CD4(-CELLS ORCHESTRATE BOTH AMPLIFICATION AND DELETION OF CD8(+) T-CELLS() T)

This review focuses on the role of CD4(+) T cells in regulating immune responses, orchestrating both the amplification and deletion of immun e cells, particularly CD8(+) T cells. These two functions, which repre sent only an apparent contradiction, appear to be two faces of the sam e process of regulation. In fact, because the immune response, once ac tivated, needs to be carefully controlled or switched off when the ant igenic stimulus is eliminated, the immune system has developed several strategies either to regulate clonal amplification or to avoid useles s expansion of activated cells. In particular, we have reported many d ata demonstrating that CD4(+) T cells may be indicated as the regulato ry element in the activation as well as the deletion of CD8(+) T cells . New data are also reported on the ability of anergic CD4(+) T cells to suppress CD8(+) T-cell activation through induction of apoptosis, a nd on the need for CD8(+) T cells for antigen recognition in inducing cell death in CD4(+) T cells. Moreover, the central role of CD4(+) T c ells in the maintenance of peripheral tolerance has been widely descri bed.