Expression of polymorphic msp1beta genes during acute anaplasma Marginale rickettsemia

Molecular characterization of Anaplasma marginale based on the msp1a and msp1b genes

Anaplasma marginale is an intracellular rickettsial bacterium causing anaplasmosis in ruminants. A. marginale is transmitted biologically by ticks and mechanically by blood-sucking vectors. Anaplasmosis occurs in tropical and subtropical areas of the world. This disease causes huge economic losses due to decreasing meat yield and milk production. The aims of this study were to determine the genetic diversity and antigenicity of A. marginale based on the msp1a and msp1b genes in cattle in Thailand. The A. marginale msp1a and msp1b genes were amplified by the polymerase chain reaction (PCR). There have been four copies of MSP1a tandem repeats among A. marginale Thailand strain, and thirteen different MSP1a tandem repeats were found including repeats B, 25, 27, M, 3, S, C, H, β, 80, 4, TH1 and TH2. Notably, this study showed two copies of the novel conserved tandem sequences namely Thailand Type 1 (TH1) and Type 2 (TH2). The phylogenetic analysis revealed that A. marginale msp1a and msp1b genes were genetically diverse and showed 9 and 5 clades with similarity ranging from 98 to 100% and 79.5 to 100%, respectively, when compared within the isolates of this study. The results of diversity analysis showed 18 and 16 haplotypes of the msp1a and msp1b genes, respectively. The entropy analyses of msp1a and msp1b nucleic acid sequences showed 39 and 900 high entropy peaks with values ranging from 0.35 to 0.85 and from 0.41 to 1.48, respectively, while those of MSP1a and MSP1b amino acid sequences exhibited 75 and 72 high entropy peaks with values ranging from 0.35 to 1.06 and from 0.41 to 1.55, respectively. In addition, B-cell and T-cell epitopes have also been investigated in this study. Hence, our results could be employed to improve the insight input of molecular phylogenetics, genetic diversity and antigenicity of A. marginale Thailand strain.

Molecular evidence of the reservoir competence of water buffalo (Bubalus bubalis) for Anaplasma marginale in Cuba

Water buffalo (Bubalus bubalis) is a potential reservoir for Anaplasma marginale in livestock ecosystems of tropical countries. However, their participation in the epidemiological process of bovine anaplasmosis in endemic areas remains unclear. In the present study, the reservoir competence of water buffalo for A. marginale was explored by focusing on the analysis of rickettsemia levels in carrier animals, and the genetic characterization of A. marginale strains from cattle and buffalo. Eight groups of cattle and water buffaloes were randomly selected from cohabiting herds in four livestock ecosystems of Cuba, together with two control groups from unrelated cattle and buffalo herds. A total of 180 adult animals (88 water buffalo and 92 cattle) were sampled. Rickettsemia in carrier animals was determined by quantitative real-time PCR. The rickettsemia (parasitemia) levels in cattle were higher than in buffaloes, however the rickettsemia in buffalo may be enough to infect R. microplus ticks. The genetic diversity of A. marginale was assessed by strain characterization and phylogenetic analysis of 27 msp1α gene sequences. The results showed genetic similarity among strains from cattle and water buffalo, suggesting the occurrence of cross-species transmission.

Characterization of recombinant MSP5 Anaplasma marginale Havana isolate

Anaplasma marginale is the causative agent of bovine anaplasmosis, a disease of worldwide economic importance. Major surface proteins (MSPs) are involved in host-pathogen and tick-pathogen interactions and they have been used as markers for the genetic characterization of A. marginale strains and phylogenetic studies. The major surface protein 5 (MSP5) is highly conserved in the genus Anaplasma and in all isolates of A. marginale. The aim of the present work was to carry out the cloning, sequencing and characterization of the recombinant MSP5 Anaplasma marginale Havana isolate. The sequence of the msp5 gene of Anaplasma marginale Havana isolate with a size of 633 pb was determined (Acc. No. AY527217). This gene was cloned into pRSETB vector and expressed in Escherichia coli. The MSP5 protein was recognized by the monoclonal antibody ANAF16C1 and it showed a high similitude percent with the gene sequence described for other Anaplasma marginale isolates. These data are very important for the development of a diagnostic test for A. marginale using the MSP5 recombinant protein.

