CD4(+) T-lymphocyte and immunoglobulin G2 responses in calves immunized with Anaplasma marginale outer membranes and protected against homologous challenge

Immunization with Anaplasma centrale Msp2 HVRs Is Less Effective than the Live A. centrale Vaccine against Anaplasmosis

Bovine anaplasmosis, caused by Anaplasma marginale, is the most prevalent tick-transmitted pathogen of livestock globally. In many parts of the world, Anaplasma centrale, a related organism, is used as a live blood-borne vaccine as it causes either no or only a mild clinical disease. Anaplasma centrale does not prevent infection with A. marginale but does prevent acute disease. Anaplasma centrale is prohibited from being used in the U.S. due to the risk of transmitting emerging pathogens. Both of these organisms encode proteins known as major surface protein 2 (Msp2), which is the most immunodominant protein for the organism. Both organisms persist in their host by evading clearance, i.e., the adaptive immune response, by recombining the hypervariable region (HVR) of msp2 with pseudogene alleles. The study goal was to test whether the Msp2 HVRs encoded by A. centrale are a sufficient source of immune stimulation to provide the clinical protection exhibited by the blood-borne vaccine. Calves were inoculated with recombinantly expressed A. centrale HVRs. Control groups were inoculated with saponin or infected with the A. centrale live vaccine and compared with the test group. A Western blot analysis demonstrated that the HVR immunizations and A. centrale live vaccine stimulated an immune response. All animals in the study became infected upon challenge with A. marginale-infected ticks. The saponin-immunized control group had a high PPE (5.4%) and larger drops in PCVs (14.6%). As expected, the A. centrale-immunized animals were protected from acute disease with lower (0.6%) parasitemia and lower drops in PCV (8.6%). The HVR-immunized group had intermediate results that were not statistically significantly different from either the negative or positive controls. This suggests that the HVR immunogen does not fully recapitulate the protective capacity of the live vaccine.

Bovine Anaplasmosis: Will there ever be an almighty effective vaccine?

Bovine anaplasmosis is a tick-borne bacterial disease with a worldwide distribution and the cause of severe economic losses in the livestock industry in many countries, including México. In the present work, we first review the elements of the immune response of the bovine, which allows ameliorating the clinical signs while eliminating the majority of the blood forms and generating an immunologic memory such that future confrontations with the pathogen will not end in disease. On the other hand, many vaccine candidates have been evaluated for the control of bovine anaplasmosis yet without no commercial worldwide effective vaccine. Lastly, the diversity of the pathogen and how this diversity has impaired the many efforts to control the disease are reviewed.

Genomic analysis on Brazilian strains of Anaplasma marginale

Anaplasma marginale is a vector-borne pathogen that causes a disease known as anaplasmosis. No sequenced genomes of Brazilian strains are yet available. The aim of this work was to compare whole genomes of Brazilian strains of A. marginale (Palmeira and Jaboticabal) with genomes of strains from other regions (USA and Australia strains). Genome sequencing of Brazilian strains was performed by means of next-generation sequencing. Reads were mapped using the genome of the Florida strain of A. marginale as a reference sequence. Single nucleotide polymorphisms (SNPs) and insertions/deletions (INDELs) were identified. The data showed that two Brazilian strains grouped together in one particular clade, which grouped in a larger American group together with North American strains. Moreover, some important differences in surface proteins between the two Brazilian isolates can be discerned. These results shed light on the evolutionary history of A. marginale and provide the first genome information on South American isolates. Assessing the genome sequences of strains from different regions is essential for increasing knowledge of the pan-genome of this bacteria.

Applications of Nanovaccines for Disease Prevention in Cattle

Vaccines are one of the most important tools available to prevent and reduce the incidence of infectious diseases in cattle. Despite their availability and widespread use to combat many important pathogens impacting cattle, several of these products demonstrate variable efficacy and safety in the field, require multiple doses, or are unstable under field conditions. Recently, nanoparticle-based vaccine platforms (nanovaccines) have emerged as promising alternatives to more traditional vaccine platforms. In particular, polymer-based nanovaccines provide sustained release of antigen payloads, stabilize such payloads, and induce enhanced antibod- and cell-mediated immune responses, both systemically and locally. To improve vaccine administrative strategies and efficacy, they can be formulated to contain multiple antigenic payloads and have the ability to protect fragile proteins from degradation. Nanovaccines are also stable at room temperature, minimizing the need for cold chain storage. Nanoparticle platforms can be synthesized for targeted delivery through intranasal, aerosol, or oral administration to induce desired mucosal immunity. In recent years, several nanovaccine platforms have emerged, based on biodegradable and biocompatible polymers, liposomes, and virus-like particles. While most nanovaccine candidates have not yet advanced beyond testing in rodent models, a growing number have shown promise for use against cattle infectious diseases. This review will highlight recent advancements in polymeric nanovaccine development and the mechanisms by which nanovaccines may interact with the bovine immune system. We will also discuss the positive implications of nanovaccines use for combating several important viral and bacterial disease syndromes and consider important future directions for nanovaccine development in beef and dairy cattle.

Immune Response to Tick-Borne Hemoparasites: Host Adaptive Immune Response Mechanisms as Potential Targets for Therapies and Vaccines

Tick-transmitted pathogens cause infectious diseases in both humans and animals. Different types of adaptive immune mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen antigens or indirectly through soluble factors, such as cytokines and/or chemokines, secreted by host cells as response. Adaptive immunity effectors, such as antibody secretion and cytotoxic and/or T helper cell responses, are mainly involved in the late and long-lasting protective immune response. Proteins and/or epitopes derived from pathogens and tick vectors have been isolated and characterized for the immune response induced in different hosts. This review was focused on the interactions between tick-borne pathogenic hemoparasites and different host effector mechanisms of T- and/or B cell-mediated adaptive immunity, describing the efforts to define immunodominant proteins or epitopes for vaccine development and/or immunotherapeutic purposes. A better understanding of these mechanisms of host immunity could lead to the assessment of possible new immunotherapies for these pathogens as well as to the prediction of possible new candidate vaccine antigens.

A vaccine using Anaplasma marginale subdominant type IV secretion system recombinant proteins was not protective against a virulent challenge

Anaplasma marginale is the most prevalent tick-borne livestock pathogen with worldwide distribution. Bovine anaplasmosis is a significant threat to cattle industry. Anaplasmosis outbreaks in endemic areas are prevented via vaccination with live A. centrale produced in splenectomized calves. Since A. centrale live vaccine can carry other pathogens and cause disease in adult cattle, research efforts are directed to develop safe recombinant subunit vaccines. Previous work found that the subdominant proteins of A. marginale type IV secretion system (T4SS) and the subdominant elongation factor-Tu (Ef-Tu) were involved in the protective immunity against the experimental challenge in cattle immunized with the A. marginale outer membrane (OM). This study evaluated the immunogenicity and protection conferred by recombinant VirB9.1, VirB9.2, VirB10, VirB11, and Ef-Tu proteins cloned and expressed in E. coli. Twenty steers were randomly clustered into four groups (G) of five animals each. Cattle from G1 and G2 were immunized with a mixture of 50 μg of each recombinant protein with Quil A® or Montanide™ adjuvants, respectively. Cattle from G3 and G4 (controls) were immunized with Quil A and Montanide adjuvants, respectively. Cattle received four immunizations at three-week intervals and were challenged with 107 A. marginale-parasitized erythrocytes 42 days after the fourth immunization. After challenge, all cattle showed clinical signs, with a significant drop of packed cell volume and a significant increase of parasitized erythrocytes (p<0.05), requiring treatment with oxytetracycline to prevent death. The levels of IgG2 induced in the immunized groups did not correlate with the observed lack of protection. Additional strategies are required to evaluate the role of these proteins and their potential utility in the development of effective vaccines.

