Fas ligand (FASL) is a 40 kDa type II membrane protein belonging to the TNF family, referred to as TNFSF6 in the new TNF superfamily nomenclature. Its specific receptor is FAS (CD95, Apo-1), a 45 kDa type I transmembrane protein of the TNF receptor family. FASL is mainly expressed on activated T cells and NK cells, while FAS is present on various cell types. The FAS/FASL system is crucial for regulating immune responses by inducing cell apoptosis, thereby maintaining homeostasis, lymphocyte self-tolerance, and immune privilege. FASL has also been reported as a potent neutrophil chemoattractant, indicating a new proinflammatory function. Additionally, a functional binding ELISA assay was used to detect the interaction between recombinant mouse FASL and recombinant human FAS.biotin-linked FASL were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100µl were then transferred to FAS-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µl stop solution to the wells and read at 450nm immediately. The binding activity of FASL and FAS was shown in Figure 1, the EC50 for this effect is 0.46 µg/mL.