RAC2 and leukemia: Carlyon et al. reported a decrease in Rac2 mRNA level in A. phagocytophilum-infected HL-60 cells (a human leukemia line) and neutrophils at 1 to 2 days postinfection (44), which may be too slow to explain the observed suppression of ROS generation in neutrophils by A. phagocytophilum that occurs within 30 min of interaction (39).