Theileria schizonts induce fundamental alterations in their host cells

The sporozoites of Theileria annulata and T. parva invade bovine leukocytes , where they differentiate into schizonts. The latter can immortalize and i nduce fundamental changes in their host cells. T. annulata infects mainly m ajor histocompatibility complex class II cells, whereas T. parva preferenti ally transforms T-lymphocytes, which proliferate continuously without the n eed for exogenously added growth factors. Most of the cell lines appear to be independent of a growth factor but may express several cytokines that in fluence the outcome of the disease. The mechanisms underlying this transfor mation are not well understood. The infected cells show increased activity of casein kinase II and Jun NH2-terminal kinase (JNK), whereas extracellula r signal-related kinase 1 and 2 and P38 are not activated. In addition, sev eral transcriptional factors such as NFkB and AP-1 are activated. It has be en postulated that parasite proteins either expressed on the surface of the schizonts or secreted into the host cell cytoplasm may interfere with the signal-transduction pathway of the host cells. A possible candidate may the casein kinase II homologue that was identified in schizonts of both T. ann ulata and T. parva.