Effects of FTY720 treatment or depletion of T cells from the transferred donor cells on circulating T cells and arthritis development in severe combined immunodeficient (SCID) mice. SCID mice, injected with lymphocytes from arthritic donors, were subjected to treatment with placebo (open circles) or FTY720 (closed triangles), as described in Materials and Methods. A separate group of SCID mice received cells from the same arthritic donors, but T cells from the donor population were depleted prior to transfer (solid circles). (a) The proportion of T cells (CD3+) among all blood leukocytes (CD45+) was monitored by flow cytometry from between day 1 after the first cell transfer and day 42 (end of experiment). Data shown are the mean ± standard error of the mean (SEM). (n = 9 to 11 mice per group; *P < 0.01 in comparison with the placebo-treated group.) (b) The SCID mice were inspected for arthritis symptoms at 4-day intervals between days 10 and 42. Incidence of proteoglycan-induced arthritis is expressed as the percentage of arthritic animals among all SCID mice in the respective groups. (c) The degree of inflammation in each paw was scored visually at 4-day intervals. Arthritis severity is expressed as the mean ± SEM of cumulative paw scores (n = 9 to 11 mice per group; *P < 0.01 in comparison with both the placebo- and FTY720-treated groups).