Recognition of conserved surface protein epitopes on Anaplasma centrale and Anaplasma marginale isolates from Israel, Kenya and the United States

Evidence confirming the phylogenetic position of Anaplasma centrale (ex Theiler 1911) Ristic and Kreier 1984

In 1911, Sir Arnold Theiler isolated and described a parasite that was very similar to Anaplasma marginale but which was more centrally located within the erythrocytes of the host cells, and was much less pathogenic than A. marginale. He named the parasite A. marginale variety centrale. The name Anaplasma centrale, referring to the same organism, was published in Validation List No. 15 in 1984, but the publication was based on an erroneous assumption that Theiler had indicated that it was a separate species. Many authors have subsequently accepted this organism as a separate species, but evidence to indicate that it is a distinct species has never been presented. The near full-length 16S rRNA gene sequence, and the deduced amino acid sequences for groEL and msp4 from several isolates of A. marginale and A. centrale from around South Africa were compared with those of the A. marginale type strain, St Maries, and the A. centrale Israel strain and other reference sequences. Phylogenetic analyses of these sequences demonstrated that A. centrale consistently forms a separate clade from A. marginale, supported by high bootstrap values (≥90 %), revealing that there is divergence between these two organisms. In addition, we discuss distinctive characteristics which have been published recently, such as differences in Msp1a/Msp1aS gene structure, as well as genome architecture that provide further evidence to suggest that A. centrale is, in fact, a separate species. Our results, therefore, provide evidence to support the existing nomenclature, and confirm that A. centrale (ex Theiler 1911) Ristic and Kreier 1984 is, indeed, a distinct species.

Rapid deletion of antigen-specific CD4+ T cells following infection represents a strategy of immune evasion and persistence for Anaplasma marginale

Acquired T cell immunity is central for protection against infection. However, the immunological consequences of exposing memory T cells to high Ag loads during acute and persistent infection with systemic pathogens are poorly understood. We investigated this by using infection with Anaplasma marginale, a ruminant pathogen that replicates to levels of 10(9) bacteria per ml of blood during acute infection and maintains mean bacteremia levels of 10(6) per ml during long-term persistent infection. We established that immunization-induced Ag-specific peripheral blood CD4(+) T cell responses were rapidly and permanently lost following infection. To determine whether these T cells were anergic, sequestered in the spleen, or physically deleted from peripheral blood, CD4(+) T lymphocytes from the peripheral blood specific for the major surface protein (MSP) 1a T cell epitope were enumerated by DRB3*1101 tetramer staining and FACS analysis throughout the course of immunization and challenge. Immunization induced significant epitope-specific T lymphocyte responses that rapidly declined near peak bacteremia to background levels. Concomitantly, the mean frequency of tetramer(+)CD4(+) cells decreased rapidly from 0.025% before challenge to a preimmunization level of 0.0003% of CD4(+) T cells. Low frequencies of tetramer(+)CD4(+) T cells in spleen, liver, and inguinal lymph nodes sampled 9-12 wk postchallenge were consistent with undetectable or unsustainable Ag-specific responses and the lack of T cell sequestration. Thus, infection of cattle with A. marginale leads to the rapid loss of Ag-specific T cells and immunologic memory, which may be a strategy for this pathogen to modulate the immune response and persist.

Comparison between indirect enzyme-linked immunosorbent assays for Anaplasma marginale antibodies with recombinant major surface protein 5 and initial body antigens

Indirect enzyme-linked immunosorbent assays (ELISAs) based on recombinant major surface protein 5 (rMSP5) and initial body (IB) antigens from a Brazilian isolate of Anaplasma marginale were developed to detect antibodies against this rickettsia in cattle. Both tests showed the same sensitivity (98.2%) and specificities (100% for rMSP5 and 93.8% for IB ELISA) which did not differ statistically. No cross-reactions were detected with Babesia bigemina antibodies, but 5 (rMSP5 ELISA) to 15% (IB ELISA) of cross-reactions were detected with B. bovis antibodies. However, such difference was not statistically significant. Prevalences of seropositive crossbred beef cattle raised extensively in Miranda county, state of Mato Grosso do Sul, Brazil, were 78.1% by rMSP5 ELISA and 79.7% by IB ELISA. In the analysis of sera from dairy calves naturally-infected with A. marginale, the dynamics of antibody production was very similar between both tests, with maternal antibodies reaching the lowest levels at 15-30 days, followed by an increase in the mean optical densities in both ELISAs, suggesting the development of active immunity against A. marginale. Results showed that all calves were seropositive by one-year old, characterizing a situation of enzootic stability. The similar performances of the ELISAs suggest that both tests can be used in epidemiological surveys for detection of antibodies to A. marginale in cattle.

Identification of a novel Anaplasma marginale appendage-associated protein that localizes with actin filaments during intraerythrocytic infection

The rickettsial pathogen Anaplasma marginale assembles an actin filament bundle during intracellular infection. Unlike other bacterial pathogens that generate actin filament tails, A. marginale infects mature erythrocytes, and the F-actin appendages are assembled on the cytoplasmic surface of a vacuole containing several organisms. To identify A. marginale molecules associated with these filaments, two complementary approaches were used: matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and tandem mass spectrometry of A. marginale proteins identified with an appendage-specific monoclonal antibody and expression screening of an A. marginale phage library. Amino acid and nucleotide sequences were mapped to a full-length gene in the genome of the St. Maries strain of A. marginale; the correct identification was confirmed by expression of full-length recombinant protein and its reactivity with appendage-specific antibodies. Interestingly, there is marked variation in the abilities of diverse A. marginale strains to assemble the F-actin appendages. Comparison of four strains, the Florida, Illinois, St. Maries, and Virginia strains, revealed substantial polymorphism in the gene encoding the appendage-associated protein, with amino acid sequence identity of as low as 34% among strains. However, this variation does not underlie the differences in expression, as there is no specific polymorphism associated with loss of ability to assemble actin appendages. In contrast, the ability to assemble an actin filament bundle reflected dramatic strain-specific differences in the expression level of the appendage-associated protein. Understanding how this protein influences the cycle of invasion, replication, and egress in the host cell may provide new insights into pathogen-host interactions.

Molecular conservation of MSP4 and MSP5 in Anaplasma marginale and A. centrale vaccine strain

Anaplasma centrale msp4 and msp5 genes were cloned and sequenced, and the recombinant proteins were expressed. The identity between Anaplasma marginale and A. centrale MSP4 was 83% in the nucleotide sequences and 91.7% in the encoded protein sequences. A. centrale msp5 nucleotide sequences shared 86.8% identity with A. marginale msp5, and there was 92.9% homology between A. centrale and A. marginale encoded amino acids of the MSP5 protein. Southern blots hybridized with probes derived from the msp4 and msp5 central regions indicate that msp4 and msp5 of A. centrale are encoded by single copy genes. Recombinant MSP4 and MSP5 fusion proteins reacted with anti-A. marginale monoclonal antibodies ANAR76A1 and ANAF16C, respectively, demonstrating the conservation of conformation-sensitive B-cell epitopes between A. centrale and A. marginale. These data demonstrate the structural and antigenic conservation of MSP4 and MSP5 in A. centrale and A. marginale. This conservation is consistent with the cross-protective immunity between A. marginale and A. centrale and supports the development of improved vaccines based upon common outer membrane proteins.

