Similarity In Protein Profiles Research Articles

The Effectiveness of MALDI ToF Mass Spectrometry in Identification of <i>Francisella tularensis</i> Strains

The aim of the study was to evaluate the effectiveness of MALDI‑ToF mass spectrometry in the identification of collection and newly isolated strains of tularemia pathogen using the database “Protein profiles of mass spectra of microorganisms belonging to I–II pathogenicity groups for the MALDI Biotyper software”.Materials and methods. We investigated 142 strains of Francisella tularensis, including 59 collection strains and 83 newly isolated ones. Bacteriological, molecular-genetic and proteomic research methods were used to identify them. The acquisition of mass spectra, analysis, generation and expansion of reference libraries were performed on a mass analyzer “Microflex LT” using FlexControl v. 3.3, FlexAnalysis v. 3.3, and MALDI Biotyper 3.0 software packages. The cluster analysis was performed using the BioNumerics 7.6 software.Results and discussion. The possibility of identifying tularemia pathogen has been assessed using the extended database for MALDI Biotyper 3.0 “Protein profiles of mass spectra of microorganisms belonging to I–II pathogenicity groups for the MALDI Biotyper software”. During identification to the species level, the significance of mass spectrometry results for collection strains and newly isolated ones was 91.5 % and 97.6 %, respectively. In determining the genus appurtenance, the reliability of identification was 100 %. Thus, the MALDI‑ToF mass spectrometry method allows for accurate species and genus identification of F. tularensis strains. Based on the cluster analysis of 66 F. tularensis strains in BioNumerics 7.6 software using «Pearson correlation» and the UPGMA algorithm, the possibility of subspecies differentiation has been evaluated. Due to the similarity of protein profiles of F. tularensis strains, a clear differentiation into subspecies could not be achieved. It is necessary to use other options for sample preparation, new generation devices with higher resolution, as well as apply additional approaches and analysis tools for successful subspecific differentiation.

Quantitative proteomics analysis reveals unique but overlapping protein signatures in HIV infections

BackgroundHuman immunodeficiency virus-1 (HIV-1) exploits human host factors to complete its life cycle. Hence, discovery of HIV-regulated host proteins markers would better our understanding of the virus life-cycle and its contribution to pathogenesis and discovery of objective diagnostic and prognostic molecules. MethodsWe conducted holistic total proteomics analysis of three closely related study populations including patients with HIV type-1 (HIV-1) and HIV type-2 (HIV-2) as well as HIV-1 elite controllers (HIV-1-EC). Peripheral blood plasma (PBP) samples were subjected to label-free quantitative liquid-chromatography tandem mass-spectrometry (LC–MS/MS). ResultsOver 314 unique PBP protein species were identified of which 100 (approx. 32%) were significantly differentially expressed (≥2 to ∞ - fold-change; p < 0.05) between the three sample cohorts. Of the 100 proteins, 91 were significantly changed between pairs of HIV-1 versus HIV-1-EC, while 83 of the 100 proteins differed significantly between HIV-2 and HIV-1-EC. Interestingly, 76 proteins (87.5%) overlap between the two data sets indicating that majority of these proteins share similar expression changes between HIV-1 and HIV-2 sample groups. Two of the identified proteins, XRCC5 and PSME1, were implicated in the early phase of the pathway network for HIV life cycle, while others were involved in infectious disease and disease of signal transduction. Among them were MAP2K1, RPL23A, RPS3, CALR, PRDX1, SOD2, LMNB1, PHB, and FGB. Despite the high degree of similarity in protein profiles of HIV-1 and HIV-2, six proteins differed significantly including ETFB, PHB2, S100A9, LMO2, PPP3R1 and Vif, a fragment of virion infectivity factor of HIV-1. Additionally, 15 proteins were uniquely expressed, and one of them (LSP1) is present only in HIV-1-EC but absent in HIV1 and HIV-2 and vice versa for the rest 14 proteins. ConclusionsAltogether, we have identified HIV-specific/related protein expression changes that might potentially be capable of early diagnosis and prognosis of HIV diseases and other related infectious diseases.

