Phenotypic changes associated with activation of CD45RA+ and CD45RO+ T cells.

Resting CD45RO+, mature/memory, T cells are phenotypically distinct from intermediate CD45RO+/CD45RA+ and CD45RA+, immature/virgin, T cells, and are characterized by high levels of expression of a number of adhesion molecules, such as CD2, CD18, CD58 and CD29. The kinetics of up-regulation of molecules, like CD25 and CD54 associated with activation, were similar in both subsets and suggested that their high level expression was associated with later events rather than initial recognition and signal transduction. CD45RA+ T cells, unlike CD45RO+ T cells, were unable to proliferate in response to mitogenic combinations of CD2 monoclonal antibodies (mAb), although in combination with submitogenic doses of PMA both up-regulation of cell-surface molecules and proliferation occurred. In addition, recruitment of CD45RA+ T cells by CD2 mAb-activated CD45RO+ T cells can occur.