Transmission of Anaplasma marginale by Boophilus microplus: retention of vector competence in the absence of vector-pathogen interaction

Whether arthropod vectors retain competence for transmission of infectious agents in the long-term absence of vector-pathogen interaction is unknown. We addressed this question by quantifying the vector competence of two tick vectors, with mutually exclusive tropical- versus temperate-region distributions, for genetically distinct tropical- and temperate-region strains of the cattle pathogen Anaplasma marginale. The tropical cattle tick Boophilus microplus, which has been eradicated from the continental United States for over 60 years, was able to acquire and transmit the temperate St. Maries (Idaho) strain of A. marginale. Similarly, the temperate-region tick Dermacentor andersoni efficiently acquired and transmitted the Puerto Rico strain of A. marginale. There were no significant quantitative differences in infection rate or number of organisms per tick following feeding on cattle with persistent infections of either A. marginale strain. In contrast, the significantly enhanced replication of the Puerto Rico strain in the salivary gland of B. microplus at the time of transmission feeding is consistent with adaptation of a pathogen strain to its available vector. However, the transmission of both strains by B. microplus demonstrates that adaptation or continual interaction between the pathogen and vector is not required for retention of vector competence. Importantly, the results clearly show that reestablishment of acaricide-resistant B. microplus in the United States would be associated with A. marginale transmission.

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.

Phylogenetic analysis of the erythrocytic Anaplasma species based on 16S rDNA and GroEL (HSP60) sequences of A. marginale, A. centrale, and A. ovis and the specific detection of A. centrale vaccine strain

Phenotypic criteria for the identification of erythrocytic ruminant Anaplasma species has relied on subjective identification methods such as host pathogenicity (virulence for cattle or sheep) and/or the location of Anaplasma inclusion bodies within the host's red cells. Sequence comparisons of new and available GenBank Accessions were investigated to elucidate the relationships among these closely related Anaplasma species. Twenty-one 16S rDNA and GroEL (HSP60) sequences from 13 Anaplasma marginale (South Africa, Namibia, Zimbabwe, Israel, USA, Australia and Uruguay), three A. centrale (South Africa and Japan), two A. ovis (USA and South Africa), and two unknown Anaplasma species isolated from wild ruminants (South Africa), were compared. 16S rDNA maximum-likelihood and distance trees separated all A. marginale (and the two wild ruminant isolates) from the two South African A. centrale (including original vaccine strain, Theiler, 1911). The Japanese A. centrale (Aomori) demonstrated the lowest sequence identity to the remaining erythrocytic Anaplasma species. A. ovis inter-species relationships could not be resolved through the 16S rDNA analyses, whereas strong bootstrap branch support is demonstrated in the GroEL distance tree using A. ovis OVI strain. All erythrocytic Anaplasma species and isolates were confirmed to belong to the same cluster showing strong branch support to Anaplasma (Ehrlichia) phagocytophilum with Ehrlichia (Cowdria) ruminantium and Rickettsia rickettsii serving as appropriate out-groups. Based on groEL sequences, a specific PCR method was developed which amplified A. centrale vaccine (Theiler, 1911) specifically. This study confirms the suitability of 16S rDNA sequences to define genera and demonstrates the usefulness of GroEL sequences for defining species of erythrocytic Anaplasma.

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.

Expression of major surface protein 2 variants with conserved T-cell epitopes in Anaplasma centrale vaccinates

Major surface protein 2 (MSP-2), identified as a protection-inducing immunogen against Anaplasma marginale challenge, is an immunodominant outer membrane protein with orthologues in all examined Anaplasma species. Although immunization with live Anaplasma centrale has long been used to induce protection against acute disease upon challenge with virulent A. marginale, its MSP-2 structure and whether MSP-2 variants are generated during persistence of the vaccine strain was unknown. In this study, we showed that the A. centrale vaccine strain persisted for a minimum of 4 years postvaccination and generated sequential MSP-2 variants. Comparison of amino acid sequences encoded by A. centrale msp-2 transcripts from the initial postimmunization period and from sequential time points during persistence of the vaccine strain revealed a central hypervariable domain flanked by conserved amino and carboxy-terminal regions. This structure corresponded to that shown in A. marginale MSP-2, where the central hypervariable region encodes variant B-cell epitopes in the extracellular domain and the flanking transmembrane domains are rich in CD4(+)-T-cell epitopes. Importantly, at least four CD4(+)-T-cell epitopes are conserved between the two species, a finding consistent with A. marginale challenge triggering a recall response of CD4(+) T cells induced by A. centrale vaccination. The genomic arrangement is conserved between A. centrale and A. marginale with multiple msp-2 pseudogenes and a single operon-linked expression site for the full-length msp-2. This conservation of both genomic structure for generating MSP-2 variants and the CD4(+)-T-cell epitopes between these two genetically distinct Anaplasma species indicates that they present a similar repertoire of MSP-2 epitopes to the immune system and that this similarity may be responsible for all or part of the A. centrale vaccine efficacy.

Analysis of the 16S rRNA gene sequence of Anaplasma centrale and its phylogenetic relatedness to other ehrlichiae

The nucleotide sequence of the Anaplasma centrale 16S rRNA gene was determined and compared with the sequences of ehrlichial bacteria. The sequence of A. centrale was closely related to Anaplasma marginale by both level-of-similarity (98.08% identical) and distance analysis. A species-specific PCR was developed based upon the alignment data. The PCR can detect A. centrale DNA extracted from 10 infected bovine red blood cells in a reaction mixture. A. centrale DNA was amplified in the reaction, but not other related ehrlichial species.

Identification of antigenic differences that discriminate between cattle vaccinated with Anaplasma centrale and cattle naturally infected with Anaplasma marginale

Monoclonal antibodies were raised against the vaccine strain of Anaplasma centrale used in Australia. A monoclonal antibody that reacted with an 80 kDa antigen was used to develop an A. centrale-specific fluorescent antibody test that will be useful for confirming species identity in patent infections. Another monoclonal antibody that reacted with a 116 kDa antigen was used to develop an A. centrale-specific competitive inhibition enzyme-linked immunosorbent assay (ELISA) for the serological identification of vaccinated cattle. The sensitivity of the ELISA was 100% in cattle experimentally infected with A. centrale, 97.1% in a vaccinated beef herd and 98.3% in a vaccinated dairy herd. The specificity of the ELISA was 98.6% in non-vaccinated cattle outside the Anaplasma marginale-endemic area, 97.9% in non-vaccinated cattle within the A. marginale-endemic area and 100% in cattle experimentally infected with A. marginale. The ELISA detected antibodies to A. centrale in cattle up to 9 years after vaccination with no apparent decrease in sensitivity. The assay has proved extremely valuable in Australia for investigating reported failures of multivalent live vaccines used to protect cattle against anaplasmosis and babesiosis, and should be similarly useful elsewhere in the world where these types of vaccines are used, e.g. Israel and South America.

