Induction of protective immunity by using Anaplasma marginale initial body membranes

Anaplasma marginale initial bodies of the Norton Zimbabwe strain were disrupted and separated into two membrane fractions banding at 1.15 and 1.22 g/cm3 by sucrose density centrifugation. The membrane fractions differed in their morphology and polypeptide composition. Membranes banding at 1.22 g/cm3 shared epitopes with surface-exposed polypeptides of the Florida strain of A. marginale, confirming the outer membrane location of these polypeptides. Immunization of cattle with either membrane fraction induced protection against homologous challenge, as demonstrated by significantly less anemia and lower peak rickettsemia values compared with those of adjuvant-immunized and nonimmunized calves. Protection correlated with antibody titer to membrane polypeptides. Although both membrane fractions induced protection, a 31-kDa polypeptide was the only common antigen to both fractions, as shown by reactivity of immune sera. Identification of membrane antigens capable of inducing protective immunity should facilitate development of vaccines against anaplasmosis suitable for use in Zimbabwe.