TCRζ^dim cells are enriched for cytokine-producing effector T cells. Fresh PBLs were stimulated with PMA and ionomycin for 6 hours prior to staining for CD3, TCRζ, and intracellular expression of (A) TNF-α, (B) IFN-γ, and (C) IL-10. Data are expressed as percent cytokine-expressing cells within TCRζ^bright or TCRζ^dim subsets for 12 healthy donors. Horizontal lines represent mean values.