Trypanosoma theileri: antibody-dependent killing by purified populations of bovine leucocytes.

Bovine leucocytes were assayed for their cytotoxic activity against Trypanosoma theileri, a large haemoflagellate parasite of cattle. Cytotoxicity was assessed by 3H-uridine release from pre-labelled parasites and also by light microscopy. Cytotoxicity proved to be totally dependent upon the presence of specific antibody. Serum and the immunoglobulin fraction of colostrum from normal adult cattle and serum from normal colostrum fed calves mediated cytotoxicity; serum from SPF colostrum deprived calves possessed no cytotoxic activity. Neutrophils, eosinophils, monocytes and macrophages obtained from both the peripheral blood and mammary gland of heifers were cytotoxic to T. theileri epimastigotes. Lymphocytes failed to mediate cytotoxicity either in the presence or absence of specific antibody. Despite the large size of this trypanosome all effector cells phagocytosed T. theileri. Phagocytosis by macrophages and eosinophils preceded specific isotope release, however neutrophils mediated 50% specific isotope release during the phagocytic period, suggesting extracellular cell-mediated lysis.