Quantitative Proteomics Analysis Reveals Unique But Overlapping Protein Signatures in HIV Infection

Human immunodeficiency virus-1 (HIV-1) exploits human host factors to complete its life cycle. Hence, it is very important to identify HIV-regulated host proteins for better understanding of the virus life cycle and its contribution to pathogenesis. This can potentially lead to identifying core target molecules that can be used as diagnostic and prognostic markers and/or as targets for potential therapeutic intervention. We present here a first holistic attempt to apply global plasma proteomics analysis of three closely related study populations including: 1) patients with HIV type 1 (HIV-1), 2) HIV-1 elite controllers (HIV-1 EC), and 3) patients infected with HIV type 2 (HIV-2). Peripheral blood plasma (PBP) samples from these groups of patients, together with healthy donors, were subjected to expression proteomics using label-free quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS). Over 314 unique PBP protein species were identified of which 100 (approx. 32%) were significantly differentially expressed (≥ 2 to ∞ - fold change; p < 0.05) between HIV-1, HIV-2 and HIV-1 EC control subjects. A total of 91 of the 100 proteins were significantly differentially expressed between pairs of HIV-1 versus HIV-1 EC, while 83 of the 100 proteins differed significantly between HIV-2 and HIV-1 EC. Interestingly, 76 proteins (87.5%) overlap between the two data sets indicating that majority of these proteins share similar expression changes between the three sample groups. Two proteins, XRCC5 and PSME1, were implicated in the early phase of the pathway network for HIV life cycle. Other identified proteins were involved in infectious disease and disease of signal transduction. Among them were MAP2K1, RPL23A, RPS3, RPS8, CALR, PRDX1, SOD2, LMNB1, LMNA, PHB, FGA, and FGB. Interestingly, despite high degree of similarity in protein profiles of HIV-1 and HIV-2, we identified only six proteins with significant expression changes (P<0.05). These include ETFB, PHB2, S100A9, LMO2, PPP3R1 and Vif, a fragment of virion infectivity factor of HIV-1. In conclusion, we have identified HIV-related protein expression changes and these proteins once validated in large sample cohort might potentially be capable of early diagnosis and prognosis of HIV diseases and other related infectious diseases. Funding: We would like to acknowledge King Abdulaziz City of Science and Technology for funding this project, advanced Strategic Program, National plan for Science, Technology and Innovation (10-BIO 1340-46). Declaration of Interest: The authors declare no competing interests. Ethical Approval: This study was conducted in accordance with the Helsinki Declaration and approved by the Research Ethics Committee and Research Advisory Council (ORA # 2110 001). All participants provided written and signed informed consents that were obtained by the institutional (KFSHRC) IRB approval.

Multiphasic strain differentiation of atypical mycobacteria from elephant trunk wash.

Background. Two non-tuberculous mycobacterial strains, UM_3 and UM_11, were isolated from the trunk wash of captive elephants in Malaysia. As they appeared to be identical phenotypes, they were investigated further by conventional and whole genome sequence-based methods of strain differentiation.Methods. Multiphasic investigations on the isolates included species identification with hsp65 PCR-sequencing, conventional biochemical tests, rapid biochemical profiling using API strips and the Biolog Phenotype Microarray analysis, protein profiling with liquid chromatography-mass spectrometry, repetitive sequence-based PCR typing and whole genome sequencing followed by phylogenomic analyses.Results. The isolates were shown to be possibly novel slow-growing schotochromogens with highly similar biological and genotypic characteristics. Both strains have a genome size of 5.2 Mbp, G+C content of 68.8%, one rRNA operon and 52 tRNAs each. They qualified for classification into the same species with their average nucleotide identity of 99.98% and tetranucleotide correlation coefficient of 0.99999. At the subspecies level, both strains showed 98.8% band similarity in the Diversilab automated repetitive sequence-based PCR typing system, 96.2% similarity in protein profiles obtained by liquid chromatography mass spectrometry, and a genomic distance that is close to zero in the phylogenomic tree constructed with conserved orthologs. Detailed epidemiological tracking revealed that the elephants shared a common habitat eight years apart, thus, strengthening the possibility of a clonal relationship between the two strains.

Proteomic Differences between Listeria monocytogenes Isolates from Food and Clinical Environments.

