Serologic diagnosis of canine and equine borreliosis: use of recombinant antigens in enzyme-linked immunosorbent assays.

Serum samples from dogs and equids suspected of having canine or equine borreliosis, respectively, were analyzed in polyvalent enzyme-linked immunosorbent assays (ELISAs) with whole-cell or recombinant antigens of Borrelia burgdorferi sensu stricto. Purified preparations of recombinant antigens included outer surface protein A (OspA), OspB, OspC, OspE, OspF, and p41-G (a fragment of flagellin). Of the 36 dog sera that reacted positively to whole-cell antigen, 32 (88.9%) contained antibodies to one or more recombinant antigens. Reactivities to OspF (88.9% positive) and p41-G (75% positive) were most prevalent. In analyses of 30 equid sera positive in an ELISA with whole cells, 24 (80%) contained antibodies to one or more recombinant antigens. Seropositivities in ELISAs with p41-G (50% positive) and OspF (46.7% positive) were more than twofold greater than in ELISAs with OspA, OspB, or OspC (10 to 20% positive). In parallel tests of eight canine and three equine sera, there was good agreement in results of Western blot (immunoblot) analyses and ELISAs. Although dog and equid sera with antibodies to whole-cell B. burgdorferi frequently reacted positively to one or more recombinant antigens, the inclusion of OspF and p41-G antigens in ELISAs was most useful in the serologic diagnosis of canine and equine borreliosis.     

Comparative reactivity of human sera to recombinant VlsE and other Borrelia burgdorferi antigens in class-specific enzyme-linked immunosorbent assays for Lyme borreliosis

A comparative study of human sera was conducted to determine which purified preparations of 11 recombinant antigens of Borrelia burgdorferi sensu stricto were diagnostically most important in enzyme-linked immunosorbent assays (ELISAs). To assess sensitivity, 20 serum samples obtained 1-6 weeks after onset of illness from 20 persons who had physician-diagnosed erythema migrans (EM) were tested for IgM and IgG antibodies. In tests for IgM antibody, seropositivity of > or = 25% was recorded when ELISAs had separate preparations of protein (p) 37, p41-G, outer-surface protein (Osp) C, OspE, OspF or VlsE antigens. Sera reacted most frequently (80% positive) with VlsE antigen in analyses for IgG antibodies. When results of both class-specific assays were considered for VlsE, OspC or OspF, 90% of the EM cases were serologically confirmed. Results of specificity testing with a further 59 sera from persons who had syphilis, louse-borne relapsing fever, oral infections, rheumatoid arthritis or human granulocytic ehrlichiosis and 28 normal sera indicated no false positive reactions when VlsE antigen was used in tests for IgM antibody. One of the 11 louse-borne relapsing fever sera cross-reacted with VlsE antigen in tests for IgG antibodies. Minor cross-reactivity also occurred when p37, OspC, OspE or OspF antigens were used. Overall, VlsE was the most suitable antigen for laboratory diagnosis of Lyme borreliosis during the early weeks of B. burgdorferi infection because of its high sensitivity and specificity.     

Reactivity of dog sera to whole-cell or recombinant antigens of Borrelia burgdorferi by ELISA and immunoblot analysis

Enzyme-linked immunosorbent assays (ELISAs) with separate preparations of 10 purified recombinant antigens of Borrelia burgdorferi sensu stricto were used to test sera from 36 dogs not vaccinated with whole cells of this agent and from five dogs vaccinated with whole-cell B. burgdorferi bacteria. All dogs lived in tick-infested areas of Connecticut and south-eastern New York state, USA. The non-vaccinated dogs had limb or joint disorder, lameness and fever during the period 1984-1991 and had antibodies to B. burgdorferi, as determined by a polyvalent ELISA with whole-cell antigen. In re-analyses of sera for total immunoglobulins in ELISAs with recombinant antigens, reactions were most frequently recorded when outer-surface protein (Osp) F, protein (p)35, p37, p39 and p-41G (a flagellin component) were tested separately. Western immunoblots of a subset of 16 sera, positive by ELISA with whole-cell antigen and representing a range of antibody titres (640-40960), verified immune responses to these or other lysed whole-cell antigens. Sera from vaccinated dogs contained antibodies to OspA, OspB, p22, p37 and p41-G. Therefore, serological reactions to OspF, p35 and p39 were the most important indicators of natural exposure to B. burgdorferi. Serum reactivities to these recombinant antigens in ELISAs can be used to help identify possible natural infections of canine borreliosis in dogs not vaccinated with whole-cell B. burgdorferi and to provide information on the geographic distribution of this bacterium.     

