Immunoglobulin E (IgE) is a key class of antibody central to type I hypersensitivity and antiparasitic immunity. Produced mainly by plasma cells in mucosal tissues, IgE is present at very low concentrations in serum compared to other immunoglobulins. It binds with high affinity to FcεRI on mast cells and basophils, sensitizing these cells for allergic reactions upon allergen exposure. Elevated IgE levels are closely linked to allergic diseases such as asthma, rhinitis, and atopic dermatitis. Beyond allergy, IgE contributes to immune surveillance against parasites and modulates immune cell functions. IgE binds CD23 (FcεRII) via its Cε3–Cε4 domains in a low‑affinity, calcium‑dependent interaction.Thus a functional ELISA assay was conducted to detect the interaction of recombinant human IgE and mouse recombinant CD23. Briefly, IgE was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to CD23-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IgE 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 IgE and recombinant mouse CD23 was shown in Figure 1, the EC50 for this effect is 0.1039µg/mL.