Highly conserved regions of the immunodominant major surface protein 2 of the genogroup II ehrlichial pathogen Anaplasma marginale are rich in naturally derived CD4+ T lymphocyte epitopes that elicit strong recall responses

Genogroup II ehrlichia, including the agent of human granulocytic ehrlichiosis, Ehrlichia phagocytophila, and the bovine pathogen Anaplasma marginale, express a markedly immunodominant outer membrane protein designated major surface protein 2 (MSP2). MSP2 is encoded by a multigene family, resulting in the expression of variant B cell epitopes. MSP2 variants are sequentially expressed in the repeated cycles of rickettsemia that characterize persistent A. marginale infection and control of each rickettsemic cycle is associated with development of a variant-specific IgG response. Importantly, these persistent rickettsemic cycles are controlled at levels 100-1000 times lower than those responsible for clinical disease during acute infection. Control of rickettsemia during persistence could result from an anamnestic Th lymphocyte response to conserved regions of MSP2 that enhances the primary Ab response against newly emergent variants. Comparison of MSP2 variants reveals conserved N and C termini flanking the central, surface-exposed hypervariable region that represents the variant B lymphocyte epitopes. We demonstrate MSP2-specific CD4(+) T lymphocyte recognition of epitopes common to several strains of A. marginale and the related pathogen A. ovis. Furthermore, T lymphocyte lines from three individuals identified six to nine overlapping peptides representing a minimum of four to seven dominant or subdominant epitopes in these conserved N and C termini. Immunodominant peptides induced high levels of IFN-gamma, a cytokine associated with protection against ehrlichia and needed for rapid generation of variant-specific IgG2. The presented data support the potential importance of a strong Th lymphocyte response to invariant MSP2 epitopes in controlling rickettsemia during persistent infection to subclinical levels.

Anaplasma marginale inactivated vaccine: dose titration against a homologous challenge

The present study was performed to dose-titrate an Anaplasma marginale experimental immunogen derived from partially purified initial bodies from three geographically different Mexican strains. Three five-bovine groups were inoculated twice on days zero and 21 with A. marginale initial bodies equivalent to 1.5 x 10(10) (group I), 3 x 10(10) (group II) or 6 x 10(10) (group III) infected erythrocytes mixed with STDCM adjuvant. A similar group served as non-vaccinated controls. All four groups were challenged with 1 x 10(8) infected erythrocytes from a donor cow with an increasing rickettsemia of strain MEX-15 on day 87 post-vaccination. The prepatent period was very similar for all four groups. All five non-vaccinated controls presented typical acute anaplasmosis syndrome reaching a mean of 30.9% rickettsemia and a loss of 73.4% in the packed cell volume (PCV). Two of five controls died of acute anaplasmosis. Within the vaccinated groups only one animal (group II) suffered acute disease and died. Although all the other vaccinated animals were free of clinical signs, they developed very low rickettsemias (3.2, 3.8 and 4.3%) and PCV losses of 49.9, 47.8, and 49.3% for groups I, II and III. The starting mean weight was very similar for all four groups. All animals lost weight following challenge but losses for groups I and II were lower and significantly different from group IV losses (P < or = 0.1). Although there were no significant differences among vaccinated groups, group III was more severely affected. Taken altogether, these results show a 93.3% protection against both illness and death for all groups; and 100% protection for groups I and III, and 80% for group II.

Biased immunoglobulin G1 isotype responses induced in cattle with DNA expressing msp1a of Anaplasma marginale

Immunization with the native major surface protein 1 (MSP1) (a heterodimer containing disulfide and noncovalently bonded polypeptides designated MSP1a and MSP1b) of the erythrocytic stage of Anaplasma marginale conferred protection against homologous challenge (G. H. Palmer, A. F. Barbet, W. C. Davis, and T. C. McGuire, Science 231:1299-1302, 1986). The MSP1a polypeptide possesses a conserved neutralization-sensitive epitope. In the present study, the immune response to DNA-mediated immunization using msp1a was studied. The plasmid pVCL/MSP1a, which encodes the complete msp1a gene of A. marginale under the control of human cytomegalovirus immediate-early enhancer/promoter and intron A, was constructed. The immune responses elicited by immunization with pVCL/MSP1a into cardiotoxin-induced regenerating muscle were evaluated in mice and cattle. Antibody reactive with native MSP1a was detected in pooled sera of immunized BALB/c mice 3 weeks following primary immunization. Two calves seronegative for A. marginale were immunized four times, at weeks 0, 3, 7, and 13, with pVCL/MSP1a. By 8 weeks, both calves responded to MSP1a with an antibody titer of 1:100, which peaked at 1:1,600 and 1:800 by 16 weeks after the initial immunization. Interestingly, immunoblotting with anti-immunoglobulin G1 (anti-IgG1) and anti-IgG2 specific monoclonal antibodies revealed a restricted IgG1 anti-MSP1a response in both animals. T-lymphocyte lines, established after the fourth immunization, proliferated specifically against A. marginale homogenate and purified MSP1 in a dose-dependent manner. These data provide a basis for an immunization strategy to direct bovine immune responses by using DNA vaccine vectors containing single or multiple genes encoding major surface proteins of A. marginale.

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

Protective immunity against the ehrlichial pathogen Anaplasma marginale has been hypothesized to require induction of immunoglobulin G2 (IgG2) antibody against outer membrane protein epitopes and coordinated activation of macrophages for phagocytosis and killing. In the present study, cell-mediated immune responses, including induction of IgG isotype switching, were characterized in calves immunized with purified outer membranes of the Florida strain of A. marginale. Importantly, these calves were subsequently shown to be protected upon experimental challenge with the Florida strain, and calves which developed the highest IgG2 titers were completely protected against infection. Peripheral blood mononuclear cells (PBMC) obtained after immunization proliferated strongly in response to both whole A. marginale homogenates and purified outer membranes, and this responsiveness persisted until the time of challenge. Responding cells were shown to be CD4(+) T cells, and CD4(+) T-cell lines cultured for 2 to 4 weeks also proliferated specifically in response to A. marginale and produced high titers of gamma interferon. The helper T-cell response included recognition of conserved epitopes, as PBMC proliferation was stimulated by the homologous Florida strain, four genetically distinct A. marginale strains, and Anaplasma ovis. The outer membrane proteins stimulating the PBMC responses in protected calves included major surface proteins (MSPs) MSP-1, MSP-2, and MSP-3, which were previously shown to induce partial protection against infection. These studies demonstrate, for the first time, potent helper T-cell responses in cattle protectively immunized with outer membranes against A. marginale challenge and identify three MSPs that are recognized by immune T cells. These experiments provide the basis for subsequent identification of the helper T-cell epitopes on MSP-1, MSP-2, and MSP-3 that are needed to evoke anamnestic antibody and effector T-cell responses elicited by protein or nucleic acid immunization.