Comparison of whole-cell antibodies and an antigenic flagellar epitope of Borrelia burgdorferi in serologic tests for diagnosis of Lyme borreliosis.

A recombinant protein (p41-G) of an antigenic region of flagellin was used in a standard and amplified enzyme-linked immunosorbent assay (ELISA) to detect antibodies to Borrelia burgdorferi, the causative agent of Lyme borreliosis. Comparable sensitivities (88 to 94%) were noted when sera from 17 persons who had erythema migrans and antibodies to whole-cell B. burgdorferi were tested against the p41-G antigen. In tests of a second study group of 36 persons who had erythema migrans but no detectable antibodies to whole-cell B. burgdorferi, 3 (8%) were positive when the p41-G antigen was used. Assay specificity likewise increased when the p41-G fragment was included in an ELISA with human sera containing treponemal antibodies. Recombinant flagellar proteins of B. burgdorferi, such as the p41-G antigen, can be used in an ELISA and may help confirm Lyme borreliosis during early stages of infection and improve specificity.     

Partial destruction of Borrelia burgdorferi within ticks that engorged on OspE- or OspF-immunized mice.

We determined whether Borrelia burgdorferi outer surface proteins (Osps) E and F could elicit immune responses useful for a Lyme disease vaccine. Thirty days after challenge with B. burgdorferi, mice produced antibodies to OspE but not OspF, whereas antibodies to OspF were present in sera of mice obtained 90 days after infection. Examination of sera from patients with Lyme disease revealed antibodies to OspF in a small number (14%) of early-stage disease patients but in a majority (58%) of patients with late-stage disease, while antibodies to OspE were rarely detected in patients. Mice immunized with recombinant OspE or OspF produced high titers of antibodies to OspE or OspF, respectively. OspF-immunized mice were partially protected from both intradermal syringe challenge and tick-mediated transmission of B. burgdorferi while vaccination with OspE did not confer immunity. B. burgdorferi organisms were, however, substantially destroyed within ticks that engorged on either OspE- (75% reduction in the number of spirochetes within the ticks, compared with controls) or OspF (90% reduction in the number of spirochetes within the ticks)-immunized mice.     

Temperature-related differential expression of antigens in the Lyme disease spirochete, Borrelia burgdorferi.

Previous studies have demonstrated that Borrelia burgdorferi in the midguts of infected ticks shows increased expression of the antigenic outer surface protein OspC after the ticks have ingested a blood meal. This differential expression is at least partly due to a change in temperature, as an increase in OspC levels is also observed when cultures are shifted from 23 to 35 degrees C. Immunoblotting of bacterial lysates with sera from infected mice indicated that the levels of several additional antigens were also increased in bacterial cultures shifted to 35 degrees C; we have identified one antigen as OspE. We have also observed differential expression of OspF, which has been proposed to be coexpressed in an operon with the gene encoding OspE.     

Antibodies to Borrelia burgdorferi OspA, OspC, OspF, and C6 Antigens as Markers for Early and Late Infection in Dogs

Lyme disease in the United States is caused by Borrelia burgdorferi sensu stricto, which is transmitted to mammals by infected ticks. Borrelia spirochetes differentially express immunogenic outer surface proteins (Osp). Our aim was to evaluate antibody responses to Osp antigens to aid the diagnosis of early infection and the management of Lyme disease. We analyzed antibody responses during the first 3 months after the experimental infection of dogs using a novel multiplex assay. Results were compared to those obtained with two commercial assays detecting C6 antigen. Multiplex analysis identified antibodies to OspC and C6 as early as 3 weeks postinfection (p.i.) and those to OspF by 5 weeks p.i. Antibodies to C6 and OspF increased throughout the study, while antibodies to OspC peaked between 7 and 11 weeks p.i. and declined thereafter. A short-term antibody response to OspA was observed in 3/8 experimentally infected dogs on day 21 p.i. Quant C6 enzyme-linked immunosorbent assay (ELISA) results matched multiplex results during the first 7 weeks p.i.; however, antibody levels subsequently declined by up to 29%. Immune responses then were analyzed in sera from 125 client-owned dogs and revealed high agreement between antibodies to OspF and C6 as robust markers for infection. Results from canine patient sera supported that OspC is an early infection marker and antibodies to OspC decline over time. The onset and decline of antibody responses to B. burgdorferi Osp antigens and C6 reflect their differential expression during infection. They provide valuable tools to determine the stage of infection, treatment outcomes, and vaccination status in dogs.     

