CD30-REGULATED APOPTOSIS IN MURINE CD8 T-CELLS AFTER CESSATION OF TCRSIGNALS

A variety of culture systems have been developed to study mechanisms o f activation-induced cell death in peripheral T lymphocytes either dur ing the initial period after exposure to an activating stimulus or fol lowing repeated stimulation of activated T cells. In this study we des cribe a new culture model for the analysis of apoptosis after withdraw al of TCR signals from activated T cells. T cells activated by anti-CD 3 antibodies for 48 h and then further cultured in the presence of IL- 2 but absence of continued CD3/TCR stimulation underwent dramatic cell death approximately 4 days following removal of the TCR stimulus. Apo ptotic cells generated in this protocol, unlike those produced by hype rstimulation, retained substantial levels of degraded DNA following fi xation, consistent with death in the G(0)/G(1) phase of the cell cycle . This ''agonist withdrawal'' cell death occurred largely within the C D8 T cell subset, with CD4 cells showing lower levels of apoptosis. Th is form of cell death did not appear to be the result of IL-2 exhausti on, since repeated addition of IL-2 during the culture period did not significantly alter the number of apoptotic cells. Apoptosis induced b y agonist withdrawal was not blocked by Fas antigen fusion protein or by anti-TNF alpha-neutralizing antibodies, suggesting a mechanism inde pendent of Fas/FasL and TNF alpha/TNF-R interactions. Cell death was, however, significantly inhibited by treatment with a CD30 fusion prote in. CD30 was found to be transiently expressed on CDS T cells immediat ely prior to death, with lower expression on CD4 cells, while CD30 lig and was found to be expressed most strongly by CD4 T cells. These resu lts suggest a role for CD30 in regulating the onset of apoptosis in CD 8 T cells after interruption of CD3/TCR. (C) 1997 Academic Press.