Immune response of BALB/c mouse immunized with recombinant MSPs proteins of Anaplasma marginale binding to immunostimulant complex (ISCOM)

Anaplasmosis, caused by Anaplasma marginale, results in significant economic losses of cattle in tropical and subtropical regions worldwide. Six major surface proteins (MSPs) were well characterized and designated as MSP1, MSP2, MSP3, MSP4, and MSP5. The objective of this study was to evaluate the humoral immune response of BALB/c mice against the recombinant MSPs, incorporated into immunostimulating complex (ISCOM). The recombinant proteins purified by Ni-NTA columns were incorporated into ISCOM and ISCOMATRIX by the lipid film hydration method. BALB/c mice immunized with ISCOM/rMSPs and ISCOMATRIX/rMSPs vaccines produced whole IgG, IgG1, and IgG2a, in contrast to the negative groups (PBS and ISCOMATRIX adjuvant). All groups that received antigen responded specifically against the rMSPs by Western blotting, showing the rMSP1a (60-105kDa), rMSP1b (100kDa), rMSP4 (47kDa), and rMSP5 (29kDa). Additional studies will have to be performed in cattle to evaluate the humoral and cellular mechanisms of this subunit vaccine and their possible use as protective vaccines against homologous and heterologous strains of A. marginale.

Applications of a cell culture system for studying the interaction ofAnaplasmamarginale with tick cells

A cell culture system for the tick-borne rickettsiaAnaplasma marginaleoffers new opportunities for research on this economically important pathogen of cattle.A. marginalemultiplies in membrane-bound inclusions in host cells. Whereas erythrocytes appear to be the only site of infection in cattle,A. marginaleundergoes a complex developmental cycle in ticks and transmission occurs via the salivary glands during feeding. We recently developed a cell culture system forA. marginaleusing a cell line derived from embryos ofIxodes scapularis. Here we review the use of this cell culture system for studying the interaction ofA. marginalewith tick cells. Several assays were developed using theA. marginale/tick cell system. An adhesion assay was developed for the identification of proteins required byA. marginalefor adhesion to tick cells. The effect of antibodies against selected major surface proteins in inhibitingA. marginaleinfection was tested in an assay that allowed further confirmation of the role of surface proteins in the infection of tick cells. A drug screening assay forA. marginalewas developed and provides a method of initial drug selection without the use of cattle. The culture system was used to test for enhancing effects of tick saliva and saliva components onA. marginaleinfection. The tick cell culture system has proved to be a good model for studyingA. marginale–tick interactions. Information gained from these studies may be applicable to other closely related tick-borne pathogens that have been propagated in the same tick cell line.

Evolution and function of tandem repeats in the major surface protein 1a of the ehrlichial pathogenAnaplasma marginale

The major surface protein (MSP) 1a of the ehrlichial cattle pathogenAnaplasma marginale, encoded by the single-copy genemsp1α, has been shown to have a neutralization-sensitive epitope and to be an adhesin for bovine erythrocytes and tick cells.msp1αhas been found to be a stable genetic marker for the identification of geographic isolates ofA. marginalethroughout development in acutely and persistently infected cattle and in ticks. The molecular weight of MSP1a varies among geographic isolates ofA. marginalebecause of a varying number of tandemly repeated peptides of 28–29 amino acids. Variation in the sequence of the tandem repeats occurs within and among isolates, and may have resulted from evolutionary pressures exerted by ligand–receptor and host–parasite interactions. These repeated sequences include markers for tick transmissibility that may be important in the identification of ehrlichial pathogens because they may influence control strategies and the design of subunit vaccines.

Analysis of the Anaplasma marginale major surface protein 1 complex protein composition by tandem mass spectrometry

The protective major surface protein 1 (MSP1) complex of Anaplasma marginale is a heteromer of MSP1a and MSP1b, encoded by a multigene family. The msp1beta sequences were highly conserved throughout infection. However, liquid chromatography-tandem mass spectrometry analysis identified only a single MSP1b protein, MSP1b1, within the MSP1 complex.

Genetic diversity of anaplasma species major surface proteins and implications for anaplasmosis serodiagnosis and vaccine development

The genus Anaplasma (Rickettsiales: Anaplasmataceae) includes several pathogens of veterinary and human medical importance. An understanding of the diversity of Anaplasma major surface proteins (MSPs), including those MSPs that modulate infection, development of persistent infections, and transmission of pathogens by ticks, is derived in part, by characterization and phylogenetic analyses of geographic strains. Information concerning the genetic diversity of Anaplasma spp. MSPs will likely influence the development of serodiagnostic assays and vaccine strategies for the control of anaplasmosis.

