Figure 1.

Regulatory T cells (Tregs) inhibit multiple stages of target cell activity. (a) Tregs appear to be unable to inhibit the early activation events (up-regulation of CD25 and CD69) of the first 6–10 hr of target CD4⁺ T-cell activation. (b) Tregs suppress proliferation of multiple immune cell types possibly via attenuation of interleukin-2 production. (c) Suppression of CD4⁺ T-cell differentiation by limiting the duration of T-cell receptor signalling or inhibiting the induction of the lineage specific transcription factors GATA3 and Tbet. (d) Treg suppression of effector T-cell cytokine production (interferon-γ and interleukin-4 by T helper type 1 and type 2 cells, respectively); inhibition of lytic granule release by CD8 effectors; inhibition of B-cell antibody production, directly or via blockade of CD4 help.