Regenerating Islet Derived Protein 3 Alpha (REG3a),also known as heptocarcinoma-intestine-pancreas (HIP) or pancreatic associated protein (PAP),is a member of to the regenerating protein family.REG3a is expressed in islet beta cells, intestinal tract and pancreatic tissues and plays an important role in mucosal barrier maintenance, innate immunity, tissue regeneration and inflammatory response.Besides,Interleukin 22 (IL22) has been identified as an interactor of REG3a, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human REG3a and recombinant human IL22. Briefly,REG3a was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IL22-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-REG3a 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 450/630nm immediately. The binding activity of recombinant human REG3a and recombinant human IL22 was shown in Figure 1, the EC50?for this effect is 0.11242ug/mL.