Theileria annulata and T. parva infect and transform different bovine mononuclear cells

Bovine peripheral blood mononuclear cells (PBMC) were labelled with monoclonal antibodies recognizing bovine MHC class II, sIgM, monocyte, T-helper and T-cytotoxic cell phenotypes. They were sorted into positive and negative populations with a fluorescence-activated cell sorter (FACS). The cell populations were infected in vitro with sporozoites of either Theileria annulata or T. parva, and the degree of infection and transformation determined. The results showed that despite the many similarities between these two parasites, they infected different cells of the immune system. T. annulata preferentially infected MHC class II-positive cells but did not infect T cells. Monocytes were infected very efficiently by T. annulata but were uninfectable with T. parva. B cells were infected much more efficiently by T. annulata than T. parva. Cell lines derived from infections with T. annulata were analysed phenotypically. Virtually all reactivity was lost for the anti-sIgM and the anti-monocyte monoclonal antibodies post-infection and no T-cell markers were detected.