The OX-119 monoclonal antibody specifically recognizes Signal-regulatory protein gamma (SIRP-gamma or SIRPγ) which is also known as CD172g or Signal-regulatory protein beta 2 (SIRP-beta-2 or SIRPβ2). SIRPγ (CD172g) is a ~55 kDa type I transmembrane glycoprotein that is encoded by SIRPG, which belongs to the SIRPβ2 subfamily within the Ig gene superfamily. The SIRPγ (CD172g) extracellular domain contains one amino-terminal IgV-like domain and two IgC-like domains, and a short cytoplasmic region with no known motifs. It is expressed on mature thymocytes, CD4+ T-cells, CD8+ T-cells, CD56-bright natural killer (NK) cells, all activated NK cells and some B cells. SIRPγ (CD172g) binds to CD47 (integrin-associated protein/IAP) that is widely expressed on most hematopoietic cells, epithelial cells, endothelial cells, fibroblasts and many tumor cell lines. SIRPγ (CD172g) may play a regulatory role in T cell-T cell interactions and may induce apoptosis through CD47.
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.