The repertoire of Anaplasma marginale antigens recognized by CD4(+) T-lymphocyte clones from protectively immunized cattle is diverse and includes major surface protein 2 (MSP-2) and MSP-3

Major surface proteins of Anaplasma marginale are vaccine candidates. We recently demonstrated that immunization of calves with outer membranes of the Florida strain of A. marginale resulted in protective immunity that correlated with a memory CD4(+) T-lymphocyte response specific for major surface protein 1 (MSP-1), MSP-2, and MSP-3 (W. C. Brown, V. Shkap, D. Zhu, T. C. McGuire, W. Tuo, T. F. McElwain, and G. H. Palmer, Infect. Immun. 66:5406-5413, 1998). As immunogens, these proteins have been shown to induce complete or partial protection against homologous challenge. To further define the T helper (Th) cell response to these and other A. marginale antigens and to determine conservation of Th cell epitopes among genetically distinct A. marginale strains, Th cell clones obtained prior to challenge from three immunized calves were characterized for antigen-specific responses. Nine distinct antigenic profiles were defined by 11 Th cell clones derived by stimulation with the Florida strain. Several clones responded to MSP-2, MSP-3, or both. All of these MSP-2- or MSP-3-specific clones and the majority of other clones that did not respond to MSPs recognized all bovine blood-passaged strains of A. marginale. These results demonstrate conservation of certain Th cell epitopes between MSP-2 and MSP-3 and show that Th cell epitopes in MSP-2, MSP-3, and undefined antigens are conserved among strains of A. marginale. Of seven clones that responded to the blood-passaged Virginia strain, two did not recognize antigen prepared from this strain cultured in tick cells, suggesting differences in the antigenic composition between these stages. Analysis of the cytokines expressed by the Th cells revealed that all clones expressed gamma interferon and tumor necrosis factor alpha, and most coexpressed interleukin-4. Our results provide a rationale for identifying Th cell epitopes conserved among different strains of A. marginale for inclusion in a nucleic acid or recombinant protein vaccine.

Construction and initial analysis of a representative lambda ZAPII expression library of the intracellular rickettsia Cowdria ruminantium: cloning of map1 and three other Cowdria genes

The causative agent of heartwater, the rickettsia Cowdria ruminantium, is very poorly understood at the molecular level owing to a profound lack of suitable tools. We have developed an immunoaffinity chromatographic method to purify C. ruminantium from host cell components and the purified rickettsial cells have been used to prepare substantially pure Cowdria DNA. This DNA has been used to construct what we believe to be the first fully representative C. ruminantium expression library. A clone containing the complete Cowdria map1 gene has been isolated and sequenced. This gene has been expressed in E. coli cells from the native Cowdria promoter, suggesting that the mechanisms for gene transcription and translation are similar between these two organisms. Parts of three other Cowdria genes have also been isolated and sequenced.

Prospects for subunit vaccines against tick-borne diseases

Tick-borne parasites are a serious impediment to the improvement of live-stock production in the developing world. The major parasites affecting cattle include Theileria parva, T. annulata, Babesia bigemina, B. bovis, Anaplasma marginale and Cowdria ruminantium. The control of these infections is dependent on the use of acaricides to decrease transmission by the tick vectors, and immunization of susceptible animals with live vaccines. The use of acaricide is hampered by the development of resistance, and live vaccines require cold chain facilities, which are generally unreliable in developing countries. There is therefore a need for improved vaccines that can circumvent these problems. There is a subunit vaccine being developed for T. parva based on the major surface antigen of the sporozoite (p67). A similar antigen, SPAG 1, has been identified as a candidate for T. annulata. Although several candidate antigens have been identified for Babesia spp., progress towards development of a subunit vaccine based on these antigens has been hampered by polymorphism among isolates and between species, and lack of knowledge of the immune effector mechanisms responsible for protection. The search for protective antigens of A. marginale has focused on outer membrane proteins; immunization with a variety of these antigens alone or in combination, has yielded promising results. As with Babesia, further definition of immune effector mechanisms is needed to optimize immunization strategies. The work on identifying the protective antigens of C. ruminantium is in its embryonic stages; however, two antigens have been identified and are currently being evaluated. There is high expectancy for subunit vaccines for all these diseases; however there is need for further work to elucidate the immune mechanisms in order to select appropriate antigen delivery systems.

Preliminary studies on the effect of Anaplasma marginale antibodies ingested by Dermacentor andersoni ticks (Acari:Ixodidae) with their blood meal on infections in salivary glands

The effect of Anaplasma marginale antibodies ingested with the tick blood meal was tested on infected male ticks that were allowed to feed on cattle immunized with the erythrocytic stage of A. marginale. The experiments were done in two trials. Trial 1 was done using splenectomized calves (two calves per treated and control groups) while ticks in trial 2 were fed on intact yearling cattle (four cattle per treated and control groups). The cattle were immunized with purified outer membrane proteins of erythrocyte-derived A. marginale using saponin (trial 1) or monophosphoryl lipid-A-trehalose dicorynomycolate adjuvant (trial 2). The corresponding control cattle received adjuvant only. All cattle were challenged using Dermacentor andersoni males infected as adults that were allowed to feed for 7 days. In trial 1, the ticks were allowed to feed a second time on susceptible calves to test whether exposure of ticks to immunized cattle affected their ability to transmit anaplasmosis. Infections in fed ticks were monitored by determining the infection rates in salivary glands with an A. marginale-specific RNA probe and light microscopy. Vaccine-derived antibodies ingested with the tick blood meal did not appear to affect the development of A. marginale in previously infected ticks. The infection rates in the salivary glands were not significantly different among ticks fed on immunized versus adjuvant control cattle. When the vaccine-exposed ticks in trial 1 were allowed to feed a second time on susceptible calves, the resulting clinical symptoms of anaplasmosis were similar to those of the controls. There was no statistically significant effect of tick exposure to the anti-erythrocytic stage antibody on the development of salivary gland infection or transmission of A. marginale by ticks.

