Increase of intracellular cAMP in primary human T cells allows TCR/CD3 plus CD28–mediated G₁ phase entry but inhibits cell cycle progression.

(A-B) T cells were cultured with TCR/CD3 plus anti-CD28 or with phorbol ester plus anti-CD28 either in media or with forskolin and IBMX. At 48 hours of culture, whole cell lysates were prepared and expression of the indicated cell cycle regulatory molecules was examined by 10% SDS-PAGE analysis followed by Western blot. (C) For detection of Rb phosphorylation the same cell lysates were analyzed by 6% SDS-PAGE followed by Western blot with Rb-specific antibody. Cyclin A was examined by stripping and reprobing the immunoblots used in panels A and B. Results are representative of 3 experiments.