Immunoglobulin A1 (IgA1) is the predominant immunoglobulin subclass found in the human mucosal immune system, particularly in secretions of the respiratory and gastrointestinal tracts. It features a unique hinge region rich in proline and O-linked glycans, which distinguishes it from IgA2. As a key first line of defense, IgA1 neutralizes pathogens and toxins, preventing their attachment to epithelial surfaces. Its primary role is to provide immune protection at mucosal barriers without provoking significant inflammation. Crucially, polymeric IgA1 binds to the Polymeric Immunoglobulin Receptor (PIGR) on the basolateral surface of epithelial cells, initiating transcytosis for its transport across the mucosa into secretions.To detect the activity of recombinant IgA1 , a functional ELISA assay was performed to evaluate the interaction between recombinant human IgA1 and recombinant bovine PIGR.Briefly, IgA1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to PIGR-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IgA1 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 IgA1 and recombinant bovine PIGR was shown in Figure 1, the EC50?for this effect is 0.11μg/mL.