Leu-8 antigen expression is diminished during cell activation but does not correlate with effector function of activated T lymphocytes.

Previous studies have suggested that there is an inverse relationship between cell activation and the expression of the Leu-8 Ag, a cell surface protein that distinguishes functionally distinct T cell populations. This was confirmed in vitro, because when resting PBL were activated with PHA there was a rapid decline in expression of the Leu-8 Ag on all lymphocyte subpopulations. A decline in Leu-8 reactivity occurred after stimulation of lymphocytes with PHA, anti-CD3 plus PMA and ionomycin plus PMA, and an intermediate decline in Leu-8 expression occurred after stimulation with Con A. However, there was little loss of expression of Leu-8 after stimulation of lymphocytes with PWM or allogeneic lymphocytes. The decline in Leu-8 expression on activated lymphocytes occurred earlier than the decline in expression of CD45R. After removal of the activation stimuli, peripheral blood T cells or Jurkat cells rapidly re-expressed Leu-8. Finally, when the expression of Leu-8 on peripheral blood CD4+, Leu-8+ T cells was reduced by prior activation with PHA, these cells continued to exhibit suppressor function for PWM-stimulated Ig synthesis. Thus, there is a rapid decline in expression of the Leu-8 Ag but no change in regulatory function of CD4+, Leu-8+ T cells during cell activation. These results suggest that the molecule recognized by anti-Leu-8 plays a role in lymphocyte activation but not directly in the effector function of CD4+, Leu8+ T cells.