Single administration of collagen type II–specific type 1 regulatory T cell cells reduces acute collagen-antibody-induced arthritis. We administered intraperitoneal injections of lipopolysaccharide (100 μg) into DBA/1 mice at day 3 after arthritis induction, followed 2 to 4 hours later by intravenous injections of 1 × 106 collagen type II–specific type 1 regulatory T cell (Col-Treg) clones (open triangles; n = 6) or saline buffer solution (closed circles; n = 6). Mice not injected with antibody were used as controls (X’s; n = 2). After T-cell infusion, the mice were evaluated daily for clinical signs of arthritis. (A) Graphed mean ± SEM data of the severity scores of arthritic mice are shown. Differences were analyzed by nonparametric Mann–Whitney U test. The data are representative of two independent experiments. *P < 0.05 with 95% confidence interval for comparison of arthritic and saline-injected control mice. (B) Disease incidence represents the percentage of arthritic mice at each time point. (C) Percentages of body weight loss are shown. (D) Graph illustrating the trafficking of type 1 regulatory T cell clones analyzed 24 hours after intravenous infusion of 1 × 106 cells in collagen antibody–induced arthritis mice (n = 6). The data are expressed as mean ± SEM of the number of transgenic positive cells detected in various organs, including joint tissues, determined by quantitative PCR using standard curves. LN, Lymph node. mLN, Mesentheric LN. Ing. LN, Inguinal LN. Pop. LN, Popliteal LN. Ax. LN, Axillary LN.