TxA₂-TP mediates the effect of COX-1 on B-cell development. (A) BM cells from WT and COX-1^−/− mice were treated with the TP antagonist SQ29548 and the TP agonist U46619, respectively. Cells were then cultured for B-cell differentiation. The frequency of pre-B cells was evaluated by flow cytometric analysis. Both representative results from (left) 1 experiment and (right) the mean ± SEM of 3 independent experiments are shown. (B) WT or COX-1^−/− mice (n = 6) were intraperitoneally injected with U46619 (5 μg/kg body weight) or phosphate-buffered saline twice weekly. The proportions of total B cells and pre-B cells were examined by flow cytometry 3 weeks after injection. (Left) Representative results from 1 mouse; the numbers in the plots indicate percentages of total living cells. (Right) Mean ± SEM from all 6 mice. (C) Purified B-cell subpopulations from BM of TP^−/− and WT controls were stimulated with IL-7 for 15 minutes; the level of p-STAT5 was determined by flow cytometric analysis. (D) BM cells from WT and COX-1^−/− mice were treated with the TP agonist U46619 or DMSO. Cells were then stimulated with IL-7 for 15 minutes. The levels of p-STAT5 in B220⁺ cells were determined by flow cytometric analysis. (C-D) (Left) Representative data from a single experiment. (Right) Mean ± SEM of MFI from 3 independent experiments. *P < .05 and **P < .01 using unpaired Student t tests.