Anaplasma marginale(Rickettsiales: Anaplasmataceae): recent advances in defining host–pathogen adaptations of a tick-borne rickettsia

The tick-borne intracellular pathogenAnaplasma marginale(Rickettsiales: Anaplasmataceae) develops persistent infections in cattle and tick hosts. While erythrocytes appear to be the only site of infection in cattle,A. marginaleundergoes a complex developmental cycle in ticks and transmission occurs via salivary glands during feeding. Many geographic isolates occur that vary in genotype, antigenic composition, morphology and infectivity for ticks. In this chapter we review recent research on the host–vector–pathogen interactions ofA. marginale. Major surface proteins (MSPs) play a crucial role in the interaction ofA. marginalewith host cells. The MSP1a protein, which is an adhesin for bovine erythrocytes and tick cells, is differentially regulated and affects infection and transmission ofA. marginalebyDermacentorspp. ticks. MSP2 undergoes antigenic variation and selection in cattle and ticks, and contributes to the maintenance of persistent infections. Phylogenetic studies ofA. marginalegeographic isolates usingmsp4andmsp1α provide information about the biogeography and evolution ofA. marginale:msp1α genotypes evolve under positive selection pressure. Isolates ofA. marginaleare maintained by independent transmission events and a mechanism of infection exclusion in cattle and ticks allows for only the infection of one isolate per animal. Prospects for development of control strategies by use of pathogen and tick-derived antigens are discussed. TheA. marginale/vector/host studies described herein could serve as a model for research on other tick-borne rickettsiae.

Immunization of bovines using a DNA vaccine (pcDNA3.1/MSP1b) prepared from the Jaboticabal strain of Anaplasma marginale

Anaplasma is a tick-borne ehrlichial pathogen of cattle that causes the disease, anaplasmosis. In the present study, a total of 11 Anaplasma marginale seronegative calves were assigned into two groups: one immunized (G1, n = 6) and one nonimmunized-control (G2, n = 5). Six calves were immunized by using a DNA vaccine containing the gene of a major surface protein, MSP1b, encoded by the plasmid identified as pcDNA3.1/MSP1b. Calves received three intramuscular inoculations of 100 microg of pcDNA3.1/MSP1b at a 20-day interval. The control group received buffer phosphate at the same schedule as the experimental group. The immune response elicited by immunization with pcDNA3.1/MSP1b was evaluated in mice and calves. Twenty days following initial immunization, specific serum antibody from four BALB/c mice bound MSP1b in immunoblots. Sixty days after the last immunization, all calves were challenged with cryopreserved A. marginale at a dose of 10(4) parasites/mL/animal by intravenous injection. Results of packed cell volume (PCV) and detection of infected erythrocytes in all experimental groups revealed that the decrease of PCV and detection of infected erythrocytes occurred at 28 to 42 days after challenge. Mean temperature values did not increase over 39.85 degrees C. Antibodies developed by immunized bovines from G2 were detected 14 days after challenge. MSP1b was characterized during the immunization period and MSP2 was the most predominant polypeptide at the challenge period. DNA of A. marginale was detected in all groups just after challenge by nested PCR assay. It can be concluded that all immunized bovines were partially protected against homologous challenge.

Glycosylation of Anaplasma marginale major surface protein 1a and its putative role in adhesion to tick cells

Anaplasma marginale, the causative agent of bovine anaplasmosis, is a tick-borne rickettsial pathogen of cattle that multiplies in erythrocytes and tick cells. Major surface protein 1a (MSP1a) and MSP1b form the MSP1 complex of A. marginale, which is involved in adhesion of the pathogen to host cells. In this study we tested the hypothesis that MSP1a and MSP1b were glycosylated, because the observed molecular weights of both proteins were greater than the deduced molecular masses. We further hypothesized that the glycosylation of MSP1a plays a role in adhesion of A. marginale to tick cells. Native and Escherichia coli-derived recombinant MSP1a and MSP1b proteins were shown by gas chromatography to be glycosylated and to contain neutral sugars. Glycosylation of MSP1a appeared to be mainly O-linked to Ser/Thr residues in the N-terminal repeated peptides. Glycosylation may play a role in adhesion of A. marginale to tick cells because chemical deglycosylation of MSP1a significantly reduced its adhesive properties. Although the MSP1a polypeptide backbone alone was adherent to tick cell extract, the glycans in the N-terminal repeats appeared to enhance binding and may cooperatively interact with one or more surface molecules on host cells. These results demonstrated that MSP1a and MSP1b are glycosylated and suggest that the glycosylation of MSP1a plays a role in the adhesion of A. marginale to tick cells.

