Cell-Mediated Immunity to Theileria-Transformed Cell Lines

Abstract

In East and Central Africa, the protozoan parasite Theileria parva causes a disease of cattle called East Coast fever (ECF). In Kenya alone between 60,000 and 85,000 cattle die from ECF every year1. Infected animals can recover from ECF either naturally2 or after treatment with tetracyclines3 or menoctone4 and are subsequently able to resist challenge with the homologous strain of parasite. That this acquired resistance is due to cell-mediated rather than humoral immunity has been suspected5,6 but never decisively shown. A major difficulty in studying immunity to ECF has been the lack of inbred animals for studying Theileria-specific immunity in the absence of allogeneic histocompatibility barriers. We have avoided this problem by measuring cell-mediated immune responses in a syngeneic system in vitro. Unidirectional mixed lymphocyte cultures (MLC) were set up using bovine peripheral blood lymphocytes (PBL) as responder cells and autologous cell lines transformed in vitro by T. parva as stimulator cells. In these cultures, DNA synthesis was induced in PBL from both normal and Theileria-immune animals. However, cytotoxic lymphocytes were induced only in cultures containing responder lymphocytes from Theileria-immune cattle. The results show that Theileria-transformed cells express antigens which are recognised by effector cells and provide evidence that cell-mediated cytotoxic mechanisms function in immunity to ECF.