Neutralization epitopes on the antigenic domain II of the Orientia tsutsugamushi 56-kDa protein revealed by monoclonal antibodies

Monoclonal antibodies (MoAbs) reactive with the authentic Orientia tsutsugamushi 56-kDa protein were generated. MoAb FS10 and FS15 showed in vitro, as well as, in vivo neutralizing activity upon O. tsutsugamushi infection. Deletion mutants of the gene for 56-kDa protein of O. tsutsugamushi Boryong were expressed to map the binding region. FS10 and FS15 are bound to amino acids (aa) located in an antigenic domain II, at residues 140–160 and 187–214, respectively. Computer modeling indicated that aa 146–153 were important for antigenicity against FS10. A sequence for aa 142–150 was highly homologous between oriential strains. These results suggest that the antigenic determinant for neutralizing MoAbs is an epitope within aa 140–160. Furthermore, this region may be important for the adhesion/invasion or intracellular survival of O. tsutsugamushi within host cells.