Listeria monocytogenes is an organism associated with a wide range of foods. It causes listeriosis, a severe illness that mainly affects people with weakened immune systems. Proteomic profiles of three different L. monocytogenes isolates were studied using 1D SDS PAGE, 2DE and mass spectrometry. The protein banding patterns generated by 1D SDS PAGE of three strains of L. monocytogenes were found to be similar. Visual observations from 2DE gel maps revealed that certain spots appeared to have intensity differences. Key differences in proteins synthesis of three strains of L. monocytogenes were found using the PDQest TM 2DE Analysis software. Comparison showed that the clinical isolate (strain SB92/844) had 53.4% and 53.9% protein profile similarity with dairy isolate (strain V7) and seafood isolate (SB92/870), respectively. The identity of selected protein spots was achieved using MALDI-TOF and ion trap mass spectrometry. It was found that certain identified proteins (i.e., a major cold shock protein and superoxide dismutase) were expressed differently between two local strains of L. monocytogenes (SB92/844, SB92/870) and one strain from overseas (V7).

Co-regulation proteomics reveals substrates and mechanisms of APC/C-dependent degradation

Using multiplexed quantitative proteomics, we analyzed cell cycle-dependent changes of the human proteome. We identified >4,400 proteins, each with a six-point abundance profile across the cell cycle. Hypothesizing that proteins with similar abundance profiles are co-regulated, we clustered the proteins with abundance profiles most similar to known Anaphase-Promoting Complex/Cyclosome (APC/C) substrates to identify additional putative APC/C substrates. This protein profile similarity screening (PPSS) analysis resulted in a shortlist enriched in kinases and kinesins. Biochemical studies on the kinesins confirmed KIFC1, KIF18A, KIF2C, and KIF4A as APC/C substrates. Furthermore, we showed that the APC/C(CDH1)-dependent degradation of KIFC1 regulates the bipolar spindle formation and proper cell division. A targeted quantitative proteomics experiment showed that KIFC1 degradation is modulated by a stabilizing CDK1-dependent phosphorylation site within the degradation motif of KIFC1. The regulation of KIFC1 (de-)phosphorylation and degradation provides insights into the fidelity and proper ordering of substrate degradation by the APC/C during mitosis.

Acclimation increases freezing stress response of Arabidopsis thaliana at proteome level

This study used 2DE to investigate how Arabidopsis thaliana modulates protein levels in response to freezing stress after sub-lethal exposure at −10°C, both in cold-acclimated and in non-acclimated plants. A map was implemented in which 62 spots, corresponding to 44 proteins, were identified. Twenty-two spots were modulated upon treatments, and the corresponding proteins proved to be related to photosynthesis, energy metabolism, and stress response. Proteins demonstrated differences between control and acclimation conditions. Most of the acclimation-responsive proteins were either not further modulated or they were down-modulated by freezing treatment, indicating that the levels reached during acclimation were sufficient to deal with freezing. Anabolic metabolism appeared to be down-regulated in favor of catabolic metabolism. Acclimated plants and plants submitted to freezing after acclimation showed greater reciprocal similarity in protein profiles than either showed when compared both to control plants and to plants frozen without acclimation. The response of non-acclimated plants was aimed at re-modulating photosynthetic apparatus activity, and at increasing the levels of proteins with antioxidant-, molecular chaperone-, or post-transcriptional regulative functions. These changes, even less effective than the acclimation strategy, might allow the injured plastids to minimize the production of non-useful metabolites and might counteract photosynthetic apparatus injuries.