Antigens and alternatives for control of Anaplasma marginale infection in cattle

Anaplasmosis, a tick-borne cattle disease caused by the rickettsia Anaplasma marginale, is endemic in tropical and subtropical areas of the world. The disease causes considerable economic loss to both the dairy and beef industries worldwide. Analyses of 16S rRNA, groESL, and surface proteins have resulted in the recent reclassification of the order Rickettsiales. The genus Anaplasma, of which A. marginale is the type species, now also includes A. bovis, A. platys, and A. phagocytophilum, which were previously known as Ehrlichia bovis, E. platys, and the E. phagocytophila group (which causes human granulocytic ehrlichiosis), respectively. Live and killed vaccines have been used for control of anaplasmosis, and both types of vaccines have advantages and disadvantages. These vaccines have been effective in preventing clinical anaplasmosis in cattle but have not blocked A. marginale infection. Thus, persistently infected cattle serve as a reservoir of infective blood for both mechanical transmission and infection of ticks. Advances in biochemical, immunologic, and molecular technologies during the last decade have been applied to research of A. marginale and related organisms. The recent development of a cell culture system for A. marginale provides a potential source of antigen for the development of improved killed and live vaccines, and the availability of cell culture-derived antigen would eliminate the use of cattle in vaccine production. Increased knowledge of A. marginale antigen repertoires and an improved understanding of bovine cellular and humoral immune responses to A. marginale, combined with the new technologies, should contribute to the development of more effective vaccines for control and prevention of anaplasmosis.

Antigenic characterization of Brazilian isolates of Anaplasma marginale

Antigenic characterization of Anaplasma marginale isolates, by identifying conserved and variable epitopes of major surface proteins (MSP), is an important tool for vaccine development against this rickettsia. The B cell epitopes of A. marginale isolates from three microregions of the State of Pernambuco and one from the State of Mato Grosso do Sul, Brazil, were characterized by indirect fluorescent antibody technique (IFAT) and Western blot (WB) with 15 monoclonal antibodies (MAbs). The epitope recognized by MAb ANA22B1 (MSP-1a) was conserved by IFAT and WB (73-81 kDa). MSP-2 epitopes recognized by MAbs ANAO58A2 and ANAO70A2 were conserved by IFAT, while ANAO50A2 and ANA66A2 epitopes were polymorphic; in the WB, the MAbs ANAO50A2 and ANAO70A2 identified bands of 45 kDa only in the Pernambuco-Mata isolate. None of the isolates reacted with MAb ANAR75C2 (MSP-3). The MSP-4 epitope recognized by MAb ANAR76A1 was conserved by IFAT, as well as the MSP-5 epitope recognized by MAb ANAF16C1 by IFAT and WB (16 kDa). The MAbs ANAR17A6, ANAR83B3, ANAR94C1, ANAO24D5 and ANAR19A6 identified conserved epitopes by IFAT. MSP-1, MSP-2 and MSP-4, which previously showed partial protection in experimental trials, are also potential immunogens to be employed in Brazil, due to the B cell epitope conservation.

Antibodies to Anaplasma marginale major surface proteins 1a and 1b inhibit infectivity for cultured tick cells

Major surface protein 1 (MSP1) of the cattle pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae) is a complex of two proteins, MSP1a and MSP1b. Previous studies demonstrated that MSP1a and MSP1b are adhesins for bovine erythrocytes, while only MSP1a proved to be an adhesin for tick cells. In this study, a tick cell culture system for propagation of A. marginale was used to develop an infection inhibition assay for testing the ability of antisera to block infection of A. marginale for cultured tick cells. A. marginale derived from cell culture was incubated with various antisera prior to inoculation onto cell monolayers. The monolayers were harvested 7 days post-inoculation and A. marginale in the cultures was quantified using an antigen detection ELISA. Antisera tested in the infection inhibition assay were derived from persistently infected cattle, from cattle immunized with A. marginale purified from bovine erythrocytes, and from rabbits and cattle that were immunized with the recombinant MSP1a, MSP1b and MSP1 complex. Antibodies from cattle persistently infected with A. marginale, cattle immunized with A. marginale from bovine erythrocytes or cattle immunized with the recombinant MSP1 complex did not inhibit the infectivity of A. marginale for tick cells. Antiserum from rabbits immunized with MSP1a and MSP1b (individually or combined) reduced infection of both the Virginia and Oklahoma isolates of A. marginale for tick cells by 25-70%. Likewise, antisera from cattle immunized with recombinant MSP1a or MSP1b inhibited infection of tick cells by 26-37%. These results further confirm the role of MSP1 complex proteins in infection of tick cells. Lack of inhibition of infection by antisera from naturally infected cattle or cattle immunized with whole organisms suggests that the bovine immune response is not directed toward blocking infection of A. marginale for tick cells and may contribute to the continued infectivity of the pathogen for ticks.

