In order to evaluate the relative sensitivity of the detection of
antibodies against various antigenic
proteins of Ehrlichia chaffeensis for the diagnosis of the
emerging infectious disease human monocytotropic
ehrlichiosis, Western immunoblotting was performed with 27 serum samples from convalescent patients with
antibodies, as demonstrated by indirect immunofluorescence assay. Among 22 patients with
antibodies reactive with the 120-kDa
protein, 15 showed reactivity with the 29/28-kDa
protein(s) and the
proteins in the 44- to 88-kDa range. Two of the serum samples with this pattern reacted with the 29/28-kDa
protein(s) of only the 91HE17 strain, and one sample reacted with only that of the Arkansas strain, indicating that the
antibodies were stimulated by strain-specific
epitopes. Overall,
antibodies to the 29/28-kDa
protein(s) were detected in only 16 patients' sera, suggesting that this
protein is less sensitive than the 120-kDa
protein. Two of 12 serum samples from healthy blood donors had
antibodies reactive with the 120-kDa
protein; one of these samples reacted also with the 29/28-kDa
protein(s) of Ehrlichia canis, suggesting that unrecognized ehrlichial
infection might have occurred, including human
infection with E. canis. A high correlation between reactivity with the 120-kDa
protein by Western immunoblotting and the recombinant 120-kDa
protein by dot blot supports the potential usefulness of this recombinant
antigen in diagnostic serology.