The cytoplasmic tail of CD28 up-regulates transcription of an RE/AP- based reporter in B cells.

The Bal17 and DT40 B cell lines were transfected with the IL-2 RE/AP reporter and an expression plasmid containing a chimeric molecule containing the extracellular and transmembrane regions of CD8 and the intracellular tail of CD28 (CD8/28) or the extracellular and transmembrane regions of CD8 alone (CD8_T). The following day, the 10⁵ live cells were unstimulated or stimulated with PMA (1 ng/mL for DT40 cells and 25 ng/mL for Bal17) and anti-CD8 antibody OKT8 at a 1:1000 dilution of ascites for 6 hours as denoted in the figure. Luciferase activity was standardized to the activation of PMA and OKT8 in CD8/28 transfected cells (n = 100). The actual average luciferase counts for PMA/OKT8 stimulation of RE/AP in CD8/28-transfected cells were 8270 in Bal17 and 80 604 in DT40. The results shown are the average of 3 independent transfections. Error bars reflect the SD from the mean.