GZMB and hemophagocytic syndrome: Although ours is the first study to report GrB protein expression in CTL and NK cells in patients with immune activation due to HLH, GrB transcripts in the blood and GrB ELISPOT measurements of PBMC have been proposed as a biomarker of immune activation to screen for CTL activation leading to graft rejection following solid organ transplants (Altimari et al., 2008; Truong et al., 2008).