The MEM-238 monoclonal antibody specifically binds to CD222, which is also known as the Insulin-like growth factor 2 Receptor (IGF2R, IGF-II Receptor), Cation-independent mannose 6-phosphate receptor (CIMPR), or Mannose-6 phosphate receptor (M6PR). CD222 is ubiquitously expressed by a variety of cell types as a cell surface type I transmembrane glycoprotein. However, in the course of receptor trafficking between the cell surface and intracellular compartments, the majority of CD222 is found within cells. Cell surface CD222 functions as a multifunctional receptor that binds to a large number of extracellular ligands including acid hydrolases, insulin-like growth factors, latent TGF-β, leukemia inhibitory factor (LIF), proliferin, prorenin, plasminogen, and Herpes simplex virus. It regulates extracellular Insulin-like growth factor II (IGF-II/IGF-2) levels by binding and internalizing the growth factor for lysosomal degradation. This effectively removes IGF-II from the circulation and tissues and thus prevents it from signaling through the growth-stimulatory Insulin-like growth factor I Receptor (IGF-1R, CD221) pathway. However, studies have reported that IGF-II may activate some cellular functions through CD222 as well. A soluble form of the CD222 extracellular region can also be detected in human serum and may play a role in regulating IGF-II activity. CD222 serves as a surface receptor for latent TGFβ and can complex with plasminogen and CD87, a urokinase-type plasminogen activator receptor, to activate latent TGF-β. CD222 also binds to a variety of Mannose 6-phosphate (M6P)-containing proteins, including extracellular and newly-synthesized lysosomal enzymes, and transports them to lysosomes.
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.