Computational protein profile similarity screening for quantitative mass spectrometry experiments

The qualitative and quantitative characterization of protein abundance profiles over a series of time points or a set of environmental conditions is becoming increasingly important. Using isobaric mass tagging experiments, mass spectrometry-based quantitative proteomics deliver accurate peptide abundance profiles for relative quantitation. Associated data analysis workflows need to provide tailored statistical treatment that (i) takes the correlation structure of the normalized peptide abundance profiles into account and (ii) allows inference of protein-level similarity. We introduce a suitable distance measure for relative abundance profiles, derive a statistical test for equality and propose a protein-level representation of peptide-level measurements. This yields a workflow that delivers a similarity ranking of protein abundance profiles with respect to a defined reference. All procedures have in common that they operate based on the true correlation structure that underlies the measurements. This optimizes power and delivers more intuitive and efficient results than existing methods that do not take these circumstances into account. We use protein profile similarity screening to identify candidate proteins whose abundances are post-transcriptionally controlled by the Anaphase Promoting Complex/Cyclosome (APC/C), a specific E3 ubiquitin ligase that is a master regulator of the cell cycle. Results are compared with an established protein correlation profiling method. The proposed procedure yields a 50.9-fold enrichment of co-regulated protein candidates and a 2.5-fold improvement over the previous method. A MATLAB toolbox is available from http://hci.iwr.uni-heidelberg.de/mip/proteomics.

Human Serum IgE Reacts with a Metarhizium anisopliae Fungal Catalase

Background: Previous studies have demonstrated that Metarhizium anisopliae extract can induce responses characteristic of human allergic asthma in a mouse model. The study objectives were (1) to identify and characterize the M. anisopliae mycelia extract (MYC) proteins that are recognized by mouse serum IgE, (2) to determine if human serum IgE reacts with these proteins, and (3) to determine if these IgE-reactive proteins are found in other fungi. Methods: Asthmatic human serum IgE, M. anisopliae crude antigen (MACA) immunized mouse serum IgE, and anti-catalase antibodies were used to probe one- and two-dimensional gel electrophoresis blots of MYC. Results: Mass spectrometry analysis identified catalase as a mouse IgE-reactive protein. This identification was confirmed by assaying catalase activity in the extract and extract immunoblots probed with anti-catalase antibody. Six adult asthmatic sera contained IgE, but not IgG, that was reactive with mycelia extract proteins. A similar protein profile was seen when blots were probed with either mouse anti-MACA IgE or anti-bovine liver catalase antibodies. Furthermore, these mouse anti-MACA and anti-catalase antibodies were cross-reactive with other mold extracts (skin prick testing mix) and Aspergillus niger catalase. Conclusions: Some human asthmatics have developed IgE that reacts with an M. anisopliae catalase, most likely due to cross-reactivity (minimal IgG development). The cross-reactivity among fungal catalases suggests that IgE-reactive catalase might be useful for exposure assessment. Additionally, the similarity of protein profiles visualized with both human and mouse serum IgE suggests that allergy hazard identification can be facilitated using a mouse model.

Community proteogenomics highlights microbial strain-variant protein expression within activated sludge performing enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) selects for polyphosphate accumulating microorganisms to achieve phosphate removal from wastewater. We used high-resolution community proteomics to identify key metabolic pathways in 'Candidatus Accumulibacter phosphatis' (A. phosphatis)-mediated EBPR and to evaluate the contributions of co-existing strains within the dominant population. Overall, 702 proteins from the A. phosphatis population were identified. Results highlight the importance of denitrification, fatty acid cycling and the glyoxylate bypass in EBPR. Strong similarity in protein profiles under anaerobic and aerobic conditions was uncovered (only 3% of A. phosphatis-associated proteins exhibited statistically significant abundance differences). By comprehensive genome-wide alignment of 13,930 orthologous proteins, we uncovered substantial differences in protein abundance for enzyme variants involved in both core-metabolism and EBPR-specific pathways among the A. phosphatis population. These findings suggest an essential role for genetic diversity in maintaining the stable performance of EBPR systems and, hence, demonstrate the power of integrated cultivation-independent genomics and proteomics for the analysis of complex biotechnological systems.

