BOVINE GAMMA DELTA TCR(+) T-LYMPHOCYTES ARE STIMULATED TO PROLIFERATEBY 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 cel ls transformed by the protozoan parasite Theileria annulata, providing a strategy in which the basis of activation of naive gamma/delta T ce lls can be investigated. Irradiated parasite-transformed cells stimula te the proliferation, but not cytolytic activity, of autologous periph eral blood mononuclear cells (PBMC) from non-immune animals. The proli ferating cells are mainly WCl+- gamma/delta T cells. The majority of W Cl+ 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 w ith irradiated T. annulata-infected cells and produce a small prolifer ative response to IL-2, but proliferate strongly to irradiated or ligh tly fixed Theileria-infected cells in combination with IL-2. The Theil eria-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. Pur ified WCl+ gamma/delta T cells stimulated with T. annulata-infected ce lls with or without IL-2 fail to produce IL-2 transcripts, but do prod uce 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 exogenou s IL-2, stimulates their proliferation.