Cell activation and cell proliferation requirements of SAg-mediated deletion of TCR Vβ8.1 DP TG thymocytes. TCR Vβ8.1 thymocytes were cultured for 60 hours alone or with BALB.D2 splenic B cells in control conditions (untreated), or in the presence of 6 μmol/L BIM (PKC inhibitor), 80 nmol/L CsA (calcineurin inhibitor), or 120 μmol/L mimosine (cell-cycle blocker). Dot plots show the CD4 versus CD8 profile (CD4-PE/CD8-FITC staining) after removing magnetically the B cells using anti-mouse Ig-coated magnetic beads (see Materials and Methods for details). The absolute cell number of DP thymocytes is indicated. The statistics corresponding to four similar experiments are given in Table 1. Histograms represent the CD69 expression and BrdU incorporation of DP thymocytes for each culture condition. The percentage of CD69⁺ (FL2 > 20) and BrdU⁺ (FL1 > 80) DP thymocytes are indicated.