Interferon regulatory factor 8 (IRF8), also known as interferon consensus sequence-binding protein, is a ?transcription factor that plays central roles in the regulation of myeloid cell fate. In both mice and humans, IRF8 is required for the differentiation of most monocyte and dendritic cell subsets, but suppresses neutrophil production. IRF8 can both act as a transcriptional activator or repressor, and it acts as a transcriptional repressor of osteoclast differentiation factors such as NFATC1 and EEIG1. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant mouse IRF8 and recombinant mouse NFATC1. Briefly, IRF8 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to NFATC1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IRF8 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 450/630 nm immediately. The binding activity of recombinant mouse IRF8 and recombinant mouse NFATC1 was shown in Figure 1, the EC50?for this effect is 0.05 ug/mL.