Characterization of salt-extractable protein antigens from Brucella abortus by crossed immunoelectrophoresis and isoelectricfocusing

Proteomics of Brucella: Technologies and Their Applications for Basic Research and Medical Microbiology

Brucellosis is a global zoonosis caused by Gram-negative, facultative intracellular bacteria of the genus Brucella (B.). Proteomics has been used to investigate a few B. melitensis and B. abortus strains, but data for other species and biovars are limited. Hence, a comprehensive analysis of proteomes will significantly contribute to understanding the enigmatic biology of brucellae. For direct identification and typing of Brucella, matrix-assisted laser desorption ionization - time of flight mass spectrometry (MALDI - TOF MS) has become a reliable tool for routine diagnosis due to its ease of handling, price and sensitivity highlighting the potential of proteome-based techniques. Proteome analysis will also help to overcome the historic but still notorious Brucella obstacles of infection medicine, the lack of safe and protective vaccines and sensitive serologic diagnostic tools by identifying the most efficient protein antigens. This perspective summarizes past and recent developments in Brucella proteomics with a focus on species identification and serodiagnosis. Future applications of proteomics in these fields are discussed.

Brucella proteomes--a review

The proteomes of selected Brucella spp. have been extensively analyzed by utilizing current proteomic technology involving 2-DE and MALDI-MS. In Brucella melitensis, more than 500 proteins were identified. The rapid and large-scale identification of proteins in this organism was accomplished by using the annotated B. melitensis genome which is now available in the GenBank. Coupled with new and powerful tools for data analysis, differentially expressed proteins were identified and categorized into several classes. A global overview of protein expression patterns emerged, thereby facilitating the simultaneous analysis of different metabolic pathways in B. melitensis. Such a global characterization would not have been possible by using time consuming and traditional biochemical approaches. The era of post-genomic technology offers new and exciting opportunities to understand the complete biology of different Brucella species.

Cell response to a salt-extractable and sonicated Brucella melitensis 16M antigen in human brucellosis

We compared the immunological responses of leukocytes taken from healthy negative controls, laboratory workers immunized with the phenol-insoluble French vaccine against brucellosis, patients acutely ill with brucellosis, and patients chronically infected with Brucella melitensis. A salt-extractable antigen (protein-rich but with traces of lipopolysaccharide) and a sonicated suspension from B. melitensis 16M were used as antigens for in vitro lymphocyte proliferation test. Quantitation of T cells showed that the ratio of CD4+/CD8+ cells decreased as the condition of the patient deteriorated. An assay to quantitate the cell-mediated immunity showed that the activities of mononuclear cells stimulated with concanavalin A increased as the disease progressed as well.

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.

Protein profiles of Brucella suis and Brucella abortus in isoelectric focusing and sodium dodecyl sulphate-polyacrylamide gel electrophoresis

The protein profiles of five field isolates of Brucella suis and four field isolates of B. abortus were examined. Isoelectric focusing of soluble proteins from cell sonicates produced 28 bands common to both species, with a further 10 bands being unique to a species. No intraspecies variation was detected. Sodium dodecyl sulfate extracted proteins were resolved by polyacrylamide gel electrophoresis. The proteins were transferred to nitrocellulose and then stained. These techniques allowed the demonstration of 35 bands which were common to both species, with a further 15 bands which were unique to one of the two species. Again, no intraspecies variation was detected.

Sodium dodecyl sulfate- and salt-extracted antigens from various Brucella species induce proliferation of bovine lymphocytes

One- and two-dimensional gel electrophoresis and cellular immunoblotting were used to compare the protein profiles and immunogenic capabilities of salt- and sodium dodecyl sulfate-extracted components isolated from different Brucella species. Cellular immunoblotting demonstrated that freshly isolated bovine peripheral blood mononuclear cells proliferated to similar molecular mass components from the various Brucella extractions. One- and two-dimensional gel electrophoresis showed similarities in protein profiles among the different Brucella species that correlated with lymphocyte reactivity. The results presented in this study provide preliminary evidence that common proteins that induce lymphocyte proliferation are present among different Brucella species, suggesting that a genuswide subunit vaccine may be feasible.

Cloning, expression, and occurrence of the Brucella Cu-Zn superoxide dismutase

Recently, the complete amino acid sequence of a protein expressed in Escherichia coli from cloned Brucella abortus DNA was reported. On the basis of amino acid homology, this protein was identified as a copper-zinc superoxide dismutase (Cu-Zn SOD) (B. L. Beck, L. B. Tabatabai, and J. E. Mayfield, Biochemistry 29:372-376, 1990). We demonstrate in this paper that the sequenced protein is the same as the previously studied salt-extractable protein BCSP20. The plasmid-encoded protein expressed from recombinant E. coli is identical to the Brucella-derived BCSP20 in molecular mass, N-terminal amino acid sequence, and cross-reactivity with homologous and heterologous rabbit sera against either the recombinant gene product or the Brucella-derived protein. A survey of the expression of the Cu-Zn SOD protein in Brucella biovars representing all species was done by Western blotting (immunoblotting) using antisera raised against the recombinant E. coli-derived protein. With the exception of B. neotomae and B. suis biovar 2, the Cu-Zn SOD protein was detectable in all Brucella species and biovars tested, including eight biovars of B. abortus.

