilodalton outer membrane protein of Brucella ovis: Evidence for antigenic shift, compared with other Brucella species, due to a deletion in the gene

The nucleotide sequences encoding the major 25-kDa outer membrane protein (OMP) (omp25 genes) of Brucella ovis 63/290, Brucella melitensis 16M, Brucella suis 1330, Brucella canis RM6/66, and Brucella neotomae 5K33 (all reference strains) were determined and compared with that of Brucella abortus 544 (P. de Wergifosse, P. Lintermans, J. N. Limet, and A. Cloeckaert, J. Bacteriol. 177:1911-1914, 1995). The major difference found was between the omp25 gene of B. ovis and those of the other Brucella species; the B. ovis gene had a 36-bp deletion located at the 3' end of the gene. The corresponding regions of other Brucella species contain two 8-bp direct repeats and two 4-bp inverted repeats, which could have been involved in the genesis of the deletion. The mechanism responsible for the genesis of the deletion appears to be related to the "slipped mispairing" mechanism described in the literature. Expression of the 25-kDa outer membrane protein (Omp25) in Brucella spp. or expression from the cloned omp25 gene in Escherichia coli cells was studied with a panel of anti-Omp25 monoclonal antibodies (MAbs). As shown by enzyme-linked immunosorbent assay (ELISA) and immunoelectron microscopy, Omp25 was exported to the outer membrane in E. coli expressing either the truncated omp25 gene of B. ovis or the entire omp25 genes of the other Brucella species. Size and antigenic shifts due to the 36-bp deletion were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting and by the differences in binding patterns in ELISA of the anti-Omp25 MAbs at the cell surface of E. coli cells harboring the appropriate gene and of cells of B. ovis and other Brucella species. In particular, MAbs directed against discontinuous epitopes of the entire Omp25 showed the absence of, or a significant reduction in, antibody reactivity with the B. ovis truncated Omp25. The results indicated that, as defined by the MAbs, exported Omp25 probably presents similar topologies in the outer membranes of E. coli and Brucella spp. and that the short deletion found in the omp25 gene of B. ovis has important consequences for the expression of surface B-cell epitopes which should be considered for the development of vaccines against B. ovis infection.

Purification and antigenic analysis of the major 25-kilodalton outer membrane protein of Brucella abortus

The major 25-kDa outer membrane protein (Omp25) of Brucella abortus was purified and antigenically characterized by use of monoclonal antibodies (mAbs). Purification was achieved from the sodium dodecyl sulphate-insoluble (SDS-I) cell wall (CW) fraction of vaccine strain B. abortus B19 which was shown by use of mAbs to contain the two major outer membrane proteins of 25 and 36 kDa linked to peptidoglycan, smooth lipopolysaccharide (S-LPS), and rough LPS (R-LPS). Purity of Omp25 was checked with a number of mAbs directed to the different components of the SDS-I fraction. In ELISA, five anti-Omp25 mAbs, which showed significant binding to B. abortus whole cells and which are probably directed to conformational epitopes well-exposed on the bacterial surface, reacted poorly or not at all with the purified Omp25. Addition of R-LPS to purified Omp25 restored the binding capacity of these mAbs, which suggested that R-LPS may play an important role in reconstitution and exposure of conformational epitopes of Omp25. Immunoelectron microscopy showed that Omp25 was inserted into the R-LPS vesicles. Four of these anti-Omp25 mAbs probably recognize the same or closely located epitopes on Omp25, since one of the mAbs conjugated to peroxidase was inhibited in its binding in ELISA by the three others. Other anti-Omp25 mAbs showed strong binding to purified denatured Omp25 and their binding capacity was not affected by the addition of R-LPS to the purified Omp25. Thus, these results confirmed, as defined by the mAbs, the presence of both sequential and at least one conformational epitope on Omp25.

