The difference of Fas ligand production observed on transcriptional expression was also confirmed by ELISA measuring Fas ligand level in patients’ plasma (CD16+/CD56- CD8+ T-LGL leukemia: 88.3 ± 14.18 pg/ml, the other CD8+ and CD4+ immunophenotypes: 16.08 ± 14.62 pg/ml, P < 0.0001; Figure 5B). The gene discussed is FASLG; the disease is T-cell large granular lymphocyte leukemia.