Effect of GP19 Peptide Hyperimmune Antiserum on Activated Macrophage during Ehrlichia canis Infection in Canine Macrophage-like Cells

SIMPLE SUMMARY: The commercial canine ehrlichiosis vaccine is still not available. A limitation of developing vaccines is the knowledge of the humoral immune response against E. canis infection is still unknown. In this study, we designed the peptide vaccine candidate, namely GP19(4-43), for inducing hyperimmune serum in rabbits. The rabbit sera were used to examine for E. canis infective inhibition in macrophage-like cells (DH82). A decrease in E. canis infection (<50% of infection) was observed on DH82 cells in the treated group with GP19(4-43) antiserum on the third day of the post-infection period. Cytokine genes in DH82 with/without rabbit sera were investigated and showed marked up-regulation of the IFNG expression level in DH82 cells in the treated group with GP19(4-43) antiserum. This study provides the preliminary information of immune response against E. canis of immunized animals and directions for genomic or/and proteomic studies involved in phagocyte-cell mediated immune response. ABSTRACT: In terms of its veterinary importance, vaccine development against Ehrlichia canis is needed. However, the effect of developing vaccines on humoral immune response against E. canis infection is still unknown. Novel GP19(4-43) was synthesized according to E. canis GP19 epitope prediction. To restrict any loss and/or illness in the host animal, rabbits were used in this study to produce GP19(4-43) hyperimmune sera. The effect of GP19(4-43) hyperimmune sera on neutralization was examined in vitro by determining the inhibition of E. canis infection of the macrophage-like cell line (DH82) in the presence of the sera. Four groups of DH82 cells received differing treatments. These included E. canis experimentally infected DH82 cells, E. canis-infected DH82 cells with control rabbit serum (untreated group), E. canis-infected DH82 cells with GP19(4-43) rabbit antiserum (treated group) and uninfected cells (negative control group), respectively. The treated group developed a decrease (p < 0.01) in the percentage of E. canis infected cells after 3 days post-infection at 48.57 ± 1.28. In addition, real-time PCR analyses of cytokine mRNA expression involved with the macrophage, humoral, and cellular immune responses were conducted. The findings revealed an upregulated expression of IFNG in the treated group during the infection. This study demonstrated neutralization in the GP19(4-43) peptide hyperimmune sera of immunized rabbits. Notably, IFN-γ production could be effectively promoted in canine macrophages in relation to the activation of macrophages and adaptive immune responses. The results of this study indicate the potential for the use of this immunogen in further investigations involving immunized and infected dogs as E. canis host species.