Identification of a glycosylated Ehrlichia canis 19-kilodalton major immunoreactive protein with a species-specific serine-rich glycopeptide epitope

Antibody reactive immunomes of Ehrlichia chaffeensis and E. canis are diverse and defined by conformational antigenic determinants

For decades, the defined antibody reactive proteins of Ehrlichia chaffeensis and E. canis were limited to a small group with linear antibody epitopes. Recently, our laboratory has utilized an immunomics-based approach to rapidly screen and identify undefined Ehrlichia chaffeensis and E. canis antigenic proteins and antibody epitopes. In this study, we analyzed the remaining portion (~50%) of the E. chaffeensis and E. canis proteomes (n = 444 and n = 405 proteins, respectively), that were not examined in previous studies, to define the complete immunomes of these important pathogens. Almost half of the E. chaffeensis proteins screened (196/444) reacted with antibodies in convalescent HME patient sera, while only 43 E. canis proteins reacted with CME dog sera. New major immunoreactive proteins were identified in E. chaffeensis (n = 7) and E. canis (n = 1), increasing the total number of E. chaffeensis (n = 14) and E. canis proteins (n = 18) that exhibited antibody reactivity comparable to well-defined major antigenic proteins (TRP120 and TRP19). All of the E. chaffeensis but only some E. canis major immunoreactive proteins contained major conformation-dependent antibody epitopes. The E. chaffeensis immunoreactive proteins were generally small (< 250 amino acids; ~27kDa) and the E. canis proteins were slightly larger (> 320 amino acids; ~35 kDa). The majority of these new Ehrlichia major immunoreactive proteins were predicted to be type I secreted effectors, some of which contained transmembrane domains. Characterization of the immunomes of E. chaffeensis and E. canis and understanding the host specific Ehrlichia immune responses will facilitate identification of protective antigens and define the biophysical epitope characteristics vital to effective vaccine development for the ehrlichioses.

Correlation between canine biochemical analytes and TRP36 ELISA seropositivity for Ehrlichia canis in Brazil

BACKGROUND

Synthetic peptides of tandem repeat proteins (TRPs) have been employed in the serologic analysis of canine monocytic ehrlichiosis (CME) and used in epidemiological studies in Brazil. Based on molecular studies of TRPs, different genotypes of Ehrlichia canis have been described, but data on their pathogenicity remain unknown.

OBJECTIVES

To correlate hepatic, renal, and muscular alterations in relation to different genotypes of E. canis in naturally exposed dogs using enzyme-linked immunosorbent assay (ELISA) with TRP19 and TRP36 synthetic protein antigens.

METHODS

Two hundred serum samples were subjected to ELISA with the antigens of TRP19 and three genotypes (US, Br, and CR) of TRP36 of E. canis circulating in Brazil. Positive sera were evaluated through eight biochemical parameters, and the results were evaluated by principal component analysis and canonical correlation.

RESULTS

ELISA revealed that 47 (23.5%) serum samples reacted to the BrTRP36 peptide, 36 (18%) reacted to the TRP19 peptide, and 8 (4%) reacted to the USTRP36 and CRTRP36 peptides separately. The most frequent biochemical alterations observed were for CK (59.4%), ALB (31.8%), GLO (28.9%), TP (28.9%), ALP (26%), urea (24.6%), creatinine (14.4%), and ALT (14.4%). The most prominent diagnostic method in canonical correlation analysis was BrTRP36, followed by TRP19, which correlated with hyperglobulinemia and hypoalbuminemia.

CONCLUSIONS

Antibodies that reacted against the Brazilian genotype of E. canis correlated positively with hyperglobulinemia and increases in serum urea and creatinine. According to our results, the Brazilian genotype of E. canis is related to the chronic phase of CME.

Evaluation of Anaplasma spp. seroprevalence in dogs and association with incidence of human anaplasmosis

Point-of-care (POC) ELISA tests are routinely used in US veterinary practices to screen canine patients for antibodies to tick-transmitted pathogens. Results are also used to monitor spatial and temporal trends in canine seroprevalence, and these data can build awareness of the risk to humans of tick-transmitted diseases such as Lyme disease and anaplasmosis. This study utilized a second-generation test that has incorporated additional Anaplasma-specific peptides into a commercial POC ELISA test to allow detection of Anaplasma spp. antibodies earlier post-infection. A convenience population consisting of 19,894 canine samples from a US commercial diagnostic laboratory were tested using the second-generation POC ELISA test to describe regional Anaplasma spp. canine seroprevalence and assess correlation to anaplasmosis cases reported to Centers for Disease Control and Prevention by state. Antibodies to Anaplasma spp. were detected in 1646 samples (8.3%) with the Northeast and Midwest US census regions having the highest proportion of positive samples. At the state level, a significant correlation was found between canine Anaplasma spp. seroprevalence and human anaplasmosis incidence (r2 = 0.64). Although estimates of canine Anaplasma spp. seroprevalence presented here using the second-generation POC ELISA are generally increased, especially in the Northeast and Midwest, the regional distribution of canine samples testing positive for Anaplasma spp. antibodies is consistent with previous reports. The observed correlation with human anaplasmosis incidence indicates that results from the second-generation POC ELISA will continue to add value in epidemiological assessment of human anaplasmosis risk.

A second-generation, point-of-care immunoassay provided improved detection of Anaplasma and Ehrlichia antibodies in PCR-positive dogs naturally infected with Anaplasma or Ehrlichia species

A validated second-generation SNAP 4Dx Plus (Idexx) incorporates new peptides for improved detection of antibodies against Anaplasma and Ehrlichia tick-borne pathogens in dogs. We compared the first- and second-generation SNAP 4Dx Plus using dogs naturally infected with Anaplasma or Ehrlichia species, or dogs seroreactive by an E. canis indirect fluorescent antibody test (IFAT). The second-generation immunoassay was more sensitive than the first-generation for dogs infected with A. phagocytophilum (51.1% and 29.2%, respectively), A. platys (63.6% and 35.3%, respectively), E. canis (96.2% and 88.3%, respectively), or E. ewingii (73.7% and 70.8%, respectively), and for dogs seroreactive by E. canis IFAT (87.3% and 83.9%, respectively). The second-generation immunoassay detected significantly more Anaplasma- or Ehrlichia-infected dogs that were Anaplasma (p < 0.001) or Ehrlichia (p = 0.031) seroreactive, respectively, than did the first-generation test. When Ehrlichia seroreactivity by E. canis IFAT and both immunoassays was compared, significantly more E. canis-infected dogs were seroreactive by E. canis IFAT than the first-generation (p = 0.006) but not the second-generation (p = 0.125) immunoassay. Significantly more E. ewingii-infected dogs were seroreactive by the first- (p = 0.011) and second-generation (p = 0.049) immunoassays than the E. canis IFAT. Medical records available for 7 dogs that were Anaplasma seroreactive by the second-generation but not the first-generation immunoassay revealed case management decisions that might have been different with an immediate anaplasmosis diagnosis, including earlier doxycycline therapy and less hospitalization. The second-generation SNAP 4Dx Plus test offered improved serologic detection of Anaplasma and Ehrlichia in naturally infected dogs.

Type 1 secretion system and effectors in Rickettsiales

Obligate intracellular bacteria in the order Rickettsiales are transmitted by arthropod vectors and cause life-threatening infections in humans and animals. While both type 1 and type 4 secretion systems (T1SS and T4SS) have been identified in this group, the most extensive studies of Rickettsiales T1SS and associated effectors have been performed in Ehrlichia. These studies have uncovered important roles for the T1SS effectors in pathobiology and immunity. To evade innate immune responses and promote intracellular survival, Ehrlichia and other related obligate pathogens secrete multiple T1SS effectors which interact with a diverse network of host targets associated with essential cellular processes. T1SS effectors have multiple functional activities during infection including acting as nucleomodulins and ligand mimetics that activate evolutionarily conserved cellular signaling pathways. In Ehrlichia, an array of newly defined major immunoreactive proteins have been identified that are predicted as T1SS substrates and have conformation-dependent antibody epitopes. These findings highlight the underappreciated and largely uncharacterized roles of T1SS effector proteins in pathobiology and immunity. This review summarizes current knowledge regarding roles of T1SS effectors in Rickettsiales members during infection and explores newly identified immunoreactive proteins as potential T1SS substrates and targets of a protective host immune response.