Serologic analysis of dogs, horses, and cottontail rabbits for antibodies to an antigenic flagellar epitope of Borrelia burgdorferi.

Enzyme-linked immunosorbent assays (ELISA) and immunoblots using either whole-cell lysates of Borrelia burgdorferi or an antigenic region of flagellin (41-G) as the antigen were performed, and the abilities of the two assays to detect antibodies to this spirochete in dog, cottontail rabbit, and horse sera were compared. Assays using whole-cell B. burgdorferi lysates as the antigen were more sensitive for detecting antibodies. ELISA with 41-G as the antigen were specific for Borrelia antibodies but were not as sensitive as the assays with whole-cell lysates coated to the solid phase. Use of recombinant full-length flagellin, rather than 41-G, as the antigen in immunoblots increased the sensitivity of each assay. However, antibodies to other bacterial antigens cross-react with whole flagellin and may account for false-positive results. Antibodies to B. burgdorferi outer surface protein A or B were usually undetected when the sera were tested by immunoblotting methods. Borrelia lysates or the 41-G antigen may be used in ELISA or immunoblots to document host exposure to this spirochete. The use of 41-G as the antigen may increase the specificity of an assay or help confirm the serologic diagnosis of Lyme borreliosis in dogs, horses, and cottontail rabbits.     

The Immunoglobulin (IgG) Antibody Response to OspA and OspB Correlates with Severe and Prolonged Lyme Arthritis and the IgG Response to P35 Correlates with Mild and Brief Arthritis

In an effort to implicate immune responses to specific Borrelia burgdorferi proteins that may have a role in chronic Lyme arthritis, we studied the natural history of the antibody response to B. burgdorferi in serial serum samples from 25 patients monitored throughout the course of Lyme disease. In these patients, the immunoglobulin G (IgM) and IgG antibody responses to 10 recombinant B. burgdorferi proteins, determined during early infection, early arthritis, and maximal arthritis, were correlated with the severity and duration of maximal arthritis. The earliest responses were usually to outer surface protein C (OspC), P35, P37, and P41; reactivity with OspE, OspF, P39, and P93 often developed weeks later; and months to years later, 64% of patients had responses to OspA and OspB. During early infection and early arthritis, the levels of IgG antibody to P35 correlated inversely with the subsequent severity or duration of maximal arthritis. In contrast, during periods of maximal arthritis, the levels of IgG antibody to OspA and OspB, especially to a C-terminal epitope of OspA, correlated directly with the severity and duration of arthritis. Thus, the higher the IgG antibody response to P35 earlier in the infection, the milder and briefer the subsequent arthritis, whereas during maximal arthritis, the higher the IgG response to OspA and OspB, the more severe and prolonged the arthritis.     

Evaluation of whole-cell and OspC enzyme-linked immunosorbent assays for discrimination of early lyme borreliosis from OspA vaccination

A recombinant Lyme borreliosis vaccine consisting of outer surface protein A (OspA) is commercially available for vaccination of humans against infection with Borrelia burgdorferi. Vaccination with OspA induces an antibody response that makes serologic interpretation of infection with B. burgdorferi difficult, especially by screening tests based on whole-cell preparations of B. burgdorferi. We show that an enzyme-linked immunosorbent assay with B. burgdorferi sensu stricto 50772, which lacks the plasmid encoding OspA and OspB, or a full-length recombinant OspC protein can identify patients infected with B. burgdorferi. We found that 69 and 65% of serum samples from patients with case-defined early Lyme borreliosis had anti-B. burgdorferi sensu stricto 50772 and anti-OspC reactivities, respectively. In addition, little or no reactivity was detected with sera obtained from individuals vaccinated with OspA. Unfortunately, 51 and 33% of sera from healthy patients and sera from patients with other illnesses were also reactive against B. burgdorferi sensu stricto 50772 and OspC, respectively. Although these assays can discriminate B. burgdorferi infection from vaccination with OspA, their lack of specificity highlights the necessity for confirming equivocal or positive reactivities with more specific serodiagnostic tests.     

