Lsk. Walker et al., Lack of activation induced cell death in human T blasts despite CD95L up-regulation: protection from apoptosis by MEK signalling, IMMUNOLOGY, 98(4), 1999, pp. 569-575
The generation of effective immunity requires that antigen-specific T cells
are activated, clonally expanded and ultimately eliminated by apoptosis. T
he involvement of CD95-mediated apoptosis in T-cell elimination is well est
ablished, but the conditions which regulate the death pathway under normal
circumstances are still emerging. Using superantigen-activated human T cell
s, we found that whilst T-cell receptor (TCR) signalling triggered up-regul
ation of CD95 ligand (CD95L), the majority of T cells were resistant to apo
ptosis induction, despite co-expressing high levels of CD95. Resistance was
maintained following direct antibody-mediated cross-linking of CD95 and wa
s not confined to early time periods following activation. Our data implica
te TCR-derived signals in protection from apoptosis and reveal a role for t
he mitogen-activated protein (MAP) kinase pathway by use of a MAP kinase ki
nase (MEK) inhibitor. Collectively these data demonstrate that resistance t
o activation-induced cell death in human T cells is prolonged rather than t
ransient, is not attributable to a lack of CD95L up-regulation and is due,
at least in part, to signalling via the MEK pathway.