Costa Rican Genotype of Ehrlichia canis: A Current Concern

Canine monocytic ehrlichiosis (CME) is endemic to Brazil, and studies have verified that dogs have been exposed to different genotypes of Ehrlichia canis. This genetic divergence can influence the clinical response of the animals. We aimed to describe clinical and hematological changes in 125 dogs that reacted to BrTRP36, USTRP36, and CRTRP36 genotypes through enzyme immunoassays and to highlight the current concern regarding infection by the Costa Rican genotype. The results showed that 52.0% reacted to the Brazilian genotype, 22.4% reacted to the Costa Rican genotype, and 16.0% reacted to the American genotype, and some co-reactions were observed. Dogs reactive to BrTRP36 were 1.24% more likely to present with medullary regeneration in cases of anemia and 3% less likely to manifest hyperproteinemia, while dogs reactive to CRTRP36 were 0.7% less likely to present with medullary regeneration. Febrile illness and neurological alterations were also statistically associated, with an 85.7% and 231.2% increased likelihood, respectively, to occur in dogs that reacted to USTRP36. The dogs with the American genotype developed clinical manifestations related to systemic inflammation, while those with the Brazilian genotype of E. canis were more dispersed in the region studied, showing greater adaptation to the hosts. We highlight the significant serocurrence of the Costa Rican genotype, which has already been described to have zoonotic potential and which showed less adaptation.

Recombinant Ehrlichia canis GP19 Protein as a Promising Vaccine Prototype Providing a Protective Immune Response in a Mouse Model

Simple summary

One of the limitations of vaccine development against E. canis infection is the indefinite knowledge of the protective immunity in the host. In this study, recombinant protein GP19 was produced as a vaccine prototype, rGP19, for inducing protective immune responses in a mouse model against E. canis. Antibody responses against E. canis were evaluated and revealed that the immunized mice with rGP19 showed higher antibody levels than in adjuvant-immunized and naive mice, both pre- and post-challenging with E. canis. DNA from blood, liver, and spleen were extracted to determine ehrlichial loads. The rGP19-immunized mice showed significantly lower ehrlichial loads in blood, liver, and spleen DNA compared with adjuvant-immunized mice. This study also detected IFN-γ-producing CD4+ T cells in the rGP19-immunized mice and then were later infected with E. canis on day 14 of the post-infection period using flow cytometry. Additionally, Cytokine mRNA expression was investigated and revealed up-regulation of IFNG and IL1 mRNA expression in rGP19-immunized mice. The present study provides evidence of rGP19 that can eliminate E. canis by manipulating both humoral and cell-mediated immune responses in the laboratory animal model.

Abstract

The intracellular bacterium Ehrlichia canis is the causative pathogen of canine monocytic ehrlichiosis (CME) in dogs. Despite its veterinary and medical importance, there is currently no available vaccine against this pathogen. In this study, the recombinant GP19 (rGP19) was produced and used as a recombinant vaccine prototype in a mouse model against experimental E. canis infection. The efficacy of the rGP19 vaccine prototype in the part of stimulating B and T cell responses and conferring protection in mice later challenged with E. canis pathogen were evaluated. The rGP19-specific antibody response was evaluated by ELISA after E. canis challenge exposure (on days 0, 7, and 14 post-challenge), and demonstrated significantly higher mean antibody levels in rGP19-immunized mice compared with adjuvant-immunized and naive mice. Significantly lower ehrlichial loads in blood, liver, and spleen DNA samples were detected in the immunized mice with rGP19 by qPCR. The up-regulation of IFNG and IL1 mRNA expression were observed in mice immunized with rGP19. In addition, this study detected IFN-γ-producing memory CD4+ T cells in the rGP19-immunized mice and later infected with E. canis on day 14 post-infection period using flow cytometry. The present study provided a piece of evidence that rGP19 may eliminate E. canis by manipulating Th1 and B cell roles and demonstrated a promising strategy in vaccine development against E. canis infection in the definitive host for further study.

Exposure of Domestic Cats to Distinct Ehrlichia canis TRP Genotypes

Cats naturally exposed to Ehrlichia canis have been described in different regions of the world, but little is known about the genotypes associated with infection in these animals. To detect E. canis-specific antibodies and investigate the E. canis TRP genotypes in cats, serum samples from 76 domestic cats reactive to crude E. canis antigens by the indirect fluorescence antibody test (IFAT) were analyzed by ELISA, using E. canis-specific peptides (i.e., TRP19 and TRP36 /BR/US/CR). Of these, 25 (32.9%) cats reacted to at least one TRP peptide, confirming their specific exposure to E. canis. Eighteen (23.7%) cats reacted to TRP19, 15 (19.8%) to BRTRP36, and 11 (14.5%) to USTRP36, but none of them reacted to CRTRP36. Eight (10.5%) cats reacted to TRP19 but not to any TRP36 genotype, demonstrating the possible existence of a new E. canis genotype infecting felines. Nevertheless, this study provides the first report of anti-E. canis-specific antibodies in domestic cats.

Effect of GP19 Peptide Hyperimmune Antiserum on Activated Macrophage during Ehrlichia canis Infection in Canine Macrophage-like Cells

In terms of its veterinary importance, vaccine development against Ehrlichia canis is needed. However, the effect of developing vaccines on humoral immune response against E. canis infection is still unknown. Novel GP19_4-43 was synthesized according to E. canis GP19 epitope prediction. To restrict any loss and/or illness in the host animal, rabbits were used in this study to produce GP19_4-43 hyperimmune sera. The effect of GP19_4-43 hyperimmune sera on neutralization was examined in vitro by determining the inhibition of E. canis infection of the macrophage-like cell line (DH82) in the presence of the sera. Four groups of DH82 cells received differing treatments. These included E. canis experimentally infected DH82 cells, E. canis-infected DH82 cells with control rabbit serum (untreated group), E. canis-infected DH82 cells with GP19_4-43 rabbit antiserum (treated group) and uninfected cells (negative control group), respectively. The treated group developed a decrease (p < 0.01) in the percentage of E. canis infected cells after 3 days post-infection at 48.57 ± 1.28. In addition, real-time PCR analyses of cytokine mRNA expression involved with the macrophage, humoral, and cellular immune responses were conducted. The findings revealed an upregulated expression of IFNG in the treated group during the infection. This study demonstrated neutralization in the GP19_4-43 peptide hyperimmune sera of immunized rabbits. Notably, IFN-γ production could be effectively promoted in canine macrophages in relation to the activation of macrophages and adaptive immune responses. The results of this study indicate the potential for the use of this immunogen in further investigations involving immunized and infected dogs as E. canis host species.

Immunoreactive Protein Repertoires of Ehrlichia chaffeensis and E. canis Reveal the Dominance of Hypothetical Proteins and Conformation-dependent Antibody Epitopes

The immunomes of Ehrlichia chaffeensis (E. ch.) and E. canis (E. ca.) have recently be revised to include immunodominant hypothetical proteins with conformational antibody epitopes. In this study, we examined 216 E. ch. and 190 E. ca. highly antigenic proteins according to ANTIGENpro and also performed a genome-wide hypothetical protein analysis (E. ch. n=104; E. ca. n=124) for immunoreactivity. Using cell-free protein expression and immunoanalysis, 118 E. ch. and 39 E. ca. proteins reacted with sera from naturally E. ch.-infected patients or E. ca.-infected dogs. Moreover, 22 E. ch. and 18 E. ca. proteins consistently and strongly reacted with a panel of patient or canine sera. A subset of E. ch. (n=18) and E. ca. (n=9) proteins were identified as immunodominant. Consistent with our previous study, most proteins were classified as hypothetical and the antibody epitopes exhibited complete or partial conformation-dependence. The majority (28/40; 70%) of E. ch. and E. ca. proteins contained transmembrane domains and 19 (48%) were predicted to be secreted effectors. The antigenic repertoires of E. ch. and E. ca. were mostly diverse and suggest that the immunomes of these closely related ehrlichiae are dominated by species-specific conformational antibody epitopes. This study reveals a significant group of previously undefined E. ch. and E. ca. antigens and reaffirms the importance of conformation-dependent epitopes as targets of anti-Ehrlichia immune responses. These findings substantially expand our understanding of host-Ehrlichia immune responses, advance efforts to define the molecular features of protective proteins and improve prospects for effective vaccines for the ehrlichioses.

