Serodiagnosis of human granulocytic ehrlichiosis by a recombinant HGE-44-based enzyme-linked immunosorbent assay

A review on the eco-epidemiology and clinical management of human granulocytic anaplasmosis and its agent in Europe

Anaplasma phagocytophilum is the agent of tick-borne fever, equine, canine and human granulocytic anaplasmosis. The common route of A. phagocytophilum transmission is through a tick bite, the main vector in Europe being Ixodes ricinus. Despite the apparently ubiquitous presence of the pathogen A. phagocytophilum in ticks and various wild and domestic animals from Europe, up to date published clinical cases of human granulocytic anaplasmosis (HGA) remain rare compared to the worldwide status. It is unclear if this reflects the epidemiological dynamics of the human infection in Europe or if the disease is underdiagnosed or underreported. Epidemiologic studies in Europe have suggested an increased occupational risk of infection for forestry workers, hunters, veterinarians, and farmers with a tick-bite history and living in endemic areas. Although the overall genetic diversity of A. phagocytophilum in Europe is higher than in the USA, the strains responsible for the human infections are related on both continents. However, the study of the genetic variability and assessment of the difference of pathogenicity and infectivity between strains to various hosts has been insufficiently explored to date. Most of the European HGA cases presented as a mild infection, common clinical signs being pyrexia, headache, myalgia and arthralgia. The diagnosis of HGA in the USA was recommended to be based on clinical signs and the patient’s history and later confirmed using specialized laboratory tests. However, in Europe since the majority of cases are presenting as mild infection, laboratory tests may be performed before the treatment in order to avoid antibiotic overuse. The drug of choice for HGA is doxycycline and because of potential for serious complication the treatment should be instituted on clinical suspicion alone.

Identification of novel immunoreactive proteins and delineation of a specific epitope of Anaplasma phagocytophilum

Human granulocytic anaplasmosis (HGA), an increasingly recognized febrile tick-borne illness, is caused by a gram-negative obligate intracellular bacterium Anaplasma phagocytophilum. Because of nonspecific clinical manifestations, diagnosis of HGA highly depends on laboratory tests. Identification of immunoreactive proteins is prerequisite for development of specific and sensitive immunoassays for HGA. In this study, we identified novel immunoreactive proteins of A. phagocytophilum. Previous studies indicated that secreted proteins of A. phagocytophilum and other bacteria can be immunoreactive antigens. Here we in silico screened A. phagocytophilum genome for encoding proteins which bear features of type IV secretion system substrates. Among seventy seven predicted proteins, fourteen proteins were determined for antigenicity and nine proteins were showed to be immunoreactive antigens. In addition, an APH1384 peptide harboring a B cell epitope predicted by bioinformatics was found specifically reacting with anti-A. phagocytophilum sera. Hereby, we identified novel immunoreactive proteins and delineated a specific epitope of A. phagocytophilum, which might be employed for HGA diagnosis.

Anaplasma phagocytophilum-Occupied Vacuole Interactions with the Host Cell Cytoskeleton

Anaplasma phagocytophilum is an obligate intracellular bacterial pathogen of humans and animals. The A. phagocytophium-occupied vacuole (ApV) is a critical host-pathogen interface. Here, we report that the intermediate filaments, keratin and vimentin, assemble on the ApV early and remain associated with the ApV throughout infection. Microtubules localize to the ApV to a lesser extent. Vimentin, keratin-8, and keratin-18 but not tubulin expression is upregulated in A. phagocytophilum infected cells. SUMO-2/3 but not SUMO-1 colocalizes with vimentin filaments that surround ApVs. PolySUMOylation of vimentin by SUMO-2/3 but not SUMO-1 decreases vimentin solubility. Consistent with this, more vimentin exists in an insoluble state in A. phagocytophilum infected cells than in uninfected cells. Knocking down the SUMO-conjugating enzyme, Ubc9, abrogates vimentin assembly at the ApV but has no effect on the bacterial load. Bacterial protein synthesis is dispensable for maintaining vimentin and SUMO-2/3 at the ApV. Withaferin A, which inhibits soluble vimentin, reduces vimentin recruitment to the ApV, optimal ApV formation, and the bacterial load when administered prior to infection but is ineffective once vimentin has assembled on the ApV. Thus, A. phagocytophilum modulates cytoskeletal component expression and co-opts polySUMOylated vimentin to aid construction of its vacuolar niche and promote optimal survival.

Seroprevalence of seven pathogens transmitted by the Ixodes ricinus tick in forestry workers in France

In order to assess the level of occupational exposure to the main pathogens transmitted by the Ixodes ricinus tick, a seroprevalence study was performed on serum samples collected in 2003 from 2975 forestry workers of northeastern France. The global seroprevalence estimated for the seven pathogens studied was 14.1% (419/2975) for Borrelia burgdorferi sl, 5.7% (164/2908) for Francisella tularensis, 2.3% (68/2941) for tick-borne encephalitis virus, 1.7% (50/2908) for Anaplasma phagocytophilum and 1.7% (48/2908) for Bartonella henselae. The seroprevalences of Babesia divergens and Babesia microti studied in a subgroup of participants seropositive for at least one of these latter pathogens were 0.1% (1/810) and 2.5% (20/810), respectively. Borrelia burgdorferi sl seroprevalence was significantly higher in Alsace and Lorraine and F. tularensis seroprevalence was significantly higher in Champagne-Ardenne and Franche-Comté. The results of this survey also suggest low rates of transmission of Bartonella henselae and F. tularensis by ticks and a different west/east distribution of Babesia species in France. The frequency and potential severity of these diseases justify continued promotion of methods of prevention of I. ricinus bites.

