CD33, also known as myeloid cell surface antigen CD33 isoform 1, is a member of the Ig superfamily that is restricted to cells of the myelomonocytic lineage but whose functions and binding properties are unknown. It can function as a sialic acid-dependent cell adhesion molecule and that binding can be modulated by endogenous sialoglycoconjugates when it is expressed in a plasma membrane. It is usually considered myeloid-specific, but it can also be found on some lymphoid cells. It contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that are implicated in inhibition of cellular activity. It has been identified to modulate the risk of Alzheimer's disease (AD) in several recent genome-wide association studies (GWAS) in Caucasians. Recombinant human CD33, fused to hIgG-His-Tag at C-terminal, expressed in insect cell and purified by using conventional chromatography techniques.