Immunoglobulin A (IgA), the most abundant antibody in human mucosal secretions, plays a pivotal role in mucosal immunity. It exists mainly as dimers linked by the J chain, forming secretory IgA (sIgA) when combined with the secretory component (SC). Synthesized by plasma cells in mucosal tissues, IgA defends against pathogens by blocking adhesion and neutralizing toxins at mucosal surfaces. IgA binds to the Polymeric Immunoglobulin Receptor (PIGR), which mediates its transcytosis across epithelial cells to mucosal surfaces.Briefly, PIGR was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IgA-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-PIGR 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.Measured by its binding ability in a functional ELISA. When Recombinant IgA is lmmobilized at 2 µg/mL(100 uLwell), the concentration of PIGR that produces 50% optimal bindingresponse is found to be approximately 0.86627 µg/mL.