Variation of Brucella abortus 2308 infection in BALB/c mice induced by prior vaccination with salt-extractable periplasmic proteins from Brucella abortus 19

The study compared the immune and protective responses induced in BALB/c mice vaccinated with six salt-extractable periplasmic protein fractions (Brucella cell surface proteins [BCSP]) of Brucella abortus 19 and later challenge exposed with B. abortus 2308. BCSP70 was precipitated with ammonium sulfate at 70% saturation, and BCSP100 was precipitated with ammonium sulfate at 100% saturation by use of supernatant fluid of BCSP70 that had been precipitated with 70% ammonium sulfate. Four subfractions were separated from BCSP100 by anion-exchange high-performance liquid chromatography (HPLC). Monophosphoryl lipid A (MPL) from Salmonella typhimurium Re mutant strain was used as a potential immune response modifier in some vaccines. Reduced or increased numbers of CFU and increased spleen size in the principal groups of mice relative to that of the nonvaccinated control group were considered protectiveness or virulence (survival) criteria. Results indicated that vaccines prepared from BCSP70 and BCSP100 were moderately protective and immunogenic. The subfractions designated BCSP100-A through BCSP100-D purified by anion-exchange HPLC were not protective when MPL was not used as an immune response modifier. However, two subfractions were associated with significant (P < 0.05) increases in CFU per spleen and splenomegaly in vaccinated mice compared with those in nonvaccinated challenge-exposed mice. MPL enhanced protection or was neutral when used with BCSP70, BCSP100, BCSP100-C, and BCSP100-D. Serologic results of an enzyme-linked immunosorbent assay indicated that MPL modulated the immunoglobulin G responses induced by BCSP70, BCSP100, and subfraction BCSP100-B vaccines only. The overall results suggest that certain proteinaceous periplasmic fractions might serve as virulence or survival factors in B. abortus infections.

Surface exposure of outer membrane protein and lipopolysaccharide epitopes in Brucella species studied by enzyme-linked immunosorbent assay and flow cytometry

Seven surface-exposed outer membrane proteins (OMPs) in Brucella supp. have been previously described (A. Cloeckaert, P. de Wergifosse, G. Dubray, and J. N. Limet, Infect. Immun. 58:3980-3987, 1990). OMPs were shown to be more accessible to monoclonal antibodies (MAbs) on rough (R) Brucella melitensis and B. abortus strains than to MAbs on their smooth (S) counterparts. In this work, we have extended this study to representatives of the main Brucella species, using MAbs specific for OMPs and S and R lipopolysaccharides (S-LPS and R-LPS). Enzyme-linked immunosorbent assay (ELISA), flow cytometry, and immunoelectron microscopy showed important differences between strains in the binding of OMP- and R-LPS-specific MAbs which were in part related to the particular expression of S-LPS, irrespective of the species. Results indicated that both the amount and the length of O polysaccharide on S-LPS greatly influenced the accessibility of OMP and R-LPS epitopes to MAbs. S-R B. melitensis EP and S B. suis 40, for instance, which express O-polysaccharide chains in small amounts and with short mean length, respectively, bound a greater number of OMP- and R-LPS-specific MAbs than the other S Brucella strains. The major 31- to 34-kDa OMP was the most exposed OMP on S strains of B. melitensis and B. suis. In most cases, flow cytometry results agreed with those of ELISA and supplied additional data, such as the homogeneity or heterogeneity of OMP expression at the strain level. However, there were some discordances between flow cytometry and ELISA results concerning the surface exposure of the 25- to 27-kDa and 31- to 34-kDa OMPs on S strains and that of minor OMPs in vaccine strain B. melitensis Rev.1. Immunoelectron microscopy confirmed the poor accessibility of OMPs to MAbs on the surface of S Brucella strains. The naturally R pathogenic species B. ovis and B. canis bound the majority of OMP-specific MAbs as well as the R-LPS-specific MAbs. Therefore, the conserved OMP and R-LPS epitopes could play a role as targets of protective antibody-mediated immunity in infections caused by naturally R B. ovis and B. canis.