Comparative studies on morphology, ITS sequence and protein profile of Alexandrium tamarense and A. catenella isolated from the China Sea

The Alexandrium tamarense species complex is a closely related cosmopolitan toxigenic group of morphology-based species, including A. tamarense, A. catenella and A. fundyense. This study investigated the morphology, internal transcribed spacer (ITS) sequence and protein profile of A. tamarense and A. catenella grown in the same culture conditions using a combination of scanning electronic microscope (SEM), molecular and proteomic approaches. The results showed that all Alexandrium strains had the plate formula of Po, 4′, 6″, 6C, 8S, 5″′, 2″″. The ventral pore, a key conventional morphological feature to discriminate A. tamarense and A. catenella, was usually present in the first apical plate of ten A. tamarense strains, however, it was found to be absent in some cells of one Alexandrium strain, ATGX01. A. tamarense and A. catenella shared an identical ITS sequence with a minor variation at intraspecific level. Protein profiles of A. catenella DH01 and A. tamarense DH01, isolated from the same region of the East China Sea, showed no significant difference, the similarity of protein profiles of the two species reached 99% with a few proteins unique to one or the other. The present results suggest that the ventral pore is not a consistent morphological feature in the Alexandrium genus, and that A. tamarense and A. catenella are conspecific and should be redesignated to one species.

Serum Protein Profile Alterations in Hemodialysis Patients

Background: Serum protein profiling patterns can reflect the pathological state of a patient and therefore may be useful for clinical diagnostics. Here, we present results from a pilot study of proteomic expression patterns in hemodialysis patients designed to evaluate the range of serum proteomic alterations in this population. Methods: Surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) was used to analyze serum obtained from patients on periodic hemodialysis treatment and healthy controls. Serum samples from patients and controls were first fractionated into six eluants on a strong anion exchange column, followed by application to four array chemistries representing cation exchange, anion exchange, metal affinity and hydrophobic surfaces. A total of 144 SELDI-TOF-MS spectra were obtained from each serum sample. Results: The overall profiles of the patient and control samples were consistent and reproducible. However, 30 well-defined protein differences were observed; 15 proteins were elevated and 15 were decreased in patients compared to controls. Serum from 1 patient exhibited novel protein peaks suggesting possible additional changes due to a secondary disease process. Conclusion: SELDI-TOF-MS demonstrated consistent serum protein profile differences between patients and controls. Similarity in protein profiles among dialysis patients suggests that patient physiological responses to end-stage renal disease and/or dialysis therapy have a major effect on serum protein profiles.

The occurrence and properties of Bacillus thuringiensis isolated from free-living animals.

To assess the prevalence and properties of Bacillus thuringiensis isolated from the intestines of small mammals. Bacillus thuringiensis was found in 11% of rodents and 17% of insectivores. Using PFGE of chromosomal DNA, SDS-PAGE of whole-cell proteins and biochemical tests (API system), 12 isolates and three reference strains were classified. Numerical analysis revealed 61% and 89% similarity of protein profiles and biochemical properties of the bacilli, respectively. The results of PFGE were consistent with the outcomes of the analysis of protein profiles. Although B. thuringiensis is not common in the intestines of small mammals, it is heterogeneous at the genotypic and phenotypic level. The results presented here help to explain the diversity and the ecological significance of B. thuringiensis. Future study should focus on the toxic activity of the isolated strains.

Usefulness of Rapid GC Analysis of Cellular Fatty Acids for Distinguishing Weissella viridescens, Weissella paramesenteroides, Weissella hellenica and some Non-identifiable, Arginine-negative Weissella Strains of Meat Origin

In an attempt to differentiate between Weissella viridescens, W. paramesenteroides, W. hellenica and some atypical arginine-negative Weissella isolates from meats, their cellular fatty acid composition was determined by a rapid GC method. Results showed that W. viridescens synthesized eicosenoic (n-C20:1) acid, while the other two species did not. Meanwhile, unlike W. paramesenteroides, W. hellenica lacked cyclopropane fatty acids with 19 carbon atoms, i.e. dihydrosterculic or lactobacillic acid. Weissella viridescens contained zero to low amounts (< 1%) of C19 cycl. Original meat isolates identified as W. viridescens or W. hellenica shared similar fatty acid profiles with the respective type strains, whereas the "wild" atypical Weissella isolates resembled more with W. paramesenteroides, and all together with Leuconostoc mesenteroides subsp. mesenteroides. Interesting variations were noted in the total C19 cycl contents among unidentified Weissella, being generally consistent with their grouping based on the type of lactate they formed and the whole-cell protein profile similarity they shared.

