The E3 monoclonal antibody specifically recognizes CD307a which is also known as Fc receptor-like protein 1 (FCRL1), Fc receptor homolog 1 (FCRH1), or Immune receptor translocation-associated protein 5 (IRTA5). CD307a (FCRL1) is a type I transmembrane glycoprotein that belongs to the IRTA gene family within the Ig gene superfamily. It has three extracellular Ig-like domains, a glutamic acid residue in its transmembrane region, and two consensus immunoreceptor tyrosine-based activation motifs (ITAMs) in its cytoplasmic domain. CD307a (FCRL1) bears sequence homology to classical Fc receptors. CD307a (FCRL1) is first expressed on pre-B cells and increases with maturation being expressed on naïve and memory B cells. It is downregulated by activated germinal center (GC) B cells. It may also be expressed by B cell-derived leukemia and lymphoma cells. CD307a may play key roles in B cell activation, differentiation and effector functions.
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.