CD157 regulates neutrophil chemotaxis in response to fMLP. (A) PMNs treated with an isotype-matched Ig, anti-CD157, or anti-CD38 (5 μg/mL, 15 minutes at 37°C) were exposed to medium (□) or 10 nM fMLP (▪). There were 5 fields counted per well, and neutrophil chemotactic response was expressed as the mean number of migrated cells per high-power field (HPF; 100×) from triplicate wells (PMNs per HPF), ± SD. Data are the average of 13 donors analyzed. ^*P < .05. (B) Inhibitory effects of anti-CD157 on fMLP-induced neutrophil chemotaxis in 13 donors. The increasing rate of fMLP-induced chemotaxis was evaluated as fMLP-induced migration/basal migration in the absence (•) or in the presence (○) of anti-CD157 mAb. P = .004. (C) fMLP-induced chemotaxis of ATRA-treated HL-60 cells and (D) DMSO-treated HL-60 cells are reduced by CD157 ligation. Number of migrated cells was calculated as in panel A. Data are the average of 3 separate experiments. ^*P < .05.