Whole-cell Protein Patterns, DNA Base Compositions and Coenzyme Q Types in the Yeast Genus Cryptococcus Kützing and Related Taxa

A numerical analysis was performed on one-dimensional whole-cell protein electrophoretic fingerprints of 90 strains belonging to the basidiomycetous anamorphic genus Cryptococcus and presumably related taxa in the genera Filobasidium and Tremella . A significant protein electrophoretic heterogeneity was observed within the species Cryptococcus albidus , C. humicola , C. laurentii and C. luteolus . This heterogeneity in protein profiles was confirmed by considerable variations in DNA base composition. A high similarity in protein profiles was confirmed by identical DNA base compositions and coenzyme Q types for some strains of C. albidus var. albidus and the strains studied of C. kuetzingii . Synonymy was also suggested for the type strain of C. elinovii and the strains studied of C. teneus . A close relatedness was demonstrated for one strain of C. luteolus and two strains of C. laurentii . Strains of Filobasidium floriforme and Cryptococcus ater , showing highly similar protein patterns, were characterized by an analogous range of mol% G+C content and an identical ubiquinone type. For the reference strains studied of the genus Tremella the data suggest close relationships between respectively Tremella coalescens and T. mesenterica , T. fuciformis and T. samoensis , and T. encephala and T. subanomala . There were no indications for a close phylogenetic relatedness between species of the genera Tremella and Cryptococcus .

Phenotypic change and altered protein expression in X-ray and methylcholanthrene-transformed C3H10T1/2 fibroblasts.

The morphology, growth properties and cellular protein patterns from parent and two transformed C3H10T1/2 cell lines were analyzed to associate the phenotypic and protein differences with cell transformation. Transformed 10T1/2 cells were obtained by colony isolation after exposure of parent 10T1/2 cells to methylcholanthrene (MCA-1 cell line) or X-ray irradiation (XR-III cell line). Compared to parent 10T1/2 and MCA-1 cells, XR-III cells were much smaller in size and exhibited the highest growth rate, greatest cell saturation density, increased plating efficiency and greater expression of proliferating cell nuclear antigen. MCA-1 cells showed intermediate characteristics between parent and XR-III cells. Among the three cell lines, only XR-III cells showed anchorage-independent growth in soft agar. When [35S]methionine-labeled whole cell lysate proteins were separated by two-dimensional polyacrylamide gel electrophoresis, computer comparison algorithms revealed a 97% similarity in protein profiles among almost 800 proteins detected from each cell line. However, comparison of proteins patterns of the transformed cell lines to that of parent 10T1/2 cells showed that 30 and 20 proteins were induced or repressed in XR-III cells and MCA-1 cells, respectively. Similarly, 81 and 24 proteins showed significant quantitative changes (threefold or greater) in XR-III and MCA-1 cells, respectively, as compared with parent 10T1/2 cell proteins. The anchorage-independent growth and increased proliferation properties of XR-III cells suggest a later stage of transformation compared to MCA-1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of Mosquito-Specific Bacillus thuringiensis Strains Coisolated from a Soil Population

Summary Ten isolates of Bacillus thuringiensis , coisolated from a single soil sample, were assigned to the three flagellar (H) antigenic serogroups: one isolate was identified as serovar kyushuensis (H antigen 11a:11c), six were referable to serovar amagiensis (H antigen 29), and the others belonged to a previously undescribed serovar. These ten isolates produced similar spherical to irregular-shaped parasporal inclusions. In oral toxicity tests, they all exhibited moderate larvicidal activity to the mosquitoes, Aedes aegypti and Culex pipiens pallens , but not to the silkworm, Bombyx mori , and the fall webworm, Hyphantria cunea . SDS-PAGE analysis revealed that the parasporal inclusions of these isolates consisted of polypeptides of 25–28, 70–80, and 140–150 kDa, showing a high similarity in protein profiles between ten isolates and the type strain of serovar kyushuensis . Strong immunological relationships were evident among inclusion proteins of these isolates and the type strain of kyushuensis , when examined by immunodiffusion and immunoblotting tests with polyclonal antibodies raised against the whole parasporal inclusion proteins. The results indicate that these B. thuringiensis isolates from a single soil microhabitat produce closely related mosquito-specific toxins, although they belong to three different H serogroups.

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.