Anaplasma phagocytophilum Rab10-dependent parasitism of the trans-Golgi network is critical for completion of the infection cycle

Anaplasma phagocytophilum is an emerging human pathogen and obligate intracellular bacterium. It inhabits a host cell-derived vacuole and cycles between replicative reticulate cell (RC) and infectious dense-cored (DC) morphotypes. Host-pathogen interactions that are critical for RC-to-DC conversion are undefined. We previously reported that A. phagocytophilum recruits green fluorescent protein (GFP)-tagged Rab10, a GTPase that directs exocytic traffic from the sphingolipid-rich trans-Golgi network (TGN) to its vacuole in a guanine nucleotide-independent manner. Here, we demonstrate that endogenous Rab10-positive TGN vesicles are not only routed to but also delivered into the A. phagocytophilum-occupied vacuole (ApV). Consistent with this finding, A. phagocytophilum incorporates sphingolipids while intracellular and retains them when naturally released from host cells. TGN vesicle delivery into the ApV is Rab10 dependent, up-regulates expression of the DC-specific marker, APH1235, and is critical for the production of infectious progeny. The A. phagocytophilum surface protein, uridine monophosphate kinase, was identified as a guanine nucleotide-independent, Rab10-specific ligand. These data delineate why Rab10 is important for the A. phagocytophilum infection cycle and expand the understanding of the benefits that exploiting host cell membrane traffic affords intracellular bacterial pathogens.

Anaplasma phagocytophilum Asp14 is an invasin that interacts with mammalian host cells via its C terminus to facilitate infection

Anaplasma phagocytophilum, a member of the family Anaplasmataceae, is the tick-transmitted obligate intracellular bacterium that causes human granulocytic anaplasmosis. The life cycle of A. phagocytophilum is biphasic, transitioning between the noninfectious reticulate cell (RC) and infectious dense-cored (DC) forms. We analyzed the bacterium's DC surface proteome by selective biotinylation of surface proteins, NeutrAvidin affinity purification, and mass spectrometry. Transcriptional profiling of selected outer membrane protein candidates over the course of infection revealed that aph_0248 (designated asp14 [14-kDa A. phagocytophilum surface protein]) expression was upregulated the most during A. phagocytophilum cellular invasion. asp14 transcription was induced during transmission feeding of A. phagocytophilum-infected ticks on mice and was upregulated when the bacterium engaged its receptor, P-selectin glycoprotein ligand 1. Asp14 localized to the A. phagocytophilum surface and was expressed during in vivo infection. Treating DC organisms with Asp14 antiserum or preincubating mammalian host cells with glutathione S-transferase (GST)-Asp14 significantly inhibited infection of host cells. Moreover, preincubating host cells with GST-tagged forms of both Asp14 and outer membrane protein A, another A. phagocytophilum invasin, pronouncedly reduced infection relative to treatment with either protein alone. The Asp14 domain that is sufficient for cellular adherence and invasion lies within the C-terminal 12 to 24 amino acids and is conserved among other Anaplasma and Ehrlichia species. These results identify Asp14 as an A. phagocytophilum surface protein that is critical for infection, delineate its invasion domain, and demonstrate the potential of targeting Asp14 in concert with OmpA for protecting against infection by A. phagocytophilum and other Anaplasmataceae pathogens.

Evaluation of an indirect enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against Anaplasma phagocytophilum in sheep

An indirect enzyme-linked immunosorbent assay (ELISA) for detection of antibodies against Anaplasma phagocytophilum in ovine serum samples was evaluated. The assay used purified A. phagocytophilum grown in tick cell cultures as antigen. Serum samples were diluted 1 in 200 and binding was detected with anti-sheep IgG conjugated to horseradish peroxidase. All tests were carried out in the presence of positive and negative control samples. Optical density (OD) values obtained for each test sample at 490 nm were used to calculate percentage positivity (PP) of each sample based on the ratio of the OD of the test sample that of the positive reference sample. Known negative samples (n=69) obtained from uninfected sheep bred and maintained in a tick-free environment and subsequently shown to be susceptible to A. phagocytophilum were used to establish the cut-off point between negative and positive samples and to establish the specificity of the test. Serum samples obtained from 92 animals 14-21 days after infection were used to establish the sensitivity of the test. Using a cut-off point of 20PP (mean+2 standard deviations of the PP of 69 control samples) the test was shown to have a sensitivity of 84.8% and a specificity of 95.7%. Lowering the cut-off point to 15PP increased the sensitivity to 94.6%, but reduced the specificity to 92.8%.

