<i>Ehrlichia ruminantium</i>
            Major Antigenic Protein Gene (
            <i>map1</i>
            ) Variants Are Not Geographically Constrained and Show No Evidence of Having Evolved under Positive Selection Pressure

Allsopp, M. T. E. P.; Dorfling, Cecelia M.; Maillard, J. C.; Bensaid, Albert; Haydon, Daniel T.; Heerden, Henriëtte van; Allsopp, B. A.

doi:10.1128/jcm.39.11.4200-4203.2001

Cited by 46 publications

(42 citation statements)

References 19 publications

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“…Indeed, the map1 gene of E. ruminantium has been reported to exhibit a high degree of sequence polymorphism (Reddy et al 1996;Allsopp et al 2001), whereas the lack of amplification by pCS20 primers (AB128/AB129 primers, Mahan et al 1992) could be attributed to the design of these primers in a comparatively less conserved region of the pCS20 sequence (Van Heerden et al 2004). Similar findings were also reported in a recent study (Allsopp et al 2007), in which the pCS20 PCR failed to give amplicons from ticks from which E. ruminantium 16S sequences were obtained; this finding was attributed to the presence of polymorphisms in one or both of the pCS20 nested amplification primer target sites thus preventing effective hybridization and chain extension.…”

Section: Discussionmentioning

confidence: 99%

“…The three different assays used primers that amplified different gene or nucleotide sequence targets in E. ruminantium, which have varying levels of sequence conservation. For example, the pCS20 assay primers amplified open reading frame 2 of unknown function of the 1,306-bp pCS20 sequence, the map1 assay primers amplified the nucleotide sequence of major antigenic protein 1 gene that belongs to a map1 multigene family that codes for an antigenic outer-membrane protein of E. ruminantium (MAP1); this map1 gene is present in all isolates of E. ruminantium originating from different geographic regions (van Vliet et al 1994;Allsopp et al 2001). The RLB primers amplified the 16S rRNA gene; this gene is widely used for bacterial characterisation (Olsen et al 1986).…”

Section: Discussionmentioning

confidence: 99%

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Molecular detection of Ehrlichia ruminantium infection in Amblyomma variegatum ticks in The Gambia

et al. 2007

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In West Africa, losses due to heartwater disease are not known because the incidence/prevalence has not been well studied or documented. To develop a diagnostic tool for molecular epidemiology, three PCR-based diagnostic assays, a nested pCS20 PCR, a nested map1 PCR and a nested reverse line blot (RLB) hybridization assay, were evaluated to determine their ability to detect infection in vector ticks, by applying them simultaneously to A. variegatum field ticks to detect Ehrlichia ruminantium, the causative agent of heartwater. The nested pCS20 PCR assay which amplified the pCS20 gene fragment showed the highest detection performance with a detection rate of 16.6%; the nested map1 PCR, which amplified the gene encoding the major antigenic protein1 (map1 gene) showed a detection rate of 11% and the RLB, based on the 16S rDNA sequence of anaplasma and ehrlichial species, detected 6.2%. The RLB, in addition, demonstrated molecular evidence of Ehrlichia ovina, Anaplasma marginale and Anaplasma ovis infections in The Gambia. Subsequently, the pCS20 assay was applied to study the prevalence and distribution of E. ruminantium tick infection rates at different sites in five divisions of The Gambia. The rates of infection in the country ranged from 1.6% to 15.1% with higher prevalences detected at sites in the westerly divisions (Western, Lower River and North Bank; range 8.3-15.1%) than in the easterly divisions (Central River and Upper River; range 1.6-7.5%). This study demonstrated a gradient in the distribution of heartwater disease risk for susceptible livestock in The Gambia which factor must be considered in the overall design of future upgrading programmes.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Molecular detection of Ehrlichia ruminantium infection in Amblyomma variegatum ticks in The Gambia

et al. 2007

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“…The map1 gene product has been investigated extensively as a potential geographic strain marker and for involvement in immune protection (1,27,29,31,32,37). However, where a complete sequence of the locus is available, the mean sequence identities (Table 1) suggest greatest diversity in the map1-2 paralog.…”

Section: Resultsmentioning

confidence: 99%

Diversity of Ehrlichia ruminantium Major Antigenic Protein 1-2 in Field Isolates and Infected Sheep

2009

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

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“…Thus, although HVR1 is highly antigenic, and is therefore likely to be exposed on the bacterial surface, polymorphic HVR2 and HVR3 may not be targets for recognition by Abs. Thus, some genetic diversity might be required for functions unrelated to immune evasion (13).…”

Section: Effective Abs Recognized Omp Hvr1mentioning

confidence: 99%

Antibodies Highly Effective in SCID Mice During Infection by the Intracellular BacteriumEhrlichia chaffeensisAre of Picomolar Affinity and Exhibit Preferential Epitope and Isotype Utilization

Chu

Reilly

et al. 2002

The Journal of Immunology

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Although often considered to be ineffective against intracellular bacteria, Abs, in the absence of lymphocytes, have been shown previously to protect SCID mice from lethal infection by the obligate intracellular bacterium Ehrlichia chaffeensis, even when administered well after infection has been established. To identify characteristics of Abs that are critical for host defense during this intracellular infection, a panel of Ehrlichia-specific mAbs was generated and analyzed. Among 100 Abs recovered, 39 recognized an amino-terminal hypervariable region of an outer membrane protein (OMP), demonstrating that the OMPs are both antigenically variable and immunodominant. A subset of 16 representative OMP-specific Abs was further examined to identify characteristics that were essential for in vivo efficacy. The highly effective Abs recognized a linear epitope within the first hypervariable region of OMP-1g. Only IgG were found to be effective, and among the effective IgG, the following hierarchy was observed: IgG2a > IgG3 = IgG2b. The most striking characteristics of the highly effective Abs were their picomolar binding affinities and long binding t1/2. Thus, although epitope recognition and isotype use may contribute to efficacy, high affinity may be a critical characteristic of Abs that can act effectively during this intracellular bacterial infection.

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Ehrlichia ruminantium Major Antigenic Protein Gene ( map1 ) Variants Are Not Geographically Constrained and Show No Evidence of Having Evolved under Positive Selection Pressure

Cited by 46 publications

References 19 publications

Molecular detection of Ehrlichia ruminantium infection in Amblyomma variegatum ticks in The Gambia

Molecular detection of Ehrlichia ruminantium infection in Amblyomma variegatum ticks in The Gambia

Diversity of Ehrlichia ruminantium Major Antigenic Protein 1-2 in Field Isolates and Infected Sheep

Antibodies Highly Effective in SCID Mice During Infection by the Intracellular BacteriumEhrlichia chaffeensisAre of Picomolar Affinity and Exhibit Preferential Epitope and Isotype Utilization

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