Growth requirements for avian gamma delta T cells include exogenous cytokines, receptor ligation and in vivo priming.

These studies analyze growth requirements for the normal gamma delta T cell population in peripheral lymphoid tissues. Avian gamma delta T cells can respond well to T cell mitogens in the presence of alpha beta T cells, but our studies indicate that they do not grow well alone. Exogenous growth factors were required in order for gamma delta T cells to proliferate in response to receptor ligation by anti-T cell receptor antibodies or other T cell mitogens. Interleukin-2 was implicated as one of the necessary growth factors that the gamma delta cells cannot produce adequately on their own. The response to dual stimulation (receptor ligation plus exogenous T cell factors) was attributable to a discrete subpopulation of gamma delta T cells that could be identified by their cell surface CD8, major histocompatibility complex class II expression and relative increase in cell size. Conversely, non-responsive gamma delta T cells did not exhibit these activation markers. These observations suggest a physiological basis for the relatively late appearance of gamma delta T cells in inflammatory responses and their failure as a population to match the growth potential of alpha beta T cells. More importantly, the results imply that the biological role of gamma delta T cells must be understood within the context of their interaction with alpha beta T cells.