IL2RA (Interleukin-2 receptor alpha chain ), also known as Tac antigen and as CD25, was initially identified as a 55kDa membrane glycoprotein which is capable of binding IL2. Besides, mouse IL2 shares 75.1% AA sequence identity with rat IL2, suggesting the exist of cross-species activity. Thus we have conducted a binding ELISA assay to detect the interaction of recombinant rat IL2RA with recombinant mouse IL2. Briefly, IL2RA were diluted serially in PBS, with 0.01%BSA (pH 7.4). Duplicate samples of 100uL were then transferred to IL2-coated microtiter wells and incubated for 2h at 37 degree C. Wells were washed with PBST and incubated for 1h with anti-IL2RA 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 degree C. Finally, add 50uL stop solution to the wells and read at 450nm immediately. The binding activity of IL2RA with IL2 was shown in Figure 1 and this effect was in a dose dependent manner.