In Vivo Depletion of Chicken T‐Cell Subsets

In the chicken three types of T‐cell receptors can be defined by monoclonal antibodies TCR1, TCR2 and TCR3, which recognize γδ T cells, and Vβ1‐ and Vβ2‐expressing αβ T cells, respectively. In the present report we have analysed means of selectively depleting the γδ T cells and the Vβ1 +αβ T cells. γδ 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 γδ T cells are affected by Tx to a lesser extent. Vβ1‐bearing αβ T cells, which comprise about 80% of the αβ T cells, were depleted by embryonic and neonatal injection of the TCR2 antibody. In the thymus such treatment depleted only the Vβ1 +αβ T cells with high density expression of T‐cell receptor. Therefore, we thymectomized TCR2‐treated animals in order to prevent development of mature Vβ1+αβ T cells from the low density immature thymocytes. Treatment of chickens with a total of 22 mg of TCR2 antibody plus Tx reduced Vβ+αβ T cells from an average of 65% to 10% of all T cells. In these TCR2 antibody‐treated animals the Vβ2‐expressing αβ T cells become the predominant type of T cell (average 85%).