Decrease of inflammation, bone erosion and B-cell response following injection of collagen type II–specific type 1 regulatory T cells at day 20 in murine collagen-induced arthritis. In the DBA/1 mice, we administered intravenous injections of collagen type II–specific type 1 regulatory T cell (Col-Treg) clones in quantities of 1 × 106 (open triangles; n = 9) or 3 × 106 (closed triangles; n = 9) or saline buffer solution (closed circles; n = 9) at day 20 postimmunization. After the T-cell infusions, the mice were clinically monitored every other day. (A) Graphed mean ± SEM data of the arthritis severity scores are shown. Differences were analyzed by nonparametric Mann–Whitney U test (*P < 0.05 with 95% confidence interval represent statistically significant differences between the arthritic and saline-injected mice). (B) The disease incidence in each group of mice is shown. (C) Bovine collagen II–specific total immunoglobulin G (IgG), IgG1 and IgG2a levels in sera collected at the time mice were killed. Values expressed in arbitrary units are mean ± SEM. Asterisk represents a significant difference between arthritic and saline-injected mice. (D) At the time mice were killed, tissue sections were taken from the hind paws and forepaws for histological staining and scored for erosion, infiltration and hyperplasia. The values shown are mean ± SEM of each paw from nine mice per group. (E) Representative images of histological sections of hind paws stained with hematoxylin and eosin in control mice (left panel) or Col-Treg–treated mice (right panel). Arrows indicate hyperplasia, inflammation or erosion. Original magnification of both images = 40×. (F) Trafficking of type 1 Treg clones was analyzed 24 hours after intravenous retro-orbital infusion of 3 × 106 Treg cells in various organs, including joint tissues (n = 9). LN, Lymph node. Nb, Number. mLN, Mesentheric LN. Ing. LN, Inguinal LN. Pop. LN, Popliteal LN. Ax. LN, Axillary LN.