Interference of cyclosporin with lymphocyte activation maintenance of the cells in a non-cycling phase and with a low intracellular pH.

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).