Interleukin 12B (IL12B)encodes a subunit of interleukin 12, a cytokine that acts on T and natural killer cells, and has a broad array of biological activities.Interleukin 12 is a disulfide-linked heterodimer composed of the 40 kD cytokine receptor like subunit encoded by this gene, and a 35 kD subunit encoded by IL12A. This cytokine is expressed by activated macrophages that serve as an essential inducer of Th1 cells development. Interleukin 12B can combind with Interleukin 12 Receptor Beta 1 (IL12Rb1). Thus a binding ELISA assay was conducted to detect the interaction of recombinant human IL12B and recombinant human IL12Rb1. Briefly, biotin-linked recombinant human IL12B were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl then transferred to IL12Rb1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with HRP conjugage for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µl stop solution to the wells and read at 450nm immediately. The binding activity of IL12B and IL12Rb1 was shown in Figure 1, and this effect was in a dose dependent manner.