Serological evidence of Ehrlichia minasensis infection in Brazilian dogs

Ehrlichia spp. are important tick-borne pathogens of animals in Brazil, and Ehrlichia canis is the most prevalent species infecting dogs. Moreover, Ehrlichia minasensis has also recently been identified as a novel ehrlichial agent that infects cattle in Brazil. The objective of this study was to determine whether dogs could be infected by E. minasensis. To investigate this possibility, sera (n = 429) collected from dogs in the Pantanal region were retrospectively analyzed for the presence of antibodies against E. canis and E. minasensis. Canine sera were screened by two isolates of E. canis in indirect immunofluorescence assay (IFA) and the majority (n = 298; 69.4%) had antibodies with endpoint titers ranging from 80 to 327,680. In order to further confirm E. canis-specific antibodies, IFA positive sera were analyzed by ELISA using E. canis-specific peptides (i.e. TRP19 and TRP36 US/BR/CR), which detected E. canis antibodies in 80.2% (239/298) of the dog sera. Fifty-nine (13.7%) samples had detectable antibodies to E. canis by IFA but were negative by E. canis peptide ELISA. These sera were then tested by E. minasensis IFA (Cuiaba strain) as antigen and 67.8% (40/59) were positive (titers ranging from 80 to 20,480). Eleven sera had antibody titers against E. minasensis at least two-fold higher than observed for E. canis and suggests that these dogs were previously infected with E. minasensis. The results of the present study suggest that multiple ehrlichial agents infect dogs in Brazil, which highlights the need to consider different Ehrlichia spp. in Brazilian dogs, particularly in areas where dogs are frequently exposed to multiple tick species. This investigation is the first to provide serologic evidence of E. minasensis infection in dogs from Brazil.

Seroprevalence and Genotypic Analysis of Ehrlichia canis Infection in Dogs and Humans in Cauca, Colombia

Ehrlichia canis infections have been reported in humans in Venezuela and Costa Rica. In this study, 506 healthy residents and 114 dogs from four municipalities (Cauca, Colombia) were surveyed and blood samples collected. Antibodies to E. canis in human and canine sera were evaluated using the Tandem repeat protein 19 (TRP19) peptide ELISA and indirect immunofluorescence assay (IFA). Ehrlichia canis TRP19 antibodies were detected in only 1/506 human sera, but the single positive sample was negative by IFA. The majority (75/114; 66%) of dogs surveyed had antibodies to the E. canis TRP19 peptide by ELISA, and eight randomly selected sera were further confirmed by E. canis IFA. Genomic DNA samples obtained from 73 E. canis TRP19 ELISA-positive dog blood samples were examined by PCR targeting the 16S ribosomal ribonucleic acid (rRNA) gene. Ehrlichia canis 16S rRNA was amplified in 30 (41%) of the dogs, and 16 amplicons were selected for DNA sequencing, which confirmed that all were E. canis. A second PCR was performed on the 16 confirmed E. canis 16S rRNA PCR-positive samples to determine the TRP36 genotype by amplifying the trp36 gene. TRP36 PCR amplicon sequencing identified nine dogs infected with the U.S. E. canis TRP36 genotype (56%), one dog with the Brazilian genotype (6%), and six dogs with the Costa Rican genotype (38%). Moreover, these molecular genotype signatures were consistent with serologic analysis using TRP36 genotype-specific peptides. Notably, there was no serologic evidence of E. canis infection in humans, suggesting that E. canis infection in dogs in Cauca is not associated with zoonotic human infection.

Canonical correlative analyses among an enzyme-linked immunosorbent assay using synthetic peptides, an indirect fluorescent antibody test, and hematologic measurements in dogs infected with Ehrlichia canis

BACKGROUND

Immunoreactive tandem repeat proteins (TRPs) in amino acid sequences were identified and employed in the serologic diagnosis of canine monocytic ehrlichiosis (CME).

OBJECTIVES

This study evaluated using TRP19 and TRP36 synthetic protein antigens with enzyme-linked immunosorbent assays (ELISAs) and compared the results with an indirect fluorescent antibody test (IFAT) to diagnose CME in the serum of dogs with suspected CME.

METHODS

The sera of 243 dogs that exhibited clinical and hematologic signs suggestive of CME had IFATs performed. An ELISA with synthetic TRP19 and TRP36 antigens from two E canis genotypes (USTRP36 and BrTRP36) that circulate in Brazil were also performed. Canonical correlations and chi-square tests were evaluated on the results of these tests.

RESULTS

Among the 243 dogs, 179 (73.6%) were reactive at an IFAT ≥ 40, 167 (68.72%) reacted at the cut-off ≥160, and 149 (61.31%) reacted at ≥640. The ELISA revealed that 172 (70.8%) dogs reacted to TRP19 peptide, 163 (67.1%) reacted to USTRP36, and 114 (46.9%) reacted to BrTRP36. The canonical correlation analyses showed that the TRP19 ELISA was the most effective diagnostic method. Serum total protein levels showed strong positive correlations with the USTRP36 peptide. Qualitative analyses revealed an association between the TRP19 peptide and the presence of anemia, thrombocytopenia, and hyperproteinemia. The IFAT results at titers of ≥160 and ≥640 were associated with thrombocytopenia.

CONCLUSIONS

The results of this study indicated that the TRP19 peptide was an excellent antigen and that the IFAT was diagnostically important in confirming the diagnosis of CME in serum samples.

Geographic Distribution of Ehrlichia canis TRP Genotypes in Brazil

Tandem repeat proteins (TRPs) are major immunoreactive proteins of Ehrlichia canis, which have been used in the serological diagnosis of different genotypes of the microorganism. TRP19 is preserved among different E. canis isolates expressed on both reticulate and dense-core cells and observed in the extracellular matrix or associated with the morula membrane. TRP36 is differentially expressed only on the surface of the dense-core form of the bacterium and exhibits more divergence among isolates. The aim of this study was to evaluate the distribution of the American (USTRP36), Brazilian (BrTRP36) and Costa Rican (CRTRP36) genotypes of E. canis in Brazil, using ELISA assays. Serum samples of 814 dogs from 49 municipalities from all over Brazil were analyzed. Our results showed that 33.9% of the samples were reactive to the USTRP36 genotype and 32.6% to the BrTRP36 genotype. The two genotypes appeared to occur equally throughout Brazil, although the frequency of seropositivity was lower in the south than in the country's other regions. Dogs that reacted to at least one of the synthetic peptides (TRP19 and TRP36) were 456 (56%). A few dogs (n = 5; 0.6%) reactive to the E. canis TRP36 genotype (CRTRP36) were also detected in the northeast and southern regions. We concluded that the American and Brazilian genotypes of E. canis are distributed evenly in Brazil, especially in the tropical region, while the temperate region in the south presented the lowest prevalence rates. This study offers the first report of dogs seropositive for the Costa Rican genotype in Brazil.

Ehrlichia chaffeensis and E. canis hypothetical protein immunoanalysis reveals small secreted immunodominant proteins and conformation-dependent antibody epitopes

Immunomolecular characterization of Ehrlichia chaffeensis (E. ch.) and E. canis (E. ca.) has defined protein orthologs, including tandem repeat proteins (TRPs) that have immunodominant linear antibody epitopes. In this study, we combined bioinformatic analysis and cell-free protein expression to identify undiscovered immunoreactive E. ch. and E. ca. hypothetical proteins. Antigenicity of the E. ch. and E. ca. ORFeomes (n = 1105 and n = 925, respectively) was analyzed by the sequence-based prediction model ANTIGENpro, and we identified ~250 ORFs in each respective ORFeome as highly antigenic. The hypothetical proteins (E. ch. n = 93 and E. ca. n = 98) present in the top 250 antigenic ORFs were further investigated in this study. By ELISA, 46 E. ch. and 30 E. ca. IVTT-expressed hypothetical proteins reacted with antibodies in sera from naturally E. ch.-infected patients or E. ca.-infected dogs. Moreover, 15 E. ch. and 16 E. ca. proteins consistently reacted with a panel of sera from patients or dogs, including many that revealed the immunoreactivity of “gold standard” TRPs. Antibody epitopes in most (>70%) of these proteins exhibited partial or complete conformation-dependence. The majority (23/31; 74%) of the major immunoreactive proteins identified were small (≤250 aa), and 20/31 (65%) were predicted to be secreted effectors. Unlike the strong linear antibody epitopes previously identified in TRP and OMP orthologs, there were contrasting differences in the E. ch. and E. ca. antigenic repertoires, epitopes and ortholog immunoreactivity. This study reveals numerous previously undefined immunodominant and subdominant antigens, and illustrates the breadth, complexity, and diversity of immunoreactive proteins/epitopes in Ehrlichia.

