Direct cellular communications between CD45R0 and CD45RA T cell subsets via CD27/CD70.

The engagement of CD27 with its ligand CD70 is considered to play an important role in T cell costimulation. In the present study, we investigated both the kinetics of CD70 expression and the contribution of its interaction with CD27 in T cell immune responses. CD70 was found to be expressed almost equally on both activated CD4 and CD8 T cells. On subsets of CD4 T cells, however, CD70 expression was induced preferentially on the CD45R0 T cell population after activation, whereas its expression was not noted on CD45RA T cells for almost 2 wk following activation. In long-term culture with media containing T cell growth factor (TCGF) and rIL-2, the expression of CD70 was increased markedly on CD45R0 T cells and minimally expressed on CD45RA T cells. In addition, strong surface expression of CD70 was observed on T cell clones originally derived from CD45R0+ CD4 T cells, whereas T cell clones originally derived from CD45RA+ CD4 T cells showed lower levels of expression. The addition of irradiated, activated CD45R0 T cells to CD45RA T cells caused a down-regulation of CD27 expression and an up-regulation of CD25 expression. These changes were blocked by addition of the anti-CD70 mAb, suggesting that direct contact between CD45R0 T cells and CD45RA T cells via CD27/CD70 occurred, leading to the activation of CD45RA T cells as measured by CD25 expression. These observations strongly support the notion that the engagement of CD27 plays an important regulatory role in the communication of subsets of CD45R0 and CD45RA T cells.