Cell-mediated immune responses to sporozoites and macroschizonts of Theileria annulata.

The nature of cell-mediated immune (CMI) responses was studied in cross-bred bovine calves, immunised by attenuated and allogeneic macroschizonts of Theileria annulata. The CMI responses were also investigated in calves, destined to survive or die of tropical theileriosis (Theileria annulata) induced by a virulent dose of sporozoites or macroschizont-infected lymphoblasts. Calves suffering fatal theileriosis showed poor CMI response. Microcytotoxicity assay revealed an enhanced population of specific cytotoxic cells amongst the peripheral blood lymphocytes (PBL) of calves resolving the infection successfully. The E rosette assay showed proliferation of T cells and the assay for macrophage migration inhibition factor (MIF) demonstrated antigen sensitised cells in the PBL. Calves, immunised by allogeneic and attenuated macroschizont-infected lymphoblasts or those recovering from virulent macroschizont-induced infection, showed protective CMI responses with patterns similar to those appearing after non-fatal sporozoite infection.