The monoclonal antibody specifically recognizes CD33, a human myelomonocytic antigen which is also known as Sialic acid-binding Ig-like lectin 3 (Siglec-3 or SIGLEC3). CD33 is a 67 kDa type I transmembrane glycoprotein that belongs to the Ig supergene family. The CD33 antigen is present on monocytes (bright) and granulocytes (dim). Granulocytes can be further subdivided into neutrophil, eosinophil, and basophil populations based on CD33 staining in combination with other cell-surface antigens. The CD33 antigen is also found on CFU-Mix, CFU-GM, CFU-Meg, a portion of BFU-E, myeloblasts, promyelocytes, myelocytes, and metamyelocytes, but not on earlier precursors. The CD33 antigen is expressed on blast cells in greater than 85% of acute myeloid leukemias (AML), and it can be aberrantly expressed in acute lymphoblastic leukemias (ALL). Normal lymphocytes, platelets, and erythrocytes do not express the CD33 antigen. CD33 can reportedly function as a sialic acid-dependent cell adhesion molecule and this function can be modulated by endogenous sialoglycoconjugates when CD33 is expressed on the membrane.
The antibody was conjugated to BD Horizon™ BUV661 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 with an Ex Max of 348-nm and an acceptor dye with an Em Max at 661-nm. BD Horizon Brilliant BUV661 can be excited by the ultraviolet laser (355 nm) and detected with a 670/25 filter and a 630 nm LP. Due to cross laser excitation of this dye, there may be significant spillover into channels detecting APC-like emissions (eg, 670/25-nm filter).
Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BUV661 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended. Different BUV661 reagents (eg, CD4 vs. CD45) can have slightly different fluorescence spillover therefore, it may also be necessary to use clone-specific compensation controls when using these reagents.