Theileriosis: cell-mediated and humoral immunity.

The protozoan parasite of cattle Theileria parva transforms lymphoid cells into permanently proliferating cell lines. Antibodies reacting with parasite antigens can be detected by several methods, but there is no evidence that they are protective. Two cellular responses to infection have been found. In immune animals powerful cytotoxicity restricted to syngeneic infected cells rapidly appears; this is thought to be mediated by T-lymphocytes and to play a major role in resistance to reinfection. In primary infections cytotoxicity against allogeneic infected and xenogeneic cells is observed late. This is thought to be due to activation of a nonspecific cytotoxic system, which contributes to the lymphocytolysis and panleukopenia, a prominent feature of the disease. If mounted early enough, the nonspecific effector mechanism could also contribute to recovery from a primary infection, when it occurs.