PRF1 and systemic lupus erythematosus: Of note, we observed a strong negative association between ROS level and perforin expression (r =  − 0.649, P = 0.012, Fig. 4G), and a weak positive association between ROS level and total apoptosis (r = 0.443, P = 0.11, Fig. 4H) in CD56dimCD57+ NK cells from SLE patients.