Monoubiquitinated proteins decorate the Anaplasma phagocytophilum-occupied vacuolar membrane

An emerging theme among vacuole-adapted bacterial pathogens is the ability to hijack ubiquitin machinery to modulate host cellular processes and secure pathogen survival. Mono- and polyubiquitination differentially dictate the subcellular localization, activity, and fate of protein substrates. Monoubiquitination directs membrane traffic from the plasma membrane to the endosome and has been shown to promote autophagy. Anaplasma phagocytophilum is an obligate intracellular bacterium that replicates within a host cell-derived vacuole that co-opts membrane traffic and numerous other host cell processes. Here, we show that monoubiquitinated proteins decorate the A. phagocytophilum-occupied vacuolar membrane (AVM) during infection of promyelocytic HL-60 cell, endothelial RF/6A cells, and to a lesser extent, embryonic tick ISE6 cells. Monoubiquitinated proteins are present on the AVM upon its formation and continue to accumulate throughout infection. Tetracycline-mediated inhibition of de novo bacterial protein synthesis promotes the loss of ubiquitinated proteins from the AVM. This effect is reversible, as removal of tetracycline restores AVM ubiquitination to pretreatment levels. These results demonstrate a novel mechanism by which A. phagocytophilum remodels the composition of its host cell-derived vacuolar membrane and present the first example of a Rickettsiales pathogen co-opting ubiquitin during intracellular residence.

Proteomic analysis of Anaplasma phagocytophilum during infection of human myeloid cells identifies a protein that is pronouncedly upregulated on the infectious dense-cored cell

Anaplasma phagocytophilum is an obligate intracellular bacterium that invades neutrophils to cause the emerging infectious disease human granulocytic anaplasmosis. A. phagocytophilum undergoes a biphasic developmental cycle, transitioning between an infectious dense-cored cell (DC) and a noninfectious reticulate cell (RC). To gain insights into the organism's biology and pathogenesis during human myeloid cell infection, we conducted proteomic analyses on A. phagocytophilum organisms purified from HL-60 cells. A total of 324 proteins were unambiguously identified, thereby verifying 23.7% of the predicted A. phagocytophilum proteome. Fifty-three identified proteins had been previously annotated as hypothetical or conserved hypothetical. The second most abundant gene product, after the well-studied major surface protein 2 (P44), was the hitherto hypothetical protein APH_1235. APH_1235 homologs are found in other Anaplasma and Ehrlichia species but not in other bacteria. The aph_1235 RNA level is increased 70-fold in the DC form relative to that in the RC form. Transcriptional upregulation of and our ability to detect APH_1235 correlate with RC to DC transition, DC exit from host cells, and subsequent DC binding and entry during the next round of infection. Immunoelectron microscopy pronouncedly detects APH_1235 on DC organisms, while detection on RC bacteria minimally, at best, exceeds background. This work represents an extensive study of the A. phagocytophilum proteome, discerns the complement of proteins that is generated during survival within human myeloid cells, and identifies APH_1235 as the first known protein that is pronouncedly upregulated on the infectious DC form.

Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum

Anaplasma phagocytophilum persists in nature by cycling between mammals and ticks. Human infection by the bite of an infected tick leads to a potentially fatal emerging disease called human granulocytic anaplasmosis. A. phagocytophilum is an obligatory intracellular bacterium that replicates inside mammalian granulocytes and the salivary gland and midgut cells of ticks. A. phagocytophilum evolved the remarkable ability to hijack the regulatory system of host cells. A. phagocytophilum alters vesicular traffic to create an intracellular membrane-bound compartment that allows replication in seclusion from lysosomes. The bacterium downregulates or actively inhibits a number of innate immune responses of mammalian host cells, and it upregulates cellular cholesterol uptake to acquire cholesterol for survival. It also upregulates several genes critical for the infection of ticks, and it prolongs tick survival at freezing temperatures. Several host factors that exacerbate infection have been identified, including interleukin-8 (IL-8) and cholesterol. Host factors that overcome infection include IL-12 and gamma interferon (IFN-γ). Two bacterial type IV secretion effectors and several bacterial proteins that associate with inclusion membranes have been identified. An understanding of the molecular mechanisms underlying A. phagocytophilum infection will foster the development of creative ideas to prevent or treat this emerging tick-borne disease.

Cloning of the major outer membrane protein expression locus in Anaplasma platys and seroreactivity of a species-specific antigen

Anaplasma platys infects peripheral blood platelets and causes infectious cyclic thrombocytopenia in canines. The genes, proteins, and antigens of A. platys are largely unknown, and an antigen for serodiagnosis of A. platys has not yet been identified. In this study, we cloned the A. platys major outer membrane protein cluster, including the P44/Msp2 expression locus (p44ES/msp2ES) and outer membrane protein (OMP), using DNA isolated from the blood of four naturally infected dogs from Venezuela and Taiwan, Republic of China. A. platys p44ES is located within a 4-kb genomic region downstream from a putative transcriptional regulator, tr1, and a homolog of the Anaplasma phagocytophilum, identified here as A. platys omp-1X. The predicted molecular masses of the four mature A. platys P44ES proteins ranged from 43.3 to 43.5 kDa. Comparative analyses of the deduced amino acid sequences of Tr1, OMP-1X, and P44/Msp2 proteins from A. platys with those from A. phagocytophilum showed sequence identities of 86.4% for Tr1, 45.9% to 46.3% for OMP-1X, and 55.0% to 56.9% for P44/Msp2. Comparison between A. platys and Anaplasma marginale proteins showed sequence identities of 73.1% for Tr1/Tr, 39.8% for OMP-1X/OMP1, and 41.5% to 42.1% for P44/Msp2. A synthetic OMP-1X peptide was shown to react with A. platys-positive sera but not with A. platys-negative sera or A. phagocytophilum-positive sera. Together, determination of the genomic locus of A. platys outer membrane proteins not only contributes to the fundamental understanding of this enigmatic pathogen but also helps in developing A. platys-specific PCR and serodiagnosis.

