Flow cytometric analysis of thymocyte apoptosis in vivo. (A) Dot plot showing forward-scatter (FFC) and side-scatter (SSC) analysis of thymocytes from an animal treated with anti-CD3 antibodies. The top left population constitutes the apoptotic/dead cells, while the bottom right is alive. The circular region depicts the total population of cells analyzed. (B) Representative dot plots from staining with annexin V and 7-AAD. Early and late apoptosis are shown in the bottom and top rectangular regions, respectively. The total level of apoptosis was determined by summarizing the values of both of these regions. (C) Mean values of total apoptosis from annexin V/7-AAD staining, showing the percentage of thymocytes that are apoptotic when treated with anti-CD3 or PBS (C = control). (▪) TβRII^-/- (C: n = 3; +anti-CD3: n = 5); and (▦) TβRII^+/- (C: n = 2; +anti CD3: n = 4). Results are expressed as mean ± SDs.