The HP-MA4 monoclonal antibody specifically recognizes several Killer Cell Immunoglobulin-like Receptors (KIRs) which are also known as CD158 molecules. HP-MA4 recognizes Killer cell immunoglobulin-like receptor 2DL1 (encoded by KIR2DL1; aka, CD158a and NKAT-1), Killer cell immunoglobulin-like receptor 2DS1 (KIR2DS1; CD158h), Killer cell immunoglobulin-like receptor 2DS3 (KIR2DS3; NKAT-7), and Killer cell immunoglobulin-like receptor 2DS5 (KIR2DS5; CD158g, NKAT-9) which are collectively known as KIR2DL1/S1/S3/S5 (CD158). These type I transmembrane glycoproteins are encoded by polymorphic genes and have 2 extracellular Ig-like domains (KIR2D, domains D1 and D2) followed by a transmembrane region and either long (L) or short (S) cytoplasmic domains. Various CD158 molecules are differentially expressed by CD56dim natural killer (NK) cells and some T cells and can regulate their cytotoxic effector functions. Although different KIR gene content varies amongst haplotypes for individuals, certain "framework" genes including KIR3DL3, KIR3DP1, KIR3DL4, and KIR3DL2, are found in all haplotypes. KIR2DL1 has a long cytoplasmic domain with two tyrosine-based inhibitory motifs (ITIM) that enables inhibitory signal transduction by ligand-bound KIR2DL1 leading to reduced cytotoxic effector cell activity. KIR2DS1, KIR2DS3, KIR2DS5 (KIR2DS1/S3/S5) proteins each have a short cytoplasmic tail with a positively charged amino acid in their transmembrane region which allows association with the DAP12 transmembrane protein. DAP12 acts as an activating signal transduction element through its immunoreceptor tyrosine-based activation motifs (ITAMs) in its cytoplasmic domain leading to upregulated cytotoxic effector cell function. Some MHC class I molecules can serve as ligands for CD158 molecules, with HLA-C ligands reported for KIR2DL1, KIR2DS1, and KIR2DS5.
The antibody was conjugated to BD Horizon™ BV421 which is part of the BD Horizon Brilliant™ Violet family of dyes. With an Ex Max near 407 nm and Em Max near 421 nm, BD Horizon™ BV421 can be excited by the violet laser (405 nm) and detected with a 450/50 nm filter. BD Horizon™ BV421 conjugates are very bright, often exhibiting a 10 fold improvement in brightness compared to Pacific Blue™ conjugates. Due to nearly identical excitation and emission properties but different spillover characteristics, BD Horizon™ BV421, Pacific Blue™, and BD Horizon™ V450 cannot be used simultaneously.