Beta-2-microglobulin (β2M, encoded by B2M) is a small, non-glycosylated protein with a molecular mass of approximately 12 kDa. It is ubiquitously expressed on the surface of nearly all nucleated cells and serves as an invariant light chain of major histocompatibility complex (MHC) class I molecules. β2M plays a critical role in stabilizing the conformation of MHC class I heavy chains and facilitating the presentation of endogenous peptide antigens to cytotoxic T lymphocytes, which is essential for cellular immune surveillance and antiviral and antitumor responses. Elevated serum β2M levels are often associated with immune activation, lymphoproliferative disorders, renal dysfunction, and certain inflammatory conditions. Structurally, it belongs to the immunoglobulin superfamily and is also involved in cell adhesion and antigen recognition processes. β2M forms a stable structural complex with CD1a to support lipid antigen presentation and T-cell recognition. Briefly, CD1a was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to β2M-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-CD1a 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 β2M is lmmobilized at 2 µg/mL(100 µLwell), the concentration of CD1a that produces 50% optimal bindingresponse is found to be approximately 0.239 µg/mL.