Analysis of the expression and cyclase activity of CD157. PMNs purified from (A) peripheral blood, (C) HL-60 cells, (E) DMSO-induced HL-60 cells, and (G) ATRA-induced HL-60 cells were incubated with anti-CD157, anti-CD38, or anti-CD11b mAbs and F(ab′)₂-RaMIg-FITC and analyzed by flow cytometry. (E, G) Analysis of basal expression (black profiles) and of the expression induced following treatment with DMSO or ATRA for 4 days (gray profiles). Gray-filled profiles are the isotype control mAb. Number of cells tested was 7 000. Results are representative of 5 experiments. (B) Evaluation of the cyclase activity of PMNs. The cyclase activity of PMNs was measured by analyzing the ability of increasing concentrations of cells to produce cGDPR in the absence (▦) or presence (▪) of NGD⁺ using a fluorimetric assay. Raji B cells were used as a positive control. Evaluation of the cyclase activity of (D) HL-60, (F) DMSO-induced HL-60 cells, and (H) ATRA-induced HL-60 cells. Cells were incubated in the absence () or in the presence (▪) of NGD⁺. The formation of the fluorescent product cGDPR was measured by a fluorescence spectrometer, set at excitation 300 nm and emission 410 nm. Each experiment was performed in triplicate, and results are expressed as means of absorbance obtained from 3 different experiments ± the standard deviation (SD). ^*P < .05; ^**P < .001.