Antigen recognition and activation of ovine gamma delta T cells.

We have investigated several aspects of gamma delta T cells in sheep. gamma delta T cells of sheep express a unique transmembrane protein termed T19 but lack the expression of particular cell-surface molecules such as CD2, CD4 and CD8 which are typically associated with alpha beta T cells. The majority of gamma delta T cells isolated from animals of all ages examined lacked the expression of CD45RA. A faster rate of activation by gamma delta T cells compared to either CD4 or CD8 T cells was seen in the time-course of IL-2 receptor alpha chain (CD25) cell-surface expression. All gamma delta T cells expressed the CD25 protein within 8 hr of activation whereas the majority of CD4 or CD8 T cells did not express CD25 until 24 hr post-concanavalin A (Con A) stimulation. This difference in the rate of expression of activation molecules was not restricted to CD25, as a similar trend was seen with cell-surface expression of major histocompatibility complex (MHC) class II molecules. We have used the distinct phenotypic profile of ovine gamma delta T cells to purify these cells by positive selection via the T19 molecule to assess their in vitro proliferative response to various antigens. Routinely, cell populations comprising more than 93% gamma delta T cells with yields of approximately 55% were obtained. Purified gamma delta T cells were capable of responding to Mycobacterium tuberculosis antigen in a primary and secondary in vitro proliferation assay and to ovalbumin in a secondary response. Ovine gamma delta T cells showed little, if any, proliferative response to allogeneic stimulator cells.