RosA suppresses TCR-induced elevation of intracellular Ca²⁺ and IP₃ production in Jurkat T cells.

(A) Reduced TCR-induced elevation of intracellular Ca²⁺release by RosA. Jurkat cells were loaded with the indicator dye fura-2/am for 45 minutes, as described in “Materials and methods.” Fura-2–loaded Jurkat cells (5 × 10⁶ cells/3 mL/sample) were preincubated in the absence or presence of various concentrations of RosA for 15 minutes and stimulated with anti-CD3 mAb (UCHT1) followed by cross-linking with antimouse IgG antibody. The arrows indicate time points for the addition of anti-CD3 mAb and antimouse IgG antibody. The R_max/R_min ratios of Ca²⁺ are representative of 4 independent experiments. (B) Inhibition of TCR-induced IP₃ production by RosA. Jurkat cells were preincubated with or without the indicated concentrations of RosA. RosA-treated Jurkat T cells were either unstimulated or stimulated as indicated earlier for 3 minutes. The amount of IP₃ was quantified using a competitive [³H] IP₃ binding assay kit. The graph shows the average and the standard error of at least 3 independent experiments.