Borrelia burgdorferi antigens that are targeted by antibody-dependent, complement-mediated killing in the rhesus monkey.

We identified surface antigens of Borrelia burgdorferi that are targeted by antibody-dependent, complement-mediated killing (ADCK) in the rhesus monkey. For this purpose, we had available serum samples from three animals infected with B. burgdorferi JD1 by needle inoculation and from two monkeys that were infected with the same B. burgdorferi strain by Ixodes scapularis tick bite. Sera from monkeys from the first group contained antibodies to OspA and OspB detectable by Western blot (immunoblot) using whole B. burgdorferi antigens, whereas serum samples from animals in the second group did not. The targeting of OspA and OspB by functional antibodies was demonstrated directly by showing that ADCK was partially inhibited when antibodies were preincubated with an excess of soluble recombinant OspA or OspB. Simultaneous addition of OspA and OspB did not result in an additive inhibitory effect on ADCK, a result that suggests that the epitopes on OspA and that on OspB targeted by antibody in this mechanism are the same, or at least cross-reacting. The targeting of non-OspA, non-OspB surface antigens was inferred from the fact that sera from tick-inoculated animals, which did not contain detectable anti-OspA or anti-OspB antibodies, were able to effect ADCK. This killing effect was not inhibitable by the addition of recombinant OspA or OspB or both proteins together. We also showed that both immunoglobulin G and M antibodies participate in the ADCK mechanism in the rhesus monkey. Rhesus complement does not kill B. burgdorferi in vitro in the absence of antibody, and antibody alone is effective in killing only at serum dilutions lower than 1:15. However, such "complement-independent" antibodies were not present in all bleeds. Two main conclusions may be drawn from the analysis of our results. First, both OspA and OspB are targeted by the ADCK mechanism in the rhesus monkey. Second, one or more B. burgdorferi surface antigens that are neither OspA nor OspB also participate in ADCK.     

A chromosomal Borrelia burgdorferi gene encodes a 22-kilodalton lipoprotein, P22, that is serologically recognized in Lyme disease.

We describe the isolation of the gene encoding a 22-kDa antigen from Borrelia burgdorferi, the etiologic agent of Lyme disease. The p22 gene is 582 nucleotides in length and encodes a protein of 194 amino acids with a predicted molecular mass of 21.8 kDa. The leader signal sequence of P22 consists of a positively charged short amino terminus, a central hydrophobic domain, and at the carboxyl terminus, a cleavage site that is presumably recognized and cleaved by a B. burgdorferi signal peptidase. P22 has 98.5% homology with the recently described B. burgdorferi protein IpLA7. P22 is processed as a lipoprotein, as demonstrated by [3H]palmitate labeling. Pulsed-field gel electrophoresis showed that p22, like LA7, is localized to the linear chromosome of B. burgdorferi. Examination of sera from patients with Lyme disease revealed that antibodies to P22 are rarely detected in patients with early-stage disease characterized by erythema migrans (2 of 20), and 35% of the patients with late-stage disease characterized by arthritis (9 of 26) developed antibodies to P22. Sera from patients with syphilis did not react with P22. When patients with late-stage disease were tested for their antibody reactivities to four other outer surface proteins (OspA), OspB, OspE, and OspF), 75% of these patients responded to P22 or to one or more outer surface proteins.     

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.     