Recombinant expression and characterization of major surface protein 4 from Anaplasma marginale

Anaplasma marginale is the rickettsia which causes the bovine anaplasmosis. The distribution of A. marginale is both tropical and subtropical regions of the world. The major surface protein 4 (MSP4) of this parasite was identified as an immunodominant protein. In this study, the full length of DNA encoding A. marginale MSP4 (AmMSP4) was cloned from the parasites. The open reading frame of msp4 coding sequence of Thailand strain is 849 bp. Phylogenetic analysis revealed that the msp4 coding sequence of A. marginale was highly conserved when compared with Anaplasma phagocytophilum. The recombinant plasmid was further transformed into the BL21-CodonPlus (DE3)-RIPL competent cells for over-expression of the recombinant major surface protein 4 of A. marginale (rAmMSP4). Sera from rabbit immunized with rAmMSP4 and from cattle infected with A. marginale were used to study the antigenicity of rAmMSP4 (35 kDa) and AmMSP4 (31 kDa). Both rAmMSP4 and AmMSP4 were recognized by these sera showing that recombinant and native AmMSP4 have conserved epitopes. Localization of Anaplasma parasites by immunofluorescence showed these parasites are distributed on both the membrane and the outside of infected erythrocytes. Regarding antigenicity, recombinant MSP4 could be used for immunodiagnostic purposes and as a possible vaccine candidate against anaplasmosis.

Sequence and immunologic conservation of Anaplasma marginale OmpA within strains from Ghana as compared to the predominant OmpA variant

A primary challenge in developing effective vaccines against obligate, intracellular, bacterial tick-borne pathogens that establish persistent infection is the identification of antigens that cross protect against multiple strains. In the case of Anaplasma marginale, the most prevalent tick-borne pathogen of cattle found worldwide, OmpA is an adhesin and thus a promising vaccine candidate. We sequenced ompA from cattle throughout Ghana naturally infected with A. marginale in order to determine the degree of variation in this gene in an area of suspected high genetic diversity. We compared the Ghanaian sequences with those available from N. America, Mexico, Australia and Puerto Rico. When considering only amino acid changes, three unique Ghanaian OmpA variants were identified. In comparison, strains from all other geographic regions, except one, shared a single OmpA variant, Variant 1, which differed from the Ghanaian variants. Next, using recombinant OmpA based on Variant 1, we determined that amino acid differences in OmpA in Ghanaian cattle as compared to OmpA Variant 1 did not alter the binding capacity of antibody directed against OmpA Variant 1, supporting the value of OmpA as a highly conserved vaccine candidate.

Immune response and biochemistry of calves immunized with rMSP1a ( Anaplasma marginale) using carbon nanotubes as carrier molecules

Vaccination against Anaplasma marginale has been considered an important control strategy for bovine anaplasmosis. Recently, mice immunized with rMSP1 a linked to carbon nanotubes (MWNT) showed significant immune responses, generating a new possibility for use of an inactivated vaccine. The objective of this study was to investigate the cellular and humoral responses in calves immunized with MWNT+rMSP1a , associated with inactivated vaccine of A. marginale produced in vitro, and evaluate the toxic effects of the MWNT on renal and hepatic function. rMSP1a was covalently linked to MWNT. Inactivated vaccine (AmUFMG2) was produced by cultivating A. marginale in IDE8 cells. Twenty-four Holstein calves were divided (four groups) and immunized subcutaneously with PBS and non-carboxylated MWNT (control, G1), AmUFMG2 (G2), MWNT+rMSP1a (G3), and AmUFMG2 with MWNT+rMSP1a (G4). Blood samples were collected for total leukocyte counts, biochemical profiling and evaluation of the cellular and humoral response. Immunization with MWNT+rMSP1a induced increase in the total number of leukocytes, NK cells, in the lymphocyte populations and higher levels of antibodies compared to calves immunized only with AmUFMG2. Furthermore, MWNT did not induce changes in the biochemical profile. These data indicate that MWNT+rMSP1a were able to induce the immune responses more efficiently than AmUFMG2 alone, without generating toxicity.

A hybrid protein containing MSP1a repeats and Omp7, Omp8 and Omp9 epitopes protect immunized BALB/c mice against anaplasmosis

Anaplasma marginale (A. marginale) has a remarkable impact on livestock production, and an effective vaccine is not currently available due to the inexistence of a small animal model. Recently, BALB/c mice were successfully infected with A. marginale, resulting in an acute and persistent anaplasmosis infection. Here, we designed a hybrid protein containing repeats of polypeptide 1a from major surface protein-1 complex (MSP1a) repeats and common epitopes of outer membrane proteins (OMPs) OMP7, OMP8 and OMP9 expressed in Escherichia coli. Our proof-of-concept assessed vaccinal effectiveness against a challenge with live bacteria. The MSP1a/OMP7/8/9 immunized BALB/C mice exhibited a strong reduction in rickettsemia and had no signs of anaplasmosis or hepatic lesions. In contrast, the non-immunized mice exhibited signs of anaplasmosis and a body weight loss associated with increases in monocyte and neutrophil counts. Furthermore, the non-immunized mice displayed atrophies with chronic inflammatory infiltrates in the spleen and increased binucleation and hydropic degeneration in the hepatocytes. Our findings demonstrated that immunization with our hybrid protein induced a strong reduction in rickettsemia and conferred protection against anaplasmosis. Therefore, given the strong evidence of the protective effect against anaplasmosis, hybrid protein designs are potential candidates for the rational design of vaccinal subunits.

Identification of a T-Cell Epitope That Is Globally Conserved among Outer Membrane Proteins (OMPs) OMP7, OMP8, and OMP9 of Anaplasma marginale Strains and with OMP7 from the A. marginale subsp. centrale Vaccine Strain

Within the protective outer membrane (OM) fraction of Anaplasma marginale, several vaccine candidates have emerged, including a family of OM proteins (OMPs) 7 to 9, which share sequence identity with each other and with the single protein OMP7 in the vaccine strain A. marginale subsp. centrale. A. marginale OMPs 7 to 9 are logical vaccine candidates because they are surface exposed, present in the OM immunogen and protective cross-linked OM proteins, recognized by immune serum IgG2 and T cells in cattle immunized with OM, and recognized by immune serum IgG2 from cattle immunized with the A. centrale vaccine strain. We report the identification of a globally conserved 9-amino-acid T-cell epitope FLLVDDAI/VV shared between A. centrale vaccine strain OMP7 and the related A. marginale OMPs 7 to 9, where position 8 of the peptide can be isoleucine or valine. The epitope is conserved in American A. marginale strains, in the Australia Gypsy Plains strain, and in multiple field isolates from Ghana. This epitope, together with additional T-cell epitopes that are present within these proteins, should be considered for inclusion in a multivalent vaccine for A. marginale that can provide protection against disease caused by globally distributed bacterial strains.

A partially purified outer membrane protein VirB9-1 for low-cost nanovaccines against Anaplasma marginale

Anaplasma marginale is a devastating tick-borne pathogen causing anaplasmosis in cattle and results in significant economic loss to the cattle industry worldwide. Currently, there is no widely accepted vaccine against A. marginale. New generation subunit vaccines against A. marginale, which are much safer, more efficient and cost-effective, are in great need. The A. marginale outer membrane protein VirB9-1 is a promising antigen for vaccination. We previously have shown that soluble recombinant VirB9-1 protein can be expressed and purified from Escherichia coli and induce a high level of humoral and cellular immunity in mice. In this study, we re-formulated the nanovaccines using the partially-purified VirB9-1 protein as the antigen and hollow nano-size silica vesicles (SV-100) as the adjuvant. We simplified the purification method to obtain the partially-purified antigen VirB9-1 with a six-fold higher yield. The new formulations using the partially-purified VirB9-1 protein achieved higher antibody and cell-mediated immune responses compared to the purified ones. This finding suggests that the partially-purified VirB9-1 protein performs better than the purified ones in the vaccination against A. marginale, and a certain level of contaminants in the protein antigen can be self-adjuvant and boost immunogenicity together with the nanoparticle adjuvant. This may lead to finding a "Goldilocks" level of contaminants. The new nanovaccine formulation using partially-purified antigens along with nanoparticle adjuvants offers an alternative strategy for making cheaper veterinary vaccines.