Expression and antigenic analysis of the recombinant TRP36 protein from Ehrlichia canis São Paulo strain for serologic tests

Ehrlichia canis is the main etiological agent of canine monocytic ehrlichiosis (CME), a globally canine infectious disease. In Brazil, CME is considered to be endemic, and its prevalence can reach 65% in some states. The diagnosis of ehrlichiosis is important for treatment and epidemiological purposes. The E. canis TRP36 (Tandem Repeat Protein) protein elicits the earliest acute-phase antibody response observed during the course of the disease. This study aimed to generate the recombinant TRP36 protein from E. canis São Paulo strain and to evaluate its potential as a tool for the serologic diagnosis of CME. The E. canis São Paulo isolate was cultivated in DH82 lineage cells, and its genomic DNA was obtained. The bacterial DNA fragment encoding the entire ORF of TRP36 was cloned into the pBAD/Thio-TOPO vector and transformed into Escherichia coli DH10B competent cells with the trp36-bearing plasmid for protein expression. To evaluate the protein antigenicity, 16 canine serum samples were previously tested (by PCR and the commercial SNAP®4Dx® serological test). The results were in accordance with the SNAP®4Dx® test. Experiments using this recombinant protein as an antigen, targeting the development of a serologic test based on ELISA methodology, are the next step to produce a reliable, affordable and useful diagnostic tool for CME in Brazil.

Ehrlichia canis TRP36 diversity in naturally infected-dogs from an urban area of Colombia

Ehrlichia canis is the etiologic agent of a highly prevalent tick-borne disease, canine monocytic ehrlichiosis (CME). Four defined E. canis genotypes based on the trp36 gene sequences have been reported, three of them identified in North or South America. The diversity of E. canis has been investigated using genetic and serologic approaches based on distinct 36 kDa tandem repeat protein (trp36) gene sequences that have been reported. The main objectives of this study were to determine the prevalence of E. canis infection in dogs from Medellín, Colombia by PCR and determine the E. canis diversity using molecular and serologic approaches. Blood was collected from dogs (n = 300) with clinical signs of CME for PCR detection of E. canis 16S rRNA, dsb and trp36 DNA. Phylogenetic analysis of trp36 gene sequences was performed using MEGA. A serological evaluation was performed using immunofluorescence microscopy and ELISA with species-specific peptides from E. canis TRP19 and TRP36 (3 genotypes) and E. chaffeensis (TRP32). E. canis DNA (16S rRNA and/or dsb) was detected in 18 % (53/300) of dogs by PCR amplification. The trp36 gene was amplified and sequenced from 35/53 16S rRNA/dsb PCR positive samples revealing three genotypes: United States (US; n = 21), Costa Rica (CR; n = 11), and Brazil (BR; n = 3). Most dogs (33/35) with detectable trp36 DNA had anti-E. canis TRP19 and TRP36 peptide antibodies that corresponded to the genotype detected by PCR. Dogs that had antibodies to the TRP19 peptide (82/300; 38 %), also had antibodies to one or more genotype-specific TRP36 peptides. Based on TRP36 serology, the dogs exhibited highest frequency of infection with the US genogroup (US = 26), followed by the CR genogroup (CR = 19) and the BR genogroup (BR = 11). Notably, 26/53 trp36 PCR positive dogs had detectable antibodies to multiple E. canis genotypes (US/BR/CR = 8, BR/CR = 7, US/CR = 6 and US/BR = 5) suggesting coinfection or multiple sequential infections with different genotypes. Colombian dogs did not have antibodies to E. chaffeensis as determined by a TRP32 species-specific ELISA. Our results demonstrate the presence of three previously defined genotypes in North and South America in Colombian dogs (US, BR, CR). These results also demonstrate that TRP19 and TRP36 serology can provide valuable information regarding E. canis exposure and the potential genotype(s) involved in infection.

Molecular characterization of Ehrlichia canis from naturally infected dogs from the state of Rio de Janeiro

The aim of the present study was to evaluate the genetic diversity of Ehrlichia canis in naturally infected dogs from six mesoregions of Rio de Janeiro state. E. canis was diagnosed with a real-time polymerase chain reaction (qPCR) targeting a 93 base pair (bp) fragment of the 16S rDNA gene. To evaluate the genetic diversity of the parasite, we amplified a positive sample from each mesoregion by distinct conventional PCR assays with targets in the gp19 (414 bp), gp36 (814 bp), and p28 (843 bp) genes. A total of 267 samples were collected from dogs in Rio de Janeiro state. Among the samples analyzed, 42.3% (n = 113/267) were 16S rDNA-qPCR positive. When performing PCR for the gp19 and gp36 genes, 100% (n = 113/113) and 5.3% (n = 6/113) of the samples amplified fragments of 414 bp and 814 bp, respectively. The six PCR-positive samples for the gp36 gene also amplified the p28 gene fragment. The characterization based on the gp19 gene demonstrated that it is highly conserved. In protein analysis (TRP36), all samples showed a tandem repeat protein (TRP) that comprised 11 replicates. Seven high-entropy amino acid sites were distributed throughout the gp36 gene. Eleven high-entropy amino acid sites were found throughout the p28 gene. There is a positive selection pressure in both genes (p ≤ 0.05). Comparing and characterizing an organism are useful for providing important information about the host's immune response and identifying new antigenic targets, as well as essential characteristics for the development of vaccines and new diagnostic tools.

Molecular Characterization of Tandem Repeat Protein 36 Gene of Ehrlichia canis Detected in Naturally Infected Dogs from Peru

Ehrlichia spp. are emerging infectious pathogens, especially in the Americas. Although Ehrlichia canis is primarily a parasite of dogs, polymerase chain reaction-confirmed human infections have been reported from Mexico, Venezuela, and Costa Rica. This study reports the presence of E. canis DNA in 13.7% of 205 dogs from urban areas in Peru and of those, five were analyzed for phylogenetic variation using the Tandem Repeat Protein 36 (TRP36) gene. The use of the TRP36 gene for such analysis was validated against 16S rRNA and heat shock protein genes using Shannon's entropy bioinformatic approach. When compared with other E. canis strains previously reported, three unique and novel E. canis strains were detected. In addition, the TRP36 amino acid tandem repeat sequences of the Peruvian strains share close similarity to an E. canis strain detected from four human blood bank samples in Costa Rica. This study reports for the first time domestic dogs infected with E. canis strains closely related to a zoonotic strain, which may be of public health concern as dogs can be chronically infected with this pathogen.

Detection of genotype-specific Ehrlichia canis exposure in Brazilian dogs by TRP36 peptide ELISA

We recently characterized a novel genotype of Ehrlichia canis based on the tandem repeat (TR) sequence of the TRP36 gene in Brazil. The TR amino acid sequence of the Brazilian (Br) genotype (ASVVPEAE) was divergent from the previously described US genotype (TEDSVSAPA) of E. canis. In this study, we developed an ELISA based on TRP36 TR synthetic peptides from both Br and US E. canis TRP36 genotypes to serologically detect and distinguish infections caused by these genotypes. Sera from 30 Brazilian dogs naturally infected with E. canis, sera from dogs experimentally infected E. canis (Jake and Cuiabá #1 strains) and E. chaffeensis (Arkansas strain) and 12 seronegative E. canis dogs were evaluated. Fifteen naturally infected Brazilian dogs had antibodies that reacted with the US TRP36 (n=9) or Br TRP36 (n=6) only, and 13 dogs had antibodies that reacted with both TPR36 peptides suggesting that these dogs were exposed to both genotypes. Most dogs (n=28) had antibodies that reacted with the highly conserved E. canis TRP19 peptide; however, two dogs had antibodies to E. canis TRP19, but did not have TRP36 antibodies, raising the possibility that another novel TRP36 genotype is circulating in Brazil. Our results demonstrate that synthetic peptides based on the TR region of E. canis TRP36 can be used to serologically distinguish infections or identify coinfections by different genotypes, and to determine the seroprevalence of various E. canis genotypes in Brazil.

