Hemopexin (HPX), a 60-kDa plasma glycoprotein encoded by the HPX gene, is predominantly synthesized in the liver and belongs to the hemopexin family. As an acute-phase protein, it exhibits the highest heme-binding affinity in plasma, functioning as a critical heme detoxifier. It sequesters free heme released during hemolysis, preventing oxidative stress and tissue damage, and transports heme to the liver for degradation and iron recycling. HPX also modulates inflammation and maintains iron homeostasis, with its expression upregulated during infection and injury. HPX does not directly bind CD163; its heme complexes are taken up via CD91, while CD163 primarily recognizes haptoglobin-hemoglobin complexes. Briefly, CD163 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μL were then transferred to HPX-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-CD163 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 human HPX is lmmobilized at 2 µg/mL(100 µL well), the concentration of CD163 that produces 50% optimal binding response is found to be approximately 1.697 µg/mL.