Recombinant immunoblot in the serodiagnosis of Lyme borreliosis

A recombinant immunoblot was developed for detection of IgM and IgG antibodies in patients with Lyme borreliosis. The recombinant antigens were the chromosomal-encodedBorrelia burgdorferi proteins p100, the flagellin and an internal flagellin fragment thereof as well as the plasmid-encoded outer surface proteins A (OspA) and C (OspC). A panel of 144 sera from patients with Lyme borreliosis (erythema migrans,n = 31; neuroborreliosis state II,n = 60; Lyme arthritis,n = 24 and acrodermatitis chronica atrophicans,n =19) have been investigated and the results have been compared to the immunofluorescence absorption test (IFA-ABS) and to two different enzyme-linked immunosorbent assays [the flagellin ELISA and a newly developed ELISA (OGP-ELISA)]. The two ELISAs were comparable in sensitivity, whereas the IFA-ABS was less sensitive for IgM antibody but equally sensitive for IgG antibody detection. Immunoblot analysis revealed that IgG antibodies are mainly reactive with p 100 and the internal flagellin fragment (sensitivity 51% and 32%, respectively) and rarely with OspC (14%). All patients with late Lyme borreliosis had IgG antibodies against the p100. IgM antibodies were predominantly directed against OspC (43%) and in a lower extent against the internal flagellin fragment and p100 (15% and 13%, respectively). The complete flagellin was not useful due to a high number of unspecific reactions with control sera and the OspA was only exceptionally reactive in Lyme borreliosis patients. The sensitivity of IgM antibody detection could be increased in cases with early Lyme borreliosis from 46% to 65% when the OspC blot was performed in addition to the flagellin ELISA, or from 56% to 65% when performed in addition to the OGP-ELISA. The recombinant blot is, therefore, a valuable diagnostic test to increase sensitivity of early antibody detection and is regarded as a valuable confirmatory test also in late disease.     

Recombinant Protein-44-Based Class-Specific Enzyme-Linked Immunosorbent Assays for Serologic Diagnosis of Human Granulocytic Ehrlichiosis

Recombinant protein 44, expressed and purified as a maltose-binding protein fusion peptide of the human granulocytic ehrlichiosis (HGE) agent (Ehrlichia phagocytophila genogroup), was used as antigen in enzyme-linked immunosorbent assays (ELISAs) to detect total antibodies, immunoglobulin (Ig) M antibodies, and IgG antibodies. Of the 67 human sera obtained from 64 HGE patients 3-5 weeks after the onset of illness and confirmed as having total immunoglobulins to whole-cell antigen by indirect fluorescent antibody analyses, 63 were positive in a polyvalent ELISA. Fifty-six and 61 sera had IgM or IgG antibodies, respectively. Fifty sera had both IgM and IgG antibodies. In specificity tests of 110 sera, one serum sample from a patient who had Lyme borreliosis reacted to the protein 44 antigen in the analysis for IgM antibody (specificity, 99%). There were no false-positive results in an ELISA for IgG antibodies. With their high sensitivity and specificity, class-specific ELISAs can be used in conjunction with indirect fluorescent antibody analyses or immunoblotting methods to help diagnose human granulocytic ehrlichiosis.     

Significantly improved accuracy of diagnosis of early Lyme disease by peptide enzyme-linked immunosorbent assay based on the borreliacidal antibody epitope of Borrelia burgdorferi OspC

Highly specific borreliacidal antibodies are induced by infection with Borrelia burgdorferi, and the immunodominant response during early Lyme disease is specific for an epitope within the 7 amino acids nearest the C terminus of OspC. We evaluated the ability of an enzyme-linked immunosorbent assay (ELISA) based on a synthetic peptide (OspC7) that matched the region to detect the response and compared the sensitivity during early Lyme disease to that for an FDA-approved Western blot. When the optical density value was adjusted to 98% specificity based on the results from testing normal or uncharacterized sera (n = 236) or sera from patients with blood factors or illnesses that commonly produce antibodies that cross-react with B. burgdorferi antigens (n = 77), 115 (73%) of 157 sera from patients likely to have early Lyme disease were positive for immunoglobulin M (IgM) antibodies and 17 (11%) also had IgG antibodies. In addition, the IgM ELISA reactivities and the titers of antibodies detected by a flow cytometric borreliacidal antibody test correlated closely (r = 0.646). Moreover, the IgM ELISA was significantly more sensitive (P < 0.001) than the Western blot procedure. The findings therefore confirmed that the peptide IgM ELISA detected OspC borreliacidal antibodies and provided strong evidence that the test can eliminate the necessity for confirming early Lyme disease by a supplementary test such as Western blotting.     

