Caspase 8 (CASP8) is a key initiator protease in the extrinsic apoptosis pathway. Upon activation by death receptors—such as Fas or TNFR1—it is recruited to death-inducing signaling complexes (DISCs). Via its N-terminal death effector domains (DEDs), CASP8 forms oligomers and undergoes autocleavage to achieve full enzymatic activity; it then cleaves downstream effector caspases to execute the apoptotic program. Beyond apoptosis, CASP8 also plays a role in regulating necroptosis, inflammatory responses, and cell differentiation processes. Mechanistically, CASP8 interacts with TNFRSF1A Associated Via Death Domain Protein (TRADD) through homotypic death domain (DD)-mediated binding, a process that facilitates the transduction of apoptotic signals.To detect the activity of recombinant CASP8, a functional ELISA assay was performed to evaluate the interaction between recombinant mouse CASP8 and recombinant human TRADD.Briefly, biotin-linked CASP8 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to TRADD-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 CASP8 and TRADD was shown in Figure 1, the EC50?for this effect is 0.51 μg/mL.