Identification of the protective 44-kilodalton recombinant antigen of Ehrlichia risticii

Protective studies were conducted with mice by using recombinantly produced antigens, polyacrylamide gel electrophoresis-fractionated antigens, and a monoclonal antibody specific to the 28-kDa antigen of Ehrlichia risticii. Analysis of E. risticii-infected cell culture used as the challenge inoculum indicated an inverse relationship between the progression of cell culture infection and the infective capability of E. risticii for mice. A recombinant 44-kDa antigen was found to protect mice considerably against challenge infection, while the monoclonal antibody and fractionated antigens were not protective. A potentiation of protection was observed when the recombinant 44-kDa antigen was combined with the recombinant 70-kDa antigen and used for mouse immunization.