2 DISTINCT ALPHA-BETA-T-CELL LINEAGES CAN BE DISTINGUISHED BY THE DIFFERENTIAL USAGE OF T-CELL RECEPTOR V-BETA-GENE SEGMENTS

Avian T cells can be divided into three subpopulations based on their expression of distinct T-cell receptors (TCR1, TCR2, and TCR3), ontogeny, and tissue distribution. The TCR1 cells appear to be the equivalent of mammalian gamma-delta-cells, but the derivation of cells expressing TCR2 and TCR3 has been unclear. Here we report that chickens contain two families of TCR-beta variable (V) gene segments, V(beta)1 and V(beta)2. Furthermore, TCR2 and TCR3 represent subsets of alpha-beta-cells that are defined by mutually exclusive usage of these two families of V(beta) gene segments. Sequence comparisons of V(beta)1 and V(beta)2 with mammalian TCR-beta V segments reveal that V(beta)1 gene segments encode the conserved amino acids used to define the mammalian V(beta) consensus subgroup 1, while V(beta)2 encodes the amino acids used to define the mammalian V(beta) subgroup II. Although the beta-chains of TCR2 and TCR3 cells are encoded by the same diversity (D), joining (j), and constant (C) region segments, V(beta)1 gene segments undergo rearrangement before V(beta)2 gene segments during T-cell development. This may result from the fact that TCR2 cells undergo V-DJ joining by deletional rearrangement, whereas TCR3 cells undergo V-DJ joining by inversional rearrangement. These data suggest that the TCR-alpha-beta-cells can be divided into two distinct and evolutionarily conserved lineages based on V(beta) gene segment usage. The clear-cut separation of these lineages in the chicken may help to define their immunologic role.