Genetic and Antigenic Diversity of Major Immmunoreactive Proteins in Globally Distributed Ehrlichia canis Strains

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

^* To whom correspondence should be addressed. Email: jemcbrid{at}utmb.edu.

	Abstract

The extent of knowledge regarding diversity of globally distributed E. canis has been limited to information gained from a few evolutionarily conserved genes. In this study, E. canis strains from the United States (US, Jake), Brazil (BR, São Paulo) and Israel (IS, 611 and IS-R, Ranana) were used to examine the antigenic and genetic diversity of four well characterized major immunoreactive protein genes/proteins. The gp36 and gp200 were the most divergent genes, and nucleotide substitutions in the gp36 tandem repeat region of the IS strain, but not IS-R strain, resulted in two amino acid differences (S P; P T) 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 IS strains, including two fewer tandem repeats in the gp140 and a single amino acid substitution in the IS gp19. 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, the gp19 was strongly reactive and present in all E. canis isolates. The gp140 and gp200 were also present in all strains, although the gp140 in the IS strain had two fewer tandem repeats and exhibited a smaller mass.