Nanoparticle-Based Delivery of Anaplasma marginale Membrane Proteins; VirB9-1 and VirB10 Produced in the Pichia pastoris Expression System

Bovine anaplasmosis or cattle-tick fever is a tick-borne haemolytic disease caused by the rickettsial haemoparasite Anaplasma marginale in tropical and subtropical areas of the world. While difficult to express, the proteins VirB9-1 and VirB10 are immunogenic components of the outer membrane type IV secretion system that have been identified as candidate antigens for vaccines targeting of A. marginale. Soluble VirB9-1 and VirB10 were successfully expressed using Pichia pastoris. When formulated with the self-adjuvanting silica vesicles, SV-100 (diameter: 50 nm, and pore entrance size: 6 nm), 200 µg of VirB9-1 and VirB10 were adsorbed per milligram of nanoparticle. The VirB9-1 and VirB10, SV-100 formulations were shown to induce higher antibody responses in mice compared to the QuilA formulations. Moreover, intracellular staining of selected cytokines demonstrated that both VirB9-1 and VirB10 formulations induced cell-mediated immune responses in mice. Importantly, the SV-100 VirB9-1 and VirB10 complexes were shown to specifically stimulate bovine T-cell linages derived from calves immunised with A. marginale outer membrane fractions, suggesting formulations will be useful for bovine immunisation and protection studies. Overall this study demonstrates the potential of self-adjuvanting silica vesicle formulations to address current deficiencies in vaccine delivery applications.

Cooperation of PD-1 and LAG-3 Contributes to T-Cell Exhaustion in Anaplasma marginale-Infected Cattle

The CD4(+) T-cell response is central for the control of Anaplasma marginale infection in cattle. However, the infection induces a functional exhaustion of antigen-specific CD4(+) T cells in cattle immunized with A. marginale outer membrane proteins or purified outer membranes (OMs), which presumably facilitates the persistence of this rickettsia. In the present study, we hypothesize that T-cell exhaustion following infection is induced by the upregulation of immunoinhibitory receptors on T cells, such as programmed death 1 (PD-1) and lymphocyte activation gene 3 (LAG-3). OM-specific T-cell responses and the kinetics of PD-1-positive (PD-1(+)) LAG-3(+) exhausted T cells were monitored in A. marginale-challenged cattle previously immunized with OMs. Consistent with data from previous studies, OM-specific proliferation of peripheral blood mononuclear cells (PBMCs) and interferon gamma (IFN-γ) production were significantly suppressed in challenged animals by 5 weeks postinfection (wpi). In addition, bacteremia and anemia also peaked in these animals at 5 wpi. Flow cytometric analysis revealed that the percentage of PD-1(+) LAG-3(+) T cells in the CD4(+), CD8(+), and γδ T-cell populations gradually increased and also peaked at 5 wpi. A large increase in the percentage of LAG-3(+) γδ T cells was also observed. Importantly, in vitro, the combined blockade of the PD-1 and LAG-3 pathways partially restored OM-specific PBMC proliferation and IFN-γ production at 5 wpi. Taken together, these results indicate that coexpression of PD-1 and LAG-3 on T cells contributes to the rapid exhaustion of A. marginale-specific T cells following infection and that these immunoinhibitory receptors regulate T-cell responses during bovine anaplasmosis.

Anaplasma marginale: Diversity, Virulence, and Vaccine Landscape through a Genomics Approach

In order to understand the genetic diversity of A. marginale, several efforts have been made around the world. This rickettsia affects a significant number of ruminants, causing bovine anaplasmosis, so the interest in its virulence and how it is transmitted have drawn interest not only from a molecular point of view but also, recently, some genomics research have been performed to elucidate genes and proteins with potential as antigens. Unfortunately, so far, we still do not have a recombinant anaplasmosis vaccine. In this review, we present a landscape of the multiple approaches carried out from the genomic perspective to generate valuable information that could be used in a holistic way to finally develop an anaplasmosis vaccine. These approaches include the analysis of the genetic diversity of A. marginale and how this affects control measures for the disease. Anaplasmosis vaccine development is also reviewed from the conventional vaccinomics to genome-base vaccinology approach based on proteomics, metabolomics, and transcriptomics analyses reported. The use of these new omics approaches will undoubtedly reveal new targets of interest in the near future, comprising information of potential antigens and the immunogenic effect of A. marginale proteins.

Immunogenicity of Outer Membrane Proteins VirB9-1 and VirB9-2, a Novel Nanovaccine against Anaplasma marginale

Anaplasma marginale is the most prevalent tick-borne livestock pathogen and poses a significant threat to cattle industry. In contrast to currently available live blood-derived vaccines against A. marginale, alternative safer and better-defined subunit vaccines will be of great significance. Two proteins (VirB9-1 and VirB9-2) from the Type IV secretion system of A. marginale have been shown to induce humoral and cellular immunity. In this study, Escherichia coli were used to express VirB9-1 and VirB9-2 proteins. Silica vesicles having a thin wall of 6 nm and pore size of 5.8 nm were used as the carrier and adjuvant to deliver these two antigens both as individual or mixed nano-formulations. High loading capacity was achieved for both proteins, and the mouse immunisation trial with individual as well as mixed nano-formulations showed high levels of antibody titres over 10⁷ and strong T-cell responses. The mixed nano-formulation also stimulated high-level recall responses in bovine T-cell proliferation assays. These results open a promising path towards the development of efficient A. marginale vaccines and provide better understanding on the role of silica vesicles to deliver multivalent vaccines as mixed nano-formulations able to activate both B-cell and T-cell immunity, for improved animal health.

Effect of feeding whole compared with cell-free colostrum on calf immune status: Vaccination response

Vaccination contributes to improved herd health and production. Boosting immune development at a young age may have long-term effects by enhancing vaccine immune response and efficacy. In the bovine, colostrum is the sole source of maternal immunity, having a substantial effect on health status in the neonate. To date, colostral antibody concentration is used to evaluate colostrum quality. However, colostrum also contains proteins and cells, which may affect immune development and future responses to vaccines. To determine the effect of maternal colostral cells on immune development, 37 female Holstein and Jersey dairy calves were bottle-fed 4 quarts total of whole colostrum (WC) or cell-free colostrum (CFC) at birth. Calves were vaccinated with 2 series of multivalent vaccines. Series A consisted of vaccines given between 1 and 4mo of life. Series B consisted of vaccines given between 5 and 10mo of life. Calf peripheral blood samples were obtained before each vaccination series and monthly for 3mo after each vaccination series. Cellular blood parameters were determined by flow cytometry. Quantitative real-time PCR was used to determine cytokine gene expression in peripheral blood mononuclear cells before vaccination series B and once a month for 2mo after vaccination series B. Calves fed CFC had fewer numbers of B cells in mo 2 after vaccination series A when compared with WC-fed calves. Calves fed CFC had decreased gene expression levels of IL-2 in mo 1 and numbers of CD4(+)CD62L(+)CD45RO(-) and CD4(+)CD62L(+)CD45RO(+) T cells in mo 0 and 1 after vaccination series B as compared with WC-fed calves. Our findings indicate a greater response to vaccines up to 6 to 10mo post-WC feeding when compared with CFC. These data suggest that adoptive transfer of maternal colostral cells at birth has a long-term effect on development of the neonatal immune system.