Vaccination of cattle with Anaplasma marginale derived from tick cell culture and bovine erythrocytes followed by challenge-exposure with infected ticks

Anaplasmosis, a hemolytic disease of cattle caused by the tick-borne pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae) has been controlled using killed vaccines made with antigen harvested from infected bovine erythrocytes. We recently developed a cell culture system for propagation of A. marginale in a continuous tick cell line. In this study, we performed a cattle trial to compare the bovine response to vaccination with A. marginale harvested from tick cell culture or bovine erythrocytes. All immunized and control cattle were then challenge-exposed by allowing male Dermacentor variabilis infected with A. marginale to feed and transmit the pathogen. Nine yearling cattle (three per group) were used for this study and were immunized with cell culture-derived A. marginale, erythrocyte-derived A. marginale or received adjuvant only to serve as controls. Each vaccine dose contained approximately 2 x 10(10) A. marginale and three immunizations were administered at weeks 1, 4 and 6. At week 8, cattle were challenge-exposed by allowing 60 D. variabilis male that were infected with A. marginale as adults to feed on the cattle. Antibody responses of cattle against major surface proteins (MSP) 1a, 1b and 5, as determined by ELISAs, peaked 2 weeks after the last immunization. Cattle immunized with infected IDE8 cell-derived antigens had a preferential recognition for MSP1b while cattle immunized with erythrocyte-derived antigens had a preferential recognition for MSP1a. Protection efficacy was evaluated using the percent infected erythrocytes (PPE), the packed cell volume (PCV), and the prepatent period. A. marginale-immunized cattle showed lower PPE and higher PCV values when compared to control animals and did not display clinical anaplasmosis. The cell culture-derived A. marginale shows promise for use as antigen in development of a new killed vaccine for anaplasmosis.

Major histocompatibility complex class II DR-restricted memory CD4(+) T lymphocytes recognize conserved immunodominant epitopes of Anaplasma marginale major surface protein 1a

Native major surface protein 1 (MSP1) of Anaplasma marginale, composed of covalently associated MSP1a and MSP1b proteins, stimulates protective immunity in cattle against homologous and heterologous strain challenge. Protective immunity against pathogens in the family Anaplasmataceae involves both CD4(+) T cells and neutralizing immunoglobulin G. Thus, an effective vaccine should contain both CD4(+) T- and B-lymphocyte epitopes that will elicit strong memory responses upon infection with homologous and heterologous strains. Previous studies demonstrated that the predominant CD4(+) T-cell response in MSP1 vaccinates is directed against the MSP1a subunit. The present study was designed to identify conserved CD4(+) T-cell epitopes in MSP1a presented by a broadly represented subset of major histocompatibility complex (MHC) class II molecules that would be suitable for inclusion in a recombinant vaccine. Transmembrane protein prediction analysis of MSP1a from the Virginia strain revealed a large hydrophilic domain (HD), extending from amino acids (aa) 1 to 366, and a hydrophobic region extending from aa 367 to 593. The N terminus (aa 1 to 67) includes one 28-aa form A repeat and one 29-aa form B repeat, which each contain an antibody neutralization-sensitive epitope [Q(E)ASTSS]. In MSP1 vaccinates, recombinant MSP1a HD (aa 1 to 366) stimulated recall proliferative responses that were comparable to those against whole MSP1a excluding the repeat region (aa 68 to 593). Peptide mapping determined a minimum of five conserved epitopes in aa 151 to 359 that stimulated CD4(+) T cells from cattle expressing DR-DQ haplotypes common in Holstein-Friesian breeds. Peptides representing three epitopes (aa 231 to 266, aa 270 to 279, and aa 290 to 319) were stimulatory for CD4(+) T-cell clones and restricted by DR. A DQ-restricted CD4(+) T-cell epitope, present in the N-terminal form B repeat (VSSQSDQASTSSQLG), was also mapped using T-cell clones from one vaccinate. Although form B repeat-specific T cells did not recognize the form A repeat peptide (VSSQS_EASTSSQLG), induction of T-cell anergy by this peptide was ruled out. The presence of multiple CD4(+) T-cell epitopes in the MSP1a HD, in addition to the neutralization-sensitive epitope, supports the testing of this immunogen for induction of protective immunity against A. marginale challenge.

