The SE5A5 monoclonal antibody specifically binds to a common epitope on CD172a/SIRPα (90 kDa) and CD172b/SIRPβ1 (50 kDa). These transmembrane glycoproteins are members of the Signal Regulatory Protein (SIRP) family that, in turn, belongs to the Immunoglobulin superfamily. The SIRP family is comprised of two subgroups, SIRPα and SIRPβ that are distinguished by the presence (α) or absence (β) of a cytoplasmic domain containing two immunoreceptor tyrosine-based inhibition motifs (ITIM). CD172a/SIRPα is expressed on CD34+ stem/progenitor cells, cardiomyocytes, monocytes, macrophages, granulocytes, dendritic cells, and in the central nervous system. It binds to CD47 and is implicated in mediating inhibitory signals via the ITIM/SHP-2 association. CD172b/SIRPβ1 does not possess a cytoplasmic domain but instead the transmembrane domain contains a positively-charged residue that can interact with another transmembrane protein, DAP-12/KARAP. DAP-12 has two immunoreceptor tyrosine-based activation motifs (ITAM) within its cytoplasmic domain that are thought to link CD172b to cellular activation signaling. CD172b is expressed on myeloid cells, including peripheral blood monocytes and granulocytes. It is not expressed on CD34+ cells. CD172a and CD172b have complementary roles in signal regulation and may work together in tuning certain cellular responses to stimuli.
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.