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.