Cyclic ADP Ribose Hydrolase (cADPRH), commonly known as CD38, is a multifunctional enzyme widely expressed on various cell surfaces. Its primary function involves catalyzing the synthesis and hydrolysis of cyclic ADP-ribose (cADPR) from NAD?. cADPR is a crucial secondary messenger that mobilizes calcium ions from intracellular stores, thereby playing a vital role in regulating calcium signaling. This process is essential for numerous physiological functions, including immune response, insulin secretion, and neural signaling. CD38's involvement in calcium homeostasis links it to metabolic diseases, aging, and immune disorders. Furthermore, it serves as a cell surface marker in hematological malignancies and is a target for therapeutic antibodies.Besides,CD19 has been identified as an interactor of cADPRH, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human cADPRH and recombinant human CD19. Briefly, biotin-linked cADPRH were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to CD19-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50μl stop solution to the wells and read at 450nm immediately. The binding activity of cADPRH and CD19 was shown in Figure 1, the EC50?for this effect is 0.25497μg/mL.