Anaplasma phagocytophilum and Ehrlichia chaffeensis: subversive manipulators of host cells

Anaplasma spp. and Ehrlichia spp. cause several emerging human infectious diseases. Anaplasma phagocytophilum and Ehrlichia chaffeensis are transmitted between mammals by blood-sucking ticks and replicate inside mammalian white blood cells and tick salivary-gland and midgut cells. Adaptation to a life in eukaryotic cells and transmission between hosts has been assisted by the deletion of many genes that are present in the genomes of free-living bacteria (including genes required for the biosynthesis of lipopolysaccharide and peptidoglycan), by the acquisition of a cholesterol uptake pathway and by the expansion of the repertoire of genes encoding the outer-membrane porins and type IV secretion system. Here, I review the specialized properties and other adaptations of these intracellular bacteria.

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.

Serosurveillance forAnaplasma phagocytophilumAntibodies in White-Tailed Deer (Odocoileus virginianus) in Iowa, USA

Cases of human granulocytic anaplasmosis have increased in number and are being identified in new geographic areas since its discovery in 1994. White-tailed deer (WTD) become infected with the causative agent, Anaplasma phagocytophilum, and serve as natural sentinels for this organism. In order to determine if A. phagocytophilum is present in the state of Iowa, sera collected from 628 WTD in 2004 from 13 sites and from 282 WTD in 1999 from a single, common site were tested by enzyme-linked immunosorbent assay and Western immunoblotting. A seroprevalence of 9.1% was found among the 2004 samples, and there was no change in seropositivity rates from 1999 to 2004 at the single, common site. As A. phagocytophilum is another tick-borne human pathogen to be identified in the state of Iowa, this study has important implications for health care providers.

Two monoclonal antibodies with defined epitopes of P44 major surface proteins neutralize Anaplasma phagocytophilum by distinct mechanisms

Anaplasma phagocytophilum is an obligatory intracellular bacterium that causes human granulocytic anaplasmosis. The polymorphic 44-kDa major outer membrane proteins of A. phagocytophilum are dominant antigens recognized by patients and infected animals. However, the ability of anti-P44 antibody to neutralize the infection has been unclear due to a mixture of P44 proteins with diverse hypervariable region amino acid sequences expressed by a given bacterial population and lack of epitope-defined antibodies. Monoclonal antibodies (MAbs) 5C11 and 3E65 are directed to different domains of P44 proteins, the N-terminal conserved region and P44-18 central hypervariable region, respectively. Passive immunization with either MAb 5C11 or 3E65 partially protects mice from infection with A. phagocytophilum. In the present study, we demonstrated that the two monoclonal antibodies recognize bacterial surface-exposed epitopes of naturally folded P44 proteins and mapped these epitopes to specific peptide sequences. The two MAbs almost completely blocked the infection of the A. phagocytophilum population that predominantly expressed P44-18 in HL-60 cells by distinct mechanisms: MAb 5C11 blocked the binding, but MAb 3E65 did not block binding or internalization. Instead, MAb 3E65 inhibited internalized A. phagocytophilum to develop into microcolonies called morulae. Some plasma from experimentally infected horses and mice reacted with these two epitopes. Taken together, these data indicate the presence of at least two distinct bacterial surface-exposed neutralization epitopes in P44 proteins. The results indicate that antibodies directed to certain epitopes of P44 proteins have a critical role in inhibiting A. phagocytophilum infection of host cells.

Seroprevalence of antibodies against Borrelia burgdorferi and Anaplasma phagocytophilum in cats

OBJECTIVE

To determine whether cats in the northeastern United States develop serum antibodies against antigens of Borrelia burgdorferi and Anaplasma phagocytophilum and whether coinfection with the 2 organisms occurs.

SAMPLE POPULATION

Serum samples from 84 healthy cats and 9 cats with lameness, fever, anorexia, or fatigue.

PROCEDURE

Serum antibodies against B. burgdorferi and A. phagocytophilum were measured with an ELISA incorporating a whole-cell preparation or purified recombinant antigens, by means of Western blot analysis, or indirect fluorescent antibody (IFA) staining.

RESULTS

ELISA results indicated that 44 of 93 (47%) sera contained antibodies against > or = 3 B. burgdorferi antigens, whereas 43 (46%) were reactive to whole-cell B. burgdorferi. Serum reactivity to protein 35, VlsE, and outer surface proteins A and F was most common. Seropositivity to > or = 3 antigens occurred at the same rate (5/9) in the 9 ill cats as in the 84 healthy cats (46% [39/84]). Of 13 sera reactive to recombinant antigens, 9 were seropositive as measured by Western blot testing with whole-cell antigen. Seropositivity rates of 30% and 38% were detected for antibodies against A phagocytophilum via IFA and ELISA testing, respectively. Fifteen (16%) sera had antibodies against both pathogens.

