Integrin Alpha M (ITGaM, also known as CD11b) is a transmembrane subunit of the heterodimeric integrin receptor Mac-1 (CD11b/CD18), widely expressed on myeloid cells including macrophages, neutrophils, and dendritic cells. It mediates cell adhesion to extracellular matrix proteins (e.g., fibrinogen, ICAM-1) and regulates phagocytosis, inflammation, and immune cell recruitment, playing critical roles in host defense against pathogens and tissue repair. ITGaM binds to complement component C3 (especially its activated fragment C3b), facilitating opsonophagocytosis and amplifying innate immune responses.Briefly, C3 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ITGaM-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-C3 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 ITGaM is lmmobilized at 2 µg/mL(100 uLwell), the concentration of C3 that produces 50% optimal bindingresponse is found to be approximately 0.130 µg/mL.