Open AccessMolecular 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
Author(s) -
Tian Luo,
Xiaofeng Zhang,
William L. Nicholson,
Bing Zhu,
Jere W. McBride
Publication year - 2010
Publication title -
clinical and vaccine immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.649
H-Index - 77
eISSN - 1556-6811
pISSN - 1556-679X
DOI - 10.1128/cvi.00331-09
Subject(s) - ehrlichia chaffeensis , ehrlichiosis , virology , ehrlichia , antibody , epitope , biology , immunology , tick
Recently, major species-specific antibody epitopes in three immunoreactive tandem repeat proteins (TRPs) ofEhrlichia 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 theE. chaffeensis 200-kDa ankyrin protein (Ank200) and the minor immunodeterminants in the N- and C-terminal regions ofE. 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 anE. 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 ofE. chaffeensis were determined by enzyme-linked immunosorbent assay (ELISA). Thirty-one HME patient serum samples that had detectableE. chaffeensis antibodies (titers from 64 to 8,192) by indirect fluorescent-antibody assay (IFA) were tested. All 31 serum samples reacted with at least oneE. 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.