Recombinant gp19 as a potential antigen for detecting anti-Ehrlichia canis antibodies in dog sera

The canine monocytic ehrlichiosis, caused by Ehrlichia canis, is endemic in several regions of Brazil. Some serological diagnostic techniques using immunodominant proteins of E. canis as antigens are available, but their specificities and sensitivities are questionable. Based on this, the objective of this study was to test the antigenic potential of the recombinant gp19 protein (rGP19) for subsequent use in diagnostic tests. The rGP19 expressed in the Escherichia coli strain BL21 (DE3) C41 was recognized in the sera from experimentally infected dogs using ELISA and Western blotting. Thus, it was possible to obtain a promising antigen with the ability to differentiate between E. canis-positive and -negative animals, even 1 week after infection.

Recombinant Ehrlichia P29 protein induces a protective immune response in a mouse model of ehrlichiosis

Ehrlichioses are emerging tick-borne bacterial diseases of humans and animals for which no vaccines are available. The diseases are caused by obligately intracellular bacteria belonging to the genus Ehrlichia. Several immunoreactive proteins of ehrlichiae have been identified based on their reactivity with immune sera from human patients and animals. These include the major outer membrane proteins, ankyrin repeat proteins and tandem repeat proteins (TRP). Polyclonal antibodies directed against the tandem repeats (TRs) of Ehrlichia chaffeensis TRP32, TRP47 and TRP120 have been shown to provide protection in mice. In the present study, we evaluated E. muris P29, which is the ortholog of E. chaffeensis TRP47 and E. canis TRP36, as a subunit vaccine in a mouse model of ehrlichiosis. Our study indicated that unlike E. chaffeensis TRP47 and E. canis TRP36, orthologs of E. muris (P29) and E. muris-like agent (EMLA) do not contain tandem repeats. Immunization of mice with recombinant E. muris P29 induced significant protection against a challenge infection. The protection induced by E. muris P29 was associated with induction of strong antibody responses. In contrast to development of P29-specific IgG antibodies following immunization, development of P29-specific IgG antibodies, but not IgM antibodies, was impaired during persistent E. muris infection. Furthermore, our study indicated that CD4+ T cells target P29 during E. muris infection and differentiate into IFN-γ-producing Th1 effector/memory cells. In conclusion, our study indicated that orthologs of E. muris P29 showed considerable variation in the central tandem repeat region among different species, induction of P29-specific IgG antibody response was impaired during persistent E. muris infection, and rP29 induced protective immune responses.

Molecular basis of antibody mediated immunity against Ehrlichia chaffeensis involves species-specific linear epitopes in tandem repeat proteins

Humoral immune mechanisms are an important component of protective immunity to Ehrlichia species. However, the molecular basis of antibody mediated immunity is not completely defined, and the role of most molecularly characterized major immunoreactive proteins is unknown. In previous studies, we mapped major species-specific continuous epitopes in three surface exposed and secreted tandem repeat proteins (TRP32, TRP47 and TRP120). In this study, we report that protection is provided by antibodies against these molecularly defined TRP epitopes using in vitro and in vivo models. Protection was demonstrated in vitro after prophylactic and therapeutic administration of epitope-specific anti-TRP antibodies, suggesting that the protective mechanisms involve extracellular and intracellular antibody-mediated effects. In vivo passive transfer of individual epitope-specific TRP sera significantly reduced the ehrlichial load and splenomegaly, and protected mice against lethal infection. Moreover, the combination of antibodies to all three TRPs provided enhanced reduction in ehrlichial load similar to that of Ehrlichia chaffeensis immune sera. IgG1 was the predominant antibody isotype in the epitope-specific TRP mouse sera. These results demonstrate that antibodies against linear epitopes in TRP32, TRP47 and TRP120 are protective during E. chaffeensis infection and involves extracellular and intracellular antibody-mediated mechanisms.

First detection and molecular characterization of Ehrlichia canis from dogs in Nigeria

The present study aimed to detect the presence of Ehrlichia canis in naturally infected dogs in Nigeria, using a combination of PCR and sequence analysis of the 16S rRNA gene and two genes encoding the tandem repeat-containing proteins (TRPs), TRP19 and TRP36. Out of a total of 100 blood samples collected from domestic dogs presented to veterinary hospitals in Jos, the capital city of Plateau State of Nigeria, 11 were positive in nested PCR for E. canis. Sequencing results for these amplicons showed that all of the 16S rDNA sequences (1623 bp) or the TRP19 coding sequences (414 bp) were identical to each other and had very high similarities (99.3-100%) with those from other E. canis strains accessible in GenBank. The TRP36 gene sequences derived from the 11 Nigerian isolates were identical to each other except for the number of the 27-bp repeat unit in a tandem repeat region, which was found to be 8, 12 or 18. Without considering the number of tandem repeats, these sequences had 100% identity to that of the reported Cameroon 71 isolate, but distinctly differed from those obtained from other geographically distant E. canis strains previously published. A phylogenetic tree of E. canis based on the TRP36 amino acid sequences showed that the Nigerian isolates and the Cameroon 71 isolate fell into a separate clade, indicating that they may share a common ancestor. Overall, this study not only provides the first molecular evidence of E. canis infections in dogs from Nigeria but also highlights the value of the TRP36 gene as a tool to classify E. canis isolates and to elucidate their phylogeographic relationships.

Ehrlichia chaffeensis TRP32 interacts with host cell targets that influence intracellular survival

Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes and survives by evading host cell defense mechanisms. Recently, molecular interactions of E. chaffeensis tandem repeat proteins 47 and 120 (TRP47 and -120) and the eukaryotic host cell have been described. In this investigation, yeast two-hybrid analysis demonstrated that an E. chaffeensis type 1 secretion system substrate, TRP32, interacts with a diverse group of human proteins associated with major biological processes of the host cell, including protein synthesis, trafficking, degradation, immune signaling, cell signaling, iron metabolism, and apoptosis. Eight target proteins, including translation elongation factor 1 alpha 1 (EF1A1), deleted in azoospermia (DAZ)-associated protein 2 (DAZAP2), ferritin light polypeptide (FTL), CD63, CD14, proteasome subunit beta type 1 (PSMB1), ring finger and CCCH-type domain 1 (RC3H1), and tumor protein p53-inducible protein 11 (TP53I11) interacted with TRP32 as determined by coimmunoprecipitation assays, colocalization with TRP32 in HeLa and THP-1 cells, and/or RNA interference. Interactions between TRP32 and host targets localized to the E. chaffeensis morulae or in the host cell cytoplasm adjacent to morulae. Common or closely related interacting partners of E. chaffeensis TRP32, TRP47, and TRP120 demonstrate a molecular convergence on common cellular processes and molecular cross talk between Ehrlichia TRPs and host targets. These findings further support the role of TRPs as effectors that promote intracellular survival.

Ehrlichia chaffeensis tandem repeat proteins and Ank200 are type 1 secretion system substrates related to the repeats-in-toxin exoprotein family

Ehrlichia chaffeensis has type 1 and 4 secretion systems (T1SS and T4SS), but the substrates have not been identified. Potential substrates include secreted tandem repeat protein (TRP) 47, TRP120, and TRP32, and the ankyrin repeat protein, Ank200, that are involved in molecular host–pathogen interactions including DNA binding and a network of protein–protein interactions with host targets associated with signaling, transcriptional regulation, vesicle trafficking, and apoptosis. In this study we report that E. chaffeensis TRP47, TRP32, TRP120, and Ank200 were not secreted in the Agrobacterium tumefaciens Cre recombinase reporter assay routinely used to identify T4SS substrates. In contrast, all TRPs and the Ank200 proteins were secreted by the Escherichia coli complemented with the hemolysin secretion system (T1SS), and secretion was reduced in a T1SS mutant (ΔTolC), demonstrating that these proteins are T1SS substrates. Moreover, T1SS secretion signals were identified in the C-terminal domains of the TRPs and Ank200, and a detailed bioinformatic analysis of E. chaffeensis TRPs and Ank200 revealed features consistent with those described in the repeats-in-toxins (RTX) family of exoproteins, including glycine- and aspartate-rich tandem repeats, homology with ATP-transporters, a non-cleavable C-terminal T1SS signal, acidic pIs, and functions consistent with other T1SS substrates. Using a heterologous E. coli T1SS, this investigation has identified the first Ehrlichia T1SS substrates supporting the conclusion that the T1SS and corresponding substrates are involved in molecular host–pathogen interactions that contribute to Ehrlichia pathobiology. Further investigation of the relationship between Ehrlichia TRPs, Ank200, and the RTX exoprotein family may lead to a greater understanding of the importance of T1SS substrates and specific functions of T1SS in the pathobiology of obligately intracellular bacteria.

