Lymphocyte Chemoattractant 1 (BLC1) , also known as CXC chemokine ligand 13 (CXCL13) is a member of the CC chemokine family andis constitutively expressed in secondary lymphoid organs. . BLC1 functions by attracting B lymphocytes to sites of inflammation, thus facilitating the immune response against pathogens. The protein is involved in various physiological processes, including B cell migration, proliferation, and differentiation. Additionally, BLC1 has been associated with several diseases, including autoimmune disorders and certain types of cancer.Chemokine C-X-C-Motif Receptor 5 (CXCR5) is the cognate receptor for BLC1,, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant humant BLC1 and recombinant human CXCR5. Briefly,BLC1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to CXCR5-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-BLC1 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 humant BLC1 and recombinant human CXCR5 was shown in Figure 1, the EC50 for this effect is 0.62ug/mL.