Treatment of immunocompetent (wild-type) BALB/c mice with FTY720 has no effect on the development of the primary form of proteoglycan (PG)-induced arthritis. (a) Short-term treatment with placebo (open circles) or FTY720 (closed triangles) started on day 49 or 50 (1 week after the third PG immunization) and ended on day 75. (b) Long-term (prophylactic) treatment was initiated after the first immunization and ended on day 70. Data shown are the mean ± standard error of the mean of cumulative arthritis scores over time (short-term treatment, n = 10 mice per group; long-term treatment, n = 16 mice per group; the difference between placebo- and FTY720-treated groups was not significant in either case). (c) Histology of the ankle joint of a placebo-treated mouse from the long-term treatment group. (d) Histology of the ankle of an FTY720-treated mouse from the long-term treatment group. Sagittal sections of decalcified and paraffin-embedded joints were stained with hematoxylin and eosin. The degree of synovial tissue hyperplasia, leukocyte infiltration, or cartilage erosion was similar in both joints. Scale bars, 250 μm. Bo, bone (talus); Jc, joint cavity; St, synovial tissue.