Cytokine Gene Expression by Peripheral Blood Leukocytes in Dogs Experimentally Infected with a New Virulent Strain of Ehrlichia canis AHMET UNVER, a,b HAIBIN HUANG, a AND YASUKO RIKIHISA a a Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio 43210-1093, USA b Department of Microbiology, Faculty of Veterinary Medicine, Kafkas University, 36100 Kars, Turkey ABSTRACT: Ehrlichia canis (E. canis) is a lipopolysaccharide (LPS)- deficient obligatory intracellular bacterium that causes canine mono- cytic ehrlichiosis, a chronic febrile disease accompanied with hemato- logical abnormality. This study analyzed temporal expression levels of IL-1, IL-2, IL-6, IL-8, IFN-, and TNF- mRNA by peripheral blood leukocytes from dogs experimentally infected with a new virulent strain of E. canis by using real-time RT-PCR. Relative levels of IL-1 and IL-8 transcripts normalized by the -actin transcript levels, were significantly upregulated, whereas those of TNF- and IFN- transcripts were only weakly upregulated in all three infected dogs, starting from 2 days up to 52 days post inoculation. The expressions of IL-2 and IL-6 genes were ex- tremely low compared with the positive control (ConA-stimulated canine peripheral blood leukocytes). This study showed that E. canis can induce chronic expression of a subset of proinflammatory cytokine genes: bal- ance, timing, and duration of these cytokine generations may contribute to the progression of canine ehrlichiosis. KEYWORDS: E. canis; IL-1; IL-8; dog INTRODUCTION Ehrlichia canis (E. canis) is the causative agent of canine monocytic ehrli- chiosis (CME) with tropism for monocytes and macrophages. CME has a worldwide distribution with a higher frequency in tropical and subtropical re- gions. 1 The disease may be manifested by fever, depression, dyspnea, anorexia, Address for correspondence: Yasuku Rikihisa, Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, 1925 Coffey Road, Columbus, Ohio 43210. Voice: 614-292-9677; fax: 614-292-6473. e-mail: rikihisa.1@osu.edu Ann. N.Y. Acad. Sci. 1078: 482–486 (2006). C  2006 New York Academy of Sciences. doi: 10.1196/annals.1374.090 482