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 gammadelta T cell population in peripheral lymphoid tissues. Avian gammadelta T cells can respond well to T cell mitogens in the presence of alphabeta T cells, but our studies indicate that they do not grow well alone. Exogenous growth factors were required in order for gammadelta 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 gammadelta 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 gammadelta 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 gammadelta T cells did not exhibit these activation markers. These observations suggest a physiological basis for the relatively late appearance of gammadelta T cells in inflammatory responses and their failure as a population to match the growth potential of alphabeta T cells. More importantly, the results imply that the biological role of gammadelta T cells must be understood within the context of their interaction with alphabeta T cells.