Recombinant GP19 Protein as a Promising Vaccine Prototype Providing a Protective Immune Response in a Mouse Model.

The intracellular bacterium is the causative pathogen of canine monocytic ehrlichiosis (CME) in dogs. Despite its veterinary and medical importance, there is currently no available vaccine against this pathogen. In this study, the recombinant GP19 (rGP19) was produced and used as a recombinant vaccine prototype in a mouse model against experimental infection. The efficacy of the rGP19 vaccine prototype in the part of stimulating B and T cell responses and conferring protection in mice later challenged with pathogen were evaluated. The rGP19-specific antibody response was evaluated by ELISA after challenge exposure (on days 0, 7, and 14 post-challenge), and demonstrated significantly higher mean antibody levels in rGP19-immunized mice compared with adjuvant-immunized and naive mice. Significantly lower ehrlichial loads in blood, liver, and spleen DNA samples were detected in the immunized mice with rGP19 by qPCR. The up-regulation of and mRNA expression were observed in mice immunized with rGP19. In addition, this study detected IFN-γ-producing memory CD4+ T cells in the rGP19-immunized mice and later infected with on day 14 post-infection period using flow cytometry. The present study provided a piece of evidence that rGP19 may eliminate by manipulating Th1 and B cell roles and demonstrated a promising strategy in vaccine development against infection in the definitive host for further study.