Tyrosine-phosphorylated Ehrlichia chaffeensis and Ehrlichia canis tandem repeat orthologs contain a major continuous cross-reactive antibody epitope in lysine-rich repeats

A small subset of major immunoreactive proteins have been identified in Ehrlichia chaffeensis and Ehrlichia canis, including three molecularly and immunologically characterized pairs of immunoreactive tandem repeat protein (TRP) orthologs with major continuous species-specific epitopes within acidic tandem repeats (TR) that stimulate strong antibody responses during infection. In this study, we identified a fourth major immunoreactive TR-containing ortholog pair and defined a major cross-reactive epitope in homologous nonidentical 24-amino-acid lysine-rich TRs. Antibodies from patients and dogs with ehrlichiosis reacted strongly with recombinant TR regions, and epitopes were mapped to the N-terminal TR region (18 amino acids) in E. chaffeensis and the complete TR (24 amino acids) in E. canis. Two less-dominant epitopes were mapped to adjacent glutamate/aspartate-rich and aspartate/tyrosine-rich regions in the acidic C terminus of E. canis TRP95 but not in E. chaffeensis TRP75. Major immunoreactive proteins in E. chaffeensis (75-kDa) and E. canis (95-kD) whole-cell lysates and supernatants were identified with TR-specific antibodies. Consistent with other ehrlichial TRPs, the TRPs identified in ehrlichial whole-cell lysates and the recombinant proteins migrated abnormally slow electrophoretically a characteristic that was demonstrated with the positively charged TR and negatively charged C-terminal domains. E. chaffeensis TRP75 and E. canis TRP95 were immunoprecipitated with anti-pTyr antibody, demonstrating that they are tyrosine phosphorylated during infection of the host cell.

Molecular and cellular pathobiology of Ehrlichia infection: targets for new therapeutics and immunomodulation strategies

Ehrlichia are small obligately intracellular bacteria in the order Rickettsiales that are transmitted by ticks and associated with emerging life-threatening human zoonoses. Vaccines are not available for human ehrlichiosis, and therapeutic options are limited to a single antibiotic class. New technologies for exploring host-pathogen interactions have yielded recent advances in understanding the molecular interactions between Ehrlichia and the eukaryotic host cell and identified new targets for therapeutic and vaccine development, including those that target pathogen virulence mechanisms or disrupt the processes associated with ehrlichial effector proteins. Animal models have also provided insight into immunopathological mechanisms that contribute significantly to understanding severe disease manifestations, which should lead to the development of immunomodulatory approaches for treating patients nearing or experiencing severe disease states. In this review, we discuss the recent advances in our understanding of molecular and cellular pathobiology and the immunobiology of Ehrlichia infection. We identify new molecular host-pathogen interactions that can be targets of new therapeutics, and discuss prospects for treating the immunological dysregulation during acute infection that leads to life-threatening complications.

Evaluation of peptide- and recombinant protein-based assays for detection of anti-Ehrlichia ewingii antibodies in experimentally and naturally infected dogs. [corrected]

OBJECTIVE

To evaluate microtiter-plate format ELISAs constructed by use of different diagnostic targets derived from the Ehrlichia ewingii p28 outer membrane protein for detection of E ewingii antibodies in experimentally and naturally infected dogs.

SAMPLE POPULATION

Serum samples from 87 kenneled dogs, 9 dogs experimentally infected with anti-E ewingii, and 180 potentially naturally exposed dogs from Missouri.

PROCEDURES

The capacities of the synthetic peptide and truncated recombinant protein to function as detection reagents in ELISAs were compared by use of PCR assay, western blot analysis, and a full-length recombinant protein ELISA. Diagnostic targets included an E ewingii synthetic peptide (EESP) and 2 recombinant proteins: a full-length E ewingii outer membrane protein (EEp28) and a truncated E ewingii outer membrane protein (EETp28)

RESULTS

A subset of Ehrlichia canis-positive samples cross-reacted in the EEp28 ELISA; none were reactive in the EESP and EETp28 ELISAs. The EESP- and EETp28-based ELISAs detected E ewingii seroconversion at approximately the same time after infection as the EEp28 ELISAs. In afield population, each of the ELISAs identified the same 35 samples as reactive and 27 samples as nonreactive. Anaplasma and E can is peptides used in a commercially available ELISA platform did not detect anti-E ewingii antibodies in experimentally infected dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The EESP and EETp28 ELISAs were suitable for specifically detecting anti-E ewingii antibodies in experimentally and naturally infected dogs.

Progress and obstacles in vaccine development for the ehrlichioses

Ehrlichia are tick-borne obligately intracellular bacteria that cause significant diseases in veterinary natural hosts, including livestock and companion animals, and are now considered important zoonotic pathogens in humans. Vaccines are needed for these veterinary and zoonotic human pathogens, but many obstacles exist that have impeded their development. These obstacles include understanding genetic and antigenic variability, influence of the host on the pathogen phenotype and immunogenicity, identification of the ehrlichial antigens that stimulate protective immunity and those that elicit immunopathology, development of animal models that faithfully reflect the immune responses of the hosts and understanding molecular host-pathogen interactions involved in immune evasion or that may be blocked by the host immune response. We review the obstacles and progress in addressing barriers associated with vaccine development to protect livestock, companion animals and humans against these host defense-evasive and cell function-manipulative, vector-transmitted pathogens.

Detection and characterization of four novel genotypes of Ehrlichia canis from dogs

The genetic diversity of Ehrlichia canis strains worldwide is currently poorly defined. The present study aimed to characterize E. canis strains in naturally infected dogs in Taiwan, using a combination of PCR and sequence analysis of the 16S rDNA and two antigen-encoding genes, gp19 and gp36. Genomic DNA was extracted from 34 parasitemic dogs and the genes of the pathogen were separately amplified, sequenced, and aligned with corresponding sequences available in GenBank. All 16S rDNA sequences (1623 bp) amplified from the Taiwanese isolates were identical and had very high similarity (99.4-100%) with previously reported E. canis sequences. Nevertheless, most of the gp19 gene sequences (414 bp) from the Taiwanese isolates had three specific nucleotide substitutions at positions 9, 323 and 371 that resulted in three amino acid changes. The gp36 gene of the Taiwanese isolates consists of three regions: a 5' end pre-repeat region (426 bp), a tandem repeat region with variable numbers of the 27-bp repeat unit depending on the isolate, and a 3' end region (87 bp). The nucleotide sequences of the 5' end region of gp36 from Taiwanese isolates were identical to each other, but unexpectedly, quite distinct from the sequences of eleven other E. canis strains previously published, with 86.7-87.2% identities only. A phylogenetic tree of E. canis strains based on the gp36 amino acid sequences showed that the Taiwanese isolates fell into a separate clade, indicating the presence of a novel strain that had not yet been characterized.

