TNFRSF9 (Tumor necrosis factor receptor superfamily member 9) is a member of the TNF-receptor superfamily. This receptor contributes to the clonal expansion, survival, and development of T cells. A binding ELISA assay was conducted to detect the interaction of TNFRSF9 and TNFa. Briefly, recombinant human TNFRSF9 were diluted serially in PBS, with 0.01%BSA (pH 7.4). Duplicate samples of 100uL were then transferred to TNFa-coated microtiter wells and incubated for 2h at 37°C. Wells were washed with PBST and incubated for 1h with anti-TNFRSF9 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 3 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37°C. Finally, add 50μL stop solution to the wells and read at 450nm immediately. The binding activity of TNFRSF9 and TNFa was shown in Figure 1, and this effect was in a dose dependent manner.