Evaluation of Anaplasma marginale major surface protein 3 (MSP3) as a diagnostic test antigen

An immunodominant surface protein, major surface protein 3 (MSP3), has been proposed as an antigen suitable for use in the diagnosis of bovine anaplasmosis. We further characterized MSP3 to examine its potential as a test antigen for the serological diagnosis of carrier cattle. The specificity of this antigen in detecting infected cattle as well as the conservation of MSP3 between strains of Anaplasma marginale was evaluated by using immunoblots of A. marginale proteins separated by one- and two-dimensional polyacrylamide gel electrophoreses. Immune sera from animals infected with Anaplasma ovis, Ehrlichia risticii, and Ehrlichia ewingii reacted with the MSP3 antigen of A. marginale. One-dimensional gel electrophoresis of A. marginale proteins demonstrated size polymorphism of MSP3 between different geographic isolates. Two-dimensional gel electrophoresis revealed at least three different antigens migrating at the 86-kDa molecular size, and sera from animals infected with different strains of A. marginale reacted with different 86-kDa antigens. These results indicate that MSP3 may share cross-reactive epitopes with antigens found in A. ovis and some Ehrlichia spp. In addition, MSP3 is not conserved between different isolates of A. marginale, and at least in the isolate from Florida, what was previously identified as MSP3 is actually a group of three or more 86-kDa antigens with different isoelectric points. The cross-reactivity of MSP3 with some Ehrlichia spp., the variability of MSP3 between isolates, and the multiple 86-kDa antigens recognized by various sera suggest that MSP3 is not a suitable candidate for use as a recombinant test antigen.

Development of conventional subunit vaccines for anaplasmosis and babesiosis

Tick-borne hemoparasitic diseases of cattle continue to impact the beef industry throughout a large portion of the world. A substantial amount of research is currently focused on development of improved vaccines. The two main approaches being followed are: (1) use of conventional inactivated or native protein subunit vaccines, and (2) development of recombinant DNA technology for expression of selected immunogens. Recombinant or synthetic peptide based vaccines hold promise owing to the exquisitely defined nature of the product. However, the development is long-term, and will require extensive testing and risk assessment before field trials can be considered. Until then, more conventional subunit immunogens may offer an attractive alternative, and can be defined immunologically better than before. This paper reviews progress in the development of improved vaccines for anaplasmosis and babesiosis with an emphasis on the characterization of culture-derived babesial exoantigens. Both in vitro and in vivo information is presented.

Live vaccines against hemoparasitic diseases in livestock

Live vaccines against hemoparasitic diseases in livestock are based on parasites derived from culture (Theileria annulata), from blood of infected animals (Babesia bovis, Babesia bigemina, Anaplasma centrale, (attenuated) Anaplasma marginale and Cowdria ruminantium), and from ticks (Theileria parva). The T. annulata attenuated cultured schizont vaccine is safe for all varieties of cattle. Blood derived vaccines are recommended mainly for young cattle, the age limit varying with the different vaccines and breeds of cattle. In older animals, monitoring of the individual response is needed. Immunization against T. parva requires simultaneous or postinoculation chemotherapy. The potential for accidental transmission of disease agents exists with all blood derived vaccines. Various degrees of resistance to field infection have been reported in animals immunized with live vaccines. Nevertheless, all of them engender a level of protection against natural challenge that justifies their use in field vaccination. Chemotherapy or chemoprophylaxis may prevent establishment of infection with the vaccinal parasites, and thus may interfere with elaboration of immunity. Outbreaks of disease in vaccinated herds, caused by antigenic variants among the tick-transmitted parasites, have been observed mainly in Babesia infections. In recent years, the main efforts towards improvement of live vaccines have been in the direction of replacing blood- and tick-derived parasites by those cultured in vitro under controlled standardized conditions.

Detection of Anaplasma ovis infection in goats by major surface protein 5 competitive inhibition enzyme-linked immunosorbent assay

A competitive inhibition enzyme-linked immunosorbent assay (ELISA) based on a major surface protein 5 (MSP5) B-cell epitope conserved among Anaplasma species was used to detect goats infected with Anaplasma ovis. We examined strains of A. ovis isolated from goats in Kenya and demonstrated that MSP5 and the target B-cell epitope, bound by monoclonal antibody ANAF16C1, were conserved. Sera from 149 goats in four regions of Kenya and from 302 goats in six U.S. states were tested for the presence of epitope-specific antibodies with the MSP5 competitive inhibition ELISA. Evidence that the assay can be used to detect A. ovis-infected goats includes the following: (i) 53 goats raised in confinement with arthropod control were all seronegative; (ii) six goats experimentally infected with A. ovis seroconverted at the same time that they developed detectable rickettsemia; (iii) seroconverted goats remained seropositive, consistent with the persistence of A. ovis in goats and the presence of anti-MSP5 antibody in cattle persistently infected with Anaplasma marginale; and (iv) 119 of 127 known A. ovis-infected goats in Kenya were seropositive. A. ovis infection, as determined serologically and by demonstration of infected erythrocytes, in goats from the four regions in Kenya was highly prevalent. In contrast, despite the presence of A. ovis and competent arthropod vectors in the United States, the prevalence of infection appeared to be very low. The high prevalence in Kenya and the occurrence of anemia in persistently infected goats may be impediments to current efforts to increase milk yields on small farms.

Molecular basis for vaccine development against anaplasmosis and babesiosis

Immunization of livestock against the erythroparasitic pathogens Anaplasma marginale, Babesia bigemina, and Babesia bovis with safe and effective killed vaccines is not yet feasible on a practical basis. However, the immune protection afforded by recovery from natural infection and premunition indicates that microbial epitopes capable of inducing immunity exist and that the bovine immune system can be primed appropriately. Induction of protection by immunization with killed parasite fractions, enriched for polypeptides with surface exposed epitopes, supports a focus on surface epitopes, including apical complex organellar epitopes in Babesia, for vaccine development. Cloning, sequencing, and expression of genes encoding these key surface polypeptides has allowed examination of polypeptide function and detailed analysis of epitope conservation in light of genetic polymorphism. In this paper, the characterization of these polypeptides at the epitope level and their roles in inducing protective immunity are reviewed. Definition of these epitopes, in combination with improved understanding of immune mechanisms, provides the basis for development of effective recombinant vaccines against anaplasmosis and babesiosis.

Putative adhesins of Anaplasma marginale: major surface polypeptides 1a and 1b

Genes for the MSP1a and MSP1b subunits of the Anaplasma marginale surface antigen complex MSP1 were previously cloned and expressed in Escherichia coli. We report here the localization of MSP1a and MSP1b polypeptides on the surface of recombinant E. coli by using a live cell indirect immunofluorescent antibody assay. Recombinant E. coli cells expressing the msp1 alpha gene or the msp1 beta gene encoding the MSP1a and MSP1b polypeptide subunits, respectively, were shown by a culture recovery adhesion assay and by direct microscopic examination to specifically adhere to bovine erythrocytes. This adhesion was more than additive when both genes were coexpressed in a single recombinant construct. Similarly, these recombinants hemagglutinated bovine erythrocytes in a microtiter hemagglutination assay. Inhibition of recombinant E. coli adhesion to bovine erythrocytes and hemagglutination inhibition were observed in the presence of homologous monospecific polyclonal antiserum raised against purified MSP1a or MSP1b polypeptide. These data suggest that the MSP1a and MSP1b polypeptides have functions as adhesins on A. marginale initial bodies, probably during erythrocyte invasion.

