Rickettsia rickettsii is the causative pathogen of
Rocky Mountain spotted fever (RMSF). Adr2, YbgF and OmpB are protective
antigens of R. rickettsii. In this study, 90 candidate
peptides were selected from these
antigens based on their high-affinity binding capacity for the
MHC class II molecule H2 I-A or H2 I-E using bioinformatic methods. Six
peptides were determined using ELISPOT assay to be immunodominant based on the IFN-γ recall responses of CD4+ T cells from mice immunized with R. rickettsii. Six nucleotide sequences encoding the immunodominant
peptides were linked in series and inserted into a plasmid for expression in Escherichia coli cells, resulting in a new, recombinant
polypeptide termed GWP. After immunization and challenge, the rickettsial load or histopathological lesions in the organs of mice immunized with GWP or pooled
peptides was significantly lower than that in organs of mice immunized with PBS or the individual
peptide OmpB399. An in vitro neutralization test revealed that sera from mice immunized with GWP, OmpB399, or pooled
peptides reduced R. rickettsii adherence to, and invasion of, vascular endothelial cells. Furthermore, significantly higher levels of
IgG,
IgG1, or
IgG2a were detected in sera from mice immunized with GWP or pooled
peptides, and significantly higher levels of IFN-γ or TNF-α secreted by CD4+ T cells from R. rickettsii-infected mice were detected after immunization with GWP. Altogether, our results indicated that
polypeptides, especially GWP, could induce a Th1-type immune response against R. rickettsii
infection, which might contribute to the rational design of
peptide-based
vaccines for RMSF.