anti-TCRab/Vb1 antibody: The antibody detects: Chicken TCR (V1) Mab TCR2 precipitates a CD3-associated heterodimer of Mr 90 kDa (two bands of Mr 40 kDa and 50 kDa upon reduction) on chicken peripheral blood T cells.1 Deglycosylation of the heterodimer yields two polypeptides of Mr 34 kDa and 29 kDa from TCR2 precipitates. In the chicken, two distinct subpopulations of T cells appear in the thymus subsequent to the appearance of T cells. These subpopulations, originally denoted as TCR2 and TCR3,1-3 arise sequentially in the thymus during ontogeny and are now known to represent two distinct V families, V1 and V2, respectively.4 The TCR2 MAb reacts with approximately 40 % of thymocytes, 40-50 % of blood mononuclear cells and 40 % of splenocytes in the chicken. Two-color immunofluorescence has revealed that most of the TCR2+ thymocytes express both CD4 and CD8 antigens. The TCR2+ cells in blood were found to express either CD4 (742 %) or CD8 (264 %). TCR2+ cells in the spleen also express either CD4 (371 %) or CD8 (644 %). Surprisingly, a relatively large subpopulation of CD8+ cells in the spleen are negative for TCR2.1-3 This observation led to the demonstration that 716 % of the TCR1()+ cells in the spleen express the CD8 marker.