ANALYSIS OF T-CELL RESPONSES IN CATTLE IMMUNIZED AGAINST HEARTWATER BY VACCINATION WITH KILLED ELEMENTARY BODIES OF COWDRIA-RUMINANTIUM

Cattle were successfully immunized against heartwater with a lysate of Cowdria ruminantium formulated in Freund's adjuvant. Vaccinated anima ls proved fully resistant to virulent challenge 3 and 10 months after vaccination. For the first time a helper T lymphocyte response to Cowd ria antigens was observed and characterized. Cowdria-specific T-cell l ines generated from vaccinated animals by vitro restimulation with Cow dria lysates are 95 to 100% CD4(+), are MHC class II restricted, and p roduce gamma interferon. They proliferate in response to autologous mo nocytes infected with live Cowdria but not to response to uninfected m onocytes. These T-cell lines will facilitate the search for Cowdria an tigens that are immunogenic for T cells and will therefore be of relev ance in the development of it subunit vaccine against the disease.