Persistent Infections and Immunity in Ruminants to Arthropod-Borne Bacteria in the Family Anaplasmataceae

Tick-transmitted gram-negative bacteria in the family Anaplasmataceae in the order Rickettsiales cause persistent infection and morbidity and mortality in ruminants. Whereas Anaplasma marginale infection is restricted to ruminants, Anaplasma phagocytophilum is promiscuous and, in addition to causing disease in sheep and cattle, notably causes disease in humans, horses, and dogs. Although the two pathogens invade and replicate in distinct blood cells (erythrocytes and neutrophils, respectively), they have evolved similar mechanisms of antigenic variation in immunodominant major surface protein 2 (MSP2) and MSP2(P44) that result in immune evasion and persistent infection. Furthermore, these bacteria have evolved distinct strategies to cause immune dysfunction, characterized as an antigen-specific CD4 T-cell exhaustion for A. marginale and a generalized immune suppression for A. phagocytophilum, that also facilitate persistence. This indicates highly adapted strategies of Anaplasma spp. to both suppress protective immune responses and evade those that do develop. However, conserved subdominant antigens are potential targets for immunization.

Subdominant Outer Membrane Antigens in Anaplasma marginale: Conservation, Antigenicity, and Protective Capacity Using Recombinant Protein

Anaplasma marginale is a tick-borne rickettsial pathogen of cattle with a worldwide distribution. Currently a safe and efficacious vaccine is unavailable. Outer membrane protein (OMP) extracts or a defined surface protein complex reproducibly induce protective immunity. However, there are several knowledge gaps limiting progress in vaccine development. First, are these OMPs conserved among the diversity of A. marginale strains circulating in endemic regions? Second, are the most highly conserved outer membrane proteins in the immunogens recognized by immunized and protected animals? Lastly, can this subset of OMPs recognized by antibody from protected vaccinates and conserved among strains recapitulate the protection of outer membrane vaccines? To address the first goal, genes encoding OMPs AM202, AM368, AM854, AM936, AM1041, and AM1096, major subdominant components of the outer membrane, were cloned and sequenced from geographically diverse strains and isolates. AM202, AM936, AM854, and AM1096 share 99.9 to 100% amino acid identity. AM1041 has 97.1 to 100% and AM368 has 98.3 to 99.9% amino acid identity. While all four of the most highly conserved OMPs were recognized by IgG from animals immunized with outer membranes, linked surface protein complexes, or unlinked surface protein complexes and shown to be protected from challenge, the highest titers and consistent recognition among vaccinates were to AM854 and AM936. Consequently, animals were immunized with recombinant AM854 and AM936 and challenged. Recombinant vaccinates and purified outer membrane vaccinates had similar IgG and IgG2 responses to both proteins. However, the recombinant vaccinates developed higher bacteremia after challenge as compared to adjuvant-only controls and outer membrane vaccinates. These results provide the first evidence that vaccination with specific antigens may exacerbate disease. Progressing from the protective capacity of outer membrane formulations to recombinant vaccines requires testing of additional antigens, optimization of the vaccine formulation and a better understanding of the protective immune response.

Evaluation of the immune response to Anaplasma marginale MSP5 protein using a HSV-1 amplicon vector system or recombinant protein

Anaplasma marginale is an intraerythrocytic vector-borne infectious agent of cattle. Immunization with the current vaccine, based on parasitized erythrocytes with live Anaplasma centrale, shows some constraints and confers partial protection, suggesting the feasibility for the development of new generation of vaccines. The aim of the present study was to assess the effect of sequential immunization of BALB/c mice, with herpesvirus amplicon vector-based vaccines combined with protein-based vaccines, on the quality of the immune response against the major surface protein 5 of A. marginale. The highest antibody titers against MSP5 were elicited in mice that received two doses of adjuvanted recombinant protein (p < 0.0001). Mice treated with a heterologous prime-boost strategy generated sustained antibody titers at least up to 200 days, and a higher specific cellular response. The results presented here showed that sequential immunization with HSV-based vectors and purified antigen enhances the quality of the immune response against A. marginale.

Immune response of calves inoculated with proteins of Anaplasma marginale bound to an immunostimulant complex

Despite our current knowledge of the immunology, pathology, and genetics of Anaplasma marginale, prevention in cattle is currently based on old standbys, including live attenuated vaccines, antibiotic treatment, and maintaining enzootic stability in cattle herds. In the present study, we evaluated the use of an immunostimulant complex (ISCOMATRIX) adjuvant, associated with a pool of recombinant major surface proteins (rMSP1a, rMSP1b, rMSP4 and rMSP5) to improve the humoral immune response triggered in calves mainly by IgG2. Ten calves were divided in three groups: 4 calves were inoculated with the ISCOMATRIX/rMSPs (G1); 2 calves were inoculated with ISCOMATRIX adjuvant (G2); and 4 calves received saline (G3). Three inoculations were administered at 21-day intervals. In G1, the calves showed significant increases in total IgG, IgG1 and IgG2 levels 21 days after the second inoculation, compared to the control group (p < 0.05), and G1 calves remained above the cut-off value 28 days after the third inoculation (p < 0.05). The post-immunized sera from calves in G1 reacted specifically for each of the rMSPs used. In conclusion, the ISCOMATRIX/rMSPs induced antigen-specific seroconversion in calves. Therefore, additional testing to explore the protection induced by rMSPs, both alone and in conjunction with proteins previously identified as subdominant epitopes, is warranted.

Knockout of an outer membrane protein operon of Anaplasma marginale by transposon mutagenesis

Background

The large amounts of data generated by genomics, transcriptomics and proteomics have increased our understanding of the biology of Anaplasma marginale. However, these data have also led to new assumptions that require testing, ideally through classical genetic mutation. One example is the definition of genes associated with virulence. Here we describe the molecular characterization of a red fluorescent and spectinomycin and streptomycin resistant A. marginale mutant generated by Himar1 transposon mutagenesis.

Results

High throughput genome sequencing to determine the Himar1-A. marginale genome junctions established that the transposon sequences were integrated within the coding region of the omp10 gene. This gene is arranged within an operon with AM1225 at the 5’ end and with omp9, omp8, omp7 and omp6 arranged in tandem at the 3’ end. RNA analysis to determine the effects of the transposon insertion on the expression of omp10 and downstream genes revealed that the Himar1 insertion not only reduced the expression of omp10 but also that of downstream genes. Transcript expression from omp9, and omp8 dropped by more than 90% in comparison with their counterparts in wild-type A. marginale. Immunoblot analysis showed a reduction in the production of Omp9 protein in these mutants compared to wild-type A. marginale.

Conclusions

These results demonstrate that transposon mutagenesis in A. marginale is possible and that this technology can be used for the creation of insertional gene knockouts that can be evaluated in natural host-vector systems.

Cross-protection between geographically distinct Anaplasma marginale isolates appears to be constrained by limited antibody responses

The rickettsia Anaplasma marginale causes the haemolytic disease bovine anaplasmosis, an economic problem in tropical and subtropical areas worldwide. The closely related but less pathogenic Anaplasma centrale is commonly used as a live vaccine to prevent anaplasmosis, but it can only be produced from infected blood. UFMG1 is a low pathogenic Brazilian strain of A. marginale, which has been shown to protect cattle against a high pathogenic Brazilian isolate. As UFMG1 can be grown in tick cells, the strain was proposed as a possible cell culture-derived vaccine. We have evaluated whether UFMG1 could protect cattle against a geographically distant heterologous strain, using A. centrale vaccination as a standard for comparison. Trial calves were infected with UFMG1, A. centrale or PBS. UFMG1-infected animals were more symptomatic than those infected with A. centrale, but none required treatment. All calves were then challenged with the Israeli A. marginale Gonen strain (one of the most prevalent strain in Israel). The A. centrale group had the mildest symptoms, while UFMG1 and control groups both had a more severe response. Nevertheless, the challenge did not cause life-threatening disease in any group. Animals infected with A. centrale had a significantly higher IgG response than UFMG1, when measured in an ELISA against initial bodies from their homologous strain or Gonen. The level of cross-reactivity of the response to initial infection correlated significantly with reduced symptoms after challenge. In conclusion, UFMG1 had limited effect in preventing disease by the geographically distant heterologous Gonen strain. While the low pathogenicity of the Gonen strain in this trial makes it impossible to conclusively state that UFMG1 would have given no protective effect against more serious disease, the comparatively low IgG response to UFMG1 suggests it would not have been as effective as A. centrale.