CONCLUSIONS AND CLINICAL RELEVANCE

Cats living in areas infested by Ixodes scapularis ticks are exposed to B. burgdorferi and A. phagocytophilum and, in some instances, may be coinfected. Most cats appeared healthy. An ELISA incorporating specific recombinant antigens may be used adjunctively with Western blot and other assays to confirm B. burgdorferi and A. phagocytophilum infection in cats.

Antigenicity of Ovine Strains of Anaplasma phagocytophilum Grown in Tick Cells and Ovine Granulocytes

Antigens prepared from ovine granulocytes and tick cells infected with ovine strains of Anaplasma phagocytophilum, the causative agent of tick-borne fever, were tested in respect of their suitability for the assay of antibodies in ovine sera by enzyme-linked immunosorbent assay (ELISA) and by indirect immunofluorescent antibody test (IFAT). Antigens prepared from tick cells were as sensitive and specific as those expressed in ovine granulocytes for the detection of specific antibodies by ELISA, but they failed to react in the IFAT with immune sera obtained from sheep previously infected with ovine strains of A. phagocytophilum.

Neutrophil NADPH oxidase is reduced at the Anaplasma phagocytophilum phagosome

The intracellular organism Anaplasma phagocytophilum causes human granulocytic ehrlichiosis and specifically infects and multiplies in neutrophilic granulocytes. Previous reports have suggested that, for its survival, this bacterium suppresses the neutrophil respiratory burst. To investigate the mechanism of survival, we first assessed the kinetics of A. phagocytophilum entry into neutrophils by using double-labeling confocal microscopy. At 30, 60, 120, and 240 min of incubation, 25, 50, 55, and 70% of neutrophils contained bacteria, respectively. The neutrophil respiratory burst in the presence of A. phagocytophilum was assessed by a kinetic cytochrome c assay and by measurement of oxygen consumption. Neutrophils in the presence of A. phagocytophilum did not produce a significant respiratory burst, but A. phagocytophilum did not inhibit the neutrophil respiratory burst when phorbol myristate acetate was added. Immunoelectron microscopy of neutrophils infected with A. phagocytophilum or Escherichia coli revealed that NADPH oxidase subunits gp91(phox) and p22(phox) were significantly reduced at the A. phagocytophilum phagosome after 1 and 4 h of incubation. In neutrophils incubated simultaneously with A. phagocytophilum and E. coli for 30, 60, and 90 min, gp91(phox) was present on 20, 14, and 10% of the A. phagocytophilum phagosomes, whereas p22(phox) was present in 11, 5, and 4% of the phagosomes, respectively. Similarly, on E. coli phagosomes, gp91(phox) was present in 62, 64, and 65%, whereas p22(phox) was detected in 54, 48, and 48%. We conclude that A. phagocytophilum does not suppress a global respiratory burst and that, under identical conditions in the same cells, A. phagocytophilum, but not E. coli, significantly reduces gp91(phox) and p22(phox) from its phagosome membrane.

Coevolution of markers of innate and adaptive immunity in skin and peripheral blood of patients with erythema migrans

We used multiparameter flow cytometry to characterize leukocyte immunophenotypes and cytokines in skin and peripheral blood of patients with erythema migrans (EM). Dermal leukocytes and cytokines were assessed in fluids aspirated from epidermal suction blisters raised over EM lesions and skin of uninfected controls. Compared with corresponding peripheral blood, EM infiltrates were enriched for T cells, monocytes/macrophages, and dendritic cells (DCs), contained lower proportions of neutrophils, and were virtually devoid of B cells. Enhanced expression of CD14 and HLA-DR by lesional neutrophils and macrophages indicated that these innate effector cells were highly activated. Staining for CD45RO and CD27 revealed that lesional T lymphocytes were predominantly Ag-experienced cells; furthermore, a subset of circulating T cells also appeared to be neosensitized. Lesional DC subsets, CD11c(+) (monocytoid) and CD11c(-) (plasmacytoid), expressed activation/maturation surface markers. Patients with multiple EM lesions had greater symptom scores and higher serum levels of IFN-alpha, TNF-alpha, and IL-2 than patients with solitary EM. IL-6 and IFN-gamma were the predominant cytokines in EM lesions; however, greater levels of both mediators were detected in blister fluids from patients with isolated EM. Circulating monocytes displayed significant increases in surface expression of Toll-like receptor (TLR)1 and TLR2, while CD11c(+) DCs showed increased expression of TLR2 and TLR4; lesional macrophages and CD11c(+) and CD11c(-) DCs exhibited increases in expression of all three TLRs. These results demonstrate that Borrelia burgdorferi triggers innate and adaptive responses during early Lyme disease and emphasize the interdependence of these two arms of the immune response in the efforts of the host to contain spirochetal infection.

