Interleukin 3 is an interleukin, a type of biological signal that can improve the body's natural response to disease as part of the immune system. It acts by binding to the interleukin 3 receptor. IL-3 synergizes with other cytokines to stimulate the growth of immature progenitor cells of all lineages, and is therefore a multi-lineage colony-stimulating factor (CSF). It prevents cell death and promotes the survival of macrophages, mast cells, and megakaryocytes. IL-3 can also support the growth and survival of myeloid progenitor cells through the activation of Janus Kinase 2 (JAK2) tyrosine kinase, and macrophage differentiation has been shown to be regulated by protein kinase C (PKC). Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant rat IL-3 and recombinant rat JAK2. Briefly, IL-3 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to JAK2-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IL-3 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, 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 nm immediately. The binding activity of IL-3 and JAK2 was shown in Figure 1, and this effect was in a dose dependent manner.