Genomic and proteomic approaches to vaccine candidate identification forAnaplasma marginale

Outer membrane protein preparations have been demonstrated to elicit protective immunity for Anaplasma marginale. Attempts to recreate this protective immunity using known surface proteins have been unsuccessful; therefore, novel outer membrane proteins have been searched for using a proteomic/genomic approach. Annotation of the whole genome sequence identified 62 outer membrane protein candidates based on sequence similarity to known surface proteins. In a proteomics approach for the identification of immunostimulatory outer membrane proteins, outer membrane preparations that were separated on 2D gels were used to immunize calves . Antisera from the calves were used to detect immunoreactive proteins, which were then selected and subjected to mass spectrometric analyses. These data were mapped back to the annotated A. marginale genome and have identified several new outer membrane proteins that are vaccine candidates.

Protective immunity induced by immunization with a live, cultured Anaplasma marginale strain

Despite significant economic losses resulting from infection with Anaplasma marginale, a tick-transmitted rickettsial pathogen of cattle, available vaccines provide, at best, only partial protection against clinical disease. The green-fluorescent protein expressing mutant of the A. marginale St. Maries strain is a live, marked vaccine candidate (AmStM-GFP). To test whether AmStM-GFP is safe and provides clinical protection, a group of calves was vaccinated, and clinical parameters, including percent parasitized erythrocytes (PPE), packed cell volume (PCV) and days required to reach peak bacteremia, were measured following inoculation and following tick challenge with wild type St. Maries strain (AmStM). These clinical parameters were compared to those obtained during infection with the A. marginale subsp. centrale vaccine strain (A. centrale) or wild type AmStM. AmStM-GFP resulted in similar clinical parameters to A. centrale, but had a lower maximum PPE, smaller drop in PCV and took longer to reach peak bacteremia than wild type AmStM. AmStM-GFP provided clinical protection, yielding a stable PCV and low bacteremia following challenge, whereas A. centrale only afforded partial clinical protection.

Epitope-based vaccines with the Anaplasma marginale MSP1a functional motif induce a balanced humoral and cellular immune response in mice

Bovine anaplasmosis is a hemoparasitic disease that causes considerable economic loss to the dairy and beef industries. Cattle immunized with the Anaplasma marginale MSP1 outer membrane protein complex presents a protective humoral immune response; however, its efficacy is variable. Immunodominant epitopes seem to be a key-limiting factor for the adaptive immunity. We have successfully demonstrated that critical motifs of the MSP1a functional epitope are essential for antibody recognition of infected animal sera, but its protective immunity is yet to be tested. We have evaluated two synthetic vaccine formulations against A. marginale, using epitope-based approach in mice. Mice infection with bovine anaplasmosis was demonstrated by qPCR analysis of erythrocytes after 15-day exposure. A proof-of-concept was obtained in this murine model, in which peptides conjugated to bovine serum albumin were used for immunization in three 15-day intervals by intraperitoneal injections before challenging with live bacteria. Blood samples were analyzed for the presence of specific IgG2a and IgG1 antibodies, as well as for the rickettsemia analysis. A panel containing the cytokines’ transcriptional profile for innate and adaptive immune responses was carried out through qPCR. Immunized BALB/c mice challenged with A. marginale presented stable body weight, reduced number of infected erythrocytes, and no mortality; and among control groups mortality rates ranged from 15% to 29%. Additionally, vaccines have significantly induced higher IgG2a than IgG1 response, followed by increased expression of pro-inflammatory cytokines. This is a successful demonstration of epitope-based vaccines, and protection against anaplasmosis may be associated with elicitation of effector functions of humoral and cellular immune responses in murine model.

Identification of multilocus genetic heterogeneity in Anaplasma marginale subsp. centrale and its restriction following tick-borne transmission

Anaplasma marginale subsp. centrale was the first vaccine used to protect against a rickettsial disease and is still in widespread use a century later. As its use preceded development of either cryopreservation or cell culture, the vaccine strain was maintained for decades by sequential passage among donor animals, excluding the natural tick-borne transmission cycle that provides a selective pressure or population "bottleneck." We demonstrated that the vaccine strain is genetically heterogeneous at 46 chromosomal loci and that heterogeneity was maintained upon inoculation into recipient animals. The number of variants per site ranged from 2 to 11 with a mean of 2.8/locus and a mode and median of 2/locus; variants included single-nucleotide polymorphisms, insertions/deletions, polynucleotide tracts, and different numbers of perfect repeats. The genetic heterogeneity is highly unlikely to be a result of strain contamination based on analysis using a panel of eight gene markers with a high power for strain discrimination. In contrast, heterogeneity appears to be a result of genetic drift in the absence of the restriction of tick passage. Heterogeneity could be reduced following tick passage, and the reduced heterogeneity could be maintained in sequential intravenous and tick-borne passages. The reduction in vaccine strain heterogeneity following tick passage did not confer an enhanced transmission phenotype, indicating that a stochastically determined population bottleneck was likely responsible as opposed to a positive selective pressure. These findings demonstrate the plasticity of an otherwise highly constrained genome and highlight the role of natural transmission cycles in shaping and maintaining the bacterial genome.

Linkage between Anaplasma marginale outer membrane proteins enhances immunogenicity but is not required for protection from challenge

The prevention of bacterial infections via immunization presents particular challenges. While outer membrane extracts are often protective, they are difficult and expensive to isolate and standardize and thus are often impractical for development and implementation in vaccination programs. In contrast, individual proteins, which are easily adapted for use in subunit vaccines, tend to be poorly protective. Consequently, identification of the specific characteristics of outer membrane-based immunogens, in terms of the antigen contents and contexts that are required for protective immunity, represents a major gap in the knowledge needed for bacterial vaccine development. Using as a model Anaplasma marginale, a persistent tick-borne bacterial pathogen of cattle, we tested two sets of immunogens to determine whether membrane context affected immunogenicity and the capacity to induce protection. The first immunogen was composed of a complex of outer membrane proteins linked by covalent bonds and known to be protective. The second immunogen was derived directly from the first one, but the proteins were individualized rather than linked. The antibody response induced by the linked immunogen was much greater than that induced by the unlinked immunogen. However, both immunogens induced protective immunity and an anamnestic response. These findings suggest that individual proteins or combinations of proteins can be successfully tested for the ability to induce protective immunity with less regard for overall membrane context. Once protective antigens are identified, immunogenicity could be enhanced by cross-linking to allow a reduced immunogen dose or fewer booster vaccinations.

Evaluating the effectiveness of an inactivated vaccine from Anaplasma marginale derived from tick cell culture

The protective efficacy of an inactivated vaccine from Anaplasma marginale that was cultured in tick cells (IDE8) for use against bovine anaplasmosis was evaluated. Five calves (Group 1) were inoculated subcutaneously, at 21-day intervals, with three doses of vaccine containing 3 × 10(9) A. marginale initial bodies. Five control calves received saline solution alone (Group 2). Thirty-two days after the final inoculation, all the calves were challenged with approximately 3 × 10(5) erythrocytes infected with A. marginale high-virulence isolate (UFMG2). The Group 1 calves seroconverted 14 days after the second dose of vaccine. After the challenge, all the animals showed patent rickettsemia. There was no significant difference (p > 0.05) between the Group 1 and 2 calves during the incubation period, patency period or convalescence period. All the animals required treatment to prevent death. The results suggest that the inactivated vaccine from A. marginale produced in IDE8 induced seroconversion in calves, but was not effective for preventing anaplasmosis induced by the UFMG2 isolate under the conditions of this experiment.

