Inhibition of CD25 induction in type 2 T cells by β-agonist. (A) Freshly isolated PBLs were treated 30 minutes with vehicle, PGE₂ (1 μM), or ISO (10 μM), then stimulated 18 hours with vehicle (—) or PHA + CD28 mAb + IL-2 (). Cells were simultaneously analyzed for expression of CD3, CRTH2, and CD25 by flow cytometry. - - - indicates isotype control. Expression of CD25 on PHA + CD28 + IL-2-stimulated T cells in CRTH2⁺ and CRTH2^- T cells is presented as histograms. Background fluorescence from isotype control mAb was superimposable for all conditions (not shown). (B) To allow statistical analyses of data, MFI of CD25 for each subject was normalized as the percent of the respective net MFI (background subtracted) in the IL-2 + PHA + CD28-only condition for both subsets. The mean ± SD is shown (n = 5). ^*P < .05 for difference from 100%. All data sets were significantly less than the respective IL-2 + PHA + CD28 condition (= 100%) (P < .05). (C) Freshly isolated PBLs were incubated with the indicated concentration of the β₂AR antagonist ICI-118551 for 10 minutes, treated 30 minutes with the indicated concentration of ISO, and then stimulated 18 hours with PHA + CD28 mAb + IL-2. MFI values of CD25 expression (background subtracted) in gated CRTH2⁺ (□) and CRTH2 (▪) T cells are reported for 1 representative of 2 independent experiments.