Cloning and nucleotide sequence of the gene coding for the major 25-kilodalton outer membrane protein of Brucella abortus

The cloning and sequencing of the Brucella abortus major 25-kDa outer membrane protein (OMP) is reported. The 25-kDa (group 3) OMP has been proposed, on the basis of amino acid composition, to be the counterpart of OmpA (D. R. Verstraete, M. T. Creasy, N. T. Caveney, C. L. Baldwin, M. W. Blab, and A. J. Winter, Infect. Immun. 35:979-989, 1982). However, the amino acid sequence predicted from the cloned B. abortus gene did not reveal significant homology with either OmpA sequences from different members of the family Enterobacteriaceae or other known protein sequences.

Growth phase-dependent variations in the outer membrane protein profile of Brucella melitensis

Changes in Brucella cell envelope protein profiles were investigated with batch cultures of B. melitensis strain 16M in a 2-litre fermenter. Analysis of expression of outer membrane proteins (OMP) (apparent molecular masses of 10, 16.5, 19, 25-27, 31-34, 36-38 and 89 kDa) and heat-shock protein DnaK (73 kDa) was performed with monoclonal antibodies (mAb) and immunoblotting techniques. Synthesis of the 89-kDa OMP and the heat-shock protein DnaK was invariant during B. melitensis growth. Expression of the 10-, 19- and 36-38-kDa minor OMPs was never detected. Variations in profiles of some OMPs, i.e. 25-27-kDa and 31-34-kDa major proteins and 16.5-kDa minor protein, occurred during growth stages, principally at the end of the exponential growth phase. These variations consisted of shifts in apparent molecular masses for the 25-27-kDa and 31-34-kDa OMPs and of peptidoglycan association for the 16.5-kDa OMP. Therefore, whereas the strong association of major OMPs with peptidoglycan was confirmed, results suggested that the 16.5-kDa minor OMP is also a peptidoglycan-associated protein.

Alteration of protective and serologic responses in BALB/c mice vaccinated with chemically modified versus nonmodified proteins of Brucella abortus 19

A study was conducted to determine whether the covalent chemical modification of Brucella abortus 19 salt-extractable proteins (BCSP) and BCSP derivatives would modulate the immune responses in BALB/c mice. Salt-extractable proteins BCSP 0-70 and BCSP 70-100 were modified with acetoacetic anhydride, and recombinant proteins rBCSP20 (20 kDa), rBCSP31 (31 kDa), and rBCSP45 (45 kDa) were modified with succinic and dodecanoyl anhydrides. Four weeks after mice were vaccinated with the different preparations, principal and control mice were challenge exposed with a virulent culture of B. abortus 2308, and mice were necropsied 2 weeks later. Serum samples were obtained immediately before mice were challenge exposed and at necropsy. Sera were tested for specific immunoglobulin M (IgM) and G (IgG) antibodies by using an enzyme-linked immunosorbent assay. Acylation decreased the immune responses (increased IgG antibodies and reduced spleen CFU and splenomegaly) induced by both BCSP 0-70 and BCSP 70-100. Modification of the recombinant proteins by dodecanoyl and succinic anhydrides had no effect on the protection induced; however, the IgG serologic responses to the homologous and heterologous proteins were altered. Monophosphoryl lipid A markedly enhanced the immunogenicity of BCSP 0-70.

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.

Escherichia hermannii (ATCC 33651) polysaccharide-protein conjugates: comparison of two conjugation methods for the induction of humoral responses in mice

Escherichia hermannii (ATCC 33651) LPS O-polysaccharide was covalently linked to a carrier (bovine serum albumin) to form conjugates either directly or with a spacer arm (adipic acid dihydrazide). The immunogenicity of both conjugates at three different doses was tested in mice. Antibodies to the conjugate were produced and were shown to react with free lipopolysaccharide. The directly-coupled conjugate was found to be more immunogenic than the indirect one (i.e. lower dose necessary for a similar response). The antibody response elicited by the directly coupled conjugate (1 microgram/animal) began at 21 days and was sustained for at least 4 months. The mouse model described here may be applicable to the testing of other conjugates composed of bacterial cell wall polysaccharides and LPS O-chains.