Subdominant antigens in bacterial vaccines: AM779 is subdominant in the Anaplasma marginale outer membrane vaccine but does not associate with protective immunity

Identification of specific antigens responsible for the ability of complex immunogens to induce protection is a major goal in development of bacterial vaccines. Much of the investigation has focused on highly abundant and highly immunodominant outer membrane proteins. Recently however, genomic and proteomic approaches have facilitated identification of minor components of the bacterial outer membrane that have previously been missed or ignored in immunological analyses. Immunization with Anaplasma marginale outer membranes or a cross-linked surface complex induces protection against bacteremia, however the components responsible for protection within these complex immunogens are unknown. Using outer membrane protein AM779 as a model, we demonstrated that this highly conserved but minor component of the A. marginale surface was immunologically sub-dominant in the context of the outer membrane or surface complex vaccines. Immunologic sub-dominance could be overcome by targeted vaccination with AM779 for T lymphocyte responses but not for antibody responses, suggesting that both abundance and intrinsic immunogenicity determine relative dominance. Importantly, immunization with AM779 supports that once priming is achieved by specific targeting, recall upon infectious challenge is achieved. While immunization with AM779 alone was not sufficient to induce protection, the ability of targeted immunization to prime the immune response to highly conserved but low abundance proteins supports continued investigation into the role of sub-dominant antigens, individually and collectively, in vaccine development for A. marginale and related bacterial pathogens.

Breadth of the CD4+ T cell response to Anaplasma marginale VirB9-1, VirB9-2 and VirB10 and MHC class II DR and DQ restriction elements

MHC class II molecules influence antigen-specific CD4+ T lymphocyte responses primed by immunization and infection. CD4+ T cell responses are important for controlling infection by many bacterial pathogens including Anaplasma marginale and are observed in cattle immunized with the protective A. marginale outer membrane (OM) vaccine. Immunogenic proteins that comprise the protective OM vaccine include type IV secretion system (T4SS) proteins VirB9-1, VirB9-2 and VirB10, candidates for inclusion in a multiepitope vaccine. Our goal was to determine the breadth of the VirB9-1, VirB9-2 and VirB10 T cell response and MHC class II restriction elements in six cattle with different MHC class II haplotypes defined by DRB3, DQA and DQB allele combinations for each animal. Overlapping peptides spanning each T4SS protein were tested in T cell proliferation assays with autologous antigen-presenting cells (APC) and artificial APC expressing combinations of bovine DR and DQ molecules. Twenty immunostimulatory peptides were identified; three representing two or more epitopes in VirB9-1, ten representing eight or more epitopes in VirB9-2 and seven representing seven or more epitopes in VirB10. Of the eight DRA/DRB3 molecules, four presented 15 peptides, which was biased as DRA/DRB3*1201 presented ten and DRA/DRB3*1101 presented four peptides. Four DQA/DQB molecules composed of two intrahaplotype and two interhaplotype pairs presented seven peptides, of which five were uniquely presented by DQ molecules. In addition, three functional mixed isotype (DQA/DRB3) restriction elements were identified. The immunogenicity and broad MHC class II presentation of multiple VirB9-1, VirB9-2 and VirB10 peptide epitopes justify their testing as a multiepitope vaccine against A. marginale.

CD4 T cell antigens from Staphylococcus aureus Newman strain identified following immunization with heat-killed bacteria

Staphylococcus aureus is a commensal bacterium associated with the skin and mucosal surfaces of humans and animals that can also cause chronic infection. The emergence of antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA) and strains causing chronic intramammary infections (IMI) in cows results in severe human and livestock infections. Conventional approaches to vaccine development have yielded only a few noneffective vaccines against MRSA or IMI strains, so there is a need for improved vaccine development. CD4 T lymphocytes are required for promoting gamma interferon (IFN-γ) mediated immunoglobulin isotype switching in B lymphocytes to produce high-affinity IgG antibodies and IFN-γ-mediated phagocyte activation for an effective resolution of bacterial infection. However, the lack of known CD4 T cell antigens from S. aureus has made it difficult to design effective vaccines. The goal of this study was to identify S. aureus proteins recognized by immune CD4 T cells. Using a reverse genetics approach, 43 antigens were selected from the S. aureus Newman strain. These included lipoproteins, proteases, transcription regulators, an alkaline shock protein, conserved-domain proteins, hemolysins, fibrinogen-binding protein, staphylokinase, exotoxin, enterotoxin, sortase, and protein A. Screening of expressed proteins for recall T cell responses in outbred, immune calves identified 13 proteins that share over 80% sequence identity among MRSA or IMI strains. These may be useful for inclusion in a broadly protective multiantigen vaccine against MRSA or IMI.

Genome-wide screening and identification of antigens for rickettsial vaccine development

The capacity to identify immunogens for vaccine development by genome-wide screening has been markedly enhanced by the availability of microbial genome sequences coupled to proteomic and bioinformatic analysis. Critical to this approach is in vivo testing in the context of a natural host–pathogen relationship, one that includes genetic diversity in the host as well as among pathogen strains. We aggregate the results of three independent genome-wide screens using in vivo immunization and protection against Anaplasma marginale as a model for discovery of vaccine antigens for rickettsial pathogens. In silico analysis identified 62 outer membrane proteins (Omp) from the 949 predicted proteins in the A. marginale genome. These 62 Omps were reduced to 10 vaccine candidates by two independent genome-wide screens using IgG2 from vaccinates protected from challenge following vaccination with outer membranes (screen 1) or bacterial surface complexes (screen 2). Omps with broadly conserved epitopes were identified by immunization with a live heterologous vaccine, A. marginale ssp. centrale (screen 3), reducing the candidates to three. The genome-wide screens identified Omps that have orthologs broadly conserved among rickettsial pathogens, highlighted the importance of identifying immunologically subdominant antigens, and supported the use of reverse vaccinology approaches in vaccine development for rickettsial diseases.

Adaptive immunity to Anaplasma pathogens and immune dysregulation: implications for bacterial persistence

Anaplasma marginale is an obligate intraerythrocytic bacterium that infects ruminants, and notably causes severe economic losses in cattle worldwide. Anaplasma phagocytophilum infects neutrophils and causes disease in many mammals, including ruminants, dogs, cats, horses, and humans. Both bacteria cause persistent infection - infected cattle never clear A. marginale and A. phagocytophilum can also cause persistent infection in ruminants and other animals for several years. This review describes correlates of the protective immune response to these two pathogens as well as subversion and dysregulation of the immune response following infection that likely contribute to long-term persistence. I also compare the immune dysfunction observed with intraerythrocytic A. marginale to that observed in other models of chronic infection resulting in high antigen loads, including malaria, a disease caused by another intraerythrocytic pathogen.

Association and evidence for linked recognition of type IV secretion system proteins VirB9-1, VirB9-2, and VirB10 in Anaplasma marginale

Like several other bacterial pathogens, Anaplasma marginale has an outer membrane that induces complete protection from infection and disease. However, the proteins that confer protective immunity and whether protection requires interacting proteins and/or linked T-cell and immunoglobulin G epitopes are not known. Our goal is to target the conserved type IV secretion system (T4SS) to identify conserved, immunogenic membrane proteins that are interacting and linked recognition candidates. Linked recognition is a process by which a B cell is optimally activated by a helper T cell that responds to the same, or physically associated, antigen. A. marginale T4SS proteins VirB2, VirB4-1, VirB4-2, VirB6-1, VirB7, VirB8-2, VirB9-1, VirB9-2, VirB10, VirB11, and VirD4 were screened for their ability to induce IgG and to stimulate CD4+ T cells from outer membrane-vaccinated cattle. VirB9-1, VirB9-2, and VirB10 induced the strongest IgG and T-cell responses in the majority of cattle, although three animals with major histocompatibility complex class II DRB3 restriction fragment length polymorphism types 8/23, 3/16, and 16/27 lacked T-cell responses to VirB9-1, VirB9-1 and VirB9-2, or VirB9-2 and VirB10, respectively. For these animals, VirB9-1-, VirB9-2-, and VirB10-specific IgG production may be associated with T-cell help provided by responses to an interacting protein partner(s). Interacting protein partners indicated by far-Western blotting were confirmed by immunoprecipitation assays and revealed, for the first time, specific interactions of VirB9-1 with VirB9-2 and VirB10. The immunogenicity and interactions of VirB9-1, VirB9-2, and VirB10 justify their testing as a linked protein vaccine against A. marginale.

