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Infect. Immun., 01 1998, 132-139, Vol 66, No. 1
N Ohashi, N Zhi, Y Zhang and Y Rikihisa
Several immunodominant major proteins ranging from 23 to 30 kDa were
identified in the outer membrane fractions of Ehrlichia chaffeensis and
Ehrlichia canis. The N-terminal amino acid sequence of a 28-kDa protein of
E. chaffeensis (one of the major proteins) was determined. The gene (p28),
almost full length, encoding the 28-kDa protein was cloned by PCR with
primers designed based on the N-terminal sequence of the E. chaffeensis
28-kDa protein and the consensus sequence between the C termini of the
Cowdria ruminantium MAP-1 and Anaplasma marginale MSP-4 proteins. The p28
gene was overexpressed, and antibody to the recombinant protein was raised
in a rabbit. The antibody and serum from a patient infected with E.
chaffeensis reacted with the recombinant protein, three proteins (29, 28,
and 25 kDa) of E. chaffeensis, and a 30-kDa protein of E. canis.
Immunoelectron microscopy with the rabbit antibody revealed that the
antigenic epitope of the 28-kDa protein was exposed on the surface of E.
chaffeensis. Southern blot analysis with a 32P-labeled p28 gene probe
revealed multiple copies of genes homologous to p28 in the E. chaffeensis
genome. Six copies of the p28 gene were cloned and sequenced from the
genomic DNA by using the same probe. The open reading frames of these gene
copies were tandemly arranged with intergenic spaces. They were
nonidentical genes and contained a semivariable region and three
hypervariable regions in the predicted protein molecules. One of the gene
copies encoded a protein with an internal amino acid sequence identical to
the chemically determined N- terminal amino acid sequence of a 23-kDa
protein of E. chaffeensis. Immunization with the recombinant P28 protein
protected mice from infection with E. chaffeensis. These findings suggest
that the 30-kDa- range proteins of E. chaffeensis represent a family of
antigenically related homologous proteins encoded by a single gene family.
Copyright © 1998, American Society for Microbiology
Immunodominant major outer membrane proteins of Ehrlichia chaffeensis are encoded by a polymorphic multigene family
Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus 43210-1093, USA.
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