T cell receptor (TCR)-dependent regulatory T cell (T(reg)) activity controls effector T cell (T(eff)) function and is inhibited by the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Protein kinase C-theta (PKC-theta) recruitment to the immunological synapse is required for full T(eff) activation. In contrast, PKC-theta was sequestered away from the T(reg) immunological synapse. Furthermore, PKC-theta blockade enhanced T(reg) function, demonstrating PKC-theta inhibits T(reg)-mediated suppression. Inhibition of PKC-theta protected T(reg) from inactivation by TNF-alpha, restored activity of defective T(reg) from rheumatoid arthritis patients, and enhanced protection of mice from inflammatory colitis. T(reg) freed of PKC-theta-mediated inhibition can function in the presence of inflammatory cytokines and thus have therapeutic potential in control of inflammatory diseases.