Interleukin 4 Receptor (IL4R) is a transmembrane protein that plays a pivotal role in the immune system, particularly in mediating type 2 immune responses. Signaling through IL4R promotes B-cell activation, antibody class switching to IgE, and differentiation of Th2 cells, while also contributing to anti-inflammatory responses and alternative macrophage activation. Dysregulation of IL4R signaling is associated with allergic diseases, asthma, and certain parasitic infections. IL4R binds its cognate ligand Interleukin 4 (IL4) with high affinity, initiating dimerization of receptor subunits and subsequent activation of the JAK-STAT signaling pathway.To detect the activity of recombinant IL4R , a functional ELISA assay was performed to evaluate the interaction between recombinant human IL4R and recombinant rabbit IL4.Briefly, IL4R was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IL4-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IL4R 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 IL4R and recombinant rabbit IL4 was shown in Figure 1, the EC50 for this effect is 0.056µg/mL.