Antibodies against whole sonicated Borrelia burgdorferi spirochetes, 41-kilodalton flagellin, and P39 protein in patients with PCR- or culture-proven late Lyme borreliosis.

The sensitivities and specificities of three enzyme-linked immunosorbent assays (ELISAs) for Borrelia burgdorferi antibodies were compared for 41 patients presenting with symptoms compatible with late Lyme borreliosis (LB) and 37 healthy controls. All subjects were living in southwestern Finland, where LB is endemic. Only patients with culture- or PCR-proven disease were enrolled in the study. The antigens of the ELISAs consisted of sonicated spirochetes, 41-kDa flagellin, and recombinant P39 protein of B. burgdorferi. Fifteen patients had strongly or moderately positive results in the serological assay(s), 19 patients had only weakly positive or borderline antibody levels, and the remaining 7 patients were seronegative by ELISA. The sensitivities of the ELISAs were 78.0% with sonicate antigen, 41.5% with 41-kDa flagellin, and 14.6% with P39 protein. The specificities of the tests were 89.2, 86.5, and 94.6%, respectively. The sonicate antigen ELISA seems to be an effective screening method. These results show that antibodies to B. burgdorferi may be present in low levels or even absent in patients with culture- or PCR-proven late LB. Therefore, in addition to serological testing, the use of PCR and cultivation is recommended in the diagnosis of LB.     

The hook protein of Borrelia burgdorferi, encoded by the flgE gene, is serologically recognized in Lyme disease.

The periplasmic flagellum of Borrelia burgdorferi consists of a unipeptide flagellar filament, a hook, and a basal body. Here, we report the cloning and expression of the hook gene, flgE, of B. burgdorferi N40. The flgE gene is 1,119 nucleotides long and is located on the 950-kb linear chromosome of B. burgdorferi. The primary protein sequence of FlgE shows 73% similarity to the FlgE protein of Treponema phagedenis and approximately 50% similarity to the FlgG proteins of both gram-positive and gram-negative bacteria. The flgE gene was cloned into an Escherichia coli expression plasmid, pMX, to produce FlgE protein. Subsequently, FlgE murine antiserum was prepared by immunizing mice with the partially purified B. burgdorferi FlgE protein. By Western blot (immunoblot) analysis, the antiserum was found to react with a 40-kDa peptide in the whole-cell lysates, confirming the expression of the flgE gene in B. burgdorferi. Additionally, antibodies to FlgE were found in serum specimens from 19 of 42 patients with Lyme disease. Moreover, when other antigens, including 41G (the immunodominant domain of flagellin), OspE, OspF, and p22, were used to test for the development of corresponding antibodies in these patients, 67% of these patients (28 of 42) reacted to at least one of these five antigens, suggesting that a combination of FlgE with other available B. burgdorferi recombinant proteins is a good candidate for substrates in assays to aid in the diagnosis of Lyme disease.     

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.     

Antibodies to granulocytic ehrlichiae in cattle from Connecticut

Enzyme-linked immunosorbent assays (ELISA) with a purified recombinant 44-kDa protein and indirect fluorescent antibody (IFA) staining methods incorporating whole-cell antigens of the human granulocytic ehrlichiosis (HGE) agent were used to detect antibodies to Ehrlichia phagocytophila genogroup organisms in cattle sera. The cattle lived in tick-infested areas of Connecticut, USA and were healthy at the times blood samples were collected in 1990, 1999 and 2000. Of the 339 serum samples analysed, 40 (12%) and 15 (4%) were positive by ELISA and IFA, respectively. Western immunoblots of a subset of sera verified antibody reactivity of six serum samples, positive by ELISA with titres of 640-2,560, to a protein with a molecular mass of c. 44 kDa. Although seroprevalence rates were low, cattle were exposed to the HGE agent at different sites and should be monitored for anaemia, leukopenia or thrombocytopenia, especially if there is evidence of unexplained decreased milk production. Different serological testing methods should be used to detect immunoglobulins.