Human granulocytic ehrlichiosis in Italy: first report on two confirmed cases

We report here the two first cases of human ehrlichiosis described in Italy. One patient presented symptoms indicative of ehrlichiosis, such as fever, conjunctivitis, and increase of hepatic enzymes; HGE was confirmed by fourfold seroconversion for HGE antigen. The second patient, a forest worker, was affected by Lyme disease, and in this case HGE was suspected because of fever, leukopenia, and seroconversion.

Ehrlichia chaffeensis: a prototypical emerging pathogen

Ehrlichia chaffeensis is an obligately intracellular, tick-transmitted bacterium that is maintained in nature in a cycle involving at least one and perhaps several vertebrate reservoir hosts. The moderate to severe disease caused by E. chaffeensis in humans, first identified in 1986 and reported for more than 1,000 patients through 2000, represents a prototypical "emerging infection." Knowledge of the biology and natural history of E. chaffeensis, and of the epidemiology, clinical features, and laboratory diagnosis of the zoonotic disease it causes (commonly referred to as human monocytic ehrlichiosis [HME]) has expanded considerably in the period since its discovery. In this review, we summarize briefly the current understanding of the microbiology, pathogenesis, and clinical manifestations associated with this pathogen but focus primarily on discussing various ecological factors responsible for the recent recognition of this important and potentially life-threatening tick-borne disease. Perhaps the most pivotal element in the emergence of HME has been the staggering increases in white-tailed deer populations in the eastern United States during the 20th century. This animal serves as a keystone host for all life stages of the principal tick vector (Amblyomma americanum) and is perhaps the most important vertebrate reservoir host for E. chaffeensis. The contributions of other components, including expansion of susceptible human populations, growth and broadening geographical distributions of other potential reservoir species and A. americanum, and improvements in confirmatory diagnostic methods, are also explored.

Differential expression of the p44 gene family in the agent of human granulocytic ehrlichiosis

Using reverse transcription-PCR targeting of the p44 genes of the agent of human granulocytic ehrlichiosis (HGE) with primers flanking the hypervariable region, we show differential expression in a murine model of HGE infection and during tick transmission. The p44 genes were differentially expressed in salivary glands of infected nymphal ticks removed during transmission feeding but not in nonfeeding infected ticks. Similarly, the p44 genes were differentially expressed in infected C3H mice, in SCID mice, and in cultured HGE bacteria. Thus, differential p44 expression exists in vivo and in vitro and could provide a basis for antigenic variation.

Disease-specific diagnosis of coinfecting tickborne zoonoses: babesiosis, human granulocytic ehrlichiosis, and Lyme disease

To determine whether a unique group of clinical and laboratory manifestations characterize certain major deer tick-transmitted human pathogens in North America, we compared the symptoms, short-term complications, and laboratory test results of New England residents who became ill due to > or =1 of these pathogens. Patients completed a uniformly structured questionnaire and submitted blood samples for serologic and polymerase chain reaction (PCR) testing after developing symptoms of Lyme disease, human babesiosis, or human granulocytic ehrlichiosis (HGE). Complete blood count with thin blood smear, PCR, and immunoglobulin M antibody tests helped differentiate the acute manifestations of these diseases. Physicians should consider use of tests designed to diagnose babesiosis and HGE in patients with Lyme disease who experience a prolonged flulike illness that fails to respond to appropriate antiborrelial therapy.

Western blot analysis of sera reactive to human monocytic ehrlichiosis and human granulocytic ehrlichiosis agents

Laboratory diagnosis of human ehrlichioses is routinely made by an indirect immunofluorescence assay (IFA) using cultured ehrlichia-infected whole cells as antigen. Concern has been raised that incorrect diagnoses of human monocytic ehrlichiosis (HME) or human granulocytic ehrlichiosis (HGE) may be made on the basis of serologic cross-reactivity between Ehrlichia chaffeensis and the agent of HGE. The present study examined whether two recombinant major outer membrane proteins, rP30 and rP44, that were previously shown to be sensitive and specific serodiagnostic antigens for HME and HGE, respectively, could be used to discriminate IFA dually reacting sera. Thirteen dually IFA-reactive sera, three sera that were IFA positive only with E. chaffeensis, and three sera that were IFA positive only with the HGE agent were examined by Western immunoblot analysis using purified whole organisms and recombinant proteins as antigens. All 16 E. chaffeensis IFA-positive sera reacted with rP30. However, none of these sera reacted with rP44, regardless of IFA reactivity with the HGE agent. The three HGE-agent-only IFA-positive sera reacted only with rP44, not with rP30. Western immunoblotting using purified E. chaffeensis and the HGE agent as antigens suggested that heat shock and other proteins, but not major outer membrane proteins, cross-react between the two organisms. Therefore, Western immunoblot analysis using rP44 and rP30 may be useful in discriminating dually HME and HGE IFA-reactive sera.