Antigenic characterization of Anaplasma marginale isolates from different regions of Brazil

Antigenic characterization of A. marginale isolates has contributed to identifying the presence of common and restricts epitopes of major surface proteins (MSPs). The data may improve vaccine development to protect against A. marginale isolates from different regions. Brazilian A. marginale isolates were characterized antigenically by Western blot with monoclonal antibodies (MAbs) against MSPs and rabbit anti-MSP-4 from Florida strain. Six A. marginale isolates from MS, MG (AUFV1), SP, PR-L1, PR-HV, RS and Florida strain were tested with ANA22B1 to MSP-1a, AMR36A6 to MSP-1b, ANAF19E2 to MSP-2, AMG75C1 and AMG76B2 to MSP-3 and ANAF16C1 to MSP-5. ANA22B1 recognized MSP-1a epitope in all A. marginale isolates, and reacted with polypeptides of different size ranging 46-105kDa. MSP2 was not detected in MS and SP isolates by ANAF19E2, and only PR-L1 and MG (AUFV1) isolates reacted with MAbs which recognize MSP3 epitope. MSP4 and MSP5 were detected in all A. marginale isolates analyzed. The results revealed conservation of MSP-1a and MSP-5 epitopes among all Brazilian isolates, and showed antigenic variability to MSP-1b, MSP-2 and MSP-3 proteins, agreeing with recent data about the genetic diversity found in the polimorphic multigene family responsible for these proteins.

Conservation of major surface protein 1 genes of Anaplasma marginale during cyclic transmission between ticks and cattle

Bovine anaplasmosis is a rickettsial disease of world-wide economic importance caused by Anaplasma marginale. Several major surface proteins with conserved gene sequences have been examined as potential candidates for vaccines and/or diagnostic assays. Major surface protein 1 (MSP1) is composed of polypeptides MSP1a and MSP1b. MSP1a is expressed from the single copy gene msp1 alpha and MSP1b is expressed by members of the msp1 beta multigene family. In order to determine if the msp1 genes are conserved, primers specific for msp1 alpha, msp1 beta(1), and msp1 beta(2) genes were synthesized and used to amplify msp1 sequences of A. marginale from tick cell cultures, from cattle during acute and chronic infections and from salivary glands of Dermacentor variabilis. Protein sequences of MSP1a, MSP1b(1) and MSP1b(2) were conserved during the life cycle of the parasite. No amino acid changes were observed in MSP1a. However, small variations were observed in the MSP1b(1) and MSP1b(2) protein sequences, which could be attributed to recombination, selection for sub-populations of A. marginale in the vertebrate host and/or PCR errors. Several isolate-specific sequences were also observed. Based on the information obtained in this study, the MSP1 protein appears to be fairly well conserved and a potential vaccine candidate.

Specific expression of Anaplasma marginale major surface protein 2 salivary gland variants occurs in the midgut and is an early event during tick transmission

Infectivity of Anaplasma spp. develops when infected ticks feed on a mammalian host (transmission feed). Specific Anaplasma marginale major surface protein 2 (MSP2) variants are selected for within the tick and are expressed within the salivary glands. The aims of this study were to determine when and where MSP2 variant selection occurs in the tick, how MSP2 expression is regulated in salivary glands of transmission-feeding ticks, and whether the number of A. marginale organisms per salivary gland is significantly increased during transmission feeding. The South Idaho strain of A. marginale was used, as MSP2 expression is restricted to two variants, SGV1 and SGV2, in Dermacentor andersoni. Using Western blot, real-time PCR, and DNA sequencing analyses it was shown that restriction and expression of MSP2 occurs early in the midgut within the first 48 h of the blood meal, when ticks acquire infection. A. marginale is present in the tick salivary glands before transmission feeding is initiated, but the msp2 mRNA and MSP2 protein levels per A. marginale organism increase only minimally and transiently in salivary glands of transmission-feeding ticks compared to that of unfed ticks. A. marginale numbers per tick increase gradually in salivary glands of both transmission-fed and unfed ticks. It is concluded that MSP2 variant selection is an early event in the tick and that MSP2 variants SGV1 and SGV2 are expressed both in the midgut and salivary glands. While MSP2 may be required for infectivity, there is no strict temporal correlation between MSP2 expression and the development of infectivity.

Adaptations of the tick-borne pathogen, Anaplasma marginale, for survival in cattle and ticks

