Hepatic IL-10–producing CD8⁺ T cells perform a regulatory function. (A) Highly purified CD8⁺ LILs pooled from two to three biopsies were cocultured with PBMCs plus soluble mAb’s to CD3 and CD28 in the presence or absence of anti–IL-10 (α–IL-10), mAb to perforin (α-perf.), or IL-2. Control cocultures were prepared in the presence of either IgG1 or IgG2b isotype, which did not produce any interference with suppressive function (data not shown). Control cultures in which PBMCs were stimulated with μAb’s to CD3 and CD28 in the presence of IL-2 or anti–IL-10 but in the absence of CD8⁺ LILs were also prepared. Each symbol represents an individual experiment performed with single LIL pool derived from two biopsies. In all experiments, 1 μCi “³H”thymidine was added to the cultures after 6 days, and the radioactivity incorporated by cells was determined after 18 hours. The cpm values were calculated after subtraction of background (Δ cpm). Statistical analysis was performed by Student’s t test for paired data. (B) The production of IL-10 was determined in the supernatant pool (not conditioned with mAb to IL-10) from cocultures indicated by symbols.