['Autoreactive T cells that proliferate in response to autoantigens are found in both autoimmune diseases and controls but have important qualitative differences in relative activation states, costimulation signal requirements and pathogenetic significance.', 'To understand the differences between autoreactive T cells in PBC versus controls, we have developed autoreactive T-cell clones (TCC) from patients with PBC and healthy controls, and have used a peptide corresponding to the CD4 major autoantigen (Ag) to define the relative proliferative response. Peripheral blood mononuclear cells (PBMC) from PBC respond to the Ag in a costimulation-independent manner, but PBMC from controls respond to the Ag in a costimulation-dependent manner. Next, we established nine autoreactive TCC from patients with PBC and eight from healthy controls.', 'Among 17 TCC, eight were the costimulation-dependent type and nine were independent. In addition, costimulation-dependent autoreactive TCC became anergic after stimulation in the presence of APC that did not provide costimulatory signals. Finally, we observed that anergic TCC exhibit regulatory functions.'] Are autoreactive T-cell responses in primary biliary cirrhosis proinflammatory whereas those of controls are regulatory?