INDUCTION OF HOMOLOGOUS IMMUNE-RESPONSE TO RICKETTSIA-TSUTSUGAMUSHI BORYONG WITH A PARTIAL 56-KILODALTON RECOMBINANT ANTIGEN FUSED WITH THEMALTOSE-BINDING PROTEIN MBP-BOR56

Although the 56-kDa protein of Rickettsia tsutsugamushi has been presu med to play important roles in generating protective immunity against scrub typhus, studies of this protein have been impeded. We used the r ecombinant 56-kDa protein of R. tsutsugamushi Boryong fused with the m altose-binding protein of Escherichia coli (MBP-Bor56) to analyze its ability to induce protective immunity in a C3H/HeDub murine model. Int raperitoneal immunization of mice with MBP-Bor56 resulted in an increa se in the 50% minimal lethal dose of more than 160 times compared with that for the control mice. Splenic mononuclear cells from the mice im munized with MBP-Bor56 showed a dose-dependent pattern of lymphocyte p roliferation response and secreted gamma interferon and interleukin-2 when stimulated with irradiated R. tsutsugamushi Boryong, which is a c ytokine profile of Th1 cells. High titers of antibody to R. tsutsugamu shi were also demonstrated by indirect immuno fluorescent antibody tes ting. These findings suggest that the 56-kDa protein of R. tsutsugamus hi is one of the candidates for a vaccine against scrub typhus.