Exploitation of interleukin-8-induced neutrophil chemotaxis by the agent of human granulocytic ehrlichiosis

The agent of human granulocytic ehrlichiosis (HGE) is an obligate intracellular bacterium with a tropism for neutrophils; however, the mechanisms of bacterial dissemination are not yet understood. Interleukin-8 (IL-8) is a chemokine that induces neutrophil migration to sites of infection for host defense against pathogens. We now show that HGE bacteria, and the HGE-44 protein, induce IL-8 secretion in a promyelocytic (HL-60) cell line that has been differentiated along the neutrophil lineage with retinoic acid and in neutrophils. Infected HL-60 cells also demonstrate upregulation of CXCR2, an IL-8 receptor, but not CXCR1. Human neutrophils migrate towards Ehrlichia sp.-infected cells in a chemotaxis chamber assay, and this movement can be blocked with antibodies to IL-8. Finally, immunocompetent and severe combined immunodeficient mice administered CXCR2 antisera, and CXCR2(-/-) mice that lack the human IL-8 receptor homologue, are much less susceptible to granulocytic ehrlichiosis than are control animals. These results demonstrate that HGE bacteria induce IL-8 production by host cells and, paradoxically, appear to exploit this chemokine to enhance infection.

Coinfecting deer-associated zoonoses: Lyme disease, babesiosis, and ehrlichiosis

The heightened worldwide recognition of the health burden of tickborne infection derives largely from the increasing incidence of Lyme disease, human babesiosis, and human granulocytic ehrlichiosis, both individually and in concert. Because these infections share the same rodent reservoir and tick vector hosts, they can be cotransmitted to human hosts. Indeed, human coinfections involving various combinations of these pathogens are common, and some tend to be particularly severe. Diagnostic procedures and clinical management of the resulting disease syndrome is rendered complex by the diversity of pathogens involved and by the unusual diversity and duration of symptoms.

Reactivity of serum samples of dogs and horses tested by use of class-specific recombinant-based enzyme-linked immunosorbent assays for detection of granulocytic ehrlichiosis

OBJECTIVE

To test serum samples of dogs and horses by use of class-specific recombinant-based ELISA for establishing a diagnosis of granulocytic ehrlichiosis attributable to infection with organisms from the Ehrlichia phagocytophila genogroup.

SAMPLE POPULATION

Serum samples from 43 client-owned dogs and 131 horses (81 with signs of acute illness and 50 without signs of disease).

PROCEDURE

Serum samples were analyzed, using ELISA with a recombinant 44-kd protein antigen for IgM and IgG antibodies to the human granulocytic ehrlichiosis (HGE) agent (NCH-1 strain). Western blot analyses, using infected human promyelocytic leukemia cells, were conducted on 38 serum samples of horses and 11 serum samples of dogs to verify reactivity to the 44-kd peptide.

RESULTS

IgM or IgG antibodies to the HGE agent were detected in 5 to 28% of dog serum samples and 5 to 37% of horse serum samples. Thirty-five of 38 (92%) horse serum samples had corresponding results on both tests (2 positive results for 26 samples and 2 negative results for 9 samples), using an ELISA for IgG antibodies or immunoblotting for total immunoglobulins. All 11 serum samples of dogs had positive results for both methods.

CONCLUSION AND CLINICAL RELEVANCE

These ELISA with recombinant 44-kd antigen are suitable for detecting IgM or IgG antibodies to the HGE agent in serum samples of dogs and horses. Positive results for serum samples of horses from Connecticut, New York, Virginia, and Georgia indicate that the HGE agent is widely distributed in tick-infested areas of the eastern United States.

Serodiagnosis of human granulocytic ehrlichiosis by using novel combinations of immunoreactive recombinant proteins

A panel of seven recombinant antigens, derived from Ehrlichia phagocytophila (the agent of human granulocytic ehrlichiosis), was evaluated by class-specific enzyme-linked immunosorbent assays (ELISAs) for utility in the diagnosis of the infection. Fourteen genomic fragments, obtained by serologic expression screening, contained open reading frames (ORFs) encoding 16 immunodominant antigens. Eleven of these antigens were members of the major surface protein (MSP) multigene family. Alignment of their predicted protein sequences revealed a pattern of conserved sequences, which contained short direct repeats, flanking a variable region. In addition, two genomic clones contained two and three MSP ORFs, respectively, indicating that these genes are clustered in tandem copies. The implications for this pattern of both genomic and protein arrangements in antigenic variations of MSPs and in their utilities in a diagnostic assay are discussed. In addition to two MSP recombinant antigens (rHGE-1 and -3) and a fusion protein of these antigens (rErf-1), five further recombinants were evaluated by ELISA. Two of these antigens (rHGE-14 and -15) were novel, while a third (rHGE-2), with no known function, has been described. The final two recombinant antigens (rHGE-9 and -17) represent overlapping segments of the ankyrin gene (ank). The addition of rHGE-9 ELISA data resulted in the detection of 78% (21 of 27) of acute-phase sera. When serologic data for all recombinants are combined, 96.2% (26 of 27) of convalescent-phase patient serum samples and 85.2% (23 of 27) of acute-phase patient serum samples are detected, indicating the potential of these antigens for use in the development of a rapid serologic assay for the detection of E. phagocytophila infection.

Concurrent babesiosis and ehrlichiosis in an elderly host

An 85-year-old man, actively infected with Babesia microti and Ehrlichia chaffeensis, presented with fatigue and thrombocytopenia. He developed rhabdomyolysis and multiple organ failure, which led to death 6 days after initial presentation. To our knowledge, concurrent acute disease due to these 2 organisms has not been reported previously, although serologic studies have shown that some patients acquire both infections in life.

