Poster abstracts
Poster number 4 submitted by Mariella Mestres-Villanueva
Ehrlichia japonica immunodominant outer membrane proteins as vaccine candidates in a fatal Human Monocytic Ehrlichiosis mouse model
Mariella A. Mestres-Villanueva (MCDB), Khem Budachetri (Dept. of Veterinary Biosciences), Mingqun Lin (Dept. of Veterinary Biosciences), Yasuko Rikihisa (Dept. of Veterinary Biosciences)
Abstract:
Ehrlichia spp. are emerging tick-borne obligatory intracellular bacteria that cause Human Monocytic Ehrlichiosis (HME), a potentially fatal and severe, influenza-like illness. The only treatment available is the antibiotic Doxycycline, and there is no vaccine available. Ehrlichia surface proteins and virulence factors have been identified and their roles in infection have been studied. Ehrlichia sp. have a multigene family encoding P28/OMP-1 immunodominant outer membrane proteins, which function as porins. Among multiple copies of P28/OMP-1s, Omp-1B is the only one expressed in ticks. We hypothesized that immunization with Omp-1B would prevent Ehrlichia transmission from ticks to mammals, thus HME. The objective of this study is to determine the vaccine potential of Omp-1B using Ehrlichia japonica in the mouse model of acute fatal HME. omp-1 was cloned from the bacterial genomic DNA into a protein expression vector, followed by expression and purification of the recombinant protein. In this pilot study, immunocompetent mice were immunized with rOmp-1B and challenged with E. japonica via intraperitoneal (i.p.) inoculation. Although mice had specific antibody titers against rOmp-1B, on day 9 post-challenge, mice were moribund and thus euthanized. There was no or low protection conferred by the immunization. For future studies, intradermal or infected tick challenge will be required for evaluation of rOmp-1B vaccine efficacy. Mouse survival curves will be generated and at euthanasia, blood, spleen, and liver samples will be collected for analysis of bacterial load and cytokine expression, via quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Cytokine-producing cell population in liver and spleen will be analyzed by flow cytometry. This project will lead to a better and more thorough understanding of the vaccination potential of ehrlichial outer membrane proteins, and the pathogenicity and immunological response in fatal ehrlichiosis.
Keywords: Ehrlichia, obligatory intracellular bacteria, immunization