Analysis of membrane protein genes in a Brazilian isolate of Anaplasma marginale

The sequencing of the complete genome of Anaplasma marginale has enabled the identification of several genes that encode membrane proteins, thereby increasing the chances of identifying candidate immunogens. Little is known regarding the genetic variability of genes that encode membrane proteins in A. marginale isolates. The aim of the present study was to determine the degree of conservation of the predicted amino acid sequences of OMP1, OMP4, OMP5, OMP7, OMP8, OMP10, OMP14, OMP15, SODb, OPAG1, OPAG3, VirB3, VirB9-1, PepA, EF-Tu and AM854 proteins in a Brazilian isolate of A. marginale compared to other isolates. Hence, primers were used to amplify these genes: omp1, omp4, omp5, omp7, omp8, omp10, omp14, omp15, sodb, opag1, opag3, virb3, VirB9-1, pepA, ef-tu and am854. After polimerase chain reaction amplification, the products were cloned and sequenced using the Sanger method and the predicted amino acid sequence were multi-aligned using the CLUSTALW and MEGA 4 programs, comparing the predicted sequences between the Brazilian, Saint Maries, Florida and A. marginale centrale isolates. With the exception of outer membrane protein (OMP) 7, all proteins exhibited 92-100% homology to the other A. marginale isolates. However, only OMP1, OMP5, EF-Tu, VirB3, SODb and VirB9-1 were selected as potential immunogens capable of promoting cross-protection between isolates due to the high degree of homology (over 72%) also found with A. (centrale) marginale.

Correlations among Anaplasma marginale parasitemia and markers of oxidative stress in crossbred calves

The present study was designed to determine the correlations among Anaplasma marginale parasitemia and markers of oxidative stress in crossbred calves. Blood was collected from 11 crossbred calves infected with A. marginale along with 11 healthy crossbred calves as controls for determination of hematology and oxidative stress indicators. Percentage of parasitemia in infected calves varied from 0.8% to 6.0%. The values of hematological indicators and antioxidant enzymes were decreased, whereas erythrocytic lipid peroxidation (LPO) and plasma nitrate (NO) level were significantly (p < 0.05) augmented in A. marginale-infected animals over healthy group. Parasitemia was positively correlated (p < 0.01) with erythrocytic LPO and plasma NO and negatively correlated (p < 0.01) with hematological indicators and antioxidant enzymes. In addition, erythrocytic LPO was negatively correlated (p < 0.01) with the hemoglobin, erythrocyte count, and packed cell volume. From the present study, it can be concluded that anaplasmosis in crossbred calves is associated with a parasitic load-dependent oxidative damage as indicated by poor antioxidant status and enhanced oxidative stress, which are contributed to severe anemia.

Identification of Anaplasma marginale outer membrane protein antigens conserved between A. marginale sensu stricto strains and the live A. marginale subsp. centrale vaccine

Live vaccination with Anaplasma marginale subsp. centrale (synonym for Anaplasma centrale) induces protection against severe disease upon challenge with A. marginale sensu stricto strains. Despite over a century of field use, the targets of protective immunity remained unknown. Using a broad proteomic approach, we identified the proteins in a challenge sensu stricto strain that were bound by the relevant antibody isotype induced by live vaccination with Anaplasma marginale subsp. centrale. A core of 15 proteins was identified in vaccinated animals across multiple major histocompatibility complex (MHC) haplotypes. This core separated into two structural/functional classes: "housekeeping" proteins involved in replication and metabolism and outer membrane proteins (OMPs). Orthologous proteins of both classes were identified within the vaccine strain and among sensu stricto strains. In contrast to the broad conservation among strains in the sequences of the housekeeping proteins, there was significantly greater divergence in the OMPs and greater divergence in both OMP sequences and the encoding locus structure between the vaccine strain and the sensu stricto strains than among the sensu stricto strains. The OMPs bound by live vaccine-induced antibody overlapped with OMPs that were immunogenic in animals vaccinated with inactivated vaccines and subsequently protected against bacteremia and disease. The identification of this core set of OMPs is consistent with the hypothesis that "subdominant" immunogens are required for vaccine-induced protection against A. marginale and provides clear direction for development of a safer, more effective vaccine.

Anaplasma marginale infection with persistent high-load bacteremia induces a dysfunctional memory CD4+ T lymphocyte response but sustained high IgG titers

Control of blood-borne infections is dependent on antigen-specific effector and memory T cells and high-affinity IgG responses. In chronic infections characterized by a high antigen load, it has been shown that antigen-specific T and B cells are vulnerable to downregulation and apoptosis. Anaplasma marginale is a persistent infection of cattle characterized by acute and chronic high-load bacteremia. We previously showed that CD4(+) T cells primed by immunization with an A. marginale outer membrane protein were rapidly deleted following infection. Furthermore, peripheral blood T cell responses to bacteria were not observed after acute infection was controlled, suggesting dysfunctional T cell priming to other A. marginale antigens. The current study more closely investigated the kinetics of A. marginale-specific CD4(+) T cell responses primed during infection. Frequent sampling of peripheral blood and spleens revealed that antigen-specific CD4(+) T cell responses were first detected at 5 to 7 weeks, but the responses were sporadic and transient thereafter. A similar pattern was observed in animals sampled weekly for nearly 1 year. Paradoxically, by 2 weeks of infection, cattle had developed high titers of A. marginale-specific IgG, which remained high throughout persistent infection. This dysfunctional CD4(+) T cell response to infection is consistent with continual downregulation or deletion of newly primed effector T cells, similar to what was observed for immunization-induced T cells following A. marginale infection. The failure to establish a strong memory T cell response during A. marginale infection likely contributes to bacterial persistence.

Molecular and antigenic characterisation of ribosomal phosphoprotein P0 from Babesia bovis

Babesia bovis is a tick-borne pathogen that remains an important constraint for the development of cattle industries in tropical and subtropical regions of the world. Effective control can be achieved by vaccination with live attenuated phenotypes of the parasite. However, these phenotypes have a number of drawbacks, which justifies the search for new, more efficient immunogens based mainly on recombinant protein technology. In the present paper, ribosomal phosphoprotein P0 from a Brazilian isolate of B. bovis was produced and evaluated with regard to conservation and antigenicity. The protein sequence displayed high conservation between different Brazilian isolates of B. bovis and several Apicomplexa parasites such as Theileria, Neospora and Toxoplasma. IgG from cattle experimentally and naturally infected with B. bovisas well as IgG1 and IgG2 from naturally infected cattle reacted with the recombinant protein. IgG from cattle experimentally infected with Babesia bigemina cross-reacted with B. bovis recombinant P0. These characteristics suggest that P0 is a potential antigen for recombinant vaccine preparations against bovine babesiosis.

The immunization-induced antibody response to the Anaplasma marginale major surface protein 2 and its association with protective immunity

Many vector-borne pathogens evade clearance via rapid variation in their immunogenic surface expressed proteins. This is exemplified by Anaplasma marginale, a tick-borne bacterial pathogen that generates major surface protein 2 (Msp2) variants to provide for immune escape and allow long-term pathogen persistence. In contrast to persistence following infection, immunization with a surface protein complex, which includes Msp2, induces a response that prevents infection upon challenge. We hypothesized that the immune response induced by immunization altered the anti-Msp2 antibody repertoire as compared to that induced during infection, shifting the immune response toward conserved and thus broadly protective epitopes. The antibody response to the conserved (CR) and hypervariable (HVR) regions encoded by the full set of msp2 variant alleles was determined for immunized animals prior to challenge and non-immunized, infected animals. While both groups of animals had a similar antibody repertoire in terms of breath and magnitude, the titers to the Msp2 CR were strongly correlated (p < 0.005) with control of bacteremia only in the infected animals. Among the immunized animals, there was no correlation between the breadth or magnitude of the anti-Msp2 antibody response and either complete protection from infection or control of bacteremia. This is consistent with separate immunologic mechanisms being responsible for control of bacteremia in infected animals as compared to immunized animals and suggests that conserved outer membrane proteins other than Msp2 are responsible for the complete clearance observed following challenge of vaccinees.

