Interleukin 4 (IL4) is a pleiotropic cytokine primarily secreted by activated T cells, mast cells, and basophils. It plays a central role in immune regulation by promoting the differentiation of naïve T cells into Th2 cells and stimulating B cell proliferation and antibody class switching to IgE and IgG1. IL4 is crucial for defense against parasitic infections and is involved in allergic responses, including asthma and atopic dermatitis. It signals through the IL4 receptor complex , activating JAK-STAT pathways to modulate gene expression. Dysregulated IL4 production is associated with autoimmune diseases, chronic inflammation, and cancer. Its dual role in both promoting and suppressing immune responses makes it a key therapeutic target.Besides,Interleukin 1 Alpha (IL1a) has been identified as an interactor of IL4, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant mouse IL4 and recombinant goat IL1a. Briefly, IL4 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IL1a-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IL4 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 mouse IL4 and recombinant goat IL1a was shown in Figure 1, the EC50 for this effect is 1.595µg/mL.