Mass spectrometric analysis of Ehrlichia chaffeensis tandem repeat proteins reveals evidence of phosphorylation and absence of glycosylation

BACKGROUND

Ehrlichia chaffeensis has a small subset of immunoreactive secreted, acidic (pI approximately 4), tandem repeat (TR)-containing proteins (TRPs), which exhibit abnormally large electrophoretic masses that have been associated with glycosylation of the TR domain.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined the extent and nature of posttranslational modifications on the native TRP47 and TRP32 using mass spectrometry. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) demonstrated that the mass of native TRP47 (33,104.5 Da) and TRP32 (22,736.8 Da) were slightly larger (179- and 288-Da, respectively) than their predicted masses. The anomalous migration of native and recombinant TRP47, and the recombinant TR domain (C-terminal region) were normalized by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) modification of negatively charged carboxylates to neutral amides. Exhaustive tandem mass spectrometric analysis (92% coverage) performed on trypsin and Asp-N digested native TRP47 identified peptides consistent with their predicted masses. Two TRP47 peptides not identified were located in the normally migrating amino (N)-terminal region of TRP47 and contained predicted phosphorylation sites (tyrosine and serine residues). Moreover, native TRP47 was immunoprecipitated from E. chaffeensis-infected cell lysate with anti-phosphotyrosine (anti-pTyr) antibody.

CONCLUSIONS/SIGNIFICANCE

TRP47 and TRP32 are not modified by glycans and the substantial net negative charge of the ehrlichial TRPs, and particularly the highly acidic TRs present within the ehrlichial TRPs, is responsible for larger-than-predicted masses. Furthermore, this study provides evidence that the N-terminal region of the TRP47 is tyrosine phosphorylated.

New insights into molecular Ehrlichia chaffeensis-host interactions

Ehrlichia chaffeensis is an obligately intracellular bacterium that exhibits tropism for mononuclear phagocytes and survives by reprogramming the host cell. Here we review new information regarding the newly characterized effector molecules and the complex network of molecular host-pathogen interactions that the organism exploits enabling it to thrive and persist intracellularly.

Molecular characterization of antibody epitopes of Ehrlichia chaffeensis ankyrin protein 200 and tandem repeat protein 47 and evaluation of synthetic immunodeterminants for serodiagnosis of human monocytotropic ehrlichiosis

Recently, major species-specific antibody epitopes in three immunoreactive tandem repeat proteins (TRPs) of Ehrlichia chaffeensis, TRP32, TRP47, and TRP120, have been identified and molecularly characterized within tandem repeat (TR) regions. In this study, we mapped the major immunodeterminants of the E. chaffeensis 200-kDa ankyrin protein (Ank200) and the minor immunodeterminants in the N- and C-terminal regions of E. chaffeensis TRP47. Major antibody epitopes of Ank200 were localized to four polypeptide regions (18-mer, 20-mer, 20-mer, and 21-mer, respectively) in terminal acidic domains, which reacted with antibodies in sera from human monocytotropic ehrlichiosis (HME) patients and an E. chaffeensis-infected dog. Two minor epitope-containing regions were identified in the N terminus and the C terminus of TRP47. The sensitivities and specificities of synthetic peptides representing these and other well-defined major immunodeterminants of E. chaffeensis were determined by enzyme-linked immunosorbent assay (ELISA). Thirty-one HME patient serum samples that had detectable E. chaffeensis antibodies (titers from 64 to 8,192) by indirect fluorescent-antibody assay (IFA) were tested. All 31 serum samples reacted with at least one E. chaffeensis peptide, 30 (96.8%) with TRP120 peptides, 27 (87.1%) with TRP32 peptides, 24 (77.4%) with TRP47 peptides, 19 (61.3%) with Ank200 peptides, and 28 (90.3%) with recombinant TRP120-TR protein. A mixture of the two most sensitive peptides from TRP120 and TRP32 did not provide enhanced analytical sensitivity compared to that provided by TRP120 alone. Our results demonstrate that the TRP120 peptide can be utilized for development of standardized sensitive point-of-care and reference laboratory immunodiagnostics for HME. This is the first study to compare analysis of molecularly defined major antibody epitopes with IFA for diagnosis of HME.

Major species-specific antibody epitopes of the Ehrlichia chaffeensis p120 and E. canis p140 orthologs in surface-exposed tandem repeat regions

Ehrlichia chaffeensis and E. canis have a small subset of tandem repeat (TR)-containing protein orthologs, including p120/p140, which elicit strong antibody responses. The TR regions of these protein orthologs are immunoreactive, but the molecular characteristics of the p120/p140 epitopes have not been determined. In this study, the immunodeterminants of the E. chaffeensis p120 and E. canis p140 were identified and molecularly defined. Major antibody epitope-containing regions of both p120 and p140 were localized to the TR regions, which reacted strongly by Western immunoblotting with antibodies in sera from E. chaffeensis-infected dogs or patients and E. canis-infected dogs, respectively. Single continuous species-specific major epitopes within the E. chaffeensis p120 and E. canis p140 TRs were mapped to homologous surface-exposed glutamate/aspartate-rich regions (19 to 22 amino acids). In addition, minor cross-reactive epitopes were localized to homologous N- and C-terminal regions of p120 and p140. Furthermore, although the native and recombinant p120 and p140 proteins exhibited higher-than-predicted molecular masses, posttranslational modifications were not present on abnormally migrating p120 and p140 TR recombinant proteins as determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

Differential expression and glycosylation of anaplasma phagocytophilum major surface protein 2 paralogs during cultivation in sialyl Lewis x-deficient host cells

Many microbial pathogens alter expression and/or posttranslational modifications of their surface proteins in response to dynamics within their host microenvironments to retain optimal interactions with their host cells and/or to evade the humoral immune response. Anaplasma phagocytophilum is an intragranulocytic bacterium that utilizes sialyl Lewis x (sLe(x))-modified P-selectin glycoprotein ligand 1 as a receptor for infecting myeloid cells. Bacterial populations that do not rely on this receptor can be obtained through cultivation in sLe(x)-defective cell lines. A. phagocytophilum major surface protein 2 [Msp2(P44)] is encoded by members of a paralogous gene family and is speculated to play roles in host adaptation. We assessed the complement of Msp2(P44) paralogs expressed by A. phagocytophilum during infection of sLe(x)-competent HL-60 cells and two HL-60 cell lines defective for sLe(x) expression. Multiple Msp2(P44) and N-terminally truncated 25- to 27-kDa isoforms having various isoelectric points and electrophoretic mobilities were expressed in each cell line. The complement of expressed msp2(p44) paralogs and the glycosyl residues modifying Msp2(P44) varied considerably among bacterial populations recovered from sLe(x)-competent and -deficient host cells. Thus, loss of host cell sLe(x) expression coincided with both differential expression and glycosylation of A. phagocytophilum Msp2(P44). This reinforces the hypothesis that this bacterium is able to generate a large variety of surface-exposed molecules that could provide great antigenic diversity and result in multiple binding properties.

A glycosylated peptide in the West Nile virus envelope protein is immunogenic during equine infection

Using a monoclonal antibody directed to domain I of the West Nile virus (WNV) envelope (E) protein, we identified a continuous (linear) epitope that was immunogenic during WNV infection of horses. Using synthetic peptides, this epitope was mapped to a 19 aa sequence (WN19: E147-165) encompassing the WNV NY99 E protein glycosylation site at position 154. The inability of WNV-positive horse and mouse sera to bind the synthetic peptides indicated that glycosylation was required for recognition of peptide WN19 by WNV-specific antibodies in sera. N-linked glycosylation of WN19 was achieved through expression of the peptide as a C-terminal fusion protein in mammalian cells and specific reactivity of WNV-positive horse sera to the glycosylated WN19 fusion protein was shown by Western blot. Additional sera collected from horses infected with Murray Valley encephalitis virus (MVEV), which is similarly glycosylated at position E154 and exhibits high sequence identity to WNV NY99 in this region, also recognized the recombinant peptide. Failure of most WNV- and MVEV-positive horse sera to recognize the epitope as a deglycosylated fusion protein confirmed that the N-linked glycan was important for antibody recognition of the peptide. Together, these results suggest that the induction of antibodies to the WN19 epitope during WNV infection of horses is generally associated with E protein glycosylation of the infecting viral strain.

Results from an indirect fluorescent antibody test using three different strains of Ehrlichia canis

An indirect fluorescent antibody (IFA) test is usually performed to detect antibodies in dogs naturally infected by Ehrlichia canis. In this work, results obtained using three different E. canis strains as antigen (a commercial antigen, the E. canis Oklahoma strain and the E. canis Madrid strain) were compared. One hundred and forty-nine serum samples obtained from dogs living in the centre of Spain were analysed. When qualitative results were evaluated, identical results were detected in 87.2% of samples for the three antigens tested. When comparing antibody titre results, differences between the Madrid strain and the commercial antigen, and between the Madrid and Oklahoma strains were statistically significant (P<0.0001). No differences were found when comparing the Oklahoma strain with the commercial antigen (P=0.562). Subtle intra-laboratory variations shown in this study suggest a higher sensitivity of the IFA test when an autochthonous strain is used as antigen.

