IL1RA (interleukin-1 receptor antagonist) is an agent that binds to the cell surface?interleukin-1 receptor?(IL-1R), which would prevent IL-1 from intracellular signal transduction. Besides, mouse IL1R1 and rat IL1R1 share similarities in amino acid sequence with the identity of 85.6%. Thus, a binding ELISA assay was constructed to detect the association of recombinant mouse IL1RA with recombinant rat IL1R1. Briefly, IL1RA were diluted serially in PBS with 0.1%BSA (pH 7.4). Duplicate samples of 100uL were then transferred to IL1R1-coated microtiter wells and incubated for 2h at 37°C. Wells were washed with PBST and incubated for 1h with anti-IL1RA 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 IL1RA with IL1R1 was shown in Figure 1 and this effect was in a dose dependent manner.