Unresponsiveness of vaccinated BALB/c mice to a second inoculation of lipopolysaccharide from Brucella abortus strain 2308

A study was conducted to determine whether the protection induced in mice by a primary inoculation of lipopolysaccharide from Brucella abortus would be enhanced by a second inoculation given at different time intervals. Protection was challenged by exposure of the mice to a virulent culture of B. abortus strain 2308. Reduced mean viable count and/or splenic weights were the criteria of protection. There was no significant difference (P greater than 0.05) in the protective responses among mice given a single inoculation. Vaccinated mice were significantly (P less than 0.05) better protected than were nonvaccinated mice. Mice given vaccinal inoculations simultaneous with challenge exposure were less protected (P less than 0.001) than were mice vaccinated prior to challenge, but were better protected (P less than 0.010) than were nonvaccinated mice.

Identification of seven surface-exposed Brucella outer membrane proteins by use of monoclonal antibodies: immunogold labeling for electron microscopy and enzyme-linked immunosorbent assay

A panel of monoclonal antibodies (MAbs) to seven Brucella outer membrane proteins were characterized. These antibodies were obtained by immunizing mice with sodium dodecyl sulfate-insoluble (SDS-I) fractions, cell walls, or whole bacterial cells of Brucella abortus or B. melitensis. Enzyme-linked immunosorbent assays were used to screen the hybridoma supernatants and to determine their binding at the surface of rough and smooth B. abortus and B. melitensis cells. The outer membrane proteins (OMPs) recognized by these antibodies were the proteins with molecular masses of 25 to 27 kDa and 36 to 38 kDa (porin) (major proteins) and the proteins with molecular masses of 10, 16.5, 19, 31 to 34, and 89 kDa (minor proteins). Surface exposure of these OMPs was visualized by electron microscopy by using the MAbs and immunogold labeling. Binding of the MAbs on whole rough bacterial cells indicates that the 10-, 16.5-, 19-, 25- to 27-, 31- to 34-, 36- to 38-, and 89-kDa OMPs are exposed at the cell surface. However, enzyme-linked immunosorbent assay results indicate a much better binding of the anti-OMP MAbs on rough strains than on the corresponding smooth strains except for the anti-19-kDa MAb. Immunoelectron microscopy showed that on smooth B. abortus cells only the 89- and 31- to 34-kDa OMPs were not accessible to the MAbs tested. Binding of the anti-31- to 34-kDa MAb at the cell surface was observed for the rough B. abortus cells and for the rough and smooth B. melitensis cells. These results indicate the importance of steric hindrance due to the presence of the long lipopolysaccharide O side chains in the accessibility of OMPs on smooth Brucella strains and should be considered when undertaking vaccine development.

Conservation of antigenicity in a 31-kDa Brucella protein

A 31-kilodalton (kDa) protein extracted from Brucella abortus was previously cloned into Escherichia coli and expressed at high levels. The E. coli-derived protein can be purified by a simple 2-step procedure entailing detergent extraction followed by ion-exchange chromatography. Subsequent analyses show that the E. coli-derived protein is identical to the Brucella-derived protein in molecular weight and isoelectric point. A partial amino acid sequence of the N-terminus of the protein of E. coli origin matches the predicted sequence, based on DNA sequence data. Using specific antiserum raised against the E. coli-derived protein, 34 strains of Brucella, representing all 6 recognized species, were examined for expression of the 31-kDa protein by Western blotting. This protein was detectable in all, but one Brucella species (B. ovis), including all 8 biovars of B. abortus tested. This degree of conservation supports further study of the 31-kDa protein for potential exploitation as a vaccine or diagnostic component.