Bovine gamma/delta TcR(+) T lymphocytes are stimulated to proliferate by autologous Theileria annuluta-infected cells in the presence of interleukin-2

An in vitro model system has been developed in which freshly isolated resting WCl+ gamma/delta TcR(+) T cells proliferate in response to cells transformed by the protozoan parasite Theileria annulata, providing a strategy in which the basis of activation of naive gamma/delta T cells can be investigated. Irradiated parasite-transformed cells stimulate the proliferation, but not cytolytic activity, of autologous peripheral blood mononuclear cells (PBMC) from non-immune animals. The proliferating cells are mainly WCl+- gamma/delta T cells. The majority of WCl+ gamma/gamma T cells in freshly isolated PBMC express CD25 at a low level that increases when stimulated with T. annulata-infected cells. Purified WCl+ gamma/delta T cells fail to proliferate when cultured with irradiated T. annulata-infected cells and produce a small proliferative response to IL-2, but proliferate strongly to irradiated or lightly fixed Theileria-infected cells in combination with IL-2. The Theileria-infected cells express cytokine transcripts encoding IL-1 alpha, IL-1 beta, IL-6 and IL-10, but not IFN gamma, IL-2, IL-4 and IL-7. Purified WCl+ gamma/delta T cells stimulated with T. annulata-infected cells with or without IL-2 fail to produce IL-2 transcripts, but do produce those for TNF alpha. These experiments show that WCl+ gamma/delta T cells recognize a surface determinant on T. annulata-infected cells, that together with a second signal, which can be provided by exogenous IL-2, stimulates their proliferation.