The 108724 monoclonal antibody specifically recognizes Axl which is also known as adhesion related kinase (ARK), JTK11, Tyro7, or UFO. Tyro-3, Axl, and Mer constitute the TAM subfamily of receptor tyrosine kinases (RTK). Axl is a single-pass type I transmembrane glycoprotein comprised of an extracellular region with two immunoglobulin (Ig)-like domains and two fibronectin type III (FNIII) domains, a transmembrane segment and a conserved intracellular tyrosine kinase domain. Axl is variably expressed by multiple cell types including monocytes, macrophages, dendritic cells, NK cells, platelets, endothelial cells, vascular smooth muscle cells, and fibroblasts. Axl binds to the vitamin K-dependent Growth arrest-specific protein 6 (Gas6) through its extracellular Ig-like domains. Ligand binding leads to receptor dimerization, and autophosphorylation of tyrosine residues within the cytoplasmic Axl domains. This results in the activation of downstream signaling pathways that control cellular adhesion, aggregation, phagocytosis/efferocytosis, proliferation, survival, and migration. Through these activities, Axl plays major roles in development, the regulation of hematopoiesis and immunity, and ensuring the integrity of the vascular system. Abnormal expression of Axl has been observed in various cancers and myeloproliferative disorders and by tumor cell lines.
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.