Anaplasma marginale type IV secretion system proteins VirB2, VirB7, VirB11, and VirD4 are immunogenic components of a protective bacterial membrane vaccine

Anaplasma and related Ehrlichia spp. are important tick-borne, Gram-negative bacterial pathogens of livestock and humans that cause acute infection and disease and can persist. Immunization of cattle with an Anaplasma marginale fraction enriched in outer membranes (OM) can provide complete protection against disease and persistent infection. Serological responses of OM vaccinees to the OM proteome previously identified over 20 antigenic proteins, including three type IV secretion system (T4SS) proteins, VirB9-1, VirB9-2, and VirB10. Subsequent studies showed that these three proteins also stimulated CD4(+) T-cell responses in OM vaccinees. The T4SS, composed of a complex of proteins spanning the inner and outer membranes of certain bacteria, is an important virulence factor but is relatively unexplored as a vaccine target. The goal of this study was to determine if additional T4SS proteins are immunogenic for animals immunized with the protective OM fraction of A. marginale. T4SS proteins expressed by in vitro transcription and translation were screened for stimulating proliferation of T cells from OM vaccinees, and immunogenic proteins were expressed as recombinant proteins in Escherichia coli and their immunogenicity was verified. VirB2, a putative VirB7, VirB11, and VirD4 were immunogenic for OM vaccinees expressing several common major histocompatibility complex (MHC) class II haplotypes. VirB2 is encoded by multiple genes that share a conserved central region, and epitope mapping revealed T-cell epitopes in this region. The discovery of novel immunogenic T4SS proteins recognized by outbred individuals with common MHC haplotypes further justifies evaluating the T4SS as a potential vaccine candidate for pathogenic bacteria.

Molecular epidemiology of bovine anaplasmosis with a particular focus in Mexico

Bovine anaplasmosis, caused by the rickettsia Anaplasma marginale, has a worldwide distribution and is the cause of great economic losses in developing countries where it is highly endemic. Transmission is carried mainly by ixodid ticks: Dermacentor spp. and Rhipicephalus (Boophilus) spp. Mechanical transmission is important in disseminating the disease within and across herds. The relationship between the rickettsia, the host and the vector is complex. Several surface proteins (Msps) have been described with functions that span from adhesins towards the erythrocyte and tick cells to evasion of the immune system of the host through the generation of antigenic variants. Biologic transmission of A. marginale through Dermacentor ticks has been well studied but many questions are unresolved as to how this organism spreads within and across herds and little is known about the role Rhipicephalus (Boophilus) ticks play in transmission in the Americas. Mechanical transmission in the absence of ticks and lack of transmission through ticks are questions that need to be addressed. Phylogenetic studies of the rickettsia show wide antigenic and genetic mosaics which affects the design of new vaccines. In the present work we will discuss the molecular elements in the relationship between the rickettsia, the tick and the mammalian host associated to the distribution and persistence of the pathogen in nature.

The natural history of Anaplasma marginale

The intracellular pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae), described by Sir Arnold Theiler in 1910, is endemic worldwide in tropical and subtropical areas. Infection of cattle with A. marginale causes bovine anaplasmosis, a mild to severe hemolytic disease that results in considerable economic loss to both dairy and beef industries. Transmission of A. marginale to cattle occurs biologically by ticks and mechanically by biting flies and by blood-contaminated fomites. Both male ticks and cattle hosts become persistently infected with A. marginale and serve as reservoirs of infection. While erythrocytes are the major site of infection in cattle, A. marginale undergoes a complex developmental cycle in ticks that begins by infection of gut cells, and transmission to susceptible hosts occurs from salivary glands during feeding. Major surface proteins (MSPs) play a crucial role in the interaction of A. marginale with host cells, and include adhesion proteins and MSPs from multigene families that undergo antigenic change and selection in cattle, thus contributing to maintenance of persistent infections. Many geographic strains of A. marginale have been identified worldwide, which vary in genotype, antigenic composition, morphology and infectivity for ticks. Isolates of A. marginale may be maintained by independent transmission events and a mechanism of infection/exclusion in cattle and ticks. The increasing numbers of A. marginale genotypes identified in some geographic regions most likely resulted from intensive cattle movement. However, concurrent A. marginale strain infections in cattle was reported, but these strains were more distantly related. Phylogenetic studies of selected geographic isolates of A. marginale, using msp4 and msp1alpha, provided information about the biogeography and evolution of A. marginale, and msp1alpha genotypes appear to have evolved under positive selection pressure. Live and killed vaccines have been used for control of anaplasmosis and both types of vaccines have advantages and disadvantages. Vaccines have effectively prevented clinical anaplasmosis in cattle but have failed to block A. marginale infection. Vaccines are needed that can prevent clinical disease and, simultaneously, prevent infection in cattle and ticks, thus eliminating these hosts as reservoirs of infection. Advances in genomics, proteomics, immunology and biochemical and molecular technologies during the last decade have been applied to research on A. marginale and related organisms, and the recent development of a cell culture system for A. marginale has provided a format for studying the pathogen/tick interface. Recent advancements and new research methodologies should provide additional opportunities for development of new strategies for control and prevention of bovine anaplasmosis.

Diversity of Ehrlichia ruminantium major antigenic protein 1-2 in field isolates and infected sheep

Proteins expressed from the map1 multigene family of Ehrlichia ruminantium are strongly recognized by immune T and B cells from infected animals or from animals that were infected and have recovered from heartwater disease (although still remaining infected carriers). Analogous multigene clusters also encode the immunodominant outer membrane proteins (OMPs) in other ehrlichial species. Recombinant protein analogs of the expressed genes and DNA vaccines based on the multigene clusters have been shown to induce protective immunity, although this was less effective in heterologous challenge situations, where the challenge strain major antigenic protein 1 (MAP1) sequence differed from the vaccine strain MAP1. Recent data for several ehrlichial species show differential expression of the OMPs in mammalian versus tick cell cultures and dominant expression of individual family members in each type of culture system. However, many genes in the clusters appear to be complete and functional and to generate mRNA transcripts. Recent data also suggest that there may be a low level of protein expression from many members of the multigene family, despite primary high-level expression from an individual member. A continuing puzzle, therefore, is the biological roles of the different members of these OMP multigene families. Complete genome sequences are now available for two geographically divergent strains of E. ruminantium (Caribbean and South Africa strains). Comparison of these sequences revealed amino acid sequence diversity in MAP1 (89% identity), which is known to confer protection in a mouse model and to be the multigene family member primarily expressed in mammalian cells. Surprisingly, however, the greatest sequence diversity (79% identity) was in the less-studied map1-2 gene. We investigated here whether this map1-2 diversity was a general feature of E. ruminantium in different cultured African strains and in organisms from infected sheep. Comparison of MAP1-2s revealed amino acid identities of 75 to 100% (mean of 86%), compared to 84 to 100% (mean of 89%) for MAP1s. Interestingly, MAP1-2s varied independently of MAP1s such that E. ruminantium strains with similar MAP1s had diverse MAP1-2s and vice versa. Different MAP1-2s were found in individual infected sheep. Different regions of a protein may be subjected to different evolutionary forces because of recombination and/or selection, which results in those regions not agreeing with a phylogeny deduced from the whole molecule. This appears to be true for both MAP1 and MAP1-2, where statistical likelihood methods detect heterogeneous evolutionary rates for segments of both molecules. Sera from infected cattle recognized a MAP1-2 variable-region peptide in enzyme-linked immunosorbent assay, but less strongly and consistently than a MAP1 peptide (MAP1B). Heterologous protective immunity may depend on recognition of a complex set of varying OMP epitopes.