Molecular and biological characterization of a newly isolated Anaplasma marginale strain

Anaplasma marginale, a rickettsial hemoparasite of cattle and other ruminants, results in significant economic losses worldwide. Distinct strains of A. marginale have been identified based on differences in tick transmissibility, molecular size of surface proteins and DNA restriction fragments, and reactivity to a panel of monoclonal antibodies. These different strains vary considerably in their virulence, antigenic composition, and ability to protect against heterologous challenge. In this paper, we report on the molecular characterization of a newly isolated strain of A. marginale, designated St. Maries, recovered from an acutely infected cow in northern Idaho. Dermacentor andersoni ticks taken from the infected animal were tested for infection by RNA probe analysis. The infection rate of male ticks (as determined by midgut infection) was 100%, and the infection rate of female ticks was 83%. Infected male ticks were able to transmit the St. Maries strain to a susceptible calf. The high infection rate in male ticks may be particularly relevant, given that male ticks are believed to be epidemiologically important in transmission of A. marginale because of their intermittent feeding behavior, which promotes interhost transfer. The newly isolated strain differs from other US strains, including strains previously isolated in Idaho and Washington, based on reactivity to a panel of monoclonal antibodies and restriction fragment length polymorphisms. These results imply that antigenically distinct strains of A. marginale may arise within the same region.(ABSTRACT TRUNCATED AT 250 WORDS)

The immunoprotective Anaplasma marginale major surface protein 2 is encoded by a polymorphic multigene family

An Anaplasma marginale Florida msp-2 gene was cloned and expressed in Escherichia coli. Pulsed-field gel electrophoresis and Southern blot analysis revealed the presence of multiple msp-2 gene copies that were widely distributed throughout the chromosomes of all three strains examined. Genomic polymorphism among copies was greatest in the 5' end of msp-2 but also occurred in 3' regions. The presence of gene-copy-specific epitopes was indicated by the reactivity of the cloned msp-2 copy with some, but not all, monoclonal antibodies that bound native MSP-2. Multiple antigenically distinct MSP-2 molecules were expressed within strains and were coexpressed by individual A. marginale organisms. These results suggest that expression of polymorphic msp-2 gene copies is responsible for the significant percentages of A. marginale organisms within strains that do not react with individual anti-MSP-2 monoclonal antibodies. Sequence analysis revealed highly significant MSP-2 homology with two rickettsial surface proteins, A. marginale MSP-4 and Cowdria ruminantium MAP-1. Immunization with MSP-4 has been shown to induce protective immunity in a manner similar to that of immunization with MSP-2. These findings support the hypothesis that A. marginale surface proteins are targets of protective immune responses but are antigenically polymorphic.

Heterologous strain challenge of cattle immunized with Anaplasma marginale outer membranes

In this study, we tested the hypothesis that outer membrane immunization would induce protection against an antigenically variant strain. Outer membranes were isolated from the Virginia strain of Anaplasma marginale using density gradient centrifugation, combined with saponin adjuvant, and used to immunize Friesian cattle in Zimbabwe. Immunized cattle developed high antibody titers (80,000-160,000) against outer membrane polypeptides including MSP-2 and MSP-5 in both the homologous Virginia and heterologous Zimbabwe strains. Outer membrane immunized cattle were protected significantly following challenge with 10(4) Zimbabwe strain parasitized erythrocytes, demonstrated by significant differences in prepatent period and peak rickettsemia compared with adjuvant immunized control cattle. One outer membrane immunized animal was completely protected against infection. However, there were no overall significant differences in severity of anemia between cattle immunized with outer membrane and the control group, indicating that a significant reduction in rickettsemia does not necessarily result in less severe anemia.

Recombinant vaccinia virus expression of Anaplasma marginale surface protein MSP-1a: effect of promoters, leader sequences and GPI anchor sequence on antibody response

Anaplasma marginale surface protein MSP-1a was expressed by recombinant vaccinia viruses with different promoters and as hybrid proteins. Transcription of msp1 alpha with P11 late promoter resulted in more MSP-1a than with P7.5 early-late promoter; however, mice immunized with the recombinants had similar antibody titres. Recombinants expressing hybrid MSP-1a with either a murine leukaemia virus or a trypanosomal glycoprotein signal sequence did not enhance antibody responses and resulted in a diffuse intracellular distribution of MSP-1a which did not accumulate in the Golgi apparatus as was noted in the absence of these signal sequences. In contrast, antibody titres to MSP-1a in mice immunized with a recombinant virus expressing hybrid MSP-1a with a trypanosomal GPI anchor signal sequence were significantly increased over all other constructs.

Antigenic profile of a pure isolate of Anaplasma marginale of Brazilian origin, using a western blot technique

Anaplasma marginale initial bodies of the Brazilian isolate AUFV1 were purified from infected erythrocytes using a combination of lysis, ultrasonic disruption and differential centrifugation. Initial bodies were solubilised with a buffer containing protease inhibitors and non-ionic detergents. Immunochemical analysis by the Western blot technique revealed at least five proteins with apparent molecular weights (MW) of 105, 100, 97, 87 and 38 kDa when homologous sera were used as primary antibodies. Sera from cattle from Mato Grosso do Sul State in Brazil revealed five proteins of 105, 100, 87, 38 and 25 kDa; other heterologous sera obtained from Illinois, USA, bound to four antigens with MW of 105, 100, 87 and 38 kDa, the latter being stronger and broader than the others. No bands were observed in the non-infected erythrocyte control when the different A. marginale sera or antibodies against Babesia bovis and Babesia bigemina were used. Antibodies from cattle infected with the A. marginale isolates bound to proteins of 105, 100, 87 and 38 kDa, indicating that there are at least four peptides common to the isolates. The major surface proteins, designated MSP-1, MSP-2 and MSP-3, are also present in the Brazilian isolate AUFV1 and the sample from the National Research Centre of Beef Cattle in Mato Grosso do Sul State. One practical consideration of this study is the possibility of cross-protection between different Anaplasma isolates including some from Brazil.

Opsonization of Anaplasma marginale mediated by bovine antibody against surface protein MSP-1

Antibody from cattle immunized with purified major surface protein-1 (MSP-1) was demonstrated to significantly enhance phagocytosis of Florida strain Anaplasma marginale by bovine macrophages in vitro. Serum immunoglobulin from individual MSP-1 immunized, protected cattle varied in ability to promote phagocytosis, however all sera were significantly opsonic as compared with sera from sham immunized control cattle.