The tick-borne cattle pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae) multiplies within membrane-bound inclusions in host cell cytoplasm. Many geographic isolates of A. marginale occur that vary in genotype, antigenic composition, morphology and infectivity for ticks. A tick cell culture system for propagation of A. marginale proved to be a good model for study of tick-pathogen interactions. Six major surface proteins (MSPs) identified on A. marginale from bovine erythrocytes were conserved on A. marginale derived from tick cells. MSP1a and MSP1b were adhesins for bovine erythrocytes, while only MSP1a was bound to be an adhesin for tick cells. The tandemly repeated portion of MSP1a was found to be necessary and sufficient for adhesion to both tick cells and bovine erythrocytes. Infectivity of A. marginale isolates for ticks was dependent on the adhesive capacity of the isolate MSP1a, which was found to involve both the adhesive properties and sequence of the repeated peptides. Cattle immunized with A. marginale derived from bovine erythrocytes or tick cells demonstrated a differential antibody response to MSP1a and MSP1b that resulted from the differential expression of these proteins in cattle and ticks cells. MSP2, derived from a multigene family, was found to undergo antigenic variation in cattle and ticks and may contribute to establishment of persistent A. marginale infections. MSP1a has been used as a stable genetic marker for geographic isolates because the molecular weight varies due to differing numbers of the tandem repeats. However, phylogenetic studies of A. marginale isolates from North America using MSP1a and MSP4 demonstrated that MSP4 was a good biogeographic marker, while MSP1a varied greatly among and within geographic areas. Infection and development of A. marginale in cattle and tick cells appears to differ and to be mediated by several surface proteins encoded from the small genome.

Immunization of cattle with Anaplasma marginale derived from tick cell culture

Anaplasmosis is a hemolytic disease of cattle caused by the ehrlichial tick-borne pathogen Anaplasma marginale. Killed vaccines used for control of anaplasmosis in the US used antigen harvested from infected bovine erythrocytes which was often contaminated with bovine cells and other pathogens. In this study, we performed an initial cattle trial to test A. marginale harvested from tick cell culture as an immunogen for cattle. Eleven yearling Holstein cattle were immunized with the cell culture-derived A. marginale and 11 cattle were non-immunized contact controls. Each vaccine dose contained approximately 2 x 10(10) A. marginale in an oil-based adjuvant. Two immunizations were administered subcutaneously 4 weeks apart and the cattle were challenge-exposed 10 weeks after the second immunization with A. marginale infected blood. Maximum antibody levels as determined by an A. marginale specific competitive ELISA were observed 2 weeks after the last immunization. Antibody responses against major surface proteins (MSPs) 1a and 1beta1 were also characterized and immunized cattle demonstrated a preferential recognition for MSP1beta1. Cattle immunized with the cell culture-derived A. marginale had a significantly lower percent reduction in the packed cell volume (P<0.05) after challenge exposure as compared with the controls and did not display clinical anaplasmosis. The cell culture-derived A. marginale shows promise for use as antigen in development of a new killed vaccine for anaplasmosis.

Major surface protein 1a effects tick infection and transmission of Anaplasma marginale

Anaplasma marginale, an ehrlichial pathogen of cattle and wild ruminants, is transmitted biologically by ticks. A developmental cycle of A. marginale occurs in a tick that begins in gut cells followed by infection of salivary glands, which are the site of transmission to cattle. Geographic isolates of A. marginale vary in their ability to be transmitted by ticks. In these experiments we studied transmission of two recent field isolates of A. marginale, an Oklahoma isolate from Wetumka, OK, and a Florida isolate from Okeechobee, FL, by two populations of Dermacentor variabilis males obtained from the same regions. The Florida and Oklahoma tick populations transmitted the Oklahoma isolate, while both tick populations failed to transmit the Florida isolate. Gut and salivary gland infections of A. marginale, as determined by quantitative PCR and microscopy, were detected in ticks exposed to the Oklahoma isolate, while these tissues were not infected in ticks exposed to the Florida isolate. An adhesion-recovery assay was used to study adhesion of the A. marginale major surface protein (MSP) 1a to gut cells from both tick populations and cultured tick cells. We demonstrated that recombinant Escherichia coli expressing Oklahoma MSP1a adhered to cultured and native D. variabilis gut cells, while recombinant E. coli expressing the Florida MSP1a were not adherent to either tick cell population. The MSP1a of the Florida isolate of A. marginale, therefore, was unable to mediate attachment to tick gut cells, thus inhibiting salivary gland infection and transmission to cattle. This is the first report of MSP1a being responsible for effecting infection and transmission of A. marginale by Dermacentor spp. ticks. The mechanism of tick infection and transmission of A. marginale is important in formulating control strategies and development of improved vaccines for anaplasmosis.

