Immunoglobulin D (IgD) is an immunoglobulin similar in structure to other immunoglobulin classes. It is composed of heavy and light polypeptide chains, has a sedimentation coefficient of approximately 7S, and can be fragmented into Fab and Fc fragments. It is present in very low concentrations in human blood, and its function is not fully understood. IgD is believed to play a role in the immune system, possibly in the regulation of immune responses or as a receptor on the surface of B cells. It is one of the five major classes of immunoglobulins, alongside IgA, IgE, IgG, and IgM.Besides,Cluster of Differentiation 79B (CD79B) has been identified as an interactor of IgD, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human IgD and recombinant human CD79B.Briefly, IgD was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to CD79B-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IgD 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 IgD and recombinant human CD79B was shown in Figure 1, the EC50?for this effect is 0.044ug/mL.