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Clinical and Vaccine Immunology, July 2008, p. 1080-1088, Vol. 15, No. 7
1071-412X/08/$08.00+0     doi:10.1128/CVI.00482-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Genetic and Antigenic Diversities of Major Immunoreactive Proteins in Globally Distributed Ehrlichia canis Strains

Departments of Pathology,¹ Microbiology and Immunology,² Center for Biodefense and Emerging Infectious Diseases,³ Institute for Human Infections and Immunity, University of Texas Medical Branch, Galveston, Texas,⁴ Israel Institute for Biological Research, Ness Ziona, Israel,⁵ School of Veterinary Medicine, Hebrew University, Rehovot, Israel⁶

Received 3 December 2007/ Returned for modification 26 January 2008/ Accepted 3 May 2008

The extent of knowledge regarding the diversity of globally distributed Ehrlichia canis strains has been limited to information gained from a few evolutionarily conserved genes. In this study, E. canis strains from the United States (strain Jake [US]), Brazil (strain São Paulo [BR]), and Israel (strain 611 [IS] and Ranana [IS-R]) were used to examine the antigenic and genetic diversities of four well-characterized major immunoreactive protein genes/proteins. gp36 and gp200 were the most divergent genes, and nucleotide substitutions in the gp36 tandem repeat region of the IS strain, but not the IS-R strain, resulted in two amino acid differences (SP and PT) in each nine-amino-acid repeat (epitope-containing region). DNA sequences of gp19 and gp140 were completely conserved in the US and BR strains, but differences were found in the Israeli strains, including two fewer tandem repeats in gp140 and a single amino acid substitution in gp19 from the IS strain. E. canis whole-cell lysates from each isolate were examined by Western immunoblotting using sera from naturally infected dogs from each country, and four major immunoreactive proteins (gp19, gp36, gp140, and gp200) were identified in each strain using protein-specific antisera. The US and BR strains exhibited highly conserved immunoreactive protein profiles, while some differences were identified in the IS strain. Sera from naturally infected Israeli dogs confirmed gene sequencing information, which demonstrated two distinct E. canis strains, defined by the gp36 gene. Conversely, gp19 was strongly reactive and present in all E. canis isolates. gp140 and gp200 were also present in all strains, although gp140 in the IS strain had two fewer tandem repeats and exhibited a smaller mass.

Published ahead of print on 14 May 2008.