CD4(+) T lymphocytes from calves immunized with Anaplasma marginale major surface protein 1 (MSP1), a heteromeric complex of MSP1a and MSP1b, preferentially recognize the MSP1a carboxyl terminus that is conserved among strains

Native major surface protein 1 (MSP1) of the ehrlichial pathogen Anaplasma marginale induces protective immunity in calves challenged with homologous and heterologous strains. MSP1 is a heteromeric complex of a single MSP1a protein covalently associated with MSP1b polypeptides, of which at least two (designated MSP1F1 and MSP1F3) in the Florida strain are expressed. Immunization with recombinant MSP1a and MSP1b alone or in combination fails to provide protection. The protective immunity in calves immunized with native MSP1 is associated with the development of opsonizing and neutralizing antibodies, but CD4(+) T-lymphocyte responses have not been evaluated. CD4(+) T lymphocytes participate in protective immunity to ehrlichial pathogens through production of gamma interferon (IFN-gamma), which promotes switching to high-affinity immunoglobulin G (IgG) and activation of phagocytic cells to produce nitric oxide. Thus, an effective vaccine for A. marginale and related organisms should contain both T- and B-lymphocyte epitopes that induce a strong memory response that can be recalled upon challenge with homologous and heterologous strains. This study was designed to determine the relative contributions of MSP1a and MSP1b proteins, which contain both variant and conserved amino acid sequences, in stimulating memory CD4(+) T-lymphocyte responses in calves immunized with native MSP1. Peripheral blood mononuclear cells and CD4(+) T-cell lines from MSP1-immunized calves proliferated vigorously in response to the immunizing strain (Florida) and heterologous strains of A. marginale. The conserved MSP1-specific response was preferentially directed to the carboxyl-terminal region of MSP1a, which stimulated high levels of IFN-gamma production by CD4(+) T cells. In contrast, there was either weak or no recognition of MSP1b proteins. Paradoxically, all calves developed high titers of IgG antibodies to both MSP1a and MSP1b polypeptides. These findings suggest that in calves immunized with MSP1 heteromeric complex, MSP1a-specific T lymphocytes may provide help to MSP1b-specific B lymphocytes. The data provide a basis for determining whether selected MSP1a CD4(+) T-lymphocyte epitopes and selected MSP1a and MSP1b B-lymphocyte epitopes presented on the same molecule can stimulate a protective immune response.

Molecular phylogeny and biogeography of North American isolates of Anaplasma marginale (Rickettsiaceae: Ehrlichieae)

Anaplasma marginale (A. marginale) is a tick-borne ehrlichial pathogen of cattle that causes the disease anaplasmosis. Six major surface proteins (MSPs) have been identified on A. marginale from cattle and ticks of which three, MSP1a, MSP4 and MSP5, are from single genes and do not vary within isolates. The other three, MSP1b, MSP2 and MSP3, are from multigene families and may vary antigenically in persistently infected cattle. Several geographic isolates have been identified in the United States which differ in morphology, protein sequence and antigenic properties. An identifying characteristic of A. marginale isolates is the molecular weight of MSP1a which varies in size among isolates due to different numbers of tandemly repeated 28-29 amino acid peptides. For these studies, genes coding for A. marginale MSP1a and MSP4, msp1alpha and msp4, respectively, from nine North American isolates were sequenced for phylogenetic analysis. The phylogenetic analysis strongly supports the existence of a south-eastern clade of A. marginale comprised of Virginia and Florida isolates. Analysis of 16S rDNA fragment sequences from the A. marginale tick vector, Dermacentor variabilis, from various areas of the United States was used to evaluate possible vector-parasite co-evolution. Our phylogenetic analysis supports identity between the most parsimonious tree from the A. marginale MSP gene data and the tree that reflected the western and eastern clades of D. variabilis. These phylogenetic analyses provide information that may be important to consider when developing control strategies for anaplasmosis in the United States.

Strain composition of the ehrlichia Anaplasma marginale within persistently infected cattle, a mammalian reservoir for tick transmission

Tick-borne ehrlichial pathogens of animals and humans require a mammalian reservoir of infection from which ticks acquire the organism for subsequent transmission. In the present study, we examined the strain structure of Anaplasma marginale, a genogroup II ehrlichial pathogen, in both an acute outbreak and in persistently infected cattle that serve as a reservoir for tick transmission. Using the msp1alpha genotype as a stable strain marker, only a single genotype was detected in a disease outbreak in a previously uninfected herd. In contrast, a diverse set of genotypes was detected in a persistently infected reservoir herd within a region where A. marginale is endemic. Genotypic diversity did not appear to be rapidly generated within an individual animal, because only a single genotype, identical to that of the inoculating strain, was detected at time points up to 2 years after experimental infection, and only a single identical genotype was found in repeat sampling of individual naturally infected cattle. Similarly, only a single genotype, identical to that of the experimentally inoculated St. Maries or South Idaho strain, was identified in the bloodmeal taken by Dermacentor andersoni ticks, in the midgut and salivary glands of the infected ticks, and in the blood of acutely infected cattle following tick transmission. The results show that mammalian reservoirs harbor genetically heterogeneous A. marginale and suggest that different genotypes are maintained by transmission within the reservoir population.