Fas ligand (FasL) is a 40 kDa type II membrane protein belonging to the TNF family. In the new TNF super family nomenclature, FasL is referred to as TNFSF6. The specific receptor for FasL is Fas (CD95, Apo-1), a 45 kDa type I transmembrane protein that is a member of the TNF receptor family. FasL is predominantly expressed on activated T cells and NK cells, while Fas is expressed on various types of cells. The Fas/FasL system plays a crucial role in modulating immune response by inducing cell apoptosis to maintain homeostasis, self-tolerance of lymphocytes, and immune privilege. FasL was reported to be a potent chemoattractant for neutrophils, suggesting a novel proinflammatory function of this molecule. A functional ELISA assay was conducted to detect the interaction of recombinant human FASL and recombinant human FAS. Briefly, FASL was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to FAS-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-FASL pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant human FASL and recombinant human FAS was shown in Figure 1, the EC50 for this effect is 0.044 ug/mL.