Genetic and antigenic diversities of major immunoreactive proteins in globally distributed Ehrlichia canis strains

The extent of knowledge regarding the diversity of globally distributed Ehrlichia canis strains has been limited to information gained from a few evolutionarily conserved genes. In this study, E. canis strains from the United States (strain Jake [US]), Brazil (strain São Paulo [BR]), and Israel (strain 611 [IS] and Ranana [IS-R]) were used to examine the antigenic and genetic diversities of four well-characterized major immunoreactive protein genes/proteins. gp36 and gp200 were the most divergent genes, and nucleotide substitutions in the gp36 tandem repeat region of the IS strain, but not the IS-R strain, resulted in two amino acid differences (S-->P and P-->T) in each nine-amino-acid repeat (epitope-containing region). DNA sequences of gp19 and gp140 were completely conserved in the US and BR strains, but differences were found in the Israeli strains, including two fewer tandem repeats in gp140 and a single amino acid substitution in gp19 from the IS strain. E. canis whole-cell lysates from each isolate were examined by Western immunoblotting using sera from naturally infected dogs from each country, and four major immunoreactive proteins (gp19, gp36, gp140, and gp200) were identified in each strain using protein-specific antisera. The US and BR strains exhibited highly conserved immunoreactive protein profiles, while some differences were identified in the IS strain. Sera from naturally infected Israeli dogs confirmed gene sequencing information, which demonstrated two distinct E. canis strains, defined by the gp36 gene. Conversely, gp19 was strongly reactive and present in all E. canis isolates. gp140 and gp200 were also present in all strains, although gp140 in the IS strain had two fewer tandem repeats and exhibited a smaller mass.

Anaplasma phagocytophilum MSP2(P44)-18 predominates and is modified into multiple isoforms in human myeloid cells

Anaplasma phagocytophilum is the etiologic agent of human granulocytic anaplasmosis. MSP2(P44), the bacterium's major surface protein, is encoded by a paralogous gene family and has been implicated in a variety of pathobiological processes, including antigenic variation, host adaptation, adhesion, porin activity, and structural integrity. The consensus among several studies performed at the DNA and RNA levels is that a heterogeneous mix of a limited number of msp2(p44) transcripts is expressed by A. phagocytophilum during in vitro cultivation. Such analyses have yet to be extended to the protein level. In this study, we used proteomic and molecular approaches to determine that MSP2(P44)-18 is the predominant if not the only paralog expressed and is modified into multiple 42- to 44-kDa isoforms by A. phagocytophilum strain HGE1 during infection of HL-60 cells. The msp2(p44) expression profile was homogeneous for msp2(p44)-18. Thus, MSP2(P44)-18 may have a fitness advantage in HL-60 cell culture in the absence of selective immune pressure. Several novel 22- to 27-kDa MSP2 isoforms lacking most of the N-terminal conserved region were also identified. A. phagocytophilum MSP2(P44) orthologs expressed by other pathogens in the family Anaplasmataceae are glycosylated. Gas chromatography revealed that recombinant MSP2(P44)-18 is modified by glucose, galactose, xylose, mannose, and trace amounts of other glycosyl residues. These data are the first to confirm differential modification of any A. phagocytophilum MSP2(P44) paralog and the first to provide evidence for expression of truncated versions of such proteins.

A variable-length PCR target protein of Ehrlichia chaffeensis contains major species-specific antibody epitopes in acidic serine-rich tandem repeats

Ehrlichia chaffeensis and E. canis have a small subset of tandem repeat (TR)-containing proteins that elicit strong host immune responses and are associated with host-pathogen interactions. In a previous study, we molecularly characterized a highly conserved 19-kDa major immunoreactive protein (gp19) of E. canis and identified the corresponding TR-containing ortholog variable-length PCR target (VLPT) protein in E. chaffeensis. In this study, the native 32-kDa VLPT protein was identified and the immunodeterminants defined in order to further understand the molecular basis of the host immune response to E. chaffeensis. Synthetic and/or recombinant polypeptides corresponding to various regions of VLPT were used to localize major antibody epitopes to the TR-containing region. Major antibody epitopes were identified in three nonidentical repeats (R2, R3, and R4), which reacted strongly with antibodies in sera from an E. chaffeensis-infected dog and human monocytotropic ehrlichiosis patients. VLPT-R3 and VLPT-R2 reacted most strongly with antibody, and the epitope was further localized to a nearly identical proximal 17-amino-acid region common between these repeats that was species specific. The epitope in R4 was distinct from that of R2 and R3 and was found to have conformational dependence. VLPT was detected in supernatants from infected cells, indicating that the protein was secreted. VLPT was localized on both reticulate and dense-core cells, and it was found extracellularly in the morula fibrillar matrix and associated with the morula membrane.

Ehrlichia canis gp200 contains dominant species-specific antibody epitopes in terminal acidic domains

Species-specific antibody epitopes within several major immunoreactive protein orthologs of Ehrlichia species have recently been identified and molecularly characterized. In this study, dominant B-cell epitopes within the acidic (pI 5.35) ankyrin repeat-containing 200-kDa major immunoreactive protein (gp200) of Ehrlichia canis were defined. The E. canis gp200 gene (4,263 bp; 1,421 amino acids) was cloned and expressed as four (N-terminal, 1,107 bp; N-internal, 910 bp; C-internal, 1,000 bp; and C-terminal, 1,280 bp) overlapping recombinant proteins. The N-terminal, C-internal, and C-terminal polypeptides (369, 332, and 426 amino acids, respectively) were strongly recognized by antibody, and the major epitope(s) in these polypeptides was mapped to four polypeptide regions (40 to 70 amino acids). Smaller overlapping recombinant polypeptides (14 to 15 amino acids) spanning these regions identified five strongly immunoreactive species-specific epitopes that exhibited conformational dependence. The majority of the epitopes (four) were located in two strongly acidic (pI 4 to 4.9) domains in the distal N- and C-terminal regions of the protein flanking the centralized ankyrin domain-containing region. The amino acid content of the epitope-containing domains included a high proportion of strongly acidic amino acids (glutamate and aspartate), and these domains appear to have important biophysical properties that influence the antibody response to gp200.

Enzyme-linked immunosorbent assay with conserved immunoreactive glycoproteins gp36 and gp19 has enhanced sensitivity and provides species-specific immunodiagnosis of Ehrlichia canis infection

Ehrlichia canis is the primary etiologic agent of canine monocytic ehrlichiosis, a globally distributed and potentially fatal disease of dogs. We previously reported on the identification of two conserved major immunoreactive antigens, gp36 and gp19, which are the first proteins to elicit an E. canis-specific antibody response, and gp200 and p28, which elicit strong antibody responses later in the acute phase of the infection. In this report, the sensitivities and specificities of five recombinant E. canis proteins for the immunodiagnosis of E. canis infection by an enzyme-linked immunosorbent assay (ELISA) were evaluated. Recombinant polypeptides gp36, gp19, and gp200 (N and C termini) exhibited 100% sensitivity and specificity for immunodiagnosis by the recombinant glycoprotein ELISA compared with the results obtained by an indirect fluorescent-antibody assay (IFA) for the detection of antibodies in dogs that were naturally infected with E. canis. Moreover, the enhanced sensitivities of gp36 and gp19 for immunodiagnosis by the recombinant glycoprotein ELISA compared to those obtained by IFA were demonstrated with dogs experimentally infected with E. canis, in which antibodies were detected as much as 2 weeks earlier, on day 14 postinoculation. gp36 and gp19 were not cross-reactive with antibodies in sera from E. chaffeensis-infected dogs and thus provided species-specific serologic discrimination between E. canis and E. chaffeensis infections. This is the first demonstration of the improved detection capability of the recombinant protein technology compared to the capability of the "gold standard" IFA and may eliminate the remaining obstacles associated with the immunodiagnosis of E. canis infections, including species-specific identification and the lack of sensitivity associated with low antibody titers early in the acute phase of the infection.