Immunization by an insoluble fraction extracted from Brucella melitensis: immunological and chemical characterization of the active substances

Development of Human Vectored Brucellosis Vaccine Formulation: Assessment of Safety and Protectiveness of Influenza Viral Vectors Expressing Brucella Immunodominant Proteins in Mice and Guinea Pigs

In this paper, we first used recombinant influenza viral vector (rIVV) subtype H5N1 expressing from the open reading frame of NS1 80 and NS1 124 amino acids of Brucella outer membrane proteins (Omp) 16 and 19, ribosomal L7/L12, and Cu-Zn superoxide dismutase (SOD) proteins to develop a human brucellosis vaccine. We made 18 combinations of IVVs in mono-, bi-, and tetravalent vaccine formulations and tested them on mice to select the safest and most effective vaccine samples. Then, the most effective vaccine candidates were further tested on guinea pigs. Safety of the rIVV-based vaccine candidate was evaluated by a mouse weight-gain test. Mice and guinea pigs were challenged with the virulent strain B. melitensis 16M. The protective effect of the rIVV-based vaccine candidate was assessed by quantitation of Brucella colonization in tissues and organs of challenged animals. All vaccine formulations were safe in mice. Tested vaccine formulations, as well as the commercial B. melitensis Rev.1 vaccine, have been found to protect mice from B. melitensis 16M infection within the range of 1.6 to 2.97 log₁₀ units (P < 0.05). Tetravalent vaccine formulations from the position of NS1 80 amino acids (0.2 ± 0.4), as well as the commercial B. melitensis Rev.1 vaccine (1.2 ± 2.6), have been found to protect guinea pigs from B. melitensis 16M infection at a significant level (P < 0.05). Thus, tetravalent vaccine formulation Flu-NS1-80-Omp16+Flu-NS1-80-L7/L12+Flu-NS1-80-Omp19+Flu-NS1-80-SOD was chosen as a potential vaccine candidate for further development of an effective human vaccine against brucellosis. These results show a promising future for the development of a safe human vaccine against brucellosis based on rIVVs.

Towards a Brucella vaccine for humans

There is currently no licensed vaccine for brucellosis in humans. Available animal vaccines may cause disease and are considered unsuitable for use in humans. However, the causative pathogen, Brucella, is among the most common causes of laboratory-acquired infections and is a Center for Disease Control category B select agent. Thus, human vaccines for brucellosis are required. This review highlights the considerations that are needed in the journey to develop a human vaccine, including animal models, and includes an assessment of the current status of novel vaccine candidates.

Vacuna fenol-insoluble contra la brucelosis humana: evaluacion del poder inmunogenico en cobayos

Se examinó una vacuna diseñada para inmunizar al hombre, preparada con extracto de fenol insoluble, para determinar si protegía a cobayos contra el desafío con la cepa virulenta B. abortus 2308. Se incluyeron en el experimento las vacunas vivas atenuadas B. abortus cepa 19 y B. melitensis Rev. 1, para comparar los resultados. Se vacunaron 93 animales en cada grupo, que fueron subdivididos en subgrupos de 31 y se los desafió con 10(4), 10³ y 10² unidades formadoras de colonias de la cepa B. abortus 2308 virulenta. El análisis global de los resultados demostró una protección del 11.9% en animales vacunados con el extracto de fenol insoluble, 65% en los vacunados con B. abortus cepa 19 y 95% en el grupo que recibió vacuna B. melitensis Rev. 1.

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.

Biological properties of a panel of murine monoclonal anti-Brucella antibodies

Immune sera have previously been shown to play a positive role in immune protection against murine experimental brucellosis. The protective properties of a panel of five anti-Brucella monoclonal antibodies (Mabs) were therefore assessed by estimation of the acceleration of the blood clearance of intravenously inoculated Brucella and of the reduction of splenic infection on Day 7 after infection. Three 'strongly protective', one 'weakly protective' and one 'non-protective' Mabs were identified. As a first step towards the study of the mechanism of this humoral protection, these Mabs were further compared for structural and functional properties such as immunoglobulin isotype, anti-Brucella specificity, anti-Brucella in vitro bacteriostasis, Brucella agglutination and complement fixation when complexed with tyndallized Brucella. No correlation was found between protection and either agglutination or direct bacteriostasis. On the other hand, the results observed suggest that isotypes (and especially the IgG2a isotype) could play an important role in in vivo immuno protection and that complement may be involved. However, the fact that one of the protective Mabs belongs to the IgA isotype, does not cross-react with the others in anti-Brucella epitopic specificity and does not fix complement underlines the probable diversity of the mechanisms involved.

