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Journal of Clinical Microbiology, June 1998, p. 1480-1488, Vol. 36, No. 6
Department of
Microbiology1 and
Division of Infectious
Diseases, Department of Medicine,2
University of Minnesota Academic Health Center, Minneapolis, Minnesota
55455
Received 24 October 1997/Returned for modification 18 February
1998/Accepted 2 March 1998
Human granulocytic ehrlichiosis (HGE) is an emerging infection
caused by an Ehrlichia species closely related to
Ehrlichia equi and Ehrlichia phagocytophila.
Recent advances in the isolation and cultivation of this organism have
allowed us to develop an immunofluorescence assay (IFA), enzyme
immunoassay (EIA), and Western immunoblotting (WB) using HL-60 cell
culture-derived human isolates. Antibody was detected in sera from
culture-confirmed HGE patients by IFA and EIA, and these samples were
reactive when analyzed by immunoblot analysis. HGE patient sera had
high antibody titers and did not react with uninfected HL-60 cells.
When IFA, EIA, and WB were used to analyze sera from healthy donors or
those with a range of other disorders, including infections caused by Ehrlichia chaffeensis, Rickettsia rickettsii,
and Coxiella burnetti, no significant cross-reactivity
could be detected by EIA or immunoblot analysis with the exception of
two of four serum samples from R. rickettsii-infected
patients that were reactive by IFA only. Sera from HGE patients did not
significantly cross-react in serologic tests for Borrelia
burgdorferi. Using sera from patients previously enrolled in two
clinical trials of treatment for early Lyme disease, we evaluated a
two-step approach for estimation of the seroprevalence of antibodies
reactive with the etiologic agent of HGE. On the basis of the
immunoblot assay results for sera from culture-confirmed HGE patients,
WB was used to confirm the specificity of the antibody detected by EIA
and IFA. EIA was found to be superior to IFA in the ability to detect
WB-confirmed antibodies to the HGE agent. When EIA and WB were used, 56 (19.9%) patients with early Lyme disease (n = 281)
had either specific immunoglobulin M (IgM) or IgG antibodies; 38 patients (13.5%) had IgM only, 6 (2.1%) had IgG only, and 12 (4.3%)
had both IgM and IgG. Therefore, Lyme disease patients are at high
potential risk for exposure to Ehrlichia. Analysis by
immunoblotting of serial samples from persons with culture-confirmed
HGE or patients with Lyme disease and antibodies to the agent of HGE
revealed a reproducible pattern of the immune response to specific
antigens. These samples confirmed the importance of the 42- to 45-kDa
antigens as early, persistent, and specific markers of HGE infection.
Other significant immunogenic proteins appear at 20, 21, 28, 30, and 60 kDa. Use of the two-test method of screening by EIA and confirming the
specificity by WB appears to offer a sound approach to the clinical
immunodiagnosis of HGE.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Immunodiagnosis of Human Granulocytic Ehrlichiosis
by Using Culture-Derived Human Isolates
*
Corresponding author. Mailing address: University of
Minnesota, Academic Health Center, 420 Delaware St. S.E., Box 196 UMHC, Minneapolis, MN 55455-0312. Phone: (612) 624-5684. Fax: (612) 626-0623. E-mail: ravyn{at}lenti.med.umn.edu.
This paper is dedicated to Mary C. Panghorn, the discoverer of
cardiolipin, at the Division of Laboratories and Research, New York
State Department of Health, Albany, New York, for her 90th birthday.
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