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™ BUV563 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 which has an Ex Max of 348 nm and an acceptor dye. The tandem has an Em Max at 563 nm. BD Horizon BUV563 can be excited by the 355 nm ultraviolet laser. On instruments with a 561 nm Yellow-Green laser, the recommended bandpass filter is 585/15 nm with a 535 nm long pass to minimize laser light leakage. When BD Horizon BUV563 is used with an instrument that does not have a 561 nm laser, a 560/40 nm filter with a 535 nm long pass may be more optimal. Due to the excitation and emission characteristics of the acceptor dye, there may be spillover into the PE and PE-CF594 detectors. However, the spillover can be corrected through compensation as with any other dye combination.