Cell-mediated immunity related to challenge exposure of cattle inoculated with virulent and attenuated strains of Anaplasma marginale.

Cattle which were given virulent Anaplasma marginale as a premunization procedure or were vaccinated with live attenuated or killed anaplasma preparations were challenge inoculated with virulent A marginale. Exposure of cattle to virulent or attenuated A marginale, which induced a strong and lasting cell-mediated response as measured by the leukocyte migration-inhibition test, protected against the development of high parasitemia, anemia, and clinical signs of disease after challenge inoculation with virulent A marginale. Cattle which were vaccinated with killed anaplasma preparations that induced transient and low-level cell-mediated responses were not protected against the development of severe anemia after challenge inoculation, although postchallenge parasitemia seemed to be controlled.