The 2D9 monoclonal antibody recognizes C57BL/6 mouse Natural killer cell receptor P1D (NKR-P1D) which is also known as NKR-P1B[B6], or CD161b. CD161b is encoded by Klrb1b (killer cell lectin-like receptor subfamily B member 1B). CD161b is expressed by a functionally distinct subset of natural killer (NK) cells that express higher levels of cytotoxicity and interferon-γ (IFN-γ) than their CD161b-low or -negative counterparts. CD161b is a type II transmembrane glycoprotein that contains an immunoreceptor tyrosine-based inhibitory motif in its cytoplasmic domain. CD161b binds to C-type lectin related protein b (Clr-b) and may play a role in regulating NK cell responses. The 2D9 antibody has slight crossreactivity with cells transfected with Klrb1a/NKRP1A, Klrb1c/NKRP1C, or Klrb1f/NKRP1F.
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.