In vitro regeneration of resting lymphocytes from stimulated lymphocytes and its inhibition by insulin.

Concanavalin A- (Con A) stimulated mouse lymphocytes were separated from unstimulated cell populations by a bovine serum albumin (BSA) density gradient centrifugation 2 days after the stimulation. The stimulated cells divided, but did not initiate a new round of DNA replication when cultured further in the absence of Con A. The divided cells became similar in various properties to unstimulated lymphocytes during a prolonged incubation, suggesting that they entered the resting state. In the present study, the process toward the resting state of lymphocytes from the proliferating state was manifested by: a) a decrease in a cell volume, b) lowering of protein content, c) a loss of responsiveness to T cell growth factor (Interleukin 2) (TCGF(IL2)) probably as a result of disappearance of TCGF(IL2) receptors, d) disappearance of insulin receptors, and e) a duration of time lag between the addition of Con A and the onset of DNA synthesis. In addition, it was found that insulin was not mitogenic for recently divided lymphocytes, but prevented these cells from entering the resting state. This suggests that there may be an in vivo system that keeps stimulated lymphocytes highly responsive to antigens for at least several days without initiating DNA synthesis and cell division.