Transformation of leukocytes by Theileria parva and T-annulata

Theileria parva and T annulata provide intriguing models for the study of p arasite-host interactions. Both parasites possess the unique property of be ing able to transform the cells they infect; T. parva transforms T and B ce lls, whereas T annulata affects B cells and monocytes/macrophages. Parasiti zed cells do not require antigenic stimulation or exogenous growth factors and acquire the ability to proliferate continuously. In vivo, parasitized c ells undergo clonal expansion and infiltrate both lymphoid and non-lymphoid tissues of the infected host. Theileria-induced transformation is entirely reversible and is accompanied by the expression of a wide range of differe nt lymphokines and cytokines, some of which may contribute to proliferation or may enhance spread and survival of the parasitized cell in the host. Th e presence of the parasite in the host-cell cytoplasm modulates the state o f activation of a number of signal transduction pathways. This, in turn, le ads to the activation of transcription factors, including nuclear factor-ka ppa B, which appear to be essential for the survival of Theileria-transform ed T cells.