Evaluation of a polyvalent enzyme-linked immunosorbent assay incorporating a recombinant p44 antigen for diagnosis of granulocytic ehrlichiosis in dogs and horses

OBJECTIVE

To develop and evaluate a polyvalent ELISA incorporating a highly specific recombinant antigen (p44) for diagnosis of granulocytic ehrlichiosis in dogs and horses.

ANIMALS

32 dogs and 43 horses.

PROCEDURE

Results of the ELISA were compared with results of indirect fluorescent antibody (IFA) staining and western immunoblotting incorporating whole-cell antigen.

RESULTS

For the canine and equine samples, percentages of samples with positive IFA staining, western immunoblotting, and ELISA results were similar. For 29 (91 %) canine samples and 30 (70%) equine samples, results of IFA staining, western immunoblotting, and the ELISA were in complete agreement. Results of the ELISA for 3 canine serum samples known to contain antibodies to Ehrlichia canis and 12 equine serum samples known to contain antibodies to E risticii were negative.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study suggest that a polyvalent ELISA incorporating a recombinant p44 antigen is suitable for detecting antibodies to E equi in dogs and horses.

Expression of a gene encoding the major antigenic protein 2 homolog of ehrlichia chaffeensis and potential application for serodiagnosis

The major antigenic protein 2 (MAP2) homolog of Ehrlichia chaffeensis was cloned and expressed. The recombinant protein was characterized and tested in an enzyme-linked immunosorbent assay (ELISA) format for potential application in the serodiagnosis of human monocytic ehrlichiosis. The recombinant protein, which contained a C-terminal polyhistidine tag, had a molecular mass of approximately 26 kDa. The antigen was clearly identified by Western immunoblotting using antihistidine antibody. However, immune sera failed to react with the recombinant on immunoblots when the antigen was denatured by heat or reduced using beta-mercaptoethanol. The recombinant MAP2 (rMAP2) was used in an ELISA format with 60 blinded serum samples. Twenty of the serum samples were previously demonstrated to contain antibodies reactive with E. chaffeensis by indirect immunofluorescence assays (IFAs). The remaining 40 samples were seronegative. All samples negative by IFA were also found to be negative for antibodies against the rMAP2 of E. chaffeensis by using the ELISA. Only 1 of 20 IFA-positive samples tested negative in the rMAP2 ELISA. There was 100% agreement using IFA-negative samples and 95% agreement using IFA-positive samples, resulting in a 97.5% overall agreement between the two assays. These data suggest that the rMAP2 homolog of E. chaffeensis may have potential as a test antigen for the serodiagnosis of human monocytic ehrlichiosis. To our knowledge, this recombinant is unique because it is thus far the only E. chaffeensis recombinant antigen that has been shown to work in an ELISA format.

Human granulocytic ehrlichiosis

Human granulocytic ehrlichiosis is a recently recognized tick-borne infectious disease, and to date >600 patients have been identified in the United States and Europe. Most patients have presented with a non-specific febrile illness occurring within 4 weeks after tick exposure or tick bite. The risk for serious illness or death increases with advancing age and delayed onset of therapy. Routine laboratory testing may reveal reduced white blood cell and platelet concentrations and mildly elevated hepatic transaminase activity in peripheral blood. A high index of suspicion is necessary to arrive at a timely clinical diagnosis. Patients suspected of having human granulocytic ehrlichiosis (HGE) should be treated with a tetracycline-class antibiotic while awaiting the outcome of confirmatory laboratory testing.

Comparison of two recombinant major outer membrane proteins of the human granulocytic ehrlichiosis agent for use in an enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assay (ELISA) for human granulocytic ehrlichiosis (HGE) using two different recombinant P44 proteins (rP44 and rP44-2hv) of the HGE agent as antigens was evaluated. Sera from a total of 72 healthy humans both from regions where HGE is nonendemic and regions where HGE is endemic were used as negative controls to determine the cutoff value for ELISA. Sera from a total of 14 patients (nine from whom the HGE agent was isolated and five who were HGE-PCR positive) were used as positive controls. One hundred nine sera from 72 patients in an area where HGE is endemic who were suspected of having HGE were examined by ELISA and indirect immunofluorescence assay (IFA). All IFA-negative sera were negative by both ELISAs. Of 39 sera that were IFA positive, 35 and 27 were positive by ELISA using rP44 and rP44-2hv, respectively, indicating that the use of rP44 is more sensitive. Western blot analysis of the four rP44-ELISA-negative IFA-positive sera using whole HGE agent as antigen suggests that these four sera were false IFA positive. There was no difference in results with or without the preabsorption of sera with Escherichia coli or with or without the cleavage of the fused protein derived from the vector. There was a significant positive correlation between IFA titers and optical densities of ELISAs. Four Ehrlichia chaffeensis-positive and 10 Borrelia burgdorferi-positive sera were negative by ELISA. However, two Babesia microti-positive sera showed strong cross-reactivity to the fused vector protein, which was eliminated after cleavage of the protein. Thus, ELISA using rP44 nonfusion protein would provide a simple, specific, and objective HGE serologic test which can be easily automated.