The Anaplasma marginale msp5 gene encodes a 19-kilodalton protein conserved in all recognized Anaplasma species

Immunization with Anaplasma marginale outer membranes induced immunity against clinical disease which correlated with antibody titer to outer membrane proteins, including a 19-kDa protein (N. Tebele, T. C. McGuire, and G. H. Palmer, Infect. Immun. 59:3199-3204, 1991). This 19-kDa protein, designated major surface protein 5 (MSP-5), was encoded by a single-copy 633-bp gene. The molecular mass of MSP-5, defined in immunoblots by binding to monoclonal antibody ANAF16C1, was conserved among all recognized species of Anaplasma: A. marginale, A. centrale, and A. ovis. Recombinant MSP-5, which absorbed the antibody reactivity of bovine immune serum to native MSP-5, was recognized by anti-A. marginale and anti-A. centrale immune sera in a competitive inhibition assay with monoclonal antibody ANAF16C1. The presence of antibody to the epitope defined by monoclonal antibody ANAF16C1 in all postinfection sera tested indicates that this epitope is a potential diagnostic antigen for use in identifying persistently infected cattle.

Anaplasmosis in Uganda. I. Use of dried blood on filter paper and serum samples for serodiagnosis of anaplasmosis--a comparative study

The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the Complement Fixation Test (CFT), DOT-ELISA, Western immunoblot and Rapid Card Agglutination Test (RCAT). Dried blood on Whatman filter paper no. 1 was eluted in 1.8 ml of PBS 0.05% Tween 20 given an initial dilution of 1:100. The reactivity in both DOT-ELISA and Western immunoblotting was similar to that obtained with the sera diluted 1:100. Filter paper samples gave lower reactivity in all the tests as compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at room temperature and those stored at 4 degrees C. Storage at room temperature did not significantly affect reactivity for up to 6 months. Eluates from filter papers stored for 6 months at room temperature continued to give similar reactivity to those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the Rapid Card Agglutination Test. It is concluded that collecting blood on filter papers is a suitable technique for large-scale screening and for seroepidemiological studies on anaplasmosis, and offers many advantages especially in developing countries where transport and cold chain facilities are a major constraint.

Anaplasmosis in Uganda. I. Use of dried blood on filter papers and serum samples for serodiagnosis of anaplasmosis--a comparative study

The suitability of blood collected on filter papers in comparison with corresponding conventional serum samples in the diagnosis of bovine anaplasmosis was studied using the complement fixation test, DOT-ELISA, Western immunoblot and rapid card agglutination test. Dried blood on Whatman filter paper no. 1 was eluted in PBS 0.05% Tween 20 giving an initial dilution of 1:10. The reactivity of the eluted samples in both DOT-ELISA and Western immunoblotting were similar to those obtained with the corresponding straight serum sample dilutions. Filter paper samples gave lower reactivity in the remaining tests when compared with corresponding serum samples. There was no significant difference in the reactivity between the eluates from filter papers stored at temperatures ranging between 15.5 and 24 degrees C and those kept refrigerated. Storage at 15.5 to 24 degrees C did not significantly affect reactivity for up to six months. Eluates from filter papers stored for six months at 15.5 to 24 degrees C continued to give similar reactivity as those from freshly prepared filter papers in both DOT-ELISA and Western blot, and in the rapid card agglutination test. It is concluded that collecting blood on filter papers is a suitable technique for large scale seroepidemiological studies on anaplasmosis and offers many advantages in developing countries where transport and cold chain facilities are a major constraint.

Crossprotective immunity between the Florida and a Zimbabwe stock of Anaplasma marginale

Cattle immunised by infection with the Florida stock of Anaplasma marginale were protected against subsequent homologous challenge, as demonstrated by complete prevention of microscopically detectable parasitaemia. Identically immunised cattle were partially protected against challenge with the Norton, Zimbabwe stock of A. marginale as determined by the significant prolongation of the prepatent period, a significantly lower peak parasitaemia, and a significantly lower percentage drop in haemoglobin concentration when compared to non-immunised calves challenged identically. The partial protection induced by live Florida stock immunisation demonstrates that while protection-inducing epitopes are shared between the two stocks, induction of complete immunity against a Zimbabwe stock may require alternative presentation of Florida stock epitopes or inclusion of additional Zimbabwe stock epitopes in the immunogen.

Induction of protective immunity by using Anaplasma marginale initial body membranes

Anaplasma marginale initial bodies of the Norton Zimbabwe strain were disrupted and separated into two membrane fractions banding at 1.15 and 1.22 g/cm3 by sucrose density centrifugation. The membrane fractions differed in their morphology and polypeptide composition. Membranes banding at 1.22 g/cm3 shared epitopes with surface-exposed polypeptides of the Florida strain of A. marginale, confirming the outer membrane location of these polypeptides. Immunization of cattle with either membrane fraction induced protection against homologous challenge, as demonstrated by significantly less anemia and lower peak rickettsemia values compared with those of adjuvant-immunized and nonimmunized calves. Protection correlated with antibody titer to membrane polypeptides. Although both membrane fractions induced protection, a 31-kDa polypeptide was the only common antigen to both fractions, as shown by reactivity of immune sera. Identification of membrane antigens capable of inducing protective immunity should facilitate development of vaccines against anaplasmosis suitable for use in Zimbabwe.

Identification of immunodominant polypeptides common between Anaplasma centrale and Anaplasma marginale

High titered antibody from rabbits immunized with Anaplasma centrale or from cattle recovered from A. centrale infection bound predominantly to several 33-36 kDa polypeptides present in both A. centrale and the Israel-NT isolate of Anaplasma marginale. High titered bovine antibody against the Israel-NT isolate of A. marginale also reacted predominantly with A. centrale polypeptides in this size range. The immunodominance of the 33-36 kDa polypeptides and their cross-reactivity indicate that these shared epitopes may be primarily responsible for the cross-protective immunity between A. centrale and A. marginale.

Detection of Anaplasma marginale rickettsemia prior to onset of clinical signs by using an antigen capture enzyme-linked immunosorbent assay

An antigen capture enzyme-linked immunosorbent assay was developed by using monoclonal antibodies to conserved epitopes on the Anaplasma marginale MSP1a surface protein. The assay sensitivity was 1.1 (+/- 0.5)% parasitized erythrocytes, and all infected cattle were detected prior to development of 2.0%-parasitized erythrocytes. Positive tests preceded the onset of anemia by a mean of 2 days. The assay was specific for anaplasmosis, as demonstrated by nonreactivity with another common hemoparasitic pathogens.

