The ZM3.8 monoclonal antibody specifically binds to CD85k which is also known as Immunoglobulin-like transcript 3 (ILT-3) and Monocyte inhibitory receptor HM18. CD85k is encoded by LILRB4 (Leukocyte immunoglobulin-like receptor, subfamily B member 4) and is expressed as a type I transmembrane glycoprotein. CD85k is comprised of two C2-type Ig domains, a transmembrane region, and a cytoplasmic tail with three immunoreceptor tyrosine-based inhibitory motifs (ITIMs). CD85k is selectively expressed by myeloid antigen presenting cells including monocytes, macrophages, and dendritic cells. CD85k functions as an inhibitory receptor. ILT3 can also function in antigen capture and presentation. It is efficiently internalized upon cross-linking, and delivers its ligand to an intracellular compartment where it is processed and ultimately presented by APCs to T cells. Thus, ILT3 is a novel inhibitory receptor that can negatively regulate activation of APCs and can be used by APCs for antigen uptake. ILT3 expression is upregulated on tolerogenic dendritic cells that can induce regulatory T cells.
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.