Clinical and histological severity of antigen-induced arthritis (AIA) in CD25-depleted mice. (a) Knee joint swelling (difference in mediolateral joint diameters of arthritic minus nonarthritic knee joints) during the time course of arthritis was higher in CD25-depleted mice. (b) Haematoxylin and eosin stained frontal knee joint sections were scored on a 0–3 point scale at day 14 of AIA for each of the following: severity of synovial hyperplasia, cellular infiltration, cartilage destruction and pannus formation. A score for inflammatory changes (Inf) was calculated by adding the points for synovial hyperplasia and infiltration, and for joint destruction (Dest) by adding the points for cartilage damage and pannus formation. Total arthritis score (Score) was calculated by adding scores for inflammatory changes and joint destruction, giving a maximal AIA score of 12 points. Representative photomicrographs of (c) a control (rat IgG-injected) and (d) a knee joint from an anti-CD25-treated mouse. Ten animals were included in each group in two independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001, versus control.