The A1/CD307d monoclonal antibody specifically recognizes CD307d which is also known as Fc receptor-like protein 4 (FCRL4), Fc receptor homolog 4 (FCRH4), or Immune receptor translocation-associated protein 1 (IRTA1). CD307d (FCRL4) is a type I transmembrane glycoprotein that belongs to the IRTA gene family within the Ig gene superfamily. It has four extracellular Ig-like domains, a helical transmembrane region, and two consensus immunoreceptor tyrosine-based inhibition motifs (ITIMs) and one immunoreceptor tyrosine-based switch motif (ITSM) in its cytoplasmic domain. CD307d (FCRL4) binds to aggregated IgA and IgG, and its highest level of expression is on memory B cells in mucosa-associated lymphoid tissues (MALT). Chromosomal abnormalities in the region of the FCRL4 gene are associated with non-Hodgkin lymphoma and multiple myeloma, and CD307d (FCRL4) may play a role in HIV-induced memory B cell dysfunction.
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.