Efficacy of purified Anaplasma marginale initial bodies as a vaccine against anaplasmosis

Anaplasma marginale initial bodies of the Florida strain were purified from infected erythrocytes using a combination of ultrasonic disruption, nonionic detergent and differential centrifugation. Immunochemical analysis revealed at least 12 A. marginale proteins in the molecular mass (m) range 81-15 kDa with a prominent band at 38 kDa. Several of these proteins remained insoluble in the presence of nonionic detergent. Preparations of purified Anaplasma initial bodies contained negligible erythrocytic contamination, as confirmed by the minimal induction of isoantibodies against bovine blood group antigens and the absence of delayed-type hypersensitivity to erythrocytic antigens in immunized animals. A total of 33 crossbred and purebred Holstein cattle were vaccinated with either 1.5, 1.0, or 0.1 mg protein of intact initial bodies, or with 1.0 mg of solubilized Anaplasma protein. The immunogens were supplemented with 3.0 mg Quil-A saponin adjuvant and administered in 2 subcutaneous injections given at a 4-week interval. A similar number of nonvaccinated cattle served as controls. Three months after vaccination, all cattle were challenged by inoculation of 10(9) virulent A. marginale of either the homologous (Florida) or heterologous (Venezuelan) strains. Vaccinated cattle showed solid protection after homologous and heterologous challenge, characterized by parasite clearance and minimal hematocrit reductions. Initial data from four field vaccine trials revealed a reduced incidence of clinical anaplasmosis among immunized animals. Use of immunogens consisting of purified A. marginale initial bodies offers a potential immunoprophylactic approach to control of bovine anaplasmosis.

Molecular basis for surface antigen size polymorphisms and conservation of a neutralization-sensitive epitope in Anaplasma marginale

Anaplasmosis is one of several tick-borne diseases severely constraining cattle production and usage in many parts of the world. Cattle can be protected from anaplasmosis by immunization with major surface protein 1, a surface protein of Anaplasma marginale carrying a neutralization-sensitive epitope. Marked size polymorphisms exist among different isolates of A. marginale in the AmF105 subunit of major surface protein 1, yet all isolates still contain the neutralization-sensitive epitope. To clarify the basis for these observations, the mspl alpha gene encoding AmF105 was cloned from four isolates and sequenced. The encoded polypeptides share a high degree of overall homology between isolates but contain a domain with various numbers of tandemly repeated sequences and three regions of clustered amino acid substitutions outside the repeat domain. The polypeptide size differences are completely explained by the variations in the numbers of tandem repeat units. We have mapped the neutralization-sensitive epitope to a sequence that is present within each repeat unit. These results identify a basis for size polymorphisms of the surface polypeptide antigen concomitant with B-cell epitope conservation in rickettsiae.

Cyclic rickettsemia during persistent Anaplasma marginale infection of cattle

Submicroscopic levels of Anaplasma marginale rickettsemia in persistently infected cattle were determined by using nucleic acid hybridization. Within individuals, the rickettsemia levels steadily increased from less than 10(4) infected erythrocytes per ml to a peak of more than 10(6) infected erythrocytes per ml and then rapidly declined. This logarithmic variation parallels the variation of the rickettsemia level seen in acute infection and suggests that cyclic emergence of antigenic variants is a mechanism of rickettsial persistence.

Present and future possibilities for the control of cowdriosis and anaplasmosis

Cowdriosis and anaplasmosis are most important tick-borne rickettsial diseases of ruminants. After a short introduction, in particular of their aetiology, epidemiology and diagnosis, present methods and future prospects for their control are briefly reviewed. The value and disadvantages of the four possible approaches, chemotherapy, tick control, the utilisation of inverse age-resistance in order to attain endemic stability, and artificial immunisation, are reviewed. Promising future developments in the field of immunisation are indicated.

Immunization of cattle with the MSP-1 surface protein complex induces protection against a structurally variant Anaplasma marginale isolate

The Anaplasma marginale surface protein complex MSP-1 of the Florida isolate is composed of a 105-kilodalton (kDa) polypeptide, which bears a neutralization-sensitive epitope, and a 100-kDa polypeptide. Antigenically similar polypeptides in the Okanogan, Wash. (Washington-O), isolate MSP-1 are 86 and 100 kDa, respectively. Immunization of cattle with Florida isolate MSP-1 induced antibody titers to both MSP-1 polypeptides and protected cattle against homologous and heterologous challenge.

Identification of an immunodominant antigenically conserved 32-kilodalton protein from Cowdria ruminantium

Western blotting (immunoblotting) of Cowdria ruminantium antigens with goat or mouse antiserum identified a periodate-resistant, proteinase K-sensitive immunodominant antigen of 32,000 daltons. This protein, designated Cr32, could be demonstrated in goat choroid plexus infected with one of two different Cowdria stocks. Antisera against nine different Cowdria stocks from Africa and the Caribbean region recognized Cr32, which indicates that this protein contains conserved antigenic determinants.

Molecular size variations in an immunoprotective protein complex among isolates of Anaplasma marginale

A major surface protein complex from the Florida isolate of Anaplasma marginale has been previously shown to induce protection in immunized cattle and has been proposed as the basis of a subunit vaccine against anaplasmosis. This complex in the Florida isolate is composed of two noncovalently associated polypeptides with molecular masses of 105 and 100 kilodaltons (kDa). The analogous protein complex from four geographically different isolates of A. marginale was immunoprecipitated and compared with the protein complex of the Florida isolate. The polypeptides of the complex varied in apparent molecular mass among the isolates. By using antibodies recognizing epitopes on each polypeptide of the Florida isolate, the antigenic identity of the polypeptides in the analogous complexes was determined. The polypeptides recognized by the neutralizing monoclonal antibody 22B1, which recognizes a 105-kDa polypeptide in the Florida isolate, ranged from 70 to 100 kDa in the other isolates. Those polypeptides recognized by rabbit antiserum R911, which recognizes a 100-kDa polypeptide in the Florida isolate, ranged from 97 to 100 kDa. The surface-exposed peptides in the complexes were compared by limited enzymatic digestion to assess structural homology among isolates. Despite the marked variations in molecular weight, there were conserved peptides between the 22B1-reactive polypeptides and between the R911-reactive peptides. Determination of the role of the conserved peptides in inducing immunity will be critical in the application of these polypeptides as the basis of a subunit vaccine for bovine anaplasmosis.

Immunization of cattle with a 36-kilodalton surface protein induces protection against homologous and heterologous Anaplasma marginale challenge

Immunization of cattle with a purified Anaplasma marginale major surface protein, AmF36, induced protection against homologous challenge with the Florida isolate. Similarly, immunized cattle were protected from challenge with the antigenically and structurally distinct Washington-O isolate of A. marginale. The degree of protection in AmF36-immunized cattle varied from complete prevention of rickettsemia to significant delay in the onset of rickettsemia compared with control immunized cattle. A single AmF36 vaccinate was not protected against homologous challenge despite development of a strong antibody response. Immunoprecipitation of A. marginale proteins with a monoclonal antibody to AmF36 identified minor molecular size heterogeneity in this protein from different isolates, including the Florida and Washington-O isolates. The apparent molecular size of this surface protein in the Florida isolate was 36 kilodaltons, whereas the analogous proteins in Washington-O and four other isolates of A. marginale from the United States had molecular masses of 33 to 34 kilodaltons. Significantly, the surface-exposed peptides of these proteins appear to be conserved among the different isolates. These results demonstrate the potential of AmF36 as a subunit immunogen for bovine anaplasmosis and indicate a structural basis for its cross-protective ability.