Brucella fractions behave as nonspecific mitogens and polyclonal B-cell activators for human lymphocytes

Two lipid-A-free fractions which were extracted from Brucella melitensis and were designated PI and SF stimulated human unsensitized mononuclear cells to proliferate and to secrete immunoglobulins. Both of these effects were observed in cultures of peripheral blood, tonsils, and cord blood lymphocytes. Neither B cells nor T cells alone proliferated in the presence of these fractions, whereas the proliferative response of T cells plus B cells was largely independent of accessory cells. Polyclonal activation was estimated by counting the cells which secreted immunoglobulins of different isotypes into culture supernatants. This phenomenon was strongly T dependent.

Proteins from Salmonella R-mutants mediating protection against Salmonella typhimurium infection in mice. II. Protection tests performed with proteins free from lipopolysaccharide

Lipopolysaccharide-free proteins obtained from R-mutants of Salmonella typhimurium, S. minnesota and S. dublin as well as those from an S-form of S. typhimurium mediated protection in mice against experimental infection with S. typhimurium. The protection was measured by LD50 and is statistically significant. The level of protection of all the preparations was similar. Non-bacterial proteins had no effect under similar experimental conditions. Protection afforded by the purified proteins was lower than that of the corresponding complex crude extract; supplementation of proteins with lipopolysaccharide and phospholipids in model membrane vesicles enhanced their potency. However, lipopolysaccharides or phospholipids alone were not able to increase the efficacy of purified proteins. Some other fractions obtained by gel filtration of the crude extract also afford protection.

Ultrastructural localization of NADPH-oxidase activity in murine peritoneal macrophages during phagocytosis of Brucella. Correlation with the production of superoxide anions

The localization of the enzyme NADPH oxidase in mouse peritoneal macrophages unstimulated or after phagocytosis of Brucella suis was investigated by electron microscopy in normal mice and mice immunized against B. suis. The enzyme was clearly visualized on mitochondrial cristae, smooth endoplasmic reticulum, and the plasma membrane; its activity correlated mainly with the state of the endoplasmic reticulum which itself reflected macrophage activation. The enzyme turnover appeared to be accelerated after phagocytosis; the phagosome membrane was seldom stained by the enzyme reaction. These macrophages were also examined for the production of superoxide anions in vitro, either unstimulated or after phagocytosis. Phagocytosis increased the production of superoxide anions, especially in immunized animals. These results are discussed with regard to the role that the products of oxidative metabolism play in the inactivation of bacteria by phagocytic cells.

Induction of autoantibodies and circulating immune complexes in mice after injection of Brucella fraction "PI" or inoculation with live Brucella suis

"PI", a vaccinating fraction with B mitogenic and polyclonal activator (PCA) activity extracted from Brucella melitensis, was i. p. injected into B6 and DB mice. In B6 mice, this led to an important but transient increase in the level of anti-ssDNA antibodies, the induction of rheumatoid factor (RF) and the appearance of circulating immune complexes (CIC). In DB mice, on the other hand, the only significant effect consisted of a slight and ephemeral peak of CIC in sera from day 7. Similarly, while i. v. inoculation of live B. suis did not influence the levels of anti-ssDNA, RF or CIC in DB mice, in the B6 mice it exerted effects which were comparable to those of PI but considerably weaker, more transient and somewhat delayed. These results are discussed in terms of the importance and significance of strain-dependence for the induction of autoimmune phenomena by PCA and microbial infections.

Studies on the immune protection to murine experimental brucellosis conferred by Brucella fractions. I. Positive role of immune serum

Mouse inoculation with three different phenol-insoluble fractions extracted from Brucella melitensis (fractions 'PI', '4A' and '5') induces an acceleration of the blood clearance of i.v. inoculated live Brucella and a diminution of the rate of multiplication of the injected bacteria in the spleen. Preincubation of the challenge inoculum in immune serum or i.p. injections of immune serum confer a good specific protection to non-immunized hosts. The results observed with fractionated sera suggest that, not only antibodies, but also other serum constituents may participate in the protective activity of immune sera. This discussed in terms of the respective importance of humoral and cellular immunity to Brucella and of the choice of the best preparations for human or animal vaccination.