The 7B11 (also known as CMSSC-7B11) monoclonal antibody specifically binds to human GARP (Glycoprotein A repetitions predominant). The LRRC32 (Leucine rich repeat containing 32) gene encodes the 662 amino acid-residue, 80 kDa transmembrane GARP glycoprotein that has an extracellular region composed primarily of 20 leucine-rich repeats. GARP is specifically expressed on Treg cells activated through the T cell receptor (TCR). Ectopic expression of GARP in human naïve T cells inhibited their proliferation and cytokine secretion upon TCR activation. Remarkably, GARP over-expression in naïve T cells induced expression of FoxP3 and endowed them with a partial suppressive function. The extracellular, but not the cytoplasmic region, of GARP was necessary for these functions. GARP serves as a receptor for latent TGF-beta which may play a role in the suppressive action of Treg cells. GARP is also expressed on platelets and other tissues, however the function on these cells is not known.
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.