The strategies of the Theileria parasite: a new twist in host–pathogen interactions

Theileria parasites infect and transform cells of the ruminant immune system. Continuous proliferation and survival of Theileria-transformed cells involves the well-orchestrated activation of several host-cell signalling pathways. Constitutive NF-κB (nuclear factor kappaB) activation is accomplished by recruiting the IKK (IκB kinase) complex, a central regulator of NF-κB pathways, to the surface of the transforming schizont, where it becomes permanently activated. Constitutive activation of the PI-3K–PKB [phosphoinositide 3-kinase–(Akt) protein kinase B] pathway is likely to be indirect and is essential for continuous proliferation. Theileria-transformed T cells express a range of anti-apoptotic proteins that can be expected to provide protection against apoptosis induced by death receptors, as well as cellular control mechanisms that are mobilised to eliminate cells that entered a cycle of uncontrolled proliferation.