Abstract
Cyclosporin can block T cell activation by mitogens as evidenced by inhibition of exogenous thymidine integration into DNA and by blockage of the cells in the G0/G1 phase of the cell cycle. The mitogenic activation sequence shows at least one cyclosporin sensitive step at or prior to the rise of cytoplasmic pH (pHi), which normally occurs after exposure to mitogen and which seems to be a permissive condition for initiation of DNA synthesis (S phase of the cell cycle).