In the chicken three types of T-cell receptors can be defined by monoclonal antibodies TCR1, TCR2 and TCR3, which recognize gamma delta T cells, and V beta 1- and V beta 2-expressing alpha beta T cells, respectively. In the present report we have analysed means of selectively depleting the gamma delta T cells and the V beta 1+ alpha beta T cells. gamma delta T cells, which represent up to 66% of all T cells in blood of a 6-month-old chicken, can be effectively depleted by neonatal thymectomy (Tx) to levels as low as 1%. Immunohistology demonstrates a similar depletion in lymphoid organs while intestinal epithelium-associated gamma delta T cells are affected by Tx to a lesser extent. V beta 1-bearing alpha beta T cells, which comprise about 80% of the alpha beta T cells, were depleted by embryonic and neonatal injection of the TCR2 antibody. In the thymus such treatment depleted only the V beta 1+ alpha beta T cells with high density expression of T-cell receptor. Therefore, we thymectomized TCR2-treated animals in order to prevent development of mature V beta 1+ alpha beta T cells from the low density immature thymocytes. Treatment of chickens with a total of 22 mg of TCR2 antibody plus Tx reduced V beta 1+ alpha beta T cells from an average of 65% to 10% of all T cells. In these TCR2 antibody-treated animals the V beta 2-expressing alpha beta T cells become the predominant type of T cell (average 85%).

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