Homotypic and heterotypic antibody responses to a 56-kilodalton protein ofOrientia tsutsugamushi

We analyzed homotypic and heterotypic antibody responses to a type-specific antigen (Tsa), a 56-kDa protein of Orientia tsutsugamushi, by using sera f rom mice immunized with strains Gilliam, Karp, Kato, and Boryong, We genera ted a series of deletion constructs of the tsa gene and expressed them as M alE fusion proteins. Variable domain I (VD I) showed strong responses to ho motypic antibodies. Antigenic domain II (AD II) from Boryong and Karp showe d cross-reactivities to each other. VD III sheaved no responses to any of t he antibodies. Sera from Kato-immunized mice showed only homotypic response s to AD III. On the other hand, sera of the mice immunized with Gilliam, Ka rp, or Boryong showed homotypic as well as heterotypic responses to this re gion, VD IV showed the strongest heterotypic antibody responses among the f ragments tested. These data suggest that VD I is important in homotypic ant ibody responses and that AD II, AD III, and VD IV are important in heteroty pic antibody responses of the mice to Tsa.