Immunogenicity of subcellular fractions of Brucella abortus: measurement by in vitro lymphocyte proliferative responses

Five groups of heifers were immunized with various subcellular fractions of Brucella abortus and tested for their responsiveness in lymphocyte proliferative responses in vitro. The five subcellular fractions used as immunogens were: (1) a mixture of recombinant outer membrane proteins fused to Escherichia coli beta-galactosidase, (2) a mixture of outer membrane proteins BaomI, BaomIIB1, and BaomIII1, (3) a mixture of outer membrane proteins 7.5 kDa and 8.8 kDa, (4) a complex of smooth lipopolysaccharide and proteins, and (5) a complex of outer membranes and peptidoglycan (OM-PG complex) from a rough strain. All immunogens were emulsified in adjuvant and administered twice at a 61-day interval. Two other groups of cows were included; one immunized with strain 19 and the other with adjuvant only. Strain 19 and the rough OM-PG complex induced responsiveness in lymphocyte proliferation assays in a high percentage of immunized cows. The smooth lipopolysaccharide-protein complex induced responsiveness in fewer cows. The lowest frequencies of responding cows were found in groups that received either recombinant proteins or purified protein mixtures. Based on these results, we concluded: (1) cellular immunity, as measured by in vitro lymphocyte proliferative responses, can be induced with subcellular fractions of B. abortus and (2) the more complex the immunogen, the greater the frequency of responding cows.

Determination of bovine lymphocyte responses to extracted proteins of Brucella abortus by using protein immunoblotting

Isolation and identification of Brucella antigenic determinants important to cellular responses have been difficult. In this study, bovine peripheral blood mononuclear (PBM) cells from cattle vaccinated with Brucella abortus 19 proliferated to extracted bacterial proteins blotted onto nitrocellulose. Proteins were extracted from gamma-irradiated B. abortus 19 with a sodium dodecyl sulfate extraction buffer. The extracted proteins were separated electrophoretically by sodium dodecyl sulfate-polyacrylamide gel electrophoresis prior to electroblotting onto nitrocellulose. Nitrocellulose sections corresponding to individual lanes of the gel (containing all separated proteins) were then cultured with the PBM cells. Primary and secondary stimulation responses of the PBM cells with the whole protein blots were similar kinetically to the responses of the PBM cells stimulated with whole irradiated B. abortus 19 or with whole irradiated B. abortus 19 blotted onto nitrocellulose. Although lipopolysaccharide was determined to be associated with the extracted proteins and transferred onto the blots, the lipopolysaccharide did not stimulate cellular proliferation, as indicated by the antigen-specific secondary responses. Stimulating PBM cells with portions of the blot containing high (greater than 45,000)-, medium (25,000 to 45,000)- or low (25,000)-molecular-weight proteins demonstrated that the responding cells were specific only to the proteins of corresponding molecular weights. These results indicate that cellular responses to individual proteins can be studied without cloning the bacterial genes or purifying the individual proteins.

Effect of pregnancy on the immune response of cattle to a Brucella vaccine

An experiment was performed to determine whether humoral- or cell-mediated immune responses of cattle to a Brucella abortus vaccine were influenced by the stage of gestation. Heifers were vaccinated 2 mth before and 2 mth after breeding with cell envelopes of B. abortus in an oil adjuvant containing trehalose dimycolate and muramyl dipeptide. Control groups received adjuvant alone or no vaccine. Following breeding, vaccinated animals were divided into pregnant and nonpregnant subgroups. Immune responses to two outer membrane proteins were measured at monthly intervals by ELISA and lymphocyte blastogenesis tests. Skin tests were performed during the ninth month of gestation. Vaccination induced sustained immune responses, but few differences were detected between pregnant and non-pregnant animals. The relative increase in IgA antibodies to group 3 protein in nonpregnant heifers exceeded that in pregnant heifers during months 4 and 6 of gestation (P less than 0.05). Dermal hypersensitivity, measured by changes in double skin thickness, was significantly greater in nonpregnant heifers to porin (P less than 0.01) and group 3 (P less than 0.05) antigens at 24 h post-injection, but no significant differences in skin thicknesses or in the nature of the lesions were observed at 48 h. Animals which received adjuvant alone demonstrated negligible responses. Pregnancy had no significant effect on the responses of lymphocytes to phytohemagglutinin (PHA) or Concanavalin A (Con A). However, plasmas from nonvaccinated pregnant heifers taken during the sixth and seventh (but not eight or ninth) months of pregnancy decreased responses of normal donor cells to PHA and Con A when compared with those in autologous plasma (P less than 0.05).

Detection of an Anaplasma marginale common surface protein present in all stages of infection

The establishment and maintenance of anaplasmosis-free cattle herds is impaired due to the lack of a rapid, sensitive, and specific serologic test to detect persistently infected cattle which serve as carriers for the organism. To develop an improved diagnostic test for anaplasmosis we screened Anaplasma marginale initial body proteins to identify a protein common to antigenically different isolates that is recognized by the host immune system at all stages of infection. Seronegative cattle were infected with either the Florida, Virginia, or North Texas isolate of A. marginale and monitored for infection by daily examination of Wright-stained blood smears for parasitized erythrocytes. Sera from cattle at different stages of infection, from acute through persistent, were used to immunoprecipitate A. marginale proteins that were metabolically radiolabeled with [35S]methionine or surface radiolabeled with 125I. Multiple A. marginale proteins were recognized by using sera either undiluted or at 1:10; however, only four or five proteins were sufficiently antigenic to elicit antibody reactive with a 1:1,000 serum dilution. A single protein with an apparent molecular mass of 86 kilodaltons was consistently recognized at all stages of infection regardless of the isolate used to infect the cattle. This protein was demonstrated to be on the surface of the A. marginale initial body and to be water soluble. We propose use of this 86-kilodalton protein to develop an improved serologic test for diagnosis of bovine anaplasmosis.