The Role of Interleukin‑2 in Memory CD8 Cell Differentiation
Onur Boyman, Jae-Ho Cho and Jonathan Sprent
The current literature on the role of interleukin (IL)‑2 in memory CD8+ T‑cell differentiation indicates a significant contribution of IL‑2 during primary and also secondary expansion of CD8+ T cells. IL‑2 seems to be responsible for optimal expansion and generation of effector functions following primary antigenic challenge. As the magnitude of T‑cell expansion determines the numbers of memory CD8+ T cells surviving after pathogen elimination, these events influence memory cell generation. Moreover, during the contraction phase of an immune response where most antigen‑specific CD8+ T cells disappear by apoptosis, IL‑2 signals are able to rescue CD8+ T cells from cell death and provide a durable increase in memory CD8+ T‑cell counts. At the memory stage, CD8+ T‑cell frequencies can be boosted by administration of exogenous IL‑2. Significantly, only CD8+ T cells that have received IL‑2 signals during initial priming are able to mediate efficient secondary expansion following renewed antigenic challenge. Thus, IL‑2 signals during different phases of an immune response are key in optimizing CD8+ T‑cell functions, thereby affecting both primary and secondary responses of these T cells.