Programmed Cell Death Protein 1 Ligand 1 (PDCD1LG1) also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1) is a 40kDa type 1 transmembrane protein that has been speculated to play a major role in suppressing the immune system during particular events such as pregnancy, tissue allografts, autoimmune disease and other disease states such as hepatitis. Besides, Programmed Cell Death Protein 1 (PDCD1) has been identified as an interactor of PDCD1LG1, thus a binding ELISA assay was conducted to detect the interaction of recombinant human PDCD1LG1 and recombinant human PDCD1. Briefly, PDCD1LG1 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100uL were then transferred to PDCD1-coated microtiter wells and incubated for 2h at 37°C. Wells were washed with PBST and incubated for 1h with anti-PDCD1LG1 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 PDCD1LG1 and PDCD1 was shown in Figure 1, and this effect was in a dose dependent manner.